Question about coax

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  • Updated 2 years ago
I had a service call recently and the tech stated that the shielding on the coax was used for data transmission. He said that the copper was used for one direction and the shielding carried a signal in the opposite direction.

I have never heard this before, surely this isn't true?
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Eric

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  • puzzled

Posted 2 years ago

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Judge and Jury

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He's an idiot  incompetent. The shield is just what it's called.  It's a conductive barrier against electromagnetic interference/leakage.  Don't invite him back.
(Edited)
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Eric

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My thoughts exactly but I've been in IT long enough to know I don't know everything.

Thanks Craig
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Markgc, Champion

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The tech is correct or partly correct. It is an electrical circuit so it must have an out and a return circuit. When dealing with RF (radio frequency) currents, the current flows on the centre conductor of the coax and the return current path is on the INSIDE of the shield.

This is where it gets a little strange. because of the skin effect at RF, there will be RF currents flowing on the inside surface of the shield but they cannot penetrate onto the outside surface of the shield., which is how the shield works. Under certain conditions currents will flow on the outside of the shield and may cause problems. This rf current flow  can be prevented by adding inductance by coiling the coax into several turns  or by adding of clamp on ferrite cores around the coax cable. This will prevent rf current flow on the outside of the shield but not on the inside of the shield surface.

http://www.w8ji.com/coaxial_line_and_shielded_wires.htm
(Edited)
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Judge and Jury

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@ Markgc...

At the atomic level, concerning the absolute path electrons travel, a complete circuit does require a return path for current to flow.  The tech referred to the data route being somewhat of a half-duplex scenario using the center conductor and the shield as separate information paths which is an error.