Hello,

Check out this simple interface for FMS:

SmartPropo

The site mentions using the DSC cable, but you can use any shielded single conductor cable. I assume you already have the Tx pin-outs for the plug. This interface is by far one of the simplest I have seen. I also built this interface for my own use too. If your radio is only capable of FM transmission, you may experience jittery simulator response, but with PCM it is very smooth. If you have any questions, don't hesitate to ask, I would be glad to help.