Ask Elmer Marv Fleischman N1AWJ Ham Radio Articles

<HOME ASK Elmer July 2001 To Present.

Stamford Amateur Radio Association Last Updated: 01/03/2004

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ASK ELMER

Dear Elmer,
I keep hearing that =93software radios=94 are the radios of the future. What
are they talking about? How are they different from what we are operating
now? Do we have to carry a computer or laptop with us to operate them?
What's the scoop?
Signed, Ana Logue

Dear Ana ,
Current radios require significantly different circuitry to operate CW, AM,
=46M, FSK as well as other modes. These modes can be incorporated into
current radios by virtue of the manufacturers ability to miniaturize the
components and assemblies. After a while there is a practical limit to how
much can be packaged within a reasonable sized case. There has to be a
sufficient number of control knobs to be able to operate with the different
modes. Microprocessors allow the manufacturers to make controls, therefor
radios multi-function, but only to a reasonable limit. After a while, the
use of too many cascaded menus makes operating the radio extremely
difficult and confusing. You spend so much time trying to find the
function you need, that your need for that function has disappeared along
with the signal and the contact. Of course you may have several radios,
each with their own mode of operation. This is probably the easiest
station to operate, but it takes a considerable amount of space, not to
mention the expense of purchasing many separate radios. What about mobile
operation? With smaller and smaller cars, there is less space to install
radios, so you have to have less radio to install and still maintain
functionality. Two modern technologies, in conjunction with some older
analog technology have been combined to solve this problem. The two
modern technologies are the =93High Speed Microprocessor=94 and =93Digital
Signal Processing (DSP)=94 . In order for DSP to work, there had to be
developed the mathematical algorithms which accurately describe the
particular radio modulation scheme. At the same time, the speed of
microprocessors had to be increased well above the RF frequencies which
were to be handled. Today we have both the mathematics and the fast
microprocessors. Now that we have the tools, what can we do with them?
We can now develop a radio which can be reconfigured by the touch of a
button to most any form of modulation we wish to use. Much of the
redundant circuitry can be eliminated from this radio making it more
reliable (but not necessarily easier to repair). Think of a radio which
would never become obsolete. Any time a new band or modulation scheme is
developed, a simple change in the software is all that is required to give
your radio these new functions. Operating this radio can be made
relatively simple, by automatically reconfiguring all of the front panel
controls to the new mode. An LCD (Liquid Crystal Display) label could be
at each knob and would change with each mode. The possibilities are
endless. Would this eliminate analog circuitry? Not at all. There are
many functions that analog circuitry can perform better that digital
circuitry, especially in the area of low noise RF amplifiers and Microwave
signal handling. What you will see is the blending of the best of both
digital and analog technology to provide you with the most advanced
communication devices. The future of radio is very exciting, and there is
more to come! This does pose a problem for the FCC, as they type accept
radios for use in the US. Since the radios can be reconfigured in the
field, how do you prevent them from operating on frequencies and modes that
were not approved? It's a good question!
Until next time Ana, 73
Elmer
Send your questions to =93ASK ELMER=94, c/o Marv , N1AWJ, PO Box 1=
13,
Ridgefield, CT 06877-0113 or e-mail

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

Dear Elmer,

I am planning several antennas on a roof of limited area. What guidelines or parameters should I consider re spacing and-or minimize interference problems. Antennas; Tri-Bander Beam, Ringo 2 meter, Ringo 440 MHz, Carolina Windom, TV antenna, FM antenna and a Disk-cone for a Scanner.

Sincerely, Wired.

Dear Wired,

You have quite an array of antennas you will have to deal with. Of course my first bit of advice is to keep them as far away from each other as possible. I know that this is an obvious statement, but with this in mind, grouping the antennas as to their function would be a start. Three of the antennas are strictly receiving antennas, so they can be grouped together in relative proximity to each other. The three antennas are the TV, FM and Disk-cone. I would recommend that they be located as far away from the other antennas as possible. The next thing to consider, is the frequency ranges and the polarization of the antennas. The TV and FM antennas are horizontally polarized, whereas the Disk-cone antenna is a vertically polarized antenna. As the frequency range of all of the antennas overlap, I would suggest spacing the antennas in a triangular pattern at least 1 wavelength apart at the lowest common frequency (which is 88 MHz or 3.4 meter wavelength, the bottom of the FM band) , if possible. This is not really critical, so don't sweat it if you can't. Signal strength is so great for FM and TV that you won't really see any differences. I would recommend that the TV antenna (which is directional), be above the FM antenna, so that FM antenna (which is omni-directional) doesn't physically or electrically block it. The Disk-cone antenna (which is omni-directional) should be at height that would not physically block the TV antenna. Now we get to the more interesting areas. The transmitting antennas. In this we must also consider the antennas bands of operation as well as their polarity. You have a Tri-band beam, a Carolina Windom, and 2 Ringo Rangers (2 m and 70 cm). Two of the antennas, the Ringo's are vertically polarized, the remainder are horizontally polarized. The two Ringo's operate on two different, but harmonically related bands. Let us consider these two antennas. Under ideal conditions, I would

mount the antennas one above other. Their radiation pattern is such that one antenna would be in the shadow of the other, so they would not interact. Lacking this I would space them a couple of wavelengths (at 70 cm) apart from each other. The further the better, but one must be practical. In most instances, there shouldn't be any appreciable interaction between the antennas, especially if your 2 meter signal is devoid of harmonics on 70 cm. Now we come to the most difficult of the antenna problems. This is with the Tri-band beam and the Carolina Windom. Both of these antennas have the same polarization and cover the same bands. Here "Distance makes the heart grow fonder", and the antennas work better. I realize that this is not too practical, and if anything we "Hams" are a practical bunch. One possible way to minimize the interaction between the two antennas, is to space them odd multiple 1/4 wavelengths apart, and one above the other. In this instance, the beam above the Windom. The greater the separation, the better off you are. When using the Windom, rotate the beam so that it is broadside to the Windom. This should minimize the coupling between the antennas. Other than the mass of the tower and beam being in the near field of the Windom, the only bands you would really have to consider is the 10, 15 and 20 meter bands in which the Beam is resonant. When using the Beam, the only time you have to consider the interaction is when the beam is aimed directly at the Windom. Height, distance (and a bit of good luck) will help. I have to admit that I personally run a Windom within 25 feet of my Tri-band Beam. I have not found any problems with interaction. I am not saying that I don't have any interaction, just that I have not had any problems.

Well Wired, I hope this points you in the right direction. I also hope that you have a big enough roof to hold all of these antennas.

73,

Elmer

ASK ELMER

Dear Elmer,

Sincerely, Wired.

Dear Wired,

Well Wired, I hope this points you in the right direction. I also hope that you have a big enough roof to hold all of these antennas.

73,

Elmer

ASK ELMER

This Ask Elmer is a continuation of last months question. In brief, the question was "How do you measure the value of a capacitor or inductor" without elaborate test equipment. One of the early and powerful methods of measuring electrical components was by ratio and comparison. The most popular, and easiest methods of measurement is by using a circuit called a "Bridge". You may have heard of Whetstone, Hay, Maxwell or other bridges in your readings. They are some of the many bridge configurations which can be used to measure the value of a component. The names, of course, are in honor of the scientist who configured that particular type of bridge circuit (and subsequently wrote about it in some scientific journal). Many of the more common bridge configurations work on a very simple principal. There is an elegance in simplicity. The principal is that there will be no current flow between points at the same voltage in a circuit. Going back to Ohm's Law, there must be a voltage difference to have a current flow. I am not considering a current flowing through a piece of wire connecting two points in a circuit. For this discussion, either end of the piece of wire is considered to be the same point. The simplest bridge to consider is the Whetstone Bridge. It consists of 3 known resistors and can measure a fourth unknown resistor. In its simplest form, the top 2 resistors are of the same value, the third is a calibrated variable resistor and the forth resistor is the unknown to be measured. The procedure is quite simple. Adjust the calibrated variable resistor until there is no tone in the headphones. Refer to the diagram.

At this point, the bridge is in balance, and the voltage drops across the top two resistors are equal to each other. There is no voltage difference across the headphones, so no sound is heard. The value of the unknown resistor is the same as the value of the known variable resistor. As this bridge works on the principal of being in balance when the voltages on the opposite arms are equal, you can extend the range of measurement by using unequal values for the known resistors. If we assign designations such as R1, R2, R3 and Rx (for the unknown), The following relationship will allow you to find any value of Rx if you know the other values:

Rx = ( R2 * R3 ) / R 1

The only requirement for the tone generator is that it be in the audio range (so you can hear it) and its voltage be reasonable so that you don't get shocked or over dissipate the components under test. You just as easily can substitute capacitors or inductors for the arms of the bridge, and the relationship and operation is the same. Going further, R1 and R3 can be resistors, and R2 can be a capacitor or inductor. This bridge will measure the impedance of the unknown inductor or capacitor. In this simple approach, only capacitors and inductors of good quality can be accurately measured. For low quality reactive components, you still use a bridge, but the arms of the bridge have more elements in them. If R2 is changed to an inductor, you can measure an inductor or if a capacitor is in place of R2 then you can measure a capacitor. If you know the impedance, and the frequency of the audio generator, you can calculate the value of the inductor or capacitor. In all cases, the bridge relies on your knowing the values of 3 of the arms to find a fourth. One of the nice features of the bridge method of measurement is that its accuracy is limited only by the accuracy of its known elements. Under certain conditions (the equal arm condition), only the value of the variable element need be known accurately, because if R1 and R2 are identical in value, they can be of most any value and the bridge still works accurately. Over the years there have been many papers and books written on the design and use of the various bridge configurations. These days, for resistance measurement, it is easier to use an ohmmeter than a bridge to measure resistors. This is not the case when measuring inductors or capacitors. This completes my discourse on measurement of inductors and capacitors. There are many other methods of component measurement, which are well beyond the scope of this article. 73, Elmer Send your questions to “ASK ELMER”, c/o Marv N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

ASK ELMER

Dear Elmer, It took a while for me to figure this out but now that I am studying for the Extra class license I have learned the difference between a non-inverting op amp and an inverting op amp. The inverting op amp changes the phase by 180 degrees. Please correct me if I am wrong about this. This brings several questions to mind. What are the advantages and disadvantages of using one form of op amp over the other? Keeping things in phase or reversing phase can be controlled as far as I see it, but why? Are there good reasons for using one over using the other? If so, what situations would be more suited for inverted op amps and which situations would be better suited for non-inverting op amps? I realize that it is possible that this might be easy or very hard to answer. I hope that it is not something that will require a book to answer. Inquiring minds want to know. Actually from Mike, KB1DXC

