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freedv(1)


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/



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