Saturday, January 13, 2018

Listening to DMR on the Rasperry Pi3 with op25 and a SDR

This past summer I blogged on how to listen to a simulcast APCO-25 trunked public safety system. Since that time was looking for a way to listen to a DMR system.  Last winter I gave the Raspberry Pi2 a try using DSD.  That didn't go so well.  I suspect because DSD was written a long time ago, and is a single threaded application that can't take advantage of the Pi's multiple cores.

Last April Transmit support was added to op25 for; DMR/YSF/P25 and D-STAR.  Just after Christmas this year, Receive support was announced.  So I had to try this!

I just heard DMR audio on a Pi3.. And it sounded good!

Linux op25 4.9.28-v7+ #998 SMP Mon May 15 16:55:39 BST 2017 arm71 GNU/Linux (Raspbian Jessie)

ppm set to 3 for me (see json file below) 
using my NooElec SDR

Note: DMR audio for the second time slot is sent on the specified port number plus two.  In example 'udp://', audio for the first slot would use56122; and 56124 for the second.

You can setup a mix of the various digital channels in the json file... It works like a scanner.. And if you want you can define SDR dongles to channels... In case you want certain channels banded to a certain hardware... for RF/antenna reasons for example.

Graham and Max have been hard at work improving op25.  And thanks to that hard work its child's play to install:

sudo apt-get update
sudo apt-get build-dep gnuradio

cd ~
git clone
cd op25

If you are wondering what your tuning offset is, the best thing is to enable the datascope plot, and adjust the ppm value by one click at a time to center the eye plot.

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