Dear Mike, The Operational Amplifier is a relatively new concept, as far as electronics is concerned. It is only about 40 years old. This type of amplifier was conceived by George Philbrick in the early days of computational electronics. It was originally developed for a device called the Analog Computer, which in one form or another is still used today. Before we answer the specifics of your question, we must define what is meant by an operational amplifier. Its unique characteristics permits its use in a multitude of applications, far beyond Analog Computers. By definition, (though not really achievable in practical amplifiers, many come close enough in some specifications to satisfy their use in specific applications) the amplifier should have an infinite input resistance-impedance, a zero output resistance-impedance, an infinite bandwidth from DC to microwaves, an infinite gain and a perfect 180 o input to output phase shift and be capable of operating over enormous input and output voltage ranges. Early Operational Amplifiers were vacuum tube devices which were physically large, rather warm and somewhat difficult to use. With the advent of the transistor and subsequently the integrated circuit, devices called operational amplifiers designed, constructed and are currently sold. Do these devices conform to the ideal specifications of an Operational Amplifier….. Hardly! They all have advantages (and in a few cases disadvantages) over the vacuum tube versions but have become more user friendly. Now I will answer your questions. Most Operational Amplifiers have DC and low frequency voltage gains exceeding 1000, and even 10,000 is quite common. If one were to set up a circuit using an operational amplifier and calculate the circuit's gain, they would find that the gain would be the ratio of two of the resistors. If the Operational Amplifier had an infinite gain (called open loop or native gain) then the circuit gain would be exactly the resistor ratio. (Refer to the diagram.)

PLACE HOLDER FOR DIAGRAM #2

The feedback in this instance is inverse (negative) feedback. The actual gain is calculated by the ratio of R2/R1. The closer this gain gets to the actual open loop gain of the amplifier, the less accurate the calculation becomes. In order for this to be reasonably true, the open loop gain on the Operational Amplifier must be at least 100 times the required (calculated) gain, and the value of the resistors used must less than 10% of the real amplifiers input resistance. Depending on your choice of Operational Amplifiers, this equation for gain can be valid to hundreds of Megahertz. Most Operational Amplifiers made today differ from the original concept by being designed with complimentary or differential inputs. This increases their utility tremendously. These inputs are called the inverting and non-inverting inputs. This permits the designer to configure extremely versatile circuit arrangements. Positive feedback is a means of obtaining oscillation and pseudo infinite gain, whereas negative feedback is a means of controlling gain and bandwidth. Another feature of having the differential input has to do with the apparent input resistance-impedance of the amplifier. In a standard configuration, (as shown in the above diagram), the input resistance is the value of resistor R1. With a differential input, the impedance of the non-inverting input can approach very high values, limited only by the physical devices leakage currents and stray leakage paths. By substituting a network for R1 and/or R2, an operational amplifier can behave as a gain controlled amplifier, a filter of any type (high pass, low pass, band pass or band reject), a voltage or current comparator an integrator or differentiator (one of their original purposes in an analog computer), an oscillator or selective amplifier.. And the list goes on and on. Over the years many, many books, white papers, application notes, etc. have been published on the uses of the Operational Amplifier. I doubt if I could do justice to an extensive bibliography, but I will reference a few for your further reading. They are as follows: ARRL ed., "Handbook for Radio Amateurs", 2000 ed., ARRL Pub. Terrell, D., "Op Amps, Design, Application and Troubleshooting", Butterworth-Heineman Pub. Roberge, J. K., "Operational Amplifiers, Theory & Practice"; J. Wiley Pub. Erst, S. J., "Electronics Equations Handbook", Tab Books Pub. Well Mike, I have just shown you the tip of the "Iceberg", and now it is up to you to go "Diving" for more. So until you resurface, 73, Elmer Send your questions to "Ask Elmer" c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

Op Amp R 1 R 2 Output Input

ASK ELMER

Dear Elmer,
What are various ways to bring in a ground to the shack
from the outside? Number, size, pattern of multiple
ground rods? Size of wire and grounding strip in shack.
Can you tie in other parts of the house with water pipes,
radiators, etc.?
Signed, Rock Solid
Dear Rock,
Many books have been written in answer to your question,
and undoubtedly many more will be. It would be
impossible to cover the subject in any great depth in
this column, but I will attempt to give you some general
hints and point you in the direction of obtaining more
complete information. There are two primary functions
for grounding. The first is for safety, both from power
line problems and for lightning protection. The second
is to secure a good RF return for your radio(s) and
antenna system. My own personal rule is that "bigger is
better", which means the larger the gauge of the
conductors in a ground system, the better off you are.
With that statement I am getting ahead of myself. First
let us consider your station in the "Shack". All of the
radios should be grounded together. I would recommend a
Copper grounding strip at least 4 inches wide behind your
equipment. Many Hams cover the back half of their
operating positions with sheet Copper flashing, and rest
their equipment upon it. All of the radios are then
connected to this grounding strip using 1/2 or 3/4 inch
copper braid. A good source for this braid is to remove
the braid from some Good Quality (Not Radio Shack) RG 8/u
cable. Let us consider grounding for power line
protection. This is probably the least troublesome
grounding procedure. In most instances, a heavy wire (8
gauge is generally sufficient) from the grounding strip
to the house ground near the power company's "service
drop" coming into the house. This point is chosen since
it is the ground for your house. A secondary choice
would be a "sweat" Copper cold water pipe, connected
directly to your water main. Do not rely upon pipes
which are threaded together, as plumbers use "compound
and wicking" or Teflon seal at the pipe joints, making
them poor conductors. A third choice would be to drive an
8 foot ground rod into the earth, as close as possible to
where the power comes into the house. For lightning
protection, a simple connection using a single 4 or 6
gauge wire to the house ground would be sufficient. I am
not considering tower or antenna lightning protection
within the scope of this article. That would have to be
an article unto itself. I would strongly recommend that
you check the grounding of all of your outlets. Many
times the house wiring is not what it is "cracked up to
be". The use of the aluminum ground wire in use in many
homes, has oxidized and makes a poor connection with the
ground connection at the outlet or junction boxes. This
should be corrected by the use of an anti-oxidizing
compound on the wires before the connection is secured.
The RF grounding of the shack is somewhat less critical.
The I say that because the critical RF grounding
generally takes place near the antenna in the form of a
counterpoise, ground rod array or other low impedance
(hopefully) connection to the earth. This too is beyond
the scope of this short article. This is not to imply
that you need not RF ground your equipment. What I
personally recommend is the use of 1/2 inch or wider
copper braid from the equipment ground connection through
the nearest window to an 8 foot ground rod driven as
close as possible to the shack into the earth. The
shorter the path for this ground the more effective it
will be. If it is more convenient, the braid can be
connected to the house water main near its entrance to
the building. There is a lot more that can be said
about grounding, and I will recommend the following
resources to further your knowledge:
ARRL, "Handbook for the Radio Amateur", ARRL pub.
On the internet:
www.lightningsafety.com
www.lightning.org
ARRL Technical Information Service page on Grounding on
the ARRL.org website
www.arrl.org/tis/info/grounding.html
This information should provide you with a good
"grounding" on grounding your shack and equipment.
Until our next earthy discussion,
73,
Elmer

ASK ELMER

Dear Elmer
What useful things can be done with an Oscilloscope in both the ham shack and also building, diagnosing and checking equipment?
Signed C. R. O'Scope

Dear CR,
This is a subject that one could, and have written many application notes and books on over the years. It's interesting that this instrument was initially thought of as having an extremely limited use (primarily only in some scientific and television applications). Wow, were they wrong! The Tektronics Corp. had built itself initially on this instrument alone. To those who are unfamiliar with an Oscilloscope, I will describe the instrument and its basic function. Most of us are familiar with a voltmeter, as a basic measuring instrument. A voltmeter measures the voltage level at a point in a circuit at any fixed instant of time. The reading does not indicate what the voltage was at an earlier time, or how it varies with time. You could write down successive measurements and then graph them to obtain this information. If the voltage was varying at a high rate, you could not keep up with the changes, no matter how fast you could write. Something like trying to copy CW at 30 WPM…. Your hand-ear coordination is just too slow. You need some help. Here is where the Oscilloscope comes in. The display on the oscilloscope consists of a screen which generally displays the measured voltage as a point (of illumination) on the vertical axis while this point of light is being swept across the screen at a defined rate of speed. What I mean as a defined rate of speed is the point of light (lets shorten this to and call it a “Beam” to save my typing) is moved across the screen at a very constant and repetitive 1 screen division per (centi, milli, micro, nano) second. Now, if the voltage varies during the time the beam is sweeping across the screen, you will see this variation. Due to the materials used to display the Beam in the Oscilloscope, and the persistence of vision of the eye, and if the voltage variations are repetitive, then you have a real time graphical representation of the voltage verses time. This is the basic Oscilloscope. There are controls to vary the speed of the Beam and the ability to synchronize the Beam with the incoming signal, and to adjust the sensitivity of the instrument to give it maximum flexibility, but these don't change its basic function.
Now that we know how the instrument works, we will discuss some of its applications both in the shack and on the test bench, without going into the details of the test procedure. The most common application in the shack is a modulation monitor. The Oscilloscope can display the RF envelope and the modulation pattern of your transmitter. Using a technique known as a “Trapezoidal pattern”, you can monitor the depth of modulation of an AM transmitter. You can, with a wideband Oscilloscope, determine of there is any distortion of your RF carrier and see if there is any spurious signals being generated by your rig. With the proper auxiliary circuitry, you can use the Oscilloscope as a spectral display, which shows the frequency and relative strength of the signals seen by your receiver. This is only the “tip of the iceberg”, as the instrument can be used wherever a voltage verses time display or voltage display in real time is needed. By the way, I always mention Voltage measurement, but you can, just as well, substitute Current or Power for Voltage. On the test bench, the primary function of the Oscilloscope is to determine of a circuit is operating properly by observing the voltages within the circuit. You can measure the signals amplitude, frequency, phase, duty cycle and period, just to mention a few. The following are a few references which can assist you in use of the Oscilloscope (besides many sites on the Internet):
ARRL ed.; “Handbook for Radio Amateurs”; ARRL Pub.; 2001
Rider, Uslan; Encyclopedia of the Cathode Ray Oscilloscope and their Uses”
“Complete Book of Oscilloscopes”; Tab Pub.; 1992
Sams, H. W.; “Oscilloscope Guide”; Prompt Pub.; 2001

