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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 SP5WWP et al.[1][2][3][4][5][6][7] M17 is primarily designed for voice communications on VHF amateur radio band and above.

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[8] and QO-100[9] geostationary satellites. M17 has received the 2021 ARRL Technical Innovation Award.[10] It has also received a grant from the Amateur Radio Digital Communications.[11] 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[12] to enable M17 support.

Bridging with other modes

Links to DMR and System Fusion exist.[13]

M17 over IP

Access nodes and repeaters[14] can be linked using reflectors. Over 130 M17 reflectors exist worldwide (May 2022).[15]

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. ^ Testing M17 on Echostar XXI at 10° East
  9. ^ AMSAT-DL Twitter entry on QO-100 wideband transponder M17 experiment (Apr 2021)
  10. ^ ARRL Board of Directors Bestows Awards
  11. ^ ARDC grants 250,000 USD to M17 Project (Apr 2021)
  12. ^ OpenRTX - free and open source firmware for ham radios
  13. ^ Douglas McLain's (AD8DP) GitHub page
  14. ^ RepeaterBook list of M17 repeaters
  15. ^ M17 reflectors list
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