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*Subject*: Re: [amsat-bb] IC-910 / 3731*From*: Anthony Monteiro <aa2tx@xxxxxxxxxxx>*Date*: Fri, 14 Nov 2003 15:39:50 -0500*In-Reply-To*: <5.1.1.6.0.20031113214203.00a89b30@pop.west.cox.net>

At 10:01 PM 11/13/2003 -0700, Scott Townley wrote: >True, I did skip a step. >This is all from direct integration of the aperture distribution, >neglecting edge diffraction and an 11.5dB edge taper: >The 4/24 case (4" dia feed blockage on a 24" dia dish) shows only a >0.084dB loss in efficiency. Interestingly enough this is very close to >the simple geometrical method I alluded to (10*log(1-0.03)=-0.132dB). I >don't claim the geometrical method to be accurate for larger cases! >Where did you get the 0.7-0.8dB figure? Hi Scott, Doing the integration, you should get more not less loss from the blockage. If you get .132 dB loss from simple geometry (i.e. as if a uniform apperture distribution) then you have to get a higher loss for the cos^2 case. Was the .084 dB a typo (did you mean .84 dB?) Anyway, I assumed a symmetrical, cos^2 distribution and I used the actual dimensions of the G3RUH patch which is 120mm or about 4.7 inch over a 60cm dish. You COULD integrate over the apperture to find the loss but I am WAY to lazy to do that unless I have to. I used a little apperture analysis program called "SABOR" from the Polytechnical University of Madrid. I would guess this was a grad student's project and you can download it for free from: http://www.gr.ssr.upm.es/sabor.htm It is very limited in what it can do but for what it handles, it is very convenient and I have found it gives pretty realistic results. 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? Cheers, Tony AA2TX ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Re: IC-910 / 3731***From:*Anthony Monteiro

**Re: IC-910 / 3731***From:*Scott Townley

**Re: IC-910 / 3731***From:*Anthony Monteiro

**Re: IC-910 / 3731***From:*Andrew Glasbrenner

**Re: IC-910 / 3731***From:*Emily Clarke

**Re: IC-910 / 3731***From:*Scott Townley

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