When a mobile radio terminal is connected to an external antenna as takes place, e.g. with hands-free facilities in motor vehicles, attenuation occurs on the signal path from the mobile radio terminal to the antenna and conversely. Although the quality of transmission and reception is to be improved by the external antenna, the attenuation has the effect that the maximum possible signal quality is not achieved.
In practice, the attenuation is approximately constant in the case of a cable-connected linking of the mobile radio terminal to the antenna and enables a compensation circuit having a constant gain factor to be operated. In the case of an electromagnetic capacitive or inductive coupling of the mobile radio terminal to the antenna signal amplifier and the antenna connected thereto, however, the attenuation can vary in dependence on the current operating state and the mobile radio terminal used. A predetermined constant gain factor is then not optimal for compensating for the instantaneous attenuation.
DE 10 2013 101 590 A1 describes a circuit arrangement for compensating for coupling attenuation in an antenna signal link in which a gain factor is adapted at a rate of change which is slower compared with the normal speed of an antenna signal power control loop between a connected mobile radio terminal and a base station of a mobile radio network. Due to the power control on the network side, however, the signal power of the mobile radio terminal is, in any case, first adapted to the present total attenuation between mobile radio terminal and base station so that the mobile radio terminals transmit with the minimal possible (optimal) power. This power control on the network side is supported by an additional adaptation of the gain factor for a predetermined limit range.
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