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[TowerTalk] Re: Lightning ground "Holy Wars"

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Subject: [TowerTalk] Re: Lightning ground "Holy Wars"
From: (Dave D'Epagnier)
Date: Tue, 2 Jun 1998 09:10:51 -0600
Tom Rauch wrote:


> 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.  
true, but try to bend a solid shield

> 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.
Both of these effects are included in the inductance formula I gave. The
"bunching" you describe, is an artifact of the self inductance of the
strip. The skin effect is handled by the -0.75 term in the formula. This
term is actually 1 minus the mu (permeability) of the conductor divided
by four times the permeability of free space, and approaches zero at
high frequencies (skin effect), which makes the -0.75 term in the
formula approach -1.
This can all be somewhat confusing, trying to write and describe derived
results on email, where formulas are difficult to write and discuss.
Maybe it's better discussed offline. I suspect that some (maybe most)
Towertalkians are tiring of this discussion anyway. I admire the
tenacity of trying to get to the bottom of the situation though.

-- Dave

> I disagree completely with the 
> any notion lightning behaves like dc.
ditto, if it behaved like dc inductance would be a moot point.

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