| 摘要 |
PURPOSE:To discriminate automatically a sound intermediate frequency (SIF) signal even in case of a converter system of only one detector by providing a limiter amplifier on a pre-stage of a mixer for converting plural sound intermediate frequency signals to a single frequency, and also discriminating a frequency of its output signal. CONSTITUTION:A video detecting signal passes through a filter corresponding to the signal, among sound intermediate frequency (SIF) input filters 1, 2, 11 and 12, and only an SIF signal is inputted to a limiter amplifier 36. An output of a limiter amplifier 26 and a output of an oscillator 24 or 25 are inputted to a mixer 22, and a output becomes only the SIF signal of 5.5MHz, and detected as an audio signal by a detecting circuit of the post-stage. Also, an output of the limiter amplifier 36 is provided to a discriminating circuit 37, too, whether it is 4.5MHz is discriminated, and a switch 32 and a switch 35 are controlled.
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