ham radio: DMR

[last updated: 2023-12-17]
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AnyTone AT-D578UV-Pro
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link to: github decode DMR
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Caveat: These DMR pages are very incomplete and very much works in progress...

• Introduction:
  • DMR = Digital Mobile Radio
    DMR is a protocol that uses a connection to the internet to relay messages between your radio and anyone on the planet that has an internet connection (and a DMR radio).
  • Broadly speaking, your individual DMR UHF radio will talk to a repeater that is connected to the internet.
          One exception to this is "local" talkgroups, which may not route your communications to the internet.
          Also, it's possible to get your internet connection via a "hotspot" rather than an internet-connected repeater. More later...
  • Repeaters are owned and managed by individuals and groups, and these groups will own and manage many repeaters, linked into a net, such that messages to any one of them are relayed to all of them.
          Popular/large networks include eg. DMR-MARC and Brandmeister,
  • A given repeater has a single frequency that you transmit on. Like all repeaters, there is an offset between transmit and received frequencies.
  • OTOH, your repeater's single frequency is expected to manage traffic from many users in your local area at the same time. Some of your local users may in fact want to talk to each other, but others may want to talk to someone in another state or country. And neither wants to hear the others' conversations. Yet they must all share the same singe frequency on your local repeater.
    The software in the repeater manages this in a couple of ways:
    DMR signals use TDMA (Time Division Multiple Access) to allow many conversations on a single frequency.
    A given user will be assigned to a specific time slot (30ms long).

    Also, conversations are separated into different "TalkGroups".

  • A Talk Group (TG) is like a chat room. Every user using the TG can hear all other users on the same TG (wherever they may be in the world). But users on one TG don't hear communications on other TG's, even though they're on the same repeater, using the same frequency. The repeater software keeps track of all this so there's no overlap or conflict.
          (However there are ways to monitor all communications on your local repeater - see "digi monitoring" later)
  • Keep an eye on the green LED on your radio. This indicates when something is coming across from the repeater. If the message being received is from someone in your TG, then you'll hear it. But if the message is from a different TG, you'll see the green light, but you won't hear anything (except for digi monitoring ...)
  • In order to communicate with a TG, your radio must be programmed (with a "codeplug") to include, in its digital message header, parameters that identify the TG you are talking to.
  • Each TG will be identified with a set of parameters: color code, time slot, TG ID, ...
  • Each repeater has its own set of TG's that it hosts. That is, not all TG's are available on every repeater (...but is there a way around this?).

• Get Started:

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