Well, CR, this was but a very brief description of the instrument's uses which is limited only by your imagination.
73,
Elmer

Send your questions to “ASK ELMER”, c/o Marv N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

ASK ELMER Dear Elmer, What useful things can be done with an Oscilloscope in the ham shack and also building, diagnosing and checking equipment. Signed C. R. O'Scope Dear CR, To continue our discussion about Oscilloscopes that started in the May issue of the Squelch Burst, we will start by discussing how to read the screen display. It is not difficult to interpret the screen display, but if you are a first time or casual user, these instructions will help you to avoid any errors in interpretation. Please refer to the diagram of a screen display below. In the most common use of the instrument, the vertical screen axis represents the voltage and the horizontal screen axis represents time in units or subunits of the second. This permits you to obtain quite a bit of information about the waveform being measured . ( CRO Screen drawing here) The measurement would be "Y" volts per division vertically and "X" nano, micro, milliseconds horizontally. With this representation you can easily measure the frequency of the waveform. This is done by measuring the time indicated from one peak of the display to the next one in seconds. This is the period of the waveform, therefore the frequency is obtained by dividing the period into 1 (calculating its reciprocal). The front panel control on the instrument permit you to adjust the horizontal resolution (this is called the sweep rate) to some convenient value for the measurement. By refining the measurement, you can even obtain the frequencies of some of the components of a complex waveform, such as an amplitude modulated RF signal. The vertical measurement is the peak to peak voltage measurement. You use the vertical gain control, calibrated in volts per division to adjust the trace to be easily read on the screen. Generally you would like a display of at least 50% of the screens graduations. If the signal is a very good sine wave, pulse, square wave or other simple geometric shape, you can easily determine its DC component, peak and RMS value, by using the appropriate arithmetic relationships. As an example, if the waveform was a good sine wave, the peak value would be 1/2 the peak to peak, and the RMS value would be 0.707 x the peak value. To measure the DC component of the waveform, you first disconnect the vertical input of the oscilloscope from the circuit being measured. Set the vertical input switch to DC response. Use the vertical positioning control to position the trace (which will be a straight horizontal line) to the horizontal center line on the screen. This represents 0 Volts. Reconnect the oscilloscope to the circuit and determine if the trace is non symmetrical about the center line. The offset about the center line is the DC component. As you are measuring an electrical signal, you do not want to influence the circuit by the act of doing the measurement. The term used is circuit loading. You want to minimize circuit loading during measurement. There are two primary elements which load a circuit. They are resistance and capacitance. To minimize the effects of these elements, a high resistance-low capacity probe is used in conjunction with the oscilloscope. Most of the probes reduce the capacitive loading by 80% and the resistive loading by 90%. It is always recommended that you use one of these probes when using the oscilloscope, unless the impedance of the circuit under test is so low that the loading of the oscilloscope can be ignored. The probe resistance effects all frequencies (DC included), whereas the effect of the probes capacitance increases with increasing frequency. To properly use the probe, you must calibrate it on the Oscilloscope that it is being used with. Calibration is quite easily done. On the Oscilloscope there is a calibration test jack. This outputs a square wave with at a known amplitude. Connect the probe to this point and adjust the Vertical Gain of the instrument to display 4 divisions or more of the square wave and the sweep speed to display 2 or 3 cycles of the waveform. The Oscilloscope vertical input must be set to DC response. On the probe, there is either a screwdriver adjustment hole (compensating screw) or the probe itself can be adjusted by turning the probe body (older Tektronix probes). Adjust the "compensating screw" in the probe so that the top of the square wave is as flat and parallel to the gradicle as possible. The next step is to adjust the vertical gain calibration control, until the peak to peak voltage as read on the screen corresponds to the marked calibration voltage. Your Oscilloscope and probe combination is now calibrated, so that any measurement that you make is relatively accurate. There is yet more to write about the Oscilloscope, but the references listed in last months "Ask Elmer" do a much better job than I possibly can in these short articles. Continued on Page 7 ASK ELMER cont. I do hope that these very brief articles were of help to you in using your Oscilloscope. It is an extremely versatile measuring instrument whose in which new uses are still being developed. 73, Elmer Send your questions to "ASK ELMER", c/o Marv , N1AWJ, PO Box 113, Ridgefield, CT o6877-0113 or e-mail

ASK ELMER

Dear Elmer,
I know that a Dipole radiates off the sides. In the Stamford area, what would
be the best orientation N-S or E-W or ? for max contact or coverage area.
Signed, Looking for Directions

Dear L F D,
This question is one which can only be answered in very general terms. As
Stamford is nearly due East of Europe and West by North West of California, one
preferred orientation would be the antenna ends would point North by North West
and South by South East. On the other hand if you are attempting to contact
Japan and the Pacific Rim countries, an orientation South by South West and
North by North East would be suggested. This would aim your signals “over the
Poles”. If you want to contact the East Coast of the Americas (both North and
South) then an orientation of East-West for the ends of the antenna. As you can
see there is no real preferred direction. This makes the assumption that you
have an “ideal” dipole in unobstructed space many, many wavelengths above
ground. The radiation pattern of the antenna is a doughnut perpendicular to the
wire, and you can be assured of radiating in the direction of choice. Obviously
this is not the case in the real world. Your antenna is probably going to be
fairly close to an imperfect ground, with many obstructions due to trees,
buildings, etc. Under these conditions, the radiation pattern of a dipole
antenna is going to be much less than ideal. I would be less then honest with
you if I say that I can predict the radiation pattern for your antenna. I would
suggest that you use one of the antenna modeling programs obtain an idea of your
particular antennas radiation pattern. A less than ideal antenna will radiate
in more than two directions depicted for an ideal dipole. Some of these
additional “lobes in the radiation pattern” might make your dipole almost
omni-directional, or if you are unlucky may just “heat the aether” sending the
radiated energy into space. If you can't model the antenna, I would suggest
that you erect it and do what hams have been doing for decades…. Test it out on
the air. One of the joys of amateur radio is experimentation, and antennas are
one of the easiest things to experiment with. You may hit upon just the right
combination of orientation, height above ground, effects due to obstructions,
and other resonant antennas or structures in the immediate area, which might
provide you with an antenna ideally suited to your particular type of operation
(luck plays a big part in the antennas operation, as does Murphy's Law). If the
dipoles are not horizontal, but are constructed as inverted "V's", or "slopers".
then the radiation pattern gets more complex. Another suggestion is to erect 2
independent dipoles, one oriented to radiate in a North East, South West
direction and the other to radiate in a North West, South East direction. With
the two dipoles at right angles to each other will afford you a better chance of
omni-directional coverage. Nothing is perfect, and everything is a compromise,
Antennas included. What you want to do is to arrive at the best compromise for
your style of operating by modeling and then experimentation. Other hams around
the country and world will be more than happy to assist you in checking out your
antenna on the air.
Well LFD, have a ball experimenting with antennas. It is an eye opening
experience.
73,
Elmer

Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113,
Ridgefield, CT 06877-0113 or e-mail

ASK ELMER
Dear Elmer,
With travel prices all over the world so incredibly low, if I now take one of the $250 round trips to Europe, what do I need to do
to use my radio there?
Signed, Wanderer

Dear Wanderer,
This being the vacation season, and travel bargains abound, I don't blame you for wanting to explore Europe. Several years ago,
several countries who were members of CEPT, (a European based international union of postal and telecommunication regulating agencies) agreed to allow licensed amateur radio operators of their respective countries to operate for short periods of time, in other countries of the union, without the need to obtain a reciprocal license. For the first time, amateur radio operators may cross international borders without having to apply to a regulating agency for permission to use an amateur radio transmitter, and paying a fee for the privilege. The United States negotiated an agreement with the SEPT countries to include it in the treaty. In order for you to operate in a SEPT country, you need to carry a copy of the FCC's public notice (DA99-2344) and an original of your current amateur radio license. The FCC's public notice may be downloaded from the ARRL website. There are 34 countries among the CEPT signatories. There are two classes of license. The Class 1 has full privileges and Tech-plus and higher classes qualify. Class 2 is VHF-UHF and a Technician class license qualifies. There is no equivalent for the Novice licensee, and they may not operate under the CEPT agreement. We have reciprocal agreements with Canada and with most Central American and South American countries. It pays to visit the ARRL's website to get the latest information on reciprocal operating privileges.
Enjoy your wandering and with Amateur Radio along, think of the many new friends you will meet in distant lands.
73,
Elmer
Send your questions to "ASK ELMER", c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

ASK ELMER Dear Elmer, From the dump I have been collecting 6 volt batteries. I wan to use two of them to power a mobile radio in a self contained briefcase pack. How can I build a charger to recharge them? Signed Wired Dear Wired, I have always heard that the local town dumps are a rich source of interesting and useful items, and you have been fortunate to find a few. I imagine that these are the “Gel-Cell” type of Lead Acid rechargeable batteries, as you didn't indicate the type in your question. Fortunately, a simple charger for the batteries will handle the “Gel-Cell” as well as a Nickel Cadmium battery of similar capacity. The simplest charger one can build is the Trickle Charger, so called as it constantly trickles a small current into the battery to maintain its charge but is capable of charging at a higher rate if the battery is fully discharged. The charger can be assembled from parts readily available in most junk boxes or purchased from Radio Shack. Below is a circuit diagram of the charger. The minimum operating voltage for C1 should be 25 V for a 6 V charger, and 50 V for a 12 V charger. Two of the component's values are to be determined by the battery that is to be charged. They are T 1 and R 1. The size of T 1 should be 12.6 V at 1 A for charging a 6 V battery, and 24 V at 1 A for charging a 12 V battery. The value of R 1 requires some simple calculation using Ohm's Law. First we must calculate the voltage across C 1. In normal operation the voltage on C1 would charge to the peak value of the rectified AC from the transformer. The voltage across C1 is 1.41 x the RMS Voltage out of T1. For a 6 V charger it would be 12.6 x 1.41 = 17.77 V. A similar calculation for the 12 V charger would result in 33.84 V. The recommended charging current for most batteries is 10% to 20% of its capacity. For safety sake, we will choose the 10% charging rate. If the battery is a 4 AH battery, then the charging rate is 400 mA for 12 hours. ASK ELMER cont. I realize that the apparent total charge exceeds 4 AH, but a battery is not 100% efficient. Some of the charging current is wasted in generating heat and gasses. A 6 V "Gel-Cell" is nominally 6.9 V when fully charged, and a 12 V battery is nominally 13.8 V. The value of R 1 is determined by the difference between the voltage across C 1 and the nominal battery voltage divided by the charging current. For the 6 V example, R 1 = ( 17.77 - 6.9 )V / 0.4 A resulting in a value of 27 Ohms. A 51 Ohm resistor is required for the 12V charger. The resistors must be large enough to handle the power that they are converting into heat. P = E x I. For the 6 V charger, P = (17.77 - 6.9) x 0.4 = 4.4 W, and for the 12 V charger 8 W. In both cases, a 10 W or larger resistor is recommended. If you construct this charger, and house it in some sort of case, you must provide adequate ventilation so that the R1 can dissipate its heat. This charger is a very basic one which is suitable for most rechargeable batteries with the exception of Lithium rechargeable cells. Lithium cells require special handling, and cannot tolerate overcharging. The above calculations, modified for the particular batteries which you want to charge will be a useful and reliable addition to your "Shack". You can, if you wish, using a tapped transformer secondary, make this a dual voltage charger. By switching different values of R1 into the circuit, make the charger extremely versatile, able to charge many sizes and types of batteries. The limit is a 1 A maximum charging current due to the ratings of the transformer and the diode. Well Wired, I think you should be all "Charged Up" and ready tear into this project. Have fun with it. Until next time. 73, Elmer Send your questions to "ASK ELMER", c/o Marv , N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

