Ron Hardin wrote:
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

My guess is that it must be a switch in the height of the reflecting
layer somehow, but I can't construct a really consistent picture.

There are several different reflective layers. The F1 and F2 layers
are the primary ones for shortwave, but on 660 KC the lower layers
may be coming into play as well. Since they are at different altitudes,
as they rise and fall you may find some times when you are getting a
strong F1 reflection, then a dead time, then a strong F2 reflection.

MW always reflects, but the attenuation varies at lower levels with
solar angle, sun killing off the reflected signal.

It's not ``grey line'' because that path is nowhere near the direction
involved.

What you need is a way of measuring propagation time throughout the
path....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."