PWM – Pulse Width Modulation
This is the most common and basic radio control protocol. In the old days when there were only RC fixed wings planes, the receivers were used to control the servos or ESC directly with standard PWM signal, one channel for each servo. Until today the same technology is still being used in many models.
PWM stands for pulse width modulation. It’s an analog signal where the length of the pulse specifies the servo output or throttle position. The length of the signal pulse normally varies between 1000µs and 2000µs (micro seconds), with 1000µs being the minimum & 2000µs the maximum.
PWM radio receiver is the most common and usually the cheapest option.
PPM – Pulse Position Modulation
PPM is also known as CPPM or PPMSUM. The advantage of PPM is that only one signal wire is needed for several channels (typically 8 channels max), instead of a number of individual wires. So you should only connect the ground, power and signal cable.
A PPM signal where basically a series of PWM signals sent one after another on the same wire, but the signal is modulated differently.
PCM – Pulse Code Modulation
PCM stands for pulse code modulation, it’s a data types similar to PPM. However PCM signal is digital signal (using ones and zeros) while PPM signal is analogue, which is the length of time the signal is on. PCM has the potential of signal error detection even error correction, but this still depends on the product you buy.
PCM is more reliable and less susceptible to interference, but additional conversion is required so the equipment tends to be more expensive.