++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 19 Mar 2001 04:21:10 -0000 From: "Ed Juge" Subject: [Elecraft] Good low-power wattmeter? I'd appreciate opinions on a good, ACCURATE, low-power HF wattmeter? I seem to have at least three choices... The Oak Hills unit sold by Morse Express looks good but I'd like to have a little more than 10 watts max for use on my K2. Anyone care to comment on its claimed "5% of full scale" accuracy? The MFJ-864 is about the same price. Anyone know how accurate it is? I own a Bird 43, but the lowest power HF element they offer is 50 watts. (I was hoping for 25.) The only price I've seen on the 50H element is about the same as the above two wattmeters. That still could be my best bet. Comments? Thanks... Ed, W5EJ ++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 18 Mar 2001 21:29:52 -0800 From: "Gene Langendorff" Subject: RE: [Elecraft] Good low-power wattmeter? Ed, I've read good things about the Ten Tec T-kit Model no. 1202 SWR/Power meter kit. Sells for $59.00 direct from Ten Tec. It has two ranges, 20 and 200 watts, but I understand that it can easily be modified for one tenth of that so your ranges would then be 2 and 20 watts. Check it out at http://www.tentec.com/Tk1202.htm. They don't mention what its accuracy is but it's supposed to be good. 73, Gene K6TTM +++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 18 Mar 2001 23:05:39 -0700 From: "Dick Knapp" Subject: [Elecraft] Good low-power wattmeter? I have a Diamond SX-200 SWR and Power meter. I think I learned of it from this list. Costs abt $90 and has 5, 20, and 200 watt scales. It has worked well for me. Dick Knapp KC7TUP ++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 19 Mar 2001 05:35:22 -0700 From: "Ken Lotts" Subject: RE: [Elecraft] Good low-power wattmeter? Ed, Here are my two cents. I was looking for the same thing and I just *recently* (last week) ordered two watt meters (they still have not arrived). The first one is the Oak Hills unit. It looks too useful.. a great price too. I am not at all worried that it is well worth the money I sent. (As it turns out, it is back ordered by about two weeks). The second one is the LDG DWM-4 (it should arrive today). http://www.ldgelectronics.com/dwm-4.html The neat thing about the LDG unit is the supposed accuracy. LDG uses separate sensors for HF Power Ranges 15 and 150 watts. Their online PDF (written by QST writer Dwayne Kincaid WD8OYG) said "the overall accuracy as compared to a Bird wattmeter is better than 0.1%" Also stated in the PDF: "The displayed values are derived from a huge look-up table stored in the microprocessor. These table values were taken from the readings of a Bird 43A wattmeter. The table was derived by comparing the A/D reading supplied by the HF and VHF/UHF sensors for various RF readings on the Bird meter. The Bird readings were then graphed, and extrapolated where needed to fill in the gaps." I bought a QRP auto tuner kit from LDG a few years ago and found it a reasonably good value. So .. I sent LDG my money last week and am waiting for the factory assembled and aligned DWM-4 with a QRP and medium power HF sensor to arrive. (I hope that it is as good as it claims to be). Ken aa7jc ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 19 Mar 2001 10:22:08 -0600 From: "Stuart Rohre" Subject: Fw: [Elecraft] Good low-power wattmeter? A great buy for Kit Builders is the Ten Tec power and watt meter kit at $49. It has two pick up sections, and an amplified meter. There is a HF section, and a VHF section, which still has relative use on 440 MHz. The advantage of having 2 m and 6m is quite a plus, as then one Power meter can serve most ham uses. It can be powered from internal 9 volt battery or external power thru a coaxial power DC connector. Best of all, besides its basic 20 watt and 200 watt scales, it can be recalibrated for QRPp use with a 2 watt scale with just a twist of a cal pot. After calibration, it agreed with two commercial power metering standards. 72, Stuart K5KVH +++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 19 Mar 2001 10:22:08 -0600 From: "Stuart Rohre" Subject: Fw: [Elecraft] Good low-power wattmeter? A great buy for Kit Builders is the Ten Tec power and watt meter kit at $49. It has two pick up sections, and an amplified meter. There is a HF section, and a VHF section, which still has relative use on 440 MHz. The advantage of having 2 m and 6m is quite a plus, as then one Power meter can serve most ham uses. It can be powered from internal 9 volt battery or external power thru a coaxial power DC connector. Best of all, besides its basic 20 watt and 200 watt scales, it can be recalibrated for QRPp use with a 2 watt scale with just a twist of a cal pot. After calibration, it agreed with two commercial power metering standards. 