[opendtv] Re: The "real" problem with OFDM in the U.S.
- From: "John Willkie" <JohnWillkie@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 8 Mar 2005 14:06:57 -0800
Bert;
You seem to be getting better on this list, but you still venture where you
don't have a clue.
As any BROADCAST ENGINEER (of which I am one) knows, separation of full
service TV stations is ONLY due to a distance calculation. Indeed, the
situation you mention -- channel 11 between New York and Baltimore required
a waiver from the FCC in the 1970's when KPIX wanted to move to the World
Trade Center. It took the better part of a decade to approve that close
spacing. The diversion from the ruless was LESS than a mile -- 2800 feet,
IIRC.
They're just a little bit more flexible with FM stations (with two possible
seat of the pants models using distance versus the classes of the various
stations) in the deminimus delta zones.
Wilderness is NEVER an issue. The ONLY deviation (except for de-mimimus
waivers, like KPIX which are rarely granted) is for low power/translator
stations. There, the FCC has permitted on a case-by-case basis, they do
permit knife-edge diffraction studies to prove that there is no actual
interference, only theoretical interference. Even then, the affected
parties can and routinely do, protest, which slows up the licensing process.
And, need it be pointed out, IN ANY CASE, if there is ACTUAL interference,
the new entrant is responsible for fixing it. Which, in the worse case,
means going dark. Even if the interference is in a single household. If
they reject the offered antenna to fix it, you make changes at the new tx
point.
TV stations SERVE their cities of license. They do NOT HAVE to serve
adjacent areas. If they can put a city grade signal over at least 98% of
their city of license (to the political boundaries) they get a construction
permit. Otherwise, they need a waiver.
Anything else is desirous on the part of the broadcaster, but is not
required by the FCC.
Wilderness indeed ...
(I usually label my WAGs.)
John Willkie
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, March 08, 2005 1:07 PM
Subject: [opendtv] Re: The "real" problem with OFDM in the U.S.
> Tom Barry wrote:
>
> > > If you want to avoid dead zones, as we must here,
> > > then adjacent markets won't be able to share
> > > frequencies. Even with the small stick approach.
> > > But the next market over can use those frequencies,
> > > *same as now*.
> >
> > Is there any topography where someone located equally
> > (at any distance) between two stations with the same
> > power and channel is not in a dead zone?
>
> On the same channel, I'd say no. That's why if there is
> no wilderness between adjacent markets, the frequencies
> of one market cannot be used in the adjacent market.
> And that buffer zone, where no reception is possible on
> a given frequency band, may either consist of a complete
> lack of signal or a lot of co-channel interference.
>
> I'm basically rebutting the oft-repeated notion that
> SFNs or small sticks will allow greater frequency reuse.
> Taken in a vacuum, that statement seems unarguable. But
> taken in context of TV transmission in real markets,
> where coverage must be ubiquitous, it's just not the
> case.
>
> Take VHF Channel 11. It is used in Baltimore and NYC.
> If the Philadelphia market were a wilderness, then
> Channel 11 could be reused in two adjacent markets.
>
> But the fact is, Phildelphia exists. The Balt Channel
> 11 must serve communities up into northern MD and must
> overlap with signals from the Philadelphia market. And
> the NYC Channel 11 must also serve communities which
> approach Phildelphia. Because people from these
> communities may commute to either market. In Phildephia
> itself, Channel 11 can go ahead and be a mess of
> co-channel interference or low signal level.
>
> So whether you create the Ch 11 coverage patterns with
> big sticks, with small sticks in SFNs, or with a
> combination of big sticks and on-channel gap fillers,
> the end result is largely the same. Frequency reuse
> will depend on HOW LARGE the markets are and on whether
> or not adjacent markets are contiguous. As things are
> now with big sticks, Channel 11 is used efficiently in
> this part of the East Coast.
>
> If you really want to use the *same* frequencies in
> adjacent markets, then you must create buffer zones
> where signals will be difficult or impossible to
> receive. There's no logical excuse to create such
> zones today, along the East Coast. Or you could
> establish a network of low power translators throughout
> the market, but that would require use of more
> frequencies, not fewer. It just creates the same
> problem on a smaller scale. That's all.
>
> So bottom line, if you have to cover large markets
> while making efficient use of frequencies, big sticks
> are a reasonable approach. Especially if these can be
> assisted by on-channel repearters, to improve the
> signal level in challenged locations.
>
> Bert
>
>
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