October 2002 Page 6 ASK ELMER Dear Elmer, O.K. So tell me about Baluns. I am told that "Balun" is a contraction of BALanced - UNbalanced (like me). I've also seen lots of Quick n' Dirty ways of making Baluns, like coiled coax, sleeves made of torroid cores or pill bottles filled with Steel wool or scrap Iron with the transmission line passing through. How do these designs work (sort of tell me) and how frequency dependant are they? Like, can a Balun for 2 meters be smaller than one for 160? What's the advantage, especially with a Dipole? Signed, Semi-Unbalanced

Dear Semi, The subject of Baluns is a lengthy one, and really cannot be described in any detail in these pages. I will try to give you a hand waving overview of what they are and do, as well as some references for your further enlightenment. You are quite correct about the origin of the name Balun. It is a contraction of BALanced-Unbalanced. In the simplest terms, a Balun is a transformer whose function is to transform an unbalanced feed line, such as coaxial cable to a balanced load , such as a dipole or other balanced antenna. It generally has, but does not have to have, a 1:1 impedance ratio. This is not the only place that a Balun is used, but for Ham Radio operators, the most common use. There are two types of Baluns, voltage and current. The voltage Balun generates a equal (balanced) voltage at its output terminals which is 180 degrees out of phase which each other. If the load into to which the Balun is connected is a truly balanced load, then the currents into the load are going to be equal and balanced. There will be no stray currents generated (especially along the outer shield of the coaxial cable, which can act as a stray radiator) and the load will absorb (use, radiate) all of the power being sent to it. I am making the assumption that the load, generator and transmission line is properly matched. In the event that the load is not perfectly balanced, the current Balun would be the appropriate choice. A current Balun (sometimes called a choke Balun) delivers an equal but out of phase current to the load. As most antennas are current driven devices, this type of Balun would be the most appropriate one to use. Because of its construction, it also acts as an effective choke, preventing stray currents from flowing down the outer shield of coaxial cable feed line. One of the more common forms of the current Balun is 10 or 15 turns of the coaxial cable feed line just prior to its being connected to a balanced antenna. Baluns can be constructed in many forms. They can be wound on torroidal or other powdered iron and/or ferrite core in order to increase their low frequency capabilities. They can be constructed of 1/4 wave transmission lines for narrow band Baluns. Any technique which will generate the transformer action is appropriate. At this point, a word of caution. A Balun (unless it is being used as an impedance matching transformer i.e., 4:1, etc.) does not improve the match between the load and the transmission line or source. Continued on Page 7 ASK ELMER cont. The following is by no means an extensive list of publications covering the theory, construction and operation of Baluns, but should assist you in a greater understanding of the devices: Straw, R.D. ed., “The ARRL Antenna Book”; ARRL pub. Sevich, J., “Transmission Line Transformers”; ARRL pub. Huchinson, C. ed., “Handbook for Radio Amateurs”, ARRL pub. DeMaw M.F., “Ferromagnet Core Design & Application H'bk”; MFJ Milligan, T.A., “Modern Antenna Design”; McGraw Hill Pub. Johnson, R.C., Jasik, H., “Antenna Engineering H'bk”; McGraw Hill Pub Well Semi, this should help you to become well balanced, at least for the current time. 73, Elmer Send your questions to “ASK ELMER”, c/o Marv , N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

October 2002 ECHOLINK By Al Goldberg, AG1B

My horizontal loop antenna was down, leaving me without ham radio. Marv Kronenberg, K1DLT, told me about EchoLink and now I am working the world without an antenna or ham equipment. All that I need is a computer built within three years and an internet connection. Plug a cheap microphone into your soundcard or computer. The loudspeakers of your computer should work OK but disconnect the powered woofer to eliminate audio feedback. Go to www.echolink.org and read what it is all about. Jonathon Taylor of the Norwalk radio club wrote the software. After downloading about 2-megabytes of software; register. If you are a licensed ham, you will be accepted and the world is yours. Over 40-thousand amateurs are already in and EchoLink is growing at about 200 a day. A dial-up internet connection is fine although large conference QSOs work better with a fast connection. I have a cable modem via Optonline. Whenever you are connected to EchoLink, your call sign appears on the listing. You can connect almost automatically for a chat and anyone can call you. A large number of repeaters are already linked to EchoLink. Many hams link their regular equipment but I fail to see the benefit. The amazing thing is that contacts are clear without interference, fading, or static. DX becomes easy as working a local station. I was on a round-robin contact with two hams in the UK and a ham in New Zealand. Try that over the air. The predecessor of EchoLink is I-Link, which is fading out fast. I understand that I-Link lists call signs in no special order thereby making these difficult to find. EchoLink lists the call signs in alphabetical and numerical order. Marv and I wonder about the future of ham radio. RF is still needed for mobile and emergency communications. The ARRL may have unpleasant vibes about this turn of events. Without ham gear; who will advertise in QST? A welcome change is that one can ragchew with DX instead of simply exchanging calls. Gone are the pileups! Give EchoLink a try!

At the last meeting it was suggested that I spend more time getting speakers for the meetings and less time working on the repeater. When I asked for someone to work on arranging speakers for meeting I got the same response I get every time I ask for a volunteer to do anything, everyone in the crowed shrinks 3 inches and stares at there shoes. Clubs work on a simple principle, a group of people get together each contributing a small amount of time and energy and the group as a whole benefits. Somehow this idea has been forgotten here and activities and duties have fallen into a rut of the same person being expected to handle a specific duty as long as they still draw breath. Then some portion of the membership complains ‘ why has so and so always got his nose in everything'. The answer is simple, somebody has to do it, since you aren't doing it, so and so has free run with it. Today ham radio has a more vital role in the safety of our communities than it had at the height of the cold war. The more real threat of terrorist activities coupled with our dependence on technology, cable TV, telephone, cell phones and, pagers, has created a necessity for amateur communication between government agencies and facilities. I'm to old and tired or I'm to busy is not an acceptable excuse, even if you can only contribute an hour of time, that's an hour someone else can stretch there legs then get back to the task at hand. Are you on the emergency call out list? Or at least get your name placed on a stand by list for when then main players get exhausted? You don't have to run the show but at least let someone know that if we do get in a tight spot, you will help. Do you have internet access? Can you download a sound file? Can you figure out how to play that sound file over a radio? Perhaps you can take some of the burden away from WA1VUU and help him with the amateur radio news line broadcast during the Sunday night 2m net. So the next time he goes out of town or his gymnastics on the cellar steps go awry, someone can fill the void until he returns. I don't know how or why things have gotten to the point that so few member are willing to contribute even a phone call ( or a postage stamp) for the club. I hope it is not because of some incident that happened over decade ago. If it is, why haven't you brought up this problem at a meeting? WE meet the first Thursday of the month, 8:00 pm, in the 4th floor cafeteria of the government center. I haven't bitten anyone in 30 years or thrown a punch in 20 and I won't make light of any concern. I need you to take some interest in what the club is doing, if you have an idea for a guest speaker and have one in mind, call them, find out what first Thursday of the month they have free and if they are willing to come. Then call me, most dates are open, June, July and December are field day planning, picnic and the annual business meeting. I have someone coming from West Mountain Radio for the October meeting, November is open.

My home phone number 203-531-9493 My email Andrew

ASK ELMER Dear Elmer, My friend and I just got our Technician Licenses and we've been attending the Dayton Hamvention for a few years now. This year we both got 2m/440 HT's so we could talk to each other while we wandered the indoor/outdoor flea market. We didn't know any of the area repeaters so we decided to communicate on a simplex frequency. Other than listening to make sure a frequency isn't in use by someone else, are there designated sub-bands for simplex communications inside the 2 meter and 440 bands? Signed, Probably off frequency. Dear P.O.F.

