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Re: N3IYR S-Band dishes



Jonatathan!
You are absolute right, you can use mesh on most freq
but one have to keep the hole size not bigger than 1/10 of 1 lambda
73 de Lars SM4IVE
----- Original Message ----- 
From: "Jonathan NAYLOR" <Jonathan.Naylor@socgen.com>
To: "amsat-bb" <amsat-bb@AMSAT.Org>
Sent: Friday, December 14, 2001 10:07 AM
Subject: Re: [amsat-bb] N3IYR S-Band dishes


> I had a quick look at the N3IYR web site last night. At
> least one statement he makes is untrue, it makes you wonder
> about the rest.
> 
> He states that you have to have a solid dish at 2.4 GHz, this
> is rubbish. Go to any decent textbook about dish antennas and
> you will find that you can use a mesh provided that the holes
> in it do not exceed a certain fraction of a wavelength. Even
> my 11 GHz satellite TV dish is perforated, albeit with very small
> holes.
> 
> His feed does indeed look like a helix, and it may be the best
> option anayway. The patch is a lovely antenna, I use the K3TZ
> designed patch and I am very happy with it, but it only works
> with dishes with a certain f/D ratio. In comparison the helix
> is flexible as it can be adjusted to suit many different f/D
> ratios depending on the number of turns. It so happens that with
> the f/D ratios that are ideal for a patch, you need a very small
> helix feed, and the helix is starting to get very inefficient. So
> the patch wins easily.
> 
> Jonathan  G4KLX / HB9DRD
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