Hi Paul,

I would go back to basics and focus on getting the bare U3S with 20m filter working. You should see some, if not many, spots from receiving stations with the basic 200mW output and a simple antenna like a wire dipole.

Are you using the external GPS unit to synchronise the time, or setting the time manually? Accurate time is a critical part of WSPR. As is frequency stability, so you need to make sure the signal is not drifting during the 2min TX cycle. There is a document here which explains some of the options to reduce drift… https://www.qrp-labs.com/images/appnotes/AN001_A4.pdf

If you don’t have accurate time (to within a second I think) or stable frequency output then you won’t be decoded and reported by remote receivers. Sorry for not addressing any of your specific questions, but I think it would be good to get the basic kit working on one band before brining in more variables of the filter switch kit and the amp.

regards,
Jim