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Re: Topband: Fw: 25G insulators

To: "Pete Smith" <>, <>
Subject: Re: Topband: Fw: 25G insulators
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Sat, 30 Aug 2003 21:06:03 -0400
List-post: <>
> and rotator position pots the same.  Isn't it reasonable to assume that
> time a tower, whether grounded or not, takes a direct strike, it is likely
> that destructive voltages will be induced in any conductors on the tower?

The ground system is very important, but how we route and connect cables is
the single most critical thing. Lightning is virtually all rapidly stepped
waveforms, and behaves exactly like RF. As you move towards the center point
impedance is higher (it is surrounded by more flux lines). Current is pushed
outwards, and the gamma is a choice path for much of the current (and
voltage drop appears from the current).

The most benign place is the middle of the tower, where a Faraday cage is
formed by the structure itself. That's where the sensitive cables should be
routed, and they should be inside shields or metal conduits bonded to the
tower at tower exit points. Feedlines should at least be grounded to the
tower at the top and bottom, or better yet inside the "cage" and grounded
where they enter and exit.

73 Tom

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