Stamford Amateur Radio Association
To use these articles you should get permission. Contact: Marv N1AWJ.
Elmer Apr 86
IMPROVED AUDIO FOR THE ICOM IC-02AT 
Check for spelling errors!
As owners and operators of the ICOM IC-02AT, 2 meter HT, we feel that we have a good reliable radio with all the bells and whistles we can use. The only serious shortcoming is the poor receive audio quality. After an exhaustive investigation (which meant that I spoke to a close friend of mine who called ICOM) a possible modification was suggested.
First a bit of an explanation as to what is going on. The ICOM designers seemed to feel that the human voice is too shrill, and to correct this a filter is needed to reduce or eliminate any audio components above 250 Hz. The filter consists of a resistor, R127 (4.7K) and a capacitor, C 117 (.22 uFd), both located on the Main Unit between the Squelch control and the Volume control.
The modification consists of replacing the .22 uFd capacitor with one of 0.047 uFd or 0.039 uFd. This will change the system roll off frequency to about 1 KHz as well as increasing the total amount of audio signal reaching the speaker. It approaches the quality of the IC2AT except that there is more audio volume.
The modification procedure is as follows:
1. Remove the battery from the radio.
2. Using a small Phillips head screwdriver, remove the 4 screws holding the battery clip on the HT, and the 5 screws securing the back of the HT.
3. Put these screws and associated hardware in a safe place.
4. Remove the Volume and Squelch knobs by pulling them off.
5. Remove the back cover from the radio and then carefully remove the front cover.
6. Remove the 2 screws holding the circuit board frame together, and separate the two circuit boards. The main board is the one whose components are on the same side as the touch tone pad and display.
7. Refer to the diagram to locate C117, and carefully remove it. Replace it with a Radio Shack 272-1068 or 272-157 0.047 uFd capacitor. The holes in the PC board are very small. If the capacitor leads don't fit through, you may have to enlarge them. Do this carefully, and from the circuit side of the board. Use a small soldering iron and be careful of bridging lands with excess solder.
8. Once complete, reassemble the transceiver.
Hope you enjoy operating a "BRAND NEW RADIO".
73,
Marv N1AWJ
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November 1986
ASK ELMER
Dear Elmer,
I am setting up my Novice station and I don't know what kind of antenna to put up. I cannot spend more than $50 on the antenna and I would like to be able to operate on all of the Novice bands. I want to get on the air as soon as possible. What do I do now ?
Signed, Anxious
Dear Anxious,
There are many ways to erect multi-band antennas at a reasonable cost. I will try to cover some of them.
The most common multi-band antenna is the "End Fed Hertz" or Long Wire antenna. The basic idea is to get as long a piece of wire as you can as high up as you can and use a simple "Transmatch" to match the feed line to the radio. This is one of the earliest forms of antennas used and is quite effective. Since this antenna is a non-resonant antenna, its impedance varies with operating frequency, and is generally greater than 300 ohms. A transmatch is required to convert the antennas impedance to the 50 ohms required by your radio. An advantage of this antenna is that it can be of any reasonable length and it will still operate. A disadvantage is that there will be a high level of RF in the shack, since the feed line is part of the antenna. Low cost transmatches such as those made by MFJ are available from your local Ham equipment dealer.
The next type of antenna is the "Multi-Band Resonant Dipoles" using good quality 300 Ohm TV Twin lead. Notice I used the plural in the name of the antenna. This is because it consists of 4 separate resonant dipoles connected in parallel. The antenna is fed with 50 or 75 ohm coaxial cable. Rather than trying to describe the antenna in words, the diagram which follows, shows the method of construction and the approximate lengths of the elements.
The ends of the twin lead should be separated from each other by several inches. The plastic insulators can be made of any form of Plexiglas, polystyrene or other good insulator. Wood is not recommended, since it will absorb moisture and loose any insulating properties it may have. Once the basic antenna is constructed, you must tune the elements. This is done by trimming a pair of wires on their specific band until the VSWR at the transmitter is less than 2:1. This procedure may take some time, but once done does not have to be repeated again for the life of the antenna. To trim the wire, simply notch the twin lead taking care not to cut too deeply into the insulation separating the two parallel wires. Doing this will insure good mechanical strength of the twin lead. Trim in 1/2 inch increments so as not to overshoot the resonant point on the antenna. It may take a few minutes longer but the results are worth it. When properly tuned, this antenna does not need a transmatch, and since it is fed with coaxial cable, there is no RF in the shack. The disadvantage of this antenna is that you need at least 110 feet of space to cover 80 meters, since it is a full dipole, shortened only by the dielectric material surrounding the wire. Note: when tuning this antenna, you tune the 10 meter portion first and then succeeding lower bands. A variation of this type of antenna is marketed by "More gain", but if you construct it yourself you will save a considerable sum of money.
The last type of antenna I will discuss is the "Trapped Dipole". I will not attempt to go into all of the details of it's construction but I will refer you to the ARRL Antenna Handbook as well as the Radio Amateurs Handbook.
Basically the "Trapped Dipole" is a resonant dipole which is segmented or cut up by using resonant traps. These traps look like high impedance points (read insulators) at their resonant frequencies and as inductors at frequencies below their resonance. Inserting these resonant traps set to 10 meters, 15 meters and 40 meters at the appropriate points in the dipole, makes the antenna look like separate antennas on each band. A second advantage is that they shorten the overall length of the antenna because of the added inductance of the traps. A disadvantage is that they narrow the bandwidth of the antenna, but they will be more than wide enough to cover the entire Novice portion of the band. A diagram of a typical "Trapped Dipole" follows:
o------uuuu-------uuuu----------o o------------uuuu-------uuuu------o
Insulator 40m 15m I I 15m 40m Insulator
I I
Transmission
line to Radio
Well anxious, I hope this helped you in your search for a low cost multi band antenna.
73, ELMER.
ASK ELMER
Dear Elmer,
I have been hearing a lot of talk about the "Sunspot Cycle" and that we are currently at it's bottom. What does this mean to me as a novice operator?
73, Confused Novice
Dear Confused,
To explain the details of the Solar Cycle in detail would be too much for this column, but I will try to give you a brief explanation.
Recall from your Novice training, that long distance communication relies on the ability of the ionosphere to reflect the transmitted signal. In order to do this, the ionosphere must be ionized or excited. The source of this excitation (ionization) is the Sun. The more active the sun is, the more ionizing radiation it emits, the more reflective the ionosphere becomes. Conversely, the less active the Sun, the more passive the ionosphere becomes, allowing the shorter wavelength (higher frequency) signals to escape into space. A measure of the suns activity is the number of "Spots" that appear per given time on the surface of the sun. The more spots, the greater the solar activity, the more reflective the ionosphere becomes. The more reflective the ionosphere, the greater the chance that a signal will bounce around the earth and be received by another station rather than be lost into space.
The Sun's activity occurs in periodic fashion, that is it goes from a maximum to a minimum activity each 11 years. (This is an average number and can vary as much as 2 years either way). When we are at a sunspot minimum, the best bands to operate are the lower frequency bands (80 and 40 meters) and conversely at a sunspot maximum the 15 and 10 meter bands become the preferred DX bands.
For further information I suggest the Radio Amateurs Handbook and the ARRL Antenna Handbook.
I hope this gave you some help in understanding the "Sunspot Cycle".
Until next time, 73
"ELMER"
Please send all questions to "ASK ELMER", c/o Marv, N1AWJ ; Glenn, KB1UL or Bob, WA1WVF, at the addresses listed on page 2 of the SQUELCH BURST.
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December 1986
ASK ELMER
Dear Elmer,
I have a problem. My house is on a small lot and I don't have any trees to string a dipole. Will a vertical antenna work for me on the Novice Bands ?
Signed, Cramped for Space
Dear Cramped,
Vertical antennas are fairly effective radiators, especially when band conditions are good. They have the advantage of a very low angle of radiation, causing long skip and being a good DX antenna. They do not take up much space, permitting their use in tight quarters and configuring them for multi-band is relatively easy.
There are some decided disadvantages with Vertical antennas. The first is that they require an extensive radial system for proper operation, and should be mounted as high as practical. This appears to be contradictory but in practice a 4 radial counterpoise resonant an each band is good enough. A severe disadvantage to the antenna is the Polarization problem. When working local or short skip contacts who are using dipoles, long wires or beams, i.e.., horizontally polarized, the Vertical antenna has a 20 dB polarization loss. This must be considered. A Vertical antenna is omni directional, which means that you don't need a rotor, but is susceptible to interference.
The bottom line is that if you are limited in space, the Vertical antenna may be the answer to your problems. If you have the space, go horizontal.
Until next time, 73,
Elmer.
Please send all questions to "ASK ELMER", c/o Marv, N1AWJ; Glenn, KB1UL or Bob, WA1WVF, at the addresses listed on page 2 of the SQUELCH BURST.
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January 1987
ASK ELMER
Dear Elmer,
I recently had a QSO where the other station said he had to go QRT and disconnect his antennas. There was a storm brewing. Wasn't he over-reacting?
Signed, Cool and calm.
Dear Cool,
I am sorry to inform you that the other station was not over-reacting. He was following good safety procedures. A Thunder Storm can produce electrical discharges in the form of a very high static electric charge as well as a dynamic movement of charges called Lightning. In both cases there is a static potential built up in the order of tens of millions of volts. Your antenna is a perfect collector of this charge. Can you imagine what would happen with 1000 volts or more applied to the antenna terminals of your radio?
Proper safety procedures dictate that you disconnect all antennas from the radios, and connect them directly to an earth ground. Ideally, the disconnect should be outside of the shack (building), so that the electrical discharge cannot induce a current into any of the other equipment in the house. Millions of volts mean currents of millions of amperes, which could easily vaporize a piece of transmission line. The ground wire should be of a heavy gauge (the heaver the better). The ground stakes should be at least 4 feet into the ground and a distance away from the foundation of the house greater than the depth of the ground stake. The effect of this grounding is to help dissipate the static charge before it grows to dangerous proportions (the lightning rod effect: a house protected with a lightning rod is less likely to be hit by lightning than one that has no lightning rod).
The whole intent of this discussion is not to scare you, but to make you aware that the old adage "An ounce of prevention is worth a pound of cure" is very true. The probability that your shack and/or your antenna will be hit by lightning is moderately remote, but it is a distinct possibility. Ground your antenna before the storm.
73, Elmer
Please send all questions to "ASK ELMER", c/o Marr, N1AWJ; Glenn, KB1UL or Bob, WA1WVF at the addresses listed on page 2 of the SQUELCH BURST.
February 1987
ASK ELMER
Dear Elmer,
At a recent Flea Market, I purchased a small CW Transceiver at a "steal". When I got home, I found out that the receiver had a VFO but the transmitter required crystals. Since I want to use the radio, I ordered some crystals. The crystal manufacturer sent me a letter asking about the frequency at series resonance or into what load capacity. What are they talking about?
Signed, Perplexed.
Dear Perplexed,
The manufacturer is trying to help you by asking these questions. They want to make sure that when you plug the crystals into your radio, the frequency marked on the crystal is the one you are transmitting on. Contrary to popular belief, a quartz crystal is not the absolute standard of frequency, its very good but not great. It like any other mechanical or electrical device can be made to move if coaxed properly. In this case, if the crystal were in a circuit which operated it at its true mechanical (electrical) resonance, it is said that the crystal is operating at its series resonant point. This is very nice, but most oscillators used in amateur radio do not operate the crystal at this point. The oscillators generally have some residual capacity remaining in the circuit. This is usually used to help trim the operating frequency of the oscillator to precisely the frequency you want allowing for manufacturing tolerances. you can use a cheaper crystal since the manufacturer doesn't have to hold very tight manufacturing tolerances.) This residual capacity is known as the crystals load capacity. In most cases, a load capacity of 24 or 32 Pico farads is used, but it can be of any value that the transceiver designer wanted. If you do not know the load capacity, but you have a copy of the radios schematic, you can easily determine it.
Find the oscillator circuit and starting at the crystal, list all of the capacitors in series with the crystal, and don't forget those at the input of the tube or transistor. Using the formula for capacitors in series, find out the total capacity. To this number add about 2 Pico farads for strays, and you have your load capacity. Simple wasn't it?
Now that you know all about it you can order those crystals with confidence.
Until next time, 73,
Elmer.
Please send all questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ; Glenn York, KB1UL; or Bob Hess, WA1WVF at the address listed on page 2 of the SQUELCH BURST.
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ASK ELMER
Dear Elmer, I was on the AMSAT bulletin board today and got a bad connection. I was downloading Keplerian elements and the following was all I got: Epoch Time: 1990 Jan 01 0000:00 UTC Inclination 23.4406 Deg RA of Node 0.0 Deg Eccentricity 0.0167133 Arg of Perigee 282.7685 Deg Mean Anomoly 357.6205 Deg Mean Motion 0.002737778522 Rev/day Decay Rate 0.0 Rev/day Semi Major Axis 149597870 Km
Can you or your readers help me determine to what these elements apply? Thanks very much. 73, Tom, W1ICH
Dear Tom, I am going to let the readership tell you what those elements relate to. The answers will appear in next months column. 73, Elmer
Send in your answers and see your name in print. Send all answers to ASK ELMER, c/o Marv Fleischman, N1AWJ, 171 Bob Hill Road, Ridgefield, Ct. 06877. Lets hear from you.
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ASK ELMER
In my last column, I posed a question to you sent in by Tom, W1ICH. He had downloaded the following Keplerian elements on the COMSAT Bulletin Board: Epoch Time 1990 Jan 01 0000:00 UTC Inclination 23.4406 Deg RA of Node 0.0 Deg Eccentricity 0.0167133 Arg of Perigee 282.7685 Deg Mean Anomoly 357.6205 Deg Mean Motion 0.002737778522 Rev/day Decay Rate 0.00 Rev/day Semi Major Axis 149597870 Km
Tom wanted to know what is this object.
I received the following answers:
Elmer, To the question posed by W1ICH in the march issue of the Squelch Burst, the only correct answer is: "THE SKY IS FALLING but who cares!!!!!" Chick Litle, C1UCK (Rick, WB1ASK)
Dear Elmer- Ref; W1ICH Conundrum Tracker Tom is a genius it's true Finding rare ones up there in the Blue But his ear to the sky Must be badly awry If Planet Earth is the best he can do!!
Sky, K1GF
I'll tell you friends, the answer true Which could be found in the last issue One need but look in the questioners place For the bottom lines of Ye Olde Jonque Boxxx, would bring a light to your face. Like the body described, the Sun in its place.
73, Elmer
ASK ELMER
Dear Elmer,
Now that we Novice operators and Technicians have Phone privileges on 10 Meters, I am a bit confused. My radio has a Mode selector with Upper and Lower Sideband. Which do I use, and when do I use the other.
Signed, Confused.
Dear Confused,
Many years ago when Single Sideband AM started to take the place of Double Sideband Exalted Carrier AM, a band plan was agreed upon by the Amateur Radio community. On bands below 40 Meters, all SSB transmissions are to be in the Lower sideband. On 20 Meters and above, the Upper sideband is to be used (this includes 10 Meters and VHF transmissions).
From a technical standpoint, there appears to be no reason to favor either sideband, therefore the band plan is arbitrary, but since it is accepted by the "Ham" community, there is no reason to change it.
I trust this helped to lessen the confusion.
73, Elmer
Elmer is here to help you with your questions on Amateur Radio. Send all correspondence to ASK ELMER, C/O Marv Fleischman, N1AWJ, PO Box 113, Ridgefield Ct. 06877
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ASK ELMER
Dear Elmer,
With the new Novice Band Expansion, and the FCC wanting back some of the 220 MHz band, I keep hearing the term ACSSB. What are they talking about?
Signed, Curious.
Dear Curious,
ACSSB stands for Amplitude Commandeered Single Sideband. In amplitude commandeering, the modulation amplitude (loudness range) is compressed similar to processing on a standard ssb transmitter. In a processing situation, the incoming audio is amplified, peak clipped and filtered to remove the fuzziness caused by the clipping. This maximizes the "Talk Power" of the SSB signal. The distortion of the signal is high but it is still fully readable. In ACSSB, the audio signal is not clipped but it is linearly compressed, so that a 10 to 1 amplitude change is compressed to a 2 to 1 amplitude change. This maximizes the "Talk Power" but does not distort the audio. At the receive end, the signal is expanded to the original amplitude range. Because it is SSB, the signal has less problems with receiver capture by an interfering signal, as well as a narrower bandwidth for transmission. This allows for more "channels" within a given band than can be provided with FM. ACSSB is not true SSB since a pilot tone is incorporated so that the receiver may be automatically tuned to the correct transmission frequency. This is to eliminate the RIT control from the receiver.
This is a brief description of a new technology based upon rather old principals. Further reading is recommended.
73, Elmer
Please send all your questions to "ASK ELMER, C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield Ct. 06877.
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July 1987
CASK ELMER
Dear Elmer,
I have a question for you. I am going to travel through Canada this summer. What do I do if I am bringing some "Ham" gear with me? Will my license be OK or do I have to write a letter to Canada to get a license, if so what is the address?
Thank you, A Concerned Ham
Dear Concerned,
Ordinarily when traveling outside the United States, you are required to obtain a temporary license or authorization from the country you are visiting, if you wish to operate Amateur Radio equipment while there. Obtaining this license or authorization generally involves contacting the countries Posts and Telecommunication authority, submitting a copy of your license with, more often than not, a payment for the temporary license. Prior to doing this you should contact the ARRL for the latest information regarding the country you wish to visit and operate in. This is true for all countries which we have reciprocal licensing agreements with (these countries are listed in the call book).
Fortunately for us, Canada and the United States have a unique relationship. Several years ago Canada and the United States signed a reciprocal licensing agreement which automatically licensees a U.S. operator full privileges of his or her current class of license, provided an equivalent class exists in Canada. This extends to all Canadian operators who wish to operate in the U.S. Since Canada does not have an equivalent Novice class, this agreement excludes Novice operators (as a general rule, a U.S. license of Technician Class or higher is required, more often General Class or higher).
While you are in Canada, you must observe all of the rules and regulations governing Amateur Radio Operation there, which includes frequencies, power levels, etc. A foreign operator using a reciprocal license in the U.S. is restricted to the bands which we are allowed to operate, and if there is a restriction in their operating frequencies in their home country, the restriction applies here. As an example, a European Ham, operating here with a reciprocal license, can only use the lower 2 MHz of the 2 meter band since they are not permitted operation in Europe from 146 thru 147.99 MHz.
While you are operating in the foreign country, the rule is that you identify your transmission (unless otherwise instructed by the licensing authority) with your U.S. call followed by mobile or portable the call prefix of the country. As an example, were I traveling in the Canadian Maritime provinces, I would identify as KA1XYZ mobile VE1.
Well Concerned, I hope you have a wonderful vacation in Canada. Canada is a beautiful country with great people, so see the sights and "Ham" it up.
73, Elmer.
Elmer is here to help you with your questions on Amateur Radio. Send all correspondence to ASK ELMER, C/O Marv Fleischman, P.O. Box 113, Ridgefield, Ct. 06877.
ASK ELMER
Dear Elmer, I recently purchased an FT-23R, 2 Meter HT with frequency capabilities expandable by "lifting a solder bridge". Yaesu will not tell me which solder bridge to lift unless I supply them with a MARS or CAP license. What are these planets? How do I get them? Help! All I want to do is monitor Railroad frequencies. Signed: Lost in Space
Dear Stargazer,
All commercially made radios are type approved by the FCC for use on specific frequencies. In order for a company like Yaesu to continue manufacturing and selling Amateur Radio equipment it must comply with the FCC rules and cannot authorize modification to transmit on other frequencies without proof of license for those frequencies. Much of this is a gray area, and manufacturers are very careful. You may, if you wish, modify the radio for receive only on out of band frequencies. The modification information is probably available from another ham with similar interests. As far as the planets, MARS is the Military Affiliate Radio Service, a service to the armed forces. Its' original function was to provide a pool of Amateur Radio operators trained in military operating procedures, to be available in time of emergency. Net operations is an important part of MARS activity. The frequencies used are assigned by the military and are not in the amateur bands. Currently MARS is used by the military for emergency operations and to carry messages from serviceman around the world to their families. Each service has its' own branch of MARS. In order to be a member of MARS, you must be a licensed Amateur Radio Operator. CAP is the Civil Air Patrol, who's function is to provide a pool of civilian aviators who can be called upon in the event of an emergency. Their organization is military in fashion, and their mission is to provide assistance to the civil authorities when called upon.
Continued on page 5
August 1987 Page 5 CASK ELMER cont.
CAP membership does not require an Amateur Radio License, and communication is very important but not the central function of the group. Many amateur radio operators are active in these organizations. If you wish any further information on these groups please contact them directly.
73, Elmer
Please send all questions to "ASK ELMER", C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield Ct. 06877. -----------------------------------------------
September 1987
ASK ELMER
Dear Elmer,
I just put up a dipole antenna, how do I tune it. I know that its' not right to tune up on the air, so is there any other way?
Signed "Puzzled".
Dear Puzzled,
You are quite right not to tune up on the air. It is, to say the very least quite discourteous to the other operators.
There is an instrument which can be quite effective in tuning up a resonant antenna such as a dipole. This instrument is the "Noise Bridge".
Noise you ask? We always want to get rid of noise and in a way we do and put it to use at the same time.
First of all, we must realize that noise consists of energy at all frequencies. This can be useful if we can select the frequency we want, it will act as an ultra-ultra low power transmitter. Well as an amateur radio operator you have access to a narrow band sensitive receiver. We have everything we need.
To use the noise bridge, the input connector is attached to the antenna cable, and the output to the input of your receiver. You tune the receiver to the frequency of interest, and turn on the noise bridge. Adjust the controls on the noise bridge to a minimum amount of noise on the receiver. (You can use the "S" meter or by listening to the noise level.)
There are two controls on the noise bridge, one for the resistive component, and one for the reactive component. The procedure is to adjust the two controls for a noise MINIMUM. If the resistive component indicates between 37 and 75 ohms and there is no reactive component is at zero, the antenna is tuned. The antenna has a VSWR of less than 1.5 to 1. If the reactive component indicates a value other than zero, use the noise bridge instruction sheet to determine the value of the reactive component. The impedance is the square root of the sum of the square of the resistive plus the square of the reactive component. A calculated value of 35 to 75 ohms still indicates a VSWR of less than 1.5 to 1.
Shorten, or lengthen the antenna until you reach these results.
By adjusting the frequency of the receiver, you can measure the antenna at any other frequency. Repeat the lengthening or shorting of the antenna until it is adjusted to a VSWR of less than 2:1 (25 to 100 ohms) over the frequencies of interest.
Have fun tuning the antenna without causing a problem to other operators using the frequency.
73, Elmer.
Please send all your questions to "ASK ELMER, C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield Ct. 06877.
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November 1987
ASK ELMER
Dear Elmer,
What is AMTOR all about? As a result of the Novice Enhancement, can I, as a novice, use this mode?
Signed: Befuddled in Belltown
Dear Befuddled,
Since the Novice Enhancement allows you to operate several specialized CW and Digital modes on the 1.25 meter and 23 centimeter bands, you may use this mode of transmission called AMTOR.
AMTOR is a is an acronym made up of "Amateur Teletype Over Radio", which is a form of Radio Teletype (RTTY). AMTOR is a CW transmission using a special 7 bit code (known as the Moore code), which allows the system to check for errors in the code as it is received. The two stations who are wish to communicate with each other first must establish contact. Station 1 will send out a call to station 2, and when station 2 receives it transmits an acknowledgement to station 1. This procedure synchronizes the two stations together with one acting as the "Talker" and the other as the "Listener". The protocol consists of the "Talker" sending 3 characters at a time to the "Listener". When revived, the listener checks the characters with a list in its computer, and if the characters are correct (a letter, number, punctuation mark, special symbol, etc.) then the "Listener" transmits an acknowledgement back to the "Talker" station. The "Talker" continues with the next 3 characters, and so on until the message is complete. If at any time the "Listener" does not receive the characters correctly, it responds negatively to the "Talker" which will resend the three characters until they are correctly received, or the computer senses that the contact should be terminated, and restarted at a later time.
Once the initial message is completed, the two stations reverse their roles, i.e.. the "Talker" becomes the "Listener", etc. This continues until the communication is complete, when the two stations break contact.
There are other special features in AMTOR such as FEC, and Listen only, and stations can be partially automated using AMTOR. The details regarding these other features are beyond the scope of this brief reply. For further information I recommend the ARRL Radio Amateurs Handbook section on AMTOR.
73, ELMER
Please send all your questions, comments and suggestions to "ASK ELMER", C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield Ct. 06877.
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December 1987
CASK ELMER
Dear Elmer,
I have got a question about the QSL Bureau. How do they work and where do I send them ? I have worked some DX and they said "QSL via bureau". I also hear some DX stations asking for "Greenbacks or Greenstamps", What are these ?
Signed, Confused
Dear Confused,
With today's international postal rates, is can become very expensive to send and receive QSL cards in any quantity. The "Outgoing QSL Bureau" set up by the ARRL is a way of inexpensively shipping cards overseas in bulk at bulk postal rates. In order to use the ARRL Outgoing QSL Bureau, you must be a member of the ARRL. When you fill out a card, instead of putting the recipients address on the face of the card, you write his call in block letters at the upper right hand corner of the card. Arrange all of your cards in alphabetical order of call signs. Bundle the cards together with the mailing label from the current issue of QST, and a check in the amount of $1.00 per pound of cards or less (i.e., if you have 3.5 pounds of cards, you send $4.00). A pound of cards is about 120 heavy QSL cards. Send all of this to the ARRL, 225 Main St., Newington, Ct. 06111, Attn. Outgoing QSL Bureau. The Bureau, when they receive your cards, will sort them into bins assigned to the incoming QSL Bureaus in each of the countries which have them. When they have collected enough cards for a shipment, the ship them, in bulk by sea mail to the incoming QSL bureau in the desired country. This can take a considerable time before the card reaches its final destination. Once the Incoming QSL bureau receives the cards, they distribute them to the hams registered with them, either directly or through local clubs. If you are not an ARRL member, you may send your cards directly to the QSL bureau of the country you desire. Their addresses are in the front section of the "Call Book".
A second reason for using the QSL bureau is that you may not have the address of the ham with which you had the contact. The local bureau has a good chance of having the address.
If you wish to QSL directly, without the QSL Bureau, you may but it is suggested that you include sufficient postage for the other ham to reply. Many times you would use "International Postal Reply Coupons", which are available from your central Post Office. Each coupon is equal to the postage for one ounce of first class surface mail. Airmail requires several "IRC's". They are relatively expensive, so many hams to save money enclose a "Greenstamp" with their QSL card. The "Greenstamp" is a US Dollar bill. If you do this be careful. This is illegal in some countries. When in doubt, DON'T.
Additional information is available from the ARRL.
Hope this puts you in the know.
73, Elmer
Please send all questions to "ASK ELMER", C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield Ct. 06877
April 1988
ASK ELMER
Dear Elmer,
My Quad antenna has a 4 to 1 SWR, and I have a lot of TVI. If I use an antenna tuner, will that correct the SWR and make the Quad work correctly? Could it reduce my TVI?
A beginner....
Dear Beg,
If you could make or buy an "Antenna Tuner", you could probably match the antenna to the feed line and transmitter. This would allow you to transfer maximum power to the antenna. It will also help keep RF out of the shack, so it may reduce local TVI. But alas, most Hams don't use "Antenna Tuners", they use "Transmatches". These match the Antenna, as it appears at the shack end of the transmission line, to the transmitter. This method only satisfies the transmitters requirement that it be loaded with a 50 Ohm load. The antenna is still mismatched to the feed line, and a high standing wave is still present on the transmission line. This high standing wave may cause the transmission line to radiate, which may cause TVI. If you are fortunate, the radiation pattern from the feed line will not intercept your TV set, and no TVI. The "Antenna Tuner" may help, the "Transmatch" may not. Will either of these make the Quad antenna work correctly? If the antenna is designed and constructed properly, they will help get the signal to the antenna and if the antenna is fed properly, it will radiate at it's maximum efficiency. Under these conditions, one can say that they would make the antenna work correctly. In the next "ASK ELMER", I will explain what is meant by VSWR, and its' significance.
Well "Beg", I hope you are all properly matched up with the answer.
73,
ELMER
Send all questions and comments to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
August 1988
ASK ELMER
Dear Elmer,
My vertical HF antenna finally came down in a windstorm, and I figured I would get up there with the big boys, so I put up a tower and a beam. I followed all the instructions, and started with the beam facing north. Yesterday, I heard a "JA" station, so I got out my map and turned my beam west, and he disappeared. I tried east, but he wasn't there either, but he was "S9+" when the beam was north. Are all my maps wrong? The North Pole is north, Japan is west or are all my maps wrong?
Signed, Getting Dizzy
Dear Dizzy,
Spin no more. North is the way west, and sometimes east, but rarely south, except when long path is the only way, then south may be west or east. Confused? Don't be. The earth, contrary to the belief of some, is a sphere, with most of the inhabited areas in the northern hemisphere. Since most maps are flat, they do not show you the shortest distance between two points on the earth ( the shortest distance on the earth's surface is not a straight line but a curved line, an arc). As most of the inhabited areas are located in the northern hemisphere, and the earth is a sphere, then to communicate with a person on the other side of the earth, the shortest distance is over the North Pole. The best way to see this is to get yourself a globe map of the earth or a "Great Circle" map of the earth centered on a city close to your location. You would be surprised how close some of those exotic DX countries are. There are times when going over the pole doesn't seem to work, but turning your beam in the opposite direction, and you have to pour water over the front end of your radio to keep it from smoking due to the 80 dB over S9 signal coming in. This is known as long path propagation. You can' rely on this happening, so use it when it's there, but follow the great circle directions for more reliable results. Hope this stops your spinning around. 73, Elmer
Send all your questions to "Ask Elmer", c/o Marv Fleischman, PO Box 113, Ridgefield CT 06877
December 1988
CASK ELMER
Dear Elmer,
I am interested in operating on RTTY, AMTOR and Packet but I am confused about one piece of equipment. Those using RTTY and AMTOR are using a "TU" between their radio and computer, whereas in Packet you use a "TNC". When I use the phone lines I need to use a "Modem". HELP! What do I really need?
Signed, Confused.
Dear Confused,
The MODEM, TNC and TU are different names for the same type of item. Their function is to translate the information as received over the radio or phone lines into digital information which the computer can use. At times this can be a trying task.
The most popular way to transmit digital signals at relatively high speed, is to convert them to an audio tone, and use this tone to modulate a SSB transmitter. Since a SSB transmitter suppresses the carrier, the transmitted signal is identical to a Frequency Shifted Signal (FSK). When detected by the "MODEM, TU or TNC", the signals are converted into a digital signal with only 2 levels (zero and >2.4 volts). These signals can be used to drive the computer. It is the computers job to control the system and to convert the digital signal into letters, numbers and symbols which we can understand.
