On 12/11/2025 21:45, K9MA wrote:
This seems very strange: At 0520Z Dec. 12, I'm hearing harmonics of 39
kHz from 3507 up. They're drifting around a lot, like SMPS harmonics,
and are 2-3 kHz wide. But they have QSB, so they're almost certainly not
local....When I watch several harmonics at once,
they peak and fade together, with no sign of selective fading.
Is anyone else hearing anything like this?
Not currently, but I have heard similarly fading local signals in the
past...
Some time before 2013. I was monitoring 27 MHz "Class C" radio service
frequencies for unique signals. I was parked in front of an office
building, waiting for the XYL to come out for lunch.
Spinning the dial I heard an unusual digital mode on a Class C
frequency, so I sat and monitored for a while.
It almost sounded like a radio modem transferring some data, bursts that
came and went, with fainter ones in the background, as if something was
responding.
There was heavy fading on occasion, some, quite deep, but no pattern to
it. I monitored for quiet some time, wondering where this signal was
coming from.
At some point, it occurred to me, the QSB was consistent with people
walking in a hallway, about 75 feet away, I could see them through a window.
Turns out, the digital signal, was coming from a server room in the
building I was parked in front of, the RF being ducted down the hallway
to my vehicle and receiver, the fading was from people entering and
leaving the hall, absorbing, or blocking the signal.
In that case, nothing exotic, just computer RFI, with changes in
"propagation" giving the appearance of DX, being caused people roaming
the hallway.
Your SMPS looking RFI, could be just that, with people/animals, milling
about the source giving the appearance of exotic DX.
Kurt
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