20 khz looks like AC compressor motor noise.
On Tue, Jul 20, 2021 at 12:19 PM Ramakrishnan Muthukrishnan <
ram@rkrishnan.org> wrote:
> Dear RFI-hackers:
>
> 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.
>
> I have tried turning off the mains and hunting for it inside the house.
> I live in a densely populated area. All the houses use power inverters
> as power disruption is quite common in this part of the world. I have
> tried powering the house directly bypassing the inverter to rule out
> whether it is coming from my own inverter. But so far, I haven't been
> able to find the source for it within my house. If anyone has seen such
> an RFI signature and can give me some clues about what it is, I can try
> to hunt for it in the neighbourhood. I see it all the time, 24 hours!
> When power goes off in the area, the inverter creates heavy QRM and so
> this gets buried in other noise. I am getting a mains filter etc. THis
> is coming from the antenna side though (I think), as without the
> antenna, I am unable to see this signal (I found other local SMPS
> sources that way and eliminated them).
>
> Any help appreciated.
>
> 73
> Ram VU3RDD
> --
> Ramakrishnan
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