[TowerTalk] Static Discharge Porcupines - great for....

[Roger (K8RI) on TT]

"As I understand it", Lightening is "more or less" the simple discharge 
of static electrical charges of greatly differing potentials.  Cloud to 
ground to cloud, etc. The discharge alternates up and down with steep 
rise and fall times with an average peak around 1 KHz and many 
frequencies, up and down with diminishing strengths as you move away 
from the peak.  These charged areas are relatively large, with the 
stroke "tending to hit the tallest object (where the charged areas are 
closest AND the charge differential the greatest).  HOWEVER  the energy 
in these charged areas is tremendous and as I said earlier, "Irregular" 
so the tallest object often does not represent the spot where the 
highest potential is located.  For instance, although a 100' tower is 
statistically the most likely target, the strike may hit the ground, or 
a house no more than 150 to 200 feet away from that tower.   The energy 
stored in that moving charge is far more than a porcupine, or lightening 
rod could bleed off to the point of preventing a strike, but they can 
serve a purpose.

The Franklin Rod's (as reminded by several on the group) purpose is not 
to prevent a strike, but rather to direct the strike away from doing 
damage.  The porcupine is incapable of preventing a lightening strike, 
but they appear to do well with reducing precipitation static.  OTOH I 
claim no experience with their use.

As I've said many times, the first few years my 45G was up, it took 3 
visually verified direct hits per summer, for 5 years, 2 the 6th, and 
none (that I know of) for the last 7 years  How many it actually took 
those first 6 years?  I have no way of knowing.

Typically the strokes between cloud and ground are between two large, 
irregular shaped, moving charges.  The descriptions of which remind me 
of two giant Amoebas (for lack of a better term.) The potential 
gradients are also irregular, so they are not represented accurately as 
a spot with a high potential in the center

I'm glad Kim posted that information, but I wish the scientific 
community would go back to averages rather than median.  The average is 
much more meaningful than knowing the number that lies half way between 
the highest and lowest figure measured, at least they are for me.  
Median is an interesting number, but average seems to be much more 
informative and typically what is used for design.  With a number of 
samples large enough to be statistically valid a single, significant 
outlier, be it high or low can substantially skew the median, but have 
little effect on the average.

The so called "super strikes", or Positive lightening, which is 
associated with sprites can move the median, but happen so seldom, they 
have little effect on the average and when it come to lightening, do we 
design for the median, average, maximum, or the best we can afford?

I know my relatively elaborate ground system did well, but how much 
concrete would I need in this soil for an equivalent ground? When I 
think of a lightening protective ground, I think of the area covered by 
that system, not the contact area of the ground rods, or concrete.  
Although the contact area of 32 8' rods is small, the ground system's 
effective area is over a quarter acre.   There is more to the protection 
than the contact area and resistance.

I'm also interested in why we had so many strikes in this area for at 
least 6 years, and so few since then.   During that peak, this area 
suffered a lot of damage. Trees completely blown apart, electrical 
appliances, wells and even house wiring destroyed. Fortunately, no fires.

73

Roger (K8RI)



On 8/8/2015 5:40 PM, R Morris wrote:
> I can't stop myself.....
>
> That's the job of the wench, holding the plastic owl, facing true north.
>
> Sent from my iPhone
>
> On Aug 8, 2015, at 17:06, kr2q at optimum.net wrote:
>
> With proper placement, these are great for keeping birds from landing on surfaces.
>
> TIC
>
> de Doug KR2Q
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-- 

73

Roger (K8RI)


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