Thanks Lee - I suspect 12v too as I think it takes power through it at the moment. It's a Funkwerk one.
I'm thinking: build a double cable which supplies +12v into the Transponder with one cable and with the data lines wired to a female RS232 connector through another cable. Then add a PL2303 based RS232 - USB cable plugged into the female connector.
I need to look into the details of the transponder though carefully first as breaking that would be expensive!
Probably won't do much on this side of things anyway at least until you think the s/w side is ready for some testing
