74
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RDM-TMC
Audio Operation
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Set Up
Audio Operation
nRadio 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 pro-
vide 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.
Operating Tips for Audio system
Station 2
Station 1 Ionosphere
FM Station
40—50km
(25—30 miles)
AM wave
FM wave
FM wave
100—200 km (60—120 miles) Ionosphere
Reflected wave
Direct
