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Re: [TenTec] Faraday cage

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Faraday cage
From: Jim Brown <k9yc@audiosystemsgroup.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 04 Apr 2009 22:34:32 -0700
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
>> They had something not right in that Faraday cage, if you had noise
>> inside.  Of course, copper does not adequately block low frequency
>> magnetic field components, and that likely was the source of your
>> noise.  Our ACE rooms at Southwest Research were doubled steel panels..
>> Same for the anechoic chambers at Dell Computers in Austin.  They have a
>> 30m room that is also lined with anechoic foam as well as being solid
>> walls of metal.  It even has an air tight remote controlled
>> pneumatically powered door.  It is acoustically and RF quiet!
Yes. A Faraday cage is, by definition, an Electric shield. It is NOT a 
magnetic shield at low frequencies.  In the near field of a field 
produced by current, the field is primarily a magnetic field.

Now, a screen room will typically be built with all coaxial cables 
bonded to the screen, which prevents shield current from penetrating the 
screen. And all non-coaxial cables will usually come through on 
feed-thru capacitors. In other words, the screen room is built with 
bonding to prevent common mode currents from penetrating the shield 
(screen). But it is BONDING that is solving that problem, NOT shielding.


Jim Brown K9YC

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