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Re: [TowerTalk] Faraday Cage

Subject: Re: [TowerTalk] Faraday Cage
From: "Jeff Carter" <>
Date: Sat, 31 May 2008 16:09:05 -0400
List-post: <">>
Well, yeah.

Think about the mission of a cage like that, which is to block RF out
of the cage.  All of it, at all frequencies, which in turn means at
all wavelengths.  The gaps in the copper have to be close enough to
block it all, at least up to the higher microwave region, where other
issues take over.

The best example I can think of that everybody knows is satellite
dishes.  There were a good many dishes sold that were mesh, but it was
"C band only" because the holes in the mesh were too big to reflect Ku
signals back to the feedhorn.  They weren't copper because conduction
wasn't wanted, reflection was.  So you see how mesh size or the
placing of conductors makes a difference.

Copper is preferred for faraday cages, if I remember what they told us
about permitivity and conductivity in college, because it's the
available material most likely to conduct the offending signals to
ground due to conduction skin depth.  That in itself was the subject
of a week's worth of mathematics that I won't bore you with.

To answer your other question, you might actually get by with what
you're proposing, so long as you don't mix your materials and create
galvanic current situations or worse, semiconductors, and so long as
you don't ever expect it to work for frequencies above whatever your
spacing turns out to be.  Those will merrily pass through.  Your cell
phone will show you that you have acquired a cell site's attention and
it'll ring, but you might find that you can't hear from 6m on down to
HF, or that you can't hear anything on your handheld shortwave
receiver, just as examples on the spacing you selected.

Good luck!  I always love to see people trying things, so few ever
bother any more.  I'd actually encourage you not to listen to anybody
and if you've got the time, build it and see what you get.  That's how
you really get your hands on and your head around what's happening,
anyway.  If you want to see any of the math, I bet it's on Wikipedia
and if not, email me and I'll find it for you.


---- Original message ----
>Date: Sat, 31 May 2008 12:48:49 -0400
>Subject: [TowerTalk] Faraday Cage
>This cage idea has always intrigued me.
>The copper mesh may be the cheapest and easiest way
>to accomplish such an arrangement, BUT, it there a
>maximum mesh size?
>It seems that one might find it just as effective to run
>a? "nest" of copper wires, say 3 feet (or other) apart
>and accomplish the same thing.
>Warren; W7WY

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