Tuesday, September 25, 2018

The Ham Ninja's DMR Tips and Tricks

As I dive into this aspect of ham radio, DMR, I thought I would share some of the tips and tricks that others have shown me or that I've figured out on my own.

I'll be updating this BLOG page when I find other things that I think people could use help with.
(Last Update 10/8/2018)

Most of what I'm about to talk about assumes you are using BrandMeister.  I'm a newbie, so if you find a mistake, leave me a comment and I'll edit the post. (Click on images for larger)

A few words about DMR

DMR: DMR starts out as scary and mysterious for existing hams, but the best way to think about it is to think of your local repeater as a little "talk group".  Your buddies are on xyz repeater so you dial it in and have a chat.  Now you know what a DMR "talk group" is!  DMR allows you to tap into a local repeater (or you can use a little mini hotspot as your own repeater) and basically jump into a talk group but it's not confined to the repeater.  Because the repeater uses the internet to link all the repeaters together, you could dial in the SoCal talk group (31066) that I usually monitor and give me a shout out.  If I'm there, I'll answer.  There are over 1300 talk groups out there and most repeaters that I've used allow you to instantly connect to one even though it isn't "static".  Here's a listing of Brandmeister talk groups.

Zones:  I really like the "Zone" feature, which is nothing more than a grouping of channels.  Zones are great for me since I only want to see some channels when when I'm at my summer home or working with my ARES team.   This is similar to the Yaesu "Bank" but Yaesu banks are hard to use, not labeled on some radios and kind of kludgy.  The way you switch banks is different on my two Yaesu HTs and I’m always forgetting how it works.  

Digital Part of DMR - Before I go on any further, I need to explain, as briefly as I can, what DMR (Digital Mobile Radio) is and how its different.  DMR is digital which does a few things right off  the bat. 
  1.  It allows repeaters to handle more than just one conversation at a time.  In this case, DMR repeaters use TDMA (time division multiple access) allowing two conversations at a time by switching back and forth between two “time slots”.  This is done so quickly you don’t notice (like on the old TDMA cell phones).
  2. Because your voice is digitized when it comes out of the radio, it makes it easy to integrate other digital technologies and add additional features.  For example, all of the BrandMeister repeaters worldwide are  linked together on the internet.
  3. Each transmission has some header info about who you are, the on-ramp that you took and what “talkgroup” you want to communicate with.
  4. Connections are without noise since it’s voice over digital, the voice is there or it isn’t.  There’s bound to be some data loss so the protocol includes some amount of forward error correction that’s being done.  So, in theory, users should get better range (but that is sortof a myth).   It's a myth because the quality is good at range compared to analog but max range is about the same.

    As I've used DMR for a while in the field I've found that the performance can be a bit frustrating.  According to this article and a Wikipedia article, your coverage won't be any better on DMR.  In fact, I'm wondering if it will be just a touch less.  DMR is just a bit misleading because of forward error correction, you get decent quality right up to the end, then you get ZERO, ZILCH, NADA, you vaporize! (attribution Bob KB6CIO).  With analog FM, you can turn off squelch and still pick up a very weak signal.  I've done this a couple of times when doing mountain top to mountain top comm.

    I'm a little bit frustrated with DMR sometimes because I'll just loose the conversation entirely, it will vaporize and I have no idea that I've lost touch with the repeater.  It finally dawned on me why I'm frustrated by this while talking to another ham this morning.  With analog as you or the other operator move to the fringe of coverage, you know the system tells you that the end is near.  It communicates this when the signal get a little more noise in it, then small drop outs begin occurring then larger drop outs then bang, the station isn't breaking squelch. 

