PURPOSE: To obtain a most suitable and easy-to-hear sound according to the state of reception by controlling the signal pass band width based on one of levels of the field intensity and a demodulation signal, and the noise level contained in said demodulation signal.
CONSTITUTION: When the reception field intensity of an antenna 11 is reduced, the level of an intermediate frequency signal supplied to a field intensity detecting circuit 21 is reduced. Then the output voltage level of the circuit 21 is raised up to increase the resistance values of variable resistances R21∼B23 respectively. The frequency f2 of active LPF18a is changed to f2'. When the voltage inverted to a low level is obtained from a phase inverter 23. Then the values of resistances R24∼R26 are reduced, and the cut-off frequency f1 of an active HPF18b is increased up to f1'. Thus a BPF18 is compressed symmetrically to the frequency characteristics shown by f1'∼f2 from those shown by f1∼f2.In case the noise component contained in the demodulation output signal is in creased, the output voltage of a noise level detecting circuit 22 is set at a high level. Then the frequency characteristics of the BPF18 is applied with the symmetrical compression in the same way.
HORIE NOBORU
SUZUKI YUKIROU
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