That being said, the loss would probably have to be significant for it
to show up as a perceivable difference in radiated RF, especially if you
were to assume that you could match any difference in impedance caused
by the oxidation. I doubt anyone can tell the difference in signal from
a dipole made with #14 wire versus one made with #22 wire.
73,
Dave AB7E
On 4/24/2018 12:26 PM, David Gilbert wrote:
I'm not sure what the effect on radiation efficiency could be, but I
can think of a possible way to see if it has any effect at all.
1. Put up a 20m dipole comprised of shiny new wire. Measure it's
impedance vs frequency curve.
2. Put up a second closely coupled dipole cut roughly 4% - 5% shorter
and made with shiny wire parallel to and spaced a few inches away from
the first dipole. Measure the impedance curve of the first dipole
again. There should be some difference.
3. Replace the second dipole with one made of heavily oxidized wire
of the same type/length and measure the impedance curve of the first
dipole a third time.
You'd want to make sure the lengths and spacings are almost exactly
the same in both cases, but if you are able to do so and the second
and third curves are not pretty similar there is possibly some effect
due to the oxidation.
Just a thought.
73,
Dave AB7E
On 4/24/2018 12:05 PM, Shawn Donley wrote:
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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