Diversity Aerial
Diversity Aerial
Diversity aerial
The aerial diversity with aerial amplifier is a system which automatically switches to the next aerial if the quality of radio signal received on the active aerial is inadequate.
The signal from the received radio station is amplified in the aerial diversity before being passed to the tuner in the headunit.
Depending on national-market version, the configuration of the aerial diversity module can vary. Depending on the level of vehicle equipment and national-market version, the aerial diversity may contain aerial amplifiers for the following aerials:
- 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
In the US version, the aerial amplifier also supports Weatherband frequencies. Weatherband is transmitted on seven channels in the frequency range of 162.400 MHz to 162.550 MHz. The Weatherband tuner is incorporated in the headunit of the FM module.
Functional description
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 Us. 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 Us direct current voltage. This is delivered by the headunit and is evaluated in the aerial diversity.
- Us = 0 Volt: AM aerial or FM aerial selected
- Us = 2,5 Volt: Diversity function enabled
- Us = 5 Volt: 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
- Us 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.
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. This information is only passed down the LIN bus to the Car Access System if this constant value is correct. This means: Radio signal from remote keys and/or ID transmitters for other vehicles (including from the same product line) will not 'wake up' the Car Access System.
Authentication of the remote control signal is then performed within the Car Access System. If the request is duly authorized, the Car Access System wakes up the vehicle and either locks or unlocks the vehicle, as appropriate.
Structure and inner electrical connection
The aerial diversity is connected to the vehicle electrical system by means of a 6-pin plug connection.
The aerial diversity is switched on via the RAD_ON line and is supplied with a direct current voltage.
The LIN bus connects the remote control receiver to the Car Access System (CAS).
The rear power distribution box links the remote control receivers to terminal 30.
Nominal values
Observe the following setpoint values for the aerial diversity:
Size Value
Voltage range 9 to 16 V
Internal resistance 6.8 k ohms
Temperature range -40 to 85 °C
Diagnosis instructions
Failure of the component:
If the aerial diversity fails, the following behavior is to be expected:
- Fault entry on Car Information Computer (CIC)
A function check of the aerial diversity can be run using the BMW diagnosis system.
Path: Function network > Body > Audio > Radio > Radio reception > Aerial diagnosis
A function check of the remote control receiver can be run using the BMW diagnosis system.
Path: Function network > Body > Locking and security functions > Central locking system> RCS receiver We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.