Aerial Amplifier With Diversity / Radio Reception

Radio reception

Unlike a domestic radio, a car radio is subject to constantly changing reception conditions (reflections). At one point reception is excellent, however, reception may be very poor after just a short distance has been covered. Reception can be best tested by driving in a circle. In this way, the rear window aerial is pointed in all directions.

Rear window aerial with aerial diversity

One aerial for AM (amplitude-modulated, medium wave) and three separate aerials for the FM range (frequency-modulated, VHF, FM1, FM2, FM3) are connected in the aerial diversity option. The diversity amplifier only operates in FM mode and is powered by the radio via an internal conductor of the intermediate frequency cable (IF cable). The three FM signals received are switched in the diversity amplifier through to the radio cyclically via the RF line. Only when the FM band is selected, the radio sends feedback concerning the quality of the aerial signal received (via the intermediate frequency signal) to the aerial diversity system. The aerial diversity system decides which of the three aerials has the best reception quality at present and switches this aerial through to the radio until the next measuring cycle is carried out. The aerial (FM1) arranged vertically in the rear window is used if no intermediate frequency signal (IF signal) is received.

Driving in circle

The diversity function of the aerial amplifier can be checked by driving in a circle. For this purpose, the vehicle must slowly trace the circle.

Procedure

Set station in FM range

Disconnect intermediate frequency cable (IF cable, smaller coaxial connector) from the aerial amplifier/diversity amplifier

Slowly drive in a circle until reception quality of the station selected deteriorates and then stop the vehicle (if there is no deterioration in reception with the station selected, repeat the same procedure with a different, more suitable station)

Once a suitable station has been found and the point is reached where reception of the station is poor, the intermediate frequency cable (IF cable) must be reconnected and, as a result, reception should improve significantly.
Reconnecting the intermediate frequency cable allows the diversity function in the aerial amplifier to select the aerial structure with the best reception. When the intermediate frequency cable is disconnected, only one aerial structure is used and no search is implemented for the best possible aerial structure.