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 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.

New Upgrade as of March 2013

       The new version 0.96 provides a 1600 bit-per-second mode that communicates at much  lower  signal  levels
       than  previously.  Communications  should  be  readable  down to 2 dB SNR, and long distance contacts are
       reported using 1 to 2 watts power. A compatibility mode for communication with the older 0.91 version  is
       included.

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.

SEE ALSO

       http://freedv.org/

fdmdv2 0.91                                       December 2012                                        FREEDV(1)