Editing Pulse-position modulation (section)

==Applications for RF communications==
Narrowband RF (radio frequency) channels with low power and long wavelengths (i.e., low frequency) are affected primarily by [[Fading#Flat versus frequency-selective fading|flat fading]], and PPM is better suited than M-FSK to be used in these scenarios. One common application with these channel characteristics, first used in the early 1960s with top-end [[high frequency|HF]] (as low as 27&nbsp;MHz) frequencies into the low-end [[very high frequency|VHF]] band frequencies (30&nbsp;MHz to 75&nbsp;MHz for RC use depending on location), is the [[radio control]] of [[model aircraft]], boats and cars, originally known as "digital proportional" radio control. PPM is employed in these systems, with the position of each pulse representing the angular position of an analogue control on the transmitter, or possible states of a binary switch. The number of pulses per frame gives the number of controllable channels available. The advantage of using PPM for this type of application is that the electronics required to decode the signal are extremely simple, which leads to small, light-weight receiver/decoder units (model aircraft require parts that are as lightweight as possible). [[Servomechanism|Servos]] made for model radio control include some of the electronics required to convert the pulse to the motor position – the receiver is required to first extract the information from the received radio signal through its [[intermediate frequency]] section, then [[multiplexing|demultiplex]] the separate channels from the serial stream, and feed the control pulses to each servo.