Hi Gary!
Yes fading seems to be very selective.
Have you ever been listening to a distant AM radio station? Give it a try :)
There it is often audible, that a "fading notch" travels through one sideband
down to lower modulation frequencies, then there is a moment of often terribly
distorted audio due to the notched out carrier (the remaining sidebands
"virtually much overmodulated"), then the "notch" goes further through the
second sideband (if this also passes your filter).
The fading is fast on shortwave, where almost all the time different skywaves
"are fighting each other" , medium fast on medium wave, and in the case of
longwave transmitters sometimes very slow (may take minutes).
Here in Berlin this longwave radio QSB appears very nicely at dusk to the 204km
away "Polskie Radio I" 225kHz transmitter. The skywave becomes stronger and
seems to equal the value of the groundwave, so constructive and destructive
interference takes place.
Have a nice evening :)
Dennis
DL6NVC
--
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