Roof antenna module, component description - GF82.62-P-3127RTU
MODEL 251.1 with CODE (494) USA version up to Model Year 2008
The roof antenna module is installed in the rear area beneath the headliner.
There are two versions of the roof antenna module, one without Keyless Go feature and one with Keyless Go feature (Keyless Go (code 889)).
Antenna amplifier
The antenna amplifier in the roof antenna module is configured depending to the national version. It amplifies and filters the signals for:
- AM, FM
- Radio remote control central locking (FZV)
- Keyless Go (KG)
- Weather band
- SIRIUS satellite radio (code 536)
The antenna amplifier and the roof antenna module is supplemented by the FM rear window antenna amplifier (A2/19), with one FM amplifier each for the FM2 antenna and the FM3 antenna. The amplified signals are required for the diversity feature (FM).
Antenna FM/AM/RRCL [FZV]
The FM/AM/RRCL antenna is designed as a wire antenna in the roof antenna module and is connected directly to the antenna amplifier.
- FM reception:
Filters and amplifies FM frequencies for radio reception. This also includes the weather band, a free information channel receivable over the entire country (USA) for auxiliary regional information.
Reception frequencies:
87.9 MHz up to 107.9 MHz
Weather band, 162.4 MHz to 162.55 MHz
- AM reception:
Filters and amplifies AM frequencies for radio reception. Reception frequencies:
530 kHz to 1710 kHz (medium wave only)
- RRCL reception:
The RRCL signals are demodulated and transferred directly to the rear SAM control unit (N10/8).
- KG reception:
The KG signal (authorization signal) is transferred directly to the Keyless Go control unit (N69/5).
Other purposes of roof antenna module
In addition to the antenna signals for the COMAND operating, display and control unit (A40/3), for the radio remote control central locking and for Keyless Go, the roof antenna module provides further antenna signals for communication and telematics.
These are:
- The signal for the telephone antenna for telephone calls
- The TELE AID antenna signal for emergency calls (TELE AID emergency call system (code 359))
- The GPS antenna signal for navigation (COMAND APS USA (with navigation) (code 530)) and for emergency calls
- The signals from the SDAR antenna. These signals are the terrestrial signal as well as the satellite signal for the SDAR control unit (N87/5) (SIRIUS satellite radio)
Antenna diversity feature (FM)
The diversity function serves to reduce reception interference. The diversity feature integrated into the roof antenna module serves for switching over between the FM antennas (FM1 to FM3) in order to allow the best possible reception.
First, the COMAND operating, display and control unit receives the signal from the active radio antenna module antennas. The COMAND operating, display and control unit generates an IR reference signal from the FM signal received. This reference signal is transmitted to the antenna amplifier module via a separate line.
The diversity feature checks whether the IR signal is free of interference after demodulation. If interference is present, the system automatically switches over to the next of the three FM antennas.
The switchover speed depends on the frequency at which interference occurs. This prevents continuous switchover between the antennas when FM reception is very poor. which itself would interference with reception.
Demodulation (RRCL)
Demodulation of the RRCL [FZV] signal takes place in the antenna amplifier of the roof antenna module. During demodulation, the useful signal is generated from the HF signal received. The wanted signal is transferred to the rear SAM control unit via a separate line.