DMR

What it is

DMR (Digital Mobile Radio) is a digital voice standard created for business and industry and widely adopted by amateurs. It is known for two features: two conversations time-share one channel, and talkgroups that let many repeaters carry the same conversation across a region or the world.

Two slots on one channel

A DMR repeater sends and receives in short bursts. Bursts alternate between slot 1 and slot 2, so two independent calls use one 12.5 kHz channel, each at half the airtime. Handheld radios transmit only during their slot, which also eases the load on the battery.

Getting in, and choosing who you talk to

Think of a DMR repeater as a building with a door and many rooms.

Term	What it is
Color code	Access code: your radio must match the repeater's. It stops a repeater answering signals meant for another on the same frequency.
Time slot	Which of the two bursts you use; the repeater's pages say which talkgroups are on which slot.
Talkgroup	A numbered conversation. Your radio only plays what it is set to hear.
Radio ID	A number identifying your radio on the network, registered to your call sign.
Code plug	The file loaded into the radio holding its channels, contacts and talkgroups.

Because everything must match, a DMR radio is programmed with a computer, not just a keypad. Mistakes are silent: the wrong color code or slot means the repeater simply ignores you.

In practice

• Listen before you key up: a talkgroup may be in use even if your radio is not set to it.
• Wide-area talkgroups carry traffic from many repeaters at once. Keep calls short and leave room for others.
• A private call goes to one radio ID rather than a talkgroup.
• Amateur DMR networks link repeaters over the internet. A hotspot gives you a low-power connection at home; see Hotspots and gateways.
• DMR radios from different makers generally interoperate on the air, though their programming software differs.

Related

• D-STARIcom's digital voice and data system.
• Yaesu System FusionC4FM digital voice.
• Hotspots and gatewaysPersonal digital-voice nodes.
• EchoLink, IRLP and AllStarLinking repeaters over the internet.
• Digital modulation: FSK, PSK and QAMHow bits become tones and phase shifts.
• Bandwidth, symbol rate and data rateHow much spectrum a signal needs and how much it can carry.