Hi Andy.
You may well be right, it's something I'm not too familiar with but found something similar regarding the SSTRAN pantry transmitter in this thread:
https://www.vintage-radio.net/forum/...=139596&page=2
I didn't realise that it can be quite a problem with wire aerial pantry transmitters. Member Argus25 points out the benefits of using a loop aerial as opposed to a wire. I hope to have a go at building the circuit he included in this thread.
As a next step I'll be using a battery supply for mictester's circuit and also use battery powered radios for the tests.
Regards
Symon