Some notes on Digital Mobile Radio
It took me a while to get a handle on Digital Mobile Radio (DMR), and it was probably equal parts having a terrible radio (the worst radio I’ve probably used) and having the wrong mindset. I think it makes a lot more sense to me now, and to prove that, I’m going to do a write up on it.
DMR basics
What is DMR? It is a standard for sending voice and data digitally over the radio. It uses the same codec as P25 (notably used by a lot of public safety agencies), and uses a twin slot TDMA configuration with narrow band (12.5 kHz) channels. Now, the way I first approached this was with an analog radio mindset. You have a frequency, maybe a CTCSS or DCS tone, and that’s all you need, and maybe a repeater offset – that’s a channel. With DMR, it’s more complicated: you have a frequency, color code, time slot, and talk group. Each radio also needs to be configured with a radio ID coordinated through radioid.net.
The first piece of DMR is the frequency. Simple enough. Then, you need to add to that color codes (the DMR equivalent of a CTCSS tone, arbitrarily chosen more or less), a slot (either 1 or 2, aka TS1 or TS2), and a talk group. All the DMR radios I’ve come across also use the concept of a zone. The frequency is chosen the same way analog frequencies are; areas will have a frequency coordinator with some standard repeater and simplex frequencies. For example, in the US at least, 146.52 MHz is the standard simplex frequency, and one of the major repeater network in California (CARLA) uses 442.075+ MHz for many of its repeaters, and one of the tone used is 127.3. Well, in DMR you’d also go to the frequency coordinator to get your frequency, and pick a color code to use with it. For simplicity’s sake, let’s pick 4 (chosen at random).
Well, now you need to figure out the time slot, but in order to talk about that, we need to talk about talk groups. A talk group is a numeric identifier (your DMR ID). A repeater will have some talk groups that it is always listening to (the static talk groups); every other talk group is linked once you transmit to that talk group (dynamic talk groups). The repeater will use something like the Brandmeister network to link these over the internet. There are also some standardized talkgroups, like 99 for simplex or 9 for repeater local. The most common convention I’ve seen, and admittedly it’s a small sample set, is to use TS1 for dynamic talk groups and TS2 for static talk groups.
One of the things I’m interested in is what you might call squad-level communications. Some local friends and I have a mutual assistance group, and if we’re coordinating something we probably just want to talk to each other. We have a pre-coordinated set of frequencies and color codes, using a standard talk group, and agreed-on time slot.
I mentioned zones earlier; this is just a way to organize channels in your radio. I might have a local zone for channels in my local area, maybe including some local repeaters. Then I might have a work zone that has repeaters near my work.
Radios
I’ve had the opportunity to use a few radios: the TYT MD380, the Anytone 878, the BTech 6X2, and the Baofeng DMR 1701. The MD380 is hands-down the worst radio I’ve ever used, so I can’t recommend it. The DMR 1701 is a perfectly acceptable DMR radio. However, I have the opportunity to use a friend’s business frequency on his ranch and we use encryption: the DMR 1701 uses AES-128 encryption, compared to the 878 and 6X2’s AES-256, making it incompatible for that purpose. Since you’re most likely not doing that, it’s not a problem and I can say it’s an acceptable entry-level DMR-capable radio, though the software is worse.
I’m almost certain the 6X2 and 878 are the same physical radio:
They look exactly the same, except the PF3 button on top is a different color. They use the same batteries, even. I will note that if you buy the 878UVIII+ off Amazon, you’ll get batteries that aren’t USB-C rechargeable, but the 6X2 comes with them. You can still get these batteries from somewhere like Powerwerx or Bridgecom, though. Their programming software looks the same as well. The upside to the 6X2 (for me, at least) is that it doesn’t come with Bluetooth – though I’ve seen a version of the 878 on Powerwerx that also doesn’t ship with Bluetooth. I got my 6X2 from Brushbeater, which is where I’d recommend you get yours too.
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