Functional description

A distinction is made between the following functions for the aerial diversity:

• Scan aerial diversity

  Up to 4 aerials are in operation for scan aerial diversity. However, only the aerial signal from the aerial with the best signal quality is sent to the headunit via a signal line.

  The aerial diversity with aerial amplifier is enabled by the RAD_ON signal whenever the headunit is switched on. This amplifies the high-frequency signals (HF signals) from AM and FM aerials, as well as the TV aerial (TV1) and the DAB antenna (frequency range: band III)

  The tuner in the headunit detects when a aerial diversity is installed and generates the signal required for the Diversity function on an intermediate frequency (HF) and changeover voltage. The IF signal is a copy of the radio station currently heard on a certain frequency (10.7 MHz). The intermediate frequency is evaluated by the electronics on the aerial diversity. If the system displays that the signal quality of the radio station being received on the active aerial is inadequate in terms of quality and field strength, the system switches to the next FM aerial. The automatic interference suppression of the headunit prevents any audible interruption as the aerials are switched.

  The changeover takes place with the help of direct current voltage. This is delivered by the headunit and is evaluated in the aerial diversity.

  • Direct current voltage = 0 V: AM aerial or FM aerial selected
  • Direct current voltage = 2.5 V: Diversity function enabled
  • Direct current voltage = 5 V: Diagnostic mode enabled

  In diagnostics mode, 8 V pulses are used to change over to the next aerial.

  A number of signals are simultaneously connected on the coaxial line. 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 headunit
  • Direct current voltage from headunit to aerial diversity
  • Intermediate frequency (HF=10.7 MHz) from headunit to aerial diversity as a basis for evaluating the quality of the HF signal.
• Phase aerial diversity

  Up to 2 aerials are in operation for the phase diversity.

  The aerial amplifier relays the amplified signals of the radio station received to the headunit via 2 aerial lines. The radio signals are digitized in the headunit. Then the two radio signals are superimposed and added. The radio signals are mixed so the generated output signal has a better signal quality than the best of the individual input signals.

  The corresponding components in the aerial amplifier are supplied with voltage from the downstream device (e.g. headunit) by means of inadvertent power feed via the aerial line.

  Inadvertent power feed is an electronics term. Inadvertent power feed means that the device receives its power supply from remote systems (e.g. aerial amplifier) via leads which are actually for the purpose of transmitting the signal. This makes use of the fact that the aerial signal is transmitted as AC voltage. The superimposed direct current voltage supply has no effect on the signal.

The RCS receiver (RCS stands for Remote Control Services) has a transmitter/receiver module and is integrated in the aerial diversity. This enables bidirectional communication to be established between remote key and/or ID transmitter and RCS receiver. The remote key is the key for the central locking system. The ID transmitter is the key for the central locking system on vehicles with Comfort Access. If the vehicle is equipped with Comfort Access, the vehicle can be unlocked or locked without active use of the ID transmitter and the engine can be started.

By pressing the unlocking or locking button on the ID transmitter, it transmits an encrypted remote control signal. The RCS aerial directs the remote control signal to the remote control receiver in the aerial diversity. The signal is then demodulated, processed and checked in the remote control receiver. That means: The radio signal contains a vehicle-specific constant 'value' which is checked by the remote control receiver. The information is only forwarded via the LIN bus to the Car Access System (CAS) or the front electronic module (FEM) if this constant value is correct. This means: Radio signals from other vehicles' remote keys or ID transmitters (including the same product line) do not cause the bus system to wake.

Authentication of the remote control signal is then carried out in the Car Access System (CAS) or the front electronic module (FEM). If the request is authorized, the Car Access System (CAS) or the front electronic module (FEM) wakes the vehicle and causes the vehicle to be unlocked or locked.

The following graphic shows the aerial diversity using the example of the F01.

Fig 1: Diversity Aerial And DAB Signal Line

Courtesy of BMW OF NORTH AMERICA, INC.