The world of amateur radio has changed. If you switch on a handheld transceiver today, the choice is no longer just between FM and SSB — you’re facing a jungle of digital voice systems. D-STAR, DMR, C4FM, M17, TETRA: five acronyms, five different philosophies, five communities. But which system is actually right for you? We’ve taken a thorough look at all five.
Why go digital in the first place?
Analog FM signals have an undeniable charm — the familiar hiss, the warm sound. But digital voice systems offer tangible advantages: crystal-clear audio with no background noise, automatic callsign transmission, GPS position reports, and above all the ability to link internet-connected repeaters worldwide. A QSO from Vienna to Tokyo on a handheld? With a hotspot and an internet connection, no problem at all.
All digital systems share one trait: the so-called cliff effect. The signal is either crystal clear or gone entirely — no gradual fade into noise like analog FM. That’s both an advantage and a disadvantage: excellent quality within range, but an abrupt drop-off at the edge with those telltale “R2-D2” artifacts.
D-STAR — The Pioneer
D-STAR (Digital Smart Technologies for Amateur Radio) is the granddaddy of digital voice systems. Developed from 1999 by the Japan Amateur Radio League (JARL) with financial backing from the Japanese telecommunications ministry, D-STAR was the first digital system designed specifically for amateur radio. Icom released the first commercial radios in 2004.
What makes D-STAR special is callsign routing: your callsign is your address on the network. You can call a specific station anywhere in the world — the system automatically finds a path through the reflector network. No other digital system offers this kind of elegance.
Technical Specifications
- Modulation: GMSK (Gaussian Minimum Shift Keying)
- Codec: AMBE (2,400 bps voice + 1,200 bps FEC)
- Bandwidth: 6 kHz — narrower than all other systems
- Simultaneous data channel: 950 bps alongside voice (GPS, text messages)
- DD mode: 128 kbps data transfer on 23 cm — a truly unique feature
- Access: FDMA (one conversation per frequency)
Infrastructure and Radios
D-STAR radios come almost exclusively from Icom — with the ID-50E (from around 350 €) as the entry-level model up to the IC-9700 (around 2,200 €) for the home station. Kenwood is the only other manufacturer with the TH-D75E (around 650 €). Cheap Chinese alternatives? None whatsoever. That makes D-STAR the most expensive entry point among all five systems.
The reflector landscape is impressive: around 888 XLX reflectors worldwide, plus hundreds of REF, XRF, and DCS reflectors. In Austria, the ÖVSV operates several D-STAR repeaters, including the well-positioned OE8XFK on the Dobratsch at 2,166 m elevation.
DMR — The Dominant Force
DMR (Digital Mobile Radio) comes from an entirely different world: developed as an ETSI standard for commercial land mobile radio (police, fire departments, transport companies), the first version was published in 2005. From 2010, resourceful hams discovered that the commercial infrastructure could be brilliantly repurposed — and the availability of cheap Chinese radios from 2014 onward triggered a massive boom.
Today, DMR is the most widely used digital voice system in amateur radio with around 300,000 registered users on RadioID.net. The two major networks — BrandMeister (over 5,500 repeaters in 100+ countries) and IPSC2/DMR+ — form a global infrastructure that is truly unmatched.
Technical Specifications
- Modulation: 4FSK (4-state Frequency Shift Keying)
- Codec: AMBE+2 (2,450 bps per time slot)
- Bandwidth: 12.5 kHz — but with two time slots thanks to TDMA
- Key feature: Two simultaneous conversations on one frequency (TDMA)
- Data rate: 9,600 bps gross
- Access: TDMA (Time Division Multiple Access)
Talkgroups Instead of Channels
DMR organizes traffic via talkgroups (TG) — virtual channels built on an international numbering system. TG 232 is the Austrian channel, TG 262 is Germany, TG 222 is Italy, and TG 91 is the worldwide English channel. When you activate a talkgroup on a repeater, you’re automatically linked via IP to all other connected stations.
In Austria, there are around 47 DMR repeaters connected to both BrandMeister and IPSC2/DMR+. The Austrian talkgroups include TG 232 (national), TG 2320–2329 (regional by OE district), and TG 910/920 (German-speaking worldwide and Europe respectively).
Radios and Prices
This is DMR’s biggest trump card: the entry price is unbeatable. A Baofeng DM-1701 starts at around 45 €, a TYT MD-UV380 from 80 €. The most recommended radio for ambitious newcomers — the AnyTone AT-D878UVII Plus with Bluetooth, GPS/APRS, and a large contact database — runs about 250 €. Commercial radios from Motorola (MOTOTRBO) and Hytera are also popular in ham radio, but considerably more expensive.
