[hfsig] Sidebands on Raspberry Pi WSPR carrier

Ron Ott ronott at sbcglobal.net
Sun Sep 4 03:01:30 EDT 2016

This is my first post to the group, my apology if I'm not following the correct protocol.
I just got a Raspberry Pi 3 working on 20m WSPR using the TAPR kit. I quickly discovered that there are sidebands 120Hz above and below the carrier frequency and these sidebands are modulated like the carrier and are only 15dB or so below it in amplitude.

In the last few days I read some chatter about others seeing such sidebands on received WSPR signals, but there was no mention of a Raspberry Pi (normally the listener wouldn't know what the sender is using).
I'd be surprised if no one else has discovered this issue, which is serious since the sidebands are pretty strong.  I suspected modulation by the main USB power source, but tried other supplies including a well regulated HP with no change.
What's the solution?
Thanks, Ron / W6XY
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