On 5/23/2020 8:58 PM, K9MA wrote:
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.
AF is not a great place to look -- virtually all RFI generated by
electronics controlling AC power will show harmonics of 60 Hz. Nearly
all RFI generated by the Power System itself will be impulse noise -- on
a waterfall, it will be horizontal lines. Electronic sources are mostly
vertical lines (or squiggles). Static (distant lightning) is impulse
noise, but irregularly spaced on the waterfall. Power line noise can be
seen as horizontal lines on a very fast waterfall; it can be constant or
intermittent. In summary, the waterfall displays are VERY different.
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.
This strongly suggests it IS a power line issue.
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.
NI6T, a serious 160M DXer, got to know the PG&E guys who did this work,
and learned something quite important. Each supervisor's job rating is
based on how of his budget is left at the end of a fiscal year. THAT'S
why so little gets fixed in that company. This is the company whose
aggressive policy of NOT maintaining their gas lines caused a massive
explosion that destroyed a lot of homes in Silicon Valley, and not
maintaining power lines caused fires that killed a lot of people and
destroyed thousands of homes.
73, Jim K9YC
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