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This is a fork of the Android Codec2 Walkie-Talkie, updated to support M17 streaming KISS protocol over Bluetooth & USB. This is an Amateur Radio DV (digital voice) communication protocol using the using open source vocoder, Codec2.

Screenshot of main Activity


This Android application is a digital voice frontend for your radio. It connects to your M17 KISS Bluetooth/USB modem, sends and receives M17 link setup and audio frames, which are encapsulated inside KISS frames. It does not deal with radio management, modulation, etc. The modem and the radio handle the M17 data link layer and physical layer.


  • Android 8.0 (API 26) or higher
  • Modem or transceiver which supports M17 KISS protocol over Bluetooth or USB


  • PTT button, push and talk, an M17 digital voice stream will be initiated and maintained with the modem.
  • USB serial connectivity (38400 bps, 8 data bits, 1 stop bit, no parity), just select this app after connecting to USB and it will use given connection.
  • BluetoothLE connectivity use the Connect/Disconnect button to connect/disconnect BLE devices. It will attempt to connect to the last connected device. Otherwise it will scan for devices.
  • Callsign Identification enter your callsign once connected in order to be able to transmit.
  • Caller Identification received callsign is clearly displayed when an M17 DV call is received.
  • User Preferences BLE device preference and user callsign will be saved for later.

Usability Notes

  • Android seems to have issues connecting to the same Bluetooth device over both BLE and "classic". The TNC3 may need to be re-paired when switching modes, such as when switching between the Mobilinkd Config app (classic) and the M17 KISS HT app (BLE).
  • Switching between BLE devices will require that the currently bonded device be powered off, initiating a connection, and then waiting for the connection to time out, resulting in a re-scan of available BLE devices. The new device should appear in the connection dialog.

Suitable radios and modems

Any radio which is advertised as 9600-baud capable should be usable for M17. However, M17 seems to place more demands on a flat TX and RX response, and relies on good low-frequency response of the modulator. Radios should also key up very quickly, with key-up times below 10ms the ideal.

  • Tested, works:
    • Mobilinkd TNC3 (BLE & USB) using experimental firmware
    • Mobilinkd NucleoTNC (USB) using stock firmware
    • Kenwood TM-V71A - This is a well-balance radio with reasonable TX and RX performance. This requires a fairly long TX Delay (12/120ms). Requires reverse TX polarity.
    • Kenwood TK-790 - This has reasonable TX performance. The modulator seems to have poor low frequency response, resulting in higher symbol errors. However, it seems seems to have quite good RX performance. This requires a short TX Delay; 6/60ms works reliably.
    • Yaesu FT-991 - This has the best TX performance, with good low-frequency respons and the lowest symbol offset error, but has the least flat RX response. This requires a short TX Delay; 6/60ms works reliably.

Related Projects


  • What does this do?
    • This app is part of a complete system, which includes an Android device, an M17 modem, and an FM transceiver to do M17 digital voice communication. It is a half-duplex transceiver.
  • Why would I want to use this?
    • This is designed to get people experimenting with M17 digital voice using equipment that they may already have available.
    • It is designed to allow M17 developers and early adopters a tool for research and development.
  • What is the current state of this project?
    • It is very new, has bugs, but is the best thing at the moment to do bi-directional voice communication with M17.
  • What equipment do I need?
    • You will need a fairly recent (Android 8.0 or newer) Android device to run the app.
    • You will need an M17 KISS TNC (Mobilinkd devices currently).
    • You will need to install experimental firmware on the Mobilinkd TNC3.
    • You will need to configure the Mobilinkd TNC using the Python config app.
    • You will need an FM radio capable of 9600 baud modulation (direct access to modulator and FM discriminator).

Developer Notes

Bluetooth support was dropped in favor of BLE because latency/jitter was significantly improved.

A change was needed to the TNC3 BLE module configuration in order to cleanly stream frames across the BLE link without significant latency/jitter.


  • Configuration screen for USB serial parameters, callsign, etc.
  • Received callsign history.