Thanks all for your suggestions.

Disconnection the power from the PA as suggested by Alan made do difference to the 28 MHz switch-on drift. Though interestingly my signal was still clearly visible on Chris's grabber a few miles away.

I have now set QRSS FSKCW6 (running only my c/s) to repeat every 16 minutes over night on park mode 4 to see what happens (operating on what the U3S readout says is 10.140.000 MHz) for calibration by the various grabbers tuned to 30m. If all goes well I'll be back on 28 MHz to see what the frequency and drift are like there via Chris's grabber again.

Cheers,

Ian