BMW SERIE 5 SPORT WAGON 2001 Manual page 209

Radio reception
The AM frequency bands (medium-
wave, long-wave and short-wave) make
it possible to receive stations from a
great distance, because the broadcast
signals travel not only along the ground
as surface waves, but also as atmo-
spheric waves that are reflected from
the ionosphere.
Frequency-modulation (FM) provides
substantially better sound quality than
AM. However, because FM transmis-
sions rely on line-of-sight broadcast
waves, their effective reception range is
limited.
Although numerous factors combine
to impose inherent limitations on the
reception quality available from mobile
radios, specially designed systems can
be employed to minimize their effects:
The Diversity Antenna system employs
several FM antennas integrated within
the rear window to provide three sepa-
rate sources for receiving broadcast
waves. An integral processor automati-
cally selects the antenna with the best
FM reception quality at any given time.
Because the ongoing antenna selection
process is completed within milli-
seconds, it remains inaudible to the
radio listener.
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