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SSTV:
SSTV is short for 'Slow Scan Television', This unlike domestic television is a
method of transmitting still pictures over a very narrow bandwidth, on frequencies
normally used for speech by Radio Amateurs .
SSTv was originally invented by Copthorne Macdonald and first used by Radio
Amateurs, but is now used by large groups of professionals such as Police &
Security services. The original idea was to find a method of transmitting a
television picture over a single speech channel. This meant that a typical (at that
time) 3MHz wide television picture had to be reduced to around 3kHz (1000:1
reduction). It was decided at the outset that the scanning rates must be very slow,
which precludes the use of moving pictures. The choice of time base for
synchronising was the readily available domestic power supply at 50 or 60 Hz
(depending on the country of origin).This gave a line speed of 16.6Hz and 120 or
128 lines per frame (against the then UK standard of 405 lines (now 625) per
frame), giving a new picture frame every 7.2 or 8 seconds.
The composition of a single SSTV line to the original specification of 8 sec is
as follows: -
The maximum bandwidth is 3kHz, therefore the SSTv signals bandwidth is
restricted to 2.3kHz, Black is represented by a 1500Hz tone and white by a
2300 Hz tone together with a sync pulse at 1200Hz well below the black level
so it would be invisible. The Sync pulses are sent at the end of each line are 5ms
in length and at the end of each frame 30ms
The original SSTV systems were based on ex-government Radar screens and
long persistence cathode ray tubes. Now most systems are computer based for
ease of use, giving full 'living' colour with up to 16 million colours and
transmission times of up to several minutes for each picture.
The difference between SSTV and Fax is blurring, but both systems are still
only one way, without the benefit of error checking we are so use to on the
Internet. This sometimes causes problems particularly when you are receiving
that 'perfect' picture from New Zealand and the last 40 lines are spoilt by
someone calling CQ CQ over the top of the picture.
Information supplied from ‘Slow Scan Television Explained’ by Mike Wooding
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THIS IS THE WEB SITE TO DOWNLOAD THE BEST SSTV PROGRAM THERE IS. THIS IS THE
ONE WE USE ALL THE TIME, IT HAS A GRAPHICS PROGRAM BUILT IN AND IS VERY SIMPLE
TO OPERATE.
WE HAVE FOUND THAT ALL MULTI PROGRAMS LIKE "HAM SCOPE", "MULTI-PSK",
" RIG BLASTER SOFTWARE" AND OTHERS ARE TO CONFUSING OR VERY LIMITING. THEY
ALSO REQUIRE THAT YOU HAVE BOTH Rx & Tx RADIOS ON THE SAME SETTINGS ( OFFSETS )
THAT YOU PUT IN THE PROGRAM SOFTWARE AND THIS IS A REAL PROBLEM GETTING THIS
DONE. THE W95SSTV PROGRAM DOES NOT NEED TO HAVE ANY SPECIAL SETTINGS FOR Tx
OR Rx. THIS ONE IS ANALOG SSTV NOT DIGITAL SSTV.
YOU WILL FIND ANALOG SSTV TRANSMISSIONS ON 14.230. THEY SOUNDS LIKE A CHEAP
LOW SIREN, WHEN PICTURES ARE BEING SENT. THIS PROGRAM IS AUTOMATIC IS WILL
SWITCH TO WHAT EVER FORMAT THE PICTURES ARE SENT AND THERE IS NO SETTINGS TO
MESS WITH LIKE THE OTHER PROGRAMS. MOST SSTV PICTURES ARE SENT "SCOTTIE 1"
WE PUT OUR PICTURES INTO THE PROGRAM FROM OUR DIGITAL CAMERAS TO SEND THEM,
BUT THEY MUST BE "JPG" FORMAT OTHERWISE THEY ARE TO BIG TO USE.
DIGITAL SSTV TRANSMISSIONS ARE ON 14.233 WE HAVE FOUND THAT ANALOG SSTV IS ALL
WE NEED TO HAVE FUN WITH SO WE STICK TO ANALOG AND 14.230 TO GET ANALOG
PICTURES FROM OTHERS OTHER THAN OURSELVES.
THE ONE THING THAT IS NOT IN THE INSTRUCTIONS IS THAT PICTURES ARE SENT AND
RECEIVED USB OR LSB ONLY AND BOTH RADIOS MUST BE SET TO USB OR LSB OTHERWISE
THINGS JUST DO NOT WORK. NEVER HAVE YOUR SOUND CARD ON YOUR COMPUTER
RUNNING OTHER PROGRAMS ONLY RUN THE SSTV PROGRAM TO PLAY SSTV. THE HELP
FILES OF W95SSTV WILL ALSO SHOW YOU HOW TO BUILD AN INTERFACE CABLE IF YOU
DO NOT ALREADY HAVE ONE.
http://www.barberdsp.com/w95sstv/w95dload.htm
WE PLAY SSTV REGULARLY ON 80M AND USE LSB FOR THE PICTURES AND CW TO
COMMUNICATE. WE USE 80M BECAUSE WE ARE TO CLOSE FOR 20M OR OTHER BANDS
AND 40M AFTER DARK HAS TO MANY AM STATIONS. THE 14.230 FOLKS USE USB FOR
PICTURES AND USB TO COMMUNICATE. IF YOU WANT TO PLAY OR HAVE PROBLEMS
CONTACT US.
JERRY, KB8TAS GAYLORD, MICHIGAN AND HARRY, NZ8F BOYNE CITY, MICHIGAN
Jerry Cokewell
cuer@gtlakes.com
SSTV FREQ. (E) EXTRA (G) GENERAL
80 M 3.845 (E) 3.868 (G)
40 M 1.171 (E) 7.238 (G)
30 M 10.130-10.140
20 M 14.230 ANALOG 14.233 DIGITAL (BOTH ALWAYS GOOD)
17 M 18.100-18.105
15 M 21.340
12 M 24.920-24.925
10 M 28.680
Links:
GOITP - Good place for SSTV information!
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