The receiver needs approximately 6V of power to operate. In a typical configuration, the ESC supplies this power to the receiver.
Some ESCs can adjust the voltage in a safe manner to avoid blowing up the receiver. Most cheaper ESCs cannot. If you supply too much to the ESC, the circuit that handles power supply to the receiver (people call it the BEC) will have trouble working things out correctly. This will either break the circuit or blow up the receiver.
If you want to use high voltage battery such as 11.1V lipo, it may be a wise thing to do to use separate power source for the receiver. To do so, you need to first cut off power supply from the ESC. On the signal wire to the receiver you simply cut the red wire. It is that simple. On the receiver there is a separate jack which says BATT. You can setup a connection to a small 6V pack OR an external battery box. You only need to connect the black wire and the red wire. There is no white wire for it.
If you are using a legacy mechanical speed controller, you may or may not need to use separate power source depending on the type of MSC/receiver you use.