I should define what the alphabet soup represents; "TU" stands for the Terminal Unit; "TNC" is a Terminal Node Controller; and the "MODEM" represents a Modulator Demodulator.
There are several manufacturers which make "TU/TNC" devices which operate all modes of digital communication and can be used with most of the popular home and business computers to provide operation on RTTY, AMTOR, CW, PACKET and FAX. These easy to use, versatile devices can easily expand your radio operating horizons.
Have FUN!
73, Elmer
Send all your questions and comments to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield CT 06877.
February 1988
NE2Q FOR I.D.
C or...how to sound like a jerk.
By Jay Kolinsky, NE2Q
This is for all you so called broadcaster type hams that use the term "FOR ID" after your call sign.
You don't know what a 'broadcaster' type ham is? Well he is the guy that likes to listen to himself talk. He usually can be spotted by his long winded transmissions without a break. He jumps from one subject to another like a jack rabbit, never leaving space for someone to comment. When he turns it over to the person that's listening, the listener is usually so bored he simply makes some excuse and moves off frequency.
The broadcaster usually uses phonetics for his call each time he turns it over, even if he just received a report of 5 by 9. He'll even use phonetics as he announces his call with each transmission on a repeater. He loves his call and uses it as much as possible. Most broadcasters are so involved with the constant announcement of their call signs they've lost the actual reason to use a call sign. Hence the use of the term...NE2Q (FOR ID).
This practice of mainly newcomers to the hobby, seems to have originated on two meter repeaters. Now it is spreading like a cancer to the H.F. bands. Guess those beginners think the DX doesn't know the purpose of call letters either and they are here to tell em'.
So if you want to start sounding like a real neophyte, start using (FOR ID) after your call. When you've mastered the art of (FOR ID) you can move onto some other extensively used broadcaster terms such as 'BY GOLLY' and 'VERY VERY FINE'.
When you really feel comfortable using these moronic terms in your ham vocabulary, you can move up to the ultimate (ID). When you meet someone in person for the first time, state your name followed by (FOR ID).
After all, most non-hams don't know yet that a name by itself is not really the proper way to identify oneself.
EXAMPLE: Good morning. My name is Jay for ID.
(FOR ID) can also be used to snare that rare exotic DX station. Simply call CQ DX and sign as follows: NE2Q4ID. The unsuspecting DX will assume you are actually NE2Q/4ID and operating portable in [4ID] land. Yes the DX will be chasing you.
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We will publish any rebuttals to the above article if you send them in. Ed.
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September 1988
CASK ELMER
Dear Elmer,
Being new to amateur radio, I want to improve my ability to handle messages, my competence as a communicator, and as an operator. Short of enrolling in a college communications program, what should I do? I would prefer to do this at home, and at my own pace.
Signed, Driven.
Dear Drive,
Are you in luck. Have I got such a deal for you, you can't resist. If your license grade is Novice or Technician, is there a net for you which will make you such an operator, you'll be the envy of all your friends and neighbors. What is this net, you ask? The Connecticut Slow Net. And where do you find such a net? Where else, 3721 KHz at 7:30 local time. And do I have a nice net manager for you, Mary Baxter, WB1GXZ. You couldn't be in better hands. So try it, you'll like it.
For those of you, who want to talk on VHF, we got one just for you. It's the Western Connecticut Net (WESTCON), found nightly on the 147.180/.780 repeater in Naugatuck CT, at 0130 Z. Boy will you learn to operate and handle traffic. I tell you, the fun you'll have, the operators you'll meet and the things you will learn, what more could you want?
Both of these nets are formal directed nets, so, you announce yourself to the Net control operator, and will they tell you where to go......
Remember, behave yourself, but have fun.
Until next time, 73.
Elmer
Send all your questions and comments to "Ask Elmer", c/o Marv Fleischman, P.O. Box 113, Ridgefield CT. 06877
February 1989
ASK ELMER
Dear Elmer,
I am interested in operating on RTTY, AMTOR and Packet but I am confused about one piece of equipment. Those using RTTY and AMTOR are using a "TU" between their radio and computer, whereas in Packet you use a "TNC". When I use the phone lines I need to use a "Modem". HELP! What do I really need?
Signed, Confused.
Dear Confused,
The MODEM, TNC and TU are different names for the same type of item. Their function is to translate the information as received over the radio or phone lines into digital information which the computer can use. At times this can be a trying task.
The most popular way to transmit digital signals at relatively high speed, is to convert them to an audio tone, and use this tone to modulate a SSB transmitter. Since a SSB transmitter suppresses the carrier, the transmitted signal is identical to a Frequency Shifted Signal (FSK). When detected by the "MODEM, TU or TNC", the signals are converted into a digital signal with only 2 levels (zero and >2.4 volts). These signals can be used to drive the computer. It is the computers job to control the system and to convert the digital signal into letters, numbers and symbols which we can understand.
I should define what the alphabet soup represents; "TU" stands for the Terminal Unit; "TNC" is a Terminal Node Controller; and the "MODEM" represents a Modulator Demodulator.
There are several manufacturers which make "TU/TNC" devices which operate all modes of digital communication and can be used with most of the popular home and business computers to provide operation on RTTY, AMTOR, CW, PACKET and FAX. These easy to use, versatile devices can easily expand your radio operating horizons.
Have FUN!
73, Elmer
Send all your questions and comments to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield CT 06877.
May 1989
ASK ELMER
Dear Elmer,
Now that I know that I can use a Transmatch to help with my TVI and RFI problems, I don't want to buy one. Their too expensive, and I want to say I made it myself. So what do I do ?
Signed, I Makum.
Dear I. M.
Have I got a simple Transmatch for you. It only requires 5 components and a case, and it will cover the 10 thru 160 meter band. If you use the right size capacitor, it can handle a full KW. The circuit consists of 2 connectors, 1- 2 pole 10 position rotary switch, 1 variable capacitor 10 to 365 pF or so, and an inductor which you will wind yourself from 12 ga copper "house service" wire. The box can be constructed from printed circuit board material and should be large enough to house all the parts with about 1 inch clearance around the unmeshed capacitor and the coil.
Below is a circuit diagram of the Transmatch. Next month, I will give you the construction information.
June 1989
CASK ELMER
Dear I. M.
I hope I have whetted your appetite so that you will construct the Transmatch. If you're ready, let's get going. Making the inductor is first. The materials we require are; 5 feet of 14 Gauge Copper wire; 12 plastic coffee stirrers (any type will do as long as they are at least 4 inches long); small bottle of thick acrylic cement (available from hobby shops); plastic tape such as Scotch tape; 12 Oz. aluminum soda can; 6 x 8 inch sheet of heavy waxed paper. For a temporary form, we will use the soda can. First cover the can with a single wrap of waxed paper to prevent any glue from sticking to the can. Use tape to secure the waxed paper. On top of the waxed paper, position 6 of the coffee stirrers evenly spaced around the can as shown below. Secure the stirrers to the waxed paper on their ends only with tape. The center 3 inches of stirrer should be free of any tape. You will be winding the inductor here. Strip 14 feet of the 14 Gauge wire, and discard the insulation. Wind 18 turns of wire as neatly spaced as you can, around the can/coffee stirrers, taking care to prevent any turns from shorting to each other. When this is completed, secure the ends of the wire with some tape to prevent unraveling. Next, position the remaining 6 coffee stirrers atop the wire and over the first 6 coffee stirrers. Secure these stirrere with tape at their ends. Using the heavy acrylic cement, cement the coffee stirrers and wire together, with the cement acting as the connecting plastic. Allow several hours for this to dry. We will continue the construction of the Transmatch next month.
July 1989
CASK ELMER
Dear I'M.
Well we built the coil, now we must attach the taps. As there are 18 turns on the coil, the first tap will be 2 turns from the ground end of the coil and each of the other taps at 6, 10 and 14 turns from the end.
First, slide the coil off of the form (the soda can). Remove all of the waxed paper and any other foreign matter (the cellophane tape, etc.) from around the coil, so that the coil is now self supporting (being held by the glued on coffee stirrers). Cut 5 pieces of 14 Ga. Copper wire about 8 inches long. Bare the ends for a distance of about 1/2 inch. Start at one end of the coil, which we will designate as the ground end of the coil, and count up 2 turns. Attach one of the 8 inch pieces of wire by wrapping it around the coil's wire, and soldering this connection. Make the connection adjacent to one of the coffee stirrer supports. Next count up 6 turns from the ground end and repeat the operation. Repeat this at 10 and 14 turns. Make sure that the taps are not shorting out the windings of the coil.
When this operation is completed, set aside the coil for future use.
The next step is to construct the housing for the Transmatch. We will use PC board material for the housing. The material can be obtained at most surplus houses, ham flea markets and Radio Shack. Of these choices, the Ham Flea Market is probably the better choice, i.e.., cheaper and better quality than Radio Shack material. We will require 4 pieces at least 10 by 10 inches by 1/16 inch thick. Next ASK ELMER we will discuss the construction of the case.
Until then 73,
ELMER.
Send your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
August 1989
ASK ELMER
Dear I.M.
In this installment of the continuing saga of the homebrew transmatch, we will construct the case.
In the early days of "Ham" radio, most projects were constructed on wooden bases, "Breadboards", without any shielding, as case construction was difficult, expensive and TVI was non-existent. Today we require very tight RF shielding to prevent all of our electric appliances from going crazy, as well as our own equipment in the shack due to high RF fields.
The overall size of the transmatch is 10 inches deep by 10 inches wide and 5 inches high. As you have obtained the four pieces of PC board material 10 inches by 10 inches, you will put aside two of the pieces which will be the top and bottom covers of the box. The remaining two pieces will be cut exactly in half. To do this you should use a straight sheet metal shear or large pair of scissors. Before you start the cut, score, the PC board material as deeply as possible. This will make the cut more accurate and easier to do. You now have 4 pieces 10 by 5 inches in size. Two will be used for the sides, and one each for the front and rear. Using some steel wool, polish the copper of the PC board material to remove any surface coatings or corrosion. It should be bright and shiny when you are done.
FRONT PANEL... There are two holes to be drilled in the front panel. These holes are 3/8 inch diameter and are located as follows: With a ruler, measure down from the 10 inch side 2 1/2 inches, and from the 5 inch side 3 1/4 inches and 6 3/4 inches. Mark these points with a pencil or marking pen. Drill a 3/8 inch diameter hole at each of these points. One hole will be used for the variable capacitor tuning, and one for the coil switch. Put this panel aside and we will drill out the rear panel.
REAR PANEL... We will be drilling a total of 7 holes on the rear panel in order to mount our RF connectors and a ground terminal. The RF connectors we will use will be the chassis mount SO-239 (Radio Shack 278-201).
On the rear panel, measure down from the 10 inch side 2 1/2 inches, and from the 5 inch side 2 inches, 5 inches and 8 inches. Mark these points. Use the 3/8 inch drill to drill a hole at the 2 and 8 inch hole locations. These will be used for the RF connectors. Place the RF connectors in these holes and mark, using a pencil, two of the four mounting holes. Using a 5/16 in drill, drill out these holes, as well as the hole at the 5 inch point on the back panel. You should have a total of 9 holes drilled out on the panel. Use #4 hardware to attach the RF connectors to the back panel. Use #6 hardware for the ground connection. Put the head of the screw on the inside of the panel so that the threaded part sticks out the rear at least 1/2 inch. Secure it with a nut and lock washer, and then loosely put two flat washers and a nut on the screw. This will act as your external ground terminal.
In the next installment we will assemble the case, and make it ready for the coil and capacitor mounting as well as the final wiring. Until then,
73.
Elmer
Send all your questions, comments to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
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September 1989
CASK ELMER
Dear I.M.
Now we are ready to assemble the case of the transmatch as well as do some front panel marking. Here we go.....
We will start by marking the front panel. Since the holes are positioned symmetrically about the center line of the panel, the hole on the left will be for the inductor switch and the hole on the right for the variable capacitor. If the PC material you are using is single sided copper, the copper side is on the inside of the case. If double sided material is used, choose the nicest looking side for the front panel. Using some steel wool or the lightly abrasive nylon scouring pads, clean the circuit board material and try to achieve a nice lustrous finish on the copper. On the outside surface, you may use decals or a marking pen to label the controls. A suggested panel labeling is shown below. Note that the switch detents every 30 degrees, and has 11 possible positions of which we are using 10.
Page October 1989
ASK ELMER
Dear I.M.
We are nearly to the end of our construction project. In this installment we will mount the inductor and complete the wiring of the Transmatch.
The inductor will be mounted directly behind the switch to make wiring easy and to allow plenty of room around the tuning capacitor. As the inductor is about 3 inches in diameter, we have about 1 inch spacing from the top and bottom of the case. To mount the inductor, I would suggest cutting pieces of a plastic fork or spoon handle ( the picnic variety), about 2 inches long. Four pieces would be enough, but you can add more if you wish. Using a soldering iron as a heat source, bend back 1/2 inch on each end of the plastic piece, to form a Z shape. (Refer to the diagram ). Using some epoxy, glue the plastic pieces to the inductor so that it forms 4 feet to support the inductor. Once the epoxy has hardened, position the inductor about 1/2 inch behind the switch and use epoxy to glue the bottom of the "feet" to the case. Once this is done, and the epoxy is hardened, we are ready to wire the transmatch. To wire, refer to the schematic in the May 1989 issue of the SQUELCH BURST, and the diagram below. Keep the wires short, but don't get carried away.
February 1990
CASK ELMERC
Dear Elmer,
HELP!!!!! My computer which I want to use on Packet causes RFI in the shack. I can't operate on some of the HF bands. What can I do to eliminate the RFI so I can operate??????
Signed, Frazzeled.
Dear Fraz,
Take heart, you are not alone with this problem. All computers are, to a greater or lesser extent, transmitters. Inside the computer there are "Clock" oscillators which operate in the ham bands or have harmonics in those bands. As a computer is a digital system, the fast switching speed of the logic IC's, as well as the long wires on the PC board as well as the cables connected to the outboard devices (printers, disk drives, monitors, etc.), act as effective miniature transmitters and antennas. Many home computers are not shielded too well, as the FCC requirements are very lax.
In order to solve the problem, there are two areas you must consider. First, is the interfering signals getting into the radio via the antenna, the power lines and connecting cables, or both. The way to determent this is to disconnect your antenna, and any cables other than the power cord from your rig. Short the antenna jack on our rig, and with the computer on, listen for the interference. Most modern rigs are very well shielded, and you will probably find no significant signals from your computer. Reconnect any plugs and cables to the rig, one at a time and repeat the test. If any of the cables cause an increase in the interfering signals, you should try to suppress them by winding a few turns of the cable around a ferrite core from an old TV defection yoke or torrid, as well as bypassing the cable at the rig with .01 uF disk capacitors. Make sure the cables to the rig are all shielded, and the shields are connected to ground. Once the cables are RFI proofed, connect the antenna to the rig. Check for the signals, and if they are there, the second area must be addressed. This is the computer itself. First, make sure that all of the computer connecting cables are shielded and grounded.
Continued on Page C
February 1990 Page
ASK ELMER cont.C
Second, use ferrite torrid and cores to reduce or eliminate the rf on the connecting cables. Finally, we must shield the computer itself. There is no guaranteed method, but one method that is fairly successful, is the use of Aluminum foil inside the case of the computer. All of the foil should be connected together and grounded. You can use thin single sided printed circuit board material in place of the foil (it will do a good job but it is more expensive). Good Luck Frazz, you'll need it.
73, Elmer.
Send all your questions, comments, ideas, etc. to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
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March 1990
CASK ELMERC
Dear Elmer,
What would the effects be of mounting a Yagi antenna, half a wave length high and between two large hills one wavelength apart at the operating frequency?
Yours truly, In a whole.
Dear In,
You picked yourself some location. I hope that the direction of your valley is north-east, south-west, or you may not talk to too many people. You are located in, what microwave engineers call a Wave guide. In effect, it is like having a highly directional beam, and a very low loss path, in the direction of the valley. Energy from your antenna will be reflected and directed by the hills with relatively little loss. If this is a problem, which I can see it might be, I would suggest lowering the Yagi to less than 1/4 wavelength off the ground. This will raise the angle of radiation, allowing you to radiate some of your signal over the hilltops and communicate in other directions. I hope this is not a 160 meter beam we are discussing, Hi, Hi. It would help to have a crank up tower, so that its' elevation can be controlled for the best signal. There are no guarantees in this situation, so I wish you luck. If these hills are that close to your shack, I would suggest building your tower on top of one of the hills. The loss in the coax will be made up for in the increases ability to radiate in a direction of your choice.
Well I hope this got you out of your hole, Whole.
Until next time, 73. Elmer
Send all your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
June 1990
ASK ELMERC
Dear Elmer,
I am in the process of assembling a station to work the 80 meter band. My antenna situation strongly suggests using a "Drooped Dipole". Trouble is, I'm at the bottom of a valley, and if I want any QSO's, I need to toss some signal over the ridges. I want to know what kind of radiation angle the drooped dipole gives, and how to increase it if I need to.
Signed, Depressed.
Dear Depressed,
Cheer up. Your drooped dipole will do the job. Any dipole, droops to some extent, and this is due to the wires own weight. Yours just droops more than usual. The important thing to remember, is that the H field ( magnetic or current generated field) is the one we are primarily concerned with. For a low radiation angle, the feed point of the dipole (the current maximum point) must be at least 1/2 wavelength above the ground. At 80 meters this is approximately 130 feet above the ground. Not too practical unless you have some very high trees. The lower the feed point, the higher the angle of radiation. An ideal dipole, elevated 1/2 wavelength above earth has a radiation angle of 30 degrees, and a nearly omni directional vertical pattern when the antenna height is at 1/8 wavelength. Rather than go into the complex calculation of radiation angle verses antenna height, I recommend the ARRL Antenna Handbook, pages 2-16 thru 2-20 for a good treatment of this topic. Using the chart on page 2-19, you can customize your antenna height to your location. If you know your location with respect to the surrounding hills, you can calculate the angle of radiation needed to just clear the mountains. If you work it right, you may use the mountains to diffract your signal to achieve the effects of a low angle of radiation for DX'ing as well as extended ground waves. Have fun experimenting.
73, Elmer
Send all of your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
September 1990
ASK ELMERC
Dear Elmer,
HELP!!!!! I cant tune my new multiband vertical antenna. Its' driving me crazy. The only thing I have been successful in doing is to get plenty of exercise running in and out of the shack and getting trained to operate a slide trombone. Is there an easier way.
Signed "Desperate".
Dear Desperate,
Don't despair, all is not lost. Most vertical antennas are very sharp on the lower bands. It is very easy to miss the tuning point. There is a method, a rather old one which relies on an instrument called the "Grid Dip Oscillator". This rather simple device has the ability to indicate the resonant frequency of any device coupled to it. At resonance, a circuit is resistive, and will absorb energy. A Grid Dip Oscillator indicates resonance by a "dip" in the grid current of a vacuum tube oscillator. The frequency indicated by the Grid Dip Oscillator is used to indicate the resonance of the antenna. All you need to do is to couple the dip oscillator to the feed line going to the antenna, by using a connector with one or two turns of wire attached to it. Check the frequency of resonance and if the frequency is too low, shorten the antenna. If too high, lengthen it. Repeat this on each band, until the entire antenna is tuned. A fine tuning is then performed using your radio on low power, and measuring the VSWR at the end of the feed line. By the way, the ideal feed line length for remotely checking an antenna on all of the bands from 80 thru 10 meters is 91 Ft 2 In. This is the 1/2 wavelength multiple on all of the bands, the measurement you make is as if you were at the base of your antenna. The diagram shows the connector with the coupling loop attached, as well as the position of the dip meter. By the way, the dip meter should be coupled lightly to the loop so that it's resonance is not effected by the loops material.
Good Luck, and 73. Elmer
Send all of your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
November 1990
ASK ELMER
Dear Elmer,
My friend and I just finished the construction of two 2 meter antennas. Both of the antennas are collinear, but their configuration and construction differ. How can we determine which is the better antenna. We have no special equipment available, but we are willing to construct simple test instruments. Can you help?
A. Real
Dear A,
Many Hams would try to use signal reports from other operators as an indication of the relative performance of their antennas. This method can give you a subjective indication of performance, but relies too heavily on local propagation and the condition and location of the receiving stations. If you are satisfied with this, you need not read further. Your question implies that you would like some type of quantative and repeatable measurements. There are many methods one can use, but a simple antenna range method is suggested. For this method you require an open space at least 5 wavelengths on all sides of the antenna. (At 2 meters this works out to about a 70 foot circle.) A parking lot, school yard or open field would work well. This 5 wavelength distance will allow you to make far field radiation measurements. To make the measurements, you require a field strength meter. Professional instruments cost many thousands of dollars, and are very elaborate, whereas you may construct a very simple one which will give you relative but repeatable readings. The cost of this instrument is about $30 or less if you can get to a Ham Flea market or you have a well stocked junk box. To construct the meter you require the following parts; 1 ea. 100 uA meter, 1N34 or 1N270 or equiv. germanium diode; .001 ufd disc capacitor; 5pF to 25pF variable capacitor; 27pF disc ceramic or mica capacitor; inductor consisting of 7 turns # 26 enamel or format on a 1/8 inch dia. form (plastic or cardboard); 10K potentiometer; Radio Shack 270-1409 replacement antenna; 1/4 inch banana jack and plug and a case to hold it all. The circuit diagram of the field strength meter as well as it's use will be in my next column.
Until next month, 73. Elmer
Send all of your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
December 1990
ASK ELMER
The continuing saga of the "Poor Mans Antenna Range", or how to tell if your aerial's better than your friends on the "Cheap".
Now you have gathered all the parts needed for your field strength meter, you are ready to construct it. I hope the case you obtained is large enough to hold everything but not so large that you need a wagon to carry it, Hi Hi.. The circuit diagram for the meter follows. The values are not carved in stone, so that small variations are allowed. If it works, your variations were ok, if not back to the shop.
To test the field strength meter, use your HT on low power, as a source of RF. Place the field strength meter's antenna at least 10 feet away from the HT's antenna. Key up the HT, and tune the variable capacitor C2 for a maximum deflection on the meter. Note that R1 should be set for maximum sensitivity initially. Use this to adjust the meters overall sensitivity. C2 is tuning the meter to the HT's operating frequency, and should always be peaked. Use a permanent felt tipped marker to make approximate frequency calibration marks on the case to allow more rapid field adjustment. Remember to identify whenever you key up your HT, and indicate you are performing a test. Stay off repeater frequencies, as you do not want to cause any QRM. In our final installment we will discuss how the antenna measurements are made and how they are graphed. So until then, sharpen your pencils.
73, Elmer
Send all of your questions and comments to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
January 1991 ASK ELMER
Dear A. Real,
This is the final installment in the "Poor Mans Antenna Range". Now that you have all of the equipment necessary, you are ready to start your comparative measurements.
As you are measuring the performance of a pair of 2 meter antennas, I would suggest the use of a 6 foot mast to support the antennas approximately 1 wavelength above the ground. You may support the mast using any means available, but a small TV tripod tower (a 2 ft. roof mount tripod is available from Radio Shack for a nominal sum) is very handy. Now a trip to your range is in order. Refer to the November issue of the Squelch Burst for suggested locations. Besides the antenna and it's mount, you should take along an "HT" with at least 1 watt output, approximately 50 ft of coax, to connect the "HT" to the test antenna, your Field Strength Meter, a pad and pencils and lastly a tape measure so that you can measure the length of your range.
Once out at your range, erect the first antenna to be tested in the center of your range. Mark off 5 wavelengths from the antenna in all directions, as this will be far field measurements. At this distance, shadowing and other effects tend to disappear. Mark off approximately 30 degree increments
around the tower, as you will be taking measurements going around a 5 wavelength circle (32 feet) in 30 degree steps.
The measurement is relatively simple as it consists of keying up the "HT" at three frequencies (low, center and high frequencies on the band) and recording the readings at each of the 30 degree positions around the 5 wavelength circle. When the measurements are made, IDENTIFY YOURSELF AT EACH TRANSMISSION AND INDICATE YOU ARE TESTING. AVOID INTERFERING WITH OTHER STATIONS. REMEMBER GOOD OPERATING PRACTICES ALWAYS PREVAIL. Record the meter readings at each point and frequency. When you are done you should have recorded 36 readings. Switch antennas and repeat the measurements. You can compare the relative performance of the two antennas directly, or you may plot the results on "Polar Coordinate" graph paper (available from the ARRL or any technical art supply store or school bookstore). If you elect to plot your results, you can easily compare the relative radiation patterns of the two antennas. To those who want to do measurements on HF antennas, and don't have a range the size of the state of CT, may scale their antennas to a higher frequency and get a good indication of their performance.
For further information the following publications are suggested:
ARRL; The ARRL Antenna Compendium
ARRL; The ARRL Antenna Handbook
ARRL; The Radio Amateurs Handbook
J. Carr, K4IPV; Antenna Data Reference Manual, Tab Books, 1979
RSGB; Radio Communication Handbook
Antennas and their measurement are one of the fields yet remaining in which amateur radio operators can still experiment on an equal footing with commercial antenna suppliers.
Well A. Real, I hope this series answers your questions and gets you out there experimenting and learning and having fun. By the way, when you complete your experiments, write an article for your club's publication. They will appreciate it.
Until next month, 73,
Elmer
November 1991
ASK ELMER
100 Hz. PL oscillator construction (Ref. 10/91)
Dear Pvt. L. Ine,
To continue with our construction and installation of the sub-audible tone encoder, we will discuss construction methods and tuning of the encoder.
To construct the encoder we will use "Surface Mount" methods, which will insure the smallest possible size.
A reasonable circuit board for this project would be the Radio Shack 276-150 General Purpose IC PC Board. All of the parts will be mounted on the circuit (copper clad) side. First prepare the 8038P chip by clipping off the bottom segments of each of the leads. Position the 8038P in the center of the circuit board with the stubs of it's leads touching their respective 3 hole lands. Solder the leads to their respective lands. Wire the components from land to land as required, dressing them as flatly on the PC board as possible. Remember to leave a space for the frequency adjust resistor Rs. Do not put components through the holes, but solder them on top of the pads. After the wiring is done trim, away the excess PC board. To wire the oscillator to a radio, connect the common to the radio ground. Connect the + input to the radio's "switched" transmit power line, and the tone out to the microphone input. If the PTT is switched through the microphone line, add a .01 uF cap. in series with the 22K resistor on the tone out line. This will DC isolate the oscillator from the PTT line. The only method of setting the frequency of the oscillator is with a frequency counter, that has 1 Hz resolution. Connect the input of the counter to pin 2 of the 8038P, and adjust Rs for 100 Hz. Increasing the value of Rs will decrease the tone's frequency. To set the tone level, a good starting point is to use another radio as a receiver, and adjust the 100K pot until you just hear the tone in the receiver's audio. Contact the repeaters control operator to set up an on-the-air test with the repeater to verify the operation of the PL oscillator.
Good Luck, and 73, Elmer.
ASK ELMER MARCH 1991
Dear Elmer, I have a ground mounted 14 MHz Quarter WaveŤ Vertical with 4 buried radials. Someone told meŤ that I should raise the base of the antenna to 10Ť Ft. or more above the ground and elevate theŤ radials. Will this work better for long distanceŤ contacts? Sparky,
Dear Sparky, This is one of these questions which is veryŤ difficult to say yes or no. There is a great dealŤ of discussion on the merits of elevating verticalŤ HF antennas to modify their performance, i.e.., toŤ change their angle of radiation. None of theŤ antenna engineering manuals or texts address thisŤ point, other than discussing the importance of aŤ good radial system or counterpoise (which is anŤ elevated radial system). My own personalŤ experience has been using a Butternut verticalŤ antenna, elevated 20 Ft. above the ground. I haveŤ 4 counterpoise on each band and the antennaŤ performs very well. I have no personal experienceŤ with a ground mounted system but I have had QSO'sŤ with many operators whose antennas were groundŤ mounted verticals. They reported very goodŤ results with their antennas. The only report onŤ this subject which I am aware of is calledŤ "VERTICAL USERS NOVICE TO EXTRA", by "DOC"Ť Danrick, AF2Y; dated 1980. The report infers thatŤ an elevated vertical performs better than a groundŤ mounted antenna. The report is based upon signalŤ reports given during QSO's verses the receivingŤ stations antenna system, location andŤ installation. I would suggest you perform your ownŤ tests for your antenna and location. Good luck! 73, Elmer
April 1991
ASK ELMER
Dear Elmer,
Please explain the operation of a MAGNETRON as used in the microwaves.
Signed, Hugh Huff. Dear Hugh,
The Magnetron is a vacuum tube which is used to generate UHF thru microwave energy. It was the first method of generating this energy at a single frequency using vacuum tube technology. (Would you believe that the spark gap technique was really the first and done by H. Hertz in the latter part of the 19 century.) To those who do not know where the Magnetron is currently used in large numbers, look at your microwave oven. In Amateur Radio the Magnetron can be used as the source of a high power ATV transmitter. Now let's take a look at how one works without going into the mathematics.
Essentially a Magnetron is a diode vacuum tube with a series of resonant circuits in the form of cylindrical cavities for its anode. These resonant circuits are surrounded by a strong external magnetic field perpendicular to the cavities and to the electron flow in the tube. A battery is connected between the cathode (negative terminal) and the anode (positive terminal) of the Magnetron. This causes a current to flow between the cathode and anode caused by electrons being released by the cathode. If the magnetic field is strong enough, it will cause the electrons to follow a circular path, and under certain conditions never be captured by the anode. Just at this point, those electrons which have the correct amount of energy, are trapped by the cavities in the anode, which are tuned to a specific frequency (cavities are microwave tuned circuits), and then re-released back into the vacuum tube to interact with the other electrons. Eventually many of the electrons have an energy level which is at the same frequency as the cavities and some of it is coupled out via a wave guide or link to the antenna. The magnetron may be modulated by varying the level of voltage supplied to it over narrow limits. This causes primarily amplitude modulation with some phase modulation. Generally the amplitude modulation is used as in the video signal for ATV. For further information, any book on microwave thermionic devices will go into much greater detail. Commercially for very stable signals, Magnetrons are not used as they require large magnets and high voltages. Newer velocity modulated vacuum tubes and solid state are preferred microwave sources. I hope this hand waving explanation gives you some insight into the devices operation.
73, Elmer.
June 1991
ASK ELMER
Dear Elmer
I've gotten very exasperated while testing transistors. I tested some Germanium devices and the meter wouldn't stay still. Also I measured the Betas of some Silicon transistors and then built amplifiers with parts values calculated by using these Beta values. They were way off their calculate characteristics. I remeasured the Betas and got something entirely different. What gives? Are transistor characteristics that skittish? Note that I measures Beta by taking changes not D.C. values.
