| 摘要 |
PURPOSE:To prevent deterioration of inside-receiving-band frequency characteristics due to a change at the time of gain control and the influence of quality difference in receiving frequencies, by detecting the inside-receiving-band frequency characteristics corresponding to the intensity of the electric field at the time of reception and individually controlling the tuning voltage of each tuning circuit so that frequency characteristics suitable for signal reception can be obtained. CONSTITUTION:In order to detect the inside-receiving-band frequency characteristics of an input tuning circuit 2, switching circuits 19 and 20 are respectively connected with terminals 13 and 15. By converting a frequency sweeping signal outputted from the switching circuit 20 into a DC voltage corresponding to the signal level by means of a signal level detecting circuit 12, inside-receiving-band frequency characteristics are known and the characteristics are compared with previously stored frequency characteristics so as to obtain the optimum frequency characteristics. Then, in order to detect the inside-receiving-band frequency characteristics of an inter-stage tuning circuit 4, change-over controlling signals are supplied to the switching circuits 19 and 20 and connect the circuits 19 and 20 to terminals 14 and 16. As mentioned above, by setting the switching circuits 19 and 20 to their opened states after the frequency characteristics of the input tuning circuit 2 and inter-stage tuning circuit 4 become the optimum, influences to the receiving circuit section are suppressed.
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