DMR 101

Digital Mobile Radio is, as the name implies, digital. Originally developed in Europe, DMR is
used worldwide. You have probably heard of MOTOTRBO, Motorola’s implementation of
DMR. Like D-STAR, we can do stuff with DMR just not possible in the analog world.

The big difference between D-STAR and DMR are the markets they were designed for. D-STAR
is from the Amateur world, and focuses on the user controlling what connections are possible
over the D-STAR network. D-STAR encourages user experimentation and customization as
well.

DMR is from the commercial world where the user just wants to “Push-To-Talk”. The focus is
on ease of use as the radio is simply a means of communication. How and where the network
connects is left to the system manager.

BrandMeister has changed DMR into a more “Amateur-Centric” mode. Much like D-STAR, the
BrandMeister network lets the used decide how a repeater is connected to the network.

DMR Concepts

Just as FM and D-STAR require more than just entering a frequency, DMR has its own unique set of parameters to program. Don’t panic, they do make sense, especially if you remember DMR is designed for the commercial market, and we have adapted it for Amateur use.

To put things simply, there are several “Big Ideas” with DMR: Radio ID, Color Code, Timeslot and Talkgroup:

  • Radio ID (Subscriber ID): DMR is digital, and networked, so each radio has a unique ID number to identify it on the network. In the D-STAR world this corresponds to the “MYCALL” parameter. To obtain a radio ID, go to: https://www.radioid.net/register#!
  • Color Code: This is the DMR version of PL.
  • Timeslot: DMR uses magic known as “Time Division Multiple Access” (TDMA). In Simple Ham English, this means the repeater can support two simultaneous conversations by alternating between two timeslots. About 30ms is given to timeslot 1, then the transmitter flips to timeslot 2 for 30ms, then back to timeslot 1, and then to timeslot 2… you get the idea. Something like the mom who speaks to her 2 kids, allotting each of them 30ms to talk. Since you transmit on just one timeslot, your radio’s battery last longer as it is really only transmitting about half the time you have the PTT keyed. In other words, the repeater’s Time is Divided such that Multiple hams can have Access (TDMA).
  • Talkgroups: DMR is designed for the commercial market where radio users typically have something in common, such as Security, Engineering, Parade Operations, etc. It isn’t very efficient to have separate repeater pairs for each group, so DMR uses “Talkgroups” to group together users who want to talk to each other. On our DMR repeaters we have several Talkgroups that allow you to talk to geographically increasing areas: local, regional, statewide, all the way up to worldwide. Talkgroups are also either “Always On” (Static for BrandMeister) or “User Activated” (Dynamic for BrandMeister). “Static” or “Always On” means just that, network traffic to this talkgroup is always on. “Dynamic” or “User Activated” talkgroups have a timer associated with them, typically 10 to 15 minutes. The practical side of this is that after 10 – 15 minutes of local inactivity on a Dynamic talkgroup, it is dropped from the network connection. To start listening to a Dynamic talkgroup, key up, and you probably want to talk at least once every 10 – 15 minutes as well in order to keep the network feed.

Channels and Zones, Oh My!

CHANNEL: Just like with your analog radio, this is where all the details are stored. Channel name, frequency, offset… and for DMR, add in color code, timeslot and talkgroup.

For an analog repeater, we have one channel with the frequency, offset PL and channel name, PAPA 3 for instance.

Remembering that a DMR repeater supports talkgroups, we will have multiple channels to define the talkgroups we wish to use on a specific repeater. Each of these channels will have the same frequency, offset and color code, but will have a different talkgroup number, name (and possibly time slot) to define the talkgroups on that DMR repeater. If there are 5 talkgroups you want to use on a DMR repeater, you will need 5 separate channels; one for each talkgroup.

If there are four DMR repeaters in your area, and you want to use the same 5 talkgroups on each DMR repeater, you now have 20 channels programmed (5 talkgroups times four repeaters = 20 channels). How do we keep all these channels organized? Especially if I only have 16 positions on the rotary channel knob? Enter our friend, the Zone.

ZONE: A zone is simply a way to organize channels. Think of it a a folder containing a group of channels. Your “Santiago Zone” will have the 5 talkgroups for the Santiago DMR repeater, the “Otay Zone” will have the same 5 talkgroups for the Otay DMR repeater, the “Santa Ynez Zone” will have the same 5 talkgroups for the Santa Ynez DMR repeater, and so on. Switch to the “Santiago Zone” and all the channels for Santiago are there. You can include analog channels too if you like. Much easier than scrolling through potentially hundreds of channels.