I programmed a marine band radio yesterday. A 5 pin header on a circuit board and 4 conductors from the programming cable. I confirmed that none of the, were carrying anything other than data by checking voltages. Maximum I found was 5v. I found which pin on both sides was ground. On the programming cable that was the sleeve of the 4 circuit 3.5mm plug I cut off. I found one pin of the header that was pin ground. Those two got joined and then I tried every combination until a read on the computer brought in data. I then tried writing it back and that worked too. So with four pins one end, and five the other, one single data connection was required. No contact at all on the others. It took start to finish, three hours of fiddling. It needs an accurate volt meter as a minimum and one capable of a sensible resistance readout too. I used a scope for my measurements. But a decent meter would have done really. However, I just reread it and saw you are just wanting to connect the audio. I misread it. To identify the transmitter input connection, the meter will show you which pin is the chassis ground. A simple test is to connect a dummy load and with an elastic band, stick it into transmit. Get a thin needle and hold it in your hand. Without touching anything with one hand, put the pin into each ‘hole’ and one will give output. That’s your input. Connect a cable to the computer’s input and open up an app that would record audio that has a meter. Touching the end of the cable in should give you a visual or audio hum when you tape it with your finger. this is your computer input. Get your radio producing noise. Interference of hiss is great. Wrap a bit of wire to the audio pin connection you know is the computer live input and prod that into each radio socket other than the one you identified as transmit audio in. When the hiss appears on the computer, that’s receive audio out from the radio. Make properly or bodge the required connection.
then I reread it again, and you said your computer has one socket for in and out on one 4 pin, so you just revise the above to detect the computer input which is likely to be not the tip but first or second ring, with the output on the tip and other ring. Ground always on the sleeve.
