Dodge 18693 Stratus Coupe, Owner'S Manual

Page: 217 / 388

Signal transmission
FM signals do not follow the earth’s surface nor are they
reflected by the upper atmosphere. For this reason, FM
broadcasts cannot be received over long distances.
AM signals follow the earth’s surface and are reflected by
the upper atmosphere. For this reason, AM broadcasts
can be received over longer distances.
Weak reception (fading)
Because of the limited range of FM transmissions and the
way FM waves spread, fading usually occurs with FM
reception.
When the broadcast is blocked by mountains or similar
obstructions, reception disturbance may result.
Reflections
The reason why one can hear FM but not AM in parking
garages, under bridges etc., is that FM signals unlike AM
signals, are reflected by solid objects such as buildings,
etc.
Because FM signals are easily reflected by buildings, this
can also cause reception disturbances.
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