Gold Coast Amateur Radio Association, Inc.

DMR - What is it?

W4BUG (Gold Coast Amateur Radio Association) has made a big step forward. We decided to do our part to help in the advancement of amateur radio by installing and operating a Motorola DMR repeater for use by the amateur community in our area. It is on the BrandMeister Network and the Repeater I.D. 310035 .

The repeater is installed at the John Knox Building along with the 146.610 Repeater. It allows a little 5 Watt HT to connect with other DMR Talk Groups (TG) and other repeaters around the world by utilizing the internet. Surely, most operators are pretty much in the dark as to what DMR really is and what it means to them. With this page, we are trying to bring DMR closer to the local HAM community and give you the knowledge to jump into the digital world of HAM radio.

DMR (Digital Mobile Radio) is a digital voice and data protocol originally developed for use in Commercial radios and later made available for HAM radio operators. DMR is available on VHF and UHF amateur radio bands but most activity is currently on the UHF band. In addition to the over-the-air protocol, DMR also provides specifications for network connectivity by using various TGs on one frequency, enabling DMR radios to be connected to the Internet or other networks and repeaters. DMR is based on the Motorola MOTO Turbo type commercial system. (DMARC)

As long as the signal strength is above a minimum threshold, the quality of the data received (AKA Packets)is better than an analog signal at the same strength. It is capable of linking other repeaters together through the Internet by using Talk Groups, so HAMS may talk to other HAMS in a different state or even a different country if so desired.

Another important aspect of DMR technology is its ability to send short messages to emergency responders in the event of a disaster. Disaster Service agencies or even County/State or Federal agencies can instantly relay and send messages to the people that need the information.

The TGs are connected between repeaters through the gateway control software of C-Bridges via the internet. The important thing to understand is that the TGs are linked together and not the repeaters. This is what allows HAM operators to make world wide QSOs with a 5 Watt HT. Each state and each country have their own unique TG numbers. Each repeater in the BrandMeister Network has a repeater ID, which also serves as its own TG. W4BUG's ID/TG is 310035. This allows a HAM operator to connect to his local repeater from anywhere in the world by finding a DMR repeater close to his/her location, program the repeater frequency into the radio and use the TG (e.g. 310035) to connect to their local repeater via the internet.

There are a few different networks out there and they are not all 100% compatible. The two most popular networks are:

• Allstar Brand Meister (Our Club Uses this one TG 310035)
• DMARC (Motorola Based)

If you are going to purchase a DMR radio, make sure they are capable of operating on Tier I and Tier II.

Tier I

DMR Tier I products are for licence-free use in the European  PMR446 band . Tier I products are specified for non-infrastructure use only (meaning without the use of repeaters). This part of the standard provides for consumer applications and low-power commercial applications, using a maximum of 0.5 watt RF power.

Note that a licence free allocation is not present at this frequency outside of Europe, which means that PMR446 radios including DMR Tier I radios can only be used legally in other countries once an appropriate radio licence is obtained by the operator.

Some DMR radios sold by Chinese manufacturers (most notably  Baofeng ) have been mis-labelled as DMR Tier I. A DMR Tier I radio would only use the PMR446 licence free frequencies, and would have a maximum transmitted power of 0.5 W as required by law for all PMR446 radios.

Although the DMR standard allows Tier I DMR radios to use continuous transmission mode, all known Tier I radios currently use TDMA, the same as Tier II. This is probably due to the battery savings that come with transmitting only half the time instead of continuously.

Tier II

DMR Tier II covers licensed conventional radio systems, mobiles and hand portables operating in PMR frequency bands from 66—960 MHz. The ETSI DMR Tier II standard is targeted at those users who need spectral efficiency , advanced voice features and integrated IP data services in licensed bands for high-power communications. A number of manufacturers have DMR Tier II compliant products on the market. ETSI DMR specifies two slot TDMA in 12.5 kHz channels for Tier II and III.

Tier III

DMR Tier III covers trunking operation in frequency bands 66—960 MHz. Tier III supports voice and short messaging handling similar to TETRA with built-in 128 character status messaging and short messaging with up to 288 bits of data in a variety of formats. It also supports packet data service in a variety of formats, including support for IPv4 and IPv6 . Tier III compliant products were launched in 2012.