The IPD system - what is it? IPD stands for Intelligent Pulse Coding, and the receiver incorporates a processor which analyses the incoming signal for validity. Like a PCM system, IPD filters out invalid signals. The difference between IPD and PCM is that the receiver does not "switch off" the "dirty" signal as field strength declines, but instead widens its tolerance. This means that control becomes less precise as field strength falls away, but remains usable for longer (greater range). The result is that you can infer the approaching limit of range from the model's behaviour, whereas PCM suddenly robs you of control. When the signal is insufficient for the receiver to interpret, a fail safe condition is actioned, thereby driving the servos to pre-selected safe positions, e.g., throttle back. An IPD receiver sees all usual PPM formats as valid, which means that all standard FM PPM transmitters can be operated in conjunction with these receivers on the appropriate frequency. IPD is faster than PCM because there are no check cycles. Practical testing has shown that IPD and PCM produce comparable results when interference occurs. But we are warned not to get complacent. Like PCM, IPD is not an excuse for incompetent R/C installation and careless cable deployment, and thorough suppression of electric motors and ignition systems is still essential.