Adde I use a traditional PC interface using optoisolators, but I guess transformers will work just fine too. I define a com port on N1MM to switch the PTT and pick it up from there. The relay in my h/b interface box steers the audio. As I contest on VHF+ I call CQ a lot. As a result my NC relay contacts are connected to the souncard audio and NO to the footswitch (mic) PTT. I do not route my mic audio via the PC soundcard in case the PC fails for some reason.
This is not an elegant solution, but I had the bits in my junkbox, so I made something that worked at the time. It hasn't broken, so I haven't changed it!
With my other radio (also via an RRC) I have used a microham interface, but am having problems with that set up at the moment.
Hope that helps?
73
Steve
M0BPQ