Mitsubishi LANCER Owner's Manual page 550

Signal transmission
FM signals do not follow the earth surface nor are they
reflected by the upper atmosphere. For this reason, FM broad-
casts cannot be received over long distances. AM signals fol-
low the earth's surface and are reflected by the upper
atmosphere. For this reason, AM broadcasts can be received
over longer distances.
FM
25 to 40 mile radius
(40 to 64 km)
Weak reception (fading)
Because of the limited range of FM signals and the way FM
waves transmit, you may experience weak or fading FM recep-
tion. When the broadcast is blocked by mountains or similar
obstructions, reception can be disturbed.
AM
100 mile radius
(160 km)
Reflection
The reason why one can hear FM but not AM in parking
garages, under bridges etc., is that FM signals, unlike AM sig-
nals, are reflected by solid objects such as buildings, etc.
Because FM signals are easily reflected by buildings, this can
also cause reception disturbances.
The direct signal from the broadcast station reaches the antenna
slightly before the reflected signal. This time difference may
cause some reception disturbance or flutter.
This problem occurs primarily in urban areas.
Comfort controls
5
5-151