You bring up an interesting question. I too, have been attending the Hamvention for the last 20 years, and one of the concerns is where is there some open frequencies in order to communicate with other people in our group. I have good news and bad news for you. First the bad news. At an event such as the Dayton Hamvention, with over 20,000 hams in attendance, finding a clear frequency to operate, on either 2m or 70 cm is, as they say in that song from the Man of LaMancha, an impossible dream. The best you can hope for is to share a frequency with several other stations, and squeeze your transmission between theirs. What you will generally find is that several operators will be using the frequency simultaneously, but because of propagation, shielding due to buildings or other fixed objects and limited power and antenna location, interference is not too terrible. Here is some good news. With the modern radios, use of the CTCSS tones to mute your radio until a message is sent specifically to you or members of your group. This does not eliminate interference, but it does quiet your radio between transmissions. This is the same method commercial users have been using for many years to share a common repeater frequency. I'm afraid that the only areas you would find clear frequencies are on 222 MHz or 1.25 GHz bands. They tend to be less used due to the limited amount of commercial portable equipment available. I am not in any way recommending that you obtain equipment for these bands, unless you wish to operate on them beyond just hamfests. As you know, all amateur radio frequencies are shared frequencies. With the exception of those bands specifically divided by the FCC, all band plans are by gentlemen's agreement. Much of the VHF and UHF bands have been allocated to repeater operation, since this has become the most popular mode of operation. This has not in any way eliminated simplex, weak signal, satellite, digital or other specialized operation on these bands. Frequencies have been set aside on each of the VHF and UHF bands to accommodate these modes of operation. Rather than go into detail on the band plan of the 2 m and 70 cm bands, I would recommend you obtaining a copy of the ARRL Repeater Directory. This publication lists the band plans for all of the VHF and UHF bands as well as the frequencies and locations of the repeaters in North America (both US and Canada). As far as the areas allocated for FM simplex operation on the 2 m and 70 cm bands, they are as follows: On 2 m, 146.40 to 146.58 MHz and 147.42 to 147.57 MHz. With 146.52 MHz as the National Simplex Calling Frequency. On 70 cm, 445.0 to 447.0 MHz with 446.00 MHz as the National Simplex Calling Frequency. This does not mean that you can't use the portion of the band allocated to repeater inputs and outputs. If there is no repeater operating on that frequency in the area (at least for a distance of 50 miles in flat terrain), there is no reason for you not to use the frequency. Just keep in mind that all frequencies are shared and you want to be a good neighbor and considerate operator. I hope this points you in the right direction and enjoy using your radio at the hamfests. 73, Elmer Send your questions and comments to “ASK ELMER”, c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113 or e-mail

Dear Elmer,

In many of the Amateur Radio and popular publications I see references to a technology called “Software Defined Radio”. What are they really talking about, and how will it impact Amateur Radio?

Signed, Intrigued

Dear Intrigued,

With the blending of digital and analog communications and the very varied modulation techniques, the need for a large number of different transmitters and receivers in order to accommodate them all. In many ham shacks, there exists a transceiver with the ability to handle AM, CW, SSB, and FM modulation. With the addition of some additional equipment, namely a “TU” (Terminal Unit) or a “TNC” (Terminal Node Controller) and possibly a computer, which allows you to operate using some of the older and newer digital modes. As an example they would be (though not limited to) RTTY, Packet, Amtor, Pactor, PSK31, SSTV and a whole host of alphabet soup. The more modes and modulation techniques desired, the more external equipment must be added. A different type of radio, detector or processing method would be required for each of the new modes of operation. Over the years, theoreticians have devised mathematical representations of each of the many modulation techniques. This lends itself to using a computer to simulate all of the functions of a radio. One of the major limiting factors has been the speed of the digital systems. As microprocessors and other digital logic devices have become faster and large semiconductor memory has become physically smaller, engineers have been able to use digital signal processing in place of analog signal processing. The advantage of digital processing is that you can change the mode of operation by simply changing the software (programming). In analog processing, you have to change the circuit. One of the drawbacks to the use of digital systems, is that they simulate analog systems. In simulation, there is always some residual error (you can simulate something closely, but not perfectly). The amount of error is determined by the number of digital “bits” processed for each piece of information. The more bits processed, the less distorted the information will be when it is recovered. The more bits processed, the faster the digital devices have to be and the larger the memory required to store the information.

A Software Defined Radio is, by its very name, one where only software is required to change the mode of operation. This would simplify the Ham Shack by reducing the pieces of equipment required to operate the various modes that are currently in vogue as well as future modes with just a change in the software. Think of being able to download the latest operating mode off the internet and configuring your radio in one evening (or less). Of course the downside is to the manufacturers, who would not be able to sell you a new radio every few years. But fear not, as they will find a way to limit your ability to upgrade or to extract money from you in one form or another. (I’ll get off my soapbox now.) At this time, an all digital radio fully software defined for the HF bands is a reality. There are still some problems to be ironed out, but it is just a matter of time. The cost for these radios are not yet in the range of the average ham operator budget, but you won’t have to wait too much longer. The prospects for the future are exciting. With the blending of digital and analog techniques most anything will be possible.

73,

Elmer

ASK ELMER

Dear Elmer,
All of the radios that I have use a Phase Locked Loop Frequency Synthesizer for tuning. I can easily understand the crystal
oscillator controlled radio, but how can a single quartz crystal produce all of the discrete frequencies needed to tune my radio.
Signed Puzzled.

Dear Puzzled,
The principals of the Frequency Synthesizer were developed early in the 1950's. Over the years they have been refined and appear in many, if not most, of the communications and entertainment devices we use today. The basic principal on which the Phase Locked Loop (PLL) Frequency Synthesizer is bases upon is signal feedback, comparison and error correction. Below is a block diagram of a simple PLL Frequency Synthesizer.

To understand its operation, we must understand the operation of each block independently, and then as a system. The first block we will discuss is the “Voltage Controlled Oscillator” (VCO). This is a free running variable frequency oscillator operating at the desired frequency range. As an example, if you wanted to operate on the 15 meter band, this oscillator would have a frequency range of 21 MHz to 21.45 MHz. The way the frequency would be varied is with an external voltage using a varactor, rather than a mechanical variable element (such as a variable capacitor or inductor).
The oscillator would be defined by it's “Transfer Characteristic” which has the units of MHz/Volt. As an example, the 15 meter unit might have a transfer characteristic of 0.45 MHz/V. This means that 1 volt will change the oscillators output frequency over the full 15 meter band. The next block is the “Variable Ratio Frequency Divider”. This is the block that controls the tuning of the entire synthesizer. We won't go into details of how a divider works, but the divider is a digital circuit which is capable of dividing the frequency of the VCO by any number (including a fractional number like 1/213.5). The division ratio is selected by the tuning dial of the radio. Instead of it being marked in division ratios, it is marked in output frequency. The next block is the “Phase Comparator”. The circuit of this block can be similar to a diode balanced mixer or a digital circuit with a similar function. The purpose of this block is to compare the phase difference between 2 frequencies and produce a DC voltage proportional to the frequency and then the phase difference. Its transfer characteristic is in Degrees/Volt when the two frequencies being compared are within 1 Hz of each other. The “Reference Oscillator” block is generally a precision crystal oscillator at some sub-multiple of the Synthesizers output frequency. Its frequency is chosen so that the demands on the variable ratio frequency divider are kept to a minimum. As with anything in electronics, compromises have to be made between the complexity of the frequency divider and the output frequency of the reference oscillator. For our discussion we will not go into the details of the compromises, as the choices will be left to the system designer. The most important requirement for the reference oscillator is that it be very stable and its output signal have a very low phase noise. We hear the term “phase noise” frequently, but many do not understand what it is and why is it important. Without going into a very long and overly technical discussion, all electronic components have associated with themselves electrical noise being generated by the random motion of electrons. In oscillators, this noise modulates (like in your FM and AM transmitter) the output signal in a random fashion. The ideal oscillator would Have an absolute unvarying output frequency. Phase noise FM modulates this signal causing it to jump around in a random fashion. The greater the phase noise the more the frequency jumps around. Intuitively, you can see that if the frequency jumps around, reception and demodulation of the signal to obtain its message becomes increasingly difficult. Ultimately, if the phase noise is great enough the signal disappears into the noise and cannot be recovered. This is rarely the case for amateur communications except in EME and other weak signal transmissions. Needless to say, the lower the phase noise the better the signal. One characteristic of phase noise is that when you frequency multiply a signal, you also multiply its phase noise proportionally. This is one of the considerations in choosing the reference oscillator frequency for a synthesizer. The last block we will discuss is the “Low Pass Filter”. This is a very standard resistor capacitor low pass filter circuit, though in some implementations it can be an electronic filter using an operational amplifier. Its function is to remove any of the high frequency noise components from the output of the phase detector, as well as control the response speed of the system to external noise, and other instabilities. Without this filter, the circuit would probably be very unstable. A good way of visualizing the function of the filter, is to think of a weight, at the end of a spring hung from the ceiling of your room. If you were to pull down on the weight and release it, it would oscillate up and down for quite some time. If there were no losses in the spring and no air friction, the weight would oscillate forever. If, you would do the same experiment in a room filled with motor oil, the weight would not oscillate forever, but would settle down fairly rapidly. The low pass filter acts like the room filled with motor oil, to get the system to settle down to its steady state condition rapidly, and essentially stay there until something pulls the weight again. The only other item I wish to mention is that strange symbol (two parallel lines) at the output of the VCO and connected to the frequency divider. This is the symbol of a signal sampler. Its function is to sample a small portion of the output signal and send it to the frequency divider.
Well Puzzled, I think you will have to remain so until the next issue of the SQUELCH BURST.
Until then,
73 and a Happy New Year!
Elmer

ASK ELMER

Dear Elmer,
What's with having so many kinds of transistors? It seems to me that their absolutely essential characteristics are only polarity,
gain, frequency cutoff. power handling capacity and material (SI or GE). Since childhood I've been under the impression that
polarities the same (NPN or PNP) if I substituted a 2N yak-yak-yak for a 2N bla-bla-bla, the circuit will POSITIVELY, ABSOLUTELY, STUBBORNLY will not work. Izzat so? Speak, O Guru, thy novice is listening.
Signed Finiky
Dear Finiky,

