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Re: [RFI] Earth isolation

To: <rfi@contesting.com>
Subject: Re: [RFI] Earth isolation
From: "Dennis Berry" <dennisberry@worldnet.att.net>
Date: Thu, 9 Sep 2004 00:22:44 -0400
List-post: <mailto:rfi@contesting.com>
----- Original Message ----- 
From: "Jim Brown" <jim@audiosystemsgroup.com>

> On Wed, 8 Sep 2004 18:20:58 -0400, Tom Rauch wrote:
> So here is this receiving antenna wired to a circuit board trace and
> from there to the chassis, and the chassis goes to "ground" via
> whatever path we provide for it. The inductance of the circuit board
> trace is an impedance in that path that is frequency dependent, and
> there will be IZ drop across it due to the receiving antenna current.
> The key to keeping this part of the RF out of the box is to prevent
> that current from flowing inside the box.


This is a real interesting discussion.  I've always struggled with grounds.
I think my mind just goes into lock up mode.  When you talk to someone who
really knows EMC/EMI issues, they make it sound so simple.  To many of us,
it is a real mystery, the old 'black magic' syndrome, so please pardon this

I can understand your comment above, somewhat.  If this is, for example,
coax coming into the receiver.  Are you saying the center lead routes around
the board and is connected to ground through various components
(impedance's)?  The outside shield is typically connected to the chassis as
it comes in to the receiver, yes?  So how does one keep the center
conductor's associated currents from flowing 'inside the box'?

And the pin 1 problem.  Is the fix just to ground the pin 1 to chassis?  Or
does that play with the 'single point ground' that is so talked about?

Thanks in advance,

    Dennis Berry

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