The Downside: Codeplug Programming
DMR does have a learning curve that can be quite steep. The so-called codeplug programming — setting up all channels, talkgroups, contacts, and zones via manufacturer-specific software (CPS) — can easily take an entire day the first time around. Tools like the open-source program qdmr by DM3MAT and pre-made codeplugs from local radio clubs help smooth out the learning curve.
C4FM / System Fusion — Yaesu’s Answer
If programming DMR codeplugs makes you break out in a sweat, you’ll love C4FM by Yaesu. Unveiled in 2013 at the ARRL Digital Communications Conference in Seattle, System Fusion takes a completely different approach: simplicity above all. Enter your callsign, set the frequency, press PTT — done. No registration, no codeplugs, no talkgroup programming.
At the heart of it is the AMS function (Automatic Mode Select): the repeater automatically detects whether an analog FM or digital C4FM signal is coming in and adapts accordingly. Analog and digital can coexist seamlessly on the same frequency — a huge advantage during the transition.
Technical Specifications
- Modulation: C4FM (Continuous Four Level Frequency Modulation)
- Codec: AMBE+2 (same as DMR)
- Bandwidth: 12.5 kHz
- DN mode: 2,450 bps voice + data simultaneously
- VW mode: Up to 7,200 bps — the best audio quality of all digital systems
- Access: FDMA (one conversation per frequency)
Audio King in VW Mode
In Voice Wide (VW) mode, C4FM uses all available bandwidth for voice encoding — at up to 7,200 bps, the highest value among all five systems. The result is audio quality that comes closest to analog wideband FM. In the narrower DN mode (Digital Narrow), C4FM sounds similar to DMR since the same AMBE+2 codec is used at the same bit rate.
Radios and Prices
C4FM radios are available exclusively from Yaesu — which is both a strength (quality, consistency) and a weakness (no alternatives, no price competition). Entry starts with the FT-70DE (around 189 €), while the new flagship for mobile operation is the FTM-510DE (around 650 €) with Super DX function and Audio Signal Processor. Networking runs through WIRES-X (Yaesu’s proprietary network) as well as thousands of community-operated YSF and FCS reflectors.
M17 — The Open-Source Rebel
And then there’s M17 — born out of frustration with the status quo. In 2019, Wojciech Kaczmarski (SP5WWP) in Warsaw developed a completely open digital protocol. The name? It comes from the club address: Mokotowska 17. The mission: a digital system that contains not a single proprietary component.
The core problem M17 aims to solve: D-STAR, DMR, and C4FM all use the AMBE codec from DVSI — a proprietary voice codec whose software license is estimated to cost between 100,000 and 1,000,000 US dollars. Each radio chip adds roughly 30 dollars to the device price. And above all: the codec cannot be freely studied, modified, or improved. For a community built on openness and a spirit of experimentation, that’s a contradiction.
Technical Specifications
- Modulation: 4FSK (same as DMR)
- Codec: Codec2 — 100% open source (GPL), developed by David Rowe (VK5DGR)
- Voice bit rate: 3,200 bps (Full Rate) or 1,600 bps (Half Rate)
- Bandwidth: approx. 9 kHz occupied, 12.5 kHz channel spacing
- Data rate: 9,600 bps gross
- Specification: GPL v2 — completely open
- Optional encryption: AES-256 (disabled by default)
The MMDVM Drama
M17 suffered a major setback in July 2025: Jonathan Naylor (G4KLX), maintainer of the MMDVM project (the software that powers virtually all hotspots and many repeaters), removed M17 support without warning. His reasoning: concerns about commercialization and encryption. The M17 Foundation strongly disagreed — royalties had never been planned, encryption was optional and also present in DMR.
The community responded with a fork: a WPSD version based on June 2025 with M17 support is maintained by the community and available at m17project.org/wpsd. The situation demonstrates both the vulnerability and the resilience of the open-source approach.
Hardware and Getting Started
The hardware selection is M17’s biggest weakness — and at the same time a sign of how young the system still is. The first commercial M17 radio is the Connect Systems CS7000-M17 Plus (around 200–300 USD) with M17 + DMR + FM. A cheaper route is via OpenRTX: the open-source firmware can be flashed onto inexpensive DMR radios like the TYT MD-UV380 (around 80 €), bringing experimental M17 support. Over 130 M17 reflectors are active worldwide (as of February 2026).
