What is Digital Mobile Radio?

Digital Mobile Radio (DMR) is a digital radio standard originally designed for commercial use and developed by the European Telecommunications Standards Institute (ETSI) in 2005. Ham radio operators have brought it into amateur radio for their own use. However, it’s not the only digital protocol that is being used in amateur radio.

Other digital voice systems being developed or adapted for use by hams:

  • D-STAR, an open standard developed for amateur radio by the Japan Amateur Radio League, with equipment by Icom and Kenwood.
  • System Fusion, a proprietary system for amateur radio by Yaesu.
  • P25, a standard developed for North American public safety services. Governed by the Telecommunications Industry Association and others.
  • NXDN, an open commercial and public safety standard initially developed by Icom (implemented as IDAS) and Kenwood (implemented as NEXEDGE), and now overseen by members of the NXDN Forum.
  • There also are a couple open systems slowly being developed for amateur radio, which are based on an open source speech codec (vocoder) called Codec 2. One is the M17 Project, and the other is called FreeDV.

If something about using DMR for Amateur Radio doesn’t make sense, remember that DMR was created for commercial use, and was never designed nor intended for amateur radio use.
– Mike’s DMR Doctrine, by Mike, K0NGA, of Rocky Mountain Ham Radio

Digital Mobile Radio networks

This is one area where DMR is a bit different from D-STAR. Just as in the D-STAR playground, some DMR repeaters are standalone and used for local communication only; however, DMR and D-STAR diverge in how they handle it when repeaters are interconnected.

In D-STAR, repeaters can be linked to reflectors. In DMR, repeaters using static talkgroups are linked together in network configurations that are decided by the system administrations, which can’t be changed by individual hams. Some repeaters also allow hams to temporarily subscribe to specified dynamic talkgroups.

Find Digital Mobile Radio repeaters in Minnesota.

DMR-MARC and DMRPlus (DMR+)

Initially, there were two main worldwide umbrella networks for amateur radio, DMR-MARC (which years ago was the largest), built on MotoTRBO products, and DMRPlus (DMR+), built on Hytera products. The two networks didn’t interconnect initially. Eventually, the two teams started collaborating on building some interconnectivity, but the use of these two networks hasn’t been growing as much as some of the other newer networks in recent years.

Brandmeister

More recently, a new worldwide network, Brandmeister, was launched. It grew to be the largest amateur radio DMR network in the world. Brandmeister users can key up to (a.k.a., temporarily subscribe to) and use any talkgroup. It’s also a very friendly network for hotspot users. 

On the Brandmeister wiki, they say:

If you are an amateur radio operator working in digital voice modes like D-Star, DMR, C4FM, APCO25 or others (not all are supported yet!), you do not need to know much about Brandmeister, and it’s very easy to operate on its infrastructure.

– Brandmeister Network Admins

“Brandmeister” is a play (in German) on the words “brand new master server.”

It’s a decentralized, worldwide, community-driven network being developed by an international team:

  • Artem, R3ABM, Moscow, Russia
  • Rudy, PD0ZRY, Ultrect, The Nederlands
  • Yentel, ON3YH, West-Flanders, Belgium
  • Robert, DK5RTA, Germany
  • Wijnand, PD0MZ, The Nederlands
  • Denis, DL3OCK, Berlin, Germany
  • Adam, SQ7LRX, Poland

They are joined by teams in countries worldwide that are bringing master servers online, as well as by other teams putting repeaters online. As of July 2019, there are 47 BrandMeister DMR Servers deployed, connecting hundreds of repeaters in more than 43 countries.

As of early 2017, BrandMeister was just a bit more than a year old: development work began in 2014, and the first master servers went online in November of 2015. It’s spreading as fast as a wildfire, which I guess is appropriate since, in German, “Brandmeister” (little “m”) means fire chief.

From the Brandmeister wiki:

BrandMeister is an operating software for master servers participating in a worldwide infrastructure network of amateur radio digital voice systems.… Brandmeister allows you to connect to MOTOROLA DMR-MARC and Hytera DMRplus networks, this means you can operate with other DMR amateur radio operators on both infrastructures at the same time.

Brandmeister has a really nice, robust User Dashboard that includes activity meters and a real-time “last heard” page.

Screen shot of the Brandmeister dashboard. Brandmeister is one of the most popular DMR networks.

TGIF Network

Another relatively new network is the TGIF network. It has a small but loyal following with hams around the United States.

Time slots

When there are so many puzzle pieces that need to be fitted together to set up a DMR radio successfully, it’s challenging to figure out where to begin.

DMR uses Time Division Multiple Access (TDMA) to generate its signal instead of the Frequency Division Multiple Access (FDMA). Specifically, DMR uses 2-slot TDMA (the slots are numbered 1 and 2, or TS1 and TS2).

What this means is that calls on two different channels can share the same frequency simultaneously. Each call is sliced up into chunks of a few milliseconds, and the slices from the two calls are interleaved on the signal. This happens so fast that we hear what we perceive of as a continuous transmission even though it’s coming in chunks, looking like this:

Time slots interleaved on the signal of a Digital Mobile Radio transmission.

This also means that when you program a DMR channel, you must specify both the frequency and the time slot, so that your radio and the repeater can encode and decode which chunks on the signal belong to the channel you’re using.

Color codes

Another fundamental piece of the puzzle is color codes (CC). Think of the as the digital version of a PL tone like you find on analog repeaters. When you want to use a DMR repeater, you need to program in the appropriate color code to open it up and have the repeater respond that it’s hearing your transmission. There are 16 color codes, 0 – 15. Why are they called color codes? Nigel, G8IFF educated us on the answer:

[I]n the early days of DMR being a Motorola commercial system, the radio programming was done by Motorola who sold you a “plug” containing diodes that you plugged into a socket on the radio’s circuit board. No user programming in those days. The color code was so called because it was indicated by a colored dot printed on the codeplug you were supplied with.

