| 摘要 |
PURPOSE:To enable a tuner itself to obtain a sufficient range of received electric field intensity, by providing a variable impedance element, controlled by a gain control signal, in the signal path extending from a radio frequency amplifier to an intermediate frequency output terminal. CONSTITUTION:A received signal supplied to input terminal 4 is selected and amplified by radio frequency circuit 5 including radio frequency amplifier 6 and supplied to mixer 7. Between this mixer 7 and output terminal 10, variable impedance means 9 is provided. So that the magnitude of the received signal will be carried in the same direction with the gain control of amplifier 6 with an AGC signal supplied from terminal 11 to amplifier 6, the means 9 varies its impedance value. Thus, AGC is exercised by both amplifier 6 and means 9 to expand the range of AGC, so that the range of the intensity of receivable electric fields can be expanded. |
