Also known as: DMR Tier II, DMR Tier 2
DMR Tier II is the licensed, conventional tier of the DMR standard. It is non-trunked — each repeater pair uses fixed frequencies — but carries two voice timeslots per 12.5 kHz channel via TDMA.12
Overview
Tier II is the workhorse of commercial DMR and the basis of amateur DMR repeaters. Because it is conventional, you tune directly to a known frequency rather than following a control channel; the two timeslots still allow two simultaneous conversations on that one carrier. Each slot is independently addressed by color code, talkgroup, and source radio ID, all embedded in the burst so a receiver reads them off the air. A single repeater can therefore host, say, a dispatch talkgroup on slot 1 and a networked amateur talkgroup on slot 2 at the same time.
Technical characteristics
| Property | Value |
|---|---|
| Access | Two-slot TDMA |
| Channel | 12.5 kHz |
| Modulation | 4FSK, 9600 bps |
| Vocoder | AMBE+2 |
| Squelch / identity | color code, slot, talkgroup, source ID |
History
Tier II was the first widely commercialised DMR tier, popularised by Motorola’s MOTOTRBO line from the late 2000s and quickly matched by other DMR Association members.12 Its two-slot efficiency and open standard let it displace both analog repeaters and older proprietary digital systems.
Deployment
Extremely common in business, utility, security, and amateur radio. Amateur networks (such as the large worldwide DMR talkgroup systems) bridge Tier II repeaters and personal hotspots over the internet, so a low-power handheld can reach global talkgroups through a nearby repeater.
Decoding it with GopherTrunk
GopherTrunk decodes both timeslots of a Tier II channel and renders
AMBE+2 audio. Color code, time
slot, and talkgroup are read off the air per call — you only configure each
repeater’s frequency. A single dongle channelizes a cluster of repeaters at once; to
cover many repeaters spread across a wide band, add one role: wideband dongle per
~2 MHz cluster, all pointed at the same system. The
dmr-tier2-multi-repeater
sample is a worked “a bunch of repeaters, different CCs and slots” config; for a
single carrier see
dmr-simplex.
For a linked “IPSC pseudo-trunk” system — several repeaters on one Color Code that
radios roam by RSSI — see
dmr-ipsc,
which adds an optional color_code: filter (drop other Color Codes sharing the
passband) and keeps the log quiet for idle repeaters between calls.
For trunked DMR, see Tier III. See Status.
Direct mode (simplex) is burst-mode, and the receiver knows it
A repeater transmits both timeslots continuously, but a handheld on a simplex
frequency (DMR direct mode, Tier I or a Tier II radio in “talkaround”) sends
one 27.5 ms burst per 60 ms frame and is silent for the other 32.5 ms. The
receiver’s level, carrier and timing trackers are gated on carrier presence
(an FM noise-quieting statistic on the discriminator, not a power threshold),
so the inter-burst noise does not inflate the symbol AGC or walk the timing
loop — without that gate a simplex handheld produced no burst sync at all
while a repeater decoded fine (issue #836). Both dmr-tier2 and dmr-tier1
decode a direct-mode transmission; dmr-tier1 restricts the sync search to
the direct-mode sync words. With an uncorrected tuner offset above ~1 kHz the
first transmission after start-up trains the coarse carrier acquirer (about
half a second of bursts) and later ones decode from their first burst; set
ppm from the offset gophertrunk capture measures to decode the first one
too. Gain matters in both directions on a nearby handheld: the tuner AGC
drives it into the ADC rail (the daemon logs front end overloaded, and
capture warns the same way), so pin a fixed gain and step down until the
warning stops.
Sources
-
Digital mobile radio — Wikipedia, for the ETSI DMR tiers, including the licensed conventional Tier II and its two-slot TDMA. ↩ ↩2
-
DMR Association — the DMR manufacturer association, for the TS 102 361 basis and Tier II conventional interoperability. ↩ ↩2