[amsat-bb] Re: IC-910 / 3731

[Gene Marcus <mmarcus@xxxxxxxxxx>]

  Tony AA2TX wrote:


>I think Paul Wade (W1GHZ) has something similar on his
>web site that will calculate the feed blockage for you
>(HDL_ANT) or something like that.
>
>Ok, so fess-up now, how do you get no blockage from a 60 cm
>prime focus dish at 2.4 GHz?
>

Tony,

I would guess that Scott is using a back-fire helical antenna. "Antennas 
2nd Edition " by Kraus page 329. It may not yield zero blockage, but it 
is certainly minimal.

A feed blockage approximation (assumes field distribution tapering 
to zero at the edge of a center feed dish) is included in a dish design 
spreadsheet found at:
 
http://home.hiwaay.net/~mmarcus/download/Dish_Design.xls

73,

Gene W3PM GM4YRE


.



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