[TowerTalk] Effects of Oxidation on Copper Antenna Wire
xdavid at cis-broadband.com
Tue Apr 24 15:37:42 EDT 2018
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.
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.
> 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.
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