How to setup a RTK Base station using a TOP168(u-blox ZED-F9P) GNSS Receiver?

Posted by jack wu on

Real Time Kinematics (RTK) technology could help to acquire the position in extremely high accuracy, however, RTK relies on RTCM correction data from a base station. If you couldn’t access a RTK base station in your area, setting up your own could be a practical alternative. In this instruction, we will step by step explaining how to set up a TOP168 GNSS Receiver as a RTK base station.


1. Download and install the configuration tool 

If you already have “u-center” software installed, please go to section 2 directly. If not, you need to download it from the u-blox website.
For TOP168 or another ZED-F9P GNSS, please select the edition which is compatible with “F9 / M9”. After download, please installing u-center software to your Windows computer, then plug in the TOP168 GNSS receiver to the usb port. Open the “device manager”, expand to “Ports (COM & LPT)” → “u-blox GNSS Receiver (COMxx)” or “USB Serial Device (COMxx)”. In my sample below, the COMxx is COM12. Note down this COM port number. In order for u-center to connect to TOP168, you need to connect to this COM port.

RTK Base Station U-center port


Open the u-center. In the menu, select “Receiver” -> “Connection” and select the COM port you noted down from the Device Manager above. This time, it is COM12.


RTK Base Station u-center port

2. Turn on RTCM3 message types

In the U-center menu, Select “View” → “Message view”. The message view windows will show up.

RTK Base u-center message view

In the “Message view” window, select “UBXCFG→MSG”. On the right panel, select 
Message “F5-05 RTCM3.3 1005”. Turn on UATR1, UATR2 and USB.
To save the setting, please click the “send” button 2 times. (In u-center, every time you want to save the settings on the current screen, you need to press the “send” button 2 times.) 

 RTK base station u-blox message configure

Other than the “F5-05 RTCM3.3 1005, do the same for Message types below.

F5-4A RTCM3.3 1074
F5-4D RTCM3.3 1077
F5-54 RTCM3.3 1084
F5-57 RTCM3.3 1087
F5-5E RTCM3.3 1094
F5-61 RTCM3.3 1097
F5-7C RTCM3.3 1124
F5-7F RTCM3.3 1127
F5-E6 RTCM3.3 1230


RTK Base Station - RTCM message configure

Turn on their UATR1, UATR2 and USB options, and press the “send” button 2 times for every message type. 

Now, on the left panel of “Message View”, if selecting “RTCM3”, you will see the RTCM message types 1074, 1077, 1084, 1087, 1094, 1097, 1124, 1127, 1230 turn from “Gray out” to “Black”.

RTK base station RTCM3 message configure

1005 might be still gray out at this moment which is fine.  It will turn to “black” font as soon as the Base Station finishes initializing. 

 3. Aquire the base station location. 

From the Message View Windows, select UBX→CFG→TMODE3. Time mode(TMODE3) is the setting to tell the receiver how to acquire the location of the base station. You have the below 1, 2 or 3 options.

0 - Disabled (Disable the RTK base station mode)
1 - Survey-in 
2 - Fixed Mode 

“Survey-in” (Option 1)

If you deploy the GNSS base station at a temporary location, you could use the “Survey-in” method to acquire the base station position. The process takes only a few minutes to complete.  Survey-in is a procedure that estimates the receiver position by building a weighted mean of all valid 3D position solutions. Two major parameters are required when configuring:

Minimum Observation Time defines the minimum observation time independent of the actual number of fixes used for the position estimate. Values can range from one day for high accuracy requirements to a few minutes for coarse position determination. Practically, we use 300 s for a quick setup.

Required Position Accuracy”, This value will affect the rover's absolute position accuracy. Practically, we use 3 m. After changing the values, please click the “send” button 2 times to save.

RTK base station - Survey-in mode

“Survey-in” usually works under an unblocked open sky. Strong GNSS reception is needed.  If you open the “Satellite Level” window of the u-center, 8 or more green vertical bars which are greater than 47dB means an acceptable signal strength. Please refer to the below diagram.


RTK Base Station - signal strength

Survey-in ends when both requirements are successfully met. The receiver begins operation in time mode and can output a base position message “RTCM3 1005”. The “1005” message will turn to black font by now.

 RTK Base Station - RTCM 1005 message

“Fixed Mode” (Option 2) 

If you deploy the GNSS base station at a permanent location, we recommend this option. 
We have another step by step instruction showing how to acquire high precision coordinates by using a PPK service.

How to get a very precise coordinate of your RTK base station?

Other than using PPK, you could also get the high precision coordinates by RTK if it is available.
The receiver position coordinates need to be entered manually. Select either LLH position format (Latitude, Longitude, and Ellipsoid height(not the Mean Sea Level height)

RTK base station Fixed Position


or ECEF position format (ECEF -X, ECEF-Y, ECEF-Z). 


RTK Base Station - Fixed mode 

The base station position accuracy should match or exceed the desired rover absolute position accuracy, because any error in the base station position will directly translate into rover position errors. Practically, we use 0.03 m for “Accuracy”. 

After settings changed, please click the “send” button 2 times to save.
If the base station is moved during operation, then new position coordinates must be configured.

4. Configure USB port output RTCM message

From the Message view Windows of u-center, select UBX → CFG → PRTSelect  Message “3 - USB” (or the interface you need to set.)
Set “Protocol out”:5 - RTCM3 or “0+1+5 - UBX+NMEA+RTCM3"
After changing the values, please click the “Send” button 2 times to save.

RTK base station output port

5. Save the configuration permanently

This step is to save all above setting changes to the device. From the Message view Windows of u-center, select UBX→CFG→CFGOn the right panel, select “Save current configuration” and highlight all Devices”, then hit the send” button 2 times.

RTK base save the configuration

By now, your GNSS receiver has been configured as a RTK Base Station which outputs RTCM correction data through the usb interface.

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