Nigel, G8IFF

Just as with analog radio CTCSS tones, you need to get the appropriate color codes from the organization operating the repeater in order to be able to use the repeater. When you program a DMR channel, in addition to the frequency and the time slot, you must specify the color code; otherwise, you won’t be able to access the repeater.


The magic formula to accessing a DMR repeater…

Frequency + Time Slot + Color Code


Let’s take a look at an example of a local Minnesota DMR repeater:

Frequency: 442.650+
Color code: 2
Time slot: 1
The above programming will get you onto the wide-area MN State time slot 1 of the N0BVE repeater located in downtown Minneapolis, Minnesota. It’s a part of the MNDMR system.

Frequency: 443.200+
Color code: 1
Time slot: 2
The above programming will get you onto the MNDMR time slot 2 of the Medina repeater located in Medina, Minnesota. This repeater is also a part of the MNDMR system.

Talkgroups

Finally … let’s talk about talkgroups!

Of course, the whole point of getting onto a DMR repeater is to talk to other hams, and you do that by visiting a talkgroup, which enables one-to-many communication, sort of like a conference call or a chat room. Anything transmitted to a talkgroup is transmitted to everyone listening to (linked to) that talkgroup.

There are worldwide, nationwide, regional, statewide, area, and local talkgroups, as well as language-based talkgroups. For example, on Brandmeister:

  • Talkgroup 91 is Worldwide
  • 93 is North America
  • 3100 is U.S. Nationwide
    Note: 3100 is an example of a talkgroup that is bridged across networks; it is U.S. Nationwide on the DMR-MARC, DMR+, and Brandmeister networks.
  • 3127 is U.S. State of Minnesota
  • 31271 is the Central MN area
  • 31272 is the Twin Cities Metro area
  • 31273 is the Northern MN area
  • 31275 is for Southern MN area
  • 3169 is U.S. Midwest Region
  • 9 is for using local communications on a single repeater
  • 2 is used when repeater owners decide to link multiple repeaters in a region together

In addition, there are the TAC channels (U.S.: 310 – 319; worldwide: 901 – 903). TAC 310, 311, and 312 are bridged between different networks, and Brandmeister is a guest on these channels. Hams that want to have longer chats in order not to tie up main channels that are more widely shared can use the TAC channels.

But what about the difference between static talkgroups and dynamic talkgroups?

Talkgroups are either static (always activated) or dynamic (user-activated). When you activate a dynamic talkgroup on a repeater’s time slot by keying up, it typically remains activated while there are transmissions on it, then drops from the repeater after some period of inactivity, for example, after 10 or 15 minutes. You don’t need to manually unlink from a talkgroup.

When you’re using a simplex hotspot on the Brandmeister network, there also are auto-static talkgroups that you can setup on your hotspot. For more info, see the article Brandmeister dynamic, static, and auto-static talkgroups.

On many repeaters in Minnesota, the talkgroups you can use on a given time slot are specified by the repeater administrator, including any dynamic talkgroups you want to use. Please see MNDMR talkgroups to understand how most MNDMR repeaters are programmed and what talkgroups they allow on TS1/TS2. If you want the freedom to use any talkgroup you’d like, you might want to invest in a hotspot.

The Pi-Star website also hosts a current and complete Brandmeister Talkgroup List, including descriptions and a link to the Brandmeister Hoseline page, where you can listen to activity. Wondering what hoseline is? Brandmeister Hoseline is live audio feed database where you can monitor any talkgroup on Brandmeister using your computer, tablet or phone.

Zones

Zones are an organizational tool, like file folders, for the channels in your DMR radio; in other words, a zone is a group of channels.

The channel selector on many DMR radios lets you choose from 16 (or more) channels. In order to get past that limitation, you can use zones. For example, a typical DMR radio that could handle 64 zones capable of storing 16 channels each, for a total capacity of 1,024 channels.

You can organize your zones however you want, for example, you might want one or more “Home” zones for channels that correspond to your favorite talkgroups that you can reach via the repeaters that are within range of your home. You might want a “Commute” zone that corresponds to the talkgroups you most often use via the repeaters that are in range as you drive to and from work. If you use a hotspot, you might want some “Hotspot” zones for the talkgroups you key up via your hotspot. You might want some other zones that correspond to the groups of talkgroups your club uses, or to nets you frequently participate in. Some people set up zones based on repeater locations.

It’s pretty easy to use zones: you create a zone, name it, and then add channels to it. Optionally, you can change the order of the channels within the zone.

Simplex frequencies

Just as you can use analog transceivers in FM mode, you can use DMR-capable transceivers to talk directly from radio-to-radio simplex. These are commonly used North America DMR simplex frequencies and are recommended for all DMR users in the United States to have programmed:

Admit criteria: Always or Channel Free

Time slot: 1

Color code: 1

Talkgroup ID: 99

UHF simplex channels:

  • 441.0000 MHz
  • 446.5000 MHz
  • 446.0750 MHz
  • 433.4500 MHz

VHF simplex channels:

  • 145.7900 MHz
  • 145.5100 MHz

DMR nets

A good resource for finding DMR nets across the United States is the Ham Radio DMR Nets Telegram group. It has a quite comprehensive list of active DMR nets. Each net is displayed an hour before it goes live, making it easy to find out what’s currently on the air: https://t.me/HamRadioDMRNets

Don’t forget the Minnesota Statewide DMR net happens every Wednesday night at 7 p.m. Keep tabs on Minnesota digital nets with our Minnesota Digital Nets Directory.

The content on this page is from amateur radio notes by Toshen, KE0FHS – It’s been modified under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.