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How to get started with M17?

You probably already have an idea of what the M17 Project is. But how can you start using this new mode? Depending on what you want to do, there are a few options.

Just like with other Digital Voice modes, some of the traffic is routed through the Internet. The nodes we use are called reflectors. Every reflector has 26 so-called modules. A module is like a room. Users present in one room can communicate with each other. Additionally, modules of different reflectors can be connected together. Over the air, M17 is similar to analog FM. To have a QSO, all you need to know is the frequency and the Channel Access Number (CAN). You can think of the CAN as an equivalent of the CTCSS (a.k.a. PL tone) known from the analog FM world. Users with the same CAN set in their radios can communicate with each other. This concept is similar to the Color Code known from DMR.

Connecting to a reflector

DroidStar android application can be used to connect to an existing reflector and have QSOs. A valid callsign and a DMR ID is needed, as the application checks if you are allowed to transmit. The application can be downloaded from Google Play. The reflector used by the M17 team is M17-M17, module C. There is a net every Friday at 17:00 UTC where everyone can ask questions and test their setups.

Having an M17 QSO over a radio

MMDVM hotspot can be used as an interface between RF and a reflector. Modified commercial off-the-shelf radio transceiver running OpenRTX custom firmware. A step-by-step guide is available at the OpenRTX project's page.
Module 17 is a small modem board for 9600-baud capable radios. All you have to do is to connect your rig to it, then a microphone/speaker with a Kenwood connector and you are set. Module 17 converts M17 baseband to audio and the other way around. A GitHub repository containing additional information can be found here.
SDRangel supports both transmission and reception and runs on both Windows and Linux. The software works with PlutoSDR, HackRF, and other SDRs, also receive-only like the RTL-SDR.
DroidStar can be used too, after connecting a dongle to your phone over USB. Then, your radio will act as a low-power handheld transceiver for the M17 mode.

Listening to local M17 RF traffic.

SDR++ by Alexandre Rouma is a great tool to start listening to M17. It runs on both Windows and Linux. This is probably the simplest method to get started.
OpenWebRX by Jakob DD5JFK is a nice web-based SDR receiver with many different demodulators/decoders available. One of them is M17. Just set the correct frequency and you are done. CANs are not distinguished, so all the traffic will be decoded.
rtl_fm + m17-cxx-demod tools by Rob WX9O, David N1AI, Jay KA1PQK, Paulo PU4THZ et al. A simple setup using RTL-SDR is enough. Then, it’s all command-line. A more detailed description is available here.