From: "Dan/W4NTI" on Thurs, Feb 24 2005 10:08 pm

Hams do contribute to the state of the art. Where do you think SSTV
came
from ? Just one example.

Bell Labs and the "PicturePhone"? :-)

Went into service on the Bell System over four decades ago, got
deleted for lack of interest/use some years ago. Worked on a
very limited bandwidth.

The genesis of Slow-Scan TV began in several places. One could
say its start was the first Facsimile...very slow data rate. A very
close cousin was early television, also done at a very slow data
rate considering their dependency on mechanical scanning. A
few amateurs tried to advance into professional ranks with the
mechanical scanning TV but none were successful.

All that was before the USA got into WW2. During WW2, TV
was rather limited but "wirephoto" facsimile got popular on wired
communications circuits. A medium-scan-rate TV system was
used on some experimental guided bombs late in WW2. "FAX"
got its acronym-name during that war and was used for graphics
such as weather maps sent out over HF radio circuits.

With the end of WW2 began the virtual explosion of broadcast
television and the availability of TV camera tubes, TV picture
tubes, newer circuit technology (DuMont "flying spot" system,
a sort of reversed light-subject-camera arrangement) and wide-
band modulation (6 MHz in the USA, included audio). There
began lots of research into Information Theory and Bandwidth
in the late 1940s which resulted in insight to necessary
bandwidths to maintain low error rates ("Shannon's Law" of
1948). Many different experiments began to send "live" TV
at reduced bandwidths and the Bell "PicturePhone" was just
such a system which did go into service in the NYC area.

Information Theory got a few boosts from greater efforts of
cryptologists during the Cold War trying to devise better codes
for sensitive communications. Information Theory eventually
morphed into the Motion Picture Experts Group (MPEG) which
had formed about the same time as the explosion of the
desktop personal computer during the 1980s. MPEG was
based on earlier work using "blocks" of picture elements and
their examination of redundancies plus the availability of new
and better digital logic circuits to process the image blocks.

Nearly all amateur "slow-scan TV" is little more than high-rate
facsimile...on the order of the "PicturePhone" imaging. None
of it is the moving picture quality found on the modern enhanced
cellular telephones using MPEG compression-expansion of
image data.

"Modern television" (defined as all-electronic scanning) is wide
bandwidth to preserve image quality. What is broadcast, even
with old-style black-and-white "original" NTSC standards, is
quite good. Any "NEMO" watcher (NEtwork MOnitor) viewing
the direct input from a microwave relay link can tell you that.
The same with the "air monitor" checking transmitted video.
Early domestic-production TV receivers deliberately limited
bandwidth to reduce costs, resulting in receiver picture quality
being awful to poor compared with what was transmitted. The
picture quality on amateur SSTV is approximately the same
as early domestic-production TV receivers, but SSTV cannot
handle motion nearly as well.

Modern FAX standards use some data compression but that
is limited. Picture quality there is reduced compared to what
was possible with older, uncompressed facsimile.

Amateur SSTV is NOT an "original" thing from hams but rather
an adaptation to stay within shrinking RF spectrum on VHF and
above available to amateurs. If it were ever standardized as to
scan rates and bandwidth, there would be a chance for
improvement. As it is, it remains a novelty, something good for
the editors of QST to crow about. "PicturePhone" went into the
dumpster long ago and SSTV will probably wind up there.