[Top] [All Lists]

[TowerTalk] Re: Lightning ground "Holy Wars"

To: <>
Subject: [TowerTalk] Re: Lightning ground "Holy Wars"
From: (Tom Rauch)
Date: Mon, 01 Jun 1998 13:35:12 +0000
To: <>
> Date:          Mon, 01 Jun 1998 08:42:49 -0600
> From:          Dave D'Epagnier <>
> Subject:       RE: [TowerTalk] Re: Lightning ground "Holy Wars"
> To:            "''" <>,
>                'Towertalk' <>

Hi Dave,

There's a few things below that are generally useful to 
towertalkians, since they apply to both lightning and RF.

First, I appreciate the info. I e-mailed you before this arrived and 
asked a few questions about the formulas. 

> By the way Tom, if you play with these formulas, the units are 
> MKS,
 > the inductance is in nH, I left a paranthesis out of the ribbon
 > equation (tough to write equations here), and the wire equation is 
> for solid wire, not tubing.

I need to get a copy of that book and will do that, unless someone 
can FAX me a copy of the pages covering the formulas. I hate spending 
money unless it's on a toy, like more wire and rope. I'm sure you 
know this, but let me bring it up again...

1.) Tubing is no different than solid wire when skin depth is much 
less than the wall thickness. At higher frequencies (and lightning is 
certainly not steady state dc) the conductor in the middle becomes 
less and less important. 

That's why copper weld antenna wire works as well as solid copper, 
the thickness of tubing matters very little at RF, and why double 
shielded cable does nothing a solid thin shield won't do at RF.  

2.) The impedance of a flat strip also becomes higher at higher 
frequencies, because of current "bunching" (that is a handle I 
hang on the effect where time-varying currents are forced to the 
outer edges of the strip). Thickness of the strip is also unimportant 
at a high enough rate of current change, because of skin effect.

That's why a smooth round conductor often has less loss resistance 
than the same surface area flat conductor at radio frequencies.

One thing missing is frequency and skin depth in the formulas. I 
think we are heading for the unanswered question about the 
frequency/energy content of lightning. I disagree completely with the 
any notion lightning behaves like dc. It makes it easy to give 
answers and solve problems, but I suspect the answers are tainted by 
the view lightning is dc or behaves like dc.

> The main point is that copper strip like the
> stuff you can get from Polyphaser (1.5"wide by 0.015" thick) is a lot
> lower inductance than the standard "wimpy" AWG#2 wire used for
> grounding, and a heck of a lot more flexible  than copper pipe (and
>  more expensive than either!).

I'm not sure about that yet because I have no idea what a Fourier 
analysis of a typical (if there is such a thing) lightning strike 
would reveal for energy content vs frequency. I do know I would never 
trust a *long*  #2 lead, and my gut instincts tell me a 1.5 inch wide 
smooth ribbon is probably better.  But sometimes instinct isn't 
always correct...... 

Someone posted something about most of the energy being in the 
several hundred kilohertz region. Can anyone verify that, or 
the percentage of energy at different frequencies?

My own personal rule, lacking solid data,  is to treat lightning more 
like RF rather than dc. I do that because any time I've seen damage 
from a hit, its behavior was more like RF energy than dc or low 
frequency ac.   

This seems to be a topic surrounded by conflicting information, 
typical when there is  a lack of solid data. I'm in the process of 
collecting as much data as I can, and appreciate the help. When I get 
enough info, I'll make it available to anyone who needs the 
references. Maybe someone who is a good author will write a nice 
factual article without any bias or sales pitches.

73, Tom W8JI

FAQ on WWW:     
Administrative requests:

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