Thanks for that. Have already acquired a UGREEN USB to RS232 DB9 Serial Adaptor Cable via eBay (with Prolific PL2303 Chipset) but the circuitry appears to be integral with the DB9 connector. However, according to the TT31 installation manual there are 2 connectors on the back of the TT31. Both Molex edge connectors, one with 24 contacts and the other with 12 contacts. Both appear to have RS232 dedicated pins. I think that the 24pin connector is already in use, with presumably only some of the pins connected, but as I recall, the 12pin connector is not used at present. This is termed the Secondary Interface. Can you advise what pins need to be connected to facilitate the ADSB Out ? Also, do I have to cannibalise the DB9 or just find or fabricate a DB9 to Molex 12 Pin edge connector ??