Recently our local electric cooperative called on K0HGW and myself to help them
find a major powerline noise source that had been plaguing them for nearly a
year, resulting in numerous complaints from area hams and SWLs. They had tried
to locate the source using an MFJ 852 Noise Meter that John had gotten for them
and modified to make it useful but got so many readings that they were
completely lost.
We took our array of noise tracking equipment to the area where they had been
working and found devastating noise coming from every direction we turned.
Several power poles were identified as having moderate noise problems and they
started tightening hardware which corrected the local problems but did not do
anything to alleviate the overall noise level.
While we were working on one particularly bad source a local farmer drove up
and told us that there was a transformer group about a mile away, near his
house, that he could often hear buzzing in the night.
Taking our equipment to the location everything started to peg out from about a
half mile away. There was a 20 to 30 MPH wind blowing but we could hear the
buzzing noise through it once we arrived at the site.
After calling in a bucket truck and disconnecting everything on the pole the
noise went away completely.
The equipment was checked and a connector on the 7200 volt primary was
discovered to have about a eighth of an inch of oxidized material inside it.
Effectively it was a very large semiconductor junction.
Apparently it had never been completely tightened against the wire.
After it was replaced with a new connector and everything hooked back up and
tightened there was still no noise.
The interesting thing was that all the other noise sources also suddenly
disappeared.
Obviously most of them were reflections of the very powerful primary source.
>From our experience, a number of them had been independent noise sources in
>themselves, but they were no longer radiating noise. Our conclusion was that
>the main noise source that we had located (with the help of the farmer) and
>eliminated was acting as a very powerful wide band transmitter and was
>exciting the other, marginal noise sources that would have not been a problem,
>otherwise.
This may be a valuable thing to consider when tracking noise sources. But,
unless you have an observant old farmer available, tracking your way through
the morass of reflected and remotely excited secondary noise sources could be a
long and frustrating process.
As the final icing on the cake, when the power company checked their records
they found that the service was a primary tap that had been disconnected years
ago and had been illegally reconnected by someone using a stolen electric meter.
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