    With DMR, the only time you know you have a problem when using a repeater is that the radio will give you an error tone if you aren't making it into the machine (this is important).  Your DMR radio transmissions are chopped up into very small increments and when it's not actually sending data, it receives data from the repeater during your entire transmission.  If it doesn't get enough of these back, you get an error tone on your radio so you know it isn't working.  Here's the problem, you only know for sure ONLY when you are transmitting.  As you approach the edge of reception range, you go from good quality to zero reception.  Sure, sometimes there is some digital interference and some R2D2 sounds to let you know but my experience is that I go from good to nothing.

    On the bright side, you know for sure if you are getting into a repeater when you don't get an error.  Also, in my experience, I can use a HT in my car with no external antenna around town with no problem.  I'm guessing my analog quality would be up and down in San Diego (which is very mountainous) but with DMR it's good until it isn't.  BTW, I'm looking forward to AnyTone coming out with a vehicle mounted DMR unit so I can switch over to the external antenna (which is currently plugged into the analog radio).

    This is a long section but the net net is that I still think that DMR is the future for a lot of reasons.
  5. Because it's digital, you can easily build or buy a little box that we refer to as a "hotspot", basically, you own personal repeater.  This allows you dedicate frequencies that you want to listen to all the time to your own repeater and experiment without taking up one of the slots on a public repeater.

Talkgroups:  If you think of a single stand-alone repeater or a few repeaters linked together as a group of people that want to talk to each other, that’s a “talkgroup”.   DMR has over 1,270 talk groups with room for more.  They do this by connecting each repeater (or the little hotspots like the one in my home) to a network of computers.  When a repeater or hotspot (I’ll just say repeater from no on) is subscribed to a talk group, any transmission that is destined for that group is heard by all the operators listening.  Just think of it as a massive website of pages where a page is a talkgroup and instead of a web page, it’s voice.  Lastly, if an operator is using a DMR repeater and wants to talk to his pals on the SoCal 31066 talk group but the repeater isn’t currently subscribed to it full-time, all she has to do is dial in the repeater and configure the radio with talk group she wants to communicate with and then transmit.  The radio sends the destination talkgroup with each transmission and the repeater will dynamically add the group to the subscribed list if it’s isn’t already.  Now the operator just joined the group and can hear everyone else no matter what their on-ramp is.  Think of it as being able to connect to any repeater in the world from any repeater with just the push of a button. 

For me, DMR using the Brandmeister network really opens up a new world of capabilities.  Users of Analog repeaters can link the repeater to another repeater,  if it is supported,  using special tones sent from their radio.  I’ve see local hams do this by linking the repeater I’m on to one in New York or elsewhere.  DMR changes this because it makes connecting to a talkgroup from anywhere in the world as easy as pressing the transmit button on your HT.  If I was in Russia, I could use a local repeater or hotspot and yak with my pals that monitor the SoCal group here in San Diego in seconds.  If you are into radio, this is pretty cool. 

There’s one catch though.  If at any time the repeater becomes disconnected from the internet, it acts like any old-school repeater by only having the capability to communicate with users on that specific repeater.  In a disaster, not a problem, just choose the “local” talk group and the repeater knows not to even try to use the Internet. 

OK Now onto DMR TIPS

Something that I learned about slots on a repeater

Something that I learned yesterday is that the Motorola repeater by me supports dynamic talk group(s) on either slot but the talk group can only reside on one slot at a time.  If the repeater is asked to dynamically create the talk group on the other slot, it's removed from the current slot.  If my buddy and I are both using the San Diego Talk Group (310670) on the same repeater but we are using different time slots we won't be able to hear each other unless we are in promiscuous mode (known as digital monitoring on the 868) on BOTH SLOTS.   I debugged the problem by going into the repeater details on brandmeister.network HERE.  When I transmitted, the talk group was dynamically created on timeslot 1, just like it should.  When my buddy transmitted, but was set for timeslot 2, the talk group was dynamically created on slot 2 and it was removed from slot 1.  Therefore, because he wasn't monitoring all traffic on the other slot (by turning on "Digi Monitor Dual Slot"), he never heard me.  

