M17 (amateur radio)

M17 uses Frequency-Division Multiple Access (FDMA) technology in which different communication streams are separated by frequency and run concurrently. It utilizes 4,800 symbols per second, 4-level frequency-shift keying (4FSK) with a root Nyquist filter applied to the symbol-mapped bitstream. Radio channels are 9 kHz wide, with channel spacing of 12.5 kHz. The gross data rate is 9,600 bits per second, with the actual data transfer at 3,200. The transmission, called stream, is divided into 40-millisecond long frames, each prepended with a 16-bit long synchronization word. A group of 6 frames form a superframe and is needed to decode the link information data. The protocol allows for low-speed data transfer (along with voice), e.g. GNSS position data. The mode has been successfully transmitted through EchoStar XXI^[14] and QO-100^[15] geostationary satellites. M17 transmissions have also been tested using the OPS-SAT experimental satellite platform.^[16][17]

M17 uses Codec 2, a low bitrate voice codec developed by David Rowe VK5DGR et al. Codec 2 was selected as the voice codec due to its open licensing and suitability for low-bitrate digital voice applications. It is based on linear predictive coding with mixed-harmonic sinusoidal excitation. The M17 protocol supports both 3200 (full-rate) and 1600 bits per second (half-rate) modes.

Three methods are used for error control: binary Golay code, punctured convolutional code and bit interleaving. Additionally, exclusive OR operation is performed between data bits and a predefined decorrelating pseudorandom stream before transmission. This ensures that there are as many symbol transitions in the baseband as possible. A 16-bit cyclic redundancy check (CRC) code is used for data integrity assurance.

The M17 protocol is designed for use in amateur radio communications.

• Callsign encoding: a 48-bit field holding up to 9 alphanumeric characters allows stations to be identified directly by callsign, eliminating the need for a centralized user-ID registration system.
• Two modes of operation: stream mode for continuous voice or data transmission, and packet mode for discrete data transfer.
  • Stream mode offers one 3200bps net bitrate channel (encoded speech or data) or two 1600bps channels (encoded speech alongside data).
  • Packet mode supports text messaging, APRS, AX.25, 6LoWPAN, Winlink, and raw binary data transfer.
• Slow-speed side channel for short and repeated data transfers, e.g. GNSS position data or telemetry.
• Network operation via reflectors and IP links, allowing repeaters and private access points (hotspots) to interconnect and route voice calls and data streams between distant stations.

With a small hardware modification, TYT MD-380, MD-390 and MD-UV380 handheld transceivers can be flashed with a custom, free, open source firmware^[18] to enable M17 support.

In July 2024, a US-based company Connect Systems, Inc. released the CS7000-M17, being the first commercial off-the-shelf handheld transceiver with native M17 support.^[19]

Links between M17 and other digital voice modes and Internet linked networks exist, with several networks providing M17 access. Modes bridged include DMR, P25, System Fusion, D-STAR, NXDN, AllStarLink, EchoLink and IRLP.^{[20][21][22][23][24]}

Access nodes and repeaters^[25] can be linked using reflectors. Over 130 M17 reflectors exist worldwide (June 2026).^[26]

The protocol's specification is released under GNU General Public License, with reference implementations released as open-source software. Development is coordinated publicly, with protocol documentation, reference code, and discussion available to the amateur radio community.

The project was started in 2019 by Wojciech Kaczmarski in Warsaw, Poland. A local amateur radio club he was a member of, was involved in digital voice communications. Kaczmarski, having experimented with TETRA and DMR, decided to create a completely non-proprietary protocol and named it after the club's street address - Mokotowska 17. As every part of the protocol was intended to be open source, Codec 2, released under the GNU LGPL 2.1 license, was chosen as the speech encoder.

• OpenRTX - free and open-source firmware for ham radios
• DroidStar - digital voice client for Android
• SDR++ - multiplatform, open-source software defined radio receiver
• SDRangel - multiplatform, open-source software defined radio receiver/transmitter
• OpenWebRX - web-based software defined radio receiver
• mrefd - M17 reflector^[27]
• rpitx - general radio frequency transmitter for Raspberry Pi^[28]
• dsd-fme - digital speech decoder^[29]
• mvoice - voice client and graphical repeater application (Raspberry and Linux)^[30]
• mspot - hotspot software^[31]

• NXDN
• D-STAR
• Speech coding
• Quadratic permutation polynomials (QPP)