72, Stuart K5KVH ++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 20 Mar 2001 20:27:23 -0800 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Good low-power wattmeter? If you want to build an accurate wattmeter at home, check out the Tandem Match article that has been in the ARRL Handbook (page 22.33 in the 2001 edition) and ARRL Antenna Book for the last decade. It can be calibrated using only a digital voltmeter and will achieve an accuracy of +/-0.1 dB for powers above 1 watt, and an SWR accuracy of 5%. SWR can be measured with only 100 mW of power if the automatic power on circuit is disabled. There is a circuit board from FAR, but its not as nice as an Elecraft board (no plated through holes and no nice assembly instruction manual). This wattmeter provides better accuracy than most hams need, but you can build it at home with no expensive test equipment and achieve as good or better performance than a Bird wattmeter. - -John KI6WX +++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 20 Mar 2001 20:49:48 -0800 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Good low-power wattmeter? - ----- Original Message ----- From: "Ron D'Eau Claire" To: Sent: Tuesday, March 20, 2001 8:11 PM Subject: RE: [Elecraft] Good low-power wattmeter? > At very low powers the barrier voltage of the diode starts to rival the > amount of r-f voltage, and that will seriously impair the accuracy of the > system. In that case you can apply a known d-c voltage to the r-f input and > see what your DMM measures at the other side of the diode to create a > 'calibration chart' for very low voltage levels. That's what you Lake > instrument is probably doing when you calibrate it with a variable voltage > input. > The peak current in an AC detecting diode is many times higher than the DC current through the diode. If you want to determine the diode calibration with a DC source, one needs to decrease the load resistance when doing the calibration. Experimental data I have indicates that increasing the DC current by a factor of 10 gives a reasonable result over a wide power range. This means that if the load resistor (this is the resistor from the DC side of the detector to ground) on the diode is 100K when detecting RF, then the load resistor for calibration should be decreased to 10K. - -John KI6WX +++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 20 Mar 2001 22:15:37 -0700 From: "James E. Fuller" Subject: Re: [Elecraft] Good low-power wattmeter? At 09:27 PM 3/20/01, John Grebenkemper, KI6WX wrote: >If you want to build an accurate wattmeter at home, check out the Tandem >Match article that has been in the ARRL Handbook (page 22.33 in the 2001 >edition) and ARRL Antenna Book for the last decade. That's an excellent construction article, and I have been looking at it thinking that it would be a good idea to build one. I also really like the similar circuit and ideas in Roy Lewallen's article in February 1990 QST, available on the ARRL TIS site, and apparently based on your earlier work. Would you comment on Roy's "Simple and Accurate QRP Directional Wattmeter"? Thanks, - -- Jim Fuller +++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 20 Mar 2001 23:02:09 -0800 From: "Ron D'Eau Claire" Subject: RE: [Elecraft] Good low-power wattmeter? John, KI6WX, wrote: "The peak current in an AC detecting diode is many times higher than the DC current through the diode. " Very true if you have a significant voltage difference across the diode so there is significant current. The simple peak reading a-c voltmeter circuit I described is at its best when no current is flowing. That's why a very high impedance (at least 10 megohm input DMM) is best to measure the d-c voltage across the cap. The diode charges up the capacitor so the only current flowing through the diode is whatever is needed to replace leakage and current drawn by the DMM. And, of course, the DMM draws only whatever current is needed by its 10 megohm input impedance. Maybe I made the explanation as clear as mud - I'm good at that - but the circuit I am talking about is the same basic one used in the K2, most r-f probes and can be found in virtually every Handbook. In r-f probes there are often a few additional parts, especially a 'scaling' resistor that works as a voltage divider with the DMM to provide direct readout of the rms