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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] M17 is primarily designed for voice communications on VHF amateur radio band and above.

Overview

Spectrogram of the M17 protocol. 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 protocol's specification is released under GNU General Public License. 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 geostationary satellite.[7] M17 has received the 2021 ARRL Technical Innovation Award.[8] It has also received a grant from the Amateur Radio Digital Communications.[9]

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

TYT MD-380, MD-390 and MD-UV380 handheld transceivers can be reflashed with a custom, free, open source firmware[10] to enable M17 support.

Bridging with other modes

Links to DMR and System Fusion exist.[11]

M17 over IP

Access nodes and repeaters can be linked using reflectors. Over 100 M17 reflectors exist worldwide (Jan 2022).[12]

See also

References


Category:Quantized radio modulation modes