To answer your question we have to look at two worlds, that of the Technical and the Commercial. From the technical point of view, Transistors are designed and built to perform a specific job. In doing so, many parameters are considered which you did not mention. Other important parameters, if it is being used in an RF circuit is its noise figure and stability, if used for a precision DC amplifier is its leakage currents and gain stability with changing current, and we must also consider its construction (mesa, planar, grown junction, etc). This is only the tip of the iceberg. To illustrate a point, many years ago I was responsible for the design a gain controlled audio amplifier project which used then popular series of grown junction transistors. At the time, several manufacturers claimed to manufacture this particular family of transistors. The amplifier was designed and several prototypes were built and extensively tested. We even substituted the transistors from several manufacturers to make certain that the circuit was tolerant to the variations found the transistors available. We could not try every manufacturer, but at least six or seven were tried and were found problem free. The amplifier was released to manufacturing, and the companies purchasing department went out obtain the components. One transistor manufacturer presented a very attractive price for the transistors, and guaranteed them to meet the published minimum electrical specs. A very large quantity of the transistors was purchased and the amplifiers were built. When the amplifiers were tested, they all failed. After several days of investigation, it was found that the transistors used, met the gross electrical specifications of the device, but having been made by a significantly different process, did not meet the detailed electrical specifications. At the time, some manufacturers were retesting the devices they made and if they met the gross electrical specs of a particular transistor, repackaging them, marking them and selling them with that part number even though they a significantly different part. Fortunately, that is not happening today. Does that mean that a transistor with a different part number will not work in your circuit? No, it does not. If the circuit is non critical, a device which meets the gross electrical specs will probably work fine. This is the basis of the replacement grade transistors (type SK, and NTE, etc.) available from many parts distributors. If, on the other hand the transistor is used in the input stages of a communication receiver or other critical application, then the exact part must be used, or one whose specifications very closely match that of the original device. On the commercial side, it is sometimes important to have a device, which is unique to a specific manufacturer. At one time, it was fairly easy and inexpensive to register a transistor and have a 2NXXX number assigned. Minor differences in the case or electrical specifications would qualify it as a new device. This was used for many years as a marketing ploy to get engineers to design in a manufacturers unique device. There are currently over 8000 registered 2N, 3N devices, of which, maybe 20% of them are unique electrically, and the others are minor variations either mechanically or electrically. These days it is somewhat more expensive and difficult to register a new device; so many manufacturers are relying upon house numbers, rather than formal registration. This permits them to claim unique characteristics for their devices, and copy write their part number so other manufacturers cannot use it. Fortunately, for all concerned, the detailed electrical and mechanical specifications for
most devices are available. This permits the engineer or technician to make an informed decision as to whether they must use a
specific device or can substitute a generic one. Most often, for simple projects, most any of several transistor types will work
without any difficulty.
Well Finicky, you must be the judge. Try it and find out. That is the fun of experimenting. Just remember, that smoke makes electronic equipment work. When you release the smoke, it stops working. Do not release the the Smoke !
73,
Elmer
Send your questions to “ASK ELMER”, c/o Marv Fleischman, N1AWJ, PO Box 113, Ridgefield, CT 06877-0113.

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Dear Elmer,
Field Day is coming up and I am a devoted environmentalist. I have been thinking of various methods of powering my QRP rig from natural, environmentally friendly sources. I can think of solar and wind power, but do you have any suggestions for a reliable power source?
Signed, Earthy

Dear Earthy,
There is a vast source of environmentally friendly energy that has remained untapped, but which has the potential to supply a
reasonable amount of emergency power in times of need. I have to admit, that until recently, I was unaware of the potential of this power source, which has been available for far more years than amateur radio has been around. The main stumbling block has been the interface between the power source and the equipment it is meant to power. Advanced technology in the processing, storage and distribution of power sources has come to the rescue. A primary requirement is to understand the sources method of power generation and its inherent distribution. Using this knowledge, we can design an appropriate method of extracting, storing and distributing this power in the most reliable, efficient and environmentally friendly manner. It is interesting, that during WW II, the military made use of remotely related, but environmentally friendly, method of powering a radio transceiver. The method that I refer to is the use of a hand powered generator used to supply power to a low power radio. One soldier would have the task of cranking the generator while another operated the radio. As I said, this is only remotely related, but you will see the connection (no pun intended, but if it works, why not). Another consideration is the method of containment and source of fuel for the power source. A significant amount of thought has to has been given to this problem, and I feel that a reasonable solution has been found. I don't think it is an optimal solution, but with the increased use of this source, undoubtedly improved methods will emerge. The power source in question produces a rather varied amount of electrical energy, depending upon its state of excitation. At minimum excitation, it produces a potential of about 25 to 40 volts at a pulse rate of 1 to 5 per second. At maximum excitation, it produces a potential in the order of 500 to 700 volts at a pulse rate of 100 to 200 pulses per second. As you can see, the power does vary considerably. Some method of storage and stabilization has to be employed to make it a useable power source. Fortunately the concept of a universal switching power supply has been used to power laptop computers for several years. These supplies operate over a voltage range of 80 to 270 v ac or dc, but with appropriate changes in design, can be made to handle the wider range from our power source. As to the storage, a lead-acid, nicad or any rechargeable battery would do that job nicely. As you can see, a reliable and continuous power source is quite practical. Even though the power source is a pulsating DC, I would retain the capability of handling an AC source, so that the polarity of the primary power source would not need to be considered. As far as fuel for the power source, it is natural, organic, fully bio-degradable, with no fossil fuel or synthetic fuel ever being used. To contain the primary power source, I would recommend a tank, at least 4 ft long and 2 ft wide containing at least 50 gallons of salt water, many salt water loving underwater plants. These plants should generate a reasonable amount of Oxygen into the water, as that is necessary part of the fuel required by the primary power source. A set of stainless steel electrodes, made from stainless screening, spaced about 3 feet apart connected to the input of the switching power supply. The screening should have large enough spacing between the wires to allow the solid fuel to pass through, but contain the primary power source. The wires should also be insulated and water resistant. The solid fuel should be dropped into the tank between the electrode and the tank wall and allowed to drift through the electrode screen as needed by the primary power source. When power is needed, the solid fuel is just dropped into the tank, and power will be generated to charge and maintain the battery charge. Periodically, spent fuel will have to be removed from the tank, but over a 2 day period this probably would not be necessary. If the tank were made of a transparent material such as Lucite or glass, you could watch the primary power source in operation. Once done with the need for the power source, one can display it in your home, as it would be of some interest to your friends and family. Actually, you would be one of the only ones in your neighborhood to have such a display, and it would always be ready for the next emergency. Were you to have several of these power sources, you could set up a QRP contest station, with one on every band. You would not have to rely upon commercial power at all for your operation. It presents quite an attractive alternative to what we are generally used to.
Well, Earthy, you are all set for field day or any other emergency situation. Let me know how it works out for you.
73, Elmer
PS. I forgot to mention that the primary power source was an Electric Eel.
73 and Happy April Elmer
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Dear Elmer,
I have an ADI AR-247, 220 FM Transceiver. Not the best unit on the
market, but it works fine. My only problem is low audio. I turned the
Deviation “± 5 kHz” up almost all the way, but audio is still low. It
works OK, but you almost have to swallow the mike. Microphone impedance
is 2.2 K?. Is there a low power 8 pin power mic on the market that
would help me get better audio? I don't want to “clip the hedges”, just
improve the audio a little. Thanks for your help.
Signed, “Mike-in-mouth along with foot”.

Dear Mike,
I must admit that your problem is not a unique one. Many operators have
not been happy with either the depth of modulation or the audio quality
of their microphone and radio. One of the more common tests that is
performed on the air is concerned with modulation quality. It is so
common, that I keep a small tape recorder in the shack which I use to
record and play back the received audio to assist in these tests. As
far as power microphones are concerned, the most common place to find
them is with suppliers of CB equipment. The probability of finding one
which would fit your particular radio is almost non-existent, but with a
8 pin connector from Radio Shack and a soldering iron, you can adapt it.
Radio Shack had (and may still have, on special order) an amplified
microphone, Part Nr. 21-1177 which can be adapted to your radio. You
will loose the touch-tone pad feature and any other control features
present on your current microphone, except for the push-to-talk. I would
suggest that you contact the manufacturer of your radio to see if they
have any suggestions or contact a company that specializes in
communications microphones such as “Heil Sound Ltd. 5800 N. Illinois,
Fairview Heights, IL 62208, (618-257-3000 or [email protected] ).”
Another possibility is that your radio may have an internal audio gain
control. Many radios do and they are usually used to limit the range of
any external controls, so that over modulation could not occur.
Inspection of the circuit diagram for your radio will indicate if you do
have one. If you do, it is a simple matter to open the radio and tweak
the control (assuming that it is not “maxed out” already). If you lack
a deviation meter to set this control up, you can ask a friend to
monitor your audio during a QSO and report on your audio. That's where
the tape recorder kept in the shack comes in handy.
This brings to mind a group of operators I know of who pride themselves
in very high quality communications audio whenever they are on the air.
They are 160 m AM'ers who spend a considerable time and effort to tailor
the amplitude and frequency response of their modulation to provide
almost commercial broadcast quality audio. I must admit that it is a
pleasure to listen in on the qso's of this group. I am not suggesting
that you do this with your radio, but it is interesting and at times
maddening to note the variations in audio quality produced by the
various radios on the air today. Especially the FM radios, which run
the gamut from great audio to a muffled mess, and should have, by their
very design, great audio. Well, Mike-in-mouth, I hope this helps you in
resolving your dilemma.
73,
Elmer
Send your questions to “ASK ELMER” c/o Marv Fleischman, N1AWJ, PO Box
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Dear Elmer, I have an ICOM 751A transceiver purchased in 1992. I'm not using it as much now that I have the Dell PC. I Pull the plug when not using it. (For safety reasons). I'm concerned about my memory. (In the Radio) Hi!. My manual tells me that the Lithium battery life is about 10 years, but could exceed that. There are no signs of abnormal operation. The manual also tells me not to attempt to change it myself. Am I safe to leave it as is for a while? My Motto as a rule is, adhering to the old adage. "If it ain't broke don't fix it" What is your advice? TNX and CUAGN 73 for now. Signed Mo Ray

Dear Mo, Many of the modern radios which are microprocessor based use various forms of backup power for their memory system. Three of the most popular are, primary long life batteries (ones that can't be recharged), secondary batteries (ones that are rechargeable) and “Ultra-Capacitors”. The “Ultra Capacitor” is a fairly modern device, which chemically simulates an extremely large capacitor with values in the Farad range. Ordinarily, capacitors made this large would be enormous in physical size, and not very practical. These “Ultra Capacitors” are large in value (think of 0.1 to 2 Farads at 3 V) and small in size, making them a good substitute for a rechargeable battery in ultra low current memory backup. When the radio is used, the power supply charges the “Ultra Capacitor”, and of course supplies power to the memory. When the radio is turned off, the “Ultra Capacitor” supplies a holding current to the memory chips, for, in some instances, as long as a year. The secondary (rechargeable) battery, acts very much as the “Ultra Capacitor”. It is capable of supplying somewhat more current then the “Ultra Capacitor” for a moderate time period. This method of memory supply backup can be found in many radios. The drawback to this system is that the early rechargeable batteries were not as reliable as the more modern batteries, and they are the most expensive battery system for the manufacturer of the radio to provide. The expense comes from the cost of the battery as well as the need for a recharging circuit. Modern memory systems use CMOS (Complementary Metal Oxide Semiconductor) memory systems which require very little current to maintain any data stored in them. Primary batteries using modern chemistries, such as Lithium Ion and Silver Oxide, have extremely low self discharge rates, that their shelf lives are in the order of 5 to 10 years. This makes them ideal candidates for unattended memory backup power sources. Many of the modern radios use these batteries for exactly that purpose. They usually admonish you not to change these batteries as they are sensitive to the excess heat from a soldering iron. The batteries, if not properly heat sunk could be damaged, or in some cases could break open or vent, releasing some of the caustic electrolyte. This can be a safety hazard if not properly handled. If done properly, then changing the battery is not a problem. It is important that you know the proper procedure for handling this type of battery. If you are in any way unsure, do not attempt it yourself, but send the radio to an authorized service agency for the battery replacement. Check the radio every month or so to see if the battery needs replacement. So Mo, as long as you know the battery is a go if the memory still shows, the frequency it knows! (Very bad “Iambic Pentameter”.) 73, Elmer

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Dear Elmer, Some operators was talking about adding a Isolator to a repeater. What is a Isolator? How does it work? Signed, Al One,

Dear Al, When designing a transmitter you would try to have the output amplifier terminate into its designed impedance (ie., 50 Ohms). Antennas, duplexers, etc are generally not that well made or ideally located, that they always present a constant impedance to their source (the radio). An ideal solution would be a device which would always present a constant impedance to the radio no matter what it was terminated into. One partial solution to the problem is the use of a Transmatch between the radio and the antenna. If the antenna impedance varied, you must retune the Transmatch. With the advent of ferrite materials. microwave engineers have found a solution to this problem (and several others that they have had) with a device called a Circulator.

