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DMR Repeaters c-Bridges and Networks
Radio tower

DMR Repeaters

In order to program a DMR repeater into a DMR radio, a couple pieces of information about the repeater are needed.

 

To program an analog FM repeater into a ham radio, a user needs the repeater transmit frequency, offset/receive frequency, and PL/DCS tone configuration to access the repeater. Different information is required for a DMR repeater: Color Code and Talk Group configuration is needed. The functionality of a PL/DCS tone is replaced by a “Color Code” (CC) or “Colour” when in Europe. There are 16 possible Color Codes, 0-15. A DMR repeater cannot be Color Code-less. Like PL, the Color Code must match the repeater or the repeater cannot be accessed.

Configuration of the repeater depends on the c-Bridge or network it is connected to.

 

C-Bridge is a communication device to route calls between different networks. There are many ham radio c-Bridges: DMR-MARC, DCI, NATS, CACTUS, K4USD, Crossroads – for example. Some c-Bridges explicitly define repeater configuration, including limiting available Talk Groups only to certain regions. For example, “Rocky Mountain regional” may not be available on Ohio repeaters. Other c-Bridges allow owners leeway in their configuration. User linking is done via Talk Groups or reflectors. Repeaters cannot be linked to directly by other repeaters or hotspots.

Brandmeister is a decentralized network of master servers.

 

Master servers are different from a c-Bridge but an oversimplification is they both provide similar linking functionality. The Brandmeister name is synonymous with DMR but it cross-links with other networks and digital systems like D-STAR and APRS. Work is being done on linking Fusion and P25. All Talk Groups and reflectors on Brandmeister are available to all repeaters and hotspots connected to that network.

Digital Repeater operation is a little different to Analogue Repeaters

As with any linked repeater system, there are significant time delays in fully establishing connections. On an analog repeater system with multiple voted inputs, it will take two or three seconds for the system to fully come up. From the time the radio is keyed, the signal has to reach the inputs, the inputs reach the voter, voter decides which input is the strongest, bring up the transmitter(s), and all receiving stations pick up the repeater’s signal. Fast-keying is one of my pet-peeves where a transmitting station quickly keys their radio and starts talking. Receiving stations only hear the last letter or two of a callsign. Delays are even longer when networking and routing packets is involved over a wide area. This is true for any networked mode: D-STAR, DMR, Fusion, Echolink, AllStar, or IRLP. When first establishing connection on a repeater, first key up for 2 to 3 seconds before saying or doing anything to being up all links. Once links are established, they tend to react quicker so that delay can be dropped to 2 seconds on subsequent transmissions.

Another note when linking DMR systems, at the time a repeater or hotspot is connected, an existing transmission might be taking place on that Talk Group. Nothing would be heard by the station that linked. They think the Talk Group is free and end up disrupting an in progress QSO by calling another station. At the point the system is linked to a Talk Group with a transmission in progress, nothing will be heard until the first station unkeys. After linking, wait a minute while making sure the Talk Group is not already in use before calling.

At some point, you will be ‘bonked’ from a repeater. This is the tone a radio might emit after attempting to access a repeater. There are many reasons for being bonked: repeater didn’t respond because it is offline, wrong Color Code is programmed for the channel, out-of-range of the repeater, an incorrect Talk Group/time slot configuration is programmed, Talk Group doesn’t exist, someone could be making a private call, or there is some other error in the radio configuration. Most likely reason: another Talk Group is in use on the same time slot.

Mobile Radio Op in truck

Each radio used on the DMR network is programmed with a unique user ID number and
y
ou MUST register your radio for it to work correctly.

 

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.

 

You can see what the Australian Network is doing in REAL TIME.

IPSC2-AUS-1 Server – (VK Repeaters)

The AUS-1 server is one of two Australian servers. The 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 and TS2 columns.

 

If a 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.

3FS IPSC2-AUS-2

IPSC2-AUS-2 Server – (VK Hotspots)

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.

 

The image above shows everyone connected to the AUS-2 server. Most hotspots are connected 24/7. You’ll see some non VKs connected at the top of the list. 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.

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.

Need a hand?

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.

VKDMR facebook
VK3FS