Introduction

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.

News

Check the GitHub Releases Page for the latest information on software releases.

December 2022	FreeDV 1.8.5 – first-time usability improvements, build fixes for macOS
October 2022	FreeDV 1.8.4 – stats auto-reset, TX audio dropout fixes FreeDV joins Software Freedom Conservancy
August 2022	FreeDV 1.8.3.1 – Codec2 1.0.5, bug fixes, Windows updates
July 2022	FreeDV 1.8.0 – PSK Reporter improvements, experimental 2020B mode, modem compression for improved RMS power, doc & build fixes
February 2022	FreeDV 1.7.0 – bug fixes, Pulse Audio for Linux, UI enhancements
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

Why FreeDV?

Amateur Radio is transitioning from analog to digital, much as it transitioned from AM to SSB in the 1950s and 1960s. 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 manufacturer’s 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 propagation.

Here is what you need:

An 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.

OR:

An 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 an 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!

Download

Installers for 32/64 bit Windows, MacOS
Now in the main Fedora and Fedora EPEL 6 & 7 repositories!
Now in the Debian Unstable repositories!

Source Code

Documentation

Several guides are available:

FreeDV User Manual in HTML or PDF – How to get started, notes on advanced and new features in the latest versions of FreeDV
FreeDV Technology – An overview of the technology inside FreeDV digital modes
SM1000 Manual – How to set up, use and reflash the SM1000
G4ABP FreeDV User Manual Appendix – Useful Tips from an experienced FreeDV user
VK5SA FreeDV Quick Start Guide
VK5DM guide to building SM1000 patch leads

Who can I Talk To?

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

Support

Please post your questions to the Digital Voice Google group.
Developers, please subscribe to the Codec 2 Mailing List.
For SM1000 support also use the Codec 2 Mailing List.

IRC Chat

For casual chat there is a #freedv IRC channel on irc.libera.chat port 6697

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.

Credits

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 website, but we appreciate all of their work.

History

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 the 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 as 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 microcontroller (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 for under $5.

FreeDV: Open Source Amateur Digital Voice