the ublox m8 gps are great see 10-12 sattelites and has very low pdop. (in the room)
but I have no succes with receiver changing.
0. connect receiver 1 (cppm) socket with pixhawk rc in socket
1. binding was succesful
2. there is just green led on d8r-xp
3. it seems only one way communication
4. because of it i can not calibrating radio, in the mission planner relevant page shows the radio channels bars which are totally grey
5. i have no idea what is the problem (telemetry port no connections under bindig nor test.
return and rebind the original d4r-ii receiver.
binding succesful but just the green led is light, two way communication is ok, radio status bars are green and you can calibrating, but very poor range (it was my original problem)
i found similar problem in hobbyking forum