value instead of the peak value of the r-f waveform. Indeed, anyone with a decent r-f voltmeter probe and a good dummy load already has a great QRP wattmeter at hand. Ron AC7AC K2 # 1289 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 21 Mar 2001 08:31:28 -0500 From: "Don Wilhelm" Subject: Re: [Elecraft] Good low-power wattmeter? Folks, Notice that the note below is from the original author of the Tandem Match, so John should know what he is talking about. I have also been eyeing the Tandem match, and have done a bit of modeling with a low power 20 dB directional coupler. This coupler variation has been described in several printings of the Tandem Match article under the sub-title "Design Variations". It uses only 10 turns on the toroids (but is otherwise the same). The advantages are that its power range will lower to 150 watts max with a 1mW minimum. The unit will auto-switch on at about 150 mW, and the frequency range reportedly increases to about 150 MHz due to the lower length of the wire on the toroids. The low power end should keep the milliwatters happy, and the high end of the range should do just fine when the K2 has its high power option installed. I found this additional information in the ARRL Antenna Book (18th Edition) on page 27-16, and my 1994 ARRL Handbook, so I'm not certain when this information stopped appearing - likely when the High Power coupler was included. (John, I just wonder why you didn't mention the 20 dB coupler). I will be ordering the boards from FAR Circuits soon. 73, Don Wilhelm -Chapel Hill, NC W3FPR home page: http://www.w3fpr.webprovider.com QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 21 Mar 2001 08:42:41 -0500 From: "Don Wilhelm" Subject: Re: [Elecraft] Good low-power wattmeter? Jim and all, Roy LeWallen's "Simple and Accurate QRP Directional Wattmeter" is a good one, and what I currently use. I built mine on the FAR Circuits board. This is also the basis for the WM-1 and WM-2 wattmeters as far as I can tell. With the diode compensation circuit, it is accurate down into the low milliwatt range. (Don't forget to match the diodes - it is important to the accuracy) The power range is limited to 10 watts, and that is a problem now that I am considering the KPA2. My only real problem with it is that I tried to save battery power by not including a "power-on" light, and sometimes leave it ON, and run down my battery - remove screws, replace battery, replace screws, vow not to do that again. (one day I may try an auto-on circuit like from the Tandem Match design. 73, Don Wilhelm -Chapel Hill, NC W3FPR home page: http://www.w3fpr.webprovider.com QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net +++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 21 Mar 2001 10:12:35 -0500 From: "Don Wilhelm" Subject: Re: [Elecraft] Good low-power wattmeter? Matching diodes is easy. You need a battery and a series resistor (plus the diode). Measure the voltage across the diode with a DVM. You will find that not all diodes have exactly the same voltage drop. Select them into piles - I try to match to the nearsest 0.01 volt or closer, so you need a DVM capable of measuring down to 10 mv - 1 mv is better. I use a 9 volt battery with a series resistor of about 1000 ohms which limits the current to 9 ma. or less. (check the specs for the diodes you are testing to make sure you don't exceed the typical current rating). Connect the diode in series with the resistor. You should read a voltage across the diode of 0.3 volts for a germanium or 0.7 volts for a silicon (if the DVM reads 9 volts, the diode is backwards - reverse it). 73, Don Wilhelm -Chapel Hill, NC W3FPR home page: http://www.w3fpr.webprovider.com QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net ++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 21 Mar 2001 19:42:01 -0800 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Good low-power wattmeter? Jim; The detector circuit used in Roy Lewallen's article is essentially the same one I used in the Tandem Match other than he used germanium diodes. I still prefer the use of 1N5711 diodes because their reverse saturation current is 2-3 orders of magnitude less than a 1N34A, and in my experiments I was able to get less error at low power with the 1N5711 even though they have a higher voltage drop. The directional coupler circuit in Roy's article is a variation on the Bruene coupler. In this circuit, a pair of transformers is used to do the voltage division rather than a capacitor voltage divider. I have never measured the transformer only version, but