[RFI] Working with Utilities

[Hare, Ed, W1RFI]

What I have seen is that noise that gets conducted onto 120- or 240-volt wiring differentially tends to diminish very rapidly with distance, even on HF.  Noise that is conducted onto ac mains in the common mode diminishes more slowly with distance, but typically goesn't get much farther than the transformer.  Most power line noises are conducted onto those overhead wires the same way we feed our antennas, so they tend to develop standing waves that can propagate for a long way along a line.

To keep a bit on target with the thread name, it is important to differentiate true "power line noise" from the many other noises that can be heard.  In very general terms:

> Power-line noise is broadband, not varying much across an amateur band other than to be somewhat broadly stronger around the frequency where the source radiator and/or susceptor antenna are resonant.

> Power-line noise typically changes with changes in humidity and to some extent, temperature.

> When demodulated in an AM receiver, power-line noise shows a strong 120-Hz component, with a 60-Hz component present in some cases.  (If you make a .wav file and run it through a free program called Audacity, you can do a spectral analysis that will show the audio peaks).

> When looked at in the time domain, power line noise is generally a bit "erratic" in nature. This is especially evident when demodulated by a Radar Engineers receiver, due to the wider bandwidth and the way it shows the noise as pulses.

> Other electrical noise such as lamp dimmers can also show a 60- or 120-Hz component, but in the time domain, the waveform is generally more uniform and repetitive.

> Switching regulators show some definitive characteristcs:
   o They are not uniform across a band, but appear every N kHz, with N typically being between 10 and 50 kHz or so.
   o Regulators tend to be somewhat drifty, as they go through temperature changes at warmup or loads change.
   o Regulators are typically responsive to changes in voltage, so surges and dips cause minor, short-lasting frequency changes.
   o Almost all power supplies, newer battery chargers, LED bulbs, invertres, fluorescent ballasts and solar systems are switching in nature.

> Digital signals can vary from just being broadband noise to having a distinct digital sound and multiple carriers.  The noise will not show a 60- or 120-Hz peak.

It is important to identify the noise source before complaing to the utility. They are not responsible for noise from non-utility equipment and a few false complaints can quickly put amateurs to the bottom of their priority list, often not scheduled until Nevuary.

Ed, W1RFI



________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of Jim Brown <jim at audiosystemsgroup.com>
Sent: Saturday, September 11, 2021 3:47 PM
To: Rfi List <rfi at contesting.com>
Subject: Re: [RFI] Working with Utilities

Lots of excellent advice here about tracking down impulse noise, which
is what power line noise is. But it's less likely to be useful for
electronically generated noise, like switch-mode power supplies and
power control electronics, like controllers for variable speed motors,
nor for systems using microprocessors.

One inportant correction though -- "Polarity" is the positive or
negative-going sense of a signal, like going through an inverting gain
stage, or turning a pair wires over. What you're talking about here is
"Polarization." And you're right that it can be very important.

73, Jim K9YC

On 9/11/2021 9:43 AM, AA5CT via RFI wrote:
>
> re: "That is half of the equation."
>
> Beg your pardon here Ed Hare.
>
> I don't know what you read into my reply Ed, but, that is not my experience with
> this technique! Note I said UHF, not VHF and with a handheld Yagi antenna. I have
> even tried a 900 MHz Yagi to do the DF, but the amount of signal there is notably
> down from that at UHF (450 MHz).
>
> Ed, it becomes QUITE apparent when using this UHF DF technique in the field
> WHERE the source is, where the RF is coming from, and its definitely NOT from
> 'all along the line' as you seem to indicate. AND its easy to note if it comes from
> a house or from hardware up on a pole.
>
> There is even a POLARITY associated with these noise sources - orienting the
> Yagi vertically and horizontally results in changes in signal strength.
>
> I don't know that you've ever tried this UHF AM rcvr plus beam technique in the
> field, Ed, but it becomes quite apparent when actually using this technique just
> where the noise, where the signal originates.
>
> Again, walk around, sniff the noise source with your HAND-HELD UHF beam
> and note WHERE the signal is strongest. You'll find it. Note: Use AM rx mode
> on the receiver, and you'll hear the characteristic 60/120 Hz (base rep rate)
> 'buzz' of the arcing source.
>
> This technique (USED to find the individual offending pole) has not failed me yet.
> And, AGAIN, I use other techniques (LIKE HF DF) to locate down to the vicinity
> of the offending pole.
>
> THIS response, this e-mail, was directed to the original poster in this thread to
> help ID and note an arcing set of BELL insulators, that was all. But Ed took it
> in a more general direction.
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