Two-way radio hands-free system for taxi, function

Function prerequisites

 Voltage not too high or too low
(recognized by the special vehicle multifunction control module (SVMCM) (N26/9))

The radio hands-free system allows the taxi driver to communicate via radio, e.g. with the taxi center. The radio hands-free system consists of the following components:

 Two-way radio (A49)

 (Electret) hands-free system microphone (B25/1)

 Left front door double-coil speaker (H4/19)

 Two-way radio selector switch (S34)

 Antenna amplifier control module (N10/5)

The power for the two-way radio is supplied by the SVMCM. When the two-way radio selector switch (S34) in the center console is actuated the two-way radio (A49) is switched to the transmit mode. Simultaneously the radio loudspeaker output (A2) is switched off. It is then possible to speak over the microphone (B25/1) in the overhead control panel.

The two-way radio signal is output on the left front door double-coil speaker (H4/19). This loudspeaker is also used with normal radio mode.

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Electret microphone
This microphone is coil-free and therefore extremely compact. It is based on the capacitor principle.
A polarized (electret) diaphragm serving as capacitor plate is moved by the sound waves. This modifies the capacity in contrast to the parallel, rigid, second capacitor plate. Electrodes are connected to both capacitor plates. The permanently changing capacity causes a voltage change which can be tapped and amplified as a signal.

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When the taxi emergency alarm (code 934) is triggered the radio hands-free system is switched to "receive" by the SVMCM.