measurements I took on the more standard capacitor divider Bruene directional coupler (used in the KAT2) showed considerable frequency variation of more than 1 dB from 1.8 to 54 MHz. Most of this variation was due to deviations from ideal components due to stray capacitance and unwanted magnetic field coupling. I went to the dual transformer approach used in the Tandem Match because these parasitic effects essentially cancel each other. The two transformer directional coupler used in the Tandem Match shows less than a 0.1 dB variation from 1 MHz to more than 70 MHz. If you want to make a simpler version of the Tandem Match without all of the analog computational circuitry, one could use Roy's detector circuit (preferably with 1N5711's and R3=R4=1 Meg and R5=100K) and the directional coupler used in the Tandem Match. - -John KI6WX - ----- Original Message ----- From: "James E. Fuller" To: "Elecraft Mailing List" Sent: Tuesday, March 20, 2001 9:15 PM Subject: Re: [Elecraft] Good low-power wattmeter? > At 09:27 PM 3/20/01, John Grebenkemper, KI6WX wrote: > >If you want to build an accurate wattmeter at home, check out the Tandem > >Match article that has been in the ARRL Handbook (page 22.33 in the 2001 > >edition) and ARRL Antenna Book for the last decade. > > That's an excellent construction article, and I have been looking at it > thinking that it would be a good idea to build one. I also really like the > similar circuit and ideas in Roy Lewallen's article in February 1990 QST, > available on the ARRL TIS site, and apparently based on your earlier work. > > Would you comment on Roy's "Simple and Accurate QRP Directional Wattmeter"? > > Thanks, > > -- > Jim Fuller ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 21 Mar 2001 20:40:29 -0800 From: "John Grebenkemper, KI6WX" Subject: Fw: [Elecraft] Good low-power wattmeter? Ron; The problem with the DC calibration and detector impedance is that it ignores the reverse saturation current of the diode. With 1N34, this current, Is, is between 0.1-1 uA. Whenever the diode is reversed biased, a current equal to Is flows through the diode independent of the voltage across the diode and it will reach this current with less than 50 mV reverse voltage on the diode. If your detector output is 1 volt into a 10 Meg DVM, you will have 0.1 uA flowing into the load resistor and as much as 1 uA flowing through the diode when it is reverse biased. When you try to compensate the detector drop with a DC voltage of 1 volt, you only have the 0.1 uA flowing through the load resistor and there is no current through the diode since it is not reversed biased. The DC calibration with a much lower estimate of the diode drop and the wattmeter corrected in this manner will over estimate the output power. I would recommend a 1N5711 detector diode (because it has a reverse saturation current of 1 nA) and a 1 Meg load resistor. The DC calibration is then done by temporarily attaching a 100 K resistor across the 1 Meg load resistor. This will result in a worst case power error of less than 5%. If you want to use a 1N34, than the load resistor should be set to 100K. I discuss this type of calibration in "Calibrating Diode Detectors", QEX, August 1990. For a discussion on diode detectors and reverse saturation current, see Roy Lewallen's "A Simple and Accurate QRP Directional Wattmeter" in the February 1990 QST. The March/April 2001 QEX contains an article "A Compensated Modular RF Voltmeter" which should be accurate (5% error) down to 100 microwatts which is about as good as one can do with an unbiased RF detector. - -John KI6WX - ----- Original Message ----- From: "Ron D'Eau Claire" To: Sent: Tuesday, March 20, 2001 11:02 PM Subject: RE: [Elecraft] Good low-power wattmeter? > John, KI6WX, wrote: > "The peak current in an AC detecting diode is many times higher than the DC > current through the diode. " > > Very true if you have a significant voltage difference across the diode so > there is significant current. The simple peak reading a-c voltmeter > circuit > I described is at its best when no current is flowing. That's why a very > high impedance (at least 10 megohm input DMM) is best to measure the d-c > voltage across the cap. The diode charges up the capacitor so the only > current flowing through the diode is whatever is needed to replace leakage > and current drawn by the DMM. And, of course, the DMM draws only whatever > current is needed by its 10 megohm input impedance. > > Maybe I made the explanation as clear as mud - I'm good at that - but the > circuit I am talking about is the