The LibraryThis is a good starting point for understanding DMR and how it is used in amateur radio.
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.
Imagine using one frequency while radio A is talking to radio B on time slot 1, and radio C is talking to radio D on time slot 2 … SIMULTANEOUSLY. Pretty neat, huh?
Here is a nice graphic from Retevis to help visualize and understand what is going on…
Although the graphic above relates to how a DMR repeater works, this same principal applies to using a simplex frequency as well.
To make matters a little more fun and complicated, each radio must have a unique Radio ID for digital identification between radios and you can also use Talkgroups to separate traffic and target specific groups of DMR users.
What Is A Radio ID?
A Radio ID is a unique number assigned to you (and your callsign) by the DMR-MARC Team. Like a telephone number or IP address, your Radio ID identifies you as a unique radio user on the various DMR networks and repeaters around the world.
We have a TON of information on Radio IDs and how you obtain one here. It’s very much worth reading!
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.
We have a TON of information on Talkgroups and how they are used here. It’s very much worth reading!