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M17 (amateur radio)

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RF spectrum of the M17 protocol

M17 is a digital radio modulation mode developed by Wojciech Kaczmarski (amateur radio call sign SP5WWP) et al. [1][2][3][4][5][6][7] M17 is primarily designed for voice communications on VHF amateur radio band and above. The project received a grant from the Amateur Radio Digital Communications in 2021[8] and 2022[9]. The protocol has been integrated into several hardware and software projects[citation needed].

Overview

Spectrogram of the M17 protocol transmission. Time is on vertical axis, advancing from bottom to top. There's a 40 milliseconds preamble visible at the beginning of the transmission.

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 position data. The mode has been successfully transmitted through EchoStar XXI[10] and QO-100[11] geostationary satellites. In 2021, Kaczmarski received the ARRL Technical Innovation Award for developing an open-source digital radio communication protocol, leading to further advancements in amateur radio.[12] The protocol's specification is released under GNU General Public License.

Voice encoding

M17 uses Codec 2, 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, punctured convolutional code and bit interleaving. Additionally, bits of data are XORed with a predefined decorrelating pseudorandom stream before transmission. This ensures that there are as many symbol transitions in the baseband 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[13] to enable M17 support.

Bridging with other modes

Links to DMR and System Fusion exist.[14]

M17 over IP

Access nodes and repeaters[15] can be linked using reflectors. Over 150 M17 reflectors exist worldwide (Dec 2022).[16]

History

The project was started in 2019 by Wojciech Kaczmarski in Warsaw, Poland. A local amateur radio club he was a member of, SP5KAB, 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 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

See also

References

  1. ^ Dan Romanchik's (KB6NU) blog entry on M17 Project (Nov 2019)
  2. ^ "Świat Radio" magazine, issue 11/2020, p. 50: "Transceiver TR-9", an article covering M17 (Polish)
  3. ^ Ham Radio 2.0 podcast, "M17 Project - New Ham Radio Digital Mode" episode (Sep 2021)
  4. ^ Linux in the Ham Shack podcast, episode 396: "M17 Deep Dive" (Mar 2021)
  5. ^ David Rowe's (VK5DGR) "M17 Open Source Radio" blog entry (Aug 2020)
  6. ^ "M17 Open Source Digital Radio System", Ham Radio Workbench podcast (Dec 2019)
  7. ^ Open Research Institute website, projects listing subpage
  8. ^ Grant: M17 Open Protocol (Apr 2021)
  9. ^ Grant: M17 Project Popularization, Research and Development (Sep 2022)
  10. ^ Testing M17 on Echostar XXI at 10° East
  11. ^ AMSAT-DL Twitter entry on QO-100 wideband transponder M17 experiment (Apr 2021)
  12. ^ ARRL Board of Directors Bestows Awards
  13. ^ OpenRTX - free and open source firmware for ham radios
  14. ^ Douglas McLain's (AD8DP) GitHub page
  15. ^ RepeaterBook list of M17 repeaters
  16. ^ M17 reflectors list
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