[RFI] FW: RFI Signature

Mon Nov 24 13:47:12 EST 2025

Thanks for the panadapter picture, Jeff.  The spectrum is remarkably uniform.

I am not familiar with the Flex panadapter display presentation.  The scale on the right side of the spectrum display suggests a noise level of -90 (units unknown, reference level unknown, but the small S-meter window says -71 dBm.  Is that the total power in the indicated passband, which appears to be about 4 kHz wide?  The bandwidth displayed in the S-meter window says '6K' - is that the actual DSP bandwidth?

I do see the faint spectral lines in the waterfall that Don, WD8DSB mentioned.

Finally, the date/time stamp on the spectrum window is from one year ago, and apparently obtained from your Flex radio (if the W4DD-1 annotation so indicates).  Were you monitoring the offending RFI source from your home or remotely near the suspect residence?

73,
Mike, K8CN
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From: RFI <rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of Jeff (W4DD) <w4dd09 at gmail.com>
Sent: Monday, November 24, 2025 11:17 AM
To: rfi at contesting.com <rfi at contesting.com>
Subject: [RFI] FW: 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.

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://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fdrive%2Ffolders%2F1jYH07St1bSd0-Coqhl76HhraKbdYX2e-%3Fusp&data=05%7C02%7Cmike.carter%40unh.edu%7C46bfc69c7ad748e135eb08de2b74fd01%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638995980445207825%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C80000%7C%7C%7C&sdata=jynEmH2qEkA%2FHhBGItq2zkY0%2F4SdOWvb3hpP%2FWWizHk%3D&reserved=0<https://drive.google.com/drive/folders/1jYH07St1bSd0-Coqhl76HhraKbdYX2e-?usp>
=drive_link

  _____

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

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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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