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[TowerTalk] Effects of Oxidation on Copper Antenna Wire

To: towertalk@contesting.com
Subject: [TowerTalk] Effects of Oxidation on Copper Antenna Wire
From: Shawn Donley <n3ae@comcast.net>
Reply-to: Shawn Donley <n3ae@comcast.net>
Date: Tue, 24 Apr 2018 15:05:11 -0400 (EDT)
List-post: <mailto:towertalk@contesting.com>
Some recent posts on grounding reminded me of something I've always wondered 
about.   How is the radiation efficiency of a copper wire HF antenna affected 
by oxidation of the copper over time?   Empirical evidence is that any effects 
are small/negligible, otherwise the dipole you put up last year would not work 
so well this year.  My limited understanding is that the two oxides of copper, 
Cuo and Cu2O, are semiconductors.  So after a while, the outside of the wire is 
covered by something approaching an insulator (relative to clean copper 
conductivity).  The depth of the oxide, as far as I could research, is on the 
order of 100 nano-meters.  OK...so the RF current is forced under the oxide and 
follows the skin depth with frequency relationship.  Not much effect on the 
current or the "RF resistance" of the wire, if I can be forgiven for using that 
term.  But what about stranded copper wire?  That's where things might get 
interesting.  Does the skin effect with clean copper wire
  cause the RF to stay on the outside of the overall collection of strands, all 
of which have good contact with their adjacent strands?  If so, what happens 
when all the individual strands are oxidized and not in low resistance contact 
with their partners?    Anyone know of actual measurements of the effects of 
oxidation or how such a measurement would be done?   Short of measuring the Q 
of a tuned circuit built with "clean" and oxidized wire inductors, I'm not sure 
how you could measure the effect and even less sure of how those measurements 
would translate to the original question...effects on the radiation efficiency 
of an antenna.


N3AE
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