RE: WMUR HDTV to start Nov 1

[Dan Strassberg <dan.strassberg@worldnet.att.net>]

At 06:31 PM 10/12/98 -0400, you wrote:
>
>Wow Won't that cause a mess with the Channel 60, 6 MHz away, whose
>transmitter is just 200 feet away on Mt. Uncanoonuc. Did WMUR choose ch.
>59? Something appears to be underhanded here, or is my guard up because of
>the WNDS.com hi-jinx.
>
The major reason that ATSC selected 8VSB (eight-level vestigial-sideband
digital modulation) over, say, the Cable-TV implementation of 64QAM
(64-level quadrature-amplitude modulation), which packs the same amount of
digital information into a 6-MHz channel, is that 8VSB is supposed to not
interfere with or receive interference from co-channel or adjacent-channel
NTSC analog transmissions. Both 8VSB and NTSC's video channel are
vestigital-sideband schemes. I believe that the 8VSB carier is near the high
edge of the channel. That is, the upper sideband is vestigial. The NTSC
video carrier is near the lower edge of the channel; the lower sideband is
vestigial. ATSC receivers are also supposed to incorporate adaptive features
that sense the presence of potentially interfering NTSC signals and somehow
modify the receiver response (in what way, I don't know) to minimize the
interference.

Also, remember that these analog and digital modulation schemes have quite a
bit in common with the analog and digital modulation schemes that several
companies have proposed for in-band, on-channel (IBOC) digital-audio
broadcasting (DAB). In IBOC DAB, the analog and digital transmissions are
supposed to coexist in the SAME channel without interfering with each other!
So far, the results haven't been terribly encouraging, but the proponents
(such as USA Digital Radio--partially funded by CBS) not only haven't given
up, they are being joined in the fray by new schemes from new competitors
(the well-heeled AT&T spinoff Lucent Technologies, for example). Each
company has proposed IBOC DAB systems for both the AM and FM bands.

Will all of this extremely sophisticated technology actually work as it's
supposed to? I'd say that the chances are slim at the outset, but the stakes
are high and the engineers will keep tweaking until the system works. A more
significant question in my mind is whether terrestrial over-the-air TV is
still relevant in this country. With 2/3 of US households on cable and
millions more receiving programming from DBS (direct-broadcast-satellite)
systems, that's a very important question. You can make a good case that the
only reason that land-based over-the-air TV broadcasts have over 1 GHz of
precious RF spectrum is that our elected representatives are afraid of the
NAB. Moreover, with outfits like Capstar relegating so much of radio to
simply rebroadcasting bird droppings with no local content, how much longer
will the public consider radio to be relevant?

- -------------------------------
Dan Strassberg (Note: Address is CASE SENSITIVE!)
ALL _LOWER_ CASE!!!--> dan.strassberg@worldnet.att.net
(617) 558-4205; Fax (617) 928-4205

------------------------------