[TowerTalk] Effects of Oxidation on Copper Antenna Wire

David Gilbert 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.

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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