Assuming you get that pattern repeating 22khz, my guess would be a
switch mode PS or similar operating at a switching freq of ~ 22Khz
connected to a harmonics rich AC line, possibly with little to no input
filtration.
I have seen similar from a battery powered hand-tool charger that was
poorly designed (no AC line side filering at all). Result was switcher
harmonics modulated by the first 6 - 8 AC line harmonics.
The point being, to me that looks more like noise from a nasty AC line
powered device than actual power line noise.
On 3/29/17 14:29, Pete Smith N4ZR wrote:
> I'm having more trouble than I expected localizing my power-line
> interference. In particular, one component of the interference varies
> from almost negligible to whopping big, as visualized on HDSDR, and
> often appears in wide bands 22 KHz apart.. See the Dropbox link
> <https://www.dropbox.com/s/qaxt7qnyl51hnp3/hum%20bars.png?dl=0> for a
> visual. You can see the hum every 120 Hz on the audio display - when I
> move the AM passband away from the hum bands, the 120-Hx
> multiplesessentially disappear. The bands themself vary, without
> apparent pattern, from very strong - as seen in the illustration- to
> invisblle/inaudible. Just now, they stuttered a few times and then
> disappeared from the waterfall (and the audio) entirely, in the course
> of a few seconds. With the AM passband in one of the hum bands, the
> base noise level is about S9; without them, it is S7, which still isn't
> great, but worst things first.
>
> Really puzzling - any advice on what I'm seeing and how to track it down
> will be much appreciated.
>
>
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