[sci.electronics] HDTV: feasible?

cfk6u@fermi.clas.Virginia.EDU (Charles F. Kramer) (05/25/91)

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cfk6u@fermi.clas.Virginia.EDU (Charles F. Kramer) (05/25/91)

	Zenith currently has a proposal in with the FCC to broadcast
digital High Definition TV signals _between_ normal TV ones, at low
power, to minimize interference.  DOes this sound feasible, practically
speaking?

Charlie Kramer
cfk6u@Virginia.edu

whit@milton.u.washington.edu (John Whitmore) (05/28/91)

In article <okeJ32w163w@zl2tnm.gp.co.nz> don@zl2tnm.gp.co.nz (Don Stokes) writes:
>cfk6u@fermi.clas.Virginia.EDU (Charles F. Kramer) writes:

>> HDTV: Feasible?

>No.  Not under current bandplans.

	It's not clear that this sort of thing is infeasible.  Standard
TV transmission includes NO data compression of any sort, and the signal
usually has a lot of information that either (1) is repetitive of other
parts of the screen or (2) is repetitive with respect to the previous
(in time) frame.  
	Variations on conditional-update and difference-signal techniques
can easily compress this sort of signal.  Much of HDTV's promise
resides in the low current cost of memory to buffer a video screen's
information so that the signal from the transmitter need not
be a continuous set of full-screen updates.

	Of course, the BEST schemes would require a lot of fancy 
decision circuitry at the transmit end, and would not be compatible
with current receivers.  We (USA) may see UHF stations with a HDTV signal
with duplicate VHF transmissions that remain NTSC (for _Never _Twice
the _Same _Color :-)    ).

	John Whitmore

dlleigh@media-lab.media.mit.edu (Darren Leigh) (05/30/91)

In article <1991May24.223204.2166@murdoch.acc.Virginia.EDU> cfk6u@fermi.clas.Virginia.EDU (Charles F. Kramer) writes:
>
>	Zenith currently has a proposal in with the FCC to broadcast
>digital High Definition TV signals _between_ normal TV ones, at low
>power, to minimize interference.  DOes this sound feasible, practically
>speaking?

I think the above is essentially correct, but it is phrased poorly.  I
understand that the current philosophy is to use the taboo UHF channels
for HDTV broadcast and use somewhat lower power than the current scheme.

Because NTSC has all those nasty, strong carriers, it is possible to get
adjacent channel interference.  Therefore, the FCC doesn't assign
adjacent channels in the same area.  HDTV signals will have a pretty
flat spectrum (due to more efficient use of the bandwidth) and will have
methods for dealing with interference.  Therefore, they can go in the
taboo channels without interfering with or being interfered by the
existing channels.

A lot of the power broadcast by a TV station is in the video carrier.  A
good HDTV system won't have this and so can broadcast more information
with less power.

There's some nice technology going into this stuff and I look forward to
it hitting the market.

Darren Leigh
dlleigh@media-lab.mit.edu
Disclaimer:  I have no connection with the MIT HDTV people.