> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Bill, W6WRT
> Sent: Friday, March 19, 2010 2:00 PM
> To: amps@contesting.com
> Subject: Re: [Amps] placement of RF choke bypass cap.
>
> ORIGINAL MESSAGE:
>
> On Fri, 19 Mar 2010 12:37:41 -0400, "Gary Schafer"
> <garyschafer@comcast.net> wrote:
>
> >
> >What do you think happens when you use a tube for an antenna element?
> >The whole element is charged. If you connect the feed line to only the
> front
> >side of the element there is still current on the back side of it.
> >How do you think the current gets around to the other side?
> >
> >But try to measure the current on the inside of the tube. You will find
> >none!
>
> REPLY:
>
> You raise an interesting question about current in a tube as opposed
> to a solid rod. In a sire or solid rod, the skin effect current is
> only present on the skin. In a tube however, I'm not so sure there is
> no current on the inner surface of the tube because that is also a
> skin. The issue is complicated because any skin current on the inside
> of the tube also "sees" the other side of the tube, unlike with a flat
> sheet where there is no other side. So that issue remains to be
> proven.
>
> Because a sheet has two "skins", and has no other side like a tube
> does, current flows on both "skins" of a sheet because it is repelled
> from the center. When one drains off current from one skin, the
> repulsion no longer exists and it is immediately replenished by
> current from he other side. Otherwise my load padder caps would not
> be connected to my load variable cap.
>
> Fascinating discussion.
>
> 73, Bill W6WRT
Bill,
My point is that there is no difference between the current on the outside
of a tube verses the current on your flat bar or a solid rod.
Each skin acts independently of the other. One side of a sheet never knows
about the other side as far as current passing thru from one skin to the
other. This is very evident in a tube which has an inner and outer skin.
Provided the material is several skin depths thick, there is never any
current on the inside.
Not because the current from one side acts against the current on the
opposite side but because the current on the "surface" sets up eddy currents
just below the surface that oppose each other and cancel the deeper
currents. No current ever makes it to the center of the rod or plate or to
the inside surface of a tube.
Current does not go "thru" the sheet or rod to get to the other side. It
flows around the edges.
If current went thru the shield of coax then the coax would not work as it
does.
There is no way for current to enter the center part of a tube or rod or
flat sheet.
73
Gary K4FMX
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