[opendtv] Re: Bolivia TV standard mystery
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 20 Dec 2006 19:51:41 -0500
Ian Mackenzie wrote:
>> Take a market area of, say, 80 mile diameter, and only
>> small 1 KW towers to cover it, on one frequency channel.
>> Even with COFDM at 1/4 GI, a passive system won't work
>> (28 mile spacing max).
>
> Why would you need lots of 1KW towers to cover a 80 mile
> area?
>
> That's just the wrong way to do it.
>
> Take Sydney Australia for example where a single VHF 3.5KW
> TX giving 50KW ERP on a single tower covers an area this
> big adequately with 2 small repeaters in a separate UHF SFN.
Sure, I agree with that completely. As an aside, the 50 KW ERP big
stick, VHF, is probably a lot more powerful than many of the VHF big
sticks we'll be seeing here. Rememeber that the VHF big sticks planned
here are all on the order of less than 20 KW, at least on the East
Coast. (I'm not sure how well that will work, but we'll see when the
time comes.)
Go to
http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-06-150A1.pdf
and look at the table half way down. You'll see, for instance, that
Channels 7 and 9 in DC will go back to their VHF allocation after analog
switch-off. The DTT transmitters of these stations are now UHF. In their
new VHF channels, they will be 15 and 17 KW ERP, repectively. Baltimore
is similar, with Channels 11 (6.91 KW) and 13 (21.4 KW) going back to
VHF. Scrolling down that table you'll see that low VHF channels, i.e.
anything between Ch 2 and Ch 6, are in the single digits of KW ERP.
So these power levels are supposed to cover the bulk of their markets.
They will not provide any sort of cookie cutter pattern Craig is talking
about, to prevent "interference" in the adjacent market, and to allow
for frequency reuse anywhere close by. As I'm sure is the case in Sydney
as well. You don't get cookie cutter patterns with single big sticks and
50 KW VHF.
What you describe is what I described, except even more fool proof. One
big stick, to provide the bulk of coverage, supplemented by gap fillers
in UHF. In your case, you would arrange it so the small sticks are low
power enough that in any potential area of interference between them, TV
receivers would instead be tuned to the big stick's signal.
By the way, ditto in Paris, where there are three small 1 KW sticks
supplementing the Eiffel Tower 35 KW big stick, and in most cases the
small sticks are on a different frequency from the Eiffel Tower
transmitters.
> Much cheaper than trying to cover the area with lots of
> small TX sites In a SFN or an "Earth Scorcher" main UHF TX.
Believe it or not, you described the "earth scorchers" we'll get here.
But I do agree it's the right way to go. I think frequency reuse is
going to be identical here and there, in built-up areas.
The dense mesh you would need to get cookie cutter patterns is simply
not practical.
Bert
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