Antenna Diversity
The antenna systems used on BMW vehicles use a diversity antenna system. This is a multiple antenna system, with a diversity switching module which continually monitors and selects the best antenna signal.
One antenna is connected for the AM band and three separate antennas for the FM range. The three FM signals received are switched in the diversity amplifier through to the radio cyclically via the RF line. The radio sends a feedback signal relating to the quality of the received antenna signal (the intermediate frequency signal) to the antenna diversity system. The antenna diversity system decides which of the three antennas has the best reception quality at present and switches this antenna through to the radio until the next measuring cycle is carried out. The antenna (FM1) arranged vertically in the rear window is used in the case of interference in the intermediate frequency signal.
Each vehicle uses a different antenna configuration. The AM and FM antennae are integrated into the rear window glass.
On vehicles such as the E53 and E39 sportwagon, the side window glass and rear spoiler are also used to house antenna system components.