Towertalk
[Top] [All Lists]

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

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Static Discharge Porcupines - great for....
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Sat, 8 Aug 2015 21:11:56 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
"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@optimum.net wrote:

With proper placement, these are great for keeping birds from landing on 
surfaces.

TIC

de Doug KR2Q
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk


--

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>