I too have had longstanding line noise problems, made worse by the fact
that I can see a long way from a hilltop location.
Our local power utility, Pacific Gas & Electric, has been sued and has
paid multimillion dollar settlements in a growing number of cases where
fires have resulted from faulty power-line facilities. In the most
recent fire, which was right here in Los Gatos, an aluminum connector
between line sections arced inside, became overheated, rained molten
aluminum down onto dry brush and darned near burned up the whole town
(luckily but sadly for the owners, only a few houses burned to the
ground before the combined area fire departments brought it under
control).
I believe that radio noise radiation can be a precursor of this type of
failure. I intend to bring this concept to the attention of the utility
and its regulator, the California Public Utility Commission You might
want to raise this issue to get some economic push behind a problem that
utilities have tended to wave off as having no cost impact for them.
Your utility is doing the right thing, trying to isolate the problem
location using an AM radio and directive antenna at UHF frequencies.
Sometimes a portable spectrum analyzer is helpful, and there's a
specialized wideband noise receiver with a pulse stretcher to match the
spectral characteristics of line noise. An AM receiver with only 3-6
kHz bandwidth isn't well matched to the sharp rise time of spark noise
pulses. You should also try to determine if the noise is spark-gap
noise (typically from 12 kV distribution, pulses only at peaks of the
voltage cycle, noise blanker tends to work on this) or corona (typically
comes from really high voltage facilities, noise blanker won't touch it,
sounds like 120 Hz buzz and is likely to be much harder to get fixed).
There's an excellent reference by Dick Adler and Ray Vincent that the
power company will have somewhere in its archives.
A likely problem is that there are multiple sources along the line.
Although loose hardware on wood poles can be a problem, the most common
source I've seen is arcing in the clevis of multiple bell insulators
used wherever the line changes direction. These are replaced to good
effect with monolithic insulators commonly known as epoxilators.
The main issue is to present this as a potential substantial cost
exposure to the utility, rather than something they might do when they
don't have more pressing problems to worry about.
Good luck and 73 e Dave, W6NL
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