Aerials

FM aerials and AM aerial

As series standard, the E70 is equipped with aerial diversity for FM. The analog radio aerials are connected to aerial diversity.

The following radio aerials are installed:

• AM aerial
  
• FM1 aerial
  
• FM2 aerial
  
• FM3 aerial
  

To enhance the electromagnetic compatibility (EMC), various measures have been implemented using additional earth connections.

Brief description of components

The following components for the aerials are described:

AM aerial

The AM aerial receives radio stations in the SW, MW and LW ranges (AM stands for 'amplitude modulation', SW stands for 'short wave'; MW stands for 'medium wave' and LW stands for 'long wave').

FM aerials

Three FM aerials are installed.

The FM aerial receives radio stations and traffic information in the FM (VHF) range (FM stands for ”Frequency modulation”).

Aerial amplifier with aerial diversity

The aerial amplifiers are located in the aerial diversity. The amplifiers are designed separately for AM and FM. The aerial diversity is installed on the inside of the luggage compartment lid, above the rear window.

The aerial amplifiers receive a DC power supply from terminal RAD_ON when the radio is switched on. The radio tuner is connected across a coaxial line with the aerial diversity.
The ”aerial diversity” function is used to select one of the FM aerials for reception. If the aerial signal of this aerial deteriorates, there is an automatic switch to the next aerial.

The order of the aerial diversity for FM is specified as:

FM1 -> FM2 -> FM1 -> FM3

Thereafter, there is a switch back to the FM1 aerial. The position of this aerial in the rear spoiler means that the FM aerial has the best reception properties. The specified order for switching over ensures that the FM aerial with the best reception properties is active most frequently.

Aerial diversity selects the next FM aerial if the following criteria occur:

• The signal level rapidly drops.
  
• At the same time, high frequencies (noises) interfere with the signal.
  

The automatic interference suppression prevents any audible interruption as the aerials are switched. Aerial diversity evaluates the signal quality and switches to the aerial with the best reception. A DC voltage (U_s) is used to switch between AM aerial signal, aerial diversity and diagnosis mode. The DC voltage (U_s) is generated by the radio and is evaluated in the aerial diversity.

• At U_s = 0 Volt, the AM/FM aerial is selected (or the self-diagnosis has a negative result).
  
• Aerial diversity is active when U_s=2.5 Volts.
  
• When U_s=5 Volts, the diagnosis mode is active.
  

A number of signals are simultaneously connected on the coaxial cable. Reciprocal interference is not possible due to the difference frequencies.

Among others, the following signals can be applied simultaneously:

• HF signal (e.g. 88-108 MHz) from aerial diversity to the radio
  
• DC voltage U_s from the radio to aerial diversity
  
  

System functions

The following system functions are described for the aerials:

• Measures to increase electromagnetic compatibility (EMC)
  
  

Measures to increase electromagnetic compatibility

For certain known fault profiles, design measures have already been implemented in production.

Check these design measures in the event of EMC faults:

1. Earth strap on the exhaust system
   Fault profile with effect:
   EMC faults are conducted through the exhaust system from the engine compartment via the exhaust system to the rear. This disrupts the aerial system.
   In areas with poor transmission power, AM reception is disrupted or is lost at an earlier stage.
   
2. Earth strap on the luggage compartment lid
   Fault profile with effect:
   corrosion means that the earth connection between the luggage compartment lid and body is lost. This means that the luggage compartment lid oscillates and is electrically undefined.
   The reception deteriorates 2 to 3 years after production of the vehicle.
   
3. Suppressor filter for the additional brake light
   Fault profile with effect:
   in the wiring harness, EMC faults occur between the additional brake light, including supply lead, and the AM aerial.
   The reception deteriorates on braking.
   
4. Cable choke
   Fault profile with effect:
   the cable choke sets the screen of the coaxial line between the head unit and aerial diversity to earth.
   In areas with poor transmission power, AM reception is disrupted or is lost at an earlier stage.
   
   

Notes for Service department

Diagnosis instructions

The aerial diagnosis runs as follows:

The self-diagnosis of the aerial diversity is triggered in the test module of the BMW diagnosis system. The self-diagnosis includes a check of the aerial inputs on the basis of a current measurement (direct current). If a fault is found, the aerial diagnosis aborts after the self-diagnosis.

If the self-diagnosis has a positive result, the FM aerials are specifically activated and evaluated with regard to field strength (check of the aerials).

Diagram of aerial diagnosis:

Subject to change.