[RFI] Fwd: 20 Meter Interference

[Dave Cole]

Did you discover this during a home power off test?

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 2/26/21 10:04 AM, K9MA wrote:
> 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 at sdellington.us>
> To:     rfi at 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
>>
>