Slow Scan TV allows transmission of still
pictures using a small bandwidth ( no more than a voice SSB
transmission). Invented by Copthorne MacDonald WA2BCW (SK) at the
end
of the 1950s, it became more popular after 1992 with the availability
of several software packages running on Personal Computers.
More information about SSTV is available in the Wikipedia
page.
BW 8 s SSTV.
This is a picture of myself, displayed in 1969 on the home-made SSTV
monitor I designed and built at that time. The SSTV format used was
8 seconds black and white and the picture appeared slowly on the face
of a remanent CRT (an old 5FP7 radar display tube).
==> NEW : December 2020. I
recently restored this old monitor: the power supply capacitors
were changed, a dead +5 V LM309 voltage regulator replaced by a
7805, etc. Then I thoroughly checked the
CRT high voltage power supply with emphasis on the HV filtering
capacitors. Next I switched the
monitor ON and everything was OK.
The remaining problem was to get
a BW 8 s SSTV audio file: they are not so common nowadays. I talked
about
that with my son Lionel and, some days later, he sent me several 8 s
SSTV WAV files generated by a Python program. The software he used is
presented here (1) (2)
I was now ready to test my old monitor. It worked successfully and I
only adjusted centering and size controls to see decent pictures on the
CRT
screen. I admit that the image quality is rather poor compared to that
we get now with color SSTV programs: don't forget its resolution is
only
128x128 pixels.
I recorded a video showing how SSTV looked more than 50 years ago. Click here to see (and listen to) this
file.
Color SSTV. At
the beginning of the 1990s, Lionel and I built a new SSTV
equipment named TVDC. The hardware was a home made modified version of
the KA2PYJ Viewport interface and we designed a fully new software
(written in Pascal and assembly language). This system, allowing
reception and transmission of the most popular SSTV/Fax modes at that
time, was described in a French amateur radio publication ("SSTV couleur et fax sur compatible PC",
Roland Cordesses & Lionel Cordesses, Radio REF July-August 1994,
pp. 23-27).
(A) 
(B)
Real Time processing.
In
2002, we tried to improve the picture quality of SSTV signals under
noisy conditions through real time processing : the above pictures
present the results obtained with this new software (A) and with a popular SSTV program (B) from the same noisy SSTV signal.
This approach was presented in the May/June 2003 issue of the ARRL magazine QEX (
"Some thoughts on "Real Time" SSTV Processing", Lionel and Roland
(F2DC) Cordesses, QEX May/June 2003, pp. 3-20).
New : ==>
The original QEX article is
downloadable from Lionel's Web
page.
You can download the sources of the described programs clicking here (# 90 kbytes)
Notes
(1)
https://github.com/dnet/pySSTV
(2) Here is the command line used by Lionel to generate the BW 8
seconds SSTV Wav file :
find /home/lionel/Pictures/F2DC_SSTV/ -type f -name "*.TGA" | parallel
python __main__.py --resize --mode Robot8BW {}
/home/lionel/Music/SSTV_F2DC/{/.}.wav