A Circulator allows RF energy to flow in one direction only. A special case of the Circulator is called an Isolator. The circulator consists of 3 transmission lines, each 120 degrees in electrical length, connected end to end (as in a circle or triangle). Some microwave engineers call this configuration a “Rat Race”. Each connection point is a port into which you can either introduce or extract an RF signal. The transmission line is surrounded by a block of ferrite material, and a small permanent magnet. When an RF signal is introduced into one of the ports, an electromagnetic field is generated in the transmission line. The purpose of the ferrite material is to direct the RF electromagnetic field to travel in one direction. The permanent magnet is used to magnetically bias the ferrite material so that it can direct the electromagnetic field. There is also some shielding to prevent the earth's magnetic field from affecting the ferrite material. Let us call each of the ports by a number, such as port 1, port 2 and port 3. With our ferrite material the RF travels in a clockwise direction. It does not make any difference which junction we start with, as long as we go in one direction. If we were to introduce an RF signal into port 1, it would travel to port 2 and then to port 3 and back to port 1. If we terminate port 2, all of the RF energy would flow to port 2, and nothing would continue to port 3. If we were to move the termination from port 2 to port 3, all of the RF would bypass port 2 and go to port 3. If we were to permanently terminate port 3 with 50 Ohm load, we have magically changed the device from a Circulator to an Isolator. If the output of your transmitter is connected to port 1, and the antenna is connected to port 2, all of RF will flow to the antenna. If the antenna is mismatched (not 50 Ohms), the reflected signal from the antenna will enter the isolator at port 2 and flow to the 50 Ohm termination at port 3. None of the reflected RF will flow back to the transmitter at port 1. This effectively isolates the transmitter from its load (antenna), hence the name Isolator. There is a caution when using any ferrite device in a transmitter.

Nothing is perfect. Ferrites are not a linear material. Doubling the RF does not necessarily double the magnetic field in the ferrite. Local temperature changes can effect the ferrite material, especially if it absorbs some of the RF. This can cause harmonics to be generated as well as the possibility of other RF products. It is important to always follow an Circulator or Isolator with a low pass or band pass filter to remove these unwanted signals.

I hope this brief explanation helps you to understand the workings of a Circulator and Isolator. Any further information would be obtained from researching texts on Microwave passive coupling structures using ferrite materials. Be prepared for a lot of math.

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Dear Elmer: When working with wire antennas, is a simple SWR meter sufficient to tune the antenna or do I need something else? Signed, Wired Up.

Dear Wired Over the years there have been many tools (instruments) pressed into service by the amateur community in the setup and testing of wire antennas. I do have to comment, albeit tongue in cheek, that there are as many different antennas as there are amateur operators. Most anything that can radiate an electromagnetic signal can be used as an antenna, and over the years, probably has been. There are many instruments being used to test out antennas, from noise bridges and grid dip oscillators to network analyzers and dedicated antenna measurement systems (one specifically made by Agilent, ie HP). The function of an SWR meter is to determine if the transmission line and the termination (load, antenna, etc.) match each other and possibly the impedance of the generator. I am making the assumption that the SWR meter you are using is one which has its own built in generator such as the MFJ units. For setting up simple resonant antennas which were designed to be matched to 50 or 75 ohms, you can generally use these SWR meters to aid in trimming these antennas to resonance. If, on the other hand, you are attempting to set up an antenna using a random wire or other non resonant antenna, the SWR meter will not be of much use, and instruments such as noise bridges or those which measure the antennas impedance directly and report its resistive and reactive components will be of greater use. Another word on resonant antennas. An instrument that has been around for many years, the “Grid Dip Meter” can be used to trim an antenna to resonance irregardless of the antennas characteristic impedance. I am saddened to say that this versatile instrument has fallen out of favor in recent years, but for the amateur radio operator it can be a highly effective measuring instrument for antennas and other resonance measurements. MFJ offers an adapter for its SWR meters converting them into a “Dip Meter”. Were I given a choice of basic instruments for antenna setup, I would choose a Grid Dip Oscillator first, a Noise Bridge (or other impedance measuring device) second and the SWR meter third. I trust that this will get you all strung out. 73, Elmer

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Dear Elmer: Recently picked up a D-104 microphone, because I have always liked the looks of it and for the 'nostalgia' factor. It appears to be an unaltered crystal element.. Any chance I can alter the characteristics of the mike electronically so that I can use it with my Ten Tec Omni V or will it require a new element? Voice from the Past.

Dear Voice, The Astatic D104 microphone was probably one of the most popular desk microphones used by Ham radio operators. There are many different ways a microphone can be constructed. Some of the more popular types are dynamic, ribbon, electret, ceramic and crystal. All of these have their advantages and disadvantages. The most common microphone construction is the electret. One of the considerations when using a microphone is its impedance. The dynamic and ribbon microphones, as well as the electret are generally low impedance microphones (600 ohms or less). The crystal and ceramic microphones are high impedance (10K ohms or more). Since we are discussing the D104, which has a crystal element, it is a high impedance microphone. The crystal element which is made of a piezoelectric material such a Rochelle Salts or Tourmaline, both naturally occurring elements. A piezoelectric material is one which generates a voltage when stressed mechanically. The piezoelectric device you are most familiar with is a Quartz crystal. It can generate a relatively high voltage but at an extremely low current, hence its high impedance. Older radios were generally made to accommodate these types of microphones. In the modern radios, the microphone input is usually a 600 ohms, to accommodate the dynamic or electret devices. Many of the transmitters supply a bias current for the electret microphone as well. The bad news is that you cannot connect the D104 directly to your radio. The good news is that it takes a simple external device to get everything working correctly. You don't need an amplifier or any other powered interface between the D104 microphone and transmitter, unless you want one. A simple matching transformer will do the job quite well. I would suggest that you adapt a Radio Shack 274-016 plug/adapter transformer to the D104 microphone. The 274-016 should be disassembled so that you can connect directly to the transformer leads. The high impedance side of the transformer is connected to the 1/4 inch plug and the 600 ohm line is connected to the XLR connector. You wan to connect the high impedance to the microphone output. The low impedance side is connected to the transmitters microphone connector. A jumper from the low side of the microphone and transformer primary (high impedance winding) to the low side of the transformer secondary (low impedance side) and the shield of the cable connecting the transformer to the radio. If you wish to construct an electronic interface for the D104, I recommend the June 2002 issue of QST on page 61 and 62, “Hints and Kinks”, “More on the D104” by G. Heidelman, K8RRH. You can construct as simple or complex an interface as you wish using this article. The D104, having a crystal element, may produce require some attenuation as it is quite sensitive. If your radio has a microphone gain control, no problem. If you don't have a microphone gain control, you may have to add an external one using a 1K potentiometer between the transformer secondary and the radio. The top of the potentiometer connects to the high side of the transformer secondary, the bottom of the potentiometer to the common/ground and the wiper arm to the transmitter's microphone input. I have had many QSO's with operators using the D104, and I was quite impressed with the audio “punch” that it had. I hope you have many enjoyable QSO's using the D104. 73, Elmer

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Dear Elmer.
I read an article in 73 Magazine about the “Round Robin” Marconi Antenna, which is just a length of 1/4 wave twin lead, a shorted 1/4 wave stub. The article claim that if one side of this is fed a signal, this will act as an effective antenna. The other wire of the 1/4 wave acts as a counterpoise. I wonder-plenty! Can this be a really good radiator if the counterpoise is that close - figure this! It should be possible to make a “Quarter Wave Rat Tail” by using a 1/4 wave of coax, shorted at the far end and with the braid connected to the hot (side) and the center connected to the grounded (side). Essentially reversed connections. If this is so great, why haven't more articles been written about it?
Signed, Rounded

Dear Rounded,
Let me start out saying that the claims of many of the antennas in the various publications should be taken with a grain of salt.
Do they radiate? Of course the do. How well radiate is another question. Not being able to obtain a copy of the particular 73 Magazine article you reference, I cannot comment on their specific performance claims. I think we should look at a Marconi antenna so that you can compare them intelligently. A Marconi antenna is defined as any vertical antenna operated against a counterpoise or radial system. With this definition, most any vertical that can be assembled, as long as it has a counterpoise or ground plain qualifies. It does not indicate whether or not the antenna will work effectively. Modeling the antenna in question would be an easy way to test the design to determine if it pays to build it. To do this I would suggest using any of the available modeling programs based upon NEC-2. Two of them which come to mind are EZNEC and NEC Win commercial programs or NEC-2 available free via the internet (http://www.nec2.org/). I would suggest reviewing the series of articles in QST on antenna modeling (Dec 01 to Feb 02) before using any of the software.
With respect to using a piece of coaxial cable with the center conductor and shield reversed as an antenna, would probably radiate, but not very well. I can't really speculate if it would match your 50 Ohm feed line. Using coaxial cable to make an antenna is presently used in the Station Master collinear antenna. There are a series of 1/2 wave and 1/4 wave sections, with their shield and center conductor connections alternately reversed to form a gain antenna.
One of the enjoyable facets of the hobby is the ability to experiment with antennas of your own creation. I would recommend that you try it and see if and how well it works. If its performance is equal to or better than a rubber ducky, you can publish your results and possibly have an antenna named after you. If it works very badly, but someone tries it, you may not want your name to be associated with it. That is your decision.
I hope I have both answered your question and inspired you to experiment further with antennas. I would also recommend, to those serious about antennas and their modeling, that the register and take the ARRL's “Antenna Modeling Course”. It is well worth the time and effort you would need to devote to this course.
73,
Elmer

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Dear Elmer: I know that you have written on this subject before, but

would like to see a review on the matter of frequency counters and how to adjust them to WWV.

