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Re: PrimeStar Dish

On Tue, May 22, 2001 at 02:11:16PM -0400, Bill Hurlock wrote:
> If I where to make the Primestar dish a center feed dish would it work?
> Wasn't sure if the dish is formed specifically for offset feed point or
> not. I was thinking of just putting a transystem at focus right in front
> of dish.


There is only one focal point for any parabolic shape.  In the
offset-fed dishes, you have a section of the paraboloid which focuses
at the point where the feed is mounted.  You can sort of picture it as
a parabolic dish with the bottom 2/3 or so cut off and the feed
beamwidth and pointing angle adjusted so that it doesn't illuminate
much area other than the dish itself.  The reason for ofsetting the
feed is to reduce signal blockage which occurs when the feed is located
within the beam.

Bob, N7XY

Bob Nielsen, N7XY                          nielsen@oz.net
Bainbridge Island, WA                      http://www.oz.net/~nielsen
IOTA NA-065, USI WA-028S 
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