Also known as: DMR, Digital Mobile Radio
Digital Mobile Radio (DMR) is an open digital two-way-radio standard from ETSI (published as TS 102 361), widely used in business, commercial, utility, and amateur radio. It places two timeslots (TDMA) in a 12.5 kHz channel using 4FSK modulation at 4800 baud and the AMBE+2 vocoder.12
Overview
DMR’s low cost and ETSI openness made it ubiquitous outside public safety. It is defined in three tiers of increasing capability: Tier I (licence-free), Tier II (licensed conventional), and Tier III (trunked with a control channel). Each carrier is shared by two independent conversations in alternating 30 ms bursts, and every call is tagged with a color code (0–15) that acts as a digital squelch so that co-channel systems do not interfere. Motorola’s MOTOTRBO is the best-known commercial implementation, and vendors layer proprietary trunking such as Capacity Plus and Hytera’s Connect Plus on top of the DMR air interface.
Technical characteristics
| Property | Value |
|---|---|
| Access | Two-slot TDMA |
| Channel | 12.5 kHz |
| Modulation | 4FSK, 4800 baud (9600 bps) |
| Vocoder | AMBE+2 (half-rate) |
| Squelch / identity | color code (4-bit), slot, talkgroup, source ID |
| Error correction | Golay, Hamming, BPTC, Reed–Solomon (by burst) |
| Trunking signalling | CSBK (control signalling block), Tier III |
Two-slot TDMA effectively yields 6.25 kHz-equivalent efficiency, letting two calls share one frequency. The 4FSK symbol stream carries a repeating burst structure: each timeslot alternates voice frames with embedded signalling (color code, link control, and — on trunked systems — CSBK messages), so the identity of a call can be read directly off the air without a separate database lookup.
History
ETSI published the DMR standard (TS 102 361, parts 1–4) in 2005, with commercial radios following soon after; the DMR Association was formed by manufacturers to promote interoperability and run compliance testing.12 Amateur DMR grew rapidly in the 2010s via internet-linked repeaters and low-cost personal hotspots that bridge a handheld to worldwide talkgroup networks.
Deployment
DMR dominates commercial and business radio worldwide and is popular with amateurs. Trunked deployments use Tier III (or a vendor mode such as Capacity Plus); most conventional business and ham systems are Tier II. Because the standard is open and the radios are inexpensive, DMR often competes directly with P25 and TETRA on cost.
Decoding it with GopherTrunk
GopherTrunk decodes both DMR timeslots, reads the color code and per-burst link control, follows Tier III (and vendor Capacity Plus / Connect Plus) trunking signalling, and renders AMBE+2 audio. A single dongle channelizes a cluster of nearby repeaters at once. Optional known-key DMR encryption handling is documented separately; keyed proprietary encryption is not defeated. See Status.
Sources
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Digital mobile radio — Wikipedia, for the ETSI DMR standard, its two-slot TDMA air interface, the tier structure, the color code, and the AMBE+2 vocoder. ↩ ↩2
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DMR Association — the manufacturer association behind DMR, for the TS 102 361 standard basis, interoperability process, and tier definitions. ↩ ↩2