[Moon-net] Fw: Feed choice OZ6OL

[Edward R. Cole]

Thiery,

Paul Wade published a very exhaustive paper in 2006 investigating the
effects of the rings of the Chapparal or "VE4MA" type of feedhorn.  This
was married with a cylindrical septum polarizer.  Do not be confused by the
name septum.  It, in itself, doesnot determine the match with dish f/d.
Paul found that the chapparal feed with rings in the same plane as the
feedhorn throat matched a dish with f/d=0.4.  AS the rings were retreacted
behind the throat of the cylindrical feed the antenna pattern increased in
beamwidth matching smaller f/d ratios.

So extrapolating from Paul's work one might guess that a chapparal feed
with rings either at the plane of the feed opening or maybe slightly in
front would match your f/d 0.43 dish.  Dishes with f/d like 0.6 or higher
one sees conical scalar feedhorns or simple smooth wall conical feedhorns.
The flared section shapes a narrower beam needed with high f/d ratios.

You might check Paul's website and see if he gives an e-mail address to
contact him with your question.

73's Ed - KL7UW

At 09:02 PM 2/7/2007 +0100, Hans.J.Oldenborg wrote:
>
>Hello Thierry,
>
>0.43  F/D er ok for septum feed , but read all information in W1GHZ 
>antennabook on line and all your trouble will go away! you also find the 
>papers for the 2006 EME  Conference there  With feed horn measurement also. 
>look at the OK1DFC  home page
>
>73 Hans OZ6OL
>
>
>----- Original Message ----- 
>From: "Thierry AVELINO" <f1hsu at wanadoo.fr>
>To: "MOON-NET" <Moon-net at list-serv.davidv.net>
>Sent: Wednesday, February 07, 2007 6:53 PM
>Subject: [Moon-net] Feed choice
>
>
>> Dear EMErs !
>>
>> I'm giving shape to an old dream ! And beginners questions spring up...
>> Starting to build my 23cm EME station, it comes to choose the type of
>> feed I'm going to use (of course!)... My dish appears to have an f / D
>> near 0.43. Is a septum feed still usable in that case ? Of course, I can
>> try... but if I make a huge error at this point, I know that it will
>> result in a terrific waste of time !
>> Am I on the wrong way ? Please let me know !
>>
>> Many thanks to you all
>>
>> 73s from Thierry, F1HSU
>>
>>
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>>
>> 
>
>
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73's,
Ed - KL7UW  
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