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M17 is an open-source digital voice protocol for amateur radio, developed by a community of radio amateurs and engineers starting in 2019. It was created to address a fundamental frustration with existing digital voice modes: DMR, D-STAR, and System Fusion all rely on the proprietary AMBE/AMBE+2 voice codec from DVSI (Digital Voice Systems, Inc.), which requires expensive licensed hardware and cannot be freely implemented in software. M17 replaces AMBE with Codec2, a fully open-source voice codec, making the entire protocol free to implement, study, modify, and improve.
Amateur radio has a strong tradition of experimentation, openness, and building your own equipment. The dominance of the proprietary AMBE codec in digital voice modes runs counter to this tradition — you cannot build your own AMBE implementation, you cannot study how it works in detail, and every radio that uses it must include a licensed chip (or pay for a software licence).
M17 was born from the idea that amateur radio deserves a digital voice standard that is entirely open: open protocol specification, open-source codec, open-source firmware, and open-source hardware designs. Everything about M17, from the RF modulation to the voice codec to the networking protocol, is documented and freely available.
M17 uses Codec2, an open-source voice codec created by David Rowe (VK5DGR). Codec2 was specifically designed for low-bitrate voice over radio, making it a natural fit for amateur use. M17 uses Codec2 at 3,200 bps, which provides voice quality roughly comparable to AMBE+2 in the DMR/Fusion modes — intelligible and clear, though not quite telephone quality (as is the case with all vocoders at these bitrates).
Because Codec2 is open-source, it can run in software on any general-purpose processor. There is no need for a dedicated DSP chip. This opens up possibilities for software-defined radios, homebrew projects, and continual improvement of the codec through community contributions.
M17 uses 4FSK (4-level Frequency Shift Keying) modulation at 4,800 symbols per second, yielding a data rate of 9,600 bps within a standard 12.5 kHz or 9 kHz channel. This is the same channel bandwidth used by analogue FM, DMR, and Fusion, making M17 compatible with existing repeater infrastructure and frequency plans.
The 9,600 bps data rate is split between voice (3,200 bps for Codec2), a data channel, and protocol overhead (framing, error correction, and link setup).
Stream and packet modes — M17 supports real-time voice streaming and packet data transmission, covering both voice communication and data applications.
Encryption support — M17's specification includes optional AES-256 encryption for voice and data. Note that encryption of amateur radio transmissions is prohibited in most countries (including the US under FCC Part 97), but the capability exists for use in jurisdictions and services where it is permitted.
Reflectors — M17 uses a reflector system for internet-linked communication, similar in concept to D-STAR reflectors and DMR talkgroups. The M17 reflector system (often called "M17 reflectors" or using the MREF software) allows repeaters and hotspots to connect and bridge conversations.
IP networking — M17's networking protocol is designed for modern IP infrastructure from the ground up, avoiding some of the legacy complexity of older systems.
M17 is still a growing ecosystem, so the hardware options are more DIY-oriented than the established modes. Current ways to get on M17 include:
MMDVM hotspots — The MMDVM (Multi-Mode Digital Voice Modem) platform, widely used for DMR and D-STAR hotspots, now supports M17. A Pi-Star or WPSD hotspot with current firmware can function as an M17 gateway. You can use an M17-capable radio or a smartphone app to connect through the hotspot.
Module17 — An open-source hardware module that adds M17 capability to existing analogue FM radios. It connects between the radio and a microphone/speaker, handling the Codec2 encoding/decoding and M17 framing. This is one of the most popular ways to get on M17 without buying a new radio.
OpenRTX — An open-source firmware project that adds M17 (and other improvements) to certain existing DMR radios, such as some TYT and Radioddity models. This allows you to repurpose an inexpensive DMR handheld for M17 use.
TR-9 and other dedicated hardware — The M17 project has developed reference hardware designs, including the TR-9 handheld transceiver. Some community members have built or are developing M17-native radios.
Software clients — Applications like M17Client and Droidstar allow you to connect to M17 reflectors directly from a computer or smartphone, using the internet rather than RF. This is useful for monitoring and for getting started without any radio hardware.
Like System Fusion, M17 does not require any special registration or ID number. Your callsign is encoded directly into the M17 protocol frames.
M17 is a community-driven project. Development happens openly, with the protocol specification, firmware source code, and hardware designs all available on the M17 project's website and GitHub repositories. The community communicates through forums, Matrix/IRC channels, and regular online meetings.
Because M17 is entirely open, it has attracted interest from amateur radio operators who are also software developers and hardware engineers — people who want to understand, modify, and improve the technology they use, rather than relying on proprietary black boxes.
M17's defining advantage is that it is completely open and patent-free. Everything from the codec to the protocol to the reference hardware is open-source. For operators who value openness and experimentation, M17 is the clear choice.
Its main limitation today is ecosystem maturity. DMR, D-STAR, and System Fusion have years of established repeater networks, commercial radio availability, and user bases. M17 is growing but is still a younger system with fewer repeaters and more DIY involved in getting on the air. That said, the pace of development is rapid, and MMDVM hotspot support means anyone with an internet connection can access the M17 reflector network.
M17 is not trying to replace DMR or D-STAR overnight — it offers an alternative for operators who want an open platform and are willing to be part of building something new.