Um, FM is NOT a band! 72MHz is the band! FM is a MODULATION type, and both PCM and PPM use FM modulation. Within that MODULATION, the digital signal must be ENCODED. There are two ways - PPM and PCM. PPM works by varying a pulse in time to equate to a value - IE, the time from one pulse to the next defines the servo position setting. In PCM, a digital value is sent over a series of pulses. Since this is a true digital signal, error checking also takes place in that if the signal is mangled by a stray pulse (interference) the RX will know and can throw out that frame. In PPM, no error checking can occur, and the errant (noise) pulse results in a glitch in your output. As such, when PPM gets close to maximum range, it will glitch like a bugger. On a PCM system, it will just feel sluggish to repond until it quits altogether (PCM lockout). The sluggishness is harder to notice than the glitches (but unlike glitching, it can't crash you) so if you are not closely in tune to your model, you MAY get in trouble with lockout in PCM, but in reality, this is rare - normally, you will lose sight of it before it would lock out.

- Tim