i am no expert, but i read that the difference is the signals are digitally encoded for PCM, the advantages are: it is less prone to interference, PCM is very popular for guys who run gass engines, because it does a better job of rejecting spark plug noise. Another advantage is the reciever is smart and can be set to a fail safe condition (engine shut down) if no valid signal is detected. I use FM and have had no problems, but PCM is the top shelf technology.