| 摘要 |
PURPOSE:To reduce noise by extracting a part of an intermediate frequency signal, amplifying, detecting and rectifying the signal, comparing the output with a prescribed value so as to attain the stereo mode or bring the mode forcibly into the monaural mode. CONSTITUTION:The sigal received by an antenna 1 and amplified by a high frequency and intermediate frequency amplifier circuit 2 is fed to a main signal detecting circuit 3 and a sub signal detecting circuit 4 and also fed to an intermediate frequency amplifier circuit 9 of a stereo/monaural switching circuit using an electric field strength. After an output of the circuit 9 is rectified by a detection circuit 10, a DC output is compared with a reference voltage 12 by a comparison circuit 11. When the DC output of the circuit 10 is higher than the reference voltage 12, stereo changeover is attained and when lower, the mode is switched forcibly into the monaural mode by controlling a changeover circuit 13. |