Signed , 39 and counting.

Dear 39,

It is important to periodically calibrate your equipment, whether it be your radios or a piece of test equipment. Both scientific and industrial laboratories maintain a rigid calibration schedule for their equipment to guarantee the accuracy of their tests and products. Many years ago, the industrialized countries of the world agreed upon a series of physical standards, so that something measured in one country will be the same in another. Our government agency is the National Institute of Standards and Technology under the Department of Commerce. Among the standards they maintain is the standard of Time, which by a simple bit of arithmetic becomes the Standard of Frequency. One of the many services they provide is the broadcast of a radio signal derived from the National Frequency Standard, housed in Fort Collins, Colorado. The frequencies that are broadcast are 60 KHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. The accuracy that is maintained is better than 1 part in 10^-14. This is far more accurate than you would need in practice unless you were manufacturing frequency or time standards. Even though the transmitted frequencies are so accurate, propagation effects degrade its accuracy by the time it reaches our location. For short term measurements, the local accuracy is probably somewhat better than 1 part in 10^-7. This translates to an error in the order of 3 Hz at 30 MHz. For measurements made on amateur radio equipment, this accuracy should be more than sufficient. Unless you have a laboratory grade frequency counter with a precision oven controlled reference oscillator, most counters are only accurate to 1 part in 10^-6 or 30 Hz at 30 MHz.

In order to calibrate your counter, you require a AM radio capable of tuning to 20 MHz. It in itself need not be accurate, as long as it receives the signal from WWV. Method 1: Connect an antenna consisting a short piece of wire to your counters reference oscillator output, and it should be near the AM radio’s antenna jack. You should be able to detect the harmonic of the counter’s reference oscillator in the radio at 20 MHz. At the same time the radio is receiving a signal from WWV. There will be a audio beat note present due to the mixing of the two signals in the receiver. Tune the frequency set trimmer in the counter to minimize the tone of the beat note. Ideally you want to hear a beat note of less than 1 Hz, which will sound like a popping noise in the loudspeaker or headphones. Counting the beats per minute will indicate how close you are to WWV. If there is no output connecter for the counters internal reference, it may be possible to pick up a signal by placing the counter close to the radio.

Method 2: In the event that your counter does not use a 1, 5 or 10 MHz internal reference, but operates from a 3.579545 MHz color burst crystal, an indirect method must be used. This requires an AM-SSB transceiver capable of receiving on 20 MHz and transmitting on 21 MHz and a dummy load. The radio will be used as a transfer oscillator. Set the power output of the radio to its lowest setting. Set the radio on SSB and tune the radio to 20 MHz. Zero beat the radio with WWV. Note the difference between the dial reading and the actual zero beat. Set the radio to 21.0 MHz, and loose couple the counter to the output of the radio near the dummy load. This may require some playing to obtain a large enough signal to operate the counter. Make sure the offset measured at 20 MHz multiplied by 1.05 is added to the frequency setting. The 1.05 makes up the frequency difference between 20 and 21 MHz. Switch the radio to AM and key the transmitter. Adjust your counters reference oscillator until the counter reads 20.000 00 MHz. With care, this calibration method should get you to within 10 Hz of the actual frequency.

A note of general caution. If your counter is not able to resolve 10 or 100 Hz, the trying to calibrate it to this precision may be a waste of your time. A basic rule of thumb is to calibrate your system to 1/10 its resolution.

Ordinarily, a standards laboratory tracks station WWVB at 60 KHz using specially designed receivers to obtain accuracies approaching that of the US Frequency Standard itself and can take several days.

I hope this gave you some insight into the rigors of calibrating frequency counters. Good luck on doing yours.

73,

Elmer

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Dear Elmer,

I am new to the world of HF radio. I am thinking about buying a new station consisting of a HF rig, Amplifier, Antenna tuner, Monitor Scope, SWR meters, Key, Mike, possibly a Phone Patch and ATV setup as well.
My question is with all this equipment, how do I set it up? In what order do the pieces go together?
Signed: KB 1- Befuddled

Dear Befuddled,
Assembling a station is an exciting time. You have a an opportunity to craft a station which suits your budget, personality and operating style. I have seen many hams assemble a station by randomly selecting equipment based only on cost. If you are on a very tight budget, this may suit you, but you would probably never be comfortable or satisfied with your station (as if we hams ever are). My personal recommendation is to choose your equipment carefully. Ask yourself, how much space do you have for equipment and most importantly antennas.

The second question, of equal importance is, what is my budget? With that as a starting point you can
choose your equipment. The most important piece of equipment is the Transceiver. I would spend most of my effort in choosing a suitable unit, as this piece of equipment would be the heart of your station. All of the other equipment will be used to augment and accessorize the radio. Once the Transceiver is chosen, you can look into the auxiliary equipment made by the radio's manufacturer or by independent manufacturers. Keeping with the radio's manufacturer's equipment will generally result in a seamless integration of the accessories, as they were generally designed to be used together. This should not in any way dissuade you from looking at other sources of equipment. Let yourself be guided by what “bells and whistles” you want in your equipment, and not what someone else thinks you should have.

Be prepared to do some assembly of cables and adapters to tie everything together. One of the primary considerations is your antennas. If you don't have an antenna which can handle a kilowatt, you would be ill advised to purchase a KW Power Amplifier, since you couldn't use it. Keep in mind that in setting up a station, the equipment is only 1/3 of the equation. The antennas are a third and the station power and grounds, etc are the last 1/3.

I would suggest that you plan out your station on a piece of graph paper. This will help you with the placement of your equipment and the location of any new power outlets, both RF and power line grounds and antenna connections. This may prevent your station from being an assemblage of one piece of equipment piled upon another. The order in which the equipment is placed or assembled is entirely up to you. There is no formula, but from my own experience, the location of the transceiver should be the central point of your operating position. The ARRL Handbook for Radio Amateurs has a chapter devoted to setting up a station with many helpful hints. There is the Heil Ham Radio Handbook with a chapter on setting up your station. A little thought and preplanning will go a long way making your station a place which is comfortable for you.

I hope you have fun setting up your new station and get many years of enjoyment operating from it.
73,

ASK ELMER

Dear Elmer, I always seem to be mystified by the magic of radio transitions. To me it all seems to be like magic. Whenever something seems mysterious it brings questions to my mind. Here is a subject that I have wondered about for quite a while. It is this 50 ohm thing. It seems to me that every single amateur transmitter wants and expects to have it's output matched to a 50 ohm impedance. It does not seem to matter for which band the transmitter is built. This brings a few questions to mind. I am pretty sure that most of them are easily answered. 1. Why have all manufacturers settled on 50 ohms, why not 75 ohms, 100 ohms, 300 ohms or any other number? 2. Is 50 ohms some magic number for which transmitters are very easily built? 3. Would it be very difficult to build transceivers that would easily match some other impedance such as 300 ohms which is closer to the impedance of some antennas? 4. Is this a standard that will always stay with us?

Always Mystified Dear Mysti, I imagine that this is a question that is on the minds of many ham operators. Would you believe, Mysti, that there is a reason for the choice of 50 Ohms as well as for special purposes 75 and 90 Ohm cables. As you well know, if you take an ohmmeter and measure the center conductor resistance of a piece of cable, you will get a very low resistance reading. Conversely, measuring the resistance between the center conductor and shield will indicate nearly an infinite resistance. The 50 Ohm, etc. has nothing to do with the DC resistance of the cable. The 50 Ohms in question is known as the “Surge Impedance” of the cable. In order to measure it you would require a very fast responding ammeter (a High Frequency Oscilloscope will do quite well for this measurement). Were you to connect a battery through a switch and the ammeter between the center conductor and shield of the coaxial cable, and then close the switch. The piece of cable should be moderately long for a fair test. If you measure the maximum current, it would be the battery voltage divided by the surge impedance of the cable. Now that we got that out of the way, why 50 Ohms? You will have to take this on faith, because I won't go into the math using Maxwell's Equations, but if you calculate a cable's loss as a function of its impedance for a given dielectric material (air, polyethylene, Teflon, etc.), you will find that for air, a 77 Ohm cable is ideal. For Polyethylene, which was the material available at the time (around 1940), 52 Ohms was the ideal value. So for a minimum loss cable, 50 Ohms was adopted. Actually this is quite convenient. A dipole antenna is 75 Ohms (one of the reasons 75 Ohm coax is used in TV systems) so they have 75 Ohm cable. At one time in the past, transmitters used tuned output circuits (as do most KW linear amplifiers). These tuned output circuits were able to match a wide variety of impedances. Manufacturers used to specify that their transmitters will match anything from 40 to 600 Ohms. The primary reason that modern transmitters are set to a constant impedance output, is that the power stages are broad banded. They do not require tuning. It would be impractical to do in transmitters what they do in the power industry (like CL&P or Con Ed), have the output stage as a constant voltage line (Zero Impedance), so that you can connect anything to it. The amount of excess power you would have to generate would be horrendous. It is infinitely more practical to have a constant impedance transmitter and use a Transmatch to transform its impedance to match your feed line and antenna. It is also very convenient to interconnect equipment using the same types of cable and connectors. By the way, the original UHF and BNC connectors were not impedance matched to their cable. This has been corrected in the modern connector, primarily the BNC connector, not necessarily the UHF connector. For HF thru VHF, this is not too critical, but be careful at UHF and very high power systems. Will this 50 Ohm standard always be with us? My crystal ball is cloudy in this respect. I would imagine that it will, at least for amateur radio use, but anything is possible. You never can tell, the music industry may claim they have the copy write on 50 Ohms and start taking everyone to court under the Digital Millennium Copy write Act. With that in mind, I hope you have been demystified. 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.