FreeDV is a Digital Voice mode for HF radio. You can run FreeDV using a free GUI application for Windows, Linux and OSX that allows any SSB radio to be used for low bit rate digital voice. Alternatively you can buy a SM1000 FreeDV adaptor that allows you to run FreeDV on any HF radio without a PC or sound card.

If you are a hardware or software developer, you can integrate FreeDV into your project using the LGPL licensed FreeDV API.

Speech is compressed down to 700-1600 bit/s then modulated onto a 1.25 kHz wide signal comprised of 16 QPSK carriers which is sent to the Mic input of a SSB radio. The signal is received by an SSB radio, then demodulated and decoded by FreeDV. FreeDV 700C is approaching SSB in it’s low SNR performance. At high SNRs FreeDV 1600 sounds like FM, with no annoying analog HF radio noise.

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 modems and Codec 2 speech codec used in FreeDV are also open source.


July 2017 Ver 1.2.2 FreeDV GUI program – improved Hamlib support, removed unused features and simplified dialogs, up to date OSX support, more documentation
February 16 2017 Ver 1.2 of FreeDV GUI program with 700C – speech quality close to FreeDV 1600 with greatly improved low SNR performance
October 18 2015 Ver 1.10 of FreeDV Quick Start Guide QSG released
September 25 2015 Ver 1.1 of FreeDV GUI program with voice keyer
August 25 2015 Ver 1.0.0 “700B” mode added that improves speech quality over 700 mode but still performs well at low SNRs


Why FreeDV?

Amateur Radio is transitioning from analog to digital, much as it transitioned from AM to SSB in the 1950’s and 1960’s. How would you feel if one or two companies owned the patents for SSB, then forced you to use their technology, made it illegal to experiment with or even understand the technology, and insisted you stay locked to it for the next 100 years? That’s exactly what was happening with digital voice. But now, hams are in control of their technology again!

FreeDV is unique as it uses 100% Open Source Software, including the speech codec. No secrets, nothing proprietary! FreeDV represents a path for 21st century Amateur Radio where Hams are free to experiment and innovate, rather than a future locked into a single manufacturers closed technology.

Demo Video

Watch this video of a FreeDV QSO.

Here is what you need:

  • A SSB receiver or transceiver
  • FreeDV software, download links are below.
  • A Windows, Linux or OSX PC with one (receive only) or two sound cards.
  • Cables to connect your PC to your SSB radio.


  • A SM1000 Digital Voice Adaptor
  • Cables to connect the SM1000 to your SSB radio

Connecting Your Radio

Those who don’t have a special connection for digital modes can use the normal audio inputs and outputs of your radio. The same cables and hardware that you use for other digital modes that are based on PC programs will work with FreeDV, but you will need a second sound interface for the microphone and speaker connections to the FreeDV program. A USB headset of the sort used by gamers is all you need for the second sound interface.

Configuring Your Radio

Turn off as much processing as possible. In general noise blankers, DSP band limit filtering and narrow bandpass filters are more likely to hurt than help, while compression, DSP noise or carrier elimination, and voice processing are definitely wrong for Digital modes. FreeDV’s HF modem does its own DSP, and in general this is true for other digital programs as well.

You can see the received effect of different settings in the S/N (signal to noise ratio) display of FreeDV. A higher S/N is better.

Drive your transmitter to an average power of about 20% of it’s PEP power. There is a 8-12 dB peak-to-average power ratio in our HF modem. Over-driving will reduce the received S/N. More is not better for DV!


Source Code


Several guides are available

Who can I Talk Too?

Login to the K7VE FreeDV QSO Finder to find other Hams using FreeDV.

USA 14.236 MHz USB Anytime Casual QSOs
Netherlands 3.720 MHz in USB Every Sunday 10:00 UTC Net
Australia VK5 7.177MHz Every Sunday 10AM Local WIA Broadcast is WIA Broadcast and call back
Australia VK3 7.177MHz Anytime FreeDV beacon
Australia VK3 14.150/14.153 MHz Every day at 3 and 4pm AET Casual QSOs
UK 3.643MHz LSB Sundays mornings at 09:00 local RSGB broadcast by Matt G6WPJ



Please post your questions to the “Digital Voice” Google group: digitalvoice at



IRC Chat

For casual chat there is a #freedv IRC channel on

Design & Key Features


  • Codec 2 voice codec and FDMDV/COHPSK modems
  • 1.25 kHz spectrum bandwidth (half SSB) with 75 Hz carrier spacing
  • FreeDV 1600 mode: 1275 bit/s voice coding, 25 bit/s text for call sign ID, 300 bit/s FEC, 16×50 baud DQPSK carriers, Differential QPSK demodulation
  • FreeDV 700(C) mode: 700 bit/s voice coding, no FEC, 14×75 baud QPSK carriers, frequency diversity to combat fading, coherent QPSK demodulation
  • No interleaving in time, 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 and Windows.
  • Open source, patent free Codec and Modem that anyone can experiment with and modify
  • Waterfall, spectrum, scatter and audio oscilloscope 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.


