Thank you for many useful directions.
As my noise is usually cancelled completely by a noise blanker,
this suggests a powerline noise. The noise persists with the local power
off so it is not generated locally. There are no neighbors close.
The noise varies in amplitude. For example, on one beam, the noise peaks at
21.2 MHz and is 10 db weaker at 200 KHz away. On another beam 100ft away,
the noise peaks at 21.0 MHz and is also 10 db weaker at 200 KHz away. The
noise is also present on 10m but is relatively weaker on 20m. So it seems:
1. The noise is originating from one location because otherwise NB
would not be able to blanket it.
2. The noise is radiated from several points, creating nulls and peaks
around.
I don't know why the noise is 24h/day, unlike a typical powerline noise,
and why VHF readings are weak.
For RFI detection I have MFJ 3 el sniffer, 80m RDF radio, a magnetic loop
tuned 20-10m that is connected to KX3, and an ultrasonic sniffer. Also
tried a 10 el 2m beam connected to FT991, for greater directionality.
Ignacy, NO9E
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