Radio reception

The following control units are involved in the radio function:

• Aerial tuner with aerial amplifier and diversity unit
  
• Audio System Controller
  
• Audio amplifier (equipment HiFi or Stereo) or Amplifier (Top HiFi)
  
• Control Display
  

Brief description of components

Rear window aerial

The rear-window aerial is subdivided into a number of reception areas in order to improve reception. The division into right and left has been made in accordance with the arrangement of the amplifiers.

Main functions

Aerial tuner

The aerial tuner is a control unit for the radio and TV reception functions.

The aerial tuner has a separate power supply.

• In the AM range, the aerial tuner converts the HF signals from the AM aerial amplified by the diversity and feeds the LF signals on the MOST.
  
• In the FM waveband, aerial diversity switches the aerial with the best reception to the tuner. The tuner amplifies the HF signals and converts them. They are sent to the ASK as LF signals.
  

The following are connected to the aerial diversity unit:

• An aerial for the AM waveband (amplitude modulation); this is used for amplifier function only;
  
• Two aerial circuits (right and left) for the FM waveband, each with two aerials: signal processing for the two left aerials and amplification is performed by the aerial diversity unit; the right aerial signals are combined into one by the aerial amplifier and passed to the aerial diversity unit as a single signal.
  

The aerial diversity unit selects the best aerial circuit by the following process:

• The aerial tuner checks the strength of the signal being received on each aerial group by continually switching back and forth between the left and right aerial group on the aerial diversity unit.
  
• The aerial diversity unit patches through the aerial with the best reception quality on the basis of the signal received from the aerial tuner.
  That aerial group is used for the next check cycle.
  
• If there is no acknowledgement regarding the reception field strength at the aerial diversity, e.g. due to an interruption in the ribbon cable between the aerial tuner and aerial diversity, the aerial diversity automatically switches to the left-hand aerial group.
  If either the CONTROL or DIAG signal is lost, no aerial group can be selectively activated through the diagnosis system.
  

Service functions

Checking FM reception

FM reception can best be checked by driving in a circle. The aerial diversity unit connects the aerial with the best reception to the aerial tuner.

Checking the aerial diversity unit

Connect the vehicle to the diagnostic system and select the control unit functions.

• Set a local sender in the FM waveband with good reception.
  
• Select control unit functions and read off the reception characteristics.
  
• Select the left aerial path and read off the reception characteristics.
  
• Select the right aerial path and read off the reception characteristics.
  
• For the remainder of the fault finding process follow the connection scheme
  

Diagnosis request