Home >> Hobbies >> Aviation

What Is a PCM Receiver?

One of the fundamental elements of any radio-controlled aircraft is its radio system. Without this key element, you would have virtually no control at all over the aircraft, turning a precision small-scale vehicle into an undirected missile. Pulse Code Modulation radio systems are common in competitive RC piloting and in high-end RC aircraft. PCM radio systems generally break down into two parts: the transmitter, which remains with the pilot, and the receiver, which is installed directly into the aircraft.

PCM Systems
- PCM radio systems are broken into two parts: a transmitter and a receiver. The transmitter sends control information to the receiver, which then sends commands to the aircraft's moving parts including servos. Servos are small actuators that control the aircraft's moving parts. Both the transmitter and receiver contain microprocessors that encode and decode information, respectively. In addition to servo position information used to control the aircraft, PCM transmissions also contain additional information such as checksums, failsafe values and identification for the aircraft.
Application
- PCM receivers are most frequently used in radio-controlled model aircraft, as opposed to other model vehicles. These receivers are always installed directly inside the aircraft itself and as a result are typically quite small and lightweight. All on-board equipment is linked directly to the receiver, which transmits instructions to servo motors, engines and other equipment.
Pros
- The additional information control available in the PCM system can make it a much safer system than the Pulse Position Modulation alternative. For example, a model helicopter loosed from its controls can wreak unbelievable havoc and severely injure someone if it makes a direct collision. However, with a PCM system a failsafe can be set so that when control is lost the engine sets to idle and the device can be brought down almost immediately before it can cause any damage. PCM systems also have somewhat longer ranges than PPM systems and send high-resolution information to and from various high-end servos, allowing extremely fine levels of control. With more complicated aircraft, fine control can make all the difference.
Cons
- PCM systems aren't without their faults: they are typically more expensive than PPM systems, are more sensitive to adjacent channels that can cause signal interference and are also typically designed with specific protocols that require a PCM receiver to be paired with a transmitter of the same brand to function. The signal hold-mode of the PCM system also masks small glitches by not transmitting them to control surface commands, which only translates into momentary control loss and can mislead the pilot about the situation until a previously detectable larger failure leads to a total loss of control.

Aviation