RE: Difference between FM and PCM
The RC industry has been real sloppy in their use of modulation and encoding terminology which has lead to a real confusing jumble. As previously mentioned above, nearly all the latest "serious" systems use FM modulation on the carrier signal. This is not your "normal" FM as in your auto radio, but a form known as Phase Shift Keying ( PSK ). The actual control info which is sent by the carrier can be Pulse Position Modulation ( PPM ) where the width of pulses in a train of pulses controls the postion of each servo channel when the Rx sorts out the proper pulse and sends it to that servo channel. Or it can be Pulse Coded Modulation ( PCM ) where the Tx sends binary numbers, one for each servo channel, and the Rx decodes this into a pulse width sent to each servo.
Thoroughly confused? Recap: Most systems are FM; some are FM/PPM and some are FM/PCM.