[RFI] RFI Signature

Tue Nov 25 13:00:23 EST 2025

I set the BW to 20KHz and made another recording.

Also uploaded the full 80M spectrum, 3500 to 4000.  Some slight banding is visible, -79 lvl @6KHz.

Also uploaded a jpg for the -73 level @ 6KHz.

Seems to have 4 running levels.  The 4 levels I have noticed always seem to be -85, -79, -73, -67 +/- 1dB (measured at 6KHz BW).  

As several have noted, strong 60Hz component but not much at 120 or 240Hz.

Has a slight rhythm to it, not PLN.

I happened to see it switch levels again, this time staying at the new level a little longer, for 15 seconds.

I will forward the accumulation of facts plus an audio clip to the ham for forwarding to the neighbor (in a nice email).  If someone thinks of something else to check, let me know.

Thanks for the ideas.

From: Don Kirk <wd8dsb at gmail.com> 
Sent: Monday, November 24, 2025 9:46 PM
To: Jeff (W4DD) <w4dd09 at gmail.com>
Cc: rfi at contesting.com
Subject: Re: [RFI] RFI Signature

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 <mailto:w4dd09 at gmail.com> > wrote:

I posted some additional pictures of the noise and an audio clip to the link
below.

From: Jeff (W4DD) <w4dd09 at gmail.com <mailto:w4dd09 at gmail.com> > 
Sent: Monday, November 24, 2025 11:17 AM
To: 'rfi at contesting.com <mailto:rfi at contesting.com> ' <rfi at contesting.com <mailto:rfi at contesting.com> >
Subject: FW: [RFI] RFI Signature

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.

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.

https://drive.google.com/drive/folders/1jYH07St1bSd0-Coqhl76HhraKbdYX2e-?usp <https://drive.google.com/drive/folders/1jYH07St1bSd0-Coqhl76HhraKbdYX2e-?usp=drive_link> 
=drive_link

  _____  

From: RFI < <mailto:rfi-bounces+mike.carter <mailto:rfi-bounces%2Bmike.carter> =unh.edu at contesting.com <mailto:unh.edu at contesting.com> >
rfi-bounces+mike.carter=unh.edu at contesting.com <mailto:unh.edu at contesting.com> > on behalf of Jeff (W4DD) <
<mailto:w4dd09 at gmail.com <mailto:w4dd09 at gmail.com> > w4dd09 at gmail.com <mailto:w4dd09 at gmail.com> >
Sent: Sunday, November 23, 2025 2:10 PM
To:  <mailto:rfi at contesting.com <mailto:rfi at contesting.com> > rfi at contesting.com <mailto:rfi at contesting.com>  <
<mailto:rfi at contesting.com <mailto:rfi at contesting.com> > rfi at contesting.com <mailto:rfi at contesting.com> >
Subject: [RFI] RFI Signature 

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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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