Jack, At $700 I will stick with my W7ZOI power meter with its 40 dB power tap and my Tandem Match! I have calibration data that Bob Friess provided on my Power meter from 1 MHz to 500 MHz (and ham band intervals in between). The Tandem Match tracks that data quite well in its basic metering, but is limited to 30 MHz with the couplers available. I really like the Tandem Match for general purposes, but the parallax from the analog meters must be taken into consideration too (op amp accuracy is a great thing indeed, nothing like analog computers using precision resistors - but then I am partly "old school").
That is certainly good enough to give me +/- 5% power measurement accuracy from 1 MHz to 500 MHz, and that is more than I require at the moment. The world of Power measurement is getting better, but it still is not down to really precise accuracy, no matter what the instrument. Thanks for the information. Perhaps one day when the ham budget allows and I have a purpose for it, I will make the investment. 73, Don W3FPR Jack Smith wrote: > Don: > > All I've done is read the spec sheet, but Minicircuits has a > relatively new sensitive termination wattmeter with USB interface for > a quite reasonable price, at least by Agilent standards. > http://www.minicircuits.com/pdfs/PWR-6G+.pdf -- it's a "virtual" > instrument as it consists of the sensor and a USB port to plug into > your computer. At $700, it isn't much more than you might pay for a > single used Agilent sensor in decent shape and calibration. > > Depending on frequency and power range, the "typical" error runs from > +/- 0.1 db to +/- 0.35 dB. power range from -30 to +20 dBm, frequency > range 1 MHz - 6 GHz. > > If I didn't already have a 437B and 8481A and 8482A sensors, I would > give the Minicircuits product serious consideration. > > Jack K8ZOA > > > Don Wilhelm wrote: >> Phil, >> >> The W2 wattmeter is similar in its detector accuracy to the Tandem >> Match (by John Grebenkemper KI6WX) in that its accuracy depends on >> matching the detector diodes with the compensation diodes. >> The "Gold Standard" of power measuring devices is the HP436A >> wattmeter, and it has a stated accuracy of +/-0.05 dB. That amounts >> to a +/-1.16% accuracy - you are not going to get much better than >> that lab instrument in an amateur grade instrument. >> The Tandem Match that KI6WX built tracks the HP436A within +/- 0.5 dB >> over a range of 10 mW to 100W (your 11.2% error), and also tracks the >> HP436A within +/-0.1 dB over a 1W to 100W range for a 2.33 % difference. >> >> Power measurement is tough on accuracy as expressed in percentage. >> Most ham grade wattmeters specify 20% of full scale. The Tandem >> Match and the W2 wattmeter are percentages of actual readings. >> >> Since power is normally best expressed in dB (because the apparent >> signal strength is related in dB), a specification of 0.5 dB is not >> bad at all. >> BTW - I believe that is the accuracy of the power reported using the >> PC link. The resolution of the LED scale is not adequate to indicate >> the degree of precision available. >> >> The directional coupler will have frequency dependencies as well as >> accuracy implications. >> >> 73, >> Don W3FPR >> >> Phil Hystad wrote: >> >>> A few questions about the W2 meter: >>> >>> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- >>> 12 %. Is this full scale accuracy and if so is half scale possibly >>> more accurate or is this the most accurate the meter is likely to >>> be. I am not even sure if it makes a difference for full scale or >>> half scale for a digital meter so that part of my question may be moot. >>> >>> 2. What does it take to achieve an accuracy better then 5 % (for >>> example), and is it possible to achieve an accuracy of 1 % or >>> better? I am curious as to where the money needs to be spent in >>> achieving such accuracy. Is it in the directional coupler? >>> >>> 3. I am thinking that the company that can build the best receiver >>> on the market (the K3) can also build the best meter. So, would >>> Elecraft principles consider a future super-accurate, best on the >>> planet, amateur radio RF/SWR power meter? Oh, I think a current >>> meter would be cool too. >>> >>> And, I know that having meter accuracy is of little importance in >>> ham radio but there is some kind of deep seated quirk in me that >>> wants accuracy just for the heck of it. Certainly 5 % is >>> achievable, right? >>> >>> 73, >>> phil, K7PEH >>> >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.709 / Virus Database: 270.14.100/2554 - Release Date: 12/09/09 > 02:32:00 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
