MadSci Network: Physics

Re: Radio reception

Area: Physics
Posted By: Keith Little, Computer Science
Date: Wed Oct 9 15:10:58 1996
Message ID: 843251013.Ph


Radio is transmitted (and received) via electromagnetic waves which
travel in straight lines, and can be disturbed by outside influences
(other stations, car ignition systems, etc).  Another influence is the
earths "Ionosphere", a region of charged particals high in the atmosphere
which is affected by solar radiation.  When the sun is up (say, noon),
emissions (and absorption) from the Ionosphere is high, causing radio
interference.  In the morning or evening, it's correspondingly low.

At night, for instance, the Ionosphere tends to reflect radio waves, and
guide them around the surface of the earth.  This is why ham radio
operators can communicate with people all over the planet.  This is known
as "Skipping" the signal (or "The Skips", for short).

Now, the reason radio interference is greater in the evening, is because
at morning, the surface of the earth is cool, so the Ionosphere receives
energy from only the sun.  But in the evening, the earths surface is warm,
which radiates infrared energy up into the ionosphere, adding to the
energy it's already receiving from the sun, increasing its emissions (and

Hope this helps,

Keith Little

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