Hi Mike,
The other copies (harmonics of 78 kHz) show exactly the same structure.
I hear the signal only on 20 meters, across the whole band. They
certainly go beyond the band, but it's hard to tell how far due to
antenna bandwidth. Looking at the whole band, I'm actually seeing
harmonics of 39 kHz, though the 78 kHz harmonics are stronger.
Looks like I'll be taking a walk this afternoon.
73,
Scott K9MA
On 7/31/2024 7:26 PM, Michael Carter wrote:
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@sdellington.us>
*Sent:* Wednesday, July 31, 2024 5:56 PM
*To:* Michael Carter <Mike.Carter@unh.edu>; rfi@contesting.com
<rfi@contesting.com>
*Subject:* Re: [RFI] New RFI Source
CAUTION: This email originated from outside of the University System.
Do not click links or open attachments unless you recognize the sender
and know the content is safe.
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@contesting.com>
<mailto:rfi-bounces+mike.carter=unh.edu@contesting.com> on behalf of
K9MA <k9ma@sdellington.us> <mailto:k9ma@sdellington.us>
*Sent:* Wednesday, July 31, 2024 5:08 PM
*To:* rfi@contesting.com <mailto:rfi@contesting.com>
<rfi@contesting.com> <mailto:rfi@contesting.com>
*Subject:* [RFI] New RFI Source
CAUTION: This email originated from outside of the University System.
Do not click links or open attachments unless you recognize the
sender and know the content is safe.
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@sdellington.us <mailto:k9ma@sdellington.us>
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Scott K9MA
k9ma@sdellington.us <mailto:k9ma@sdellington.us>
--
Scott K9MA
k9ma@sdellington.us
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