| 摘要 |
PURPOSE:To make it possible to display stereophonic and monaural operations and also to perform operation corresponding to the lowering of a S/N ratio in a weak electric field, by providing an AM stereophonic demodulator circuit on the moat roller system with a simple stereophonic-monaural switching function. CONSTITUTION:The demodulator circuit on the moat roller system which transmits a steriophonic signal by pi/2-out-of-phase signals lagging and leading a reference signal by phase differences of pi/4 is provided with PLL circuit 32 which generates the reference signal for demodulation. This circuit 32 detects the mean level of output and input signals of LPF46 and the detection signal is applied to adder circuits 48 and 49 via change-over switch circuit 50. This circuit 50 is closed by the output of AND circuit 51 to which the outputs of LPF46, rectifier circuit 44 and change-over switch 52 are supplied to put the system in the stereophonic mode; and its output is displayed by stereo indication lamp 57 and even if the S/N lowers, operation is carried out corresponding to it. |
