[RFI] Fw: RFI Signature

[Michael Carter]

Inadvertently sent this only to Jeff W4DD.

73,
Mike, K8CN
________________________________
From: Michael Carter <Mike.Carter at unh.edu>
Sent: Sunday, November 23, 2025 2:47 PM
To: Jeff (W4DD) <w4dd09 at gmail.com>
Subject: Re: [RFI] RFI Signature

Hi Jeff,

No direct experience here with RFI sources having the characteristics you described.  The fact that different RFI signal levels occur repeatedly, although not periodically, suggests to me a demand-driven source where the power demand fluctuates based on use rather than time-of-day or weather.  Although these potential sources both involve SMPS internally, they have a demand-driven character:


  1.
PoE - power over Ethernet "Power Sourcing Equipment" has an autonegotiation process for determining the powered device's wattage/current needs. A dual-signature powered device might cause variable current demand on the respective pairs of the Ethernet cable, which could in turn cause the shifts in RFI intensity.
  2.
VSD - a Variable Speed Drive incorporated in HVAC equipment would also present variable frequency and voltage levels on the converter output based on demand of the motor drive.  While these parameters are not necesarily discretized, the demand profile might be such that discrete RFI levels are produced.

Here I'm presuming that the RFI is not conducted onto the AC mains and is being radiated from wiring within the suspect residence.

Your findings will be of much interest to me.

Thanks, and 73,

Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of Jeff (W4DD) <w4dd09 at gmail.com>
Sent: Sunday, November 23, 2025 2:10 PM
To: 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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