Its a 4-channel.

You Y-cable connect the battery with one of the servos. That RX sort of expects to be used with an electronic speed control that has "BEC" function... supplying the RX with power from the motor battery.

If you read the lable... it says 4/B at one of the connection points... suggesting that if no 4th servo s used... that's where you hook the battery up. (and you could always read the instructions that came with it.... they explain this quite well... I have one of these RX's.)