So if you ever run into an issue where you are monitoring both slots, a common thing to do, have him/her turn on monitoring.  If they hear you then they are using the other slot on the same repeater.  This isn't something that you would run into often, but as usage of DMR repeaters in your area climbs, you may see an increased occurrence.  It's easy to see what slot you are using on the 868 by looking at the little "T" in the blue box on the second line.

The first programmable button on the left side of the radio can be set to quickly turn on "Digi Monitor "Single Slot" or "Duel Slot".  If you think you are having this problem, click it until it says "Duel Slot".  If all of a sudden you hear your party on the line, that's the issue.

The Anytone radio allows you to fix the problem on the radio within 30 seconds.  All you need to do is find a channel you setup on the other time slot and then use the instructions on my Anytone tips page in section titled "Using a talk group on the fly"  If you need to change the slot assigned to a channel you created long term, you can go into the menus or just program it from your PC when you get home.

Using Brandmeister.network Repeater page to debug your comms

One of the best tools to better understand how the Brandmeister system works, understand how your neighborhood repeater is setup, or debug why something isn't working is to actually look at what's going on.  Brandmeister.Network is a super powererful tool available to anyone.  

To see how a repeater is setup, go to brandmeister.network, click on repeaters, then search for your repeater.  At the top of the page is some general info about the repeater, and in this case, which time slot they prefer you use when creating dynamic talk group, groups that aren't static.  

If important to know what talk groups are "static" or always on for the repeater you plan to use.  If you use one of the talk groups that the repeater is always subscribed to, you want to make sure you setup your radio with so that you use the same slot.  If you use the wrong slot, you will unnecessarily cause the repeater to subscribe to the group for both slots and use the entire repeater, or it could cause a problem.  Also, if you are moving into the area, and setting up the repeater on your radio, it's always good to know what "static" groups it carries.  That way, when you are in promiscuous mode (listening to all traffic), you'll be able to figure out what's going on.  Having those setup in your radio allows you to quickly join the party.  

The "static talk groups" are on the left side of the page under "Slot details".  Talk groups that have a little pad-lock symbol on them indicates that it's static and always on that slot, or "subscribed" to traffic for that slot.

This page also displays the "Last Heard" for the repeater with some important details.  As a test, transmit on the repeater's frequency then refresh the page.  You should see your call-sign, and how long ago the repeater heard you.  The other important column is "Destination", which indicates the talkgroup that you were trying to use, and under "Options" it shows which time slot you used.  All of this info helps you debug any issues you think you might be having when setting up a channel on your radio.  

One last thing that I use this page for is to see how busy the repeater is and what its being used for.  Before I left on a trip to another state, I looked for repeaters that were busy so that I could monitor and see how it's being used, or other repeaters that are not being used much at all and therefore the locals wouldn't mind me creating a dynamic group on their machine so that I could chat with my palls on SoCal.

Using Brandmeister.network "Last Heard" page to see who's talking and better understand what's going on.

One other thing I've use brandmeister.network for is to see if a talkgroup is being utilized or just to see who last transmitted because I missed their call-sign.  

For instance, I knew that the hurricane net wasn't being used by going to the "Last Heard" page for that talk group and looking at the activity.  What I saw was a lot of traffic, but the duration was 0 or 1 second.  That probably meant there were people like me hitting a repeater to create a dynamic subscription but no actual talking.   

To see activity on a particular talk group do the following.
  1. Click on "Last Heard" on the left hand navigator.
  2. Click on the little plus (+) sign that is in the search box.  Note that once you use it, turns into a "-". 
  3. Click on "Add rule" on the right.
  4. There is a pull down on the left, click and choose "Destination ID".
  5. Enter the destination ID, 3199 in my example for the Hurricane net.
  6. Click "Search", located on the right.
As you can see from the first column, "Time", it's not very busy, and secondly, it's not active because the duration is really short (the first two are probably due to people kerchunking the repeater with that talkgroup.


-- Chris Claborne
aka Christian Claborne

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