[TowerTalk] UV and WX deterioration of THHN insulation, and effects

[Roger (K8RI) on TT]

Around here (5 mi W of Midland MI), with prevailing winds from the SW to 
N through W which is either woods or open fields for miles. There is a 
small village (Sanford) about 3 to 4 miles NNW.  Bare copper turns black 
within days. This makes the stranded antenna wire almost impossible to 
solder. (I use Copper split nuts)  Solid, bare Copper does the same. 
Rubbing the solid Copper with bare fingers leaves a black residue on the 
fingers although with time the wire become rough to the touch.  It will 
still make your fingers black, but it takes either an acid etch, or 
abrasive pad to restore the Copper luster.  If acid etch is used the 
connection must be thoroughly washed or even neutralized with a baking 
soda solution.

I've never left the jacket on house wire. OTOH I've found it necessary 
to "stretch" the #12 or #10 wire to harden it, otherwise 75 meter 
antennas get longer over time. I've seen over a 6" change in the overall 
length in a year or two, for #12 that was not hardened. There was no 
measurable change in the hardened wire. I wonder if this too is a factor 
when the insulation is left on. There is a very noticeable difference in 
the force required to bend the stretched/hardened wire compared to new, 
unstretched wire.

I have no idea as to what's in the air.

I've mentioned before that exposed solder joints as in the coax on C3i 
antennas erodes in just a few years to the point that light finger 
pressure will cause the joint to separate.  Liquid electrical tape cures 
that problem.  Two coats of clear Krylon is gone within just a few months.

73, Roger (K8RI)

On 12/30/2016 10:03 PM, Jim Thomson wrote:
> UV and weather degraded THHN wire was replaced with new bare wire and
> 60 ohms resistance disappeared that was visible only at RF. The wires
> were all pulled between posts, and the old wire was NOT sagging. The
> old wire was never subjected to the stresses of having an end fastened
> to a tree.
>
> The term resistance refers to the R value from an RF analyzer that
> supplies a value for X separately. E.g. R + jX .
>
> The missing consideration here *might* be the presumption of a smooth
> surface between a conducting and non-conducting layer. Close
> examination of the degraded wire taken from our radial replacement
> experience did NOT reveal a smooth surface.
>
> Instead the surface resembled the surface of a football or basketball,
> the small "bumps" that constitute an aid to gripping. Except the
> mounds and valleys between them were smaller in size, and more easily
> seen with a magnifying glass.
>
> What if, from the viewpoint of inside the un-degraded copper the
> transition from copper to degraded copper looked more like the roof of
> a cave, with stalactites, with a very irregular roof. Then what
> happens to the effective resistance of a glued-to-the-skin current
> forced to transit all these irregularities. Stated differently, what
> if a layer between absolutely conducting and absolutely not conducting
> actually exists and is not smooth and monolithic, but crumbly and
> irregular as all-get-out.
>
> N6LF has agreed to make some space in his schedule and analyze some
> samples of the wire in question, which I will be supplying to him
> shortly.
>
> We have some other experiments planned with some of the old wire.
>
> We are hardly done.
>
> 73 and a prosperous New Year to all.
> Guy K2AV ###  Wind a coil, say 10-20 uh, with the bad THHN, then another identical coil,but with brand new THNN.   Perhaps close wind it, then measure the UH at various freqs.My B+K  875B  LCR meter does the uh readings at just 1 khz.  Some will also take the readings at 100 khz and higher.  Then take a HP Q meter, and measure the Q of each coil,at various RF freqs, say in the middle of each of the 9 HF bands... perhaps 6m as well.  That should end the argument one way or the other, right then and there. Jim   VE7RF Jim   VE7RF
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-- 

73

Roger (K8RI)