[RFI] RFI Signature

Mon Nov 24 21:46:21 EST 2025

Hi Jeff,

What was the bandwidth setting for the audio clip?  Looking at the audio it
has heavy 60 Hz content (not 120 Hz).  It has an overall repeating pattern
at a frequency of 60 Hz.  When dealing with power line noise I typically
see spikes at a frequency of 120 Hz (arcing at least once time during each
half cycle of the sine wave).  I know some power line arcing can happen
during just one half of the sinewave but I've never encountered that
situation.  If the bandwidth of your AM audio recording was less than 20
KHz, can you post another audio clip using a bandwidth of at least 20 KHz
(I prefer 25 KHz)?

Thanks,
Don wd8dsb

On Mon, Nov 24, 2025 at 8:46 PM Jeff (W4DD) <w4dd09 at gmail.com> wrote:

>
>
> I posted some additional pictures of the noise and an audio clip to the
> link
> below.
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> From: Jeff (W4DD) <w4dd09 at gmail.com>
> Sent: Monday, November 24, 2025 11:17 AM
> To: 'rfi at contesting.com' <rfi at contesting.com>
> Subject: FW: [RFI] RFI Signature
>
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> Thanks to all that replied.  Some interesting thoughts to consider.  I had
> a
> couple of Laughs also since several experts mentioned things I had been
> thinking.  I had pulled out a lawn tool battery charger (K9MA) and
> experimented with that.  It did produce a similar spectrum display, but I
> still can't account for why the source would be mostly at power level 2 or
> 3.  Seems like the battery would eventually be charge and it would drop to
> level 4, which we seldom see.  My battery was fully charged and the noise
> level was very low.
>
>
>
> A demand driven device (K8CN), seems logical.  It is not related to wx and
> does not change based on outdoor temperature so likely not HVAC.  POE is an
> interesting idea I had not considered.
>
>
>
> A ckt brkr based sniffer (WD8DSB).  I actually built one of those (thanks
> Don).  Unfortunately, the neighbor is resistant to anyone entering the
> home.
> This is also a remote assist, so I don't get to actually visit the site.
>
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> For those that asked, here is a waterfall capture.  Noise at the -71/-72
> level (level 2 of 4 levels).
>
> Antenna is a multiband vertical, tuned to 3540KHz.
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> https://drive.google.com/drive/folders/1jYH07St1bSd0-Coqhl76HhraKbdYX2e-?usp
> =drive_link
> <https://drive.google.com/drive/folders/1jYH07St1bSd0-Coqhl76HhraKbdYX2e-?usp=drive_link>
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>   _____
>
> From: RFI < <mailto:rfi-bounces+mike.carter=unh.edu at contesting.com>
> rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of Jeff (W4DD) <
> <mailto:w4dd09 at gmail.com> w4dd09 at gmail.com>
> Sent: Sunday, November 23, 2025 2:10 PM
> To:  <mailto:rfi at contesting.com> rfi at contesting.com <
> <mailto:rfi at contesting.com> rfi at contesting.com>
> Subject: [RFI] RFI Signature
>
>
>
> [You don't often get email from  <mailto:w4dd09 at gmail.com>
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> Learn why this is important at
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>
> I am working on a RFI case that we believe is coming from a nearby home.
> The owner is a little cooperative, but is not interested in doing a ckt
> breaker test.  The noise exhibits some interesting characteristics that may
> help us in suggesting he unplug a device.  Perhaps someone has seen this
> before.
>
>
>
>
>
> 1.      On the pan adapter, looks like power line noise.  Random dots
> across
> the screen.
> 2.      No repeating clusters of noise vs frequency that might suggest a
> SMPS.
> 3.      No correlation to sunlight or darkness.  No correlation to time of
> day.
> 4.      Has distinct levels of interference; we have noted -85dBm, -78dBm,
> -72dBm (S-9), -66dBm.  Interesting the levels are about 6dB apart.  -78 and
> -72 are most common.
> 5.      The neighbor has a solar system installed roughly 2 years ago, but
> as mentioned, no correlation to sunlight/darkness or time of day.
> 6.      Affects mostly 80M but can be heard on other bands
>
>
>
> Has anyone seen 4 levels of noise from a device before?
>
>
>
> Thanks for any ideas.
>
>
>
>
>
> Jeff, W4DD
>
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