FreeDV screenshot

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 (1600 and 700D modes) 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.

FreeDV is being developed 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 Lesser Public License version 2.1. The modems and Codec 2 speech codec used in FreeDV are also open source.


September 2021 FreeDV 1.6.1 – bug fixes and reliable PSK reporter feature
August 2021 SM1000 v5 firmware FreeDV 700E and 700D/E Tx band Pass Filter
August 2021 FreeDV 1.6.0 with many small bug fixes and enhancements
April 2021 FreeDV 1.5.3 with automatic mode detection, and Tx level slider
Feb 2021 FreeDV 1.5.2 with new FreeDV 700E mode, experimental PSK Reporter, PDF and HTML User Manual
July 2020 FreeDV Technology doc and v4 SM1000 firmware
Nov 2019 FreeDV GUI 1.4 Beta – includes improvements to 700C/700D and the new 2020 mode
July 2019 Ver 2 SM1000 firmware – includes FreeDV 700D. Read More …

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.

Controlled testing suggests FreeDV is comparable to and in some cases works better than SSB on low SNR channels.

FreeDV 2020 is built around leading edge neural net speech coding (LPCNet), putting Ham radio at the forefront of digital radio innovation. It provides 8 kHz wide audio bandwidth, while using just 1600 Hz of RF bandwidth.

Urban HF noise is a growing problem for SSB communications. Hams around the world are using the advanced FEC and modem technology in FreeDV to overcome urban HF noise in channels where SSB is unusable.

FreeDV 1600 and 2020 is being used over the QO-100 satellite, and for experimental combinations of Internet and HF radio to overcome poor propogation.

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

If you don’t have a built in sound card for digital modes you 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 its 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 To?

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

Argentina 7.045 MHz LSB Mon, Wed, Fri 1800 UTC Radio Club Coronel Pringles, listen on the LU4EEC KiwiSDR
Australia 7.177 MHz Anytime Casual QSOs
Netherlands 3.625 MHz LSB 700D Every Sunday 1000 UTC Net
UK 3.643 MHz LSB 700D Sundays mornings at 09:00 Local RSGB broadcast by Matt G6WPJ
UK 3.693 & 3.697 MHz LSB 700D 1600 Local Daily Net
USA 14.236 MHz USB Anytime Casual QSOs


IRC Chat

For casual chat there is a #freedv IRC channel on

Key Features

  • Cross platform, runs on Linux, Windows and OSX.
  • 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 Mooneer Salam K6AQ and David Rowe, VK5DGR. Richard Shaw KF5OIM maintains the Cmake build system 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.


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 and 700D has even been ported to a “bare metal” STM32F4 micro-controller (168MHz, FPU, 128k RAM, 500k flash).

FreeDV requires a floating point processor.  While it might be possible to create a fixed-point implementation, there is little incentive to do so since floating point processors capable of running FreeDV are now available under $5.