The first step to differentiate between an arcing or sparking noise source and
the millions of devices that an generate noise is to tune the band. If the
noise is not steady with frequency, but appears in broad humps even N kHz (with
N typically being 10 to 100 kHz spacing), it is not power-line noise, but a
device.
If it is steady with frequency, put your receiver into the AM mode and see if
it contains a 60- or 120-Hz buzz or hum. It is useful to make a recording of
it as a .wav file and use a program called Audacity to analyze the spectrum. If
you see 60, 120, 180, 240 Hz, etc, it is confirmed that it is electrical.
It can still be a device, especially if 60 Hz is present. (The 60 Hz may be
attenuated because your receiver rolls off below 200 Hz, but you can also look
for 180 Hz.)
You can also look at it using Audacity in the time domain. If it is steady
across the band, but its waveform is very regular, especially if it contains 60
Hz, it could be a device like a lamp dimmer, or OLD fluourescent ballast that
transforms 120 VAC to a higher voltage for the bulbs. (Newer ballasts are
switching power supplies.)
Power-line noise can rarely have a 60-Hz component, but is almost always
showing mostly 120 Hz and harmonics thereof. Seen in the time domain, it is not
as perfectly regular as a device would be, and is often a bit erratic as the
wind blows lines about. If the noise changes with the presence or absence of
rain, it is clearly outdoors, and this is amost always power line noise.
Yes, it is the power company's responsibility to find it, but in practice, if
you can isolate the pole, you have a much better probability of getting it
fixed. You need correlation between noises out there and your noise, because
some noises do NOT propagate down lines, but are heard only very close to the
source. There are three ways to correlate. The best is to get a noise
signature using a Radar Engineers receiver. Take a signature from your antenna,
then take another signature at a suspect source. You can also follow the
noise all the way from the source to your station. If it is strong at the
source and diminishes slowly with distance (usually with a standing wave on the
line), and you can hear it less strongly in your driveway, that is a fair
correlation. If you have a directional antenna that peaks in the direction of
the source, that is an added confirmation. If it a very strong source and it
is close to you, ie within 100 feet or so, that is almost certainly a noise
you hear. In any of these cases, report the noise to the power company.
They often fix it. If they don't, contact Steve Anderson at ARRL and he can
start our "FCC" process for you.
If the noise does not have multiple peaks up and down the band, and no
significant 60- or 120-Hz component, it may be cable or DSL leakage.
If the noise does come in peaks vs frequency, it is a device. In that case, go
to the RFI page at ARRL.org and read the "Where Is It" information. An SDR
waterfall will also tell you a lot. If you see those peaks every N kHz, and
they seem to wander around a bit, or take sudden little frequency shifts, it is
almost some sort of of switching supply or regulator. In that case, follow the
"Where Is It" steps, with the most important being to switch off every breaker
in your house. If the noise goes away, turn them back on one at a time, note
whether the noise returns, then off again, so you don't get confused by
multiple sources. Also, be aware of battery backups, UPS devices, etc.
Ed, W1RFI
________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org@contesting.com> on behalf of Pete Smith
N4ZR <pete.n4zr@gmail.com>
Sent: Wednesday, February 1, 2023 9:27 AM
To: rfi@contesting.com <rfi@contesting.com>
Subject: Re: [RFI] Noise Level During Power Outage
How about a big dose of 60 and 120-buzz?
73, Pete N4ZR
On 2/1/2023 3:33 AM, Jim Brown wrote:
> On 1/31/2023 9:21 PM, K9MA wrote:
>> My QTH is in an older residential area, surrounded by overhead power
>> lines. Line noise is a constant problem. We recently had a major
>> power outage, so I measured the noise levels to get a baseline with
>> little line noise.
>
> Hi Scott,
>
> How do you know that it's line noise, not electronic noise? 25 years
> ago, line noise was a good assumption for anything we heard on the
> bands, but in almost any developed area, the average home has a couple
> of dozen electronic sources, everything from switch-mode power
> supplies for everything that plugs into the wall, variable speed
> controllers for motors, computers and lots of other stuff with
> microprocessors in them, and on, and on. When the power goes out, so
> do all of those electronic noise sources (except for those that UPSs
> keep running).
>
> The slides for talks I've done at Pacificon, Visalia, and to some
> clubs, show how to use a well-adjusted waterfall to differentiate
> between impulse noise (which is what line noise is) and electronic noise.
>
> http://k9yc.com/KillingReceiveNoise.pdf
>
> Yes, those with ear experience can nearly always tell the difference.
>
> NK7Z has wonderful advice and resources on his site about using 24
> hour very wide waterfalls to yield clues about operating hours of both
> impulse and electronic sources, and also recognizing multiple
> electronic sources.
>
> 73, Jim K9YC
> _______________________________________________
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> RFI@contesting.com
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