On 12/28/16 10:55 AM, Jim Brown wrote:
Scientific discussions (and disagreement) is healthy, and should not be
viewed at hostility!
I think two challenges in approaching the "does discolored wire have
more loss" question (and all the related, is the insulation lossy, etc.)
are:
1) characterizing the change in condition - If I leave a piece of THHN
out for 2 years, it will be different than someone in FL or ME.
We have all seen the discolored copper under the insulation, and clearly
there has been a chemical change, because it's harder to solder. The
chemical composition is unknown.
2) measuring the change - I suspect that the change is "less than single
digit percent"
3) If we're going to go beyond anecdote, to data, there has to be some
theory for what that discoloration is. The 1970 paper linked yesterday
talked about how over hundreds of samples, there was no consistency.
So let's talk about "standardized corrosion and degradation".
You can buy all sorts of "tarnish" chemistry for copper at craft stores
- it's used to put verdigris on your shiny new bronze sculpture. It may
not be representative of what we're seeing in antennas, but at least it
is repeatable.
You could put a pile of wire into a salt water bath and let it sit for a
while
You could put a pile of wire into UV light for a while.
You could soak that THHN in water (i would expect some effect from water
content). Nylon, for instance, is fairly hygroscopic, and at microwave
frequencies, it's pretty easy to measure the change in epsilon with
moisture content (mostly because water has epsilon 80.. it doesn't take
much)
Hot water might make it go faster.
Now to the measurement side..
I would propose that a good way would be to wind an inductor of a
reasonable dimensions - it's repeatable, and the inductance and
resistance is calculatable from well known equations. Measuring Q of an
inductor is something that is pretty well known, and since the fields of
the coil are reasonably well contained, the surroundings won't have much
of an effect: I'm thinking about a coil that's on the order of a few
inches, spacewound supported on a styrofoam post 6 feet off the ground,
outside.
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