[RFI] Fwd: 20 Meter Interference

[Dave Cole]

Thanks for the follow up sir...  Congratulations on the end of your RFI.

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 2:36 PM, K9MA wrote:
> 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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> 
>