At 12:38 PM 7/12/2006, Jim Lux wrote:
>At 12:18 PM 7/12/2006, Gary Schafer wrote:
> >If the shield of a coax cable carries a lightning strike about half of the
> >energy gets transferred to the center conductor of the cable and propagates
> >down the cable just like a radio signal would. This includes the propagation
> >delay caused by the velocity factor of the coax.
> >The energy gets inside the coax from the low frequency and DC energy carried
> >by the shield. This penetrates, as the skin effect falls apart, where the
> >skin effect would normally keep it on the outside. The field that is now on
> >the inside of the cable gets induced onto the center conductor.
> >The effect is called transfer impedance.
> >However if there is no center conductor in the pipe the high frequencies
> >will not be able to propagate down the inside and will die out.
Here's a gedanken experiment... Imagine you have a huge block of copper,
miles on a side, and you've bored a 1" diameter hole through it. you
magically couple a current into the inner wall of this hole (say, by a
short loop probe)... will that signal propagate? In the inverse case, a 1"
bar of copper, with the probe outside, it certainly will.
>yes, but how fast does it die out? It's not going to propagate in a
>waveguide mode very far, but does it propagate another way?
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