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43
Terrain
The terrain (hilly, mountainous, tall buildings) of the
area over which the signal travels may prevent the
FM signal from being noise-free.
Repeated pops and hisses which are heard during
an otherwise clear broadcast can occur near the
station because of the “line of sight” characteristic
of FM radio waves.
If there is a building or large structure between the
antenna and station, some of the signal “bends”
around the building, but certain spots receive almost
no signal. Moving out of the “shadow” of the
structure will allow the station to return to normal.
When the radio waves are reflected off objects or
structures, the reflected signal cancels the normal
signal, causing the antenna to pick up noise and
distortion. Cancellation effects are most prominent
in metropolitan areas, but also can become quite
severe in hilly terrain and depressed roadways.
To minimize these conditions, a stereo/mono blend
circuit has been incorporated into this system. This
feature automatically switches a weak stereo signal
to a clearer monaural signal, which improves the
quality of reception.
Several sources of static are normal conditions on
AM frequencies. These can be caused by power
lines, electric fences, traffic lights and
thunderstorms.
Another reception phenomenon is Strong Signal
Capture and Overload. This can occur when
listening to a weak station and when passing
another broadcast tower. The close station may
capture the more distant station, although the
displayed frequency does not change. While passing
the tower, the station may switch back and forth a
few times before returning to the original station.
File:04fnasc.ex
Update:Mon Jun 17 14:15:17 1996
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