DIGITAL VOICE AND SSTV/FILE TRANSFER SOFTWARE
FOR RADIO AMATEURS
Digital
Voice (DV)
There have
been many computer-based systems and software that have been developed
to transmit and receive digital voice in a normal SSB bandwidth for use
on the HF bands.
FreeDV is most popular and probably the only active computer-based digital voice mode.
On a waterfall display a FreeDV signal occupies audio frequencies between around 1kHz and 2kHz.
At 0900 UK time on Sunday
mornings GB2RS News is broadcast in FreeDV 700D on 3.643MHz LSB, also
at 2030 UK time there is sometimes a FreeDV net on 1.997MHz LSB
See HERE for details on the new FreeDV digital voice software and HERE for KK5JY's SmallDV for the Raspberry Pi.
FreeDV is incompatable with AOR Digital Voice,
D-STAR and System Fusion.
File
Transfer and Digital SSTV
A few
digital file transfer and digital SSTV systems have been developed and
used but a DRM (Digital Radio Modiale) based system commonly known
as EasyPal and a text and digital SSTV system called KG-STV are now the
main players.
In Easypal most files
transferred are pictures in JPEG2000 format (.jp2) which is
supported by IrfanView. HTML and text have also been
transferred but it is primarily a digital SSTV system.
Unlike analogue
SSTV, Easypal
pictures can be of almost any dimension because the actual image file is
transmitted rather than each individual pixel.
See VK3EVL's
web site for information on EasyPal.
KG-STV is a transmission mode used for transmitting and receiving pictures similar to
analogue SSTV. Short text-based messages can also be transmitted.
The
really clever thing about both Easypal and KG-STV is that if any part or parts of
the
transmission are received incorrectly due to interference, fading or
any distortion the station that has errors in the received file can
send a Bad Segment Request (BSR) and then the corrupted and missing
parts can be retransmitted to repair the damaged file.
In my opinion KG-STV is better because it can run
on a slow computer, it has a less cluttered user-interface and the
received picture builds up piece by piece as it is being decoded - a
bit like the line-by-line display of an analogue SSTV image or like an image would load on an old home computer from cassette.
Click HERE for more
information on KG-STV.
Frequencies and Operating
Main
frequencies for EasyPal here in UK and Europe are 3.736MHz, 5.335MHz, 7.058MHz,
14.233MHz, 21.343MHz and 144.550MHz. 14.236MHz is also used
in
North
America.
The 80m
frequencies are
very active in the evenings, Activity
can
be heard on 144.550MHz FM around the English Midlands mainly in the
evenings. and weekend afternoons.
Easypal and KG-STV use the same sideband as
normal analogue SSTV and SSB speech i.e. LSB below 10MHz and USB above.
The
suggested
frequencies for KG-STV
are 1.841MHz, 3.600MHz, 7.052MHz, 10.141MHz [ITU Regions 2 & 3
only], 14.111MHz, 18.111MHz, 21.111MHz, 24.935MHz and 28.686MHz.
Both EasyPal and KG-STV can be found on QO-100 between 10489.615MHz and 10489.635MHz USB.
Below are some
pictures received
in EasyPal (all
actual size)
Old Software
Have a look at N1SU's
web site to download old DRMDV and FDMDV software.
DIGTRX is rarely used now but more information can be found HERE.
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