How to check RTK fix from base on the rover?

Q&A forumHow to check RTK fix from base on the rover?
Leonardo Garberoglio asked 11 months ago

Hi, I’m testing ardusimple kit for the first time. I place the base on the roof of my house and the rover on the ground. I’m connected with my PC on rover module.
I see Xbee->GPS LED blinking so rover received base correction. Rover fix is DGNSS and sometime FLOAT. HDOP=0.6. How can I verify (connected to the rover).
Is there a way to know why don’t have rtk fix? I mean, could I know if the problem is from the base o from the rover?
“NO RTK” Led on base is always on. “NO RTK” Led on rover is off after a couple of minutes from base power on.
What are the posible fix types in the rover?
Thank

Ardusimple Staff replied 11 months ago

Starting checks:
1. Changing default configuration
2. Signals not good enough: you can have good HDOP but if signals are low the quality of RTK will also be low. Install the rover antenna on a metal surface larger than 10centimeter.
3. Poor radio link, i.e. losing a lot of RTCM messages.

1 Answers
Best Answer
clive1 answered 11 months ago

The BASE should be in TIME mode, this is not an “RTK” mode, but rather that it has a fixed and static location it can broadcast, along with observations from that location.
You can check messages received at the ROVER using UBX-RXM-RTCM
The ROVER can have the following fix types NONE, 2D, 3D, 3D/GNSS, FLOAT RTK, FIXED RTK, and perhaps others, but 99.9% likely to be one of these.
Poor quality or noisy measurements from the Base can result in the Rover being stuck in Float or less indefinitely. Poor quality or noisy measurements at the Rover will also give sub-optimal results. Lack of reception of RTCM3 packets will also cause Rover to report more conventional fixes. 

Leonardo Garberoglio replied 11 months ago

Ok, I think it is working right now (base station on top of my house roof and a 20cm ground plane just in case), I can see in u-center that (rover) fix type is 3D/DGNSS/FIXED (it’s FIXED, not FIXED RTK and it shows all three fix types) and position points “on the map” are inside of 10cm circle. If I move the rover around it fix type change to FLOAT for a couple of seconds and then FIXED again. If I turn off base station rover fix type change to 3D.

clive1 replied 11 months ago

FIXED (RTK) and FLOAT (RTK) are both RTK modes, depending on the software and NMEA sentences involved these might be displayed with/without “RTK” explicitly being stated.

https://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_GGA.html

None of the NMEA messages output a “TIME” mode, to see this you need UBX-NAV-PVT or one of the other messages reporting that mode.

Leonardo Garberoglio replied 11 months ago

Thank Clive, it is clear now.