BMW 3-series convertible, Полное руководство по автомобилю

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FM Antenna Diversity
The E93 Convertible features a four FM antenna diversity module
that is made up of the following antennas:
• FM1 and FM3 antenna in the rear window
• FM1 and FM3 antenna in the side trim panel
• FM2 and FM4 antenna in the rear bumper
• Antenna amplifier on the C-pillar
• Antenna amplifier on the left and right shoulder
• Antenna amplifier in diversity module.
The switchover between the antennas in the rear window and side
trim panels takes place by means of a signal from the Convertible
top module CTM.
The sequence of FM antenna diversity is not defined as on
previous models. On the E93, the reception quality and field
strength of all antennas are checked and stored in a memory.
The next best FM antenna in the list is selected if the signal quality
of the radio station received at the active antenna is insufficient in
terms of quality and field strength. The antennas are evaluated and
the list updated at the same time as the switchover between the
individual antennas.
Changeover takes place in such a way that no interruption is heard.
The high frequency signal (RF) of the active FM antenna is routed
from the antenna diversity module via a coaxial cable to the tuner
for the radio or navigation system. The signal is demodulated in
the tuner and output via the speakers as an audio signal.
The radio or navigation system detects whether a diversity module
is installed and generates the changeover voltage “Us” necessary
for diversity operation and the intermediate frequency signal (IF).
The IF is evaluated by the electronic circuitry in the diversity
module and is a copy of the radio station currently heard on the
fixed frequency of 10.7 MHz.
The changeover between AM/FM1 reception and diagnosis mode
takes place with the aid of the changeover voltage “Us”.
This voltage is generated by the radio and used in the diversity
module for evaluation purposes.
Diversity mode is active at “Us” = 2.5 Volts. AM mode is active or
the FM1 antenna selected at “Us” = 0 Volts. Diagnosis mode is
active at “Us” = 5 Volts.
Up to three signals can be transmitted simultaneously on the
coaxial cable:
• RF signal (e.g. 87.5 - 108 MHz) from diversity module to radio
• Control voltage “Us” from radio to diversity module
• Intermediate frequency (IF = 10.7 MHz) from radio to diversity
module as basis for assessing the quality of the RF signal.
Mutual influencing is not possible due to the different frequencies.
The frequency is 87.5-108 MHz.
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E93 Complete Vehicle Workbook