[Towertalk] More on Lightning protection

[Pete Smith]

At 07:54 AM 5/15/02 -0400, N6ZO@aol.com wrote:
>I
>was told that if there was a lightning strike in the area,  the navy WANTED
>to be sure that any strike to be taken by the towers and not the sub.  Don't
>know how often they are successful at taking lightning strikes but there are
>no signs warning people away from the towers.
>
>Wonder what else they did to those towers to ATTRACT lightning?

Chapter 15 of the original Polyphaser "Grounds" book describes a radius of 
protection that is conferred by a grounded tower, based on the physics of 
the step leader that precedes lightning.  They say that the tower will take 
the hit and confer 96 percent protection on things in the protected 
zone.  Presumably it's the same, though more complex, for those 250-foot 
towers with the conductor between.  If I read the book correctly, objects 
up to 100 feet in height directly under the horizontal wire or adjacent to 
either tower are protected to this level of confidence, declining to zero 
protection at 150 feet away from the wire or either tower.

On the other hand, I recall an anecdote from W0UN describing how severe 
lightning storms would come across the Colorado prairie toward his field of 
towers, striking frequently as they came, but would stop as they approached 
his towers, and resume once past them.  That sounds as if some sort of 
other lightning prevention mechanism was at work, and perhaps the 
Polyphaser discussion isn't the whole story.

73, Pete N4ZR

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