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On Using Radio with RTK Module

1st Jan 2024

Setting RTK module to base mode output RTCM MSM4 data by default. The data rate is less than 960 bytes/sec, around 600 bytes/sec. 

To use radio with UART port to send RTK base data to the RTK rover, the radio air data rate must be set to no less than 9600bps; although the radio UART interface is to be set to 115200bps for default RTK module baud rate. Higher the air data rate lower the radio operating range, and vice versa. 

Before hooking up radio to the RTK module, one need to first check that it could continuously stream data at given baud rate from one laptop port to another using some terminal program to send a file without losing a single byte of data at short range. 

Some radio requires proper data framing, unable to support streaming of data continuously. One can only use radio that supports continuous data streaming if there is no microcontroller between the RTK base and the radio to control proper data framing. 

Once the radio has been verified to be able to stream data continuously without error, UART connecting the radio to the RTK module should correctly send base data to the rover for direct line of sight operation. 

For correct RTK operation using radio, the RTK Age count seen on GNSS Viewer should be within couple seconds. An increasing RTK Age count signals problem with the radio operation, either (1) insufficient air data rate, or (2) the radio might need proper data framing. 

If there is problem getting stable RTK Fix using radio, please check below: 

1. First check you are familiar with RTK base/rover operation, able to get stable RTK Fix by direct wire connection between base and rover. 

2. Make sure the radio used could support continuous steaming of data doing above described file sending test using terminal program. If short distance works, problem with long distance, increase the radio output power level. Or use 2 laptop to send a file from one to the other to check data correctness. 

Some radios that we have seen some customers use that could stream data continuously and work with our RTK modules are: 

Digi XBee-PRO 900HP 

Digi XTend 900 MHz 

Digi XBee PRO XSC S3B 

RFD900+