On 1/3/2021 4:32 PM, G4SDG wrote:
I've also successfully used the FST4 modes but am distinctly uneasy about the effect the trips might have on my FETS and/or power supply! It's odd that nobody else from the LF/MF fraternity has mentioned it though.This is interesting. I was part of the early FST4/W test group but I never realized this ramped amplitude was happening. In general I would say it is not good news with class D and E amplifiers which were never designed for amplitude varying waveforms.
I've been having problems with FST4/W transmissions with T/R period of 120s or less. Sometimes, but not always, my class D amplifier gets into an abnormal state with significant oscillation in output amplitude immediately at the start of a transmission and never recovers unless I ramp the drain voltage down drastically and then bring it back up. I never mentioned it because others didn't seem to be having issues and I thought it was something unique to my equipment. Now I don't know what to think. I have never had it happen with WSPR or JT9. What seems really strange is that FST4/W seems OK at T/R periods of 300s and up. So I'm not sure if my problem is related to this or not.