What is DMR?
Digital Mobile Radio (DMR) was developed by the European Telecommunications Standards Institute (ETSI) and is used worldwide by professional mobile radio users.
DMR is divided into three tiers. Tier I is a single channel specification originally for the European unlicensed dPMR446 service. It is a single channel FDMA 6.25 kHz bandwidth; the standard supports peer-to-peer (mode 1), repeater (mode 2) and linked repeater (mode 3) configurations. The use of the Tier I standard has been expanded into radios for use in other than the unlicensed dPMR446 service.
Tier II is 2-slot TDMA 12.5 kHz wide peer-to-peer and repeater mode specification, resulting in a spectrum efficiency of 6.25 kHz per channel. Each time slot can be either voice and/or data depending upon system needs. IP Site Connect (IPSC) for interconnecting repeaters over the Internet is vendor specific and is not part of the ETSI standards at this time. Most amateur radio implementations of DMR are using voice on both time slots.
Tier III builds upon Tier II, adding trunking operation involving multiple repeaters at a single site. Not all manufacturers’ trunking implementation is Tier III compatible. Vender specific protocols have expanded the trunking to multiple site operations.
It is Tier II that amateurs are implementing in their Mototrbo™ and Hytera infrastructure networks and the focus of this page.
The current implementation of DMR utilizes the DSVI AMBE+2™ vocoder by agreement of the manufactures, it is not specified in the ESTI standard. Most of the radio manufacturers have implemented the vocoder in licensed software. The forward error correction in the AMBE+2™ is an improvement of the voice quality of older vocoders such as used by D-Star™.
Amateur Mototrbo™ and Hytera DMR networks, pretty much operate the same. Amateur Mototrbo™ networks are much larger, cover many more areas, and most are interconnected. Not all the amateur DMR repeaters are connected to the wide area networks. Some are standalone, either because they have yet to obtain an ISP connection at their repeater site or because they just want to use the repeater for local communications.
DMR Tier II/Tier III occupies a 12.5 kHz bandwidth that two channels share using Time-Division Multiple Access (TDMA). This results in spectrum efficiency of 6.25 kHz per channel. Comparing the spectrum efficiency of DMR to a wideband analog FM, DMR only uses 25% of the bandwidth per talk channel. Each channel can carry either voice and/or data depending on system design. The two time slots are called Time Slot 1 (TS1) and Time Slot 2 (TS2).
For the amateur, this means one repeater allows two separate channels at the same time. Currently most amateur DMR repeater system implementations utilize both channels for voice and some limited text messaging. Typically one channel (time slot) is used for wide-area and the second is local and regional Talk Groups.
For repeater operators, a single two-slot TDMA repeater offers a significant savings over two standalone repeaters to obtain two separate communication channels as only one repeater, one duplexer, and one antenna system is required. The utilization of TDMA offers about a 40% battery savings on transmit, extending talking time over non-TDMA and analog transmissions for portable users.
Talk Groups (TG) are a way for groups of users to share a time slot, without distracting and disrupting other users of the time slot. It should be noted that only one Talk Group can be using a time slot at a time. If your radio is not programmed to listen to a Talk Group, you will not hear that Talk Group’s traffic.
The DMR-MARC Mototrbo™ network supports a number of Talk Groups on TS1 including World Wide (TG1, PTT), North America (TG3), and World Wide English (TG13). TS2 is for local, state, and regional Talk Groups. The DCI/TRBO network uses TG3163 for North America and TG3161 for World Wide, and TG3 for World Wide English on TS2.
The DMR standard also supports private calls (one-to-one), encryption, and data. Private calls are not allowed by most of the amateur networks and many consider private calls not amateur friendly; private calls tie up a large number of repeater time slots across the network. Encryption is not legal on amateur radio in the USA but is allowed in Canada! Data and text messaging is supported on some networks.
For simplex traffic, the accepted standard in the amateur community is to use TG99 on TS1 with CC1.
DMR in the Durham Region Area
The following DMR repeaters are available in the Durham Region area.
VE3OBI – Oshawa – 442.1375 – CC1 (Testing)
VE3SBX – Ajax – 442.3625 – CC3
VE3LBN – Oshawa – 443.9875 – CC3
VA3WIK – Singhampton – 442.1875 – CC4
VE3NUS – Toronto – 444.2875 – CC1
9 = Local/Region
91 = Worldwide
93 = North America
99 = Simplex
302 = Canada
310 = TAC-310
311 = TAC-311
3023 = Ontario
VA3XPR – Toronto – 442.3375 – CC1 (Disabled due to jamming)
1 = World Wide
2 = Local 1
3 = North America
8 = Golden Horseshoe Area
9 = Local 2
13 = WW English
113 = UAE 1
123 = UAE 2
302 = Canada
310 = TAC310
3023 = Ontario
3022 = Quebec
3024 = Manitoba
3026 = Alberta
3029 = New Brunswick
3027 = British Columbia
9998 = Parrot
9999 = Audio Test
Presently, all Toronto area DMR-MARC repeaters have been disabled due to jamming/interference.