Re: NEC-LIST: Copper oxide.

>>From a radiation point of view, why would the oxide layer on copper not have
the same effect as the oxide layer on aluminum? The latter hasn't deterred
the use of "billions" of yagis as TV antennas.

Malcolm M Bibby

"Jim Lux" <james.p.lux_at_jpl.nasa.gov> writes:
> "Chuck Counselman" <ccc_at_space.mit.edu> writes:
> > At 7:35 AM -0800 1/10/04, Jim Lux wrote:
> > >Copper Oxide is a fairly good insulator. The layer is thin, typically.
It
> > >probably wouldn't have a huge effect. What really bites you is if the
> > >conductor is covered with a thick layer of something resistive or
lossy.
> >
> >
> > Two questions:
> >
> > 1. Have measurement data been published, showing whether stranded
> > copper wire with various degrees of surface oxididation/corrosion is
> > more, or less, lossy than solid copper wire of the same gauge, at HF?
>
> I haven't seen any rigorous data, just anecdotal stuff.
> Corrosion is probably a bigger problem than simple oxidation.
>
>
> >
> > In wire antennas for HF I use finely stranded (copper) wire because
> > it does not fatigue and break as quickly as solid wire does. I use
> > _insulated_ wire, and I seal the ends of the insulation at splices
> > etc., in order to keep the surfaces of the strands from
> > oxidizing/corroding. (Acid rain is an issue where I live.) However,
> > it has occurred to me that if each strand had an effectively
> > insulating coating, then I'd have something akin to Litz wire, and
> > the loss at HF would be less than if the strands were clean.
>
> Except that, unlike Litz wire, it's unlikely that each strand has a nice
> complete uniform coating of oxide so there will be some connections, and
> they'll be horrible transitional forms which are resistive. There is some
> measurement data from folks building tesla coils (at about 100-300 kHz)
> where AC resistances of stranded wire are higher than that for same AWG
> solid.
>
> It's probably like the problems with braid at HF.
>
> >
> > Mostly I use such thick (low-number-gauge) wire that its loss is
> > trivial, so my question is mainly academic; but I _am_ an academic.
> > :-) [For balloon-supported HF antennas I use very fine Litz wire,
> > which can't be beat for RF conductance per unit weight.]
> >
> >
> > 2. The fact that copper oxide (and possibly other copper corrosion
> > products; I don't know) can be semiconducting raises the possibility
> > that stranded wire in a high-power transmitting antenna could
> > generate harmonics and intermodulation products. What has been
> > published about _this_ possibility?
>
> Exactly what I was thinking.. I don't know enough about this whole oxide
> semiconductor thing, and how much structure has to do with it.
>
> >
> >
> > Tnx es 73 de Chuck, W1HIS
> >
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>
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