[hfsig] 20m WSPR shield for Raspberry Pi

Keith Wilson keith.wilson.pcs at gmail.com
Fri Mar 22 14:36:02 EDT 2019

I have the 20m WSPR shield working on a new Raspberry Pi 3 B+.  I see
apparent mixing products in the output, 120 Hz away from fundamental, when
using a USB power bank to power the Pi.  Since these are not coming from a
switching power supply, where are they coming from?  These products start
at about 30 dB below the fundamental.

Also, with a scope I measure the voltage output at 12V peak to peak into
quality 50 ohm dummy load.  This is 0.36W, higher than the 20dBm (0.10W)
specified.  Is this too good to be true?

Note the shield was not designed for the Raspberry Pi 3 B+ so it can't be
fully inserted on the 40 pin GPIO plug, but seems stable enough partially
inserted.  Getting WSPR reports from across the USA and occasional overseas
reports too.

Keith - KE4TH

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