| 摘要 |
PURPOSE:To reduce noises in detuning, by providing a limiter circuit to an AM stereophonic difference signal amplifier. CONSTITUTION:An AM stereophonic broadcast wave is received by an antenna 1 and applied to an envelope detecting circuit 6 through a high-frequency amplifying circuit 2, a mixing circuit 3 and an intermediate-frequency amplifying circuit 5 to obtain a sum signal L+R. Part of the output of the intermediate- frequency amplifying circuit 5 is passed through a limiter circuit 7, a frequency detecting circuit 8, an integral circuit 9, and a low-frequency amplifying circuit 10 to obtain a signal L-R, and both the signals are converted into signals L and R through an inverting amplifier 11 and adders 12 and 13. When a stereophonic broadcast is received and complete tuning is achieved, an AND circuit 18 generated a high-level output by the outputs of a tuning-band detecting circuit 15, a carrier detecting circuit 16, and a stereophonic pilot signal detecting circuit 17, and the transistor (TR)Q1 of a stereophonic/monaural switching circuit 20 turns off. In a detuning state, the TRQ1 turns on to generate a monaural output, but the output of the amplifier 10 is decreased by a limiter 23, reducing noises in switching. |
