Stranded wire has plenty of spaces for water to capillary wick the
length of the wire. Once I tried to make a pressure tight connection
from insulated stranded wire - it leaked like a sieve.
Way back, I asked my boatyard mechanic why he was soldering crimped
terminals, his answer was "in three years you will thank me". If there
are chloride contaminants in the air, the corrosion process is greatly
accelerated. (see
https://pomametals.com/wp-content/uploads/2018/04/salt-air-inland-coastal-map.jpg)
I have observed that some insulation, particularly older rubber
insulated wire, has contaminants that accelerate corrosion, yielding the
black oxide, a real PITA to clean for soldering.
Grant KZ1W
On 1/3/2020 20:31, Shawn Donley wrote:
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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