same basic one used in the K2, most r-f > probes and can be found in virtually every Handbook. In r-f probes there are > often a few additional parts, especially a 'scaling' resistor that works as > a voltage divider with the DMM to provide direct readout of the rms value > instead of the peak value of the r-f waveform. > > Indeed, anyone with a decent r-f voltmeter probe and a good dummy load > already has a great QRP wattmeter at hand. > > Ron AC7AC > K2 # 1289 ++++++++++++++++++++++++++++++++++++++ - ----- Original Message ----- From: "John O. Newell" Subject: Re: [Elecraft] Wattmeters > You missed a thread on these by less than a week. LDG > has a very interesting meter that will accept up to four I had done some digging at that time of that thread and I don't think I actually posted the results. The QST article made some fabulous claims for accuracy and LDG, while not echoing them, didn't dispute them either. The 68HC11 has a 10 bit A/D which could have better than 0.1% of full scale resolution, and somewhat poorer accuracy. The software, however, uses the A/D in 8 bit mode, which makes the resolution somewhere closer to 0.5%. There is a calibration table to deal with component nonlinearities, but that is only as good as it could be if your components happened to be the ones used to create the table. In addition, during the lookup they throw away a couple more bits of resolution, so at best, the meter is accurate to 1% of full scale, probably less. There are calibration pots which appear to be single turn, and probably can't be set within 1% anyway. All that being said, it still looks like a dandy meter. Just don't count on astonishing accuracy. Good accuracy, yes, but a lot of digits on the display doesn't necessarily indicate that it's as accurate as there are digits. On the other hand, I doubt you could actually read an analog meter any more closely. However, "full scale" is 150 watts, since that is the range of the 'QRP' sensor and hence what the A/D sees. The 15 watt range merely switches the decimal point on the display. So keep in mind, when the thing says FWD:__0.12, what it really means is "less than a couple of watts". 72/73 de WB8RCR http://members.home.com/wb8rcr/index.htm didileydadidah QRP-L #1446 Code Warriors #35 +++++++++++++++++++++++++++ Date: Fri, 05 Apr 2002 01:47:45 -0700 To: Scott T Emery , elecraft at mailman.qth.net From: =?iso-8859-1?Q?=22D=2ER=2E_Weiss_KI=D8RP=22?= Subject: Re: [Elecraft] QRP (maybe QRO?) wattmetters I also use the Daiwa CN-101, which has ranges of 15, 150, and 1500 Watts. Dave Weiss KI0RP K2 #2249 At 10:36 PM 4/4/02 -0800, you wrote: > Are there other QRP (and higher?) meters I should consider >before making my final decision? ++++++++++++++++++++++++ From: "Pauli Nunez EA3BLQ" To: "Scott T Emery" , Subject: Re: [Elecraft] QRP (maybe QRO?) wattmetters Date: Fri, 5 Apr 2002 12:58:14 +0200 Hi Scott and all, I use a LEADER LPM-880 Power Meter (5, 20 and 120W scale) which also features a 50 Ohm Dummy Load. It came very handy when aligning the K2 and calibrating the ATU. Currently I have it connected to the ANT-2 output connector of the K2 so as to prevent the use of that outlet without any load. There's a second hand one being sold for 50$ at http://www.skywave.co.uk/acatalog/Skywave_Catalogue_SECOND_HAND_15.html. There is no picture available. Any way you can see it at my web site http://www.qsl.net/ea3blq , My K2's Page menu option. It's the third picture named "Basic K2 and aligning instruments" Best 73 Pauli EA3BLQ K2 # 1044 URL: http://www.qsl.net/ea3blq/ ea3blq at menta.net ea3blq at arrl.net ea3blq at qsl.net ++++++++++++++++++++ Date: Wed, 01 May 2002 17:22:24 -0600 To: "Elecraft" From: Larry East Subject: Re: [Elecraft] Palstar WM150L SWR Meter At 12:10 PM 5/1/02 -0500, Mike McCoy wrote: >Might want to check out the Autek Research WM-1 'Deluxe Computing >SWR/Wattmeter" as well. > >http://www.autekresearch.com/wm1.htm > >Its range is 20/200/2000w with selectable peak and average readings. Half >scale reading on the 20 w range is 5w so it's great for QRP. I have one and >love it. I have an Autek WM-1 and it is a nice meter, but it's accuracy degenerates very quickly below 10W. This is not uncommon for Wattmeters that are not specifically designed for low power (could well be the case for the Palstar meter). A good inexpensive QRP Wattmeter is the OHR WM-2; it has good accuracy down to about 25 mW or so. Full scale selections are 100mW, 1W and 10W. There is an easy "peak reading" mod posted on the ARCI web site; www.qrparci.org -- look for the "Technical/Projects" link). 