[Elecraft] Accuracy of Wattmeter W2 under 2 Watt

[Hajo Dezelski]

Hi Ron,

I bought the unit from a ham, who finds pleasure and has the equipment to
calibrate. And he did it to the unit and the sensors.   This is all
documented and well done.   So I could measure my wspr output of 500 uW
were I reached the 1 Mio km per Watt goal.
But I had the troubles described above, so although I hate tinkering I will
change my profession and will become a box maker ;-) and will report ...
after I have done my homework.

73 de Hajo
Am 26.10.2015 8:52 nachm. schrieb "Ron D'Eau Claire" <ron at cobi.biz>:

> 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:elecraft-bounces at mailman.qth.net] On Behalf Of Hajo
> Dezelski
> Sent: Monday, October 26, 2015 11:47 AM
> To: elecraft at mailman.qth.net
> 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.
>
>