Challenges sending commands over Mavlink from GCS running Mission Planner with dual airside RFD900x radios

Ground Control Software Mission Planner
1

Hello,

I’ve configured my aircraft with two RFD900x radios (one for GCS other for transmitter with TXMOD).

The first radio is connected to the Telem1 (Serial1) port on my orange cube and is configured to communicate with GCS running mission planner. The second radio is connected to Telem2 (Serial2) configured to communicate with the RFD-TXMOD V2 on my TX16S transmitter, and is also sending Mavlink data for Yaapu telemetry. The radios are spaced about 30cm apart.

When I power everything up, I am able to sync with MP, and I am clearly receiving telemetry on both the transmitter and MP. However, MP struggles and frequently fails to send commands to the autopilot (usually preflight calibration/arm/disarm), resulting in “No Response from MAV” error message.

I am stumped. I don’t believe it is a problem with the radio configuration. Can the autopilot only receive commands from a single Mavlink stream, i.e. it will listen to the transmitter but ignore the GCS?

2

Does the radio on Telem2 (Serial2) have it’s own BEC to supply power?
Are both sets of radios on different NetIDs?
That is:

  • the radios on Telem1 and GCS (USB) have a one NetID
  • the radios on Telem2 and TXMOD have another NetID

Do they operate Ok independantly (without the other pair switched on) ?

Probably supply your param file and a couple of screenshots of the RFD radio settings.

3

Hello Shawn,

Thank you and sorry for slow reply, I was away for a bit, but had more time to troubleshoot.

I discovered that if GCS was close to the aircraft, there was no delay in sending commands. However more than 20ft or so, Mission Planner would hang and often fail to send the command. I also found that it does not have trouble sending commands if the TX is turned off. This makes me think of some RF interference issues (they have separate net IDs and everything was set to 30dBm)

Reading through documentation for the RFD900 modem, I saw that the use of monopole antennas is not recommended without a large ground plane. I’d never had trouble with monopole antennas before the second modem (I don’t do long range flights). I switched out for the dipole antennas on the aircraft, and I have not since had any issues since.