Every other history on this site keeps circling the same problem. D-STAR, DMR, P25, and NXDN are all open or openly published frameworks wrapped around a closed, patented voice codec from a single vendor — a compromise hams accepted because, when those modes were designed, there was no free alternative. M17 is the mode that refuses the compromise. It was built from a blank sheet to be open all the way down: protocol, codec, modulation, even the hardware documentation. It is younger and smaller than the others, and that smallness is almost the point — it is the one digital voice mode amateur radio fully owns. (For the people who built the open-source side of this whole story, see With Thanks: The Hams Who Built Digital Voice.)
M17 began at the turn of 2018–2019 in Warsaw, Poland, with Wojciech Kaczmarski, SP5WWP. His local amateur radio club was active in digital voice, and Kaczmarski — who had already experimented with TETRA and DMR — decided to build a digital protocol with no proprietary parts at all. He named it after the club's street address: Mokotowska 17, shortened to M17.
What made the idea possible was a piece of the puzzle that simply hadn't existed when the older modes were designed: a free, high-quality voice codec. Codec 2, created by Australian engineer David Rowe (VK5DGR) and long championed by open-source advocate Bruce Perens, delivers AMBE-class voice quality with no patents and no license fees. Kaczmarski took on the job of building a complete, fully non-proprietary digital radio standard around it. Where D-STAR and DMR had to license AMBE from DVSI because it was the only option, M17 had a choice the others never did.
The defining feature of M17 is not a clever waveform — it is that nothing in it is hidden. The protocol specification is released under the GPL; Codec 2 supplies the open voice path; the over-the-air modulation is 4-level FSK with documented, root-raised-cosine pulse shaping; and even the hardware designs are published. There is also no central authority anywhere in the system. M17 needs no registration server and no callsign database: your callsign is your identity, encoded directly into every frame using a compact base-40 scheme. The chokepoints that the other modes spent a decade engineering around — closed codecs, single vendors, central trust servers — were simply designed out from the start. The protocol carries both a voice (stream) mode and a data (packet) mode, and supports AES-256 encryption where legal, switched off by default.
Because M17 is open, no single company owns the radios — a cluster of community projects do. OpenRTX, a libre replacement firmware, brought M17 to inexpensive commercial handhelds such as the TYT MD-380 and MD-UV380 (with some hardware modding), building on the earlier reverse-engineering of md380tools and OpenGD77. Module17, an open-hardware M17 modem board supported by OpenRTX thanks to Mathis Schmieder (DB9MAT), gave the project a clean dedicated interface. The project also developed the TR-9, a fully open handheld. On the commercial side, Connect Systems released the CS7000-M17 and CS7000-M17 PLUS — the first off-the-shelf M17 handhelds, both supported by OpenRTX.
Getting on M17 from home usually means a hotspot — a small box that links a low-power handheld to the worldwide reflectors over the internet — and here M17 has built its own dedicated path. The purpose-built hardware is the CC1200 hat, an open-hardware Raspberry Pi board created by the M17 Project around the Texas Instruments CC1200 sub-GHz transceiver. Unlike a multimode hotspot, it does exactly one thing: the CC1200 chip transmits and receives M17's 4FSK signal directly on the 2 m or 70 cm band, while the Raspberry Pi behind it runs the M17 gateway that carries your traffic to and from a reflector, with a web dashboard for control. Assembled boards can be ordered through the project, with the proceeds supporting M17 development.
The software side is largely the work of Tom Early (N7TAE), who has given M17 a complete native stack that owes nothing to any multimode package. His MSPOT is a single, self-contained M17-only hotspot-or-repeater application: it carries its own built-in gateway that links to both M17 and URF reflectors, it is deliberately tiny, and rather than a web page it is driven entirely by commands keyed from the radio, answering back with spoken voice messages — well suited to a mobile, phone-tethered repeater. For operating with no RF at all, his mvoice turns a Linux computer or Raspberry Pi with a headset into a full M17 node, linking or callsign-routing to reflectors and handling both voice (via Codec 2) and packet-mode text. Between the CC1200 hat, MSPOT, and mvoice, an M17 operator has a path onto the air that is open from end to end.
M17's reflector is mrefd, also by N7TAE — up to 26 modules, handling both stream and packet traffic. It grew out of the PyM17 reference work, where SP5WWP, N7TAE, and others hammered out the IP framing before N7TAE layered a full reflector protocol on top. By the mid-2020s the network had grown to roughly thirty repeaters and well over a hundred reflectors worldwide, with proper IPv6 support and bridges into the other digital modes; DVRef lists them all. (The M17-JET reflector behind this site runs mrefd.)
For an all-volunteer open project, M17 has earned notable support. It received grants from Amateur Radio Digital Communications (ARDC) in 2021 and 2022, and SP5WWP's work drew recognition from the ARRL in 2021. The protocol has been presented at technical conferences including TAPR's, and continues to develop in the open, with its specification, reference code, and discussion all public.
M17 is the answer to the question the rest of this site keeps asking. Every other digital voice mode here pairs an open framework with a closed, patented voice — a bargain hams struck because AMBE was once the only game in town. M17's wager is that it no longer has to be: with Codec 2, the entire stack can be free, from the waveform to the vocoder to the firmware to the reflector. It is the smallest of the modes on these pages, but it is the only one with no fine print — the one amateur radio built, owns, and can read end to end.