[RFI] Fwd: 20 Meter Interference

[K9MA]

Yes, I discovered it by running the radio on a battery and turning off 
circuit breakers.

The culprit definitely was the wall wart. The cyclic pattern apparently 
was due to the device intermittently loading it.

73,
Scott K9MA

On 2/26/2021 2:13 PM, Dave Cole wrote:
> 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
>>>
>>
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-- 
Scott  K9MA

k9ma at sdellington.us