[TowerTalk] Tower Grounding Query!

[Kurt Andress]

wa4dou@excite.com wrote:
> 

SNIP

>  1 )Seems likely that the shorter tower has as much probability of being hit
> by lightning at either height(21 vrs. 31 ft.). and even though it will be in
> the shadow of the taller tower. I've read over the years that a tower tends
> to produce a cone of protection around it equal to a radius of about 2.5
> times the tower height. At 21 ft. high, is it as likely, less likely, to be
> struck as the taller tower? If as likely, then i see nothing to desire in
> the 21 footer and will opt for the 31 footer. Or would both be less likely
> to be hit by virtue of being in the shadow of the 55 footer?( hope the
> question is clear!)
> 

Roy,

At the Polyphaser seminar I attended a few years ago, it was explained
that the "cone of protetction" is not really a cone.
For a strike of average strength, the strike leader operates on
approximately a 150' radius.
The "area of protection" (region of ~ 5% chance of getting hit) can be
described by rolling a 300' diameter ball along the ground. Where the
ball contacts any part of a atructure, one can expect equal probability
of a strike as any other similar points. Anything below the arc of the
ball is considered in the protected zone.

Lower than average energy strikes operate with smaller radii (reducing
the protection zone), larger strikes use larger ones.

I think that the prudent approach would be to give both towers the
treatment.

-- 
73, Kurt, K7NV 

YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/

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