M17 - an open source HW&SW DMR-like system


1. What's M17?

  • It's a truly open, free to use digital radio system. The M17 standard, all schematics, PCB layouts and source code is available for free at my GitHub page.

2. How long have you been workikng on it?

  • For about 1 year.

3. Why M17?

  • Mainly because there's no open platform for developing digital radio. Also, the DMR system, although the standard by ETSI is open, isn't really amateur-friendly. You can't really experiment with it. M17 provides all that DMR misses and adds better voice quality to that.

4. Are there any disadvantages of M17 when compared to DMR?

  • M17 uses Frequency Division Multiple Access (FDMA) instead of Time Division Multiple Access (TDMA), which doesn't allow two simultaneous links to be established on one channel. The Physical Layer is described here.

5. What's the vocoder you use?

  • It's Codec2 by David Rowe. It outperforms codec used in DMR.

6. Why not just implement Codec2 into existing DMR standard?

  • As it was said before: there are no open platforms for experimenting with DMR. It's no fun using something, that's only available at commercial retail. Is that true ham spirit?

7. What is the encoded speech bitrate?

  • The standard value is 3200 bits per second, but the M17 specification is still a subject to change. At some point, we might add a support for variable bitrate aswell.

8. Does the M17 support any encryption? (if it is legal for the user)

  • Yes, we are going to add support for the Advanced Encryption System (AES) with keys of different length.

9. How do you identificate users?

  • User IDs are generated based on their callsigns. We use base 40 to encode that into a 48-bit value. IDs in this form can be translated into their DMR equivalent by using a look-up table.

10. Can I use M17 on my DMR radio?

  • Most likely - no.

11. Can I send data with M17?

  • Yes, it will be possible to send data packets alone or as embedded data along with the voice channel.

12. Can I link M17 with my DMR repeater?

  • Why not? :)

13. What are the radio internals?

  • There's an STM32F7 family microcontroller along with an RF front-end chip. Of course there is more to that - an RF power amplifier and so on. There is even an accelerometer (ADXL345) and a place for a GNSS module.

14. Can I send APRS frames with it?

  • Likely, yes, since the codec is based on sinusoidal coding principle. But why doing that, if you can send data with... FSK instead of a bunch of beeps? Wy use APRS if there's no error correction at all?

15. Is M17 compatible with DMR?

  • No. It shares the same Physical Layer though.

16. Can your radio be switched to use DMR instead of M17?

  • There is a great chance it could, but it wouldn't be compatible with all radios - we use a different codec for the speech.

17. How many of you work on the M17?

  • There are about 30 registered users on the forum.