ZED-F9P rover not seeing RTCM corrections via RFD900+ radio bridge

GPS/GNSS Development Boards
1

Good morning all!

I am currently building a mapping quadcopter. I teach UAS at a local college, so the mapping/photogrammetry part of this isn’t too difficult for me. I’m trying to do all this with development boards, rather than commercially designed RTK components.

I have two SparkFun GPS-RTK-SMA ZED-F9P breakout boards and two RFD900+ telemetry radios. So far, I have accomplished the following:

  1. Both GPS boards powered up and achieved 3D lock.
  2. The rover GPS in the aircraft will achieve RTK Fixed status when receiving NTRIP corrections via USB-C from a laptop with u-center software active.
  3. The two RFD900+ are communicating–I used a terminal program called PuTTy on two computers to send text via the two RFD900 radios
  4. I have had the base connected in its planned configuration and transmitting RTCM messages over the RFD900 link from the u-center NTRIP correction stream.
  5. I used the rover RFD900 setup as a serial port on another computer. It received gibberish (as expected) from the base RFD900, indicating the RTCM messages were getting through.

My last hurdle is getting the ZED-F9P rover board to accept RTCM corrections from the RFD900 radio. The radio’s Pin 9 (supposedly TX) is connected to the GPS board’s RX2, and the radio and rover share a common ground. Does anyone have any idea why the rover ZED-F9P is not receiving the RTCM messages over the radio link from the base?

2

When you were testing with PuTTy: what wires were being used? If the radios are full duplex and/or sending one another ACKs I think they need RX and TX on both sides…from the last paragraph it sounds like only Radio Tx & F9P Rx are being used, I’d try wiring the other 2 and re-test

3

Good afternoon, and thanks so much for the suggestion. I did more troubleshooting today and determined my issue was a baud rate mismatch between the radios and the GPS boards. Everything is running smoothly at 57,600 now. I was able to test my NTRIP correction workflow (both radios, a laptop as the correction source, and the rover ZED-F9P). I got 3D/Fixed within just a few minutes. I love these SparkFun GPS breakout boards!

4

Awesome! That totally makes sense