0 radio channels detected on PX4/Pixhawk 2.4.8

I am trying to configure a quad with the Pixhawk 2
.4.8 flight controller, Spektrum DX6 tx, and a Lemon PPM receiver. Using a standard bind mode, the rx binds just fine, and my system goes through all setup steps until it is time to configure the radio. I get the error message that 0 radio channels are detected. I have tried to re-bind the rx through QGroundControl, and none of the three modes will bind.