[RFI] Fwd: 20 Meter Interference

K9MA k9ma at sdellington.us
Fri Feb 26 13:04:41 EST 2021

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?


Scott K9MA

-------- Forwarded Message --------
Subject: 	Re: [RFI] 20 Meter Interference
Date: 	Tue, 23 Feb 2021 20:25:09 -0600
From: 	K9MA <k9ma at sdellington.us>
To: 	rfi at contesting.com

The spectra images didn't come through, so here are the links:



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 at sdellington.us

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