Hajo: A power meter based on the AD8307, such as the PM2 uses, can be very accurate and sensitive but requires calibration. The AD3807 takes RF in and produces a dc output proportional to the logarithm of the input signal amplitude.
I have a homebrew version based on a design by W7ZOI that works FB down to below -90 dbM. That's the native sensitivity of the AD8307. You are quite right that shielding is needed otherwise any local source of RF can upset the readings. I presume the PM2 has an input attenuator but any RF getting to the AD8307 chip can cause errors. If you have a steady source of RF nearby (i.e. a broadcast station) it can introduce a fixed error in addition to the jigger you saw from the RS232 bus. That will depend upon how they have terminated the input to the AD8307. I suggested a solution that is not dependent upon specialized test equipment most Hams don't have handy or depending upon the manufacturer's calibration data. If that is not an issue, by all means the PM2 is suitable. 73 and have fun! Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Hajo Dezelski Sent: Monday, October 26, 2015 11:47 AM To: [email protected] Subject: Re: [Elecraft] Accuracy of Wattmeter W2 under 2 Watt Hello, Thanks for your suggestions. It seems that the owners of the W2 use it for higher power settings than qrpp. So it is natural that nobody could answer my questions. So I will continue to use my Pm2 http://www.foxdelta.com/products/pm2.htm . But in a private discussion I was pointed to a solution of the irritating numbers shown on the display. I have no cabinet and the cable from the RS232 was too long and not shielded. So there was some hf going direct into the circuits. So I will build a box and take some ferrits and hopefully will be happy. Thanks for the advice and your time. 73 de Hajo DL1SDZ Gruss Hajo --- Cela est bien dit, ...,mais il fault cultiver notre jardin. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
