DMR 505 is the national channel – it keys every VK repeater. 505 is fine for short QSOs, BUT as per normal repeater practice, please leave a break between overs on 505 for other stations. If you wish to have a long QSO, then please QSY to leave the channel free for others and the slot free for other stations on 380x TGs. If 505 is busy: TG9 on slot 1 can be used to work another station on your local repeater only.
D-STAR, DMR and C4FM are common digital modes used in amateur radio globally today, and here in Australia too. This technology is on the rise, but which one do you choose, or is it a mix of all three? Read on.
DMR (Digital Mobile Radio) is an international standard for digital radios that has been in use since 2005. With thousands of amateur repeaters already on the air globally, the DMR infrastructure is well established and is on pace to surpass D-STAR and System Fusion.
D-STAR was the first digital system specifically designed for Amateur Radio and was developed in the late 1990s by the Japan Amateur Radio League D-STAR also provides specifications for network connectivity, enabling D-STAR radios to be connected to the Internet or other networks, allowing streams of voice or packet data to be routed via amateur radio. Today, both Icom ( such as the IC-9700 and IC-705) and Kenwood make D-STAR radio equipment.
Digital Mobile Radio is an open digital mode standardized by the European Telecommunications Standards Institute (ETSI). It was first published in 2005 and is used in commercial products around the world. Open means the specifications are available for anyone to use, modify, add, or remove features as one sees fit. DMR uses two-slot Time-Division Multiple Access (TDMA) allowing two channels in 12.5 kHz of bandwidth using the AMBE+2 proprietary codec (or vocoder, voice encoder). TDMA is old cellphone technology in use before LTE and GSM. “Spectrum efficiency of 6.25 kHz” is often used which is ‘blah blah’ marketing speak for ‘it really uses 12.5 kHz, half the time.’
ETSI’s objective was to have a low cost, interoperable, digital system. In reality, manufactures added their own proprietary features that make their radios non-interoperable with other manufactures. Motorola’s system is called MotoTRBO which is a DMR capable radio with their own proprietary features. Motorola did not create nor invent DMR but they help bring it to the U.S.
Source: Jeffry Kopcak K8JTK
DMR is the first time a commercial system was adopted for ham use. Most of the terms heard in relation to DMR are carryovers from the commercial world. In comparison, D-STAR and Fusion were specifically designed for ham radio use. D-STAR, Fusion, and DMR are all open standards. This means commercial gear is setup for commercial users while ham gear is setup for the way hams use radios. All three use the proprietary AMBE codec allowing 12.5 kHz wide transmissions. DMR achieves two simultaneous transmissions in the same bandwidth. D-STAR uses the AMBE codec while DMR and Fusion use AMBE+2.
DMR (Digital Mobile Radio) is a land-mobile radio network standard developed by the European Telecommunications Standards Institute. DMR was designed with three tiers. DMR tiers 1 and 2 (conventional) were first published in 2005, and DMR 3 (Trunked version) was published in 2012.
DMR uses two-slot TDMA in a 12.5 kHz channel. Each slot alternates every 30ms. In plain speak, a slot is like a traditional FM simplex channel. In the case of DMR, there are 2 slots, so you can have two voice channels on the one frequency. Each slot can carry independent voice conversations – this means that each DMR repeater provides two simultaneous voice channels.
That’s it really for how we get 2 QSOs on the one RF channel. If you’re comfortable with this, read on for how we use Talk Groups inside these slots.
IDs are personal. You can have one ID on many radios. It’s like a digital callsign. Don’t share it.
ID numbers are managed centrally and may be obtained here.
Before we talk about talk groups, let’s revisit a few acronyms in the Digital Radio World, as well as a few other things you need to know.
DMR – Digital Mobile Radio – a commercial technology associated with Motorola.
D-STAR – 1st generation digital radio specifically for amateur radio.
TDMA – Time Division Multiple Access – a channel access method.
C4FM – Next generation digital radio specifically for amateur radio.
Generally speaking, to access anything digital, you need a digital radio. These vary in features and cost but keep in mind nearly all DMR in Australia is on 7ocm. D-STAR and C4FM are more prolific on both VHF and UHF. Some digital protocols are used on HF too.
