RadioBanter - View Single Post - Different Power at Different Times of Day

January 14th 04, 10:18 PM

ospam (Sid Schweiger) wrote

Radio waves radiate more or less in all directions from an AM tower, meaning
that some of them radiate skyward.

The ionosphere, in the presence of solar radiation (i.e., during the day),
absorbs the radio waves. In the absence of solar radiation (i.e., during the
night), it becomes a reflector, bouncing the signals back to earth hundreds or
thousands of miles beyond the transmitting tower. This can create interference
with stations on the same or adjacent frequencies at night, where no such
interference would occur during the day. To avoid such interference, many
stations must either cut transmitter power at night, or employ directional
antennas...or sometimes both.

Thanks, that's very interesting. Now, why is it that the ionosphere
absorbs radio waves in the presence of solar radiation, but not in its
absence?