| 摘要 |
PURPOSE:To attain the improvement of a SN ratio as well as the simplification of wiring as to the sensitivity change-over unit of a ratio receiver, by reducing the number of shielding wires for connections between a printed substrate and the sensitivity change-over unit provided to the operation board of the receiver by improving the constitutions of an antenna input circuit and a tuner circuit. CONSTITUTION:While antenna 1 is connected to antenna tuner circuit 2 via diode D3, resistance R2 as an impedance element with input impedance greater than that of tuner circuit 2 is connected between the output side of diode D3 and earth. In addition, diode D3 is provided at its input side with sensitivity change-over switch S1 with its one terminal connected to power supply 6 and the circuit consisting of power limiting resistance R1 and diodes D1 and D2 connected in series, and capacitor C1 is connected between resistance R1 and the earth. Then, the switching of sensitivity is done through conducting and cutting-off of diode D3 to eliminate the variance of the terminal process of shielding wires, thereby improving the SN ratio. |