72/73, Larry W1HUE/7 ++++++++++++++++++ To: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Palstar WM150L SWR Meter From: Pete Goudreau Date: Wed, 1 May 2002 21:56:52 -0500 Tom Hammond N=D8SS wrote: >>> I have an Autek WM-1 and it is a nice meter, but it's accuracy >>> degenerates very quickly below 10W. >> So it's not the same circuit design as the Tandem Match then. Makes >> more sense then to build the TM, I guess. > That, and the fact that the designer of the Tandem Match is a member > of this reflector, John Grebenkemper, KI6WX. Well, dang, how cool is that? Just finished printing out the QRP Directional Wattmeter article by Lewallen, W7EL, along with the datasheets of the 3046 and the 3146 (discontinued) to make sure it was still buildable -- it is. I'm not a big fan of the TI Excalibur opamps but they obviously worked fine in the Tandem Match and I'm not disposed to change them. Looks like the biggest work is in generating meter faces for the unit. Thanks for the tip, Pete, AD5HD ++++++++++++++++ Date: Wed, 01 May 2002 23:17:48 -0700 From: "John Grebenkemper, KI6WX" Subject: Re: [Elecraft] Palstar WM150L SWR Meter To: Elecraft Mailing List One of the goals of the original Tandem Match design was to have a linear output for both SWR and power. This was done because, in those days (20 years ago), there was no easy way to re-draw meter scales and a simple digital voltmeter could be used to display both power and SWR. The circuit could be simplified if you are willing to take non-linear scales. The directional coupler shown in the design provides a power range of 0.1 watts to 2 kW, but you need a watt or so of power to get a good reading of the SWR. If you wind the two transformers with 10 turns on the secondary, you will decrease the power range by a factor of 10. There is a circuit board available from FAR, but I have heard of problems with its quality (its definitely not an Elecraft quality board). You can use almost any op amp you want as long as you provide the proper power to it and it has a very high input impedance. I could re-design the Tandem Match today using a quad op amp and a PIC processor. Interestingly, you probably couldn't build that version 20 years from now whereas you can build the 20 year old design today. -John KI6WX ++++++++++++++++ Date: Sun, 5 May 2002 16:33:41 -0500 From: Nick Kennedy To: Low Power Amateur Radio Discussion Subject: [126161] RE: Plea!!--I've gone power mad!! My latest obsession is power. Measuring it, that is. Until recently, I didn't even have a simple QRP level power meter. But lately I've gotten a little taken with power measuring schemes and built (1) A W7EL QRP power meter, (2), The Microwatter, from QST, and (3), the Kanga power instrument also from QST. The W7EL is a great little meter from the February, 1990 QST. It's an in-line meter that measures power in three ranges-- 100 mW, 1 W and 10 W. I was able to find out that my various 5-watt QRP rigs really weren't. Time to do some tweaking. And the low ranges should be good for inter-stage testing on some projects. The Microwatter is from QST, June 1997. It's a terminating wattmeter that can measure from -50 dBm (10 nanowatts) to -20 dBm (10 microwatts). You can get the board and couple of semi-hard to find parts in a deal from Far Circuits. With all this talk about little-bitty dBm's from the experts, I just thought I had to do this one. Not sure exactly why, but it's just too cool to be able to measure down into the nanowatt region. So I finally get the Microwatter about half done and up pops the "Simple RF-Power Measurement" circuit in the June 2001 QST by Wes Hayward and Bob Larkin. It exploits the latest power measuring ICs to produce a simple circuit that can measure down to -70 dBM (0.1 nanowatts) up to +13 dBm (20 milliwatts), plus there's a power dividing tap that can extend the top end up to +50 dBm (100 watts). This one is available as a kit of parts from Kanga at a fairly reasonable price. An article in the current QEX shows some extensions. Scaling the ouput voltage to give a direct readout in dBm on your DVM seems like a worthwhile mod. I originally thought that one of the logarithmic meters like the Microwatter or the Hayward/Larkin meter would be good for measuring crystal parameters. (The latest rage and something I want to break in to.) But on reflection, the accuracy I'd want would probably be better obtained from a simple peak reading diode type instrument with an amplifier in front of it, then with a wide-range logarithmic power meter. Something like the circuits in W1FB's