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Re: [RFI] Earth isolation

To: rfi@contesting.com
Subject: Re: [RFI] Earth isolation
From: "Ian White, G3SEK" <G3SEK@ifwtech.co.uk>
Reply-to: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
Date: Thu, 9 Sep 2004 08:07:12 +0100
List-post: <mailto:rfi@contesting.com>
Tom Rauch wrote:

I think I know what you meant, but I'm not sure I agree with that picture. RF that is accidentally picked up doesn't need to flow anywhere. It isn't a bucket of something we have to pour out somewhere.

Sorry, Tom, but it is precisely that! Kirchhoff's Law applies rigorously inside the shack: whatever RF current comes in, must have some path out again. If it didn't have, it wouldn't come in.

(There are some exceptions, particularly on the higher bands where wiring lengths inside the shack are a significant fraction of a wavelength; but they don't overturn the basic principle. Particularly on the low bands, I've measured a good balance between incoming and outgoing currents.)

I do agree that feedline chokes are needed on almost all antennas, and they should always be the first thing you try. But they may only be part of the solution.

In some situations (which may not apply to you personally, Tom, but they do apply to some others) it may be necessary to choke both the entry path *and* the exit path to get a complete solution.

-- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek _______________________________________________ RFI mailing list RFI@contesting.com http://lists.contesting.com/mailman/listinfo/rfi

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