Re: [amsat-bb] Re: patch feed and proper dish

[Joseph Murray <k0vty@xxxxxxxx>]

Hi Ron 

I indeed would like a review of the outer edge of dish construction and
the effects on several things.
I have noticed that when buying a dish and specifying a given diameter . 
 The diameter is in my case smaller than asked for .
Is there is a possibility that the diameter of a dish is really that
dimension before the outer edge is formed  .
If this is correct that all measures of a dish are affected such as
height and F/D.
If you tackle this please also include the outer edge that has a specific
non rolled outer edge which is rolled only so far then the material
straighten to be a flat surface which extends further than the material
in a rolled edge would provide for . 

Thanks for offering to do this

Joe K0VTY
===================
On Sun, 14 Oct 2001 11:16:10 -0400 Ronald Long <rlong3@columbus.rr.com>
writes:
> I would like to add one more comment to my previous post on this 
> topic.
> 
> Some 'modern' solid dishes have a rounded outer edge. This is not 
> just to 
> make them look pretty or for some structural reason. A properly 
> designed 
> rounded edge cuts down on edge diffraction with consequent reduction 
> in 
> back lobes in the final pattern. What is properly designed? If there 
> is 
> interest I'll dig out a reference. As I recall it has to do with 
> frequency 
> and radius of the 'roll'. By the way the 62cm solid dish I mentioned 
> does 
> have a rolled edge although I have not pursued its dimensions vs. 
> 2.4GHz. 
> This dish is a one of a kind that I bought several years ago at one 
> of the 
> AMSAT-NA symposiums. It seems to be military in that it is painted 
> olive drab.
> 
> ron w8gus.
> 
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