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FAQ

M17 Spec GitHub

TR-9 Radio GitHub


  • What is M17?

M17 is a truly open, free to use digital radio system. The M17 standard, all schematics, PCB layouts and source code is available to use for free at the GitHub pages.

  • How long has M17 been worked on?

As of 2019, about 1 year.

  • Why develop M17?

Mainly because there is no open platform for developing digital radio. By example, the DMR system while an ETSI open standard, is not amateur radio friendly. It cannot be experimented with. M17 aims to address this issue along with others, and provide better voice quality.

  • What is the main difference of M17 to existing digital standards, like DMR?

M17 uses Frequency Division Multiple Access (FDMA) instead of Time Division Multiple Access (TDMA). FDMA allows for two simultaneous links to be esablished on one channel. Please read the M17 Specifications on the GitHub page found at https://github.com/sp5wwp/M17_spec.

  • What vocoder is being used for M17?

M17 uses Codec2, written and developed by David Rowe. Codec2 outperforms existing proprietary and patented (non-free) vocoders currently available.

  • Why not just implement Codec2 on top of an existing standard?

As stated before, there are no open platforms to experiment with regarding digital voice. Current platforms were designed and developed to be a commercial success, instead of a social and hobbyist success.

  • What is the encoded speech bitrate?

The standard value is 3200 bits per second, but the M17 specification is subject to change. A variable bitrate may be supported in the future.

  • Does M17 support encryption?

Yes, support for the Advanced Encryption System (AES) will be added with keys of different length. Encryption may be enabled where it is legal, or disabled completely.

  • How are users identified?

User IDs are generated based on their callsigns. Base40 is used to encode the callsign into a 48-bit value. The user’s ID can also be translated to a DMR Radio ID equivalent using a lookup table.

  • Can M17 be used on a DMR radio?

Most likely not.

  • Can I send data using M17?

Yes, it will be possible to send data packets exclusively or alongside digital voice streams.

  • Can I link M17 with my DMR repeater?

Sure!

  • What are the radio internals?

The TR-9 radio includes an STM32F7 family microcontroller along with an ADF7021 RF front-end. An RF power amplifier, accelerometer and a GNSS module are also included.

  • Can I send APRS frames with it?

Most likely, yes since the codec is based on sinusoidal coding principle. But why bother doing that if the data can be sent using FSK instead of a bunch of beeps? Why use APRS if there is no error correction at all?

  • Is M17 compatible with other digital voice modes, like DMR?

No.

  • Can I switch an existing digital voice radio to be used with M17?

There is a great chance that could be done, but it would not be compatible with all radios - a different codec is used for speech.

  • How many people are working on M17?

There are about 47 registered users on the forum. On IRC there is an average of about 25 people.