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/