[RFI] 80m RFI with QSB

[Facility 406]

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