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. [http://www.dmrassociation.org]

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. [http://www.dpmr-mou.org]

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™ [http://www.motorolasolutions.com] and Hytera [http://www.hytera.com] infrastructure networks and the focus of this booklet. The IPSC protocols used by the different brand repeaters are not compatible; it is doubtful the equipment manufacturers will ever standardize for business reasons. Any brand DMR (Tier II) user radio will work on any Tier II system, although some manufacturers offer proprietary features.

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, from the end user standpoint, operate the same. Amateur Mototrbo™ networks are much
larger, cover many more areas, and most are interconnected. I look forward to the day when the multiple vendor infrastructures can be interconnected by the amateur community. 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. Some standalones are operating in dual-mode (analog/digital). Mototrbo™ repeaters operating in dual-mode do not support interconnection via the Internet using IPSC.

Some hams have installed DMR repeaters in a vehicle, using 3G/4G cellular wireless services for Internet access. Others have implemented remote bases to interconnect to other networks or radios; it is important to remember that the wide area networks typically have policies prohibiting interconnected traffic, but what is implemented locally and stays local is acceptable. While some may consider network policies prohibiting interconnection to different types of networks political, these policies are really about keeping large networks functioning. Users sometimes don’t realize the hours put in by network operators or the
extent of their efforts that are required to keep a linked system running smoothly. There are sometimes issues of poor quality from interconnected technologies because of the vocoding process that would degrade the quality of the network. DMR-MARC has a sandbox available for persons interested in developing and experimenting that is separate from and off the main DMR-MARC network [http://www.dmr-marc.net/sandbox.html].

Back during the early era of amateur analog repeaters, most everyone used surplus commercial radios. Over time, equipment designed for and targeted to the radio amateur reached the amateur radio marketplace. Today in the DMR marketplace you can find used commercial gear, but new DMR radios are now available with street prices within the range of a typical ham budget. Some amateur DMR users are just using their commercial radios from work with a few extra channels programmed in.

Currently, no manufacturer is marketing an “Amateur” DMR radio; they are building DMR radios for the broader world market. Because of FCC Rules & Regulations for commercial users, DMR radios do not offer FPP (Front Panel Programming) as is the norm for other amateur radios. This is really not an issue because most DMR radios have enough channels to program all possible channels you may want to operate. Most of the DMR radios require a programming cable to program the radio using manufacturer software, while some radios support programming using BlueTooth and even over-the-air programming.

There are police and fire departments, local/state governments and many businesses using DMR Tier II and Tier III; any Tier III capable radio will also work on Tier II systems but neither will work on Tier I. If you have a DMR radio for work, you may be able to program it to also work on amateur repeaters (make sure you have permission) and you will need to contact DMR-MARC about a usable subscriber ID that will work on both networks.

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