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From: lyndon%ALBERTA%UQV-MTS%UMich-MTS.MAILNET@ncc.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: (none)
Message-ID: <8609160547.AA13541@ucbvax.Berkeley.EDU>
Date: Mon, 15-Sep-86 10:05:48 EDT
Article-I.D.: ucbvax.8609160547.AA13541
Posted: Mon Sep 15 10:05:48 1986
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From: lyndon@ncc.UUCP (Lyndon Nerenberg)
Newsgroups: net.video,mod.protocols.tcp-ip
Subject: Re: Ethernet between buildings
Message-ID: <722@ncc.UUCP>
Date: Sat, 13-Sep-86 19:32:57 MDT
References: <611.rbbb.titan@Rice>
Organization: Nexus Computing Corp.,  Edmonton, AB
Lines: 35
Summary: Not a wives tale!

I am cross-posting as this sort of relates to the discussion in
mod.protocols.tcp-ip about grounding ethernet cables...

In article <611.rbbb.titan@Rice>, rbbb@rice.edu (David Chase) writes:
>    ...     A sort of old wives tale of lightning protection says that you
> should put a tight loop in a wire near a good ground; the lightning sees
> that as a great big inductor, and hops over to the good ground.
>
> David

The "signal" introduced into a cable by a lightning strike consists of
extremely high frequency radiation. It does not take much inductance to
throw up a "brick wall" to it. Many television stations run their feeds
through a single loop at the base of the tower, then to the transmitter
shack. The RF from a lightning strike will (hopefully :-) take the easier
path from the feed line, through the base of the tower, to ground.

I handled the transmitter plant installation and setup for a local FM BCST
station a couple of years back. The antenna was located on top of a
building at the University. We were unable to properly ground the tower,
so we threw up a loop inside the roof house for the elevators ( *lots*
of metal in there :-)

I know a number of amateur radio op's in town who do the same thing - 2
turns of the feedline at the base (approx. 3 feet in diameter) before
entering the house. I can't say that any of them have been hit, so I won't
guarantee results. Then again, I have watched local TV broadcast towers take
direct hits without going off the air.

I'm sure a posting to net.ham-radio would provide some further information
on practical experiences of dealing with lightning hits.
--

Lyndon Nerenberg (VE6BBM)                 {ihnp4,ubc-vision}!alberta!ncc!lyndon
Systems Group - A Div. of Nexus Computing Corp.                 Envoy_100: Unix