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Re: Re: IC-910 / 3731



And Gene would be right.  For completeness, Jerry K5OE was very close.  I 
wasn't trying to turn it into a guessing game, but we all love antennas, 
don't we?  I'm going to try and get a quick web article on it done in the 
next week (maybe even this weekend).  It's only a bit more involved than an 
end-fire ("normal", in the sense of "usually thought of") helix, but I bet 
someone out there can improve on my implementation.

I'm also going to try and put some stuff up on feed blockage.  The most 
commonly published approximation seems to be for the -inf dB edge taper 
(like Gene mentions), but that's also a worst-case scenario, as the effects 
of central blockage get worse with increasing edge taper.


At 08:22 2003-11-15, Gene Marcus wrote:
>  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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Scott Townley NX7U
Gilbert, AZ  DM43di
http://members.cox.net/nx7u

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