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.