"Meindert Sprang" wrote
"Jack Painter" wrote in message
news3lvc.5786$Y21.4832@lakeread02...
C'mon ol' salt, you should know the inside of copper pipe is
electrically
identical to both sides of copper strap when a bonding connection is
made
to
either. Skin effect of electrical current is felt equally on both in
_that_
condition.

No it isn't. Consider a massive rod of 1". RF flows at the outside due to
skin effect. No remove the innards of the rod, leaving, say 1/16" of wall.
Why would current suddenly flow at the inner surface? It isn't, for the
same
reason it was on the outside when the rod was massive.

Besides, heavy coils in radio stations are all tubes and cooled by running
water through them. Due to the skinn effect, the water is not 'touched' by
the RF.

Electromagnetic induction on a material from one outside
direction sees skin effect on the outside surface only of a closed
structure, cabinet, pipe, etc. But we are not talking about EMF's.

Yes we are. And EMF is exactly the reason why the electrons start to
repell
eachother. And the only place where they are as far apart as possible is
on
the outside of the tube.

Meindert, water is not a good conductor, with average tap water having
100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with
water. Even at RF frequencies, where skin effect is most pronounced, a
bonded connection made equally to both inside and outside of a copper pipe
should exhibit skin effect throughout most of the entire cross section of
the copper pipe. This is because the wall thickness of the copper pipe is
not materially different from copper strap.

Example:

For copper tubing used as a inductor in antenna tuners:

coil length
R= ---------------------------------------
conductivity *skindepth*2pi*coil radius

Now, applying voltage to the outer surface only of copper tubing with closed
ends, whether by EMF attachment or bonded connection to the outside only,
would exhibit surface-only skin effect similar to if a faraday cage was
constructed of the same copper strap we are talking about. The outside
surface would carry most current. But if the voltage connection was bonded
to both inside and outside of an opening of the faraday box or the copper
tubing, then current via skin effect would be nearly constant on the inside
and outside surfaces of the box, defeating the faraday effect. The
condition I originally described, that of a bonded connection, applies
voltage equally and carries current equally on the entire skin of the
conductor, inside and out, 360 degrees, as efficiently as a piece of copper
strap of similar cross section.

Best regards,

Jack Painter
Virginia Beach, Va