DMR Basics

What is DMR?

DMR stands for Digital Mobile Radio and uses the Motorola TRBO protocol for communications. Like other digital modes such as D-Star, C4FM and APCO P25, the TRBO protocol converts your voice into a digital form and sends it out via RF (with other bits of information included) and allows you to communicate to other DMR radios and also DMR repeaters, which are networked together around the world via the internet.

What makes DMR stand out from some of the other digital modes is that it utilizes TDMA (Time-Division Multiple Access) to divide a single frequency into 2 distinct “channels” or time slots. By doing this, you can have two conversations going on at the SAME TIME, using one frequency.

Static or Dynamic

On a BrandMeister repeater, talkgroups can be static (permanently activated by the administrator) or dynamic (temporarily activated by a user).

The administrators determine how their repeaters are configured. Some allow only specific static talkgroups to be used on each time slot. Others allow users to activate dynamic talkgroups, in which case, the convention is:

  • Users are allowed to activate dynamic wide-area talkgroups on time slot 1.

  • Time slot 2 is used for static local talkgroups.

When you activate a dynamic talkgroup on a repeater's time slot by keying up, it remains activated on the repeater as long as you continue transmitting on it. When you stop transmitting, it automatically gets dropped from the repeater after a period of inactivity, typically 15 minutes.

Note: BrandMeister administrators allow dynamic talkgroups, while some other networks can be more restrictive. To understand how a specific repeater is set up, talk to people who use it, visit its website, or contact its administrator.

When you link to a talkgroup via a personal hotspot, the dynamic, static, and auto-static behavior depends on whether it's a simplex or duplex hotspot.

What is a Static Talkgroup?

A static talkgroup is one that is permanently activated on a particular timeslot by the repeater sysop. This type of static assignment passes ALL traffic from the DMR network over the air on the timeslot it is assigned to.

For example, if a statewide talkgroup is assigned to the local repeater on timeslot 1, anytime someone keys that talkgroup on the network, regardless of where they are, the audio will be retransmitted locally.

In simple terms, this networks many repeaters together full-time for that particular talkgroup.

What Is A Talkgroup?

A DMR talkgroup is simply a way of grouping many Radio IDs into a single digital contact. Or put another way, a talkgroup is a method of organizing radio traffic specific to the DMR users that all want to hear the same thing and not be bothered by other radio traffic on a DMR network that they are not interested in hearing.

Talkgroups can exist for many purposes. You can have talkgroups for countries, states, counties, regions, cities, special interest groups etc. Just about any group of DMR users could have a talkgroup assigned to them if they wished to organize traffic that they can all monitor and take part in, without having to talk to each other one by one.

Talkgroups are also specific to individual DMR networks, BUT they all generally follow the same numbering scheme. So you need to make sure that you know what the various talkgroups are for each of the DMR networks that you may use.

For example, Talkgroup 3129 on the MARC network might not be the same as Talkgroup 3129 on the Brandmeister network.

What is all this color code and time slots and talk group mumbo jumbo?

Lets answer this one item at a time.

1) Color Code is just a fancy name for what would be “CTCSS” or “PL” in the analog radio world.

2) Time slots are what makes DMR unique. Your transmit signal is broken into 30mS digital packets and the transmitter switches on and off rapidly. Doing this allows two signals to share the same channel at the same time. One on Time Slot 1 and one on Time Slot 2.

3) Talk groups are the group calls so those listening to that group number can hear you. People have to have that group programmed in their radio and listening on THAT group and THAT assigned Time Slot.

Simplex hotspots

With simplex hotspots, a new behavior is introduced: auto-static.

When you link to a BrandMeister talkgroup via a simplex hotspot, it is activated as an "auto-static" talkgroup, which behaves like a dynamic talkgroup, except that it won't time out and drop, even if you aren't transmitting on it. This means that when using a simplex hotspot, you can continue listening to a linked talkgroup for longer than 15 minutes without having to key up to keep the activation alive.

If you have activated an auto-static talkgroup, and then you link to a different talkgroup, the new one becomes auto-static, while the original one becomes dynamic. If you don't transmit again on the original one, it behaves like a regular dynamic talkgroup: after 15 minutes, it will time out and drop.

The auto-static feature makes operating a simplex hotspot even simpler, since you don't need to access BrandMeister SelfCare in order to manage static activations as much as you might do so with a duplex hotspot.

However, even though the the auto-static feature makes it unnecessary to use static talkgroups with simplex hotspots in many cases, you do still have the option to use BrandMeister SelfCare for your simplex hotspot in order to set up static talkgroups as well as to schedule talkgroups to become static.

What is a Code Plug?

a code plug is a file that contains all of the programming information for a radio. It defines not only the frequencies on which a radio can transmit and receive, but also which talk groups that the radio can communicate over, as well as other operating parameters.

What is Promiscuous Mode?

It lets you listen to all talk groups on any time slot on any color code. When you receive a signal and you want to switch to that time slot – talk group combination. The type of radio you have depends on how it is used and if your radio has the capability to perform this function.