A talkgroup is like CTCSS tones on conventional radio. Let’s say you’re on a popular analogue simplex channel that has lots of traffic and you only want to hear one or a group of stations talk. You could ask them to run a CTCSS tone. Most modern radios have 50 CTCSS frequencies to use.
Talkgroups have the same function as CTCSS tones except there are thousands of possibilities. In Australia, Talkgroup 505 on slot 2 is an Australia wide calling channel. It opens every repeater and hotspot (if the owner has it programmed) in the country. If you were to use talkgroup 505 on slot 1 it would fall on deaf ears. With me here? Once you’ve established a contact on 505, it’s good practice to QSY to another talkgroup, preferably on timeslot 1. 3809 for example.
There are 2 timeslots per radio frequency, therefore, a maximum of 2 conversations – one on slot one, and one on slot two.
So only one talk group on a slot at any given point in time. For example, TG505 – all VK Repeaters (which is a slot 2 talkgroup) and TG3803 – all VK3 repeaters (which is also a slot two talkgroup) cannot operate simultaneously.
Just when you thought you had a handle on DMR…
The MARC in DMR-MARC stands for Motorola Amateur Radio Club Worldwide Network. It is one of the original DMR network coordinators and is still to this day extremely popular and reliable. If you’re in VK, this is predominantly an RF network. Both networks are accessible from Australia.
The DMR-MARC Network is connected around the world by master servers which in turn connect repeaters to each other in over 74 countries through more than 500 repeaters.
The major difference between DMR-MARC and BrandMeister is that BrandMeister allows a local user to key up and route any desired talk group whereas the DMR-MARC network only allows a local user to key up and route talk groups as defined by the DMR-MARC sysop. Both Networks have static talk groups and dynamic talk groups.
Now that you really do have a handle on DMR…
As of June 2019, The VKDMR server is one of two Australian servers. This server is for VK RF Repeaters only. The second server is yet to be publically announced. The VKDMR server is part of the worldwide Amateur Radio DMR digital voice network, which connects Amateur Radio repeaters and hotspots together. Users with a valid Amateur Radio license may connect their Repeaters and Dongles freely and use it within the local and international Amateur Radio regulations.
The top panel of the site shows connected stations. A real-time summary of the network is below. Here you can see the two timeslots in action. You’ll note the hard-wired talkgroups in the TS1 (Timeslot 1) and TS2 (Timeslot 2) columns.
If this site is active, the TS1-INFO or TS2-INFO columns will display the digital ID and Callsign of the user. Orange signifies an output and green an input to the system. The TS1 and TS2 show the fixed (non-user activated) talkgroups on their respective slots.
This is the second Australian server connecting DMR to the network. This role of this server is primarily for hotspots. A hotspot is a small modem that acts as a personal access point for an operator. This allows an amateur to access DMR even if they can’t access a local repeater. A user uses a digital handheld to transmit to the hotspot which is connected to this server via their home internet connection or mobile phone.
Most hotspots are connected 24/7. There are no restrictions on who can connect to the server except for one – all users MUST be a licenced radio amateur. Radio IDs are ONLY issued to licenced amateurs after authentication. This is why the ID allocation system is not real time.
New servers for hotsposts and repeaters became active in October.
Users need to program TG 310, TG 143, TG 133, TG 3 or TG 153 as a normal group talkgroup via timeslot 1.
You can also see the IPSC_MASTER dashboard too. This will give you a good indication of traffic worldwide.
For more information join the VK DMR Network Facebook group. https://www.facebook.com/groups/743300879089972/
When you’re programming your new digital radio or hotspot, make sure you have these servers on a screen near you so you can see if you’re connecting to the right timeslot and on the right talk group.
DMR is an exciting new mode for the what seems to be the ever-evolving hobby of amateur radio.
As it’s always changing with new radios, new repeaters, and different ways of doing things, it would pay to join The VK DMR Network group on Facebook. Here you can keep up with all the goings-on in DMR, and of course, if you get stuck or confused, chances are you aren’t Robinson Caruso and someone in the group will be able to help out.
It is a closed group so be sure to ask for membership which shouldn’t take too long.
Click the map above to find DMR-Marc repeaters.
