> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Jim Lux
> Sent: Wednesday, July 12, 2006 2:43 PM
> To: Gary Schafer; 'Michael Tope'; 'JC Smith'
> Cc: 'towerTalk'
> Subject: Re: [TowerTalk] signals on inside of a pipe.. RE: TT SHUTDOWN
> (was: 4 awg copper wire and Amp locks)
>
> 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.
If the current is DC it will flow anywhere in the copper block. If it is AC
current it will be forced to the outer surface of the block. Eddy currents
will cancel the current around the hole and at all areas but the outer
surface. If the current originates at the center it may never come out.
:>)
73
Gary K4FMX
>
>
>
>
>
> >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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