RFD900+ does not work in Cube with External Power Supply

Hi all,

I have a PixHawk 2 (Cube) and I am using RFD900+ connected in TELEM1 port. The problem is that I want to power the RFD from my Mauch BEC, in order to use full TX power on my telemetry.

When I remove the jumper between pins 4 and 6 of RFD and power the module externally from my BEC thru pins 2 and 4, the RFD enters in bootloader mode (red LED solid on RFD) when I turn the system on.

I have to disconnect the power supply and reconnect again in order to make it work.

I tested disconnecting RTS and CTS pins between Cube and RFD, and then the problem disappear, but without these pins the telemetry link is unstable and slow, can not even load PX4 parameters in QGC.

I have tested the simple external power connection in ArduPilot and it works well.

Anyone knows how to fix this problem in PX4 Autopilot?

I would try leaving the ground pin connected to the AP board then supply BEC power to the ground and positive side.

Measure the native voltage the AP is providing to the telemetry radio and compare it to your BEC voltage when connected. If there is a large difference, that may be the issue.

I’m having the exact same problem. I have the RFD 900+ radios updated to the latest version 1.13. I’ve attach the common ground. I’m measuring 5.08v on the external power supply and 5.30v from the AP board. Has anyone else come across this issue? What was the fix?

Hello Ricky. I wasn’t able to deal with this strange behavior in PX4 Code, but I tried Ardupilot and it works perfectly. Seems to be something related to the way the PX4 Firmware initializes the communication with RFD900 Radios.