| 摘要 |
PROBLEM TO BE SOLVED: To prevent a satellite wave reception antenna receiving an excess input from being malfunctioned. SOLUTION: An output level detector 19 is connected to an output stage of a low noise block 12 and a voltage varactor diode 13 is inserted to an antenna matching circuit 14. The output level detector 19 drives a DC amplifier 20 in response to an output level to control the voltage variable capacitance diode 13. When an input level to an antenna exceeds a permissible input level, the output level detector 19 detects an excess input from an output level of the low noise block 12, controls the static capacitance of the voltage variable capacitance diode 13 mismatch the impedance of the antenna matching circuit 14 and shuts off the antenna input so as to prevent a low noise amplifier 15 from being malfunctioned.
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