FreeDV is being maintained and extended by David Rowe, VK5DGR. Richard Shaw KF5OIM maintains the Cmake build system, Windows and Fedora packaging. Walter, K5WH is leading Windows testing in the USA. Debian packaging thanks to A. Maitland Bottoms (aa4hs) and the Debian Hamradio Maintainers.

As development continues, many people are helping whom we have not credited on this web site, but we appreciate all of their work.


In 2012 FreeDV was coded from scratch by David Witten (GUI, architecture) and David Rowe (Codec 2, modem implementation, integration).

The FreeDV design and user interface is based on FDMDV, which was developed by Francesco Lanza, HB9TLK. Francesco received advice on modem design from Peter Martinez G3PLX, who has also advised David on the FDMDV modem used in FreeDV.

Mel Whitten, K0PFX has contributed greatly to the design, testing and promotion of several Digital Voice systems, including FDMDV. This practical experience has led to the current design – a fast sync, no FEC, low latency system that gives a “SSB” type feel for operators. Mel and a team of alpha testers (Gerry, N4DVR; Jim, K3DCC; Rick, WA6NUT; Tony, K2MO) provided feedback on usability and design of FreeDV.

Bruce Perens has been a thought leader on open source, patent free voice codecs for Amateur Radio. He has inspired, promoted and encouraged the development of Codec 2 and FreeDV.


Google DigitalVoice group
FDMDV Digital Voice Resource Page
Codec 2 Voice Codec
Why Open Source Digital Voice Is Important
FreeDV Specification
Notes for users of Tigertronics rig interfaces
K7VE’s FreeDV QSO Finder
David Rowe interviewed about CODEC2 Episode 81 Bruce Parens and Mel Whitten interview at Dayton Hamvention 2013


Q1: Is there any way to save the screen settings when you drag the tabs to multiple windows on the main screen?
A1: No, as we can’t work out how to support saving and restoring this information with wxWidgets.
Q2: The Tools – Record/Play file feature doesn’t work with my wave file!
A2: Currently the “Play File – Mic In” feature only supports 8 kHz sample rate, 16 bit integer samples. Try converting your wave file to that format.
Q3: Hamlib PTT support doesn’t work with my radio! It works fine with Fldigi, and other programs.
Q4: This is always a mis-match between the serial parameters Hamlib is using with FreeDV and your radio. For example you may have changed the default serial rate on your radio. Carefully check the serial parameters on your radio match those used by FreeDV in the PTT Dialog.

Adding FreeDV To Your Hardware Product or Software Project

If you are a hardware or software developer, you can integrate FreeDV into your project using the LGPL licensed FreeDV API.

No license fees are required to use FreeDV. Including it in your project is a simple as compiling a library of C code. FreeDV does not require an operating system, it runs happily “bare metal” on small machines such as micro-controllers. It does require a hardware Floating Point Unit (FPU).

The FreeDV stack is gcc compilable C software that runs in about 1% of the CPU resources on a modern PC. FreeDV 1600 has even been ported to a “bare metal” STM32F4 micro-controller (168MHz, FPU, 128k RAM, 500k flash).

Read more about using FreeDV in your project.

Help Wanted

We are looking for people to help in the following areas:

  • FreeDV GUI re-factoring and maintenance. C and basic C++ skills (but not DSP). See TODO list at bottom of freedv-dev README.txt
  • Porting DSP code from GNU Octave (Matlab) to C. You need basic Octave, C, and basic DSP skills. Take a look at codec2-dev/octave/fm.m and codec2-dev/src/fm.c for an example.
  • SM1000 STM32F4 maintenance. You need embedded C development skills on Linux (but not DSP). Similar to Arduino without the IDE. Tasks like building User Interface (UI) features.
  • See also the “Can I Help” section of the Codec 2 Page.


How much have you spent on Ham radio gear this year? How did it compare to FreeDV? FreeDV represents an open and free future for digital voice over Ham Radio. You can help by donating via PayPal (which also allows credit card donations):

Donation in US$:

The FreeDV developers have donated 1000’s of hours of highly skilled engineering time. Your donation will reduce the out of pocket costs of the developers for hardware, travel, and FreeDV promotion at Ham events.

Buying a SM1000 FreeDV adaptor allows you to run FreeDV on any HF radio without a PC or sound card. This supports David Rowe, the primary developer of FreeDV and Codec 2.