Provided by: freedv_1.2.2-3_amd64 
NAME
freedv - Digital Voice for HF
DESCRIPTION
FreeDV is a GUI application that allows any SSB radio to be used for low bit rate digital voice.
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 Lesser General Public
License version 2.1. The FDMDV modem and Codec 2 Speech codec used in FreeDV are also open source.
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 is exactly what was happening with digital voice. But
now, hams are in control of their technology again.
FreeDV is unique as it uses 100 percent Open Source Software, including the audio 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.
http://freedv.org/tiki-index.php?page=video
Here is what you need:
A SSB receiver or transceiver
FreeDV software
A computer with one (receive only) or two sound cards.
Cables to connect your computer to your SSB radio.
Test your Transmitter Frequency Response
When you play this 10 second 1 kHz to 2 kHz sweep .wav file(external link) through your transmitter, the
power level should remain constant. If not, look for filtering and processing to turn off.
Connecting Your Radio
If you are lucky enough to have a "9600" input and output on your radio, this is the best connection for
every digital mode, even 1200 packet, and your audio box should be configured for 9600 or "no pre-
emphasis/de-emphasis" if it has that setting. If the radio's configuration menu has a 1200/9600 setting,
leave it permanently on 9600.
The "9600" and "1200" settings are misnamed. "9600" should really be called "direct connection", and
"1200" should be called "processed". The audio processing in your radio does not help any digital mode.
Configuring Your Radio
Turn off as much processing as possible. In general noise blankers, DSP band limit filtering, and narrow
bandpass filters are likely to hurt rather than help. Compression, DSP noise and carrier elimination, and
voice processing are definitely wrong for Digital modes. FreeDV's FDM modem does its own DSP, and in
general this is true for other digital programs as well. The only things that we would expect to hurt the
signal are intrusion of the opposite sideband, images of out-of-passband signals, and intermodulation
distortion. You can see the effect of different settings in the S/N display of FreeDV.
Drive your transmitter and amplifier so that it emits 10%% to 20%% of its rated power continuously. There
is a 12 dB peak-to-average power ratio in the FDM modem, and peak clipping in your amplifier will reduce
the received S/N. Modern transmitters and amplifiers are only as linear, and only have as much headroom,
as is necessary for voice SSB. Ask manufacturers and reviewers to start rating linearity and headroom for
digital modes.
PTT Configuration
Tools-PTT Dialog
Hamlib comes with a default serial rate for each radio. If your radio has a different serial rate change
the Serial Rate drop down box to match your radio.
When "Test" is pressed, the "Serial Params" field is populated and displayed. This will help track down
any mis-matches between Hamlib and your radio.
Serial PTT support is complex. We get many reports that FreeDV Hamlib PTT doesn't work on a particular
radio, but may work fine with other programs such as Fldigi. 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.
If you are really stuck, download Hamlib (Debian package libhamlib-utils) and test your radio's PTT using
the command line rigctl program.
Voice Keyer
Voice Keyer Button on Front Page Options-PTT Dialog
Puts FreeDV and your radio into transmit, reads a wave file of your voice to call CQ, then switches to
receive to see if anyone is replying. If you press space bar the voice keyer stops. If a signal with a
valid sync is received for a few seconds the voice keyer stops.
Options-PTT dialog can be used to select the wave file, set the Rx delay, and number of times the tx/rx
cycle repeats.
The wave file for the voice keyer should be in 8kHz mono 16 bit sample form. Use a free application such
as Audacity to convert a file you have recorded to this format.
Test Frame Histogram
Test Frame Histogram tab on Front Page
Displays BER of each carrier when in "test frame" mode. As each QPSK carrier has 2 bits there are 2*Nc
histogram points.
Ideally all carriers will have about the same BER (+/- 20% after 5000 total bit errors). However
problems can occur with filtering in the tx path. If one carrier has less power, then it will have a
higher BER. The errors in this carrier will tend to dominate overall BER. For example if one carrier is
attenuated due to SSB filter ripple in the tx path then the BER on that carrier will be higher. This is
bad news for DV.
Suggested usage:
i) Transmit FreeDV in test frame mode. Use a 2nd rx (or get a friend) to monitor your rx signal with
FreeDV in test frame mode.
ii) Adjust your rx SNR to get a BER of a few % (e.g. reduce tx power, use a short antenna for the rx,
point your beam away, adjust rx RF gain).
iii) Monitor the error histogram for a few minutes, until you have say 5000 total bit errors. You have a
problem if the BER of any carrier is more than 20% different from the rest.
A typical issue will be one carrier at 1.0, the others at 0.5, indicating the poorer carrier BER is twice
the larger.
Full Duplex Testing with loopback
Options - Half Duplex check box
FreeDV GUI can operate in full duplex mode which is useful for development of listening to your own
FreeDV signal as only one PC is required. Normal operation is half duplex.
Tx and Rx signals can be looped back via an analog connection between the sound cards.
On Linux, using the Alsa loopback module:
$ sudo modprobe snd-aloop
$ ./freedv
In Tools - Audio Config - Receive Tab - From Radio select -> Loopback: Loopback PCM (hw:1,0)
- Transmit Tab - To Radio select -> Loopback: Loopback PCM (hw:1,1)
Design & Key Features
Design:
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, 16x50 baud DQPSK carriers,
Differential QPSK demodulation
FreeDV 700(C) mode: 700 bit/s voice coding, no FEC, 14x75
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.
Credits
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.
As development continues, many people are helping whom we have not credited, but we appreciate all of
their work.
This manual page was written by Maitland Bottoms for the Debian project (but may be used by others).
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 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.
SEE ALSO
http://freedv.org/ For casual chat there is a #freedv IRC channel on freenode.net