I had something very much the same. It turned out to be a variable speed fan
motor on the HVAC. Could be coming from your Nextdoor. My problem started
after I replace he HVAC unit. Common mode chokes on the fan motor leads fix
the problem.
Tom
Wb4jwm
Sent from my iPhone
> On Jul 20, 2021, at 1:23 PM, Jim Brown <jim@audiosystemsgroup.com> wrote:
>
> The typical home in the US has dozens of electronic noise sources, mostly
> switch-mode power supplies (SMPS), but also devices that have microprocessors
> built in -- everything from refrigerators to home entertainment products to
> computers to battery chargers. Our antennas hear those sources and those of
> our neighbors. The clearly defined peaks and straight verticals (stable
> frequency) tell us that it's running on a clock, so most likely something
> with a microprocessor.
>
> RFI, however, is like peeling an onion -- eliminate the strongest noise
> sources, and we'll see many additional weaker ones. This app note ran in
> National Contest Journal several years ago, and the slide deck was for a talk
> at the Visalia DX convention.
> http://k9yc.com/KillingReceiveNoise.pdf
> http://k9yc.com/KillingRXNoiseVisalia.pdf
>
> NA6O has shared his design of a loop for direction finding here.
> http://wb9jps.com/Gary_Johnson/RFI_files/Handheld_DF_Antenna.pdf
>
> And DXEngineering is preparing to sell a much larger one designed by WD8DSB.
> https://www.dxengineering.com/parts/dxe-noiseloop
>
> 73, Jim K9YC
>
>
>> On 7/20/2021 9:18 AM, Ramakrishnan Muthukrishnan wrote:
>> I have been experiencing QRM from some unknown source for the past several
>> months, a picture of it is here: <http://rkrishnan.org/files/40m-qrm.png>
>> This happens in every band and is repeats at 20khz. The signal is steady and
>> not wobbly like one sometimes see in SMPS created QRM. When listening to
>> SSB, I turn on the notch filter function on the SDR to get rid of the
>> "carrier" like signal. But that only does a bit.
>
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