| 摘要 |
PURPOSE:To detect a desired station in a LOCAL (low sensitivity) mode in a shorter time than a DX (high sensitivity) with an auto-tuning type radio receiver containing a sensitivity switch circuit, by operating changeover switches simultaneously with interlocking among the sensitivity switch circuit, a sweep time setting circuit and an integration circuit respectively. CONSTITUTION:Resistances R3 and R4 are connected in series, and a series circuit of a resistance R5 and a changeover switch S1 is connected to a joint of the resistances R3 and R4. Thus a sensitivity switch circuit 14 is obtained. A series circuit of a resistance R2' and a changeover switch S2 is connected in parallel to a resistance R2 of a parallel circuit of a capacitor C2 and the R2 of a sweep time setting circuit 13. Then a series circuit of a resistance R1' and a changeover switch S3 is connected in parallel to a resistance R1 of an integration circuit 11. The switches S1, S2 and S3 are operated with interlocking to each other. When the S1 of the circuit 14 is turned on, the level is lowered for the signal which is supplied to a high frequency amplifying circuit 2. As a result, the sweep stop sensitivity is reduced. At the same time, the S2 is also turned on. This reduces the time constant of the circuit 13 and then accelerates the sweep speed. |
