| 摘要 |
PURPOSE:To perform proper reception in comformity with a sudden change of an electric field intensity, by controlling a variable coupled circuit of a high frequency circuit and intermediate frequency circuit by means of an AGC signal. CONSTITUTION:In an area where the electric field intensity is weak, a high AGC voltage is given to varactor diodes VC1 and VC2 through a resistor R2 and it becomes difficult for high-frequency signals to pass through the diodes VC1 and VC2 because their capacities becomes smaller. Therefore, the degree of coupling between intermediate frequency transformers 3 and 4 becomes loose and their selectivity waveform becomes sharp. As a result, the broadcasting can be listened without any interference with broadcasting from adjacent stations. On the other hand, in an area where the electric field intensity is strong, a low AGC voltage is given to the diodes VC1 and VC2 and their capacities become larger, and then, a high frequency signal can easily pass through the diodes VC1 and VC2. Therefore, the degree of coupling of the transformers 3 and 4 becomes closer and the selectivity waveform becomes wider in band width. Therefore, the tone quality can be improved.
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