[hpsdr] [Hpsdr] Call for Comments - ALEX

[Chris Albertson]

--- Henry Vredegoor <henry.vredegoor at gmail.com> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Chris, Ray, All,
> 
> This is what I meant.
> Open up a piece of equipment and if there is any metal shielding
> used, it is
> most probably tinned steel for this exact reason. 
> (Use a magnet to test this.)

It's easy to see what material is used but harder to
see why it was selected.

Current prices:  Aluminum = $2,700 per ton, cold rolled
electro galvanized steel $700 per ton.  That pretty
much explains why they use steel.  Steel is not better
then aluminum as a magnetic shield, it's just cheaper.

If you did want to shield from static magnetic field you
would want something with very high permibility and a bit
thicker than sheet metal.

Shields don't stop fields the way lead stops xrays or kevlar
stops bullets.  Aluminum works because the current in the
skin of the metal box itself generates a electromagnetic
field inside the box that exactly cancels the one outside.
The electronics inside the box "sees" the sum of the two
fields, nothing is "blocked"  so any conductive material will
work.  Conductive paint is common

Here is a good introduction.
http://en.wikipedia.org/wiki/Electromagnetic_shielding


Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Office: 310-336-5189  Christopher.J.Albertson at aero.org
  KG6OMK/AG


       
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