Ask A Scientist Physics Archive

name         Amanda M.
status       student
age          17

Question -   How can you receive a Chicago AM radio station in North
Carolina?  Why is that possible?
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The short simple answer is that certain radio frequencies reflect off the
ionosphere and the ground so that the radio wave keeps bouncing back and
forth. This is of course going to be sensitive to atmospheric conditions for
weak signals, and a given receiver may pick up interference of radio waves
of like frequencies. This is why the NIST does not have numerous radio
transmissions of "standard time" -- to many signals get in the way of each
other.

Under certain atmospheric conditions some transmissions of short wave
lengths can also propagate "over the horizon". I personally was able to
receive a TV station from Havana, Cuba in South Carolina. I'm not sure what
these "strange" conditions are however.

Vince Calder
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