| 摘要 |
PURPOSE:To set an input impedance in the prescribed frequency band to a constant value in terms of a circuit for fetching a signal of the specific frequency by connecting an element for constituting an input impedance and a reverse circuit to an input circuit of said circuit. CONSTITUTION:A high Q tuning circuit for tuning a voice carrier is constituted of capacitors C12, C13 and C14 and a coil L8, while a high Q trap circuit for tuning a video carrier of an adjacent channel is constituted of capacitors C10 and C11 and a coil L7. By connecting serially a parallel resonance circuit for consisting of a coil L20 and a capacitor C20 to a resistance R20, a reverse circuit of an input tmpedance of said circuit is constituted and connected to a terminal 21. This type of circuit can be expressed by an equivalent circuit as shown in attached papers. When the coil L20, the capacitor C20 and the resistance R20 are selected so as to satisfy the prescribed conditions, the input impedance can be constant in the prescribed frequency band.
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