Bandwidth Limiting values for external radios

Document created by Geoffrey Kirk on Jan 10, 2019Last modified by Geoffrey Kirk on Jan 10, 2019
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When an internal radio is being used at the base station the system automatically adjusts the amount of data that is sent every second so that the radio network does not get overloaded. This is why it is important to select the number of correct number of 450MHz repeaters when setting up your base station.

 

If you send more data than the radio network can support then the normal failure mode is that the repeaters and the base station will jam each other, causing the % of packets that can be received by the rover to be greatly reduced. Often rovers will be able to receive 30% or less of the base observables (aka corrections) packets

 

 

Trimtalk V1 Over Air RateNumber of repeatersMax Bytes per secondApproximate Number GPS+GLONASS SVs
CMR+ Format 
9600075044
9600145025
960021507 (GPS Only)
4800036520
4800121510 (11 GPS only)
48002Not RecommendedN/A
192000151591
19200191854
19200231818

 

 

Notes: 

  • These numbers are for a Trimble radio, 3rd party radios may have different values.
  • The number of repeaters is the number of hops to get to the repeater. If the base is in the the middle of two repeaters normally you can operate both repeaters as Repeater #1

 

Formats with support for BW Limiting

CMR+: Recommended

RTCM V3: Not recommend for GPS+GLONASS application as will have less SV's transmitted that CMR+. As as rule of thumb reduce the number of SV's listed above by 5.

 

CMRx: Does not correctly BW limit in all situations. With CMRx's greatly reduced size Vs CMR/RTCM V3 it can often send the information on all the SV's in view without BW limiting 

 

CMR is not recommended for use with repeaters in 450MHz radio networks.

RTCM V2 is not recommended for use with a radio network

 

It is never recommended to output both RTCM and a CMR/CMR+/CMRx messages on the same data link.

 

Setting the Bandwidth Limiting:

 

This can be done using the Web UI of the GNSS receiver.

 

Select the output stream in the I/O Summary page.

 

There is a check box for Bandwidth Limit:

 

Check this and enter the value from the table above.

 

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