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 > > ______________________________________________________________ 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