Frustrated
Dear Frustrated,
Before I attempt to answer your question, let me define Beta. Beta is the DC current gain of a transistor as measured in the common emitter configuration. To measure Beta, is biased at the collector current of interest. An incremental base current change is made, and the corresponding collector current is measured. The ratio of the change in base current to the change in collector current is the Beta. A persistent problem is that the measurement of Bets is affected by leakage currents between the base and emitter of the transistor. These leakage currents are relatively small in Silicon transistors but are significant in Germanium transistors. A second problem is that Beta is affected by temperature (in a Silicon transistor the base to emitter voltage decreases by 2 mV per degree Celsius, and 1.5 mV in a Germanium unit) and can significantly alter the transistors operating point. If the room temperature increased or the transistors have been operating for a while, the temperature of the transistor has increased causing the Beta to increase. In order to minimize this problem, bias circuits with some type of current or voltage feedback must be employed. The greater the amount of feedback, the smaller the effect of changing temperature, but generally the lower the amplification of the transistor stage. (You don't get something for nothing.)
Well Frustrated, I hope this answered some of your questions.
73, Elmer.
July 1991
ASK ELMER
Dear Elmer,
I have a Vertical Antenna and I want to mount, but not on the house. What are the various ways I can get this up in my back yard? I was thinking of cropping a smallish tree and attaching it to the top of it. Any sense in this? Anyhow Elmer, what methods do you recommend? Am willing to consider any solutions, outrageous or not.
73, U. Pintheair
Dear U.,
Installing a Vertical antenna is one of the easiest things you can do. The higher the vertical antenna the better it seems to perform. It should be mounted away from trees, unless the trees are under it as a support. As a vertical antenna bends in a wind, adjacent trees will tend to snag it and may cause a mechanical or electrical failure. One of the best supports for a Vertical antenna is a flag pole. Not only will this support your antenna, it will show the neighbors how patriotic you are and probably reduce the TVI complaints. (How could somebody with a flag flying cause trouble. It must be some CB'er down the block.) Your idea of putting it on a cropped tree will probably work fine, as long as the tree can support the antenna in a wind. Trees bend. Consider, all verticals need an counterpoise (ground radials) as a pseudo ground. These do not have to be horizontal, but should be mounted in a way so they would not snap in a moderate wind. If you must mount the antenna in a tree, I suggest a robust one. As for the counterpoise (radials), it may be attacked to the trunk o the tree. If you have an Cushcraft R5 vertical, it does not need any radials, and may be mounted on a smaller tree with greater sway. It limits your operation to 20 Meters and down ( remember wavelength is the reciprocal of frequency). Of course, you may elect to erect a tower, and mount the vertical upon it. I would recommend a beam, but you use what you have on the tower. The possibilities are endless. Use your imagination.
Have fun, 73.
Elmer
January 1992
ASK ELMER
Dear Elmer,
I was wondering the other day, what steps should I take regarding my antenna/coax. for the winter. What effects of cold weather, rain, snow, ice are most troublesome? How do conditions affect SWR? I have a Diamond X200 on my deck.
Signed, Worried.
Dear Worried,
Under normal conditions the relatively mild winters we have here in the coastal Fairfield County area, pose very few problems with respect to outside antennas and feed lines. I am making the assumption that the installation was correctly done, with properly assembled antenna supports and connectors. We will now consider some of the problems which can be encountered due to weather. One of the most common prelims is due to moisture condensing in the connectors, and in the traps and matching networks of antennas. Pure water is really not a problem as it is a good insulator, but we never get pure (distilled) water, therefore we have a poor conductor/insulator which can act as an additional RF load where you don't want it. During winter, this water can if it gets into enclosed spaces as in antenna traps can freeze. Freezing water EXPANDS, and could mechanically damage the trap or Balun. To prevent this, use a good sealant to close all possible entry points for water, and make sure that drain holes are unclogged and pointing towards the ground. Coaxial connectors are a problem area, as dirty water can act as an RF load, so the use of RTV Silicone rubber, Coax Seal or some other sealant to "encapsulate" the connectors. A trick which works very well is to wrap the connectors with Aluminum foil and then use a sealant around it. This will prevent the connectors from corroding and allow easy access to the connectors should the need arise. Another problem is with the coaxial cable. Foam dielectric cable is very low loss but can easily absorb moisture. This changes the properties of the dielectric and the cables surge impedance (a 50 Ohm cable may be locally 20 Ohms due to moisture absorption).
To prevent this, seal the ends of the foam cable with RTV lightly applied to the dielectric end before assembling the connector. Then seal the connector. The same holds true for Air dielectric cable (Belden 9913).
The other problem encountered in the winter is Ice loading of the antenna. Most antennas are designed to withstand fairly severe Ice loading. By the way, Ice loading is when Ice forms around the antenna and supports. Be careful not to operate your rotator under heavy Ice loading as it may be more load than your rotator can handle safely. Let the Sun do most of the work for you in reducing Ice loading. Ice, as it has a different dielectric constant than air, will detune your antenna, severely if it coats the entire antenna. The antenna will still work, but I would suggest that you use a Transmatch at the output of your rig to match your feed line and antenna to your radio. By the way, the most tolerant antenna and feed system is a wire antenna fed with open wire (500 Ohm) line. This antenna is a high impedance antenna, and open wire line can withstand a severe standing wave without deterioration or breakdown and keep it's losses to a minimum. I just requires a different setting of the transmatch.
I trust this will give you some answers to your questions. "THINK WARM"
73, Elmer
February 1992
ASK ELMER
Dear Elmer,
I hear so much talk about VSWR and I am totally confused. When I ask 3 other hams about it I get 4 answers, and none of them seem to make any sense. What are they talking about? Help!!!!F. Ed Line
Dear F. Ed,There appears to be many misconceptions about VSWR. VSWR is the abbreviation for Voltage Standing Wave Ratio, a number which indicates the quality of the match between a generator and it's load including any transmission media or line between them. In order to understand this ratio, consider an RF generator connected to a transmission line which is then terminated in an open circuit. The generator puts a time varying voltage (AC) at it's end of the transmission line which starts a current flowing down the transmission line. The current continues until it reaches the open end of the line, at which time it reverses its direction and heads back to the generator. This return current generates a voltage which is time displaced from the voltage supplied by the generator (out of phase) since an electrical signal travels at the speed of light or less (depending on the material through which it flows) which algebraically adds to the voltage being supplied by the generator. This causes a pseudo wave to be generated which is stationary with respect to time but whose amplitude varies with distance along the transmission line. This pseudo wave is called the STANDING WAVE. As it is easier to measure the voltage on a line, it becomes the VOLTAGE STANDING WAVE. Let us consider a transmission line terminated in it's correct load (the same as it's characteristic impedance, such as 50 Ohms). Then all of the current generated by the generator is absorbed by the load and none flows back to the generator. No standing wave. If we were to measure the maximum voltage and the minimum voltage across the transmission line, the VSWR is the ratio of the maximum to minimum voltage ( Vmax \ Vmin = VSWR), and varies from 1 to infinity. A ratio of 1 is a perfectly matched line and load, whereas infinity is total mismatch. In practical terms, a VSWR of 2:1 or less is considered a very good match. Beyond this some remedial action is required (transmatch, etc). Using standard mathematical methods, you can calculate forward and reflected powers as well as the effective line impedance. For additional reading I recommend , "Antenna Impedance Matching" by W. N. Caron published by the ARRL.Until next time, 73.
Elmer
March 1992
ASK ELMER
Dear Elmer,
In the early days of radio, we rarely used a Transmatch between the transmitter and the antenna. Now it is almost a necessity. What's changed?
Perplexed
Dear Perp,
In the early days all of the radios glowed in the dark. They all had Vacuum Tube finals, which were tuned to the particular operating frequency. The tuned output networks were narrow band matching networks, therefore they were their own Transmitters. A Vacuum tube is a very forgiving device. For short periods of time it can withstand a great mismatch (it only glows brighter during that time), whereas modern solid state devices go into a rapid self destruct mode when improperly matched.
Modern radios with solid state finals, use broadband matching networks rather than tuned networks. This permits rapid change in operating frequency without having to "retune the finals" as in days of old. Since antennas are only matched over narrow bands, and the solid state finals cannot tolerate a severe mismatch, some method of impedance matching is required. Enter the Transmatch. The Transmatch is a fairly simple device, consisting of inductors and capacitors (as few as one inductor or one capacitor) which can be adjusted to make the transmitters load appear to be resistive and 50 Ohms. (There is nothing magical about 50 Ohms, it was just a convenient number which was settled upon by the military during WW II. In reality, 75 Ohms would have been a better choice as most resonant dipole antennas are 75 Ohms impedance. 75 Ohms is considered the best compromise between physical cable size, power handling capacity and loss for HF and VHF operation.) But you can't win them all, Hi, Hi. Well, Perplexed, I hope you are aglow with knowledge, in a well matched condition.
73, Elmer.
Send your questions to "ASK ELMER", c/o MarvŤ
Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CTŤ 06877.
ASK ELMER
June1992
Dear Elmer,
Would it be possible to construct a Directional Antenna (even if it's for receive only, in lieu of the "Rubber Duckey") for may hand held Marine VHF (156-158 MHz)?
Signed, Nautical.
Dear Nautical,
In the previous articles we have discussed the "Phased Vertical's" and the "Quad." antennas, and we will end our discussion with the "Uda-Yagi" or "Yagi" Beam antenna.
A simple three element antenna will produce a directional gain of about 7 dB when compared to a simple resonant dipole antenna. The "Beam" consists of a director element, a driven element and a reflector element. The driven element is cut to the center frequency (157 MHz) using the relationship Length in feet = 475/f(MHZ), the director length in feet is 455/f(MHz) and the reflector length in feet is 500/f(MHZ). The spacing of the elements are 0.2 wavelengths (2352/f MHz = spacing in inches) between the reflector and the driven element and 0.175 (2058/fMHz = spacing in inches) wavelength between the driven element and the director. The elements can be made out of 1/4 inch aluminum tubing and secured with epoxy to a piece of 1 inch diameter PVC pipe. Only the driven element must be cut in half so that it may be fed with coax. The impedance of the antenna is going to be about 30 Ohms, so a "Gamma" match or other matching device should be used between the coax cable and the driven element. Details for the construction of the "Gamma" match can be found in the ARRL Antenna Book. I recommend this book for anyone constructing their own antennas. Remember that VHF marine is vertically polarized, so the antenna must be mounted on edge. The support mast should be either behind the reflector or made of an insulating material. I am neglecting to show a diagram of the antenna since I ran out of space, but most Hams are familiar with their construction.
Well Nautical, I hope you are having fun constructing and testing antennas.
73, Elmer.
„„
Send all your questions, submissions and comments to Ť
„„
"ASK ELMER", C/O Marv Fleischman, P.O. Box 113, Ť
„„
Ridgefield, CT 06877.
Aug1992 ASK ELMER
Dear Elmer, I keep hearing about DXpeditions. Are they something special or does everyone do this? Why are they always asking for donations? I thought once you bought all of your gear, everything else was free. Sincerely, C. Lou Mein.
Dear Lou, One of the areas of our hobby is DXing, or looking for that rare contact with a country with only one or two operators. There are in this world, for the purposes of Amateur Radio, approximately 318 "countries". These countries can be major geographical entities, such as the U.S., Canada, France, etc., or they can be a pile of rocks in the middle of the ocean, claimed or administered by one to the larger countries. Many of these "Rock Piles" have their own amateur radio call sign prefix, but there is nobody living there. In order to establish contact with these "countries", an individual or more generally a group of intrepid Hams will travel to these places and set up a station. For a short period of time, they will operate the station logging all of the contacts that they make. They will then return to the land of the living to perform the fun task of replying to all of the QSL cards sent to them. It takes a very special type of Ham-adventurer to go on a DXpedition, as you exist under primitive conditions, go deaf and hoarse and get "Telegraphers Wrist" (carpal tunnel syndrome) all for the joy of giving the worlds Hams the chance of logging the rare country. Even though some of the equipment is either donated or supplied by the expeditionary, there is the small problem of food, transportation, fuel, etc. This costs money, so, they ask their fellow hams for help. Many times QST, CQ or 73 magazines have stories about DXpeditions. It makes fascinating reading. Would you like to leave your easy chair for a couple week stint on a rock pile? All this following a week or two of not too comfortable traveling. Think about it. Well Lou, I hope this answers your question on DXpeditions, and fires you up to join the next one. 73, Elmer
Send all of your questions and comments to "ASK ELMER", C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877
NOVEMBER 1992
ASK ELMER
Dear Elmer, I am purchasing a new communications receiver for the shack and I am attempting to compare the various specs. What do they mean? Signed, C. Urious (Continued from last month)
Dear C., To continue with our discussion; SENSITIVITY: Normally the sensitivity of a radio is defined as the level of signal appearing at the antenna terminals which will produce a usable output from the receiver. The output is considered usable when it is at least 10 dB above the receivers internal noise level. The receivers noise level is bandwidth dependent, therefore the apparent sensitivity increases with a decreasing (narrower) bandwidth. Most communication receivers have a sensitivity of 0.25 uV with a bandwidth of 2.4 KHz. The noise level decrease follows the relationship; N(dB) = 10 Log (BW1/BW2), where BW1 and BW2 are the respective bandwidths. Therefore, if the bandwidth is reduced to 240 Hz, using the relationship, the noise floor will decrease by 10dB. This means that the relative sensitivity will be 0.08 uV for the same 10 dB output signal to noise ratio. This may not hold true for AM in modern radios, as only one sideband of the double sideband signal is used, causing the signal to noise ratio to degrade at least 3 dB, and the carrier to sideband amplitude ratio providing some of the other loss. In FM radios, the sensitivity is given as micro volts to produce 12 dB SINAD. This is signal plus noise plus distortion (which will appear as additional noise added to the signal). This measurement is based upon a deviation of 2.1 KHz at a 1KHz rate. Most good radios will have a sensitivity of less than 0.5 uV for 12 dB SINAD. Many times these numbers will be given with the radio's preamplifier on (if it has one). To be continued in further issues. 73, Elmer
Send your questions, comments to "ASK ELMER", C/O Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
ASK ELMER
Dear Elmer,
I am purchasing a new communications receiver for the shack and I am attempting to compare various specs. What do they mean? Signed, C. Urious (Continued form last month)
Dear C., To continue our discussion;
Selectivity: One of the more important specifications in communications receivers is the I.F. selectivity. This indicates the ability of the radio to separate the various signals from each other without resorting to exotic means. An ideal radio should have a pass band that is rectangular in shape, so that it carves out a precise slot in the frequency domain. In practical terms, no filter is ideal (rectangular in pass band shape), but is more rounded and trapezoidal in form. The specifications are generally given as a pass band at the -6 dB and the -60 dB attenuation levels. If the filter were ideal, the bandwidth at the -6 dB and -60 dB points would be identical, but in practical terms the best that the shape can be is about 1:1.2. This means that the -60 dB bandwidth is 1.2 times as wide as the -6 dB bandwidth. Radios with these narrow filters would be relatively expensive and difficult to tune, so a more reasonable ratio is about 1:1.5 to 1:2. Normally 8 poles of crystal filtering will produce a 1:2 ratio, and any additional filtering will improve it. Rarely do you encounter a manufacturer that will specify the selectivity below -60 dB, which is very important when there is a strong signal in the presence of a weak one, and you want to hear the weak one. It is best to say, that the smaller the ratio, the better the radio.
Dynamic Range: This specification indicates the range over which the radio will operate without requiring any attenuators in the signal path.
Continued on Page
ASK ELMER cont.
Most quality radios will be capable of operating over a range of at least 95 dB. Were this range small, a strong signal will overload a weaker one
causing distortion products to appear as spurious signals. Generally pre-amplifiers will compress the dynamic range as they have high gain and would overload the radio's input stage. In amateur radio strong signals are more of a problem than the weak ones. Look for a radio which has a dynamic range of at least 102 to 105 dB. The narrower the I.F. bandwidth, generally the greater the dynamic range, as the radio's residual noise decreases with decreasing bandwidth. The range is generally measured from just above the noise floor of the radio.
In our next installment I will discuss the radio's noise characteristics.
Until next month, 73.
Elmer
Send all of your questions and comments to "ASK ELMER", C/O Marv Fleischman, P.O. Box 113, Ridgefield, CT 06877.
ASK ELMER
Dear Elmer,
I am purchasing a communications receiver for the shack and I am attempting to compare various specs. What do they mean?
Signed, C. Urious (Continued from last month.)
Dear C.
To conclude our discussion, consider the following:
With today's crowded spectrum, any spurious signal could cause unwanted secondary signals. These spurious signals could blank out the desired signal, or make it difficult to copy a weak signal in the presence of a strong signal. One of the major causes of receiver spurious signal generation is "Phase Noise" generated by the receivers synthesizer. No synthesizer or oscillator is absolutely frequency stable, they all move to a greater or lesser extent. This movement produces an series of sidebands around the center frequency. The greater the instability, the higher the sidebands amplitude and the greater it's bandwidth. The movement
is random in nature, as is noise, therefore it generates all frequencies. If the amplitude of the sidebands are sufficiently great, the receiver cannot distinguish it from a desired signal. In fact, the amplitude of the sidebands may approach or exceed the amplitude of the weak signal, so which are you going to hear? If the receiver has a sensitivity which permits it to receive a signal of -120 dBm, and the noise sidebands are in the order of -120 dBm, the signal may be lost in the noise. A second problem is when a strong signal is mixed with a noisy signal from the receivers synthesizer, spurious signals are produced which can be stronger than the desired signal you want to copy. (A good reference on receiver specifications is "Communications Receivers Principals and Design" by Ulrich Rohde and T.T.N. Bucher, McGraw-Hill, 1988.) Most manufacturers do not publish the Phase Noise specifications of their receivers, and you must rely on independent testing labs to obtain the information. Generally the ARRL provides a good source of information in their "QST" Product Reviews.
Phase Noise is specified as -XXX dBc (Decibels below the carrier ), Single Sideband, generally normalized to a 1 Hz bandwidth for uniformity, and at a given distance from the carrier, i.e.. 1 KHz. A good receiver will have a Phase Noise below -110 dBc/Hz at 10KHz from the carrier. (Note: To convert from broadband noise measurement to the 1Hz, subtract 10dB for each decade reduction in bandwidth. Example: If the noise is -80 dBc in a 1KHz bandwidth, it will be -110 dBc/Hz).
A second source of noise which is considered in receivers is known as "Front End" noise. All physical objects produce noise form the random motion of the molecules from which they are made. Generally, this noise is of no consequence, but in a radio, this noise is amplified along with the signal, and may be so great as to completely mask the desired signal. The lowest possible level of noise is that of a resistor whose value is the same as the impedance of the amplifier input. The noise power is proportional to the value of the resistor, the absolute temperature, Boltzmann's constant and the measurement bandwidth. The noise of a receiver is generally given as XX Db over the absolute minimum noise of the ideal resistor (much of the time the resistor is 50 Ohms) in a given bandwidth. This figure is rarely given for HF receivers, as the front end noise is generally much lower than atmospheric noise. On VHF and higher radios, this noise figure becomes more and more important as bandwidths increase and signals become weaker due to atmospheric attenuation. For most VHF and UHF amateur radios, a noise figure of less than 3 dB is considered very good. The smaller the number the better. By the way, there are methods of digging weak signals out of the noise, using techniques called autocorrelation and cross correlation, but these topics will not be discussed at this time. If you wish to think about it, noise is random, and signals are coherent, and that's all it takes.
Well C. there are many more specifications that we might discuss about communication receivers, but I suggest going to the literature to research the topic further. As with any facet of communications, we have only touched the surface, but I hope it has given you a chance to consider the various specifications and weigh your requirements verses your pocketbook. For additional reading I would recommend the old standby, "The Radio Amateurs Handbook", ARRL, 1993 and a rather old book "Radiations Designers Handbook", F. Langford Smith, RCA, 1953.
Enjoy your new radio when you get it.
I wish you and all of my readers a "Joyous Holiday Season", and a Happy, Healthy New Year.
73, Elmer.
Continued on Page 6
February 1993
ASK ELMER
Dear Elmer,
Articles on antenna transmission lines point to "Open Wire" or "Ladder Lines" as less loss than Coax. Why is this and under what conditions does this become significant?
Signed A. T. Aloss.
Dear A.T.
From the start of modern communications, one of the primary concerns of any station operator is to get as much of the signal from the transmitter to the antenna, and from the receiving antenna to the input of the receiver. The means by which this is accomplished is by using a "Transmission Line" from the antenna and the radio. This transmission line can take many forms such as; single conductor wire; twisted pair of wires; twin lead insulated transmission line; open wire twin lead transmission line; coaxial cable; coaxial cable; wave guide; etc. This list is by no means complete but indicates a range of transmission media from the simplest to the complex. Each type of "Line" has it's strong and weak points. One consideration of many is the amount of attenuation the line has for the particular signal in question. The main contributors to attenuation on a transmission line is caused resistive losses (IR losses), radiation losses and dielectric losses. All of the losses are both frequency and power dependent. Let us first consider Coaxial Cable. It consists of a center conductor surrounded by a dielectric and then encased within an outer conductor. Resistive losses in this cable are those within the center conductor, based upon its DC resistance and then modified by the reduction of conductor as a function of increasing frequency due to the "Skin Effect". Dielectric losses are due to the absorption of some of the energy into the dielectric material surrounding the center conductor. As frequency increases, this loss increases, as materials loose efficiency with increasing frequency. Coaxial cable using more air and less polyethylene, has reduced losses. Due to the construction of the cable, some polyethylene must be used to support the center conductor, therefore dielectric losses are always present. Open wire line consists of two wires separated by some widely spaced insulators. Most of the dielectric between the wires consists of Air which is very low loss. All other things being equal, open wire line would be less lossy. Generally the higher in frequency you operate, and the longer the length of transmission line, the more sense it makes to use open wire line. In the HF band, 160 meters thru 10 meters, coaxial cable loss is generally very small, and need not be considered, except for very long runs. At the higher frequencies, open wire line appears to be the line of choice, except that open wire line must be kept at least 1/4 wavelength away from any surface so as not to cause any unbalance in the line or dielectric absorption. In open areas it works fine but it is not recommended for use around walls, etc. I would recommend reading the ARRL Amateurs Handbook chapter on Transmission Lines for more information.
Well A. T., I hope this "points" you in the right direction.
73, Elmer.
March 1993 ASK ELMER
Dear Elmer, I noticed that you have been answering questions on manufacturers' specs. for transceivers. My questions concern a few of the controls. I don't understand why they work the way they do. On receive, when I turn the RF gain control down the "S" meter reading goes up. Shouldn't it be the other way around? There is a control for attenuating the incoming signal by 10, 20 or 30 dB. Isn't this the same as turning down the RF Gain? Why do I need both controls? There is a control for the Noise Blanker level. I have never turned it down from max. Is this knob there just to confuse me? Lastly, on the meter switch, there are settings for reading the collector current and voltage. Why do I need to know this? Signed, Oscar Lator
Dear Oscar, Let me congratulate you for being the first person to question the operation of the controls on the radio. They do appear to operate strangely. The RF Gain control varies the biasing on the IF amplifiers in the radio to change their gain. The AGC (Automatic Gain Control) does exactly the same thing except that it uses the actual IF signal level to control the gain. Both controls reduce the gain by increasing
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the bias, therefore the meter will read the same Bias voltage no matter which method is used to reduce the gain of the IF amplifiers. Notice when CW is received, and the AGC is disabled, the RF Gain control must be used to prevent the IF amplifiers from saturating on large signals. The input attenuator is used to prevent strong signals from overloading the front end of the radio. Neither the AGC nor the RF gain control affect the input RF amplifiers and the first mixer. These stages are very sensitive and have a limited dynamic range, therefore a very strong signal can overload these stages and cause spurious signals to be generated. The input attenuator prevents this. One of the problems in DX ing is the reception of a weak signal in the presence of a strong one. If the front end overloads, you will have no chance of hearing the weak signal. At times the attenuator will enhance a weak signal. The dilemma of the Noise Blanker threshold control is one which confounds everyone. In theory, there are some types of burst noise which can be suppressed by just lightly clamping the signal (I have yet to find any) and some which require severe clipping (all that I have ever encountered). For those times when you may need it, the give you a control. Doesn't this give you a warm fuzzy feeling knowing it's there?
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The last part of your question regarding the need for monitoring the collector current and voltage of your power output stage ("Finals"), is used only for trouble-shooting. The voltage and current values are used to indicate proper operation of the transmitter's power amplifier. In the event of problems, this is the first place you look to see if your power supply is operating (voltage indication) and the amplifiers are working (current increase during transmit). Many commercial transmitters hare more extensive front panel metering to aid in the repair and maintenance of the radio.
Well Oscar, I hope your questions have been answered to your satisfaction, and you will rest easily in the knowledge that you command the controls of your radio. 73, Elmer.
Send all of your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, P>O> Box 113, Ridgefield CT 06877
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Dear Elmer,
I just purchased a VSWR meter at a local flea market, and opened it up. There is not much in there, and I can't figure out how it works. Can you explained it to me?
Signed, Reflective
Dear Reflective,
The principal of a VSWR meter or "Reflectometer" is fairly simple. The Reflectometer is a balanced bridge (something like a Wheatstone Bridge for measuring resistors) circuit.
Before we discuss the construction of the meter, we must briefly discuss the what occurs when a load is connected to a transmission line. When the load is matched to the transmission line, it is pure resistor. If the resistor has the same impedance as the arms of the bridge, it is in balance and no voltages will appear across the bridges metering terminals. If the load is not matched, an error voltage will appear, which is proportional to the amount of unbalance. We then detect the resultant signal and meter it. We can calibrate the scale in relative amplitude, which is a measure of the VSWR. When you look inside the VSWR meter, you will see the voltmeter and the transformer, as well as a couple of diodes to detect the signals and the meter.
Now you know why there is so few components in the meter.
73, Elmer.
June 1993 Page ASK ELMER
Dear Uncle Elmer:
I'm Ken Fused. I'm also confused. This is not strictly a Ham Radio question but maybe you can make up an answer anyway. From time to time, I like to listen to the air-to-ground communications on my scanner. Considering how high up the airplanes are, and the need for clear reception, why do the use AM? Isn't that old technology? Wouldn't SSB or even FM be clearer or at least use up less spectrum? After all, our repeaters use FM, no? I'm looking forward to your answer. Sincerely, Ken.
Dear Ken, I think I can answer your question in one word, and then elaborate. As Tevya in "Fiddler on the Roof" said, TRADITION! Initially all communications from air to ground were CW, but as time progressed, the required more rapid communication, and AM (double-sideband) was the reigning technology. FM was considered too new and SSB was experimental and both were considered possibly unreliable. Once all the aircraft, both commercial and private all over the world converted to AM, it would be extremely difficult and expensive to change modes. You cannot have mixed mode transmission when safety is the prime requisite. We can barely get several countries to agree on lesser topics, a mode change would be international incident. In my opinion, reduced carrier SSB would probably be the best mode of communications. The reasoning is that an AM radio could receive it with minimum modification, as could a SSB radio without modification. It is not prone to selective fading as is AM (double sideband), nor does it have the
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problem of FM capture. (FM capture is the effect whereby a stronger FM signal captures the radio completely from the slightly weaker station.) As the carrier is present, one does not have to be generated in the receiver as in standard SSB, but being reduced, more of the transmitted energy is going into the sideband (which carries the information). Well Ken, that's the saga of the air to ground communication modes, and I leave you with the word I started with "Tradition". Keep listening to the control towers, and maybe one day you will understand what they say (I haven't been able to when I listen, and I don't know how the pilots understand them).
73, Elmer.
Send all of your questions to "ASK ELMER" c/o Marv Fleischman, PO Box 113, Ridgefield, CT 06877.
July 1993
ASK ELMER
Dear Elmer,
It is that time of year for Es. Can you tell us VHF types what causes this type of propagation. I know a good indicator, for those without cable, is to look at channel 2. What is co-channeling? Despite "PL", how can this affect our repeater on 2 M?
Signed H. E. Skipped.
Dear H.
You are right, it is the season for "Es", or Sporadic E propagation. Most HF and VHF propagation is influenced by the upper layers of our atmosphere. These layers have the ability to diffracting the signal causing the phenomenon called "skip". Were it not for these layers, all of the HF and VHF signals would travel merrily into space lost forever in the vast cosmos. The lowest of these layers is the "E", located about 60 miles above the earth's surface. This layer is generally responsible for HF skip of intermediate distances up to 1000 miles. During the evening the "E" layer usually disappears. Under certain conditions of strong local ionization by the sun, a series of random charged clouds are formed within the layer which can reflect signals in the 30 MHz thru 150 MHz. As there clouds are random in occurrence and location, they are sporadic, hence Sporadic E. Under these conditions VHF signals can be reflected causing a skip distance between 400 and 1500 miles. As the lower TV channels are in the VHF range, they can act as a good indicator for "Es". Due to "Es" conditions, you can be viewing a show on channel 2 when a second broadcast competes with your show for your TV set. A distant station which normally would be well beyond your viewing area is now stronger than your local station. This is called co-channel interference, is the cause of more complaints by TV viewers and blame heaped upon amateur radio operators for this interference. If you do experience co-channel interference, run, don't walk to your VHF radio and try some DX'ing. You may be pleasantly surprised at who you can "work" and where. The most dramatic results would be on the 6 meter band. While "Es" conditions can be fun, they can be a problem for repeaters, as distant signals would either activate your local repeater or even capture your own radio instead of the signal from your local repeater. Be it either boon or bain, "Es" is here. Use it, and enjoy its DX opportunities, for it is with us for so short a time.
Well H.E. 73, Elmer.
September 1993 ASK ELMER
Dear Elmer, More and more radios with computer interfaces are being advertised. If I buy a new radio (I am using a Hallicrafter Sky Buddy and a Harvey Wells Bandmaster in my station) will I have to buy a computer? My slide rule still works fine as long as you keep putting batteries in it. Signed, O. L. Tymer
Dear O.L. More and more operators are attempting some form of automated operation with their radios. It started innocently enough with VHF radios having memories, then scanning and soon they had full blown computers inside of them to control all of the features they seemed to offer. (By the way, if you ever tried to program some of the VHF radios, even with the instruction manual, you may be in for quite a time). With HF radios becoming more versatile (read that as complex), manufacturers figured that it would be nice to have some form of external control. Since computers and amateur radio are in some ways related, why not control the radios with a computer. Contesters said "Great" since logging would be simplified, and QSL'ing would be less of a chore. This opened up "Pandora's Box" because I can see the ultimate computerized radio. The computer will be listening to the packet DX cluster, constantly checking prefixes for ones that the operator needs. When one is found, it turns the HF radio on, sets its frequency to the one reported on the cluster, using a voice synthesizer or CW generator,
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calls the DX station, logs the contact when it is made, prints the QSL card and sends it to the DX station by FAX, receives the DX card by return FAX. When the computer collects enough cards, it automatically sends them via FAX to the League for the DXCC or other award. Meanwhile the operator is in front of the TV set swilling beer and watching the game. hats why you will have to buy a computer when you buy your new rig. Sorry O.L. but your slide rule doesn't cut it any more ( by the way I have a couple of slide rules but I can't find the battery compartment). 73, Elmer.