TETRA — When Professional Radio Meets Amateur Radio
TETRA (Terrestrial Trunked Radio) — most people know this acronym from emergency services radio: police, fire departments, ambulance services. What many don’t realize: in several European countries, resourceful hams have built their own TETRA networks. What started as an experiment with decommissioned government radios has now grown into a serious fifth digital mode in amateur radio.
The TETRA standard was ratified by ETSI back in 1995 — making it even older than D-STAR. The technology is optimized for reliability and efficiency: on a single 25 kHz channel, TDMA with four time slots enables up to four simultaneous conversations. That’s twice as many as DMR and four times as many as D-STAR or C4FM.
Technical Specifications
- Modulation: π/4-DQPSK (Differential Quaternary Phase Shift Keying)
- Codec: ACELP (Algebraic Code-Excited Linear Prediction) — 4,567 bps
- Bandwidth: 25 kHz — with 4 TDMA time slots
- Key feature: Four simultaneous conversations on one frequency
- Data rate: 7,200 bps per time slot (28,800 bps total)
- Access: TDMA (Time Division Multiple Access)
- Encryption: TEA1/TEA2/TEA3 (not used in amateur radio)
The Amateur TETRA Network
The amateur TETRA movement got its start through decommissioned emergency services radios: Motorola MTH800, Sepura STP8040, and similar professional radios are available on the used market from around 30–80 €. The rugged build quality of these radios — waterproof, shockproof, built for tough conditions — is a welcome bonus.
Worldwide, over 97 amateur TETRA repeaters are now active in more than 15 countries. Germany leads with 39 repeaters forming the largest network, followed by the Netherlands, Belgium, and Austria. Linking is done via SVXLink (IP-based) and increasingly through TetraPack software, which enables integration with the BrandMeister network. The central coordination hub is hamtetra.com.
Special Features and Open Source
What’s interesting about TETRA: the ACELP voice codec takes a completely different approach from AMBE — and delivers surprisingly good audio quality at 4,567 bps. Open-source projects like osmo-tetra (part of the Osmocom project), HamTetra, and SXceiver provide experimental software implementations. This means TETRA can be received — and partially transmitted — on SDR hardware, making it a paradise for experimenters.
One downside: TETRA radios are only available used — there are no new amateur radio transceivers with TETRA. Programming is done via manufacturer-specific software (CPS), similar to DMR, and requires some initial learning.
The Big Comparison
Enough theory — here are the hard facts side by side:
| Feature | D-STAR | DMR | C4FM | M17 | TETRA |
|---|---|---|---|---|---|
| Developer | JARL (1999) | ETSI (2005) | Yaesu (2013) | Community (2019) | ETSI (1995) |
| Voice Codec | AMBE | AMBE+2 | AMBE+2 | Codec2 (open) | ACELP |
| Voice Bit Rate | 2,400 bps | 2,450 bps | up to 7,200 bps | 3,200 bps | 4,567 bps |
| Bandwidth | 6 kHz | 12.5 kHz (2 slots) | 12.5 kHz | ~9 kHz | 25 kHz (4 slots) |
| Conversations/Freq. | 1 | 2 (TDMA) | 1 | 1 | 4 (TDMA) |
| Audio Quality | Acceptable | Good | Very good (VW) | Good | Very good |
| Cheapest Radio | ~350 € | ~45 € | ~189 € | ~80 € (OpenRTX) | ~30 € (used) |
| Manufacturers | Icom, Kenwood | Many | Yaesu only | Connect Systems | Motorola, Sepura (used) |
| Programming | Medium | Complex | Very easy | Medium | Complex |
| Open Source | Protocol yes, codec no | Standard yes, codec no | No | 100% open | osmo-tetra, HamTetra |
| OE Repeaters | Several | ~47 | Several | None | ~10 |
| Users Worldwide | Tens of thousands | ~300,000 | Many | Growing | Growing |
Hotspots: Your Gateway to the Digital World
No matter which system you choose — a hotspot dramatically extends your reach. These small devices connect your radio to the respective network via the internet. Here are your options:
- DIY MMDVM + Raspberry Pi: From around 40–60 € self-built. Supports D-STAR, DMR, C4FM, M17 (with community fork). Software: WPSD or Pi-Star.
- Ready-made MMDVM hotspots: From around 80–120 € (AURSINC, Radioddity, etc.)
