Radio Calibration no signals


I am new to this and I have manged to see Mission Planner working fine. I did accelerometer calibration, but there is no signal showing when I do the radio calibration.

Do you guys know why?
Hardware: I am using a Navio2. The sbus on the receiver is connected to the sbus port on Navio2 as well as the servo wires. If I plug all servo wires into the receiver, it works.