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
Jan 1994
ASK ELMER Dear Uncle Elmer, You don't want to know how, but I recently screwed up big-time. I accidentally crossed the leads on a NiCad cell, and wound up charging it with reversed polarity. It was left there overnight. Is there any hope? Also, is it true that if I don't keep a plug in the wall socket all of the electricity leaks out? Help! Yours truly, Ken Ductor
Dear Ken, I have good news and bad news for you. I'll start with the bad news so you will have something to look forward to. Your NiCad is headed for the big charger in the sky. Reverse charging a NiCad causes irreversible damage to the cell. The two worst conditions for a NiCad cell is reverse charging and allowing the cell to remain so deeply dis- charged that it reverses its own polarity. Both cases of reversed polarity damage the cells electrodes, severely reducing the cells capacity even if the polarity reversal can be corrected. (There is a condition when the NiCad cell can act as a primary cell, ie., non-rechargeable, with reversed polarity.) I recommend a trip to the battery store to turn in the old cell for recycling and purchasing a replacement. Now the good news!!!!! You are safe! All of the electricity doesn't leak out of an uncover- erred wall socket. A little does, but the amount is so insignificant that you would have a very difficult time measuring it. You should worry about any equipment eventually connected to the outlet. You must be very careful to keep all of the smoke from leaking out of your equipment. It is smoke that makes all of the electronic equipment work. When the smoke leaks out, the equipment stops operating. There is something to say for all of the smoke free environments. Well Ken, buy that battery and plug that outlet, then you can rest easily. 73, Elmer
Send all of your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877.
March 1994 ASK ELMER Dear Uncle Elmer, My YL says "NO Beams On The Roof", as long as she lives here! So I plug along with my Dipole trying to reach out to the world with modest success. I have a big attic and can fit a beam in it, but the floor has a massive number of metal heating ducts. I can get the antenna about four feet above the vents. Will the metal ducts seriously influence the SWR because of their proximity to the antenna? Possibly, I should put a vertical multi band antenna in the attic as there is plenty; of head room because of the steep slope of the roof. Signed, Poo R. D'xer.
Dear Poo, I would not suggest using a beam in the attic with the heating ducts so close to the antenna. Not only will the SWR of the antenna change, but the reflections will be so great that you may be able to contact "ET's" rather than another ham. If the beam verses the dipole were your only choice, I would recommend retaining the dipole. You can try experimenting with the height, length or shape of the dipole to improve its operation. Under the best of conditions, an attic anten- na is a compromise, so make the best of it. The idea of using a multi band vertical in the attic is an interesting one. Having a 30 foot high peak in the attic is unusual, but if your attic is that high take advantage of it. A vertical antenna, for the higher bands ordinarily does not do as well as a equivalent dipole, as most of the transmitted signals are horizon- tally polarized. There is the belief that once a signal takes one bounce it looses its polarization, and a vertical antenna works as well as a dipole. My personal experiences have not substantiated this claim (other operators may find this to be true with their setups). The bottom line is that the vertical will give you omni-directional capabilities, and the duct- work will work in your favor. The ducts will act as a ground plane (counterpoise) which the vertical antenna can work against. This will improve the antennas operation by helping to lower its angle of radiation. There is one thing to be concerned about, and that is roof flashing. This may act to alter the antennas radiation pattern. Only experimentation will see if this happens. By the way you can, if the attic is long enough, put two verticals and phase them to obtain directivity, but this is another story. O Poo, good luck. 73, Elmer
Send all your questions and to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
May1994 ASK ELMER
Dear Elmer, I have heard of Grid Dip Meters or Tunnel Dippers. What are they and how do I use them to find the frequency of my antenna system off the air? What else can I do with these devices? Signed, Dippy.
Dear Dippy, In the good old days of Vacuum Tubes, (when the only good radio glowed in the dark), the instruments used were not as sophisticated as they are now. When you wanted to measure the frequency of a tuned circuit, you used a signal generator and an RF voltmeter to make the measurement. This required the removal of the tuned circuit from the radio or other equipment, setting up the test equipment so as not to load the tuned circuit, and making the measurement. At times this was not possible, so some other method of measurement was sought out. It was discovered that a Vacuum Tube Oscillator's tuned circuit was coupled to another tuned circuit, energy was transferred when the two tuned circuits were at the same frequency. In a self biased Vacuum Tube oscillator, the control grid self bias is a sensitive measure of the energy in the oscillator. When energy is transferred form the oscillator to another tuned circuit, there is a decrease in the control grid bias voltage, hence a dip in the grid voltage or "Grid Dip Oscillator". In reality, any oscillator, vacuum tube, transistor or tunnel diode will indicate a decrease in either it's RF voltage or supply current when energy is coupled out of it.
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If you calibrate the tuning indicator (knob) on the oscillator, and attach a voltmeter or micro ammeter to it to indicate the loss of energy, you have a very effective means of measuring the frequency of a resonant circuit without removing the circuit under test from its equipment. Back to my "favorite subject" antennas. Many antennas are resonant antennas, ie., they are cut to some particular operating frequency. A "Grid Dip Oscillator" can measure the frequency of any tuned circuit. To do this measurement, all you need do is to make a connector with a 1 turn coupling coil of wire from its hot lead to shield. Put the connec- tor on the end of your feed line, and lightly couple the Grid Dip Oscillators coil to it. Vary the frequency of the Grid Dip Oscillator thru it's frequency range until you see a dip in the meter reading. If the tuned circuit under test has a high "Q", the dip will be very sharp, so do the measurement with care. The frequency at which the dip occurs is the resonant frequency of the antenna. By the way, if the antenna feed line is open wire line, just connect the ends together as a 1 turn coil and proceed with the measurement. The "Dipper" is a versatile instrument and to go into all of its possible uses would take a book. There is one other use I must mention, that of the absorption wave meter. If you disable the oscillator, the Dipper will act as a wave meter. When brought close to an active transmitters exciter, it can measure the frequency of the transmitter by absorbing some of the exciters signal and indicating a peak on the Dippers meter as you tune the Dipper. Well that is the tip of the iceberg. 73, Elmer Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877. ASK ELMER Dear Elmer, As a user of handheld radio equipment, I am constantly worried that my batteries will go dead right in the middle of a QSO. I always take the time to fully discharge my Nickel Cadmium batteries before recharging to prev- ent loss of capacity. Am I wasting my time or should you fully discharge batteries before recharging? Signed, M. Ory
Dear M. Without going into the subject of battery chemistry, each type of storage cell has its own peculiarities. The Ni-Cad cell, being the most common of the small high capacity cells, is the one which is more prone to overcharging. When this cell is overcharged, it looses capacity, by converting some of the active chemicals to an inactive state. This can be partially corrected by discharging the cell to its minimum charge condition, and then slowly recharging it. In the case of the Ni-Cad cell, this means a terminal vol- tage below 0.8 volt. A fully charged cell has a terminal voltage greater than 1.2 volts. Continued overcharging of the cell, can reduce the cells capacity to less than 20 percent of its original capacity. Simple precautions will prevent this. Periodically discharge the cell (battery) fully and then recharge it. You need not do this at every recharging, but a good rule is 4 or 5 times a year, depending upon your usage. When you discharge the battery, take care not to allow the cell voltage to drop below 0.4 volt, as this can damage the cell. Reasonable care will allow the Ni-Cad battery to have a long and useful life. Hope you are all charged up.
73, Elmer.
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877. ASK ELMER
Dear Elmer, I have a CB (forgive the name) radio in the car with a "Mag Mount" antenna. As I under- stand, the CB band is the former 11 meter Ham band. How can I prune the antenna to work on 10 meters? Signed, A. C. Onvert
Dear A.C. I prefer to pare an antenna rather than prune it, as a pare is not shriveled as a prune is. Most of the "Mag-mount" antennas are short- ened quarter wave antennas with a bottom loading coil. The purpose of the loading coil is to help resonate the short whip which acts as a capacitor. You have two choices in paring the antenna. You may remove turns from the inductor, or you may decrease the length of the whip. A full quarter wave- length antenna cut for 28.4 MHz, would be 8.24 ft. long. This antenna would have an effective bandwidth of 5% to 10%, which would permit the operation over much of the 10 meter band without the need of a transmatch. As the antenna is shortened, and resonated with a loading coil, it's effective bandwidth is reduced ( the antennas "Q" increases), limiting it's usefulness. Most 11 meter mag- mount antennas are about 36 inches long, which is very short compared to the full 1/4 wave. In order to resonate the antenna on 10 meters and retain the longest possible radia- tor, I would attempt to reduce the size of the loading inductor. In many antennas, this is impractical, as the coils are sealed. In that event, trimming the whip is the only practical alternative. It is very important to have some method of measuring the antennas resonance such as a Grid Dip Oscillator, a self contained VSWR meter, an Antenna Bridge or other instrument. When trimming the whip, I would suggest substituting a piece of heavy Aluminum grounding wire as a substitute for the whip. Trim the Aluminum to resonance, then trim the whip about 1 inch longer. Measure the resonance of the whip and trim 1/4 inch at a time until resonance is reached. You're all set and ready to go. See you on 10 Meters. 73, Elmer. Send all your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877. DEC1994
ASK ELMER
Dear Elmer, When I transmit on my ham rig, my wife hears me on the telephone if she is using it. How can I prevent this? Signed Gabby
Dear Gabby, This is a common problem for ham operators but there are many solutions to this problem. The first and second solutions are obvious, ie., don't transmit when she is on the tele- phone or disconnect the telephone when you are on the air. This will solve the problem but may cause other "domestic" problems which are not so easily solved. Before we discuss some of the other solutions, let us inves- tigate the causes of the problem. Transmit- ters generate RF energy which is radiated into space by the antenna. Other antennas pick up this radiation and send it to a receiver. Telephone systems consist of long runs of wire which can act as fairly effi- cient antennas. These wires carry the energy to the telephone receiver which have elements within them capable of detecting RF signals. They are moderately good radios, and the detected RF can be produce a stronger signal than the telephone's normal signal. In order to reduce or eliminate this interference, we must suppress the RF going into the tele- phone. This can be done by using one or all of the following methods: 1. Disconnect the wires going into the telephone from the house line and wrap several turns of this wire around a ferrite torroid or rod to form a lossy choke. This choke should be located as close as possible to the telephone. Inside the telephone, use some 0.01 uF 400 Volt disc ceramic capacitors across the wires coming from the house line. The combined components make an effective RF filter. Use some additional 0.01 uF 400 Volt capacitors across the line from the handset to reduce any pickup from the handset wires. There is no guarantee that this will be 100% effective, but it will reduce the problem.
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2. In some mild cases, simply wrapping the house line in aluminum foil and grounding it will shield the phone from the RF.
3. There are a few "bomb proof" tele- phones being sold by some dealers which have been designed by hams and actually tested by the FCC. A list of these phones is available from your FCC field office. Each situation is different, and you must experiment to find the best solution for your particular problem.
I hope this will assist you in solving your particular problem. A useful resource is your local clubs RFI committee. They can provide you will helpful suggestions and assistance.
So Gabby, stay off the phone and stay on the air. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877. Feb1995
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Dear Elmer, I have been hearing about microstrip used in UHF and Microwave equipment. It sounds like a mini paint and varnish remover. I use sand- paper myself but is that what they are really talking about? Signed C.O. Axe
Dear C.O. Contrary to your belief, microstrip is the name of a type of transmission line. It seems that with smaller and smaller devices, bulky coaxial cable was no longer practical, a new line had to be developed. If you were to look at a microstrip transmission line it would look just like a wire on a P.C. board. The big difference is that the width of the wire is well defined and the material of the P.C. board is electrically well character- ized. Let us make a piece of microstrip, at least in our minds. We will start with a piece of coaxial cable. If we examine the cable, it consists of a center conductor of known diameter, surrounded by an insulator (dielec- tric) with a well defined dielectric con- stant, which in turn is surrounded by a conductive shield. The center conductor and the shield make up two plates of a capacitor whose value is proportional to the plate surface areas, the thickness and constant of the dielectric between them. All coaxial cable of a constant impedance and the same dielectric have the same value of capacitance per unit length ie., all 50 Ohm cable is 29 pF per foot, all 75 Ohm cable is 21 pF per foot. All of the electrical field is con- tained within the dielectric, between the two conductors. If we were to squeeze this coaxial cable between rollers, we would not materially change its capacity, but most of the electric field would be in the thinner area of the coax, near the center conductor. Very little field would be contained at the distant edges of the coax. If this is the case, we can slice the distant edges of the coax off, as long as we provide a connection between the two remaining pieces of shield. We now have a simple sandwich. This sandwich is called stripline. Continued on Page
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As most of the electric field would be con- tained within the insulator with the highest dielectric constant, we may slice away the top insulation and shield, leaving only the center conductor, lower insulator and lower shield. By widening the center conductor to make up for the reduced capacitance (in very simplistic terms), we have produces a trans- mission line which can be etched upon a printed circuit board and still maintain a constant impedance. This is microstrip. Microstrip has many advantages because of its size and simplicity, but its losses are higher than coaxial cable and it does not provide the shielding of coaxial cable. It is a convenient compromise. Microstrip is used in transformers, filters, couplers and anywhere short pieces of transmission line can be used. Well C.O., This microstrip uses no sandpaper but is still a smooth operator. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 March 1995 ASK ELMER
Dear Elmer, I live on a third floor at my QTH. How can I ground my rig. I had no choice but to run a long wire to a Copper rod and connect a counterpoise, but I still can't get good performance from my random wire ( a long random wire greater than 250 feet).I have an MFJ "Artificial Ground" but I don't get good results and I don"t know how to use it prop- erly. Any pointers? Signed "Floating". P.S. I have a Transmatch, but it helps only so much! None of the bands tune up very well.
Dear Floating, You do have a problem! Fortunately, there are some things you can do to improve your situation. Let's take it a step at a time. With respect to the grounding, for safety's sake, a ground wire to a cold water pipe in your apartment and the electrical outlet box. A good RF ground will take more work. One of the best methods is to connect a tuned line (counterpoise) on each band which you oper- ate. This may be accomplished by using some 4 conductor rotor cable, where each conductor is cut to 1/4 wavelength on a different band. Use as many cables as required to cover all of the bands. Remember that these cables are connected directly to your radio's ground terminal (all in parallel). The ideal situa- tion is to feed these cables out the window, or as in as many directions as possible to establish a pseudo ground. It is best to have the open end of the counterpoise away from the shack, as there is a large standing wave developed on the wire, with the highest voltage at the end. The radio will see zero volts (ground). The Copper rod into the ground is a good idea, but it should be connected to the house ground for lightning protection. The MFJ artificial ground is a tuned circuit which attempts to resonate a short piece of wire on the band you are operating. It is not an effective counter- poise, but it is better than nothing. By the way, I don't expect you to have wires all over your room to obtain a good ground. You have to be practical.
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You must do the best you can with the limited resources at your disposal. The way I would
use the MFJ "Artificial Ground" would be to connect as long a wire to it as I could, and then tune it for the maximum ground current at the frequency I want to operate at. This would assure that your rig thinks it has a good ground. It really doesn't, but most rigs aren't too smart. It is best to have the MFJ unit very close to the rig's ground, otherwise there can be false readings. With respect to the transmatch, it should be one which can handle extremes in impedance. A long wire antenna's impedance can vary from nearly a short circuit to many thousands of ohms. Some of the better units contain a step up transformer to handle the very high impe- dances. If you always use a transmatch, I would suggest that the counterpoise be con- nected to it, rather than the rig, as this is where the transition from a 50 ohm system to the outside world takes place. Well "Floating", I hope this keeps you well "Grounded". 73, Elmer
Send all of your questions to ASK ELMER, c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridge- field, CT 06877. May1995 ASK ELMER Dear Uncle Elmer,
HF is dead. I can't get any Dxing done. I want to get into satellites so I don't have to worry about sun spot cycles. At present I have a 2 meter-440 FM rig and an HF rig. I understand that satellites work 10 meters and UHF/VHF. I lack one of those fancy sideband UHF/VHF rigs. Does this mean I can't work satellites? I heard stories about hams reaching satellites with handy talkies. Is this possible? 73, "Lost In Space"
Dear "Wanderer", In order to work the satellites, you require a 2 meter/70 cm rig with ssb. The 10 meter HF rig with cw/ssb will be helpful in one of the satellites modes of operation. An amateur radio satellite is not a simple repeater, handling one QSO at a time. Communications are handled by a Transponder, which can handle several QSO's simultaneously. A repeater works by having a fixed frequency transmitter and receiver linked to repeat a transmission. A transponder, is abroad band frequency converter, which converts all of the signals received by it by a fixed amount to its transmitter. As an example, if we were operating Mode J, we would transmit (up link) between 145.820 and 145.860 MHz and the satellite would convert the frequency and transmit it (down link) on 435.930 thru 435.970 MHz. This is a fixed shift of 290.150 MHz to the up link frequency. You can easily see how many transmissions can occur simultaneously. Amateur radio satel- lites do not use FM as it a mode of communi- cations which is wasteful of power and band- width. In FM, the full carrier must always be present at full power which can diminish the limited power resources of the satellite.
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In ssb, power is only required during actual modulation, and the power (being a form of amplitude modulation) is not always at the maximum value. The transponder's output power is directly proportional to the power of the received signal. A second problem with FM is that it requires twice the band- width of ssb, reducing the number of simulta- neous transmissions via the satellite. You can use your HF cw/ssb rig for the down link of mode A operation, but you will need a 2 meter ssb rig for the up link. Some of the Russian satellites use this mode. The most inexpensive way you can operate "OSCAR" is to build or purchase a transverter. Construc- tion articles have been published in the various magazines, or purchase something like the Ten-Tec 2510 transverter to be used with your HF rig. As far as hams contacting the satellite with HT's, unless the HT is ssb, this is not possible unless it was done as a controlled experiment. Hams have operated the space shuttle using HT's, as the operation there is on 2 meter FM. I hope you have found yourself and will try operating the satellites. It is a fun form of communication, especially in this time of decreased HF propagation. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877. July1995
ASK ELMER
Dear Elmer, I am interested in getting an amplifier for my shack to be used on both CW and SSB. I was told that they have to be linear (whatev- er that means) to work on SSB. The amplifier I use on my 2 meter rig is a class "C" ampli- fier, which works great. Why can't I use one like it tuned to the HF bands. (they are a lot cheaper.) Signed, F. Rugal
Dear F. In a word, NO! Now let's get to the reasons. The types of modulation you are using will determine if you require an amplifier whose output is directly proportional to its input, otherwise known as linear. CW, the original form of "Digital Modulation", since it con- sists of RF or no RF to convey its informa- tion. Any amplifier will do to convey this information, since the signal is either on or off. In FM, the intelligence (if there is any) is conveyed by changing its frequency, and not its amplitude. An amplifier need not be linear to handle this signal, since its amplitude does not convey any information. Now we get to SSB (Single Sideband), which is a form of AM (Amplitude Modulation). AM, as its name implies, conveys its information by varying the amplitude of the RF. This vary- ing amplitude, conveys not only the volume of the information but also its form or shape. If the modulation were a pure tone, it's shape would be a sine wave ( a smooth regular waveform without any sharp changes in its form). If the amplifier used, was not line- ar, the shape of the sine wave would be deformed, and would not sound right. If this were speech, it would be distorted, possibly being unrecognizable. Were it a TV picture, it would not look anything like the original picture. There are two common types of linear amplifiers, Class A and Class B. These classes of amplifier describe the duration of current flow in the amplifier. A class A amplifier always has a current flow- ing in its output which is proportional to the input signal at all times. This type of amplifier may be used for linear amplifica- tion for all types of signals. Continued on Page
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It is the most linear of amplifiers, but it is the most power inefficient. The class B amplifier, has current flowing only during one half of the input cycle. Its output amplitude is directly proportional to the amplitude of the input signal, making it linear. A second stage working in push-pull with the first, or the use of a tuned circuit to supply the second half of the output. I suggest reading the ARRL's "Radio Amateurs Handbook" for a more detailed explanation of amplifier classes. As you can see, you need a linear amplifier to amplify a SSB signal, otherwise it may not be usable. So F. Rugal, spend the extra for a "Linear", or get a better antenna system. 73, Elmer.
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877 Sept1995 ASK ELMER Dear Elmer, I am just getting into packet radio. I have it all set up it works just fine. I can connect with a few stations but I can't seem to get into the BB's or the chat mode on some stations. I would also like to know if there is a local BBS in Stamford that I can log into to get messages from and to my home BBS. Right now I use a station in NYC to connect to London and Burbank, CA. Please Help???? Thank You. Signed R. U. There P.S. This is my third request for info. You always ask for new topics in the news letter but never print mine. How come?
Dear R. U. I must humbly apologize for myself as well as the nameless person who was asked to respond to your question. He never responded, so I have taken the challenge (as I don't use packet at this time) to get some answers. The first item I checked into is if their is a local BBS in Stamford. I'm sorry to say that I could not locate any. It appears that the last one left about a year ago, and everyone told me to digipeat thru K1EIC-2 in Shelton on 146.050 to Jay's BBS (N4GAA) and to connect using the alias BBS-GAA. Another possibility, closer to home would be to connect to WB1U in Norwalk on 145.03 or on 441.05. One of the first things after con- necting is to send a "?" to get a help screen. This will indicate that to get into the "chat" mode which is called the "confer- ence" mode, you need to send a "c". Once in this mode, all commands must be preceded by a "." in the first column, then the command letter ie., .h for help, .w to list current users and .q to return to the BBS. I can't give you all the details of operating the BBS, as it would be too much for this column. The help screen will give you a more complete rundown of the capabilities of the BBS. This is only the tip of the iceberg, as packet has expanded to provide communication links nationwide as well as internationally. I hope this helps to answer your questions. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877. Dec1995 ASK ELMER
Dear Elmer: I want to use my new computer with my radio, but when I turn it on, I get so much noise in my radio it makes it impossible to use. What's happening? What can I do to get rid of the noise and let me get on packet? Signed, Q. Arem
Dear Q, We will continue our discussion of computer RFI reduction that we started in last months ASK ELMER. If the cables radiation has been significantly reduced or eliminated using the methods discussed last month, and there is still significant RFI due to the computer, we must now look to the main components of the computer. Using the pick-up loop to continue to sniff out sources of radiation, move it along the case of the computer. Many pre- assembled computers have cases made of a conductive plastic. This is supposed to suppress the radiated RFI from the computer. They are not that good, and do allow a sig- nificant radiated signal. One easy way of suppressing this signal is to line the case with aluminum foil. Make sure that the foil is connected to the common ground of the computer, and covers the case as completely as possible. You can easily verify the foils effectiveness using the pick-up loop. This same procedure is used to shield the monitor (which is generally the second greatest source of computer RFI). A third source is the keyboard and its cable. Aluminum foil and grounding is very effective in suppressing its RFI. All computer peripherals do contain oscillators and fast digital circuits. They all radiate to some extent and must be checked using the pick-up loop. Lastly, I cannot stress the importance of properly grounding your rig, and making sure there are no exposed unshielded or unbalanced antenna feeds near the computer. It is only common sense to route all of these wires away from the computer. By the way, some TNC's and TU's are also RFI generators in their own right. These methods work for them as well. I hope you are successful in eliminating the QRM in your shack. 73, Elmer Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877. Jan1996 ASK ELMER
Dear Elmer, Help looking for the birds. I would like to know all about working the satellites. sometimes hear them on 10 meters (29.???). How do you get into them (what band and frequency up link and down link)? Do you need a large antenna and lots of power? What class of license do you need to work them? Is there a computer program to track them? Thank you for help looking for the birds. Signed, Greg (the Bird watcher)
Dear Greg, In last months column we discussed the fre- quencies where the satellites could be found. This month we will discuss antennas and power requirements. One of the nice things about operating the satellites is that there are no natural or man made obstructions between the satellite and your rig. We assume that the satellite is well above the horizon. This means that the only major power loss will be due to the inverse square law of radiation, and some losses due to atmospheric adsorp- tion. The inverse square law says that as you double the distance the power is 1/4 of the original power, triple the distance and the power is reduced to 1/9, etc. The re- ceiver in the satellites transponder is relatively sensitive, so power levels in the range of 5 to 20 watts would be sufficient. Many stations have the capability of higher power, but adjust their power down to share the resources of the transponder equally with the other stations using satellite. The methods of power adjustment is to adjust the power level so that the echo of your own signal equals the satellites beacon signal strength as received at your station. As far as antennas are concerned, the "Bird" may be worked using a pair of simple "Turn- stile" antennas to elaborate arrays of Continued on Page
ASK ELMER cont.
circularly polarized yagis, with dual rota- tors to track the satellite from horizon to horizon. The more elaborate the antenna system, the lower transmitter power required, and the stronger will be the received signal. The drawback in the elaborate array is the need to accurately track the "Bird". This can be done manually, but tends to be labori- ous if you wish to work the "Bird" during its full flight across the sky. Many operators rely on computer tracking programs, of which there are several, to locate the "Bird" and in some instances to control the antenna rotators. The fancier the antenna the more accurate the tracking has to be. A satellite has a limited amount of on board power which it has to share with many users. The output power of the transponder is necessarily low, so a good antenna and receive preamplifier is recommended. To be continued in future columns. 73, Elmer
Send all of your questions to "ASK ELMER" c/o MAarv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877. March 1996 ASK ELMER Dear Elmer, Help looking for the birds. I would like to know all about working the satellites. I sometimes hear them on 10 meters (29.???). How do you get into them (what band and frequency, Uplink and Downlink)? Do you need a large antenna and lots of power? What class of license do you need? Is there a computer program to track them? Thank you for your help looking for the birds. Signed, Greg, (the bird watcher).
Dear Greg, We could go on and on about satellite opera- tion. This will be the last in the series on "Bird Watching", as I don't want to beat the topic to death. We will close the topic by covering sources of information on the satel- lite. I would recommend that one or more of these publications grace your reference shelves in your shack.
AMSAT Publications: A Beginners Guide to OSCAR-13 by K. Berglund AMSAT-NA Digital Satellite Guide by AMSAT The RS Satellites Operating Guide by AMSAT How to Use The Amateur Radio Satellites Mode S: The Book by AMSAT Decoding Telemetry from the Amateur Satel- lites Proceedings of the AMSAT-NA Space Symposium AMSAT Journal
ARRL Publications: Satellite Experimenters Hdbk by M. Davidoff The ARRL Handbook for Radio Amateurs ARRL Satellite Anthology Radio Communications Handbook by RSGB
The above list is representative and not complete by any means. I would suggest a visit to the AMSAT home page on the Internet for the latest information. Their address is HTTP://www.amsat.org. Well I hope this gets you into the right orbit and flying with the birds. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877. May 1996 ASK ELMER
Dear Elmer, What difference does a Balun transformer have on a dipole antenna? It would seem to me if a dipole is fed by an unbalanced coax, one leg serves as a counterpoise for the other. With a Balun, they radiate more evenly. Am I right? Signed Off Center
Dear O.C. Well, you're off but your on. Lets look at a dipole antenna. You can look at a dipole antenna as a balanced transformer which matches your generator (transmitter) to the 377 ohms of free space ( or alt least cost effective space as nothing is free in this world). The returns for the transformer is a center tap which is the earth. A Balun transformer converts an unbalanced feed line to a balanced load, so it satisfies the feed requirements of the dipole. If you feed a dipole with unbalanced line (coaxial cable), the element connected to the outer conductor will act as the transformer due to coupling from the other element and phasing of the RF energy. What generally happens is that there is a standing wave on the outer conductor of the coax. This can act as a radiator which may disturb the pattern of the dipole or (depending on the frequency, length of coax and other items) bring some of the RF into the shack. In most cases, you needn't worry about it. If you are running very high power, the RF in the shack can cause problems with some of your equipment. To eliminate this, you can make an RF choke with the coaxial cable. In a way, this can form a sort of a Balun, as the antenna is its own transformer, and the feed line has no RF on its outer conductor. To do this, coil about 10 turns of the coax feed line about 1 or 2 feet below the antenna, and secure it there so that it won't break the antenna from its weight. In lieu of the 10 turns of feed line, you can substitute some Ferrite cores slid around the coax cable about 1 foot from the antenna. I would recommend 3 or 4 cores to make a reasonable choke out of the coaxial cables shield.
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As far as the radiation pattern, the feed line's influence is really minimal consider-
ing the other obstructions (trees, buildings, etc.) in the near field of the antenna. Many commercial wire dipole and beam antennas are fed with coaxial cable without the use of a separate Balun. It is interesting to note that an ideal dipole is a 75 ohm antenna, which we routinely feed with 50 ohm cable. This does not cause any practical difference in the operation of the antenna, and the small mismatch really doesn't bother your rig. All of the power your rig can put out is radiated (in one way or another). In conclusion, don't worry about the Balun. There nice, but you may not need it. Well O.C, did I get you off center? Until next time, 73. Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
June 1996 ASK ELMER
Dear Elmer, Concerning the G5RV antenna, I can't get it "high and in the clear" at all. I need to zig it and zag it and I hear that this antenna won't function that way. I can get the 29'6" matching section pretty straight, but not much else. Signed, Cramped
Dear Cramped, The G5RV antenna is a popular multi band antenna designed for use in space limited areas. It uses its feed line as part of the radiating element. The antenna is basically a 20 meter dipole fed with a combination of open wire line and coaxial cable, causing it to have multiple resonances on several of the amateur radio bands. In order for the anten- na to have a reasonable radiation pattern, the dipole must be reasonably straight. It can be set up either as a flat dipole or an inverted "V", but cannot tolerate too many bends in the elements. The antenna does require a transmatch for operation on all of the bands, though it may match (within a VSWR of <2:1) on some of the bands as a function of the feed line's length and impedance as well as the antennas height above ground. A second requirement is that the antenna's feed point be as high as possible to obtain a low radiation angle. If this can't be accom- plished, I would not recommend the use of the G5RV type of antenna. Let us make the assumption that you have purchased the G5RV antenna kit and it can't be returned. I would then suggest that it be put up as best as you can and see what hap- pens. All antennas will radiate the energy supplied to it, and will act as a receiving antenna in one way or another. Use a trans- match to match the feed line to your radio and go to it. You may find that it works for you. If it doesn't work, I would suggest either a random length of wire (as long as possible) fed with coax cable and a trans- match to match the feed line to your radio. These antennas do work relatively well. A second recommendation is a multi band verti- cal which will operate in a limited space.
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As a reference I would recommend the ARRL "Antenna Handbook" and the ARRL "Antenna Compendium". Volume 4 of the Compendium has an extensive article on the G5RV antenna. For the amateur radio operator, antennas is one of the last areas of experimentation open to them. Go experiment and have fun. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877.
