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## [TowerTalk] Re: Lightning ground "Holy Wars"

 To: [TowerTalk] Re: Lightning ground "Holy Wars" DAVED@ctilidar.com (Dave D'Epagnier) 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. > Absolutely > 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. -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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