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Old January 30th 09, 08:59 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default Contrary current flow within a radiator

Michael Coslo wrote:
Warning - dilletente alert! Maybe even worth an embarrassing dolt cringe

This question may have been asked before, but is there a physical
experiment that is good for verifying skin effect?

Initially, It seemed pretty straightforward, but giving some thought to
the matter indicates it "ain't necessarily so".

I'm assuming that any thick conductor is going to have "skin" to any
where I can put a sensor, so even if I drilled an internal sensor, the
drill tunnel would form a part of the skin.

Giving that some thought, is it possible to make say a ribbed conductor
that resembled a tubular heat sink, would this device allow for more
current flow because of the greater amount of skin exposed compared to a
solid tube?

Just a little thought experiment.

- 73 de Mike N3LI -


An experiment to verify skin effect:

Make or obtain a self-contained RF signal source. Put it into a
completely sealed conductive box -- PC board material soldered together
with no gaps would be fine. Then try to detect any signal outside the
box. If the RF current could penetrate the conductive material, that is,
if there were no skin effect, you'll be able to detect the signal.

Here's another: http://w8ji.com/skindepth.htm.

The problem with your ribbed conductor is the same general thing that
causes skin effect -- currents cause fields which repel other currents.
The result would be more current on the tips of the ribs and less
current in the valleys.

You can make a pretty good surface current sniffer by winding a bunch of
turns of wire on 1/2 of a ferrite core, and connecting it to a scope or
other detector. Put the two core piece ends on the surface, so it looks
like an upside down U when on a flat horizontal conductor.

Roy Lewallen, W7EL
 
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