July1996 ASK ELMER Dear Elmer, What is a "Patch" antenna and how would I design one for 2 meters? Signed Patches
Dear Patches, You asked for it, so here we go..... A Patch antenna is a microwave antenna con- sisting of a resonant conducting surface above a ground plane. It is a piece of transmission line, known as micro strip line, which radiates along it's edges. It is a very inefficient radiator and moderately directive. Its poor efficiency is due to the absorption of the energy by the dielectric material. To make a Patch antenna multi directional, several have to be used in an array. In order for the antenna to operate (radiate), the patch must be 1/2 wavelength which at 2 meters is nearly 38 inches. That makes it fairly large. Being micro strip, and having an insulator other than air bet- ween the patch and the ground plane, the antenna is shortened, but not enough to make it useful at 2 meters. The operating band- width of the patch antenna is a function of the type of insulating material and its thickness. The smaller the patch antenna is for its frequency of operation, the narrower its bandwidth. A second problem is matching the antenna to your feed line. Calculating the feed point will approximate the correct place, but you must experiment to determine the exact point. Patch antennas can be made in other shapes, but loose bandwidth and efficiency compared to the rectangular shape. The design of a Patch antenna is beyond the scope of this article, but for those who are interested, I recommend the following refer- ences; Milligan, T., "Modern Antenna Design", McGraw Hill Book Co., 1985; Johnson R., Jasik H., "Antenna Engineering Handbook", 2nd Ed., 1984, McGraw Hill Book Co. Rather than using a patch antenna, a simple dipole or vertical will be easier to con- struct, operate and have a more useful radia- tion pattern. I hope this patch of informa- tion has added a patch to your quilt of knowledge. 73, Elmer Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113 Ridge- field, CT 06877.
August 1996
ASK ELMER
Dear Uncle Elmer. How do people in China send CW if they do not know English or know the Roman alphabet? Signed, The Ugly American
Dear Ugly, That's a good question. When Samuel F. B. Morse invented his code, he did not envision it's use by people that use pictures rather than letters to communicate. Chinese and Japanese ( a derivative of Chinese) use symbols for words and phrases which does not lend itself to using a simple code to represent it. Japanese, has gotten around this by generating an alphabet of sorts, used primarily to spell non Japanese words. This can be encoded using the Morse dits and dahs, and has a limited use. Chinese does not have this "alphabet", so they must learn English or other alphabetized language. All of the other languages, wheth- er they use the Roman, Greek, Hebrew, Arabic, etc., do have Morse code symbols. In order to get around this problem, the international "Q" signals were devised. They have the same meaning in all languages. There are some differences in the "Q" signals adopted by the IARU (International Amateur Radio Union) and those used by the military and commercial services. One of the major factors in the development of FAX for general use was the difficulty in transmitting written communications using Idographs over wire or by radio. Currently, a significant effort is being made to develop a keyboard for word processors that will represent the Chinese and Japanese written language. It is not an easy task. To cap this discussion off, we are very lucky that many amateur radio operators learn enough English to be able to communicate using the "Continental Morse Code". By the way, for those who are not familiar with the Morse code, there are two types in use in the US. The "Continental or International" Morse code and the "American" Morse Code. The American Morse code differs in that it uses long and short dahs as well as dits and spaces to represent characters.
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Morse had never considered that his code would be copied by ear. He had devised a reader which printed the incoming code onto a thin strip of paper, from which the ticker tape was subsequently developed. The tele- graph operators at the time taught themselves to decode the sounds made by the stylus hammer and write down the characters. It was a faster method, since you didn't have to read the paper tape then decode the message. After a while, the paper tape was done away with, and all Morse code was copied by ear. American Morse code was used primarily by the railroads and Western Union. It is not in use today other than by some "old timers" who like to confuse us youngsters.
Well Ugly, I hope you have undergone a beau- tification. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, P.O. Box 113, Ridgefield, CT 06877.
Sept. 1996 ASK ELMER
Dear Elmer, I recently put up a multi band dipole antenna, which I fed with coaxial cable. My friend told me to use ladder line instead of the coax to feed the dipole. I use a Trans- match to match my tranceiver to the feed line & antenna so I can cover all of the HF bands. Would changing improve my systems perfor- mance? Signed F. Ed Line.
Dear F. Ed, We Hams are always looking to improve our antenna systems, so this question is fre- quently asked. The best answer I can give you is a qualified maybe. In order to under- stand why, we must look into the function of the antenna's feed line. As it's name im- plies, the feed line connects the generator to the load. In our case the generator is the tranceiver and it's transmatch, whereas the load is the antenna. Under ideal condi- tions, the feed line should introduce no losses to the signal going to or from the antenna. In the real world, all feed lines introduce loss in various ways. The losses are due to "I*R" (resistive) drops, radiation losses, dielectric absorption, mismatch ( a form of I*R loss) and losses in any device which connects the feed line to the antenna and tranceiver. Of the two types of feed line we are considering, Coaxial Cable has the greater loss per unit length. If we compare RG8/u cable verses 450 Ohm open wire line, the losses are approximately 1.3dB per 100 Ft. for RG8/u and 0.1dB per 100 Ft. for open wire line at 30MHz. Most of the losses in the coaxial cable are due to the dielectric between the center conductor and the shield. This assumes that the open wire line is far away from trees, buildings, etc. as these effect the balance of the line as well as the radiation losses. Any "Balun" or transformer in the Transmatch used to convert the unbal- anced output of the tranceiver to a balanced output, generally has a loss in the order of 0.5 to 1dB, so for all practical purposes, we can say that the losses of the two feed line systems are about the same. If this is the case, why use open wire line?
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Open wire line more closely matches the impedance of non-resonant dipole antennas, and is a balanced line so it correctly feeds a dipole which is a balanced antenna. You could use a Balun/matching transformer at the antenna end of a coaxial cable feed line, but you would now have to add the additional losses of the Balun into the system. In the case of a non-resonant dipole, the voltages generated at the antenna can be very high (thousands of volts due to the standing wave on the antenna), and open wire line has a breakdown voltage in the order of tens of thousands of volts. RG8/u has a breakdown voltage of 4000 volts maximum (RG8x cable has a breakdown of 300 volts, and RG 58/u about 400 volts). If the coaxial cable does break down, there is a deposit of carbonized parti- cles left which may cause a high voltage short across the cable. Open wire line is the best choice to feed a non-resonant dipole. If the dipole antenna is resonant on all of the bands you are operating on, the impedance of a dipole antenna is ideally 75 Ohms. This is very close to the impedance of the coaxial cable. This would eliminate the need for a Transmatch, as the mismatch would be minimal, and would keep the voltage across the coaxial cable well below its breakdown voltage. A simple choke may be made by wrapping 10 turns of the coaxial cable into a coil about 8 inches in diameter just before you connect it to the antenna. This will act as sort of a Balun, preventing RF from radiating from the coaxial cable's shield. I know that this answer does not cover all of the possibili- ties, so I recommend you read refer to chapt- er 16 in the "Handbook for Radio Amateurs", ARRL, and the "Antenna Handbook", ARRL. I hope you find a match. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877. Nov1996
ASK ELMER
Uncle Elmer, I see that we are fast approaching N1ZZZ. So what happens next? No more ham licenses or what? Can they just add and extra letter to the right of the number so that we can restart the system? By the way 26 to the fourth power is 456,976 - a lot of licenses if we can get four let- ters.
Signed, Confused and worried
Dear Confused, There are many ways that the FCC can extend the number of call signs in a given call sign block. By the way, a call sign block is defined as 1X2 or 2X1 for Extra Class, 2X2 for Advanced, 1X3 for Technician and General Classes and 2X3 for Novice Class operators. The first way is to go through their call sign database and find all of the abandoned call signs due to upgrades or non-renewals. This would free more than 100,000 call signs and make them available for reissue. This was done in the late 1940's and early 1950's. Currently the FCC's policy is not to do this as their computer system is not set up for this. Even though the vanity call sign pro- gram allows them to search their database for unused call signs and reissue them, they will not, at this time, do it. A second method is to issue the call sign of the next lower call sign block to new licensees. This is currently being done as it does not require any additional effort or monetary expendi- ture. As an example, a licensee who upgrades to Extra Class is being issued a 2X2 call sign instead of the 1X2 or 2X1 call sign originally set up for that class. Technician and General class operators are being issued 2X3 call signs as are the Novice class opera- tors. According to the FCC, the call sign's arrangement and district (ie., areas 1 thru 0) were for the convenience of the Amateur Radio operator, and are of no significance to the FCC. There are available approximately 300,000 call signs in each call district using the 2X3 arrangement. With this in mind,
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there is no imperative for the FCC to change the system. A third choice is the system you suggest, which would increase the number of available call signs to over 11 million per district. It's possible that when the 2X3's run out, the FCC will use one of the suggest- ed methods. At this time they are not chang- ing their policy. Additional information on call sign assignments are published in the W5YI Report, QST and World Radio. I trust this will ease your concern. 73, Elmer
Send all of your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877 or e-mail December 1996 ASK ELMER Dear Elmer, The antenna handbook mentions circulators and isolators, but does not explain what they are or how they work. Signed, Alone and Dizzy
Dear A & D, In order to answer the question we must define what is the function of an Isolator or Circulator. First, an Isolator and a Circu- lator have basically the same function, differing only in their construction and termination. They are three port devices, meaning they have three connection points. These devices let energy flow only in one direction, thereby isolating the signal source from next stage. One of it's uses is to isolate an antenna a transmitter. Any signal coming from the antenna will be iso- lated (severely attenuated) and directed to another port. In this way a transmitter who's final amplifier is very sensitive to load VSWR, the transmitted signal is directed to the antenna, and the reflected signal is directed to another port connected to a dummy load. the reflected signal never go back to the transmitter. One very nice way to pro- tect your radio. Think of the Isolator and Circulator as a revolving door permitting one way traffic only. You probably use a form of isolator without realizing it. The direc- tional coupler (ie, VSWR indicators, Bird directional Watt meters, etc.) used in con- junction with your tranceiver. The principal of operation relies on the phasing of a wave. If two signals arrive at a point out of phase with each other, they will cancel each other out. If they arrive in phase with each other they will add together. You can construct a device using transmission lines or ferro- magnetics (read that as a special ferrite materials biased with permanent magnets) which can selectively phase and direct the signals. If the device uses transmission lines alone it is called an Isolator, if it uses the ferro-magnetic system it is called a Circulator. A second difference is that the Isolator always has its third port terminat- ed. These devices operate over a limited frequency range, generally about an octave (2:1) and are rarely used below 500 MHz due to size limitations. Continued on Page December 1996 Page ASK ELMER cont.
The lower the frequency, the larger the transmission lines become. Theoretically, if you had all the room in the world, you could construct one at 60 Hz if you wanted to. One of the most common application of the Circulator is as a diplexer, where the trans- mitter is connected to port 1, the antenna to port 2, and the receiver to port 3. If the antenna is well matched, all of the transmit- ters energy will go to the antenna and none to the receiver input, and a incoming signal from the antenna will go to the receiver. No T/R switches or relays are needed. For those who want to get into the details (the math can be very challenging), I suggest the following references: Rizzi, P.; "Microwave Engineering, Passive Circuits", Chapt. 8, Reciprocal Multi port Junctions. Itoh, T.; "Numerical Techniques for Microwave and Millimeter-Wave Passive Struc- tures", Chapt. 4, Planar Circuit Analysis. If these two references don't get you, there are some which are more obtuse that I can suggest. Any book on an overview of mi- crowave structures would be recommended. Check your local library. This should keep you going around in circles until next time. 73, Elmer
Send all of your questions to "Ask Elmer" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877 or e-mail October 1996 ASK ELMER
Dear Elmer, Is it possible to build a repeater that switched very fast between transmit and receive so as to use only 1 frequency? Signed Speedy
Dear Speedy, I could answer your question simply by saying "yes", and leave it at that, but deep in my heart I know that you deserve an explanation. In order to accomplish apparent simultaneous transmit and receive, we would have to per- form a form of "time slicing". This is not a new technique as it has been used by the telephone companies for many years. This is the method they use to allow many conversa- tions to be carried over a single twisted pair. In the case of telephone, they rapidly select each "conversation" or connection in sequence at the transmitting end switching station. The speed is very high compared to the frequency in speech, so that when it is assembled at the local telephone switching station at the other end and sent to your home, it appears to be continuous connection. This is a form of high speed multiplexing. In the case of the amateur repeater, the incoming audio signal from its receiver would be electronically delayed for a millisecond or so and the receiver switched off for about a millisecond. The delayed audio would be sent to the transmitter. The transmitter would transmit that signal for a millisecond, and then be switched off. The receiver would then listen for the next millisecond and the sequence would be repeated alternatively switching between the receiver and transmit- ter. It is important that the switching time be in the order of a few microseconds, other- wise the gaps may cause speech distortion. To a listening station it would appear that the transmission was continuous. The only caveat would be in the vicinity of the origi- nating station, competition between the repeaters output and the originating stations signal could cause interference problems, ie., FM capture, distorted audio if both signals were to reach the receiving station at similar signal strengths.
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Even though the system is possible, and a low tech form of single frequency repeaters are available, I don't know how practical it would be. The problems I envision with a fast switching system would be spurious signals generated by the switching, and the capabilities of the RF amplifiers to handle the signals properly. I hope this doesn't slow you down Speedy. 73 Elmer
Send all your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877 or e-mail
January 1997 ASK ELMER Dear Uncle Elmer, Recently I put my rechargeable battery from my HT into the charger stand. The next day I unplugged the charger but left the battery in place for several days before I remembered to take it out. My question is this; I know there is probably a diode in there to prevent current flow out of the cells, but can I leave it in for such a long time? Signed, Klaus B. Amplifier
Dear Klaus, Nickel Cadmium batteries are one of the most misunderstood devices. Though used to power numerous devices, they are succeptable to many conditions which could cause the battery to loose charge or shorten its life. Many of the charging stands are made to quick charge the battery, and are convenient supports foe the equipment the battery powers. Leaving the battery in the charging stand which does not have a reverse polarity diode, will cause the battery to discharge through the charger. This may injure the charger, but most assur- edly it would shorten the life of the bat- tery. The series diode is always used in modern chargers. In the better chargers, there is a sensing circuit to prevent the overcharging of the battery. Overcharging a Nickel Cadmium battery will shorten its useful life. As both of these features are incorporated into modern chargers, it is safe to leave the battery in the charging stand. I feel a brief discussion of do's and dont's are in order. Nickel Cadmium batteries have a memory, they remember the amount of charge they have taken and reduce their capacity to that level. It is recommended that the battery should be periodically discharged to a level of 0.8 volts per cell and then re- charged. Quick charging does not charge a battery to its rated capacity, but a slow charge does. If you want to get the maximum life out of the battery, it should be dis- charged then charged at a rate of 10% of its capacity for 12 to 15 hours. To the best of my knowledge, they have not solved the memory problem without going to a different cell chemistry (such as Nickel Metal Hydride, etc). As they age, the batteries self dis- charge increases.
Continued on Page January 1997 Page ASK ELMER cont.
This means that you should use the battery as soon as possible following a charge. Some older batteries will self discharge in as short as 24 to 48 hours after charging. There is no way to reverse this process. Always keep a minimal charge on a Nickel Cadmium battery, and never, never let it go into reverse polarity. This can destroy the battery, even if you successfully restore polarity, its capacity will be greatly dimin- ished. Well to again answer the original question, yes you may leave the battery in the charger without harming the battery. Well Klaus, I hope you gained incite from this. Until next month, 73 Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman. N1AWJ, PO Box 113, Ridgefield, CT 06877 or e-mail
Feb1997 ASK ELMER
Dear Elmer, I anticipate some difficult QTH's and bad places to operate. Can you give me some pointers on making a random wire as good as possible? Signed, Cramped.
Dear Cramped, One of the nice things about a "Random Wire Antenna" is that it is a random wire. We can cover the general "rules" of these antennas with the following list: 1. Make the wire as long as possible. 2. Make it as high as possible. 3. Keep it far as possible from metal structures, trees or other items which will absorb the radiated signal. 4. Make certain that the insulator at the far end of the wire can withstand the high voltages that may be generated due to the standing wave. 5. Make the wire as heavy as possible to limit the I*R (resis- tive) losses. 6. Try to keep the wire as straight as possible, or minimize the number of bends. If bends are required, make them as gentle and sweeping as practical. The support insulators at the bends should be able to withstand high voltages. 7. Make sure that your RF grounding system for your radio is a good one. A significant amount of power can be lost with a poor grounding system. If a good grounding system cannot be made, a possible compromise would be some resonant radials used as a counterpoise. You do what you can to get the signal out of the shack and into the antenna. 8. Use a good quality Transmatch between the transmitter and the antenna feed line. Try to keep the RF out of the shack and in the antenna. Ideally, the Transmatch would be at the antenna's feed point, and remotely tuned. The Transmatch would be fed with good quality coaxial cable, and grounded as close as possible. This ideal is rarely achieved. It is the unusual installation where all of these rules can be followed, but as they say, "The more the merrier". I wish you luck in erecting your long wire antenna. Many hams have used them quite successfully. 73, Elmer
Send your questions to Ask Elmer, c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 or e-mail March1997 ASK ELMER
Dear Uncle Elmer,
I am now getting deeply into DXing. I send out QSL cards via the mail, however, I know that there is a way to send QSL cards via the bureau which will cut down on my postage expense.
Please explain to me how this bureau thing works. Exactly where do I send my QSL cards? Can I send them a few at a time or must I first collect a whole package of them to send to the bureau? How do I address the individ- ual cards themselves? Up to now I used the address in the Call Book. Do I do the same when using the bureau or must I also include some other information in the addressing?
What is the cost? Do I pay the bureau a handling fee?
Lastly, how do I get cards back from the bureau that others have sent to me?
Signed, New at this
Walter N1NOO
Dear Walter, You really picked an interesting time to get into DXing.. At a sunspot minimum?? Oh well, the "Hunt and Chase" is all the more reward- ing. This doesn't answer your question...so on to the question. Yes Walter there is an "Outgoing QSL Bureau", but I have good news and bad news for you. The good news is that the bureau is main- tained by the ARRL, and the cost of sending the QSL cards is $3.00 per pound of cards or $1.00 for 10 cards or less. The bad news, for some, is that the bureau is only for ARRL members. (This service and the subscription to QST is a major incentive to join the ARRL but there are so many more reasons.) The way the bureau works is very simple... You address your cards by putting the sta- tions call sign in the upper right side of the card (where a stamp would ordinarily be placed) and then arrange your cards by call sign in alpha-numeric order.
Continued on Page ASK ELMER cont.
You bundle your cards with the label from the current issue of QST (to prove membership) and a check in the amount of $3.00 per pound of cards. Ship it to the ARRL, Outgoing QSL
Bureau, 225 Main St., Newington CT 06111. I would suggest that you contact the league for an information sheet on the QSL bureaus, as there are some prefixes that are not served due to a lack of the foreign QSL bureau. Those few, you must QSL directly. I can say from personal experience, that the Outgoing QSL bureau works very well, and is a service that is greatly appreciated. We will discuss the workings of the incoming QSL bureau at another time. I will say that the incoming QSL bureau does not require ARRL membership... but that's for later. Happy DXing and 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 or via e-mail
April 1997 ASK ELMER Dear Uncle Elmer,
I am now getting deeply into DXing. I send out QSL cards via the mail, however, I know that there is a way to send QSL cards via the bureau which will cut down on my postage expense.
Please explain to me how this bureau thing works. Exactly where do I send my QSL cards? Can I send them a few at a time or must I first collect a whole package of them to send to the bureau? How do I address the individ- ual cards themselves? Up to now I used the address in the Call Book. Do I do the same when using the bureau or must I also include some other information in the addressing?
What is the cost? Do I pay the bureau a handling fee?
Lastly, how do I get cards back from the bureau that others have sent to me?
Signed, New at this
Dear New, I will now answer the second part of your question regarding the "Incoming QSL Bureau". When a foreign operator sends a card to his outgoing QSL Bureau, they send it to our central QSL collecting group, which happens to be the ARRL. The League then separates the cards into their call area groups and sends them on to the respective incoming bureaus. The incoming QSL bureaus are volun- teer groups who sort and then ship the cards to the operators to whom they were addressed. When the incoming bureau for a particular call district gets a batch of cards, they sort them into call letter groups bases on the suffix of the station call sign. If your call was W1QZK, the cards would be sent to the sorter who handles the letter "Q". The sorter(s) would then break the cards down into the individual stations envelopes. When the envelopes are filled, they are shipped to the appropriate operator.
Continued on Page Page April 1997 ASK ELMER cont.
In order for a ham to have cards set to him or her, they must supply the sorter with envelopes and postage. Some incoming bureaus will accept cash-check or envelopes and loose stamps, others pre-stamped addressed envel- opes only. All supplied envelopes should be 6 X 9 inches in size, pre-addressed and have your call sign written in the upper left corner. Have sufficient postage for at least 2 ounces of cards. Send at least 4 envelopes at a time so they will have a sufficient number on hand if you get a large number of cards. You do NOT have to be an ARRL member to use the service. The incoming bureau DOES NOT collect and store cards for hams who do not supply envelopes, etc. These cards are thrown out. This service is provided to hams by hams without charge, and is done in the sorter's own home. Consider the space re- quirements...No envelopes, no cards! In our area "W1", the address of the Bureau is; W1 QSL Bureau, PO Box 80216, Springfield, MA 01138-0216. For those members in 2 land, the address is; ARRL 2nd District QSL Bureau, NJDXA, PO Box 599, Morris Plains, NJ 07950. Any correspondence with the bureau requires a SASE for a reply. Contact the W1 or W2 bureau enclosing SASE for more information. The ARRL home page on the Internet at "http://www.arrl.org" has information on both the incomming and outgo- ing QSL bureaus. Remember, these hams han- dling your cards are providing us with a great service, and if you use them, an occa- sional thank you note goes a long way. Hope this lets you get all of those QSL cards you were expecting. 73, Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 or e-mail May 1997 ASK ELMER
Hi Elmer,
A radio amateur that lives about two miles from me says when I'm transmitting on 20 meters at 14.160 he cannot hear anything from his radio on the entire band other than an s9 noise completely across it.
He says I'm 60 over 9 when he listens direct- ly on my frequency. He says he cannot operate when I get on the band. He just got a more modern radio and he does not seem to be having this problem with it. Only his older radio seems to be having interference when I'm transmitting. Other nearby hams are not experiencing this interference.
What could be the problem Elmer? Jay NE2Q
Dear Jay, It appears that the ham who lives about two miles from you has a classic case of "Front End Overload". This problem is prevalent in any broadband receivers, be they communica- tion or broadcast. This occurs most frequent- ly on TV sets because there is a lack of or inadequate filtering at the antenna termi- nals. It generally manifests itself as a complete loss of signal, with the screen going either totally black or white. Ordinarily, communication receivers are designed to have a very large dynamic range, so that it can listen to a weak station in the presence of a strong one (assuming the IF filters bandwidth would permit it). If the radio's first mixer is defective, or there is a resonant element which is tuned to the interfering frequency causing a large voltage to be developed, then the radio will experi- ence overload. Another cause could be a noisy local oscillator in the receiver which would produce a spurious signal, mixing with the incoming large signal, producing a large spurious signal at the IF frequency. Any of these causes would produce a signal which would pass through the receiver's IF amplifi- er and basically capture the radio.
Continued on page May 1997 Page ASK ELMER cont.
In the case of the ham whose radio is blanked out, I would suggest that he look at possible resonant elements in his antenna system. At a distance of 2 miles and only when you transmit on only one specific frequency I can not see any other direct cause. The spurious signal being generated by the radio's local oscillator is a less likely possibility as this happens on one frequency only. The measure of a receivers immunity to this type of interference is called "Blocking Dynamic Range". In most modern radios the blocking dynamic range extends to over 300mV at the antenna with some radios exceeding 3V. If you were to calculate the signal strength of your signal at a distance of 2 miles, it would be in the realm of 100's of micro volts, not hundreds of millivolts. (This calculation may be done by use of the "Radar Equation", published in most texts on anten- na's and propagation). I hope this answered your question, and provided some insight into a possible cure for the problem. Until next month, Happy QRM! 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 or by e-mail June 1997 ASK ELMER
Dear Elmer, I'm new to ham radio, and I know that all antennas must be grounded. My question is exactly where on the antenna do you place the ground wire, and what's the best way to connect it? Signed, Chris, KB1BZK
Dear Chris, To ground or not to ground, that is the question. Weather it is nobler in the minds of hams to suffer the shocks and lightning strikes or to bury them, never to flash again. To ground, always at the closest point to the antenna and make sure that the entire antenna has a direct path to the ground. There is no specific point on an antenna where the ground should be placed, but you don't want to ruin the antenna's performance by putting it in the middle of the radiating element. Most vertical anten- nas have a low DC resistance connection from the radiating element to the mast, which then can be connected to ground. With dipoles, it is recommended that a choke be placed across the feed point of the dipole antenna to provide this low DC resistance path and a high impedance path to RF. A similar choke can be connected to the feed line and routed to ground. I would suggest a choke which could carry a reasonable amount of current, as static discharges, lightning strikes generate very high instantaneous currents. A word about the wire going to ground... Make it heavy..8 gauge or heavier because it must survive, at least for a second or so. I will not cover the ground field, as it is covered in many publications. I will say the old adage "The more the merrier" when it comes to ground rods, to assure a good ground connec- tion. Do not use the water pipes in your house for this grounding. In some instances they may be plastic, and you are trying to keep the lightning out of the house! Well Chris, I trust that you are well grounded in the art of grounds. 73, Elmer Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877 or e-mail August 1997 ASK ELMER
Dear Elmer, I have an older rig with tube type finals that need replacing (6146). Do I have to re- neutralize the finals? How do I tell? Signed, O. C. Lator
Dear OC, In most cases yes, but let me explain what is happening and why. In all active devices.. Vacuum Tubes, Transistors several things happen due to coupling capacity and lead inductance. An ideal device should exhibit an output voltage which is 180 degrees out of phase with the input voltage. If this were to really happen, any output signal coupled through stray capacity to the input would tend to decrease the signal. This is negative feedback. A very stable condition. In reality, as frequency increases, the phase shift does not remain at 180 degrees but shifts towards 0 degrees. If the amplifier gain is high enough, and the phase shift is greater than 180 degrees plus 90 degrees (due to phase shift in stray inductance and ca- pacitance), there is a tendency for the amplifier to become unstable. Positive feed- back takes place and you start to oscillate. In order to decrease this condition, you intentionally couple some of the output signal back to the input of the amplifier through a network so it cancels the positive feedback. This stabilizes the amplifier. This is called neutralization. If the tubes that you replaced were made by the same manufacturer, and they didn't change processes, you would probably not have to neutralize the stage. Generally this does not happen. You can tell if neutralizing is required by tuning up on the 10 meter band into a dummy load. In a stable amplifier, the dip in the plate current, when tuning does not change appreciably with the adjustment of the loading capacitor. If it is difficult to dip the plate current, or if it will not dip at all, neutralization of the amplifier is called for. The procedure is too long for inclusion in this column, but the instruction manual for your radio should contain complete instructions for the procedure.
Continued on page
Page August 1997 ASK ELMER cont.
If you have not worked with high voltages and transmitter finals, ask for assistance from an experienced ham or have it professionally done. If you attempt the neutralization procedure, observe all the safety rules. Though not a difficult operation, it is NOT a casual procedure. Be aware of everything you do as you are working with several hundred to several thousand volts. Follow the instruc- tions exactly, and use the tools indicated in the procedure. A properly neutralized final is a joy to use, and very tolerant of exter- nal mismatches. Until we are next neutralized, 73, Elmer
Send your questions to "ASK ELMER",c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail
October 1997
ASK ELMER
Dear Elmer, I have a 2 meter FM rig that the microphone went bad on. I replaced it with a preamp type CB mike. A friend says that if I turn the gain up too high, the radio will over deviate and violate the FCC rules. I say the radios deviation is controlled internally. Who is right? Signed W.A. O'Vrmod
Dear W.A., In order to answer this question, I think a review of modulation is in order. There are many ways to modulate an RF carrier to allow it to carry "intelligence" (Hi, Hi). The two most common forms of modulation are, Ampli- tude and Frequency modulation. Amplitude modulation, as its name implies, varies the amplitude of the RF carrier in step with the amplitude (loudness) of the audio modulation. The frequency of the modulation (pitch) determines the space in the frequency spec- trum that the modulated signal will occupy. If a filter is placed in the modulator, the radio limits the modulation bandwidth, so that the 5 KHz bandwidth limit for a modulat- ed signal is not exceeded. Shouting into the microphone only serves to increase the modu- lations amplitude until a condition of over modulation occurs. This will cause a dis- torted signal to be transmitted, which may violate FCC rules, depending on the amount of distortion. In Frequency modulation, the pitch of the modulating signal controls the modulation "Rate" (the speed at which it changes frequency) and the amplitude of the modulating signal controls the "Deviation" of the carrier (the signals bandwidth). The carriers amplitude is constant at all times. Over modulation would cause the carrier to over deviate beyond the limits set in the FCC rules. Over deviation can also cause other problems, such as, adjacent channel interfer- ence (in the case of repeaters) and severe audio distortion. One method of setting the modulation level on your transmitter is to have a friend listen to the output of your radio on an HT.
Continued on Page
Page October 1997
ASK ELMER cont.
Compare its volume with that of a local re- peater. Use the repeaters ID, if it is a synthesized voice as your reference. A CW ID is somewhat more difficult to use, but you can use it. When they are the same, you can be fairly certain that your radio is deviat- ing properly. Of course, if you have access to a "Deviation Meter" or a "Communications Monitor" you can set your modulation level precisely, but these are not readily avail- able to the average operator. Well W.A., this should get you deviating properly. 73, Elmer
Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail December 1997
ASK ELMER
Dear Elmer, How do those little white EZ passes work, and when it says low funds, where do I put the money in it? How do they know it's me, since the box doesn't have any batteries? Can I get real close to the car in front of me and have him pay? Signed C. Heap.
Dear C, As this is the season to be generous, I will answer this question, even though it has nothing to do with Amateur Radio it does come under the umbrella of communications (digital mode). I think the way to answer this is to tell you about a concept called the "Smart Rock". The "Smart Rock" is a very low pow- ered transmitter receiver combination. It is normally in a sleep mode, consuming only microwatts of power to maintain its dormant mode. During this time the receiver is on, waiting for a command signal from the some external source. Once it receives this signal, it turns itself on and transmits its information in very short time. It then turns itself off awaiting the next interroga- tion form an external source. The "White Box" on the windshield of your car is the "Smart Rock". When you enter the toll area, there is loop antenna buried in the road under your automobile. It senses the pres- ence of the car and turns on a transmitter which interrogates your "Smart Rock". Within the transmitter in your car, there is stored your unique ID, which is transmitted to the interrogating receiver at the toll area. This ID is sent to a central computer with all of the information on it as to your identity, account status, etc. It will then indicate if your account is fully funded or you are low in funds. . It then signals you by raising the toll gate and/or lighting a low fund warning indicator. This all happens in a fraction of a second.To refill your account you have to refer to the instructions sent to you with the EZ Pass tranceiver. Each agency has its own requirements The battery in your tranceiver in the car will last at least 10 years (it's shelf life, as it is used infrequently and at a very low power).
