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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