TWOOFREQUENCY SIGNAL DISCRIMINATING CIRCUIT

摘要

PURPOSE:To make it possible to constitute a two-frequency signal discriminating circuit without a reed filter, by discriminating existence of two input signal frequencies different from each other on a basis of the level of the output voltage of an amplifier with amplitude limit. CONSTITUTION:The pilot signal demodulated in demodulator 2 is supplied as one input of phase comparator 8. Meanwhile, voltage control oscillator 10 is so constituted that the oscillation frequency can be voltage-controlled by the output obtained by making the output of phase comparator 8 into a DC in rectifying circuit 11, and oscillation frequency fVCO is selected between 922.5Hz and 982.5Hz of the pilot signal and is supplied as the other input of phase comparator 8. Phase comparator 8 outputs a low level for the input of frequency 922.5Hz lower than fVCO and outputs a high level for the input of frequency 982.5Hz higher than fVCO, thus discriminating two different frequencies.