NO RTK LED is always ON and the GPS is drifting a lot

Q&A forumCategory: QuestionsNO RTK LED is always ON and the GPS is drifting a lot
Dragos Calin asked 1 week ago
Hello,
I buy a simpleRTK2B – Starter Kit MR and I try to use it for a robot navigation.
There are several problems:

  1. Open sky, at least 12 satellites with signal over 40dB, but the NO RTK LED is always ON. 
  2. The latitude and longitude is always drifts even the robot is not moving. The drift in the first minute is around 0.2 to 1 meter if the base and rover is communicating. The drift is increasing to several meters in one minute if only the rover is working.

I try to find out what is happening using your guides/tutorials/forum but none of them seems to fit to my problem.

clive1
replied 1 week ago

Perhaps start with the Base, make sure the GNSS antenna is as high up as possible. Look at an Antenna Sky View map to see if you have any obstructions to the sight-lines. Honestly with the available constellations you should be seeing 20-30 satellites. If the Base is not working optimally it’s going to drag down the whole system.

Make sure the Base is in TIME mode, and transmitting a full complement of RTCM3 messages.

At the Rover make sure you’re receiving all the RTCM3 messages. Check UBX-RXM-RTCM reporting. Look at UBX-NAV-SIG to understand the signals in use, and the source of supporting data.

If the Rover is not getting into Float or Fixed RTK modes, you’re going to need to look at the data being received, and the GNSS performance.

clive1
replied 1 week ago

GNSS really should not have long term “DRIFT”, it might reasonably be expected to dither around with in a circle of some radius. If the radius is beyond 3m you should look at the ground plane used with the antenna, the position of the antenna, and the electromagnetic/electrical noise in the system.

Dragos Calin
replied 1 week ago

Thank you for your fast response!

* TMODE1 and TMODE2 is on 0-Disable
* TMODE3 is on 1-Survey-in
I checked the -> UBX-RXM-RTCM reporting and I don’t have any data. Could you please guide me how to fix this issue?

Dragos Calin
replied 1 week ago

Thank you for your fast response!

* TMODE1 and TMODE2 is on 0-Disable
* TMODE3 is on 1-Survey-in
I checked the -> UBX-RXM-RTCM reporting and I don’t have any data. Could you please guide me how to fix this issue?

clive1
replied 1 week ago

I really can’t afford to spend a lot of time supporting you. You’ll probably need to read through the docs and tutorials first, and apply problem solving skills.

If the *ROVER* doesn’t show any RTCM3 messages via UBX-RXM-RTCM it’s suggestive that a) the Base isn’t sending them (needs to have completed a survey), or b) that you have a data-link issue on the radio side.

On the *BASE* you can see if the SURVEY-IN completed properly via UBX-NAV-SVIN, which will provide progress information about the position, number of points collected, and the overall accuracy. Check that it’s in TIME mode using UBX-NAV-PVT

uBlox has extensive documentation and white-papers for the part and RTK concepts.