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Re: [TenTec] RFI question for Orion and other TT rigs

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] RFI question for Orion and other TT rigs
From: Sinisa Hristov <shristov@ptt.yu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 28 Jun 2005 22:55:56 -0400
List-post: <mailto:tentec@contesting.com>
James Duffer wrote:

> I am not sure about the effectiveness of aluminium in shielding "magnetic"
> fields.  It seems that a high mu metal is the way to go for magnetic
> shielding.  That is what they used on CRTs to prevent magnetic interference.

At 60 Hz or audio frequencies aluminium is not effective
in shielding against magnetic fields.

However, at radio frequencies it works very well, provided
that the circuit to be protected is completely enclosed and
the shield thickness is large compared to the skin depth.

For example, Agilent's E8358A network analyzer (300 kHz - 9 GHz)
uses aluminium shielding exclusively and has no problem in
achieving ~140 dB dynamic range. Orion uses ~1.8 mm aluminium sheets,
which is almost 30 times the skin depth at 1.8 MHz. That can
provide ~250 dB attenuation of the magnetic field.


Sinisa  YT1NT, VE3EA
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