Is it normal to have to have the "Interface Cable" plugged into the serial port, even if I just want to use the "TX" that comes with AFP? I don't have any other radio, I just want to use the one that comes with AFP, but the sim won't run unless the interface cable is also plugged in.

Thanks,
Roger

Yeah both will have to be plugged in. One goes into a com port and one into a game port. The game port is obviously the interface you are using. The other one will contain the dongle the software needs to run.