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5
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145
Interior Features
Appendix
Radio Reception
AM characteristics
AM signals bend around such things as
buildings or mountains and bounce off the
ionosphere.
Therefore, they can reach longer distances
than FM signals.
Because of this, two stations may
sometimes be picked up on the same
frequency at the same time.
Station 2
Station 1
Ionosphere
FM characteristics
An FM broadcast range is usually about
40—50 km (25—30 miles) from the
source. Because of extra coding needed to
break the sound into two channels, stereo
FM has even less range than monaural
(non-stereo) FM.
FM Station
40—50km
(25—30 miles)
Signals from an FM transmitter are similar
to beams of light because they do not
bend around corners, but they do reÀ ect.
Unlike AM signals, FM signals cannot
travel beyond the horizon. Therefore, FM
stations cannot be received at the great
distances possible with AM reception.
AM wave
FM wave
FM wave
100—200 km (60—120 miles)
Ionosphere
Atmospheric conditions can also affect
FM reception. High humidity will cause
poor reception. However, cloudy days may
provide better reception than clear days.
Multipath noise
Since FM signals can be reÀ ected by
obstructions, it is possible to receive both
the direct signal and the reÀ ected signal
at the same time. This causes a slight
delay in reception and may be heard as a
broken sound or a distortion. This problem
may also be encountered when in close
proximity to the transmitter.
Reflected wave
Direct
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