Design Notebook (ARRL) or Jim Kortege's circuits in the Atlanticon Compendium will be my best bet. It was fun to just hook that super-sensitive power meter up to a wire antenna and see what the signals would look like unamplified. I had a good idea, because an AM BC station a couple miles away used to block me big time on 160. So I made a coil and variable capacitor resonator like an old crystal radio (even used a toilet paper tube) and fed the output to the meter instead of to a crystal and headphone. The meter jumped way upscale, but tuning didn't have much effect. Guess I need to brush up on my crystal set theory. Maybe the 50 ohm tap and load are killing the Q. One of the neat things on the AM BC thing is seeing the power indication deflect downward on modulation peaks. How come it does that? I'd have expected the opposite. OK--plea answered? 72--Nick, WA5BDU +++++++++++++++++++++ From: "Stuart Rohre" To: Cc: , Subject: Re: [Elecraft] other SWR Power meter for QRP Date: Wed, 16 Oct 2002 15:30:26 -0500 The VFD has lots of features for the fixed station running high power, but the Bird requires NO AC nor Batteries. For QRP at the most popular levels of 5 watts, and 10 w pep ssb, there is an excellent value kit power meter. A very good, and calibration easy meter for QRP use is the Ten Tec T kit SWR Power Meter. Mine was $49.95, and an easy build from an excellent manual. They may have gone up a bit, but still are an excellent buy. To convert from 20 watt scale to 2 watt scale, I just turned a calibration pot, to make a known power of 2 watts read that. The scales can be 20w or 200 w as built, unless you recalibrate. It does need one 9 volt battery, but has low drain. It also has pickups for both HF and for VHF/UHF. Although not sold as a 440 MHz unit, I found it works fine for finding a good swr null with 440 equipment. 72, Stuart K5KVH +++++++++++++++++++ From: "Don Brown" To: "Elecraft" Date: Sun, 27 Oct 2002 16:01:51 -0600 Subject: [Elecraft] Modifying the OHR 100W dummy load for the WM-2 Hi There was a question about modifying the OHR 100 watt dummy load so you c= ould use the OHR WM-2 wattmeter to indicate up to 100 watts for testing a= nd calibration of the KPA100. I think I have found a simpler and better w= ay to do this. By converting the load into a pi network attenuator with 2= 0 db reduction the WM-2 will read 100 watts when the load is dissipating = 100 watts. This can be done with just one resistor and a BNC chassis moun= t connector. You will need a 62 ohm 2 - 3 watt resistor MOS or carbon com= p type (you can use a 51 ohm 2 watt and a 10 ohm 1/4 watt in series) and = a chassis mount BNC connector. Mount the chassis mount connector next to = the SO239 connector on the back of the dummy load. Remove the circuit boa= rd and make a cut in the circuit trace between the last resistor and the = ground screw at the back right of the board. Then make a cut in the trace= between the 4th and 5th resistor from the back right. This will isolate = 4 - 1K resistors in parallel from ground forming a 250 ohm resistor with = one side connected to the dummy load that is now 62.5 ohms. connect the 6= 2 ohm resistor across the BNC connector and run a short wire from the iso= lated side of the 250 ohm resistor (the outside end of the last resistor = in the string on the right. This completes the mod. You now have a pi net= work with a 62 ohm power resistor to ground and a 250 ohm resistor in ser= ies with another 62 ohm to ground on the output. The input and output is = 50 ohms and a 20 db reduction in power. If you are using the load without= the WM-2 then you will need to terminate the output BNC with a 50 ohm 2 = watt resistor or the load will be a couple of ohms high If you want to ma= ke the load as accurate as possible then add a 2500 ohm 1 or 2 watt MOS r= esistor across one of the load resistors but this should not be necessary= in most cases. To use the load connect the WM-2 to the BNC connector and place a 2 watt = or higher 50 ohm load on the WM-2 antenna connector. set the WM-2 to the = 1 watt full scale range and it will read from 0 to 100 watts. Use the 10 = watt scale and multiply by 10. The accuracy is quite good through 15 mete= rs but falls off a little above 12 meters probably due to stray capacitan= ce or the WM-2 response may fall off a little at the high end. Don Brown KD5NDB ++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Date: Thu, 7 Nov 2002 11:26:21 -0800 Subject: [Elecraft] Power Measurement Instrument A less-expensive and much more versatile option to the OHR WM-2 is the nice