What is DMR?

DMR stands for Digital Mobile Radio. This is an internationally established standard for two-way radio traffic. The DMR standard allows equipment from different manufacturers to work together on the same network and with all functions defined within the standard.

The aim of the DMR standard was to develop a digital radio system that remained low in both cost and complexity, yet allowed equipment from different manufacturers to work together. This way, users can decide for themselves which devices they purchase and they are not tied to a patented system that is expensive to maintain or replace.

The development and maintenance of the DMR standard is the responsibility of the European Telecommunications Standards Institute (ETSI). The system was first ratified in 2005 and has since been overhauled and modified several times, most recently in November 2018. There are 3 DMR Tiers.

Below are some frequently asked questions about DMR listed and answered.

Yes and no. Basic functionalities such as a voice message are always possible. If the chosen manufacturer has performed interoperability tests, you may even be able to use functionalities that fall outside the defined DMR standard.

It is best to check which features you are using now and see if they are unique to the current equipment before deciding which new products to purchase.

At what frequency does DMR equipment work?
Digital Mobile Radio operates on frequencies between 30 MHz (Megahertz) and 1000 MHz, or 1 GHz (Gigahertz). This frequency range is divided into two categories.

1. Very High Frequency (VHF) - The range between 30MHz and 300MHz.
2. Ultra High Frequency (UHF) - The range between 300MHz and 1 GHz.

Most DMR equipment falls within the 136 - 174 MHz and 403 - 527 MHz parts of the spectrum. Each country has its own organizations that issue licenses for different frequencies.

Some DMR frequencies are designated as license-free (for DMR Tier I) while others require a license before you can use them.

It depends on. If you have a small amount of users and only the basic communication requirements, DMR Tier I (see also: what are DMR tiers?) Radios will probably meet your requirements. These are easy to use and do not require a license.

It is important to remember that Tier I equipment has a shorter range and is more sensitive to influences from other users. If you need a more complex system you will need to apply for a license.

Both DMR and TETRA are standards developed by the European Telecommunications Standards Institute (ETSI), aimed at different types of users. Where DMR focuses on the commercial market, TETRA focuses on public safety. This is best reflected in the various interoperability tests that these two systems are familiar with.

Interoperability for DMR systems is tested one on one by manufacturers. In comparison, TETRA products must be tested by an independent third party comparing multiple manufacturers. DMR tests contain only 6 mandatory interoperability functionalities, whereas TETRA requires no fewer than 49 mandatory properties to be tested.

That high number of tests for TETRA equipment allows public safety organizations, such as the police and fire departments, to make independent purchasing decisions without worrying about compatibility between their systems in an emergency. In addition, the stricter TETRA tests do not allow manufacturers to add new and interesting functions like the DMR standard does.

The answer to this question depends mainly on the equipment you use and the infrastructure built around it. The International Space Station, for illustration, orbits the Earth at a distance of 408km and uses DMR to communicate with Earth. Indeed, there are few obstructions between the station and the antennas on the ground, making the signal easy to receive.

For comparison: a DMR Tier I radio can work well within a building up to maybe 100m.

DMR radio systems can reach as far as you want, provided the correct infrastructure is installed; so-called DMR Repeaters can amplify signals over a large area.

Additional pieces of connection can be created by spreading data between repeaters with other technologies such as the internet.

DMR radios can communicate with each other without a centralized system, but this is by no means always an ideal situation. Signals between radios can be hindered by line of sight obstructions such as trees, buildings or hills.

By adding a DMR Repeater, the radios can send their communication through a central point that repeats the message to the rest of the system. By installing a Repeater at a height (often on top of a building), calls to the Repeater are less hindered by obstructions. This makes it possible for radios far from the Repeater in opposite directions to communicate with each other. This artificially increases the range of the system.

Repeater stations can be linked together by retransmitting the received signals (parrots) or by forwarding the received signals to other Repeaters by an alternative method (eg the Internet).