Some flight controllers such as the Pixhawk autopilot only support PPM (pulse position modulation) compatible receivers. If you have a PWM (pulse width modulated) receiver, you will need a PPM encoder such as this one for it to work with a PPM only FC.This PPM encoder will encode regular PWM inputs into a single PPM output. This allows you to combine up to 8 channels from a regular RC receiver to a single wire PPM input for your flight controller e.g. Pixhawk or APM. The nice thing about PPM is that it will enable you to reduce all channels to a single wire, excluding ground and power lines.

IMPORTANT THINGS TO BE WATCH WHILE POWERING THE ENCODER:
The jumper JP1 has been included to provide some flexibility in the way you power the receiver, servos and PPM Encoder. Often the power for the receiver, servos and PPM Encoder will come from the autopilot board.
In this case, JP1 should be in place (shorted).

On another way, if the receiver or any servos directly connected to the separate/additional power source and the autopilot’s +5V is also connected to the PPM Encoder via the PPM connector – THEN YOU MUST REMOVE jumper JP1. This will isolate the autopilot power supply from the separate receiver power supply.
FEATURES:
Support the input channels   : 8
Output                                       : PPM SUM × 1 / MUX × 1
Dimensions                              : 28 x 19 x 5 mm
Weight                                       : 12 gm. (containing all the input and output wires)