Configuring GPS/APRS on MTM800e

There are a number of steps involved in configuring GPS to work with APRS via SVXLink on an MTM800e. Here’s what’s involved

CPS Settings

Here’s a list of screenshots taken from my CPS with the changes you need to make highlighted in yellow.

Ensure the radio ISSI is 9999 for your base station:

Ensure GPS is disabled on your base station radio:

Ensure the below highlighted options are set correctly in Data Services > Short Data Service

Ensure the below two options are correctly set in Data Services > SDS Remote Control

Ensure the below are set correctly in Data Services > AT Commands

CPS Lab Settings

You’ll need a copy of the DEPOT tool to change these settings within LAB mode > Decimal.


Ensure your SVXLink.conf file includes the APRSPATH string with your callsign. I’ve used 10 in my example below as my base station.


Also ensure you add a string under Tetra_Users for your portable radio ISSI. There’s no need to add the base station ISSI (9999).



  • 901 is the MCC
  • 16383 is the MNC
  • 5050997 is the ISSI of your portable radio that you want to show on the map
  • -1 is the portable number. You could use anything between -1 and -9 here
  • \E is the icon that’s displayed on APRS.FI. You can use the details here to pick your own icon:
  • 0 is added before the MCC, and before the ISSI to ensure the string is the correct length.

Testing APRS

Once configured, fire up your portable radio and head outside to get a GPS lock. The GPS symbol should appear solid once you have a lock. This can take a few minutes!

Once done, key up and keep an eye on your your SVXLINK log file, or better yet review the APRS.FI raw log files.

If you see the following, it means your radio doesn’t have a GPS lock yet. Wait a few minutes and try again.

Once your radio has a GPS lock, it’ll appear in the APRS.FI Raw logs and on the APRS.FI map.


If APRS isnt working for you, there’s a good chance something is miss-configured on the MTM800e (base station radio).

To troubleshoot, connect the radio’s serial to USB cable to your PC and open Putty. Connect via Serial to the correct COM port of the radio.

Once connected, type AT and hit ENTER. You should see OK appear.

Now type AT+CTSP? and hit ENTER

You should get a list of AT commands that are currently set on your radio:

The one causing the issue here is 0,3,10 – we need to set this as 1,3,10 to route the GPS LIP data to the PEI port so that the Raspberry PI and SVXLINK receives the GPS data.

You can try running AT+CTSP=1,3,10 and if you get an OK you’re good to go! If you however receive Error Code 3 (which means not allowed), this is caused by a miss-configured setting on the MTM800e under lab mode. Take a look at the above screen shots again and ensure your configuration specifically matches it.

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