I’ve written a couple of times in the past about various digital voice modes and if I’m honest, I’ve been quite scathing of them. I make no secret of the fact that I’m very happy to use repeaters for local natter but don’t like the idea of linking remote repeaters together via the internet to work “DX”.
When I use D-STAR, I tend to unlink the local repeater from the reflector and call through it to see if any locals are listening.
I’m a founder member of the Martello Tower Group and we run a number of analogue and digital repeaters. We recently moved GB7CL, our DMR repeater to a site just a couple of miles away from where I live and I’d openly said that once that happened, I’d get myself a DMR wireless.
I’ve now had a DMR radio for about a month and have spent a lot of time sorting out the configuration and learning how to use it – It’s quite a steep learning curve but I found a base “code plug” and tweaked it slightly to suit my requirements.
The obvious comparison is with D-STAR. The first thing to notice about DMR is that the audio is significantly better than D-STAR which is down to higher bandwidth and a better audio CODEC. It’s not uncommon for me to hear someone I know working D-STAR and barely be able to recognise their voice. That’s not the situation with DMR, everyone sounds as I’d expect them to do.
What I like very much about DMR is how the Regional “Talk Groups” work. DMR repeaters are centrally controlled and certain talk groups are linked together by region. For example, Talk Group 840 links together repeaters in Ipswich (GB7AL and GB7MK), Clacton-on-Sea (GB7CL), Tring (GB7CT), Norwich (GB7DS), Pointon (GB7FU), Halstead GB7HA), Attleborough (GB7ND), Peterborough (GB7PE), Cambridge (GB7PY), Leicester (GB7SK) and Bury St. Edmunds (GB7WS).
In practise, if you transmit on the East England Talk Group 840, you’ll be relayed through all the above repeaters simultaneously. This is very much how we used to have the analogue repeaters GB3CE and GB3CL in Clacton-on-Sea and Colchester configured except we were linking via RF and not an internet backbone.
I have no problems with this form of linking, in fact I think it’s fantastic to have multiple local/regional repeaters joined together like this.
In addition to this, there’s a larger Talk Group (801) covering the whole of the South East which consists of twenty repeaters all linked in the same way.
There are other regional Talk Groups configured and the best way to demonstrate this is to have a look at the link on the DMR-UK web site here where you can sort the list by regional talk group to see exactly what’s in each one.
In addition there are other talk groups designated as World Wide, UK Wide and Europe where. as the name suggests, anyone calling through them will be relayed through every repeater in the group.
However you don’t have to access multiple repeaters at the same time. Each repeater has two local talk groups which are entirely self contained so they can be used in exactly the same way as a traditional stand-alone repeater.
This page gives a list of all the talk groups which are available on each repeater.
Another nice feature of DMR is the ability to automatically ‘roam’ across the network so if one goes out of range of one repeater, the radio will automatically switch to another one. As I don’t have a DMR wireless in my car, I’ve had no experience of this but I have listened to stations driving around who have commented that they’ve just roamed to another repeater.
Each repeater has two “Time Slots” (TS). Effectively this means that two QSOs can happen at the same time, doubling the capacity of the repeater. TS1 is used for national and international talk groups and TS2 is used for local and regional talk groups.
The above probably sounds incredibly complicated and when I first switched on my DMR radio, I was totally overwhelmed. I spent a lot of time reading the DMR-UK site and along with listening around the network, I’ve quickly picked it all up and I’ve got my head around most of it.
Whereas D-STAR radios are almost exclusively manufactured by Icom (except the recent Kenwood TH-D74E), there are a few different DMR manufacturers. In the UK the most common seems to be the Tytera (TYT) UHF MD-380, available from China for as little as £70 via eBay or a little more if you buy from a supplier based in the UK. There is also a recent mobile dual band radio, the TYT-9600 although I understand that’s going through some teething problems because it’s so new. At time of writing this is only available from one UK supplier.
I’ve often heard DMR described as “The poor man’s D-STAR”. Although it’s significantly cheaper to buy a DMR wireless than a D-STAR one, I don’t think that’s a good comparison. Compared to D-STAR with the random linking of reflectors and the relatively poor audio quality, I think I prefer DMR.
I like the way the network is configured centrally into regional talk groups, I like the roaming feature, I really like that by selecting the local channels, it can just be used as an unconnected repeater.
With all these positives, is there anything I don’t like about DMR? I’m not a great fan of the huge learning curve. I can see that it can be quite complicated and can understand why some people aren’t able to get their head around it. I think that by forcing myself to be a DMR SWL for a good few weeks, I’ve been able to get a decent grounding in how it works and how to operate it. I don’t like using things I don’t understand.
A few days ago, I visited an area which I don’t have programmed into my DMR radio. Because of the complexities of setting these things up, I couldn’t use it. Unlike an analogue radio, I couldn’t simply tune my wireless to the local repeater, set up the CTCSS tone (or whistle at 1,750Hz) and speak through it. It was effectively useless. This is the same for D-STAR as well though, it’s not just a limitation of DMR. At least with D-STAR I have the entire UK repeater network configured and using the built in GPS, it can always find the closest repeater to me. I don’t think this feature is available on any DMR wirelesses yet.
I’m also quite frustrated by the terminology that seems to be coming into amateur radio from the commercial side. Everyone talks about a “code plug” which is really just a list of frequencies, offsets and memories and links them together. We’ve been doing this for years, programming memories and setting up radios but for some reason we’ve now adopted a commercial term. Also, there’s a “colour” linked to each channel which is the CTCSS tone. Why not just say that you’re programming the radio and using (103.5 or whatever) CTCSS?
The World Wide and Europe Wide talk groups don’t interest me in the slightest.
What radio did I buy?
Despite saying that I don’t like handhelds, I bought one. I didn’t go with a very cheap Chinese import because I’ve heard too many horror stories about them arriving broken or failing after just a few weeks and being impossible (or prohibitively expensive) to return them. I bought mine from a UK supplier via Amazon because I figured that I’d have a better chance of any returns if it arrived faulty or stopped working within the warranty period. I also had some credit on Amazon so the actual cash I had to spend made it a very reasonable price.
I wasn’t prepared to pay £280 for a dual band mobile radio for a mode I may have hated and I’d also read too many bad things about the MD-9600 and the poor firmware to consider one just yet.
This is what I bought.