| 摘要 |
PURPOSE:To enable a supervision over the operations of both a receiving high- frequency amplifier and receiving local oscillator, by inputting the output of the receiving local oscillator to a mixer together with a received signal after two-wave common amplification and then by monitoring the mixture electric current. CONSTITUTION:Received signal fr is inputted to coupler 12 via input circuit 11 and output fL of local oscillator 13 is also inputted to coupler 12, which outputs signals fr and fL. Those two signals are amplified in common by high-frequency amplifier 14 and then sent to coupler 15. Coupler 15 separates signal fr and output fL mutually and they are inputted to frequency mixer 19 by way of filters 17 and 16. The output of mixer 19 is sent to the next stage via intermediate-frequency amplifying circuit 20. In the abovementioned circuit, no input is supplied to mixer 19 if amplifier 14 is not in operation and the mixture electric current never reaches a fixed value unless oscillator 13 is in operation. Therefore, mixer 19 monitors the mixture electric current to make sure that both amplifier 14 and oscillator 13 are in operation. |
