Interior Comfort; Audio System; Radio Reception- Page 179

6-11

Interior Comfort

Audio System

Form No. 8S18-EA-03I

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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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