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Re: Dish surface 'flatness'



Peter,
I suggest that the surface irregularities be less than 1/8 Wave length.
Parabolic shape is important. I recommend some excellent practical advice
and charts in the VHF/UHF Manual published by the RSGB. It is easy to
understand and well written.

Art, KC6UQH

-----Original Message-----
From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On
Behalf Of Peter Ellis
Sent: Friday, July 25, 2008 3:00 PM
To: amsat-bb@amsat.org
Subject: [amsat-bb] Dish surface 'flatness'

I am now the proud owner of a very 'second-hand' 3m mesh-covered 
skeleton dish.

The mesh covering is metaphorical, rather than actual. I watched the 
dish on its back while as a group of small children rolled the dish back 
and forth and trampled holes in the mesh. That's the reason I was able 
to ask for it. "Please take it away," was the manager's reply to my query.

Now, I need to re-mesh the dish, but I need to decide what 'flatness' 
('true-ness') the surface should be. There has to be a formula, that 
encompasses things like: frequency of operation, curvature or focus 
distance, etc.

I've done some looking online, but can't find it readily.

Suggestions, and discussion, please?

Please note: If you're going to also make product, brand name, or 
supplier suggestions, then be generic as suppliers and products in VK 
(Australia) will differ from where most list members will be sited.

With thanks,
Peter
VK1KEP
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