I finally got an audio recording of my PRC-320, thanks to Rainer (DG7LAL). In this case I was using the two extra sections that make up a 5.5m long whip antenna. Again with full power and the 1.1Ah battery.
It seems that everything is OK. You cannot ask more from a rig like this. I am really satisfied with the result, which encourages me to undertake further field tests. I will keep you updated.