BMW 7 Series: FM Antenna Diversity

In the F01/F02, an FM antenna diversity is standard equipment.

The FM antenna diversity comprises:

• FM1, FM2 and FM3 antennas
• FM antenna amplifier with diversity module

The FM1 to FM3 antennas route their RF signal to the antenna amplifier in the antenna diversity module.

The signal quality of the currently selected FM antenna (FM1 to FM3) is now evaluated in the antenna diversity module.

The high-frequency signal from the active FM antenna at any particular time is fed by the antenna amplifier and antenna diversity module via a coaxial cable to the tuner module in the head unit.

Fig. 111: Tuner Module Input Frequency Graph

INDEX REFERENCE CHART

1. Station frequency prior to selection by customer

The tuner module in the CIC is now informed of the station selected by the customer using iDrive. As a result, the tuner module in the CIC selects the matching frequency. This is done by setting a bandpass filter. The bandpass filter suppresses all frequencies above and below the selected station frequencies.

Fig. 112: Frequency Graph After Station Selection

INDEX REFERENCE CHART

1. Station frequency after selection by customer

The remaining RF signal is then demodulated in the tuner and output in the form of an audio signal through the speakers.

The tuner module in the CIC detects that an antenna diversity module is installed and generates the changeover voltage (Us) and the signal of the intermediate frequency (IF) necessary for diversity operation.

Selection of the individual antennas (diversity function)

The intermediate frequency is an RF signal (10.7 MHz) and is evaluated by the electronic circuitry inside the diversity module. The antenna diversity module will switch to the next FM antenna if the signal quality of the current radio station on the active antenna deteriorates to a certain level in terms of quality and field strength.

The changeover takes place in a way that no interruption can be heard.

Selection of the various reception modes of the antenna diversity module

The changeover between AM reception, FM diversity operation and diagnostic mode occurs in response to the DC voltage Us.

This is performed in the head unit and analyzed in the diversity module with the following criteria:

• Diversity mode is active when Us = 2.5 V.
• AM mode is active, or the FM1 antenna is selected, when Us = 0 V.
• Diversity mode is active at Us = 5 V.
• The changeover in diagnosis mode to the next antenna takes place by 8 V pulses.

AM Diversity

For AM services (SW, MW and LW) no antenna diversity system is provided as there is only one AM antenna.

Remote Control Services (FBD)

In addition to the antennas listed above there are the antennas for the remote control services (FBD) and the nine antennas for comfort access (four antennas on the outside and five in the interior).

FM Rejector Circuit

The two rejector circuit modules for FM are located on the left and right of the rear window.

One rejector circuit is intended for the power supply of the lower section of the rear window.

The second circuit is for the upper section of the rear window defogger which is powered by the AM restrictor described in the following pages.

INDEX REFERENCE CHART

1. Rejector circuit on left side Terminal 31, rear window: lower section of rear window
2. Threaded ground connection to vehicle body
3. Rejector circuit on left-side Terminal 31, connection, vehicle wiring harness

Fig. 113: Identifying Left Side Antenna Amplifier

INDEX REFERENCE CHART

1. Rejector circuit on right side Terminal 30, rear window: lower section of rear window
2. Threaded ground connection to vehicle body
3. Rejector circuit on right side Terminal 30, connection, vehicle wiring harness

Fig. 114: Identifying Right Side Antenna Amplifier

HBL Filter

The HBL filter is fitted to suppress interference pulses from the additional brake light during radio reception.

HBL stands for high-level brake light (third brake light).

A pulse-modulated signal (PWM) activates the third brake light. This kind of activation (PWM rectangular signal) can cause high-frequency interference. This is especially common with AM reception. The reason for this is that the audio information is contained in the amplitudes in the AM signal.

INDEX REFERENCE CHART

1. HBL filter - connection to additional brake light and for powering the diversity module with antenna amplifier
2. Securing screw with ground connection
3. HBL filter, connection to vehicle wiring harness

Fig. 115: Identifying HBL (High Level Brake Light) Filter

AM Restrictor

AM reception has been improved on the F01/F02.

Due to the great distances with relatively few radio broadcasting towers, in less populated areas of the US AM radio is more accessible than FM radio.

Interference frequencies from the vehicle electrical system pose reception problems in terms of the quality of AM radio. In an unrestricted antenna system, these interference frequencies spread from the vehicle electrical system through the power supply to the rear window defogger into the antenna system.

The AM restrictor was specially developed to address this issue.

The AM restrictor supplies voltage to the upper section of the rear window. In addition, the rejector circuit components provide sound quality filtering.

The main component is a coil which acts as an extremely high resistance to RF signal, resulting in significantly improved AM reception.

Fig. 116: Identifying AM Restrictor Components

INDEX REFERENCE CHART

1. Interference suppression coil for AM range
2. Positive supply to rear window
3. Positive supply from vehicle wiring harness
4. Ground supply from vehicle wiring harness
5. Ground supply to rear window

Roof Antenna

The roof antenna housing is always fitted regardless of the equipment options on the vehicle.

The roof antenna includes the following components:

• Mobile phone antenna
• Telematics Control Unit (TCU) telephone antenna
• GPS antenna
• SDARS satellite radio reception antenna

Fig. 117: Identifying F01/F02 Roof Antenna Components

INDEX REFERENCE CHART

1. Telephone antennas for telematics control unit (TCU)
2. Telephone antennas for mobile phone
3. GPS antenna
4. SDARS antenna for satellite reception
5. SDARS signal, satellite and terrestrial (violet connection)
6. Telephone signal: mobile phone; metal color connector; Bordeaux violet coding connector
7. GPS signal (blue color connector)
8. Telephone signal: TCU; metal color connector; grey color coding connector

READ NEXT: