It’s a mess.

This post is my attempt at a summary of amateur radio digital voice modes, and what I think of them.

I’m not an expert, so if you have more experience then your opinion is likely more valid than mine. But hopefully at least I’m getting the facts right. Please correct me where I’m mistaken.

Analog and digital voice

In the beginning there was only analog. Traditionally on HF you used SSB, and on VHF/UHF you use FM. Analog works, and while yes there are different modes, radios tend to support all of them, or at least the common ones (e.g. most VHF/UHF radios don’t support SSB, because most traffic there is FM). Usually HT traffic is VHF/UHF FM, and for SSB while there is LSB and USB, radios will support both.

But analog isn’t perfect. By going digital we can send metadata such as call signs, positions, and even pictures and files. And for audio quality digital will get rid of the static of analog noise. Digital works better for longer distances, uses less spectrum, and retains voice clarity much longer.

Yes, there’s a sharp cliff when digital voice modes can no longer reach. One second it sounds perfect, the next you can understand nothing. That’s the nature of digital. It works perfectly until it doesn’t work at all. But in the conditions where digital just barely works, analog is an awful mess of static where you only maybe can hear anything.

Digital also enables some fancy things I’ll describe, such as repeating across the Internet.

Analog amateur radio has EchoLink for doing similar things, but both because I’ve not used it, and because it’s not using digital modes, I won’t say more about that in this post.

Digital landscape

Here’s where the mess comes in.

There’s four different standards, completely incompatible (but see below about the OpenSpot3).

DMR, D-Star, P25, and C4FM/SystemFusion.

I’ve not used P25, so I don’t have anything to say about it. The rest are very alike, but not quite the same.

For simplex (direct radio to radio) they’re pretty much exactly the same. They sound about the same, they work the same (switch from FM to the digital mode, done), and there are no surprises.

D-Star and SystemFusion were designed heavily protected by patents (some of which are now expired), trade secrets, and (because of this) have a heavy tie to the radio manufacturer.

D-Star radios are sold by Kenwood and Icom. C4FM/SystemFusion is sold by Yaesu.

DMR has more vendors.

All three of these systems, unlike analog amateur radio, require you to register your callsign on a website, in order to use fully. They’ll work in simplex without it, but e.g. for SystemFusion Yaesu requires you to register an account with them to get full use of the system, inputting both your callsign and your radio serial number.

The patents, trade secrets, and login requirements to me go very much against the spirit of amateur radio. And I’ve ranted about that before.

Digital mode repeaters don’t need to decode the voice. They simply repeat and route the data as-is. This means you can build a repeater or write a reflector (see below) without being able to decode the voice, but it still feels wrong.

There are other digital voice modes, such as FreeDV. I wish every handset would support FreeDV, but not only do you currently need a computer to do FreeDV (thus it’s a different thing from what I’m describing here), operationally it’s also less interesting. FreeDV is a solution for simplex, or repeaters. For operators it’s less of a “system” that needs explaining. Implementors just need a codec2 implementation and to read the very short FreeDV spec, and that’s it.

So that’s why I’m staying with DMR, D-Star and SystemFusion in this blog post.

DMR

DMR is popular because of its licensing situation with multiple manufacturers, which drives down prices.

DMR came out of commercial radio, and is a bit strange when used for amateur radio.

It has features that don’t make sense for amateur radio. E.g. a radio can be sent a “kill code”, to be remotely disabled. That makes sense if your security guard accidentally triggers their radio every two seconds by the way they walk, and HQ can shut that interference down centrally. But with amateur radio there is no “centrally”. Each amateur radio operator is their own licensee.

You need to register in order to get a DMR ID, and can’t properly even program your radio without it.

DMR radios are programmed more “closed”. The programming software is meant to be used by an expert to create a set of configurations for the whole organization to be distributed to all users in departments, and a config is called a “Code Plug”. So think of it as the security guards getting radios with the “security guard code plug”. It doesn’t have to be programmed that way, but this is the use case they’ve made natural.

Many DMR radios can’t be put in frequency mode. The AnyTone 878UV can, but funnily it can’t show the frequency and channel name at the same time. You have to go into the menus to switch to showing one or the other.

So the experience of using a DMR radio is one where the expectation is that you are just handed a radio, with channels programmed, and you are to use those channels because that’s what your organization is licensed to do.

So DMR doesn’t feel like amateur radio. Which makes sense. It came from commercial radio, where these choices made sense.

DMR uses limited TDMA. There are two time slots. And instead of the PL tones of analog repeaters, it uses “color codes”, numbered 0-15.

DMR repeaters connect to “servers”, which belong to a “talk group” networks. Talk groups exist so that you can use the same repeater for your security guards as for your lighting crew, without them needing to hear each other. Pretty neat.

For amateur radio talk groups use a global database (assuming your repeater is connected to a server in the BrandMeister system. There are others I think). You can see the full list of BrandMeister, but for example:

  • Talk group 1 is “the local repeater”
  • Talk group 91 is “World-wide”, and has lots of activity
  • Talk group 2411 is “SM Tactical” (SM for Sweden), whatever that means

You can set up to listen to multiple talk groups in a a “receiver list”, when you’re tuned to a repeater. You won’t hear other talk groups when the repeater broadcasts them, unless you hold down the Monitor button if you have one. You also have a talk group set for when you push to talk (PTT). The active PTT talk group is implicitly in the recever list.

The first time you PTT with a new talk group to a repeater, it will realize that someone (you) is interested in that talk group and will start “subscribing” to it and broadcast it for your enjoyment.

This PTT system means that there are many MANY kerchunkings on DMR talkgroups, which interferes with actual conversation.

DMR doesn’t transmit much metadata. You’re only identified with your DMR ID (remember to register), and every receiver has to be programmed with the now ~160000 DMR IDs for your call sign to show up when you talk to people.

There was no problem registering. Annoying that you have to, but not a problem. Annoying also that you have to periodically reprogram your radio to keep the list of ~160000 DMR IDs up to date.

D-Star

D-Star was designed by the Japan Amateur Radio League, so was for amateur radio from the beginning. At the time it was apparently not feasible to actually have an open standard, so the voice codec was a proprietary patented one, and you had to pay $25 for a chip to be able to encode/decode it.

There’s some open source code out there now, so maybe in the future more radios will get it. Though I don’t see Yaesu adding it, even if it’s free. They want to continue pushing their own closed system.

D-Star merges “servers” and “talk groups” into one thing, and calls it “reflectors”. So a repeater or hotspot is connected to a reflector, and that is the group that you are chatting with. Much simpler.

It’s polite to ask on the repeater if anyone minds if you link the repeater to another reflector (unlinking whatever reflector it’s currently linked to) before you key that in, but you can do it directly from your radio. Some repeaters may be locked to a specific reflector.

D-Star supports sending not only your call sign and name whenever you talk, but you can also embed your GPS coordinates if you want.

A popular reflector is “30 Charlie” (REF030C). There’s a full list of official reflectors, but there are other sets of reflectors too, and you can even run your own.

You need to register to get started. I think otherwise reflectors will drop your traffic, but I’m not sure. One problem with D-Star is that you’re supposed to register via your local repeater. But if you’re on a hotspot because you don’t have any repeaters nearby, then it can be hard to get registered.

I had my registration rejected because it was not local, but after complaining to various places eventually my registration went through. I don’t know who pressed what button to fix it, because people were not exactly good at replying to my emailed requests.

C4FM/SystemFusion

SystemFusion is very similar to D-Star. Just incompatible. It also uses reflectors.

SystemFusion seems to have a more advanced system for querying metadata though. This may be part of what Yaesu calls “WIRES-X”. When you’re in range of a repeater you can leave voice, text, or photo messages on it, retrieve news, and get a list of reflectors. A handheld radio is not exactly great for browsing things, but it’s there and seems kinda cool.

Other than that, yeah for operators it’s D-Star, but not compatible. Registration was not a problem, unlike with D-Star.

I’m told (thanks reddit) that registering with Yaesu only gives you the added the benefit of being able to use your radio as a hotspot (see below for what a hotspot is), connected to your computer. The other parts should work without registering.

Using a radio as a hotspot has the benefit over other hotspots in that it can run at much higher power than the milliwatts that normal hotspots use.

P25

I may fill in this section when I have first hand experience with it. For now I have nothing to say.

Hotspot

If you don’t have a repeater near where you live, or you want to surf around reflectors / talk groups like a madman, then you can get a little gateway into the talk group / reflector systems.

How it works is that you use your normal radio, but instead of talking to a repeater you talk to your own little mini-repeater, that is your gateway between the Internet and radio. I say “repeater” but it can’t be used to repeat between two radios, only between the Internet and your radio.

You can build a repeater using two hotspots connected to the same reflector, and running on different frequencies, but hotspots don’t have high power, so this may be of limited use.

There are others, but just get the OpenSpot3. It does all three systems, and (unlike every other hotspot, including OpenSpot2), it does cross mode! It also has a built in battery, so with it’s wifi on the internet side, and RF to your radio, it’s extremely handy.

With it you can have a DMR radio, and cross mode so that you’re talking to people on a D-Star reflector. Pretty magic!

I have the OpenSpot2, which doesn’t have a battery or cross mode, but even that one is very awesome.

Comparing digital modes

To me they sound about the same. D-Star seems to have more variability between implementations, where some sound more robotic.

DMR is weird. I understand it to be the most popular, but it’s always clear that amateur radio was not the primary design choice for it.

D-Star and SystemFusion are both closed systems, in my opinion. But other than that pretty equal. SystemFusion/WIRES-X has fancy mailboxes, as described above.

You should use the system that has repeaters nearby, or the same system your friends use.