The jumper SJ1 has been included to provide some flexibility in the way you power the receiver, servos and PPM Encoder.
SJ1 soldered: The +5 Volts from the receiver and the PPM output are connected. The receiver will draw
the power from whatever autopilot board is attached to the PPM output.
SJ1 open (not soldered): The +5 Volts from the Servos and the PPM output are separated.
The receiver needs an separate power source.
Note that failure to remove SJ1 can damage the autopilot's +5v switching regulator when too much current is drawn so its usually best to keep it removed.
You can also find the manual here