XBee Pro S3B's not communicating

I have two XBee Pro S3B’s connected to F9P GPS sensors for RTK. For RTK to work, the XBee radios have to send messages back and forth. I have not been able to make this communication happen. I set both baud rates to 115,200 using XCTU. The F9P units are telling me that one of them is sending messages from the GPS to the XBee. But the other unit is not sending any messages. Is there any way to test if these two radios are communicating independently?

Additional information:
Product identification: XBP9B-DPWT-011 rev A
IC 1846A-XB900 HP
Firmware Version 1075 installed


Try running the range test function in XCTU.

I can’t do a range test because the two radios are not communicating. This test requires you to select two radio modules on the same network, one local and one remote. When I mount the two XBee’s on the two GPS boards, they don’t communicate and XCTU does not recognize them. If I put one of the XBee’s on the USB to UART adaptor, I can see it in XCTU, but it doesn’t recognize any other modules on the network. I ordered another USB to UART adaptor so that I will be able to do a radio range test. Until then I’m stuck.

UPDATE: I bought two Waveshare USB-UART adaptors and plugged in two XBee Pro S3B radios. One is connected to the PC as base, and one is powered externally as rover. I can get them to communicate at 5.8 kbps using the Throughput utility in XCTU. The Range Test works sometimes but keeps crashing and resetting. The Spectrum Analyzer works sometimes but keeps resetting with an error message "error sending packet: for input string “5"”.

Although it appears that these two radios are working, when I plug them into the simpleRTK2B boards, they don’t communicate. The simpleRTK2B boards contain the ublox F9P GPS sensors, and this pair is designed to do RTK positioning. Does anyone have any experience with setting up an RTK system like this using the XBee radios?