A local SWL who is friend, yes I do have some, called me wondering
about the
threads regarding fading. Will has only been into SW a few years and
comes
from a non electrical background and the debate got him wondering. I
found
a link that I sent him and he said it made it much clearer.

For those amoung use who might not have a clear visualization I offer
this link.
http://www.tpub.com/content/et/14092/css/14092_19.htm

If the "reflection" or refraction points, E and/or F, move then the
signal at A
will suffer from distortion. Not much movement is required to really
"mess" a
signal up. A similar effect can be heard on the song "Itchycoo Park" by
the
group Small Faces where two reel to reels, each with the audio
information,
were mixed and one was slowed down by touching the outer reel edge, a
technique called "Flanging". The slightly different audio sources mix
creating
a comb fitler effect. Higher audio frequencies are effected more then
lower,
hence the interest in effective audio low pass filters.

When done with white or pink audio noise and viewed with a FFT program,
"notches" or deep valleys appear in the display. Today effects boxes
use
digital delay lines to achieve this effect.

Terry