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-------- Original message --------From: Jim Brown <jim@audiosystemsgroup.com>
Date: 5/24/20 00:27 (GMT-05:00) To: rfi@contesting.com Subject: Re: [RFI]
Noise centered around 20 meters 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
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