I posted some additional pictures of the noise and an audio clip to the link
below.
From: Jeff (W4DD) <w4dd09@gmail.com>
Sent: Monday, November 24, 2025 11:17 AM
To: 'rfi@contesting.com' <rfi@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
=drive_link
_____
From: RFI < <mailto:rfi-bounces+mike.carter=unh.edu@contesting.com>
rfi-bounces+mike.carter=unh.edu@contesting.com> on behalf of Jeff (W4DD) <
<mailto:w4dd09@gmail.com> w4dd09@gmail.com>
Sent: Sunday, November 23, 2025 2:10 PM
To: <mailto:rfi@contesting.com> rfi@contesting.com <
<mailto:rfi@contesting.com> rfi@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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