Hi Pete,
According to the docs on adjusting the PA bias, this should be possible to sort out if you can put a sensitive ammeter in the +ve supply line.
https://github.com/df8oe/UHSDR/wiki/Adj ... alibrationEssentially you set the audio input to Line In (NOT MIC), key up and see what the current draw is.
Then you increase the PA bias in the menu (PA Configuration Menu > PA Bias) in small steps until the current draw on TX is 500mA greater than your first reading.
Do you have a sensitive (minimum resolution 10mA) ammeter or multimeter you could try this with?
Stefan MI0PYN