[hfsig] 20m WSPR shield for Raspberry Pi

Bruce Raymond bruce at raymondtech.net
Mon Apr 15 19:34:36 EDT 2019

Hi Keith,

You're very thorough - quite a virtue in its own right.

I have to admit to being lazy. I connect the transmitter to a 50 ohm 
dummy load and measure the voltage across the load with my scope. I just 
use (Vp-p^2)/400 as the power output and figure it's close enough.

73 Bruce

Keith Wilson wrote on 4/15/2019 4:20 PM:
> Gentlemen - an update to my power output measurements on the 20m 
> Raspberry Pi board:
> The (impedance unknown, alligator clips to BNC) cable between the 
> board and the dummy load was affecting the dummy load impedance.  The 
> SWR was showing about 1.55 with a RigExpert!
> I tried an alternate method using the Flex panadapter and sampling 
> with an Alpha Delta coax switch, attenuation about 90 dB.  The WSPR 
> board signal was down about 15 dB vs a 5 W signal.  So that gives an 
> output of 22 dBm which looks pretty good.  I also tried a 0.5 Watt 
> signal and the Flex panadapter looked pretty accurate i.e. down 9-10 
> dB from the 5 W signal.  I think this is a better test!
> Keith - KE4TH
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