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.

{Edit/update April 2020}
Max just added a way to specify talk group id's for DMR:
There are two new json keys defined for the channel entry - examples
   "whitelist":  "4,6,8"
   "blacklist": "9"
The talk group id's are specified as a string (comma separated list) with the entries in decimal. 

Wednesday, January 10, 2018


Before the latest ARRL shit storm erupted, I had written in November 2017 my section manager (KA1RB).  Pay attention to my 6th paragraph where I commented to KA1RB that I never see any division directors or section mangers make public FCC comment, thus I have no idea if they represent my interests.

You may have noticed I wrote to my section manger instead of Kermit, W9XA, my division director.  I haven't been impressed with Kermit, W9XA since he replaced W9GIG.  Not that I thought Dick Isely was that great anyway.  At least Pat, KA9RB responds enthusiastically, and comes off as having an open ear.  An impression I wasn't left with when I'd communicate with Dick or Kermit.

That was me who shyed away from your table at the fest when you brought up renewing.  I figured I can articulate my issues via email here better.  As a side note, that was probably the best Appleton fest I have seen in recent years.

I am considering not renewing this year.  I have been a member off and on, and more steadily the last few years.  Honestly I think the ARRL does a piss poor job of steering amateur radio. Maybe they don't want to, but ultimately someone should in my opinion. The don't even attempt to create enthusiasm about anything new.  I always admired Wayne Green despite some flaws, in that he inspired a more hand-on approach and promoted new ideas.  (I ended up being the somewhat silent curator to collect scans of his magazine, that he later signed off for release into the public domain, if you weren't aware)

I have brought up in past communications that I saw good things come from the HSMM working group around 2001 that was created under the direction of Jim Haynie, W5JBP. I had hoped other working groups would be formed, SDR and so forth as there seemed to be good ideas, enthusiasm, and promotion stemming from the HSMM WG.  I haven’t really heard much about the Technology Task Force since Brennan N4QX took over for Paul Rinaldo, W4RI, which is disappointing.

Anyway the ~$50 that someone might send the ARRL, in my opinion is better donated to an open source ham radio software project in my opinion.  I think folks like Jonathan Naylor, G4KLX are some of the unsung heros of ham radio.  Might just have to bring this up at a local meeting.

There was a recent entry license survey which I am sure you are aware of.  And since I got into the hobby in my high school days in the mid 90's I recall two big license changes.  I wasn’t paying attention at the time of those, but I would be interested in learning how those came about.   I assume they were ARRL endorsed/initiated to some degree.  Of course I am referring to the first was around 2000, where 5 WPM became the highest code test, and they consolidated the license classes, eliminating novice and advanced classes.  Then around 2006, when the code test went away all together.

So why the ARRL doesn't endorse some major rule changes bugs me. Seems like the bottom line to them is just to have a good number of folks entering the hobby.  And while I feel that is important, there are other important things like undoing some of these decades old rules to there is at least a chance of things moving forward on their merits. The bottom line is I don't know where they stand on things, let alone even where my division director feels personally.

Someone with the league really ought to write on what you can and can't expect ARRL to do and why.  Maybe that will help me.  Some years back I had similar confusion/frustrations with TAPR.
Thanks, any feedback will be used in making my renewal decision. Though I think the biggest thing that will help me make my decision will be this “vision of the future” that needs to be conveyed it to our current membership.  That is the shimmer of hope I have with the League right now.
Steve, KB9MWR

I am still waiting with money in hand for this vision, and some sort of action from the ARRL higher powers to indicate a willingness to move into 2018 with more transparency and a more democratic voice for it's membership.