Hello Spence,
That is basically what I had to do to use this interface. I had to have access to to the RYS pin on the pc side of the CAT cable.
So I just I need to splice into the serial cable and tap the RTS pin from the PC to the opticoupler and ground. Then I made the cross over ( null modem) to the radio inside the project box going to the serial port on radio. Then just added the audio lines to the pc and radio.
