[RFI] New RFI Source

[Michael Carter]

Scott, do the spectral copies at 78 kHz intervals
mimic the sideband structure shown in your K4
screen capture?

Over what frequency range can you see the
spectral copies (limited by antenna bandwidth,
I suppose)?

The120 Hz spaced fine spectral lines in the
main lobe suggest to me a 120 Hz square
wave modulating an underlying 'carrier' signal.
AC power line signal rectified
in the power supply for the device and coupled
into the 'clock' carrier and its harmonics?

The more distant sidebands don't exhibit the
fine 120 Hz structure of the main lobe.  That's
what's puzzling me.

I'll be very interested to see what your DF'ing
leads to......

73,
Mike, K8CN
________________________________
From: K9MA <k9ma at sdellington.us>
Sent: Wednesday, July 31, 2024 5:56 PM
To: Michael Carter <Mike.Carter at unh.edu>; rfi at contesting.com <rfi at contesting.com>
Subject: Re: [RFI] New RFI Source


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The carriers within that main lobe appear to be 120 Hz apart, so likely line related. They seem to vary in amplitude, but are very stable in frequency.

73,
Scott K9MA


On 7/31/2024 4:28 PM, Michael Carter wrote:
Hi Scott,

The sidebands are not typical of any SMPS I've
looked at spectrally.  The fine spectral structure
inside the main lobe suggest 60 Hz or 120 Hz
modulation of the nominal 'carrier', but the
sideband spacing of ~ 1 kHz from the main lobe
is odd.

What do you see when you zoom into the
main lobe?  Can you guesstimate the
spacing of the strongest sidelobes
within that lump?

73,
Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu at contesting.com><mailto:rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of K9MA <k9ma at sdellington.us><mailto:k9ma at sdellington.us>
Sent: Wednesday, July 31, 2024 5:08 PM
To: rfi at contesting.com<mailto:rfi at contesting.com> <rfi at contesting.com><mailto:rfi at contesting.com>
Subject: [RFI] New RFI Source

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This RFI source has appeared recently:

https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsdellington.us%2Fhr%2FRFI%2F24.07.31.png&data=05%7C02%7Cmike.carter%40unh.edu%7C5b47864c626340c4b55208dcb1a4e911%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638580569052206306%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=I3QbXdcat4zw3df8oU7lalFjpj9VCt3Qcf%2FvhKK3Hfs%3D&reserved=0<https://sdellington.us/hr/RFI/24.07.31.png>

It appears to be harmonics of about 78 kHz. However, unlike most SMPS
RFI, it is very stable. It disappears at night, suggesting a solar
system, but it persists, weakly, an hour or so after sunset. Maybe a
solar system comm link, with a supercapacitor? However, I'm not aware of
any new solar systems nearby.  Anyone seen anything like this before?

Needless to say, I'll be out tracking it soon.

73,

--
Scott  K9MA

k9ma at sdellington.us<mailto:k9ma at sdellington.us>
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--
Scott  K9MA

k9ma at sdellington.us<mailto:k9ma at sdellington.us>