| 摘要 |
PURPOSE:To always set the oscillating frequency of a local oscillating light source to a correct position by giving an intensity difference between frequency components of frequency shift modulation signals and obtaining the information setting correctly the oscillating frequency of the local oscillation light source from the intensity difference. CONSTITUTION:An intermediate frequency signal outputted from a photo receiver 7 is divided into three by a power branch device 9 via an intermediate frequency amplifier 8. One is led to a demodulation system and demodulated by a frequency discrimination detection system 10. The remaining two signals are subject to peak value detection by peak value detection circuits 3, 14 via BPFs 11, 12 and the result is inputted to a comparator circuit 15. The circuit 15 outputs a control signal 16 when the two inputs are at a prescribed level or over and it is discriminated that the peak value corresponding to the center frequency is larger to operate an intermediate frequency stabilizing system 19. A control signal 17 from the circuit 15 clamps a current injected from a bias circuit 18 to a local oscillating source 5 to a prescribed value. When the input to the circuit 15 does not satisfy this condition, the signal 17 sweeps the injection current from the circuit 18 to change the frequency of the oscillation source and continues it until the frequency is set to a proper position. |
