programmable in some radios), it will command the servos to a preset "failsafe" position .  As soon as the Receiver receives a good frame, it will come out of Hold or Failsafe, and send that position data to the servos.

This is why an aircraft with a PCM radio will not exhibit the "jitters" like a PPM radio when an unwanted signal is introduced into the system. 

Early  PCM systems divided the servo's rotation into 256 discrete positions. What this meant is that the arc of the servo throw is divided into 256 steps and the servo pulse width generated by the decoder is based on the binary number 1 through 256, A binary 1 would represent maximum throw in one direction with a binary 256 representing maximum throw in the opposite direction. A binary 128 would represent centered.

Modeling demands soon forced manufactures to provide more precision 512 step systems, and finally the 1024 systems. These higher resolution systems required the transmitting of more data between the transmitter and receiver which reduced the number of updates per second that the servo received. The typical PCM radio send about 20 frames per second versus the 50 frames per second sent by a PPM system. To achieve 256 steps, 8 data bits per channel must be sent or a total of 80 data bits for a 10 channel system. 512 system would require 9 bits per channel for a total of 90, and 1024 requires 10 bits per channel for a total of 100. Adding the sync and checksum data may extended each of these an additional 16 to 20 bits.   

Although the PCM method of operation will eliminate the "Jerking" when an interference situation occurs, it should be noted that PPM and PCM encoding/decoding has nothing to do with the capability of the receiver to reject unwanted signals.

The PCM concept of encoding/decoding was originally developed in the pre 1991 era to address the interference problems of those days. With the new narrow band, dual conversion receivers, used today, PPM receivers may work as reliably in may

area. In todays narrow band environment, FM and dual conversion usually reduces the receivers susceptibility to interference over AM or single conversion, with dual conversion being the most influential factor.

The Computer Radio:   

The term "PCM" and "Computer Radio" are not analogous. Although all PCM radios are computer radios, not all  "computer radios" are PCM. Today's computer radios are available in both PPM and PCM versions. The "computer radio" is probably the most significant advancement of the last decade. In the computer radio, the transmitters encoder has been replaced with a microprocessor. Once this was done, the capability of controlling the servo pulse became unlimited. Todays computer radio's not only allow full control over the throw, rate, linearity, and reversing  of the servo's operation, but also provide many additional mixing features, while allowing you  to setup and store these configuration for multiple aircrafts.