[TowerTalk] lightning

[Bob Otto]

Hello aa7e,

First, I'm no "expert" on grounding systems!  <G>

I do have a comment though on one point you made.  In all the
literature on grounding systems I've read, there is no place where
they say you must go to the water table.  That would be nearly
impossible for most.  Think about it -- your house ground (and
everyone else's) doesn't go in at the level of the water table, or you
will have one very wet basement <G>  Also, the water table will vary
depending on time of year, water conditions, etc.

The effectiveness of a ground system depends on the soil conditions.
Most of the time you will have enough moisture content, and soil
chemical composition to have a very effective ground if you use 8'
ground rods.  Many will work quite well with 4' ground rods.

73's from.......

Bob Otto
N8NGA@one.net
Cincinnati, Ohio

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Friday, October 27, 2000, 9:27:14 AM, you wrote:

ajc> I have just moved from Oregon to central Florida.  As such, I have a
ajc> renewed interest in lightning protection.

ajc> Coming from the TV broadcast industry, maybe I can inject another issue
ajc> on the subject.

ajc> As we all know, a square wave contains energy at all frequencies. 
ajc> Similarly, lightning contains energy all the way up to 50 MHz or so.  So
ajc> often, grounding systems are designed as if all the energy was at or near
ajc> DC.  As a case in point, a translator station had a problem with
ajc> lightning so they installed a new and "improved" grounding system.  As a
ajc> result, the lightning problem was made even worse.

ajc> The problem was traced to long lengths of wire between the tower and the
ajc> grounding rods.  Although these might have been effective at DC, they
ajc> appeared as open circuits at the higher frequencies.

ajc> Since the watertable in my local area is 30 feet down, I have been told
ajc> that grounding rods need to be drilled down to that level.  I would have
ajc> thought that such a system might have the same problem.  I am thinking
ajc> that the solution might be to parallel the rods with a copper sheet mat
ajc> just below the surface.  This mat would provide some sort of grounding at
ajc> the higher frequency content of the lightning energy.  Any comments would
ajc> be gratefully received.


ajc> 73, AA7E


ajc> aa7e@juno.com

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