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
25– 30 mi (40—50 km) 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 direct signal and 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.
Flutter/Skip Noise
Signals from an FM transmitter move in
straight lines and become weak in
valleys, between tall buildings,
mountains, and other obstacles. When
a vehicle passes through such an
area, the reception conditions may
change suddenly, resulting in annoying
noise.
Weak Signal Noise
In suburban areas, broadcast signals
become weak because of distance
from the transmitter. Reception in such
fringe areas is characterized by sound
breakup.
Strong Signal Noise
This occurs very close to a transmitter
tower. The broadcast signals are
extremely strong, so the result is noise
and sound breakup at the radio
receiver.
Station Drift Noise
When a vehicle reaches the area of two
strong stations broadcasting at similar
frequencies, the original station may
be temporarily lost and the second
station picked up. At this time, there will
be some noise from this disturbance.
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