Continued on Page
Page December 1997 ASK ELMER cont.
Getting real close to the car in front of you will not permit you to got through the toll gate, as the sensor in the road will sense the first car leaving the gate and then your car's presence. There would have to be zero space between the cars to make the sensor in the road sense only one vehicle. Though not impossible, very highly improbable. The idea of "Smart Rocks" is one which can be used in many situations. Consider a wooded path for hikers with smart rocks placed at reasonable intervals. A hiker could follow the path from one rock to another no matter what the weather conditions or time of day, and never have a fear of getting lost. The same idea for vehicles. An automatic system of road markers to a reader in the car indi- cating your location without having to rely on the GPS system, or to augment the GPS system. The "Smart Automobile". Well C, I hope you walked your "Smart Rock" or was that your "Pet Rock"... whatever... 73 Elmer
Send all of your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield. CT 06877-0113 or e-mail February 1998 ASK ELMER
Uncle Elmer
I just purchased a Direct TV small dish television satellite system. I am told that the footprint of the signal is basically the same as the shape of the continental USA. According to the information package, the footprint is so exact that without special equipment, the signal can not be received more than200 miles outside of the Continental USA. I understand how they can shape a transmit antenna to get a circular footprint, but how do they achieve an irregularly shaped foot- print? Signed, Bevis & Buthead (from MTV for the uninformed) N1NOO
Dear B & B,
There are many ways to shape the radiation pattern of an antenna, but not one which would, by itself, be as irregularly shaped as the outline of the U.S. The satellite used in rebroadcasting the TV signal is in a "Geosynchronous Orbit" around the earth. This means that its relative position to the earth remains unchanged as the earth rotates. This is done by having the satellite posi- tioned high enough that its orbital speed exactly matches the earth's rotational speed. In order to shape the "footprint", several satellites and antennas are used, each in a different position so that they ultimately cover the outline of the US. The only prob- lem that occurs is at the areas where the satellite footprints overlap. What is gener- ally done is the phase of the transmission is set up so that the signals reach the receiv- ing antennas together, hopefully at the same time. Ghosting is inevitable at this point, but with proper planning, it can be minimized by positioning the receiving antenna to favor one particular satellite over another. The receiving antenna has a narrow beam width ( it is a parabolic dish which acts like a lens). By so doing, the favored satellites signal is so much stronger than the interfer- ing signal, that the ghosting is negligible. I don't know how accurate the 200 mile recep- tion limit is, but by proper location of the satellite and antenna beam width, curvature of the earth would prevent reception beyond the 200 miles. I hope you have your footprint firmly plant- ed. Until next month, 73.
Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail April 1998 ASK ELMER
Dear Elmer,
My next door neighbor has a lamp in her bedroom which lights up whenever I go on the air. She says that I am the only one who lights up her light. For some reason my wife doesn't appreciate her saying that. How can I get it to stop? Signed A. G. Lowe
Dear A.G. If the "Light of Your Life" takes a "Dim View" of the "Light in Your Life" there might be a be way for you to see the "Light at the End of the Tunnel". The "Light in your Life" is probably one of the "Touch" lamps which were popular a few years ago. They use a form of a proximity switch which senses the change in capacity between the lamp and the house ground. Your hand and body act as one plate of the capaci- tor, the lamp base and support as the other plate. This is a very sensitive circuit, and can easily be activated by a strong RF field. By its very nature, it cannot be shielded, so you have to reduce the amount of RF getting to the lamp circuitry. One of the first things to do is to wrap the lamp cord around some ferrite cores to reduce the effect of any RF getting in through the power line. Sometimes, a wrap of aluminum foil around the entire length of the power cord, and then connecting a wire from the foil to the wall junction box. This may act as an RF shield. Beyond this, without either opening up the lamp to do some work on it (which may cause more problems than it cures) or you or your neighbor moving to a new house, there is little that you can do. Sometimes moving your antenna location may reduce or eliminate the problem. Anything to reduce the RF field in your neighbors house around the lamp. There have been many novelty products designed for the consumer which were never designed to operate in an area with moderate RF levels. At this time, entertainment equipment such as TV's, Audio systems remain highly succeptable to interference by most any device which radiates an RF signal (either intentionally or not intentionally such as computers, etc.) I hope this throws a beam of light onto the problem and leads to a solution. 73, Elmer
Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail MAY 1998 ASK ELMER
Dear Elmer, I've just moved into a top floor apt (3rd Floor) in a huge house. As a beginner in Amateur Radio, what type of antenna do you think or suggest I start with, or should I build my own? A, In the house, B, on the roof, c, outside the house? Marlene
Dear Marlene, Choosing a first antenna can be both fun and confusion. There are so many types to choose from. The first question you have to ask yourself is "What bands do I want to operate on"? The answer to this question will help narrow down the choices of antennas (slight- ly). The second question is "What will I be allowed to put up", as both the property owner (if that is you, then this is not a problem), the community, condo association, restrictive deed or city/town will permit. This sounds more complex than it really is. If you are renting, check with your landlord to see if they have any objections to an outside antenna. If there are none, then for general HF operation, I would recommend a multi-band dipole as the easiest antenna to erect (and one of the least expensive). This does assume that there is a tree or other support for the antenna besides the side of the house and there is at least 50 feet between the two end supports of the antenna. If this is not possible, there are vertical antennas available, but they are expensive purchased new. You can get a good deal pur- chasing a used one at an amateur radio flea market or in "Ye Olde Jonque Boxxx". If you are looking to operate on VHF/UHF FM, I would suggest a multi-band vertical covering the 2M and 70cm bands. If an external antenna is not permitted, simple indoor antennas can be constructed for VHF/UHF which are quite effective (J-Poles, 1/4 wave vert., etc.) and inexpensive. As a first antenna I would not recommend a tower and beam as they are quite expensive and take a considerable effort to erect. There may be local zoning restrictions and/or permits which have to be obtained. This is more for the established station. Most of all, you can be very creative with antennas. Continued on Page Page May 1998 ASK ELMER cont.
There are so many different types which are adaptable to a first station that it would be difficult for me to list them in this brief article. I would suggest the following references published by the ARRL: "The Handbook For Radio Amateurs" "ARRL Antenna Book" "FM and Repeaters" "Antenna Compendium" Enjoy constructing and operating your new station. It is an exciting and rewarding time. Especially when you make your first contact and your first DX contact from your new station. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail
July1998 ASK ELMER
Dear Elmer, If I find a used radio, how can I check its value?
Signed G. Reedy
Dear G.
There is no one source for determining the value of used equipment. To a great extent, used equipment is a buyers market. Much of the equipments value is based upon what you are willing to pay for it. There are some places which you may be able to determine a price range for the equipment in question, but only if the items are relatively popular. In print media, the QST classifieds, Amateur Radio Trader magazine, The Ham Trader Yellow Sheets, Nuts and Volts Magazine classifieds and the Amateur Electronic Supply catalog used equipment list to name some of the more popular sources. On the Internet, the follow- ing URL's deal in used equipment:
http://www.ring.com/trading/hamradio.htm http://www.cqinternet.com/ http://www-windows.1251.stack.net/~victor/ hamradio/www_1.st.html In some areas, a local repeater may have a club "Swap Meet" which may be a source of information. If the radio falls into the collectors cate- gory, then it becomes more difficult to determine its value. In this case, the radios value is determined by what you are willing to pay and what the seller will let it go for, and how collectible is the radio and what is its condition. There have been price guides to collectible radios published over the years, but they are outdated as soon as they are published. They can give you an indication of the radio's rarity, and a estimated value at least a year prior to the publication, but little more. Well G., I hope this gives you some direction on that "Boat Anchor" or "Battleship" you are dreaming about. 73, Elmer Oct1998 ASK ELMER Dear Elmer, I read an article which said that modern resistors are made with a spiral of Carbon film. Doesn't this give it a lot of inductance and wouldn't it affect circuits at radio frequencies? Signed "Q".
Dear "Q", 10Q for the "Ask Elmer" question... it was sorely needed. And now to the mysteries of modern components. The article was quite correct. Modern axial leaded resistors are made by depositing a coating of resistance material on a ceramic tube and then adjusting its resistance value by cutting a spiral groove into it. The components are not made one at a time, but a very long spiral tube is made, and the average resistance per unit of tube length is measured. The machine then cuts a continuous spiral into the resist material for the entire length of the tube. The tube is then sliced up into the correct length for the resistor body size, end conducting bands are plated onto the resistor body and end caps with leads are attached. Finally an insulating dip is applied to the resistor and the value of the resistor is painted on the body. This process is extremely accurate and can produce resistors with tolerances of better than 1%. Your assessment of the resistors use at high frequencies is also correct. They are not recommended for use as elements in RF attenuators or loads, but are perfectly good for use as isolation elements in HF circuits. If you require a resistor for critical RF use, you can use either Carbon Composition resistors (which are becoming increasingly hard to find and expensive), or Metallized Film Chip Resistors. The chip resistors are made by depositing a metallization onto a ceramic substrate and then adjusting its resistance by using a laser to cut away some of the metalization. The inductance of these resistors is very very low, and can be used into the microwave region. The negative is that they are tricky to solder into your circuit, and they cannot handle much power (the ones most available to the Ham or Experimenter) unless specially made for high power. I have mentioned two types of resistor material, Carbon Composition, and Metal Film. There is a third material, Deposited Carbon Film, which most of the low cost resistors are made of. I will not go into the properties of the materials other than to say that Metal Film is the most stable material, and Carbon Composition the least stable. (There are wirewound resistors but they are not suitable for other than low frequency or power use, but are the most stable and can be made to the the tightest tolerances.) As an experimenter you must always consider that a component is not just a simple element, such as a resistor, but is a circuit consisting of resistance, capacitance and inductance. At low frequencies it is primarily a resistor but as the frequency increases it may be a completely different element. But that is for another future question. Until that time, "Q", I will leave you with the thought "There is no place like Ohm"! 73, Elmer Nov1998 ASK ELMER
Dear Elmer, So many new radios are using DSP filters. Everyone seems to tell me that I should only consider a radio with them. What are they and are they really any good? Signed I Byte
Dear I B,
Let us start out with a translation of the initials DSP. They stand for Digital Signal Processor. Basically it describes the tech- nique used to produce whatever function the designers desire. In this instance, it is being used as a filter, similar to the crys- tal filter in your present radio. We must look at the advantages and disadvantages of this technology in order to make an informed decision on the selection any new radios. Basically, electronics today is divided into three areas. They are, analog, digital and mixed signal. The analog techniques are well established, and most devices in one form or another use this to accomplish their task. The crystal filter in your radio is an analog filter, consisting of Quartz crystals, capacitors, inductors and other real compon- ents. The effect of combining the components together in an appropriate fashion, is to create a filter which will allow a narrow band of frequencies to pass, rejecting all others. We can change the characteristics of this filter by changing the values of the electrical components. The only limitations on this filter are those imposed upon us by the laws of Physics and the availability of components. Physical size may also be a restriction, but we will ignore it for this discussion. All electrical filters can be described mathematically. In fact, all of the electrical filters have names which are the names of the mathematical equation describing the filter (ie., Tchebychev, Butterworth, Cauer, Bessel, etc.) With the advent of microprocessors, it became possible to solve mathematical relationships very rapidly. If you were able to convert the analog electrical signal into a digital one, you could then mathematically work on it to change its characteristics, just like a filter.
Continued on page ASK ELMER cont.
Once done, you have to convert the digital signal back to an analog one so that we may interface with it (hear it, see it, etc.). In order to accomplish this, two complimenta- ry devices were developed, the analog to digital and the digital to analog converters. The only other problem remaining is that we must do this operation in real time. It really wouldn't be any good if it took 10 minutes to do the job, as it would tend to make the radio and the QSO rather impracti- cal. This required very fast digital elec- tronics as well as very efficient programs. Fortunately, these have been recently devel- oped, so we are able to implement digital filtering. The current limitation is still the speed of the digital system. I won't go into the arithmetic, but in real terms, the current limits of digital filtering is about 10 MHz, using very very fast and expensive components. Not very practical for the moderately priced radio. This then limits the frequency range of the digital filter. Most of the radios have their digital filters in the 15 to 50 KHz range. This limits the places where a digital filter can be used as well as requiring the radio to have addition- al circuitry to accommodate the filter. As you can see, todays radio is really a mixed signal device. Because of a mathematical relationship, a digital filter must be pre- ceded by an analog one (of simple design). A digital filter's characteristics can be changed by modifying the mathematics, and not the hardware. This allows a very sophisti- cated and versatile filter to be implemented easily and inexpensively. The major disad- vantage is that the radio must be designed specifically for the DSP system, its limited frequency range and because of the complexity (many electrical components) is not as reli- able. This, in time, will improve and one day you will see an all digital radio. At this time, my suggestion is to look at the overall operation of the radio, whether analog or mixed signal, and get the one which fits your operating needs. 73, Elmer
Send all of your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridge- field, CT 06877-0113 e-mail Dec1998 ASK ELMER
Dear Elmer, I've been looking over some construction articles and books from days of yore (remember Layfayette Radio? Carl and Jerry? Sigh!) A lot of these projects still look very appealing, and I wonder how I could substitute modern semiconductors for the older ones (2N107, 2N155, etc.). What could I expect? Anything complicated? Signed, Wistful
Dear Wistful, You do bring back fun memories of days gone by. To those of us who still like to lift a soldering iron and build some of our own essence into the equipment we use, I doff my hat in your direction. Of late this has been a lost art in the amateur radio community. The construction articles in those old books and magazines with using bygone parts are, to a great extent, still viable. There are three types of parts which you may have difficulty in obtaining. They are, Semiconductors (transistors and diodes), Integrated Circuits and Vacuum Tubes. In the case of vacuum tubes, I have seen a great variety available at ham flea markets, so patience pays off. At one time, a couple of companies attempted to manufacture and market solid state substitutes for some popular vacuum tubes (primarily for the Drake and Collins radios). This did not last too long, so if you require a vacuum tube, go flea market hunting. Integrated circuits present a greater problem. In many instances with Linear Integrated Circuits, such as Operational Amplifiers, Comparitors, and other universal circuits, substitutions can be easily made. The best way to make these substitutions is to list the key specifications of the original part and then list the key specs of available parts. You will find that in most instances a direct substitution can be made. When you require specialized circuits... therein lies the rub... unless you become very lucky, you will have to either adapt a similar device or several devices to simulate the desired function. Not necessarily an easy task, but very satisfying accomplishment. There are one or two manufacturers and distributors of obsolete integrated circuits and transistors in the country. Alas, they are not interested in sales to the general public, and the parts are expensive (as many are obsolete military qualified parts). On rare occasions, flea markets are a source for some items... but don't count on it. In some instances you may be able to obtain substitutions for the more popular devices through the SK and ECG replacement series. These are generally available from suppliers to the radio and TV service trade (i.e., MCM Electronics in Dayton Ohio). The same applies to logic IC's, but with standard logic, interfamily substitutions can be readily made (HCMOS for TTL, etc.) Special function IC's of course will be more difficult to substitute, if not impossible because of their uniqueness. One must, at times, be creative.... which can be very satisfying when it works and very frustrating when it doesn't. The good news, is that transistors can be easily substituted. Since older Germanium devices can be replaced with modern Silicon devices. You must make sure of the polarity and some of the other basic characteristics, but the variety of devices available today make substitution relatively easy. Diodes are available in both Silicon and Germanium, so there is no problem here. Some very specialized devices... well.. that's another matter (Tunnel Diodes, snap diodes, etc.) I doubt that you will encounter these devices in your projects, so I would not be too concerned. A source of substitute semiconductor and IC devices, available through distributors ( they do not sell direct) is NTE Electronics, Inc. , Bloomfield, NJ (Internet address is
http://www.nteinc.com ). Have a lot of fun updating building those old projects, and let us hear of your successes. 73, Elmer January 1999
ASK ELMER
Dear Elmer, I'm forever building and trying out antennas, and it is great fun. During the winter months it is hard putting up new antennas, so is there some way I can test new antennas in- doors??? How about a computer? Signed, Hung Up
Dear Hung, Antenna building is one of the ways hams can experiment and contribute to advancing the "Radio Art". You could build compact anten- nas and test them indoors or you could build a setup to design and test your antennas at microwave frequencies indoors. This is not a practical solution as it is limiting with respect to the space you have available and expensive when it comes to the specialized equipment required. Fortunately, the computer comes to the rescue. Many years ago, the government and commercial interests required a method of designing and evaluating radiat- ing structures (antennas) for radar. A group of Physicists and Engineers at the Naval Research Labs started to do some work in modeling electromagnetic radiators. They used a large mainframe computer to do the job. Over the years, the PC has become very powerful. These scientists have rewritten much of the software to run on a PC. All of this software is available free off the Internet. The web site is of "The Applied Computational Electromagnetics Society" at
http://www.emclab.umr.edu/aces/ . Their ftp site has all of the software for the PC, for free download. There is no operating instruc- tions with the software, but there are some example files, and with some concerted effort you may be able to use the software. The software is called "NEC" and "MINNINEC". NEC is the full program which requires a very powerful machine, whereas MINNINEC will run on a moderate PC. There is a silver lining to all of this. Some enterprising hams have taken the trouble to write a shell program and connect the various bits and pieces so that it becomes a very usable program. Three come to mind, and all are reasonably priced.
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January 1999 Page
ASK ELMER cont.
The first, which I use is called, EZNEC and ELNEC by Roy Lewallen, W7EL which has very user friendly interface. The others are MININEC for Windows by EM Scientific, Inc. and AO 6.5 by Brian Beezley, K6STI. I cannot comment on either of these two programs as I have seen them but never personally used them. They all use either NEC2 or MININEC as a base. These programs allow you to model your antenna and the surrounding area and tell you how the antennas will perform. You must realize, that these programs have limi- tations. The results you obtain are only as good as the model you describe. They can be used to compare antenna designs, but the only true test of the antenna is finally erecting it and doing an on the air test. This can be done when better weather comes around. During the winter months, have fun on your computer. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail Apr1999 ASK ELMER Dear Elmer, I recently bought a Dip Meter. Does the Club have a "Standard Dip' I can use to calibrate it? How do I work it? What's it do? Signed D. O. Udip
Dear Dippy, Spoken like a true Ham.... You go to a flea market, and purchase a "Boat Anchor" or "Battleship", that you can't live without... until you get it home! Fortunately... you bought a "Gem". The full name of the device is a "Grid Dip Oscillator", and at one time, it was the most convenient way to measure a resonant circuit's frequency, without having to apply power to the circuit under test. Today they use "Network Analyzers" which are considerably more accurate and unbelievably more expensive and complex to use. But back to the "Grid Dip Oscillator" which we will use it's initials "GDO" for the sake of brevity. The principal behind the device is relatively simple. If you have an oscillator and couple it to a resonant circuit, the resonant circuit will absorb some of the oscillators energy when the oscillators frequency is the same as the resonant frequency of the resonant circuit. If you are able to measure the change in the oscillator's energy, and the oscillator's frequency is known at the point of maximum energy transfer.... you then know the frequency of the resonant circuit. In vacuum tube oscillators, a way of measuring the activity of the oscillator was to measure change in the grid (this is the control electrode of the vacuum tube) self bias voltage. When the circuit under test absorbs the maximum energy, the grid voltage of the oscillator would drop to its lowest point... hence the name "Grid Dip Oscillator". More modern devices use transistors and measure the oscillators level using other means, but the results the same. We still call these "GDO's". As to the use of the GDO, a few basic procedures: 1. Use the minimum amount of coupling between the coil of the GDO and the circuit under test.. which means that you try to keep the GDO as far as possible from the circuit under test and still get a useable reading (dip). 2. Tune the GDO slowly, as you may miss the dip because it may be very sharp (generally due to a high "Q" circuit). Note that there is no "Standard Dip" as all of the measurement are relative, and dependant upon many factors such as coupling, Q, etc.
3. Try to keep the position steady during the measurement, as movement can appear as a false dip. Be aware of surrounding items which could couple and cause false dips, especially if you are doing the measurement within a piece of equipment with many resonant circuits. (i.e., a transmitter or receiver). An area where the GDO really shines is in tuning resonant antennas, such as dipoles, beams, multi-band verticals and antenna "traps". To do this measurement, simply couple the GDO to the antenna feedline. The coupling would be through a 1 or 2 turn inductor connected to the feedline, and the GDO's inductor lightly coupled to the feedline inductor. Tune the GDO for a dip and determine the antenna's resonance. You may then lengthen or shorten the antenna to bring it to resonance in the center of your operating band. The GDO will always tell you which way to go. If you have a trapped antenna which is not operating properly, you can easily use the GDO to check the frequency of the trap to see if it is tuned properly and/or retune it. If you do any construction, the GDO provides an easy way to pretune the circuits, both as a signal source and as a method of adjusting resonant circuits. The GDO can be used to measure unknown inductors or capacitors. To do this, you simply have some capacitors or inductors in your junk box to use as known values. To measure an inductor's value, connect a known capacitor across its leads to form a resonant circuit. Simply use the GDO to determine the resonant frequency of the test circuit... knowing the frequency and the capacity, you can easily calculate the inductance. (L = 1 / (4 * PI2 * F 2) * C). Conversely, a capacitor can be measured in a similar fashion. (L is inductance in Henries; PI is 3.1415; F is frequency in Hertz and C is capacity in Farads.) As an aside, many GDO's can also be used as an absorption wavemeter... which is a fancy way of saying "it can measure the frequency of a transmitter". To do this, the transmitter must be powered, and delivering some energy to a load. Couple the GDO's coil, lightly to the transmitter, and tune the GDO for a PEAK reading. Read the frequency off the GDO's dial. There have been several books written about the use of a GDO, but alas they are all out of print. Be resourceful, experiment, and you will find many uses for the GDO.... I have! Well, D.O. I hope you realize that you have really bought a useful piece of equipment. Happy dipping! 73, Elmer May 1999 ASK ELMER
Dear Elmer, Why is the repeater offset on 2 meters both 600 KHz and 1 MHz? What ever is it on 220 MHz (does anyone ever use that band) and why 5 MHz on 440 MHz? How come the offsets aren't standard on all the bands? Signed, Confused
Dear Confused, Over the years I have heard many people ask the same questions, but I have never heard a complete answer. I am going to try to clarify some of the questions, but in many instances I still hear many conflicting stories. Here goes...... Under the ideal circumstances, you would like the greatest sepa- ration between repeater inputs and output frequencies, which ease the requirements on input filters and duplexers. The greater the separation, the simpler (read that as "and cheaper") the require- ments for the repeater system become. There are practical limi- tations, such as the frequency limits of the assigned band ( ie., the 2 meter band limits are 144.000 MHz to 147.999 MHz), as well as the agreed upon or assigned band plan. The answer for the 2 meter is fairly well known. The original separation was to be 1 MHz. At the time, the early commercial repeaters available on the surplus market could have their input & output frequencies shift- ed that amount. Eventually, a large quantity of Motorola repeat- ers became available, but they could only be separated by a maximum of 600 KHz. This became the defacto standard for the 2 meter band. I've heard a similar story about the 440 MHz band, but as usual, I can't seem to get anyone to verify it. To a great extent, the frequency "split" is chosen based upon very practical considerations. Most hams do not have the resources to design and construct their own repeaters, so the must rely upon modify- ing surplus (or new) commercial ones. As far as usage of the bands are concerned, I can say from practical experience, repeat- er usage is down from the peak of the mid 80's. There are several 220 MHz repeaters in use today, but with the decrease in Novice license class operators, 220 MHz has lost many of its users. The repeater splits for the various bands are; 10 meters is 100 KHz; 2 meters is 600 KHz (1 MHz is still used in some locations); 220 MHz is 1.6 MHz; 440 MHz is 5 MHz; 902 MHz is 12 MHz; 1.24 GHz is 12 Mhz. I haven't figured out the 6 meter split, as it varies over the band. I won't even venture into attempting to rational- ize the band plans for repeater operation. Their evolution is even beyond my wildest nightmares. To this day it is still in flux, depending upon the area of the country ( phase of the moon, number of or lack of repeater coordination groups, etc.) I hope I was able to shine a little light into those murky areas of repeater operation. 73, Elmer Send all of your questions to "ASK ELMER". c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail June 1999 ASK ELMER Dear Elmer, With the Internet gaining such popularity, is "Ham" radio becoming obsolete? Signed, Out of Internet
Dear Out, You have posed a question which has troubled many people in the Amateur Radio community. Prior to the Internet gaining such popularity as it has today, the statistics indicated that the "Ham" radio ranks were growing. If you were to look at the number of new operators and the renewals for the last 2 years, you will see the trend reversing. This net decrease in the ranks of operators has been seen in the declining attendance at regional and national conventions. I have just returned from the Dayton Hamvention which I have been attending for the last 15 years, and I have noticed that the number of vendors and the size of the crowds have both decreased significantly. That is the bad news. The good news is that Amateur Radio is NOT OBSOLETE! It is currently going through a series of changes to find new directions. The Internet has taken some of the glamour from the service, but Amateur Radio has so many facets that no single item can replace it. I can cite many instances where the advent of the cellular telephone was going to displace Amateur Radio in public service applications. In every event where both cellular telephone and Amateur Radio was used concurrently, cellular telephone proved to be totally inadequate and highly inefficient (this is where the cell service was donated, so cost was not a consideration). Getting back to the Internet, communications requires a telephone connection (either wireline or cellular), whereas Amateur Radio is not constrained to use a commercial service. For public service and emergency use, Amateur Radio still is and will be, for the foreseeable future, the only reliable method of communication. This too has been proven many times in the recent past when Amateur Radio has come to the aid of the various disaster relief organizations in the field. RACES and Skywarn, to name just 2 groups, have indirectly helped to save countless lives and property prior to and following natural disasters. As we all know, as Amateur Radio operators, that the variety of communications modes are vast. In my humble opinion (here goes the soap box) we have to let the public know about "Ham" radio. The general public has a short memory. There are so many things that vie for their attention, most very well funded commercial products and services. I feel that we have not done much in the way of making the public aware of Amateur Radio. Many people who I personally have spoken to, still consider "Ham" radio and CB the same thing. Some people never even heard of the service. Mention Amateur Radio and you get a blank stare. Say Ham Radio and they say, you're one of those people. We have to change the public's perception of the service. We, as Amateur Radio operators individually and through our clubs and organizations, have to maintain a constant public awareness campaign. In order to have our service grow and prosper, we each have to be a spokesman for the service. We must compete with the commercial services through advertisement in mass media, speaking to clubs and service organizations, getting into the school systems, holding license classes and making local politicians aware of our services. We have to show the public that "Ham Radio" has and does what the Internet can not. Is "Ham Radio" obsolete... NO! Not by a long shot... but it is up to you to keep it alive and growing! 73, Elmer July 1999 ASK ELMER
Dear Elmer, I was on my way to work and 10 Meters opened up in a serious way. Next thing I heard as a gentleman from Argentina explaining that they were celebrating the anniversary of the first long distance radio contact from Argentina. I was able to contact him from the car. I was very excited to say the least, but he asked me to QSL via "the bureau", and I have no idea how to go about it. Signed, Excited
Dear Excited, There are several way to obtain QSL cards (contact confirmations) in Amateur Radio. The 3 most popular are to send a QSL card directly to the station, send a card to the stations QSL manager and send a card to the stations local QSL bureau. Many amateur radio organizations throughout the world have, as a service to the local Hams, a single address where QSL cards may be sent for distribution. These are generally volunteer groups which re- ceive, sort and deliver QSL cards to the Hams in their country which in many cases is an improvement over the local postal service. The drawback to the bureau is that speed is not of paramount importance. Your card will get to the station, but in its own time. There are several ways to use these bureaus, but 2 of the most popular ways are as follows:
1. You sort your QSL cards into individual packages depending on the country and then send them by post to the countries QSL bureau. The address of the bureau can be found in the front section of the "Amateur Radio Call Book", on the various call sign CD rom's and on several internet sites. Depending on the number of cards and number of destinations, the postage can become sizable, though considerably less than sending individual cards.
2. If you are a member of the ARRL, you may use their "Outgoing QSL Service". The service is a very low cost method of sending QSL cards to other QSL bureaus around the world. To use the service, you must arrange your cards alphabetically and send them to the ARRL Outgoing QSL Service, 225 Main Street, Newington, CT 06111. Enclosed with the cards should be some proof of current ARRL membership (photocopy of the QST address label will do) and a check or money order to cover postage/handling at $6 per pound of cards (approx. 150 cards) or $1 for 1 to 10 cards, $2 for 11 to 20 cards $3 for 21 to 30 cards. The service will bundle your cards with others and ship them out in bulk shipments to the foreign bureaus. Not every country has a QSL bureau. A listing of the countries not served by the Outgoing QSL Service is on the ARRL website, http://www.arrl.org/qsl/qslout.html.
The bureaus are a great service to the amateur radio community, but the volunteers are rarely thanked for their selfless work. I for one, take doff my hat in appreciation for the volunteers who man these bureaus. Next month I will discuss the Incoming QSL Bureau. Until then, happy QSLing. 73, Elmer Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail ASK ELMER Aug 1999
Dear Elmer, Last month you discussed the outgoing QSL Bureau, but I also want to receive QSL cards. Do we have an Incoming QSL operation? Signed Excited Too.
