Hi Chris,
Try a 1:1 RF ferrite decoupling trasformer, right behind the PA. Maybe
also on the PA input. Try to use a battery for the PA, just for one WSPR
sequence, to see if that solves the problem. If it does, then use common
mode chokes in the PA supply cable. Avoid ground loops. Use shielded
circuits only.
73, Stefan
Am 17.06.2017 13:20, schrieb Chris Osborn:
GA LF,
I have a recurring problem with my home made LF WSPR TX :-
As the PC's audio signal shuts down (after the nominal 2 minute
transmission time) it picks up RF - this is fed back to the TX input
causing several seconds of instability.
Has anyone else had this trouble and/or knows of a simple solution?
I've tried putting ferrite rings around the PC's input and output
cables which solved the problem for a while.
In desperation I'm considering adding a monostable to ground the TX
input for a few seconds after the PC's AF shuts down, but this will be
a last resort.
Any useful advice or comments would be most welcome.
73
Chris (G3XIZ)
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