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Hi Graham,

>Can i gather that the US broadcasters are only transmitting HD
>because the government said they have to, and not because they
>want to or have a demand for it.

The official regulations of the Federal Communications Commission state only
that broadcasters must transmit at least one free digital signal that is
equivalent in quality to today's NTSC service.  Whether it's HD or not is up
to the broadcasters, not the government.

The MPEG-2 technology that enables HDTV broadcasting also makes it possible
to fit four to six SD channels in the bandwidth previously occupied by a
single channel.   For cable companies, this makes it at least theoretically
possible to have up to 500 channels on a system (where they'd find enough
programming to fill that many is another story).  The three major U.S.
networks, whose main business is the advertising of national brand products,
do not wish to dilute their audiences by multicasting.  So they've become
the major impetus for HDTV broadcasting in the hopes that one high-quality
picture will attract more (affluent) viewers than lots of mediocre pictures.

Interestingly enough, the networks have only been able to fully commit the
stations they own and operate to full-time HDTV.  The majority of their
affiliates have indicated that they will transmit HD during primetime, and
multi-channel SD at other hours.  The networks themselves even talked of
doing this, which is what raised the ire of the U.S. Congress.

Where the U.S. Congress gets into the act is because of the recent discovery
that licenses to radio frequency spectrum can be auctioned to commercial
interests at good profit to the U.S. Treasury.  Since the beginning, the
radio and TV broadcasting industry in the U.S. has justified its free use of
the airwaves on the [debatable] grounds that it provides a public service.
But with DTV, a broadcaster could theoretically sell 5/6 of its capacity for
private uses and keep its license through public SD programming in the
remaining sixth, which hardly seems fair.  Also, it was found economically
impossible to replace the existing analog TV system in one shot; the only
sensible way to do it is to "sunset" NTSC while the new digital system
unfolds.  So every existing TV broadcaster was given a second digital
channel--also free--with the proviso that their analog channels would revert
to the government once 85% of the households in their service areas had
acquired the ability to receive digital TV.  That the broadcasters also
received the right to lease their new channels for non-television purposes
in the interim really got some Congressional committees steamed up.

> I cant imagine the upverted 525 to XXX pictures are to

Although it isn't possible to reconstruct information that isn't in the
original 525 material, upconverters have been demonstrated which work
surprisingly well.

> What are the domestic TV manufacturers supplying, a TV that will
>take 1080, 720, 480, P or i as well as 525. or do you have to choose
>between a CBS  TV or an NBC TV

There are actually 36 possible permutations of lines, frames, and scans
(interlaced or progressive).  At present, set manufacturers have indicated
that they will receive all of them, then do conversions as needed to
whatever the internal format of the display is.

Best regards,
Christopher Bacon

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