It turned out to be a wireless doorbell extender, right in the shack.
Once again proving that one should check your own home first. I'm not
sure if it's the wall wart or the device itself. It seems to have
magically fixed itself after power cycling, but I'm sure it will be back.
I suspect the 1.1 second interval between noise pulses is the polling
period of the device, when it draws current from the wall wart. If a
ferrite core on the power lead doesn't fix it, I'll just unplug it when
operating. Who wants to be disturbed by the doorbell then, anyway?
73,
Scott K9MA
-------- Forwarded Message --------
Subject: Re: [RFI] 20 Meter Interference
Date: Tue, 23 Feb 2021 20:25:09 -0600
From: K9MA <k9ma@sdellington.us>
To: rfi@contesting.com
The spectra images didn't come through, so here are the links:
http://sdellington.us/hr/RFI/20m_K9MA.jpg
<http://sdellington.us/hr/RFI/20m_K9MA.jpg>
http://sdellington.us/hr/RFI/20m1_K9MA.jpg
<http://sdellington.us/hr/RFI/20m1_K9MA.jpg>
73,
Scott K9MA
On 2/23/2021 7:46 PM, K9MA wrote:
I've recently started seeing this signal on 20 meters, probably local,
as it is present late at night when the band is dead. It is a swept
signal, typically starting at about 13.625, sweeping upward to a sharp
cutoff at about 14.125. The total sweep seems to be about 500 kHz. The
sweep slows down near the upper limit and seems to dwell there. Sweep
repeats about once per second. It seems to be amplitude modulated
during the sweep, so it shows up as a series of pulses on the
waterfall display. While the frequency range seems fairly stable, it
does move around a bit. I can't tell whether the frequency change is
systematic or random.
In the attached images, the blue trace is the peak signal, accumulated
over many sweeps. The yellow one is the actual signal, without
averaging, which I caught near the upper end of the sweep. The
waterfall shows the pulsed modulation. Resolution bandwidth is about
440 Hz.
Any idea what this might be?
73,
Scott K9MA
--
Scott K9MA
k9ma@sdellington.us
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