Dear Too, Fortunately there are incoming QSL bureaus in the US, organized by the ARRL. You do not need to be a member of the ARRL to use this service. Each call area has its own bureau, staffed by volunteers, who sort the incoming QSL cards and send them to those hams who have sent them a supply of envelopes and postage. The foreign QSL cards are bulk shipped to the ARRL, QSL Bureau, who in turn separates the cards by call area. They send the separated cards to the individual call area incoming QSL bureaus, who distribute the cards to their "alphabetical" sorters. The sorters then sort the cards by call into envelopes which have been supplied by the hams either directly, or by purchasing envelopes and postage from the bureau (at cost, as no profit is made on this operation). Each call area bureau has its own guidelines as far as envelopes and postage, but they all accept a standardized envelope with postage attached for at least 2 ounces first class mail. The standardized envelope is a 5 X 7.5 or 6 X 9 self addressed envelope, with your call sign neatly printed on the upper left corner of the envelope. It is suggested that you send 4 to 6 envelopes to the bureau but please don't send too many, as they have limited storage facilities (it is generally in the volunteers home). You will be notified when additional envelopes or postage is required. In our area, the 1st and 2nd call area QSL bureaus are of interest to us. They are as follows: W1 QSL Bureau YCCC PO Box 80216 Springfield, MA 01138-0216 (e-mail to [email protected])
ARRL 2nd District QSL Bureau NJDXA PO Box 599 Morris Plains, NJ 07950-0599 (e-mail to Ron Levy, K2CO at [email protected])
To obtain information from the bureaus, send a letter to the bureaus to the attention of the QSL Bureau Manager, with a SASE to assure a reply. I previously mentioned the volunteer "alphabetical" sorters are the ones who do all of the real work of sorting, packing and mailing out the envelopes full of QSL cards. They do a lot of work and with nary a "tnx OM-YL" from those that use their services. Each sorter is assigned those call signs whose prefix is between two letters of the alphabet. Such as A & B. The sort order is based upon the same order as in the Call Book. Therefor the same sorter will handle AZ1F, WA1FZZ, K1FE, etc. What happens to those cards for which there are no envelopes... With limited space, the sorters or bureau cannot retain the cards, so after a short time they are discarded. Get your envelopes up to your QSL Bureau, so those cards addressed to you will be sent to you and not to the nearest landfill. You feel great when that envelope arrives from the QSL Bureau with those cards you have been waiting for. Have fun QSL'ing. 73, Elmer Sept 1999 ASK ELMER
Dear Elmer, What is this stuff about antenna gain? Is it good or bad? I get a feeling that it means that somehow you get a stronger signal out with a high gain antenna, but I am not certain. Signed, Mike
Dear Mike, You have hit on a question that has troubled many a new (and for the most part several old) opera- tors. Let me start out paraphrasing the First Law of Thermodynamics, "You can't get something for nothing". With this in mind, let us discuss antennas in general terms. We will start with an "Isotropic Radiator", or a point source. This has a radia- tion pattern which is perfectly spherical with the source in its center. All of its energy is being radiated uniformly in all directions. I should mention that the energy drops off in a well de- fined manner which follows the "Inverse Square Law". In understandable terms, this means that if you double the distance away from the source, the signal strength decreases by a factor of 4, if you triple the distance, it decreases by a factor of 9, and so on. If we were to change the shape of the radiation pattern, by changing the type of antenna, we concentrate the available energy. In the instance we go from a point source (Isotropic Radiator) to a 1/4 wave vertical, the radiation pattern takes the form of a torus (doughnut shaped), with the antenna through it's center hole. This in effect has taken the energy that would normally been radiated in the direction of the doughnut hole and added it to the energy radiating from the doughnuts edge. In effect, you have increased the gain of the system. In real terms, the antenna is said to have a gain of X dBi. "X" is a function of the pattern shape, and the term dBi means Decibels referenced to an Isotropic radiator. One has to be very careful, as manufacturers of commercial antennas like to infer that their antennas have the highest gains, and will use the dBi gain figures. In reality, an Isotropic Radiator does not exist, so gains will be referenced to a Dipole antenna in free space. The reason free space is used as a reference is that there is no grounds or other items to change the antennas radiation pattern. Antenna gains referenced to a dipole would be X dBd. These numbers would be lower than those referenced to the isotropic radiator. An ideal 1/2 wave dipole in free space, has a gain over an isotropic radia- tor of 2.14 dB. Remember that this gain is only in the antennas preferred direction of radiation, and there will be little or no energy in other directions.
Continued on Page ASK ELMER cont.
This is a very desirable condition, since you can then direct the antennas energy to suit your needs. In this vein, beam antennas, colinear vertical antennas and other complex structures were designed to use this effect to your maximum advantage. Be advised that all is not a bed of roses. All antennas are not the perfect radiators you would want them to be. They are affected by the condition of the surrounding area, (ground conditions) and losses in the materials used to construct the antenna as well as the position of the antenna with respect to the earth. All of these conditions will modify the antennas radiation pattern, and so doing, change it's apparent gain. With all of this said, you can with a good antenna system, make your 100 Watt transmitter appear to have the power (in one direction) of a Kilowatt rig. I hope this answers, at least in part your question about antenna gain. I almost forgot to mention that gain is both for transmit- ting as well as receiving. Before I leave you, thanks to Tom Frenaye, K1KI who found a couple of errors in the August "Ask Elmer" article. The Web site for the W1 QSL Bureau is
[email protected] , or visit the web site
http://www.yccc.org/Resources/qslburo.htm . And the example AZ1F would be in Argentina, not the US, as we have the block AA to AL.
73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail Oct 1999 ASK ELMER Dear Elmer, I have heard that I can't do any business with the FCC unless I register myself with them. I thought that my having a license issued by the FCC was all that was required. Signed, Concerned
Dear Concerned, There is a bit of confusion concerning the new Universal Licensing System (ULS) instituted by the FCC. One of its purposes is to simplify the paperwork that the agency has to handle by standardizing on one application for most licensed services. The FCC has created a Form 605 which takes the place or the venerable Form 610, which we knew (and “loved”). In addition to requiring all of the usual information, the new form requires you to enter your “Taxpayer Identification Number” (TIN) to conform with congressional requirement that they be able to track delinquent taxpayers or your FCC assigned License ID number. According to the FCC, your TIN will not be released to the public in any of their open databases (which remains to be seen), but all of the other information supplied becomes part of the public record. Everyone who has an FCC license has to register themselves into the ULS database. The FCC will not automatically register you as they require your TIN as part of the registration. If you do not register, you will not be able to renew your license or transact any business with the FCC. Registration is quite easy, and takes only a few minutes. The most convenient way to register is electronically via the internet. Log onto
http://www.fcc.gov/uls and then click onto registration. The information they require is your name, address, city, state, TIN and telephone number. Optionally you may list your e-mail address and fax number, but they are not required. For your telephone number not to be part of the public record, you may enter 10 zeros in place of the number. Once this is done, you will go to the next screen in which you can enter your callsign. There is space for many callsigns for commercial registration.
You need only fill in your one callsign and then submit the form. To keep your TIN secure, they ask you to input a password (twice) and a verification password in the event that you forget yours and need to retrieve it from the FCC. This is so that you can modify or update the database as required (change of address, etc.). For all of your effort, the FCC returns a copy of your TIN, a License ID, a copy of your password and password verification. Copy down this information, as it will not appear again. The License ID can be used on any form or document submitted to the FCC in lieu of your TIN. If you have any administrative questions about the ULS, contact the FCC at 1-888-225-5322, menu item 2. If you have problems with the ULS registration site, the FCC maintains a ULS Tech. support at 1-202-414-1250 or e-mail to
[email protected] . To all of you concerned hams out there I would recommend that you register at your earliest convenience. To those who do not have an internet connection, there will be alternate forms of registration made available to you. One possible method of getting onto the internet to register, is at your local public library. Many of them have a connection to the internet. 73, Elmer November 1999 ASK ELMER Dear Elmer, The recent experience with "Floyd" has brought a good question to my mind. This storm caused me to be without power for over 26 hours. I had my handy talky with batteries for 2 meters but it sure would have been nice to have HF capabilities during the power outage. Would you please advice me how I could set up my HF rig for battery back-up in case I have to go through another power failure. I am not looking for a real elaborate setup but it would be great if I could get at least quite a few hours of listening and perhaps an hour or 2 of transmitting from the set up. Of course keeping expenses down would be helpful, Also it would be nice if I could expect a reasonable life expectancy out of the backup with perhaps a monthly schedule for charging the system. Another consideration would be that it would have to be safe to keep inside my home. I have heard of all different types of batteries and the entire battery issue is totally confused from all of the issues with smaller units like my HT. I rarely hear of battery issue regarding HF rigs. The rig that I want to power has 100 watts output but I find that I rarely need much more that about 35 watts unless I run into poor conditions. I think that my rig will draw about 20 amps with continuous transmit. It is important that I do not do anything that could damage the radio. I do not know if trying to run with insufficient power could be harmful. I could probably think of many more questions regarding this issue, but this is sufficient for starter. I realize that answering all of this could take up quite a bit of room, perhaps it could be handled over more than one month, a series, so to speak. Thanks a Bunch, Mike
Dear Mike, You pose an interesting series of questions which, to my knowledge, are not often addressed in the literature. Many modern HF radios, are manufac- tured to operate directly from 12 volts DC. These radios are the easiest to power from an external battery source, so I will address these radios in this months column. Before we discuss the pros and cons of batteries, we should discuss power requirements in gross terms. Most HF radios are rated for 100 Watts output, and require 12 to 13.8 Volts at 20 Amperes peak. One hour of Key Down full carrier, would require an power expenditure of 240 Watt-Hours (based upon a 12 Volt battery supply). In typical situation we wish to get 1 hour of operation consisting of 1/2 hour of trans- mit and 1/2 hour of receive. The assumption is that Continued on Page November 1999 Page ASK ELMER cont.
the average transmit power is 70% of peak (based upon RTTY, Packet or SSB operation. CW takes less power and FM takes 100%), and receive power is 10% of transmit power. This reduces the total power requirements to 96 Watt-Hours to operate a radio. This shows that for 1 hour of emergency use, a very large battery is not required. Now let us look at the various batteries available to the average Ham operator. I will not bother to dis- cuss any primary cells (ones that cannot be re- charged), since using them would not be very practical and would be expensive. Secondary cells will be discussed (rechargeable cells). In common usage are Lead-Acid both wet and gel, Nickel- Cadmium, Nickel-Metal Hydride and Lithium-Ion batteries. Currently, the cost of Nickel-Cadmium, Nickel-Metal Hydride and Lithium-Ion batteries is prohibitive, their only advantage being their smaller size compared to Lead-Acid batteries. They have other disadvantages with respect to their requirements for charge mantainence and recharging. That leaves the venerable Lead-Acid battery as the most practical emergency battery. They are available from every Auto parts and accessory store at very reasonable prices. The next decision is to the type of battery, liquid electrolyte or gel. To a great extent, this is determined by the size of the cell. Both types are made in all sizes, but gel cells are normally available in the smaller sizes. Their advantage is that they can operate in any position, and the electrolyte cannot spill out. In our application, this can be important from a safety standpoint. With proper handling, wet electrolyte batteries can be very safe to use. We must choose a battery that fits our emergency operating needs. A typical alarm type gel cell would have a capacity of 7 Ampere-Hours, giving you 84 Watt-Hours of capacity. Slightly less than 1 hour of emergency operation. A wet electrolyte "Lawn Tractor" battery has a minimum capacity of 30 Amp-Hours through automobile batteries with capacities of up to 100 Amp-Hours. This can give you from 3.75 to 12.5 or more hours of emergency operation before the batteries need a recharge. Now that you have chosen a battery, we will dis- cuss connecting the battery to the radio, charging requirements and storage requirements next month. 73, Elmer Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT o6877-0113 .e-mail Dec 1999 ASK ELMER The current question for Ask Elmer has to do with emergency power for rigs in your shack. I have been gratified with the responses to the first part of the article, so in this columm , I am going to print them. 73, Elmer Send all your questions and responses to "ASK ELMER", C/O Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-2025 or e-mail to [email protected]. EMERGENCY POWER Ask Elmer recently discussed a battery means to power ham radio during a power outage for 26 hours during “Floyd.” That's OK for doing without lights, well water, refrigerator (freezer?) and central heating during the winter. More often than hurricanes, tree limbs fall on power lines during ice and windstorms --- instant blackout! Ham radio becomes a minor annoyance when the essentials of modern living suddenly disappear. Look to Field Day for the solution; a motor-generator set. If it is only ham radio you want, then a 1kw MG hardly bigger than a small chain saw will suffice to run your 100-watt transceiver and a few other things like a lamp and an antenna rotator. Operate the beast outside to avoid asphyxiation and run the line cord through a window into the shack. Sure it'll bother the neighbors but you're not going to operate all night. If you live in a private house in a well-wooded area, then consider a more permanent, total solution. Install a motor-generator of between 4 and 8kw in an outdoor weather-proof enclosure like a plastic shed for garbage cans or garden supplies. Keep it locked most of the time but operate the MG with one or more of the doors open. Install a female receptacle in a weather resistant box on the wall of the house and a manual switch box inside adjacent to the main breaker panel. Your mains supply usually is 230v, single phase, three wire. One is a ground and the other two supplies 115v to the panel. Get a licensed electrician if you are not familiar with power wiring. The Home Depot, warehouse clubs, etc. sell MG sets and switchbox kits. The latter prevents your MG from energizing the power lines when some unfortunate lineman is messing with them. Basically, the house circuits that will be energized with emergency power must be transferred from the main panel to the switchbox. Among other things, these have two circuit breakers coupled with a rocker arm that avoids both being on simultaneously. One breaker supplies mains power and the other breaker supplies emergency power to the circuits being energized. When an outage occurs, open the shed and connect the flexible line from the MG to the female receptacle on the house. Fire up the MG set for a few minutes and then go inside to manually throw the rocker-arm breakers to disconnect main power and connect MG power to the selected circuits. Presto, you're on your own. It is a good idea to keep the MG tank filled with gas. Add an apropriate amount of fuel stabilizer to prevent the gasoline from gumming. Stopping the MG by switching off the fuel supply will empty the carburetor and keep it cleaner. Give me a shout for more details. Al, K1JWX.
Okay, Marv. You do know how to get me to chip in with my 2 cents worth. Bring up a topic which has marine overtones such as this month's discussion of emergency battery supplies for HF radios.
Gel cells vs. Flooded (Pb-Acid) From an emergency usage point of view, the biggest attraction of gel cells is probably their low self-discharge rate. At 68 deg. this should be on the order of 3% per month vs. 6-7% for flooded. This means the batteries are much less susceptible to "Oh, I forgot to charge them" when the lights go off. The drawback is cost and chargability. A Group U-1 31 ah gel cell sells for about $80 while a Group 24 73 ah is $140. Comparable deep cycle floode batteries are about $40 and $85 (these are high quality deep cycle batteries). Now comes the charging problem - gel cells won't tolerate over-voltage charging at all. You've got to hold them to 14.1 volts whereas flooded like to be charged at 14.4v. Unless you get a charger specifically designed to charge gel cells (read expensive), you're going to fry your gel cells in no time. If you stick with flooded, you can use the same charge that many of us have sitting around the house already.
Desirable Battery Capacity In thinking through this topic, one has to ask "Why would a ham need HF radio during emergencies when we already have cell phones, landline phones, and the internet?" My answer is to provide health and welfare traffic capabilities that won't be served by any other public service group. Who else is going to let Aunt Minnie tell her family that she's okay even though all the phones lines are down. Certainly not the police or fire department. Probably not the Red Cross. Ham radio. That's who. How will we do it?
Seems to me that the logical setup is a local network of hams connected byVHF/UHF or local phone service (in the Florida Keys, experience shows thisis frequently available in the midst of disaster even when the lines to the outside world are cut) and then a connection from the local hams to the internet. It is this last link that will use HF, but in all likelihood, a digital connection rather than voice connection is the preferred method. Specifically, one can use a Netlink MBO to handle traffic to and from theinternet using Pactor I or II, Clover, etc.
This is now starting to become a really powerful solution because with most people knowing at least someone outside the disaster area with an internet connection, they can pass traffic to them and ask them to pass it on to their other friends. In addition, by avoiding the necessity for two operators (one in the disaster area and one outside) to be on the air full time, you can make the whole system much less operator intensive and permit the local ham radio operator to do more than just sit around waiting to pass traffic.
Having postulated this emergency system, one can now start to ask how much battery capacity is needed. The answer is "not much." I operate Pactor II and PSK31 and for both modes 20 watts is about the maximum needed for solid communication with a relatively poor antenna. Just to get an idea of amp-hours needed per day of the emergency, I'll postulate the following: Connections with a Netlink MBO to pass internet traffic per day: Once per hour = 24 operating sessions Session schedule incl. waiting for busy MBO, uploading, and downloading: Wait (transmitting 50% of time for 5 minutes) = 2.5 min. Transmit time, 2.5 min. receive time Upload messages (transmit 80% of time for 3 min.) = 2.4 min. Transmit, 0.6 min. receive Download messages (transmit 20% of time, for 6 min) = 1.2 min Transmit, 4.8 min. receive Total per session = about 6 min. transmit and 8 min. receive. Assume 50% transmit efficiency, i.e. 20 watts/0.5 = 30 watts/12v = 2.5 amps and the same receive efficiency you assumed = 2.0 amps This means that a session will consume 6 x 2.5 + 8 x 2.0 = 31 amp-minutes or 0.5 a-h. Multiplying the 0.5 ah per session times 24 sessions per day, we come up with 12 ah per disaster day. This is pretty small. One fully charged U-1 battery which can be discharged 50 % before recharging should provide over a day's communication while a Group 24 should provide for 3 days before recharging is even suggested.
Note that I'm not disagreeing with your "Lawn Tractor" (U-1) and automobile battery conclusions in your article. I am however, saying that you shouldn't discharge a flooded battery to less than the 50% level and that only if it's a true deep discharge which most Lawn Tractor batteries are not. What I do is to get the same answers but using a much lower draw mode to stay within the 50% limit. In addition, I thought you might be interested in my view of how ham radio can play an important and complementary role to other major public service organizations in an emergency.
73, Tom, K1TC
January 2000 ASK ELMER
The current question has to do with emergency power in the shack. Last month we had some of our members responses to the original question. Both were extremely interesting and informative. This article is the last of the series on Emergency Power in the Shack.
Many radios, both older and some of the newer ones, cannot operate directly off a battery sup- ply. It is to the Hams that own these radios that I am directing this months response. There are available two convenient methods of supplying power to equipment which cannot operate directly off batteries. These two methods, both rely on batteries (generators are intentionally excluded as they were covered in the responses of last month). The first is the use of an "Uninter- ruptable Power Source", primarily manufactured for computers. These devices are an inexpensive way of providing 115 volt 60 Hz power to your radios, as well as providing some limited isolation between the power line and your radio for protec- tion against line transients. The beauty of using these devices is that they are completely self contained and plug compatible with your radios. They contain all of the required battery charging and switchover circuitry. The only special re- quirement in the selection of this supply is to make sure that it doesn't require an input from a computer to moderate its operation. Many do not require any external control, but there are some that use software to do a staged shutdown of a computer system. In choosing the appropriate unit, they are rated in the amount of power they can supply for approximately 15 minutes of opera- tion. The smallest supplies that I have seen listed are rated at 130 Watts (200 VA) for not much more than the price of a battery. Of course they are available thru several kilowatts at prices approaching several kilobucks. There is the possibility of obtaining a small unit and replac- ing the battery with one of higher capacity. Hams are known for their creativity and resourceful- ness. The second method is a variation on the same theme. If you would rather assemble your own emergency supply, then the use of an power invert- er is the way to go. These are available from automobile supply houses and camping equipment suppliers. A relatively inexpensive inverter is capable of handling several hundred watts of power continuously. All that is required for a system is an appropriate battery, the inverter and a battery charger. The battery charger and the inverter can be constructed or purchased.
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It is very important that batteries be kept in well ventilated areas. All batteries outgas during charging to a greater or lesser extent. Sealed cells have an absorber for the gasses built into them, but if overcharged, they have the ability to vent excess gasses into the atmosphere. Do not overcharge the batteries as it reduces battery life and causes outgassing. Monitor the electrolyte levels in unsealed batteries so that the plates of the cells are not exposed to air. As in all cases, safety must be paramount. These are, after all, emergency power systems, and you don't want to be the "emergency". I hope this series of articles has helped you in getting your shack set up for operation in the event of a power outage. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail Feb 2000 ASK ELMER Uncle Elmer, I was studying a navigation chart of the Mediterranean Sea, and I noted a small uninhabited island that is little more than a rock smack dab in the middle of the Mediterranean at about 36 degrees north and 3 degrees west. It is owned by Spain but it is about 50 miles off shore and it is nearer Morocco than Spain. Would this place have a call sign region assigned to it which would make it one of those places that adventuresome hams go on their DXpeditions? What qualifies a place which warrants its own callsign region? The name of the isle is de Alboran. Sincerely, Lost in Space.
Dear Lost, You pose an interesting question. Callsign prefixes are assigned by the ITU to each political entity. As an example, the US is assigned, K, N, W and AA through AK and Spain is assigned EA through EH and so on. It is up to the country to assign any special callsign within their prefix block to any subdivision, be it a possession, island, or other territory which is directly controlled by them. As an example, in the same area as the isle de Alboran is Mellila, also a possession of Spain, which has a prefix of EA9. It is rather unlikely, but not impossible, that a country would assign a special prefix to an uninhabited islet, unless it was for some special use or other good reason. In all probability, the isle in question is probably included with Ceuta and Mellila as EA9 (I did not verify the islands callsign assignment. but it appears to be a logical assumption) were someone to operate a DXpedition from it. This poses the question of whether the island qualifies as a separate country under the rules for DXCC (DX Century Club) award. The DXCC is an ARRL sponsored award for working 100 (or more) countries on one or several bands and/or various modes. There are more DXCC countries listed than there are political entities. This is because the DXCC rules are based not only on political boundaries but on geographic location. I won't go into the details of how a location becomes a DXCC country, but I would suggest that you visit the ARRL's website at http://www/arrl.org/awards/dxcc/rules.html to get all the details. It is quite possible for a DXpedition to petition the DXCC committee to include a specific island that you plan to visit in its list of Continued on page 6 February 2000 Page 6 ASK ELMER cont. countries. If is does, then you visit the island, operate the pile-up and give a lot of hams a new country contact. If not, you can still go there, operate, and just have some fun. There is another group that is active in contacting those remote islands. The group is called IOTA (Islands on the Air). They try to contact as many islands and island groups as possible for awards. Both Ham operators and SWL's may participate in this group's activities. It is managed by the RSGB (Radio Society of Great Britain). In the event you participate in a DXpedition to one of these remote islands, atolls, shoals, rocks, etc., choose wisely, so that your feet don't get wet at high tide. Well Lost, I hope you you have found a path to your island. 73, Elmer March 2000 ASK ELMER Dear Elmer How do I make a H-plane receiving antenna for 325KHz? My Differential GPS receiver can use a 4-8 foot vertical antenna against a good ground plane or an ungrounded H-plane which is much smaller and doesn't require a ground. I know the H in H-plane stands for horizontally polarized and I think that maybe all that is required is to wind a whole lot of wire on a 6" diameter plastic pipe. Can you help? 73, Tom K1TC
Dear Tom, In order to answer your question, a brief review of some basic background information on electro- magnetics. According to our friend James Clerk Maxwell (and at times I do feel old enough to have known him), an electromagnetic field is composed of two elements. From its name you can gather that these fields are the electric and magnetic fields. They are perpendicular to each other (or in mathematical terms "orthogonal") and are con- stantly rotating around a central imaginary axis. These fields are named the "E" field for the elec- tric component and the "H" field for the magnetic component. You need both of these fields, togeth- er, to transmit power, though you can favor either of these fields to receive the energy. Attempting to delve any deeper into the theory, other than this "hand waving" explanation is beyond the scope of this discussion. Getting back to the specifics of your question, it appears that you want an antenna which will favor the "H" or magnetic field. Most antennas that are used by Ham operators are "H" field antennas. On occasion, there are articles describing very short vertical antennas with high impedance pre- amplifiers attached, used for short wave recep- tion. These antennas are the "E" field antennas. They do work, but are not too practical for use as transmitting antennas due to their very high impedances. Do not confuse an antennas polariza- tion, ie., horizontal or vertical with the "E" and "H" fields. Both polarizations have both fields, they just start out in different orientations. Even the antenna used in your AM shirt pocket portable radio are "H" field antennas. In your particular case, you can make an antenna by reso- nating a ferrite loop antenna removed from a broadcast band radio. This should work quite well for you. At one time, Palomar Engineering and MFJ made a low frequency "H" field receiving antenna and preamplifier. I don't know if they are still available.
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I recently constructed a loop antenna for 60 KHz, which where NIST (National Institute for Standards and Technology) transmits the most accurate US frequency standard from Ft. Collins, CO. It consisted of 20 turns of #26 gauge wire with a inner diameter of 36 inches. I resonated the loop with a .047 microfarad capacitor at 60 KHz. This allowed me to receive the 60 KHz transmission with a relatively strong signal (measured at my receiv- er at 0.1 microvolt). Antennas at higher frequen- cies tend to become more efficient. It is import- ant to realize that these loop antennas are quite directional. You must orient them to maximize the signal reception. By the way, if you have an old 500 KHz Loran antenna, it can be retuned as well to 325 KHz. I hope this gets you up and running on the LF bands. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail
Apr 2000 ASK ELMER Dear Elmer, I am so confused about the new licensing system. I have a Tech Plus license issued in 1985. Under the new rules, I think I qualify for a general Class license. What do I need for proof and what is the procedure? Signed, Bea Fuddled Dear Bea, For those who have been licensed as a Technician prior to March 21, 1987 will be qualified for the General Class license after April 15, 2000. You must appear at a VE session with proof that your license was issued prior to March 21, 1987. This proof can consist of the original license, or photocopy, a CSCE from the FCC or a VE, an original or photocopy of a listing in the 1987 or earlier Callbook or other recognized and verifiable listing. A current license or an expired one within the 2 year grace period is also required. Fill out the NCVEC605 form, and pay the $6.90 session fee. It is as simple as that. I would imagine the most troublesome part is obtaining proof of having a license prior to March 21, 2000. The VE team will be as reasonable as possible, but the proof must be obvious to the team, as they do not have the resources to do any research at the sessions. If you hold a Technician Plus license after March 21, 1987 but before February 1, 1991, you can only claim credit for Element 1, the 5 WPM code. You must take the new Element 3 to qualify for the General Class License. It appears that under the new rules, if you have ever held a valid Novice, Tech Plus or higher license, current or expired, you have credit for Element 1 (5 WPM code). Credits for other elements require a current license, CSCE or in some cases be within the 2 year grace period. I would recommend that those who have a Tech Plus license granted after March 21, 1987 try to take the Element 3b examination prior to April 15, as it is a 35 question test rather than the new 50 question test. In truth, if you know the material, the 50 question test should really be no more difficult than the new 50 question test. The same goes for the Advanced Class licensee going for the Extra Class license. Good luck to you all. I hope this removes the confusion. 73, Elmer May 2000 ASK ELMER
Dear Elmer,On several occasions I have been asked during a QSO to help evaluate the sound quality of other station as they change microphones or set- tings on their radio. Since this is all subjec- tive, is their any better way to give the station an audio quality report? Signed, Helpful
Dear Helpful As a courtesy to the other station, an accurate report on their audio quality is greatly appreci- ated. Good audio quality helps to make communica- tion between stations easier and more enjoyable. When doing these tests, make sure that your radio is properly tuned for the best audio quality. As an additional courtesy,I have a small cassette tape recorder permanently set up near my radio. This permits me to record the other stations transmission and then play it back to them. They can then judge for themselves how they sound to the receiving station. When you do this, you have to make sure that your radio is properly set up for good quality audio. There are two ways this can be accomplished. The simplest, is to record the sound from the loudspeaker, and then play the tape back through the microphone. A more perma- nent setup may be more convenient. Using a switch box, you can connect the auxiliary input of the tape recorder to the auxiliary output of your radio, and connect the headphone output of the tape recorder to the microphone input of your radio. This eliminates any extraneous noise from the shack getting into the recording (such as fan noise, voices, etc.) The construction of a switch box is rather simple. A double pole double throw toggle switch, some wire, a box and a few connec- tors are all you need to do the job. The switch is used to disconnect the microphone from your radio and connect the mic. input to the headphone output of your recorder. The speaker or headphone output of your radio can be permanently connected to the auxiliary input on your tape recorder. Make sure that you do not disable the radios speaker when you connect the tape recorder. Once you have decided which technique you are going to use, you have to adjust your recorder output levels so that you are transmitting a well modulated, low distortion signal. This is almost a catch 22 situation, but with the help of another local station this can be easily done. All you need do is to establish a QSO with a local ham who will help you to evaluate your audio quality. Once done, try to fix the volume control on the tape recorder so that it doesn't change. Note down the settings on your radio,so that you can return to them when you need to and you are all ready to go. Continued on Page
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By the way, this setup can also be used in a contest situation. The tape recorder can be used as a backup log for contest contacts, or with a short tape to send out "CQ Contest, etc." in order to save your voice for the actual contest QSO. Over the years I have found the portable casette tape recorder to be a very handy asset in the shack. 73, Elmer
Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail June 2000 ASK ELMER Subject; coax vs. less expensive alternatives with wire antennas. I have a dipole antenna that I connect to my rig with 50V Coax cable through an antenna tuner. It seems to work quite well. I built this when I first entered amateur radio. I was told that the coax was the way to go, so that is what I used. Since I have been learning more with time I have also built a folded dipole antenna with 300‡ TV antenna lead. I also send it through the tuner. I originally built this as a light easy to use portable antenna. I seem to do equally as well with it. In fact, my first contact using this antenna was with GB4MD, who was transmitting from the original Marconi site, Country of License: ENGLAND - SPECIAL STATIONS - U.K. I was only using 10 watts and received a 559 report. Both antennas are being used on 20 meters. The 300 V antenna lead costs $.10 per foot for pretty heavy outside lead, coax can cost well over $1.00 per foot, even relatively inexpensive coax costs about $.50 per foot. So, here is the question; why do we use coax and how do we justify the high cost when very good results are attainable much less expensively? After trying this experiment with the very simple inexpensive folded dipole made from the 300V TV antenna lead and having fairly good success, it does not make sense to me to use the very expensive coax. As far as I know, most Amateurs have and use an antenna tuner, at least some of the time, so matching the impedance to the radio is not difficult. Perhaps there are other factors that enter into the equation that I am not considering, which is very likely. Naturally, if there is something else that I should be considering besides the cost and effectiveness I am interested in knowing more about it. Mike Dear Mike, To answer your question, we have to go back to the early days of radio. Antennas were generally long wire (Marconi, etc) and were fed with a single wire feedline from the "Spark Gap" transmitter. Everything radiated, feedline, antenna, even the key. The feedline had to be well insulated from any conductors as fairly high voltages were developed. Over time, and with the advent of vacuum tube transmitters and receivers, other types of antennas were developed, both balanced and unbalanced. For the unbalanced antenna, the single wire remained the most popular, and a twin conductor line was developed and used for balanced antennas. These feedlines work very well as long as they can be well insulated and kept away from any other electrical conductor. In both civilian and military applications, the radio room (shack) would be located in close proximity to the antenna, so that the feedline need only be insulated as it came through the outer wall of the shack. In marine applications, they had to locate the "radio shack" close to the antenna because of the antenna's feedline. This was really impractical in a cargo ship or warship both from the standpoint of available space and security. They wanted communications to be below deck, well protected. Coaxial cable had been developed in the early 1930's and was pressed into service. Since the cable consisted of a center conductor surrounded by an insulator and then a grounded outer shield, it was ideal for routing within the walls of an all metal warship. You could also have multiple cables within close proximity to each other with minimum interaction. The detractors were that you had to be careful not to exceed the voltage or power rating of the cable. The voltage rating could easily be exceeded if the antenna was not matched to the feedline, and a large standing wave was developed in the cable. With an open wire or a balanced line, a high standing wave would cause some small losses in the line, but the line could withstand extremely high voltages without breaking down. Coaxial cable could not tolerate high standing waves, so antennas had to be designed to have the same impedance as the cable or matching networks had to be used. When the antenna, feedline and transmitter were impedance matched, you achieved maximum power transfer and minimum loss in the cable. By the way, a cable impedance of 50V was entirely arbitrary, as one in the 75 to 90V range is really the best compromise between cable size, power handling and signal attenuation. Note that a resonant dipole antenna is ideally 75V. Hams today use all types of feedlines, including waveguides for microwave transmission depending on their needs and location and expense. Coaxial cable is the most convenient and easiest to install , but any feedline that does the job for you is the correct one to use. You must always keep in mind their advantages and limitations and you can't go wrong. I trust that this has given you some insight into your feedline choices. 73, Elmer July 2000 ASK ELMER
Uncle Elmer,
My radar set sends and receives frequencies to determine locations. The assumption is that my set is receiving the echo of its own radio pulse that I sent out. How does a radar set keep from receiving the pulse instead that was sent by another radar set thereby giving a false message to my radar receiving set? They cannot all be on separate frequencies as there are too many radar sets out there and I doubt if they use a PL system. The Red Baron
Dear Red, You are correct in your assumption that civilian radar sets do not use a "PL" system to prevent interference. Let us briefly describe how a radar system works, before we discuss the problem of interference. The two most common types of radar systems are the "Doppler Shift" and the "Elapsed Time" systems. Most of the radar systems used on small pleasure craft (boats or light planes) use the "Elapsed Time" method of ranging. "Doppler Shift" is generally used in speed sensing radars. The way the radar system works is that a short RF pulse is transmitted in a given direction, which turns on the receiver and starts a clock. The pulse duration is in the order of a microsecond. The receiver may be held open for a millisecond and then the process is repeated. The receiver is listening for an echo of the original pulse. If it receives an echo, it then stops the clock. An on board computer, knowing the speed of light in air and the time it took for the pulse to be sent out and the echo returned, can calculate the distance to the object that caused the echo. If this process is repeated while slowly rotating a highly directional antenna, a profile of distant objects can be generated. This in turn, using a microprocessor, and a display, can be used to graphically depict the contours of the coast, other boats or objects atop the water. The ques- tion of interference by other boats with similar radar sets has been posed. If a signal from another radar happened to be received by your set, it will cause your system to show a false echo. What the manufacturers of the radar systems rely upon to minimize this is the very narrow beamwidth of the antenna. An interfering signal must be precisely within the beamwidth of your antenna. Not too likely. The signal must arrive at the receiver during the time it is turned on (remember the receiver is on only for a millisecond or so), after which the antenna has changed its position.