r-f power meter described by Hayward, W7ZOI and Larkin, W7PUA, in the June 2001 issue of QST. It is based on the Analog Devices AD8307 chip and looks like it can be built for under $50 using all new parts. I'm currently collecting the parts for mine, so I haven't built it yet. But every test instrument that Wes, W7ZOI, has described that I have built works exactly like he predicts. I am bringing it up now because I see a number of posts about power measurement options on the reflector. It does NOT require any exotic gear to calibrate and, unlike most "commercial" watt meters and kits, allows measurements of very low powers. This meter will measure r-f levels down to less than -70 dBm (that's less than 0.1 NANOwatt!) and up to +50 dBm (100 watts) and show a response flat within 1 dB to 500 MHz when built as shown. As usual, Hayward includes a lot of information about test setups for using the device to test low-level oscillators, evaluate filters when used with a signal generator and for evaluating impedance matches in transmission lines. His "workshop" experiments showing how to use a new test instrument have always been a fun exercises of their own that have never failed to teach me something. Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Thu, 07 Nov 2002 13:37:57 -0600 From: "George, W5YR" Organization: AT&T WorldNet Service To: rondec at easystreet.com Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Power Measurement Instrument Sounds like Steve Weber's "RMS Power Meter" which he kitted a year or so back. Excellent kit and meter . . . 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas ++++++++++++++++++ From: "Stuart Rohre" To: , Subject: Re: [Elecraft] Power Measurement Instrument Date: Thu, 7 Nov 2002 17:59:35 -0600 And another best buy in RF power and SWR meter kits, is the Ten Tec HF and VHF one. It sells for $59, and covers 2m, and HF with two pickups. Accuracy seems as good as the Bird I had to compare it with. It has battery power, or can operate off wall wart DC supply. Ranges come with instruction for setting 20 watt full scale or 200 watts, but cal pot allows resetting either scale to 2 watts full scale. The VHF pick up also seems to work fine at 440 UHF band. Accuracy on 2 watt scale was linear down to 1/2 watt or better. It is a well documented kit, a snap for a K2 builder! 72, Stuart K5KVH ++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Subject: RE: [Elecraft] Power Measurement Instrument Date: Fri, 8 Nov 2002 20:11:18 -0800 Yes, there are a lot of good power meters out there. My reason for bringing up the Hayward/Larkin design that was published in the June 2001 QST what that it has a range none of the others can touch. It reads accurately all the way down to - 70 dBm (< 0.1 Nanowatt). I've built receivers that aren't that sensitive . That makes it useful for troubleshooting low level stages in rigs, doing filter characterization with a simple signal generator, doing gain measurements in low-level amplifiers, making return-loss measurements in transmission lines as well as acting as a very sensitive bridge meter for SWR measurements. With its ability to measure power all the way up to +50 dBM (100 watts) it's perfect for measuring the output of most transmitters, including the K2/100. There is one company (http://www.bright.net/~kanga/kanga/power_meter.htm) who kits the parts for the meter and sells them for $40. It includes everything except a 0-1 ma meter movement (Hayward used a Radio Shack meter) and an enclosure. This is no Elecraft kit. It's simply the parts needed to build the unit following the article in QST. But it's really quite straightforward and the price is very hard to beat! Same disclaimer as my first post: I have not built mine yet, but I've built most of the homebrew test equipment that Hayward had designed over the past three decades and I've never been disappointed in the results. Also, I've never failed to learn something in the process. Ron AC7AC K2 # 1289 ++++++++++++++++ Date: Sat, 09 Nov 2002 13:16:18 -0800 To: From: Larry Weaver Subject: RE: [Elecraft] Power Measurement Instrument I built one of these from the Kanga parts. It was useful in building the K2. With the pad, It can handle 100 watts. Accurate readings can be obtained by connecting a DMM for readout rather than the meter. It's sensitivity also makes it an excellent field strength meter with highly linear readout jn dB--plus it works up to 500 MHZ. I've used it to compare HT antennas for 70 cm. Also makes a good "rf sniffer." I built mine "dead bug" style. 73...Larry N6TW ++++++++++++++