John, there were always three primary causes of noise we found that affected
frequencies up to 100MHz.
1.) The most common were slack spans where a wire hangs loosly with belly or
sag in the span, and the insulators are bell-type with pins and clips
holding them to other hardare or each other. This problem normally breaks up
in wind or disappears when the line is wet. New insulators (the polymer
ribbed covering over a fiberglass core) really help reduce this problem, if
they can't suck up on a span hard enough to remove slack.
2.) The second most common was loose external clamps, tie wires and
connections with fasteners. This problem also is not stable with weather or
motion. Generally it changes from day to day or with shaking or vibration.
3.) The last is arcs inside hardware such as transformers and arrestors.
This is a fairly stable noise regardless of weather and generally is pretty
strong compared to other noises and extends down in frequency pretty good.
You also will generally NOT hear these noises with a ultrasonic detector.
Newer style arrestors were particularly bad about being accoustically very
quiet while generating trash. IMO they were much more of a problem than old
air gap types.
I have never seen or even heard of a stand moving away from a conductor
bundle, and so I never knew of one making noise. I don't think noise is
possible on your primaries from something like that.
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