6-15
Interior Comfort
Audio System
Form No. 8S06-EA-03H
▼
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.
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.
Signals from an FM transmitter are
similar to beams of light because they do
not bend around corners, but they do
reflect. Unlike AM signals, FM signals
cannot travel beyond the horizon.
Therefore, FM stations cannot be received
at the great distances possible with AM
reception.
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 reflected by
obstructions, it is possible to receive both
the direct signal and the reflected 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.
Ionosphere
Station 1 Station 2
FM Station
40—50 km
(25—30 miles)
Ionosphere
100—200 km (60—120 miles)
FM wave
FM wave
AM wave
Direct
Reflected wave
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