| 摘要 |
PURPOSE:To achieve the stabilization of circuit and the simplification, by leading out the frequency component of the difference between two audio intermediate frequencies to produce the identifying signal. CONSTITUTION:The circuit consists of BPF21, 24 leading the signal component of the difference between two audio intermediate frequencies, amplifiers 22, 25, rectifying circuits 23, 26, and comparator 27. With this constitution, in case of different audio broadcast, the signal component of 242 kHz is led out with BPF 21, and after it is amplified at the amplifier 22, it is converted into DC signal at the circuit 23 and fed to the comparator 27. Further, in case of STEREO broadcast, the signal component in 258 kHz is picked up at BPF 24 and after amplified at the amplifier 25, it is converted into DC signal at the rectifying circuit 26 and fed to the comparator 27. The comparison circuit 27 compares the output of the circuits 23 and 24, and greater output among the boty outputs is led out as the identification signal to the output terminal 28. Thus, the presence of multiplex broadcast and the types of broadcast can easily be identified. |
