Portable RTK Base Station Setup
Introduction
This is a portable solution that sends the RTK corrections via a Sik Telemetry Radio link directly to the vehicle’s RTK GPS, rather than through Mission Planner. With one exception, it allows one to setup an RTK Fixed Baseline station and have it update the vehicle’s GPS with RTCM corrections without having to use a PC running Mission Planner in the field.
The exception is that, without modification, the portable base cannot “survey” itself in at a new location automatically, which is required for it to send valid RTCM corrections to the Rover or Vehicle. So, if the base station location changes, you must attach it to a PC and use the Ublox U-Center application to have the survey-in process restarted. Its still an improvement by not having to have the PC out in the field adjacent to the base RTK GPS unit.
However, if one removes the backup batteries on the base unit GPS such that it “cold” starts every power up, the Base GPS can start a new survey-in automatically.
System Configuration
Portable RTK Base Station
Connect as follows if you are usingthe Sik Telemetry Module:
H-RTK
Sik Radio
VCC
<-->
5V
TX
<-->
RX
RX
<-->
TX
GND
<-->
GND
H-RTK (UART2)
Power Module (or 5V Bec)
VCC 5V
<-->
5V
GND
<-->
GND
Rover (with Direct RTCM Feed from Base)
Connect as follows if you are using Sik Telemetry Radio.
H-RTK (UART2)
Sik Radio
VCC
<-->
5V
TX
<-->
RX
RX
<-->
TX
GND
<-->
GND
Connect RTK UART to the GPS1 Port on the Flight Controller. If you are not using a flight controller (Ex, recording device), you connect this device to the USB port, and provide power to the UART1 to power the RTK and Telemetry Radio.
UBLOX U-Center Setup
If you are not familiar with the UBLOX U-Center app, watch some tutorials on the web. U-Center has many views and features, but for this exercise, you only need to:
Attach a USB cable to the unit
Start U-Center and on the Receiver tab, select the Connection for the USB COM port that appears; the baud rate is unimportant.
Under the View tab, select the Configuration view to set the parameters below for the Base and Rover(Vehicle) units.
For Base RTK:
Attach USB to the unit, start the UBLOX U-Center app, connect, and in the U-Center configuration view, set:
PRT: UART1, 57600 baud, RCTM3 out, UBX in…press send button in lower left
TMODE3: Survey-in, 60seconds, 2 meters…press send
MSG: RTCM3.3 - 1005, UART1 in/out, 1sec…press send RTCM3.3 - 1074, UART1 in/out, 1sec…press send RTCM3.3 - 1084, UART1 in/out, 1sec…press send RTCM3.3 - 1094, UART1 in/out, 1sec…press send RTCM3.3 - 1124, UART1 in/out, 1sec…press send RTCM3.3 - 1230, UART1 in/out, 5sec…press send
CFG: Save current configuration to FLASH…press send
For the Rover unit:
Attach the USB and use U-Center to set:
PRT: UART2, 57600Kbaud, RCTM3 in, UBX out…press send
CFG: Save current configuration to FLASH…press send
Set GPS_TYPE=1 in ArduPilot, do not set GPS to any moving base types, or the configuration will be changed and not work.
When you power the base unit, it will take it 30 seconds for the unit to acquire lock and start the survey process. For the above survey parameters (60s of <2m radius survey points), it will take 5-10 minutes to finish the survey, assuming a clear sky view. During the survey process, the Rover unit will flash its RTCM LED, and assuming the Rover unit has good satellite acquisition, it will move its FIX status from the normal 3D or 3D/DGNSS to “RTKfloat”. Once the survey at the BASE completes, it will move to full precision and report as “RTKfixed” status, if a GCS is monitoring.
Without modifying the base GPS to remove its backup batteries, you will either have to let the unit drain its battery backup (a few days to sometimes a week), or use U-Center to configure the TMODE3 to change slightly one of the params (add a second, for example) and press send to re-start the survey. You can disconnect it from power and then position it later to its location, repower, and the survey will continue and ultimately be completed.
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