Some good reading on this topic can be found at
https://rudys.typepad.com/files/qex-nov-dec-2k-antenna-wire-conductors.pdf
I discovered Rudy's paper after searching for information on the effect of
conductor oxidation (stranded antenna wire). It's always bothered me that
with stranded wire (hard drawn copper or copperweld) the strands are somewhat
"insulated" from one another by surface oxidation. If skin effect forces
currents to the outside of the net diameter of the stranded wire, what effect
does the surface oxidation have on losses? I suppose if the radiation
resistance of the antenna is high, the effect on efficiency is small. But not
so for antennas with a low radiation resistance.
Rudy's paper is the only source I've found that attempted measurements
(indirectly via Q of coils wound with oxidized wire).
Doing some antenna work this past weekend (unusual warm weather) I also
discovered that some ladder line I have shows significant oxidation on the
conductors, many feet away (50+) from the end of the ladder line. It's
stranded #14 copperweld ladder line. No obvious cracks in the insulation that
would let water in. Perhaps the corrosion is due to interaction with the
insulation material itself. I separated the strands on a cut end and found
them all to be visually blacked rather than the expected shiny copper. After
cleaning up the ends of the strands with #400 paper, I measured as much as 2
Ohms resistance between strands with my DVM (that's strand to strand on the
same end of an open feedline). No idea what the losses may be at RF.
N3AE
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