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Re: Multi band dish feeds



This is exactly how the Arecibo radio telescope works.
The dish points straight up, and the feed is moved around
to see different parts of the sky.   That telescope is
only using about 50% of its total dish area at any moment.

Note that the dish theoretically needs to be a sphere instead
of a parabola, and you theoretically need something right
in front of the feed to correct for the fact that the reflector
is a sphere.

Kraus (ch 12-12) describes this and gives several references.

Doug Braun
NA1DB

At 02:10 AM 3/15/01 , Edward R. Cole wrote:
>Howard etal:
>
>After sending you my reply, I got to thinking more about the idea of
>feeding a portion of my 8-foot dish in an offset mode.  
>
>I think a really neat method of multi-feeding a dish would be using a
>normal center-fed dish that is twice the diameter you need.  If you need a
>2-foot offset dish with feeds for four bands, then get a 4-foot dish and
>mount your four feeds so each feed looks at 1/4 of the dish surface [from
>the dish center to the edge]. 


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