Two Types of Signals
There are two basic types of radio signals: AM (Ampli-
tude Modulation), in which the transmitted sound causes
the amplitude, or height, of the radio waves to vary; and
FM (Frequency Modulation), in which the frequency of
the wave is varied to carry the sound.
Electrical Disturbance
Radio waves may pick up electrical disturbances during
transmission. They mainly affect the wave amplitude,
and thus remain a part of the AM reception. They
interfere very little with the frequency variations that
carry the FM signal.
AM Reception
AM sound is based on wave amplitude, so AM reception
can be disrupted by such things as lightning, power lines
and neon signs.
FM Reception
Because FM transmission is based on frequency varia-
tions, interference that consists of amplitude variations
can be filtered out, leaving the reception relatively clear,
which is the major feature of FM radio.
NOTE:
•
For vehicles not equipped with the Electronic Vehicle
Information Center (EVIC), the radio and steering
wheel radio controls (if equipped) will remain active
for 45 seconds after the ignition switch is turned to the
LOCK position. Opening either front door will cancel
this feature.
•
For vehicles equipped with the EVIC, the radio and
steering wheel radio controls (if equipped) will remain
active for up to 10 minutes after the ignition switch is
turned to the LOCK position. Opening either front
door will cancel this feature. The time is program-
mable. For details, refer to “Key-Off Power Delay,”
UNDERSTANDING YOUR INSTRUMENT PANEL 231
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