David, it seems that you understand the answer to my question
beautifully. Unfortunately, I can't understand it. Would you mind
dropping the complexity of your answer a couple of notches and
re-iterating? Thanks. --Matt

"David Eduardo" wrote

At night, nearly every AM in the US gets skywave intereference, due to the
nature of AM night propagation. Distant signals interfere with what are
unobstructed day signals, even if the station has the same power.

Huh? Why only at night? Why unobstructed in the daytime only? What
is a skywave?

The only exceptions are clear channel stations, which get a coverage
increase due to skywave and being on realtively protected channels.

What is a clear channel station?

Stations, to operate at night (nearly 35% don't) have to protect other
stations on the same frequency, sometimes as much as 1000 miles or more
away. Because of this, at night they may cut power or directionalize where
htey send it to avoid interference, or both.

Why do they have to protect other stations? From what? And why only
at night?

The ionesphere makes AM signals skip form just before sunset to just after
sunrise. This is why many US stations are daytime only, since they could not
run at night without causing interference to others.

How does the ionosphere make AM signals skip, and why only at night?

It's due to the laws of physics. Newer stations protect older ones. And many
can not even run at night.

Why do newer stations protect older ones? Why can't they run at
night?