[Antennas] Current Flow in Coax?

[D.J.J. Ring, Jr.]

Andy,

That's an excellent reply.

73

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On Fri, Sep 28, 2012 at 12:59 AM, Andy <AI.egrps1+qth at gmail.com> wrote:

> > I understand this must be the case to cancel radiation from the coax,
> but can
> > someone point me to a technical explanation of how the forces operate to
> "pull"
> > the current to the inside of the shield?
>
> One way to look at it is this:
>
> If the electric and magnetic fields are properly contained within the
> coax and none are on the outside, then those fields ... which are what
> cause the current to flow ... can only move electrons on those
> surfaces they touch ... namely, the inner wire and the inside wall of
> the shield.  The RF fields themselves do not penetrate through good
> conductors, so the fields that are inside, can't move electrons on the
> outside wall of the coax shield.
>
> The only way to get current on the outside of the shield, is for there
> to be (electro-)magnetic fields on the outside of the coax.  Likewise,
> the reverse is true; the two go hand-in-hand.  Wherever there is RF
> current, there are electro-magnetic fields adjacent to it, and
> vice-versa.
>
> The way I see it, the forces do not precisely "pull" the current to
> the inside of the shield.  Rather, there is nothing there (no fields)
> on the outside of the shield, or many skin-depths into the metal
> thickness, that could make current flow there.  So the result is that
> the current ends up being confined mostly to the inner wall, not
> precisely that it was "pulled" there by some sort of force.
>
> Andy
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