| 摘要 |
PURPOSE:To attain automatic gain control based on a desired signal only by judging the strength of a received radio wave based on an IF signal outputted from a teristorial trap circuit so as to control the gain of an intermediate frequency amplifier. CONSTITUTION:A radio wave from a satellite and a disturbed radio wave by an on-ground microwave line are converted into desired and disturbing signals IF by a converter 2a and a tuner circuit 4. I this case, since a disturbing signal is included in the IF signal, a changeover device 10 is turned off. That is, since the input/output sides of a teristorial trap circuit 6 are not short-circuited, the disturbing signal is attenuated by the circuit 6. Then the IF signal through the circuit 6 is inputted to a 2nd amplifier circuit 7 and an AGC circuit 11. Then the AGC voltage to control the gain of the intermediate frequency amplifier is outputted to the tuner circuit 4 and a 1st amplifier 5 and the 2nd amplifier 7 based on the desired signal stronger than the disturbing signal of the IF signal to be inputted.
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