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Re: [RFI] Earth isolation

To: "Dennis Berry" <dennisberry@worldnet.att.net>,"Jim Brown" <jim@audiosystemsgroup.com>, <rfi@contesting.com>
Subject: Re: [RFI] Earth isolation
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Thu, 9 Sep 2004 10:03:52 -0400
List-post: <mailto:rfi@contesting.com>
> 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
> (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

Jim handled that all well Dennis, but let me add a few

Most of the RF-in-shack problems come from Marconi antennas
(antennas that need a ground) having a marginal ground, or
balanced antennas that are really not perfectly balanced or
worse yet fed with unbalanced lines.

You can see some modeled common mode currents and links on
my web site at:


Some equipment has problems also. There is a high-dollar
antenna tuner that uses insulated cover mounting screws and
the case becomes hot with RF on higher bands.

There is also the misconception that moving a balun to the
INPUT of a tuner makes the system better balanced. A whole
new wave of antenna tuners that aren't any better than
tuners with the same balun on the output are now on the
market. I'll eventually have something specific up on my
site for this problem and the about the folklore that moving
the balun does something universally good.

Poor RF designs, as Jim pointed out, are everywhere. The
problem is getting worse as engineers "think less and react

73 Tom

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