That was the other baffling thing about this case: it had all the
characteristics of power line noise, yet it appeared to be coming from a
house. The spectrum was very broad and flat, unlike switching supplies,
etc. The AM audio spectrum showed harmonics of 120 Hz. This particular
source, when it is active, is very steady, without the usual
fluctuations that make it easier to verify that it is the same source
the home receiver is hearing on 20 meters, although there is often some
correlation. (I relay the noise from the home receiver via 2 meters, so
I can listen to it simultaneously with the VHF tracker. This has served
me well.) I have tracked down a few other sources, but they're always
easy to distinguish from power line noise.
The clincher, in this case, is that the source goes silent when it is
wet, returns when it dries out. I've made 3 or 4 trips over to a
particular power pole now to verify that it is strong on the VHF tracker
when it's strong at home, and vice versa. This is not a subtle source:
it is several blocks away, and raises my noise level by 20 dB. The VHF
tracker isn't calibrated, but near the source the difference is far
greater than that. I haven't yet quite caught it in the act of making
the transition, when it is erratic, but I expect I will if it ever stops
raining.
I've been tracking down line noise in the neighborhood for about 30
years, quite successfully, using these techniques. My local utility has
no tracking capability at all, so I have to do it for them. Nor do they
have much interest in fixing anything after I've tracked it down,
unfortunately. I envy the folks who have more cooperative and capable
utilities.
73,
Scott K9MA
On 5/23/2020 21:54, Jim Brown wrote:
On 5/23/2020 7:31 PM, K9MA wrote:
The next time I went back there, the tracker pointed to a power pole
across the street from her house, and has ever since. All I can
figure is that there might have been multiple sources which added up
in such a way as to make it look like it was coming from that house.
So now I'm back to doing battle with the power company.
Scott,
Have you done what Dave and I have both suggested and looked at it on
the waterfall of a good receiver? My troubleshooting guide shows how
to distinguish between power line noise and electronic noise. Have you
followed Dave's excellent advice about using a very long, very slow
waterfall to see when various noise sources start and stop?
73, Jim K9YC
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Scott K9MA
k9ma@sdellington.us
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