| 摘要 |
<p>PURPOSE:To prevent the deterioration of a circuit quality, which is caused by nonlinear distortion of the IF amplifier, by detecting an input high frequency level by the diode provided on the receiving frequency converter, and lowering the conversion efficiency of the receiving frequency converter, in case of a level which generates 2 nonlinear distortions in the IF amplifier. CONSTITUTION:A signal level which has been input to the prehigh frequency amplifier 1 is detected by a diode current of the receiving frequency converter 5 connected to the circulator 3, and when the signal level which has been detected in this way exceeds the level for generating the nonlinar by the preintermediate frequency amplifier 6 and the main intermediate frequency amplifier 7, its detected DC signal is provided to the control circuit 11. And, by the output of the control circuit 11, the variable attenuator 12 for providing a local oscillation signal from the local oscillator 4 to the circulator 3 is controlled, the conversion efficiency of the frequency converter 5 is lowered, the nonlinear distortion generated by the amplifiers 6, 7 when the input electric field to the amplifier 1 is large is prevented, and the circuit quality is elevated.</p> |