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July 2000 Page
This too is not very likely. In a very crowded area, you may receive a false echo or two, but this is always corrected by the time the antenna makes its next sweep. So Red, you can rely upon your radar system the next time you are out there in your Fokker biplane menacing the commercial aircraft over Kennedy airport.
Please send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail Sept. 2000 ASK ELMER
Dear Uncle Elmer, I just purchased as set of walkie-talkies that utilizes the new Family Band that operates near the Ham 440 band. From what I can tell this like the new Citizens Band of 1990's/2000 only it is FM and a lot better - none of that annoying ''skip'' that CB had & a shorter antenna.
The new set comes with 14 preset channels. What can you tell me about this new type radio and what are the output power restrictions? Very truly yours, Toys 'R' Me
Dear Me, The radios you are asking about are classified under the relatively new "Family Radio Service". The FCC under pressure from the commercial commun- ity (read that as Radio Shack, Motorola, etc.) was looking for a way to sell more radios. The CB craze had fizzled,and the 49 MHz CB radio sales were also in the doldrums, so they strong armed the FCC to set up a low powered UHF, license free, radio service for short range, point to point, voice communications. This in not to infer that it was a bad idea, just its initial reasoning (though not what they presented to the FCC for approval). The regulations are covered in Part 95, subpart B of the Code of Federal Regulations. The radios are limited to narrow band FM modula- tion with a maximum Effective Radiated Power of 500 milliwatts. The rules are specific, that all radios must be FCC type accepted, and no modifica- tions of any sort may be made nor non-approved accessories be attached to the transmitter (such as other antennas, amplifiers, phone patches, etc.) The 14 channels have a 50KHz spacing start- ing at 462.5625 MHz, with a maximum deviation of +/- 2.5 KHz and maximum rate (audio response) of 3.125 KHz. PL encoding and squelch are permitted. I personally have not used these radios, but the comments I have heard from those who have, are very favorable. The effective range of these radios could be up to 2 miles, but more practical- ly about 1/2 mile, especially in a city environ- ment. This appears to be a commercial idea that went right. It remains to be seen if it becomes the commercial success that the various companies who originally proposed it hoped it to be. Enjoy your "Toys". 73, Elmer
Send your questions to ASK ELMER, c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail ASK ELMER Oct 2000
Dear Elmer, What's the scoop on torroid cores? Like I hear about “Powdered Iron” and “Ferrite” and a few other materials as well! What's Ferrite anyway, and what difference do these all make? Signed Ferrous,
Dear Ferrous, In the manufacture of inductors and transformers, there is a need to have a material which could concentrate the magnetic field so as to increase the inductors or transformers efficiency. Many years ago it was discovered that Iron, Nickel and Cobalt and some of their compounds had magnetic properties. In the early days, inductors and transformers were wound using either air or laminated Iron cores. Laminated Iron cores was perfectly good as long as the operating frequency was kept in the audio range (below about 50 kHz). Above this frequency, airwound inductors and transformers were used to minimize losses. The problem with the laminated Iron was that you couldn't make them thin enough to keep the losses down. The higher in frequency the inductor is used, the smaller the individual pieces of the core material must be. Practically, the laminations can be made a few thousandths of an inch thick, but they still must have a rather large height and width in order to be mechanically stable. Ideally, it would be nice if we could grind up the Iron into a powder and somehow separate and insulate each grain of the powder from each other. This would make the core material very, very small and efficient at high frequencies. We would then have to find some way to glue all the grains together to make a useable core on which we could wind the wires of the inductor or transformer. A process for doing this was developed in the late 1930's. It was now possible to manufacture high frequency inductors and transformers usinf this material. In the late 1940's, scientists, knowing that Iron, Nickel and Cobalt compounds had magnetic properties, combined them in a way to improve thier magnetic efficency (increased permiability), and naming the material Ferrite. This permitted the manufacture of smaller inductors and transformers, yet mantaining their high effieiency. The method of manufacture consisted of using a glue or binder and moding the powdered Iron into the desired shape, whereas Ferrite materials were molded using heat and preassure to form the shape, in a process known as sintering. This formed a very hard ceramic like material. There are several electrical differences between the materials. Powdered Iron has a relatively low permiability (ability to concentrate the magnetic field), but has very low losses at very high frequencies. It is electrical stable with temperature compared to Ferrite material. It generally, is the material of choice for use in VHF and UHF circuits. Ferrite can be manufactured to have a wide variety of electrical characteristics. It can have a very high permiability, but tends to be more unstable with temperature and in high external magnetic fields. Ferrites are the material of choice in low frequency to the lower VHF coils. It can be formulated to be a very lossy material over a wide band of frequencies, thereby being used as an RF supressor or absorber. By using Ferrite beads, etc. on wires and on the outside of coaxial cables, you can supress the conduction of unwanted RF without requiring a specially designed network or other device. Ferrites and Powdered Irons are very versitile materials, and I have only touched on their uses. I hope this brief explination irons out some of the differences between Powdered Iron and Ferrite. 73, Elmer November 2000 ASK ELMER
Uncle Elmer,
Why is it that aviation frequencies are AM and not FM when they are in wavelength range that you would think of a being FM such as 126.4 for NY Approach? The Red Baron
Dear Red,
I think that this question has been asked by many Hams. I don't know if the answer will completely satisfy you, but here goes..... Aircraft commu- nication is mired areas of international politics, bureaucracy and in some instances even safety and technology. To propose a change which involves several hundred countries, airlines, corporate and private aircraft, airports is a horrendous under- taking. I would also mention that trying to get several hundred countries to agree on anything is a "Herculean" task. It's hard enough to get two to agree. One has to be very sure that the pro- posed technology is an improvement upon that which is in current use. FM, by the way is not. FM has the problem of the "capture effect" which could be disastrous, as well as being wasteful of both power and bandwidth. The current communication mode is double sideband AM, which is wasteful of both of these items but less so. AM does not have the "capture effect" problem. Vestigial single sideband AM would be both more power efficient and require a narrower bandwidth. It could be imple- mented without a major modification to the air- craft radios. I would venture a guess that most aircraft radios utilize only one sideband and the carrier in their receivers as do most Ham and consumer AM radios. I would propose a form of SSB for aircraft communication, which would be the most efficient form of communication using current technology. The problem with SSB, is the "Donald Duck" effect, when it is slightly off tune. Some method of reliably autotuning a radio would be needed before this can happen. A pilot has no time to play with the tuning controls of a radio to hear clearly.... especially in an emergency. One of the positive advantages of using SSB, is that you can receive standard AM transmissions when properly tuned in. Well Red, you may want to start the ball rolling in contacting the agencies in the various governments to change the mode of aircraft communication... I wish you the best of luck. 73, Elmer
Send your questions to "ASK ELMER",c/o Marv Fleischman, PO Box 113, Ridgefield, CT 06877-0113 e-mail ASK ELMER Dec. 2000 Dear Elmer, I was playing with some ferrite cores today to suppress some unwanted RF noise getting out from things like computer cables and getting into my rig and stopping RF from my rig getting into my computers audio cables. I had moderate success but one thing I found is that the tubular shaped ferrite had a much better effect at stopping noise than the larger square 'o' shaped cores. Both styles were clamp on types I used one complete turn around the tubes and tried the "o" shaped core with 5-10 turns around them but the tube type still worked better. Why? Ferretingout D' Noise
Dear Ferret, I really couldn't give you a precise answer to your question as I don't know the characteristics of the Ferrite materials, the frequencies and waveform of the radiated signals nor any of the physical parameters of the cores. I can give you some educated guesses as to what is happening. I think we should break this discussion into two parts. The first part will deal with the Ferrite material itself, and the second part will deal with application of the cores. Ferrite material is a composed of Iron, Nickel and Cobalt oxides heated and fused into a solid form. Depending upon the composition of the material, the Ferrite takes on characteristics which favor specific frequency ranges and are lossy at others. These characteristics can be put to very good use in suppressing RF radiation. In the frequency range in which the Ferrite material is lossy, it will absorb some of the RF energy induced into it (converting it to heat). Fortunately we are talking of extremely low levels of power (picowatts), so the amount of heat is negligible. Any energy absorbed cannot radiate, so this is one mechanism used in suppressing RFI (Radio Frequency Interference). Not all Ferrite material is useable in suppressing all possible RFI. You have to be selective in the material you use, by knowing the frequency range of the signal you are trying to suppress. Using the wrong material will do more to frustrate you than reduce the radiated RFI. A second method of suppression is to use the Ferrite material to increase the inductance of the piece of wire, hoping that there are some bypass capacitors at either end of the wire to reduce conducted RFI. Increasing the number of turns increases the wires inductance (therefore its reactance), and may reduce the level of RF present on or picked up by the wire. This type of suppression is generally (but not exclusively) more effective on device experiencing the RFI and not on the device producing it. I would guess that the Ferrite tubes had a greater suppression effect because of the material itself. It is probably a lossy material at the fundamental frequencies of the RFI from the computer, thereby suppressing the fundamental and harmonic frequencies. Computers are a complex "unintentional" radiator (as classified by the FCC). Those made for use in the commercial world tend to radiate more energy than those made for the home. In determining which type of Ferrite material should be used to suppers RFI, manufacturers perform measurements using very specialized instruments, in RF screened rooms. Following these measurements they choose their suppression materials carefully based upon costs and meeting the FCC's requirements. I hope this gave you some insight into the world of RFI suppression using Ferrites. 73, Elmer January 2001 ASK ELMER Dear Elmer..... I read that the ARRL uses an Inverted-V antenna for their member broadcasts on 80/75 meters because of the omni-directional characteristics of the antenna......Will all Inverted-V antennas give an omni-directional pattern? Luke Skywire
Dear Luke, Before we get into the specifics of the radiation pattern of an Inverted Vee antenna, we should describe it to those who are unfamiliar with its construction. An Inverted Vee antenna is a dipole antenna whose ends have been brought together to form a V shape. The center of the V (the feed- point of the antenna) is elevated higher than its ends, thereby giving it the appearance and the name "Inverted Vee". It is well known that a dipole antenna in free space (well away from the earth) will have a radiation pattern which looks like a doughnut and is perpendicular to the direc- tion of the elements. (Think of a doughnut with the antenna elements sticking out from either side of the center hole.) As soon as you start to ap- proach the earth, this doughnut pattern distorts due to the earth's absorption and reflection. A similar thing happens when the ends of the antenna are brought together. This is due to the interac- tion of the fields radiating from the elements, as well as reflection from the earth. It is quite conceivable that there is a combination of operat- ing frequency, antenna height and element angle which would make the Inverted Vee into an omni- directional radiator. The statement that all Inverted Vee antennas are omni-directional, is therefore not true. Many different patterns emerge when these antennas are designed and con- structed. I recently helped erect an Inverted V at a friends home in a very restricted space. The pattern that emerged on 40 meters was that of a cloverleaf (to the best of our measurements). The best way to determine the probable pattern of a specific antenna, is to model it using one of the several NEC programs available to the amateur radio operator. Two of the more popular programs were featured in the November and December 2000 issues of QST in an article by L. Cebik, W4RNL. Some sources of useful information on antennas are the Handbook for Radio Amateurs and the several Antenna compendium's all published by the ARRL. For those who wish more detailed technical (mathematical) information, I recommend Johnson & Jasic, "The Antenna Engineering Handbook". With the growing complexity of the modern radio, anten- nas remain one of the last bastions of experimen- tation for the radio amateur. I hope your inter- est in antennas continues to grow. 73, Elmer Send your questions to "ASK ELMER" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail ASK ELMER Feb. 2001 Dear Elmer.... The Switching Power Supply in my Computer sends out this "hash' noise that my receiver picks up......Where can I find specific information on how to "Hash Proof' my power supply? A Listener
Dear Listener, You pose an interesting question. I have to admit that I didn't know any specific publications that would tell you how to hash proof your switching power supply, so I did some research. There is no “magic bullet” which will guarantee to quiet down your supply. There are various methods, many of them trial and error, which will take you in the right direction. A switching supply must be designed with low emi/rfi (electromagnetic/radio frequency interference) as a design criteria. I did turn up some interesting and useful references, as well as a very good internet website. The website is "http://www.smpstech.com/ " which belongs to the Switching Mode Power Supply Design Group. The following references were found which address noise reduction in power supplies:
73 Magazine Edit.; "The Power Supply Handbook"; Tab Books Pub.
Ott, H. W.; "Noise Reduction Techniques in Electronic Systems"; John Wiley Pub.; 1988
Ozenbaugh; "EMI Filter Design"; Marcel Dekker Pub; 1996
And for those of you who may have access to old (obsolete) military specifications, I would recommend MIL-HDBK-241B; "Design Guide for EMI Reduction in Power Supplies". Many other amateur radio publications have some articles on the use of Ferrite material to suppress RFI, but I don't know of any one which covers the subject with a 'how to, step by step" set of procedures. Modern switching power supplies made for amateur radio use are generally quite good. The noisiest switching supplies are those made for consumer use especially those in home computers. The FCC has specifications regarding how much RFI these devices may emit, but if there are many of them in a given location, they can create quite a noisy enviroment. There was a Product Review by Joe Bottiglieri, AA1GW in the January, 2000 QST, page 70, as well as in the September 2000, QST page 76. The articles compared the noise level of several general purpose switching power supplies being used in amateur radio stations. I hope these publications will assist you in cleaning up your switching power supply. By the way, if you intend to add a commercial line filter on the input side of your switching supply... Be Careful! Some switching power supplies become unstable when these filters are added. There is an article on the website discussing this possibility. Good luck on your clean-up project. 73, Elmer March 2001 ASK ELMER Dear Elmer......
I heard theses guys on 20 Mtrs talking about 'working the gray-line"...... Is that a some kind of Special Event Train? signed, I.M. Tryen
Dear I. M. The "Long Grey Line" is considered to be the Corps of Cadets of the Military Acadamy at West Point. Even though they have an amateur radio station at the school, I know that they are not referring to it. As everyone knows (except the flatlanders, who just won't admit it) the earth is approximating a sphere which spins upon its axis. It completes one revolution approximately every 24 hours. As it rotates, there is an area of the earth which is in either bright sunlight or the dark of night. In between these areas is a thin area which is in the "Twilight Zone". This is known as the "Terminator". (No relation to Arnold Schwartzeneger) The direction of the Gray Line is approximately North/South and does wiggle a bit. Propigation along this region becomes very efficient as the "D" layer, an HF absorbing layer in the Ionisphere disappears on the sunny side. On the dark side it may not have had a chance to form, so HF signals have minimum attenuation along this path. This can make for very good DX contacts at sunrise and at sunset. As the earth is tilted on its axis, the path of the Gray Line changes throughout the year, and even morning to evening. This permits you to work may different parts of the world using the Gray Line. I personally have worked the Gray Line, and it is a lot of fun, but there is one proviso... someone has to be up at the same time to work you at some other point on the Gray Line. I found that when you do make the contact, the signals are fairly strong, but the contact is not for rag chewers. In my experience, the contact didn't last for more than 10 or 15 minutes. I can't attribute that to the changing Gray Line, or it may have been that they just didn't want to talk to me any longer. The only way to find out is to rise up early in the morning and give it a try. Enjoy The Terminator! 73, Elmer Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06977-0113 e-mail ASK ELMER April 2001
Dear Elmer..... I was looking to upgrade the stock, hand-held microphone that came with my H.F. station at home. There are so many choices. 'Full-Range' to 'Dx'ers Dream. What should I be looking for? signed, W.E Talkalot
Dear W. One of the primary goals of a "QSO" is to get the message across. Another goal would be to be heard distinctly in a "Pile-up" by the DX station. You can deliver a whopping 5x9 plus signal and still not be very intelligible because of the combined characteristics of your environment (read this as the shack acoustics), you own voice pitch, the characteristics of the microphone, the transmitters audio response, and the type of modulation (AM, SSB, FM, PM). For this discussion we will assume that the receiving station has a state of the art receiver which does not introduce any audio distortion and you are operating on a frequency where this is no interfering signals. In reality, radios of this type are not very common, especially in an amateur radio operators shack. I have to say something about the stock microphones. Many of these microphones, though inexpensive, are very good. Some of them allow you to modify the response of the microphone to suit your voice and operating conditions. Before you go and spend your hard earned money for a special "communications" microphone, I would suggest that you test the microphone on the air. Most stations will be happy to give you a report on your audio quality. Some stations have a recorder in the shack tied to their rig, so they can record and retransmit your signal, so you can hear how you sound to them. The drawback of this technique is that you are going through two radios, which will modify the sound somewhat. Most times very little. If the reports of your audio are unsatisfactory, and a change in the microphone is indicated (we are saying that your rig is not the problem), let us look at what the various microphones will do for us. The differences in the microphones are in the their frequency response, sensitivity, noise canceling ability and adjustability (to locally modify these features). Probably the most important characteristic is the microphones frequency response. If you are a "DXer", you would probably want a microphone with an accentuated high frequency response to help cut through the noise of a pile-up. On the other hand, a "rag chewer" would want a microphone with a relatively flat response for easy listening. A mobile operator or one who has a noisy shack, would want a noise canceling microphone as well as a tailored frequency response. I will not say which brand or type of microphone is better than another, as that is an individual preference and strictly subjective. I would strongly recommend that any microphone chosen, be tested in the operating environment on your own radio. On the air tests in QSO are the only real way to evaluate a new microphone. I would disregard the advertising "hype", and perform my own tests. A problem is that most dealers will not allow you to test out a microphone and take it back if it is not satisfactory. It may be possible to borrow a microphone from a friend or one of the members of your local radio club for evaluation. If you would like transmit very high quality audio, you would probably require a studio microphone and an audio processor similar to those used in a broadcast studio. I do know several operators who are diehard AMers. They have elaborate microphone and audio consoles tied to their radios. One of their goals is to produce the best quality audio within the allotted bandwidth, that they can, for real arm-chair copy during a net or other QSO. I have listened to them, on 160 meter AM, and they sound as if I was listening to a broadcast radio. I have to say that you are the final arbiter of what you want to achieve and how you want to do it. Have fun with it. 73, Elmer May 2001 ASK ELMER
Dear Elmer......... As I listen on the ham bands I hear talk about upgrades to Kenwood, Yeasu and Icom gear....... Most of the fellows have stated that they do the upgrades themselves. I've gone to some of the Mfgs sites on the Internet and don't seem to find much specific information about these 'upgrades' ....where else can I look? The Searcher
Dear Searcher, When you posed this question, I really was certain that there were many avenues to obtain information regarding radio modifications. I knew that the manufacturers would not be very forthcoming re- garding mods to their equipment since they want you to return the equipment to them, as they feel that their technicians have both the knowledge and the resources to properly do the job. Many of us are equally of not better equipped and qualified to modify equipment in our own workshop. I must say, that unless you feel confident in your cap- abilities, equipment modification is not for the faint of heart. Some, of course, is relatively simple... so go to it... other mods can be quite complicated, requiring some advanced assembly and test equipment. It is here that you must evaluate the pros and cons of doing your own modifications. Once the decision is made that you do want to perform your own mods, the Internet is a tremen- dous source of information. The following sites are some of the better ones for the latest mods to both current and older equipment:
Racine Megacycle Club www2.wi.net
Hamrad Amateur Radio Res. www.hamrad.com
WB4HFN Amateur Radio Website pacnet.ne.mediaone.net/wb4hfn/equipmods/Modifications.htm
Oakland University Amateur Radio Archives www.acs.oakland.edu/barc/archives.html
OZ2AGP Website www.mods.dk
Hamsters Radio Mod. Database hamster.ivey.uwo.ca (This is a search engine where you enter the radios manufacturer, model or other info.)
I must caution you that many of these mods were posted by other Hams, as well as by the equipment manufacturers service department and may or may not be a complete set of instructions. One has to approach the modification of their equipment with some caution.
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ASK ELMER cont.
Prior to doing the modification, I would suggest that you obtain as much information as you can regarding it, both on its complexity and the mods utility. QSO's with other owners of the same equipment who have done the mod is the most use- ful. At one time there were on the air user group nets for all of the major ham equipment manufac- turers, but I think that they have all disap- peared. At one time a good source of information was the Yaesu, Icom and Kenwood news letters run by International Radio Corp., but I think that too has disappeared. It is also recommended to have a copy of the equipment's service manual in the event of problems with the modified radio. Good luck in modifying your radio, as I have done many mods on my radios over the years with great success. 73, Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 e-mail
ASK ELMER June 2001 Elmer, I listen to the tech net on 146.85 and Dick(K2RIW) uses the term "visuar" (check spelling on this word). I would love to have an understandable explanation of this word, and how visuar relates to SWR and the output that can be expected. Signed Reflective. Dear Reflective, I have to admit that it took me a moment to recognize the “word” that you were asking about. It did give me quite a chuckle, but I have to say that the question is a very good one. The actual “word” is really a set of initials which over the years has turned into a noun by many in the Ham radio community. The term is really VSWR. The initials stand for Voltage Standing Wave Ratio. A we have some room in this issue, I will take this opportunity to turn this into a short tutorial. Maximum power transfer between a generator and its load occurs when the load's impedance equals that of the generator. You can prove this for yourself using Ohms law. Calculate the power in a resistor of 25 Ohms, 50 Ohms and 100 Ohms when driven by a generator with a voltage of 2 V and an Impedance of 50 Ohms. The circuit would be a simple series circuit with the generator in series with a 50 Ohm resistor (which simulates its impedance) and the load resistors mentioned above. First we must calculate the voltage across the load resistor for each of the above load resistors. To do this, calculate the current for each of the loads. The currents, using Ohms Law (I = E / [R load + R generator]) would be 26.6 mA, 20 mA and 13.3 mA respectively. Power = I 2 * R load. Therefore, the power into 25 Ohm load is 17.78mW, 50 Ohm load is 20 mW and 100 Ohm load is 17.78 mW. From this calculation you can easily see that the maximum power is delivered to the load of 50 Ohms. Try the calculation yourself for other generator impedance's and loads. It does work! This is known as a matched generator and load. In reality, the generator and load are not adjacent to each other. Just think of your rig and its antenna. There is a transmission line between them. In order to maintain this condition of maximum power transfer, the impedance of the transmission line should match that of the load. Energy sent down a transmission line takes a finite amount of time to reach the load. Consider a transmission line which is infinite in length. If you were to connect a generator to it, it would appear to the generator that it is connected to the impedance of the transmission line. If the line is infinite in length, the energy would be sent down the line and never get to the end. Great way to fool the generator. In reality, transmission lines are never that long. On a practical line, the energy sent down the line who's impedance is different from the load, some of the energy will be reflected back from the load. This energy would travel back to the generator, whose impedance is different then its own, and it would reflect back up the line. This energy, traveling back and forth would cause some constructive and destructive interference (read this as adding and subtracting energy) along the transmission line. The wave pattern which would be set up on the transmission line is called a Standing Wave. The reason it is called a Standing Wave is that it does not move up and down the line over time, but holds its position relative to the ends of the line. If you would like to see a standing wave, you can tie a string tightly between two nails. Then pluck the string, and watch the pattern it generates. This is a standing wave pattern. Musical instruments rely on this phenomena to produce sound. We have now established the concept of the standing wave. We have been discussing power, because power does the work. Power consists of voltage and current (P = E x I), so we can express the standing wave in terms of either of these quantities. Both power and current are troublesome to measure, so voltage wins out. In order to have a measure of the quality of the match between the generator, transmission line, and load impedance's, we will measure the magnitude of the standing wave pattern on the transmission line. As long as the length of the line is greater than 1/2 wavelength, you can use a voltage probe on the line and measure its minimum and maximum voltage (the points of constructive and destructive interference) as you travel down the line from the generator to the load. The ratio of the maximum to minimum voltage is known as the VSWR. At one time this was the only method to accurately measure the VSWR using a device called a "Slotted Line" for coaxial cable or a "Lecher Line" for a balanced system. The Slotted Line was just as the name implies, a precision coaxial transmission line with a slot cut through the shield so a probe could be inserted to measure the voltages along the line. Today we have instruments such as the "Reflectometer" which greatly simplifies the measurement of a lines VSWR. The importance of maintaining a low VSWR in a transmission line is to reduce the losses in the transmission line and assure a maximum power transfer to the load. A high VSWR can cause problems with voltage breakdown in a cable at the high voltage point. This is a fairly common occurrence when cables have been stressed due to weather or mechanical problems. It is good practice to keep the VSWR below 2:1. If this is not possible, then the cable should be chosen to withstand the high voltages and currents that will be generated due to the standing wave. This is one reason why open wire transmission line is used to feed multi-band random length dipole antennas. The open wire line can withstand the very high voltages generated due to a mismatch between the transmission line and the antenna. I hope this answers your question , probably in more detail than you wanted... but this is what happens when I have to fill up space. 73, Elmer
ASK ELMER
Sept, 2001
Dear Elmer,
I have come across a rather strange phenomenum. I have a 7 AH 12
volt gell cell battery and it was due to be charged. I tested the battery
with my digital meter. The way I charge the battery is with a wall wort
battery charger. I measured the voltage of the charger and it read 17.89
volts and the battery read 11.72 volts. After I connected the wall wort to
the battery I decided to take another reading. This reading gave me quite
a surprise. I was expecting to read either the higher voltage of the wall
wort or something in between the wall wort and the battery. Instead, I got
a reading almost exactly as that of the battery, 11.75 volts.
The question is, why do I not get the same reading as the wall
wort, 17.89 volts? At least I know that I can run a radio from the battery
even though I have the battery hooked up to a charger with higher voltage
that the radio should have presented to it. By the way, I got the battery
charged up to slightly over 14 volts and disconnected the charger. Now
I am running it back down again. Ain't life grand?
Befuddled
Dear Befuddled,
To properly answer your question we have to discuss the some of the
charasteristics of rechargable batteries and in reality, batteries in general. A
battery consists of a group of cells connected in series. Each cell has a
terminal voltage which is determined by the cell's chemistry, i.e., a Nickel
Cadmium cell has a terminal voltage of 1.2 volts, a Lead Acid cell has a
terminal voltage of 2.0 volts, etc. This terminal voltage is just a nominal
voltage, and does vary with the cell's state of charge. A Lead Acid cell at full
charge can exhibit a terminal voltage of 2.35 volts, and 1.85 volts at full
discharge. Associated with each cell is an internal resistance caused by the
materials used in the cell as well as its chemistry and its construction. If the
cells are in good condition, this internal resistance is fairly small, making
the battery look like a constant voltage supply. A constant voltage supply is
one whose terminal voltage does not vary with changes in current drawn from it.
(The I X R voltage drop which would be predicted by Ohm's Law. Where R is the
internal resistance of the battery and I is the current being drawn from the
battery.) Now we must look at the characteristics of the plug-in "Wall Wort'
power supply. Most of these supplies consist of a transformer, a full wave
bridge rectifier and a single capacitor to supply a filtered DC to power an
electronic device. These power supplies are not voltage regulated, so their
ratings are given at a specified current, i.e., 12 V @ 100 mA, etc. When
unloaded, these power supplies exhibit a terminal voltage which can be
considerably higher than their rated voltage due to their relatively large
internal resistance (much more than that of a battery). The reason for this
relatively high internal resistance is the effective resistance of the
transformer, the diode bridge's resistance and efficiency in converting the AC
to pulsating DC and the size of the capacitor storing the resulting DC.
We can now discuss the measurements you made on your charging system.
The 17.89 volts you measured as the open circuit terminal voltage of the "Wall
Wort" is the peak voltage stored on it's capacitor. As this is a peak voltage,
multiply it by 0.707 to obtain the RMS no load voltage output of the transformer
(I am neglecting the small voltage drop in the diode bridge rectifier) . This
gives you 12.65 volts out of the transformer. This generally means that at the
"Wall Wort's" rated current, its output voltage would be 12.6 volts, and would
be lower if the current being drawn from it is higher. Again this is the I X R
drop due to the internal resistances predicted by Ohm's Law. Since the battery's
terminal voltage increases with its increasing state of charge, the amount of
current supplied by the "Wall Wort" is steadily decreasing, as it is limited
only by the "Wall Wort's" internal resistance (Ohm's Law in action). This is why
you measured 14 volts when the battery was at full charge. At this point the
battery's terminal voltage would not increase significantly, as it is fully
charged, and any additional charging would just cause the battery to get warm
due to overcharging. At this end of the charging cycle, the battery should be
removed from the charger, or the charging current be reduced to a maintenance
trickle charge. I have to admit that you have been extremely fortunate in your
choice of battery charger. Because small "Wall Wort's" have a relatively high
internal resistance, you have not overcharged the battery by exceeding its
maximum charging current, nor over-dissipated the "Wall Wort" causing it to
fail. For some additional information on batteries and charging, I would suggest
reading chapter 11, pages 20 through 23 in "The Handbook for Radio Amateurs,
2001" by the ARRL.
I trust that your question has been answered to your satisfaction, and you are
no longer Befuddled but "Charged Up" with knowledge.
73,
Elmer