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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