Antennas

FM antennas and AM antennas

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

The following radio antennas are installed:

• AM antenna
  
• FM1 antenna
  
• FM2 antenna
  
• FM3 antenna
  

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

Brief description of components

The following components for the antennas are described:

AM antenna

The AM antenna 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 antennas

Three FM antennas are installed.

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

Antenna amplifier with antenna diversity

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

The antenna 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 antenna diversity.
The ”antenna diversity” function is used to select one of the FM antennas for reception. If the antenna signal of this antenna deteriorates, there is an automatic switch to the next antenna.

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

FM1 -> FM2 -> FM1 -> FM3

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

Antenna diversity selects the next FM antenna 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 antennas are switched. Antenna diversity evaluates the signal quality and switches to the antenna with the best reception. A DC voltage (U_s) is used to switch between AM antenna signal, antenna diversity and diagnosis mode. The DC voltage (U_s) is generated by the radio and is evaluated in the antenna diversity.

• At U_s = 0 Volt, the AM/FM antenna is selected (or the self-diagnosis has a negative result).
  
• Antenna 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 antenna diversity to the radio
  
• DC voltage U_s from the radio to antenna diversity
  
  

System functions

The following system functions are described for the antennas:

• 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 antenna 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 antenna.
   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 antenna 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 antenna diagnosis runs as follows:

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

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

Diagram of antenna diagnosis:

No liability can be accepted for printing or other faults. Subject to changes of a technical nature