[mythtv-users] Satellite footprints (was: Mooting architecture for a DataDirect replacement)

[Rod Smith]

On Friday 22 June 2007 12:15, Mike Perkins wrote:
> Dan Ritter wrote:
> > And why the .na. in the middle? Because the overlap in
> > programming between Washington DC and La Paz is probably
> > small. And satellites visible across the US, northern Mexico and
> > southern Canada are probably not visible from Rio de Janeiro.
>
> You do know that all those satellites are positioned above the equator,
> no? Otherwise they're in an inclined orbit, which means they would
> wander up and down in latitute, and it would be a devil of a job to keep
> the dish aligned to them...

Yes, but communications satellites (at least those used for digital TV, which 
is the technology with which I'm most familiar) typically serve a subset of 
the hemisphere that's visible from the satellite. Think of it like a 
flashlight beam; the satellite might point its "flashlight" at the US to 
cover that market, with a good deal of splashover into Mexico and Canada. 
That beam won't reach as far south as Brazil, though. US satellite providers 
use even smaller "spot beams" to carry local stations. This enables the same 
frequencies to be re-used to carry stations for different markets -- viewers 
in Boston and Seattle might tune to the same transponder to watch their 
respective local stations and be physically unable to receive each others' 
locals. I don't know the extent to which frequencies are re-used between 
nations in this way, but I'd be surprised if there weren't any re-use, 
particularly between extreme northern and southern nations.

-- 
Rod Smith
http://www.rodsbooks.com