- SharkRF openSPOT 4 Pro: Around 200–300 € — plug-and-play with built-in battery and hardware transcoding between different systems
Particularly attractive is the cross-mode capability of modern hotspots and reflectors: XLX reflectors can convert D-STAR, DMR, and C4FM signals in real time, allowing users of different systems to communicate with each other.
Note about TETRA: TETRA uses its own infrastructure and is not operated via MMDVM hotspots. Access is through dedicated TETRA repeaters or experimental SDR setups.
The Elephants in the Room: AMBE and Openness
Beyond all the technical discussion, there’s one topic that has been dividing the community for years: the proprietary AMBE codec. Three of the five systems (D-STAR, DMR, C4FM) use variants of this codec from DVSI — a company that charges six- to seven-figure sums for software licenses. This means: you cannot build a fully standards-compliant D-STAR, DMR, or C4FM radio without paying DVSI.
For many hams — who uphold the spirit of openness, experimentation, and free knowledge sharing — that’s a contradiction. The AMBE patents for the older D-STAR variant did expire in October 2017, but the AMBE+2 patents (DMR, C4FM) are not expected to expire until around 2028.
M17 and its Codec2 are the direct answer to this problem — and they prove that high-quality digital voice transmission is possible without proprietary codecs. TETRA takes a middle path: the ACELP codec is not open, but projects like osmo-tetra provide free implementations of the transport layer.
Which System Is Right for You?
The honest answer: it depends. Here are our recommendations by user type:
“I just want to get on the air”
→ C4FM (System Fusion). No system is easier to use. No registration process, no codeplug programming. Buy a Yaesu FT-70DE, enter your callsign, set the frequency — done. The AMS function ensures you can reach both analog and digital stations.
“Budget matters to me”
→ DMR or TETRA. With DMR, you’re in for as little as 45 €; with TETRA, even from 30 € with a used emergency services radio. DMR offers the larger network, TETRA the more rugged professional form factor. Tip: ask your local radio club for a ready-made codeplug for your area.
“Audio quality matters most to me”
→ C4FM in VW mode. With up to 7,200 bps voice bit rate, Yaesu’s Voice Wide mode delivers the best audio quality of all five systems — almost as natural as analog wideband FM. TETRA with its ACELP codec is a strong runner-up.
“Open standards matter to me”
→ M17. The only system with 100% open components: open protocol, open codec, open firmware. Ideal for tinkerers and everyone who wants to live the amateur radio spirit in code. The hardware selection is still limited, but the community keeps growing.
“I want to reach specific stations worldwide”
→ D-STAR. Callsign routing remains unique. Add to that the powerful DD mode for data transfer and the most mature network infrastructure. The price is higher, but for many users the functionality justifies it.
“I want the professional radio experience and rugged hardware”
→ TETRA. Decommissioned emergency services radios from Motorola or Sepura offer a build quality that no amateur radio transceiver can match — waterproof, shockproof, built for extreme conditions. On top of that, there’s the fascinating technology with four time slots per channel. Already well covered by repeaters in Austria and Germany.
The Situation in Austria
In Austria (OE), DMR is the most widespread with around 47 repeaters connected to BrandMeister and IPSC2/DMR+. The talkgroups follow the international scheme with TG 232 as the national channel. D-STAR and C4FM are also represented with several repeaters.
Particularly interesting is the TETRA scene in Austria: coordinated by OE1KBC (Kurt), the community operates around 10 TETRA repeaters on the 70 cm band. Linking is done via SVXLink, and the repeaters are documented at hamtetra.com. The ÖVSV wiki offers comprehensive information for getting started.
M17 is currently only usable in Austria via hotspots, as there are no dedicated M17 repeaters yet. To get started, we recommend reaching out to your local radio club — you’ll often find experienced operators there who are happy to help with your first steps into the digital world. The ÖVSV repeater database provides a complete overview of all digital repeaters in Austria.
Conclusion: Diversity Over Monoculture
There is no “best” digital system — there is only the best system for you. DMR scores with user numbers and price, C4FM with user-friendliness and audio, D-STAR with elegant routing and data features, M17 with uncompromising openness, and TETRA with professional hardware and impressive channel efficiency.
The good news: thanks to cross-mode bridging via XLX reflectors and MMDVM hotspots, the boundaries between systems are increasingly blurring. And with a multimode hotspot, you can sample all of these worlds before committing to one system (or several).
One thing is certain: the future of amateur radio is digital — and more diverse than ever. 73!