[hpsdr] [Hpsdr] Call for Comments - ALEX

[Henry Vredegoor]

Hi Chris, All,

Thank you for pointing me to the Wiki.

I agree that the shielding of ELECTRIC fields can be done by any good
conducting material.

But I think shielding of DYNAMIC MAGNETIC fields (like in EMI) can
practically best be done by using some magnetically conductive materials.
Since we are using a lot of inductors of powdered iron O-cores, I assume
that dynamic magnetic fields are predominant in the filter boards?

So, IMHO, I still think steel would be better, although I learned from the
discussion that it is less of a factor (wrt. frequency) than I thought.

I think one should also differentiate between conducted EMI/shielding and
induced EMI and shielding in reasoning.

73's,

Henry.

> -----Original Message-----
> From: hpsdr-bounces at lists.hpsdr.org 
> [mailto:hpsdr-bounces at lists.hpsdr.org] On Behalf Of Chris Albertson
> Sent: woensdag 25 juli 2007 21:04
> To: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] [Hpsdr] Call for Comments - ALEX
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> --- 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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