Nigel Goodwin writes:
>As for 50Hz field, what's the problem, it gives 25 pictures a second,
>film only gives 24 :-).

        That's true, but film projectors usually show each frame three
times so the flicker is actually 72 flashes per second.
The flicker that one actually sees on the screen  is at twice the frame
rate because of the interlace factor.  I do not have enough vision to
report on this first hand, but some people say that there is just enough
difference between the 50 and 60 HZ field rate to make it slightly
noticeable.

        I was a technician in the Audio Visual Center here before my
present job and we, one day, got a little PAL/NTSC crash course.

        One of the things we did was to help customers with their video
problems and we had a man whose daughter lived in Australia and who wanted
to be able to exchange videos with his daughter and her family.

        The man had bought a multi standard VCR which could play just about
any video format there was as long as you had a monitor meant for that
format.  His daughter had nicely bought a little monochrome TV from a
store in Australia.  The trouble was that the VCR's RF modulator worked
in the UHF channels and the TV had no UHF.

        Just for fun, we borrowed a NTSC monitor meant for a C64 computer
and twiddled the vertical and horizontal sync until it matched the PAL
signal.  We had a perfect monochrome picture with a little overscan
probably due to the lower vertical frequency.  The sync and luminance
signals for PAL are exactly the same as for NTSC, but of course there was
no color at all due to the different color burst frequency and even if
that had matched, no telling what the screen would have looked like with
half the lines reversed for red and blue.

        The documentation said that some 3.58 MHZ-based PAL systems used
in Latin America might produce color but it would be wrong if received on
an NTSC set.

        By the way, our customer bought a multi standard Panasonic monitor
and his daughter did the same in Australia and so that's how they solved
their video problems.

>What's the state of things in the USA, digital MPEG2 is due to start
>later this year in the UK - both terrestrial and satellite. It remains
>to be seen how good it is!.

        I just called the four major television stations in Oklahoma City
and asked them when they expected to start MPEG2 broadcasting.  The Public
Broadcaster said that they have an additional year on everything compared
with the commercial broadcasters so they are looking at 1999 to bring up
their UHF transmitter.  The two commercial stations who gave me an answer
both gave times in late 1999.  They must vacate their present VHF
assignment by 2006.

        I am guessing that this is fairly representative of what most of
the United States will be dealing with.  The largest cities will start
broadcasting MPEG2 this year and it will trickle down to smaller areas in
the next several years.  There are eight levels of video quality ranging
from about 400 lines up to 1100 lines so it won't all be HDTV by any means.

Martin McCormick