Mark,
I have been using the Walston system for about three years now. We have used them with PCM and PPM without any problems. Just to see if there would be any interference I attached mine right next to my FM receiver in a prop aircraft without any problems. We have used it in our jets here in Hawaii and we were also using it with all the Skymaster jets at Superman. It works great as I have found aircraft buried in the swamp that I could not see even though I was almost standing on the aircraft. We have also used it on helicopters.
Larry