[RFI] Noise centered around 20 meters

[Jim Brown]

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