[Moon-net] Fw: Feed choice

[Edward R. Cole]

At 08:54 AM 2/8/2007 +0100, DEHAYS Dominique wrote:
>
>Hi all ,
>
>if my informations are acurate ,  there will be a "SUPER VE4MA" feed with 
>Septum polarizer described in DUBUS for 23 and 13cm  ( maybe in the next 
>issue? ). So you will get good information.
>I had the opportunity to read it in avance ( tnx to the author). I just 
>wonder one thing : there is some calculations done in the article , one of 
>them is feed horn diameter. I saw that this diameter is different for 
>linear and for circular polarisation , I wonder why? Anybody knows?
>
>73's Dom/F6DRO/JN03TJ 
>
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Dom,

I have read most of the articles written by Zdenek OK1DFC and Paul W1GHZ
and the original IEEE paper from which the current design is derived.
Simply put, the septum polarizer operates near the lower cutoff frequency
of the waveguide.  For a linear polarzed feed one might want to operate a
little farther above cutoff to reduce losses.  Just a guess!  The ham
septum designs are scaled from the original design.  The IEEE designers
empirically determined their dimensions, lacking the computer capabilities
back in when their study was done.  Therefore, there is no formulas or
theoretical design to work from.
73's,
Ed - KL7UW  
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