Portable RTK Base Station Setup

Introduction

This is a portable solution sends the RTK corrections via a Sik Telemetry Radio link directly the to vehicle’s RTK GPS, rather than thru 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 at 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

H-RTK UART1 & UART2 VCC ports are connected internally, so if you powered one, the other will output power also. But if you supply power the RTK module with USB-C ONLY, the UART1 & UART2 VCC port will not output power.

Portable RTK base Station

Connect as follow if you are using 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 follow if you are using Sik Telemetry Radio.

H-RTK (UART2)		Sik Radio
VCC	<-->	5V
TX	<-->	RX
RX	<-->	TX
GND	<-->	GND

Connect RTK UART to GPS1 Port on 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 power to power the RTK and Telemetry Radio.

If you are using a Telemetry Radio that requires a higher than 5V, then you must power the Telemetry Radio separately from battery or a proper power source.

UBLOX U-Center Setup

If you are not familiar with 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, baud rate is unimportant.

• Under 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 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 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 params (60s of <2m radius survey points), it will take 5-10 minutes to finish the survey assuming 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, and repower, and the survey will continue and ultimately complete.

Reference Discussion: https://discuss.ardupilot.org/t/simple-portable-rtk-base-station/87694