BMW har en veldig avansert antennestyring.
Depending on the series, vehicle equipment and national-market version, the configuration of the aerial diversity module can vary. The aerial diversity may therefore include the following aerial connections:
FM aerials (UKW)
AM aerial (MW, KW, LW)
VICS aerial (VICS stands for Vehicle Information and Communication System; Japan navigation system)
DAB aerial (frequency range: band III)
TV 1 aerial
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.