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FreeDV, the new HF digital audio program | Radioaficion Ham Radio

FreeDV, the new HF digital audio program


FreeDV, the new HF digital audio program for Radio Amateurs.

FreeDV is a GUI application for Windows and Linux that allows any SSB radio to be used for low bit rate digital voice.

Speech is compressed down to 1400 bit/s then modulated onto a 1100 Hz wide QPSK signal which is sent to the Mic input of a SSB radio. On receive, the signal is received by the SSB radio, then demodulated and decoded by FreeDV.

FreeDV was built by an international team of Radio Amateurs working together on coding, design, user interface and testing. FreeDV is open source software, released under the GNU Public License version 2.1. The FDMDV modem and Codec 2 Speech codec used in FreeDV are also open source.


Design & Key Features


  • Codec 2 voice codec and FDMDV modem
  • 50 baud 14 QPSK voice data
  • 1 Center BPSK carrier with 2x power for fast and robust synchronisation.
  • 1.125 kHz spectrum bandwidth (half SSB) with 75 Hz carrier spacing
  • 1400 bit/s data rate with 1375 bit/s open source Codec 2 voice coding and 25 bit/s text for call sign ID
  • No interleaving in time or FEC philosophy resulting in low latency, fast synchronization and quick recovery from fades.
  • 44.1 or 48kHz sample rate sound card compatible

Key Features:

  • Cross platform, runs on Linux or Windows
  • Open source, patent free Codec and Modem that anyone can experiment with and modify
  • Waterfall, spectrum, scatter and audio oscilliscope displays.
  • Adjustable squelch
  • Fast/slow SNR estimation
  • Microphone and Speaker signal audio Equaliser
  • Control of Transmitter PTT via RS232 levels
  • Works with one (receive only) or two (transmit and receive) sound cards, for example a built in sound card and USB headphones.

Demo Video

Watch this video of a FreeDV QSO.

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