M17 is a

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

radio modulation mode developed by Wojciech Kaczmarski ( amateur radio call sign SP5WWP) et al. M17 is primarily designed for voice communications on VHF

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...

band and above. The project received a grant from the Amateur Radio Digital Communications in 2021 and 2022. The protocol has been integrated into several hardware and software projects.

Overview

M17 utilizes 4800 symbols per second 4FSK with a root Nyquist filter applied to the bitstream. Radio channels are 9 kHz wide, with channel spacing of 12.5 kHz. The gross data rate is 9600 bits per second, with the actual data transfer at 3200. Protocol allows for low-speed data transfer (along with voice), e.g.

GNSS A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pre ...

position data. The mode has been successfully transmitted through

EchoStar XXI EchoStar XXI (formerly known as TerreStar 2) is a European communications satellite which is operated by Echostar Corporation. It was constructed by Space Systems/Loral, based on the SSL 1300 satellite bus, and carries S band transponders which ...

and QO-100 geostationary satellites. In 2021, Kaczmarski received the

ARRL The American Radio Relay League (ARRL) is the largest membership association of amateur radio enthusiasts in the United States. ARRL is a non-profit organization, and was co-founded on April 6, 1914, by Hiram Percy Maxim and Clarence D. Tuska of ...

Technical Innovation Award for developing an open-source digital radio communication protocol, leading to further advancements in amateur radio. The protocol's specification is released under

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the Four Freedoms (Free software), four freedoms to run, study, share, and modify the software. The license was th ...

Voice encoding

M17 uses

Codec 2 Codec 2 is a low-bitrate speech audio codec (speech coding) that is patent free and open source. Codec 2 compresses speech using sinusoidal coding, a method specialized for human speech. Bit rates of 3200 to 450 bit/s have been successfully cre ...

, a low bitrate voice codec developed by David Rowe VK5DGR et al. Codec 2 was designed to be used for amateur radio and other high compression voice applications. The protocol supports both 3200 (full-rate) and 1600 bits per second (half-rate) modes.

Error control

Three methods are used for error control:

binary Golay code In mathematics and electronics engineering, a binary Golay code is a type of linear error-correcting code used in digital communications. The binary Golay code, along with the ternary Golay code, has a particularly deep and interesting connection ...

, punctured

convolutional code In telecommunication, a convolutional code is a type of error-correcting code that generates parity symbols via the sliding application of a boolean polynomial function to a data stream. The sliding application represents the 'convolution' of the ...

and

bit interleaving In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea is ...

. Additionally, bits of data are

XORed Exclusive or or exclusive disjunction is a Logical connective, logical operation that is true if and only if its arguments differ (one is true, the other is false). It is Table of logic symbols, symbolized by the prefix operator J and by the ...

with a predefined decorrelating pseudorandom stream before transmission. This ensures that there are as many symbol transitions in the

baseband In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...

as possible.

Hardware support

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 to enable M17 support.

Bridging with other modes

Links to DMR and System Fusion exist.

M17 over IP

Access nodes and repeaters can be linked using ''reflectors''. Over 150 M17 reflectors exist worldwide (Dec 2022).M17 reflectors list
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History

The project was started in 2019 by Wojciech Kaczmarski in

Warsaw Warsaw ( pl, Warszawa, ), officially the Capital City of Warsaw,, abbreviation: ''m.st. Warszawa'' is the capital and largest city of Poland. The metropolis stands on the River Vistula in east-central Poland, and its population is officia ...

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...

. A local amateur radio club he was a member of, SP5KAB, was involved in digital voice communications. Kaczmarski, having experimented with

TETRA Terrestrial Trunked Radio (TETRA; formerly known as Trans-European Trunked Radio), a European standard for a trunked radio system, is a professional mobile radio and two-way transceiver specification. TETRA was specifically designed for use by go ...

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 GPL 2 license, has been chosen as the speech encoder.

Applications and projects with M17 support

* 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 * rpitx