JPS5926139B2 - Sensitivity switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sensitivity switching device for a radio receiver, and an object of the present invention is to eliminate the need to run a shielded wire from a printed circuit board to a sensitivity switching switch provided on an operating surface of a radio receiver.

2. Description of the Related Art In radio receivers, particularly FM receivers for car radios, it has been conventional practice to reduce reception sensitivity when receiving radio waves with strong electric field strength.

Usually, as shown in Fig. 1, a switch 3 is provided between the antenna 1 and the antenna tuning circuit 2, and when reducing the receiving sensitivity, the antenna tuning circuit 2 is connected to a capacitor or a resistor (shown as a capacitor 4 in Fig. 1). It is grounded through. (
In FIG. 1, the switch 3 is in a position where the sensitivity is not reduced. ) At this time, lead wires must be routed from the printed circuit board to the switch 3 provided on the operation surface of the radio receiver, but since it is a high frequency circuit, it is necessary to use a shielded wire 5 as the lead wire. However, there are disadvantages in that the S/N ratio deteriorates due to the capacitance of the shielded wire, and the shielded wire is relatively expensive. The present invention eliminates these drawbacks, and one embodiment of the present invention will be described below with reference to FIG.

1 is an antenna, and 2 is an antenna tuning circuit.

Terminal 6 is connected to a power source and maintains a high potential. Further, the terminal 6 is connected to ground via diodes D1 and D2, a resistor R1, and a switch 51. Diode D4, D2
A branch from the signal line is connected between them via a capacitor C1, and a connection point between the diode D2 and the resistor R1 is grounded via the capacitor C2. To explain the operation of this circuit, first, when the switch 51 is open, the diodes D1 and D2 are in a cutoff state, and the signal does not pass through the capacitor C1 and is in a highly sensitive receiving state.

Next, when the switch 51 is closed, the diodes D, D2 become conductive, and a direct current flows through the diodes D1, D2, the resistor R1, and the switch 51. Therefore, the received signal is sent to capacitor C1. It falls to ground via diode D2, capacitor C2 or capacitor C1, diode D1, and the power supply circuit. The resistor R1 is a resistor for adjusting the current of the diodes D4 and D2, and its value is selected to be considerably larger than the impedance of the capacitor C2, so that almost no signal flows through the resistor R1. Since the received signal falls to the ground in this way, the reception sensitivity can be lowered.
In this case, the sensitivity can be adjusted by appropriately selecting the capacitance of the capacitors C1 and C2. Note that there is no problem even if the capacitor C1 is a resistor. As described above, according to the circuit configuration of the present invention, almost only direct current flows between the resistor R1 and the switch 51, and of course it is not a signal line, so there is no need to use a shielded wire, and furthermore, the other end of the switch 51 is Since it is grounded, you only need to ground it to the chassis on the spot, and you only need one wire to connect to switch S1. Therefore,
Since only the signal lines need to be routed around, the S/N ratio is improved.

Furthermore, variations in sensitivity due to variations in the end treatment of the shielded wires are eliminated. Furthermore, since only one wire is needed to reach the switch, the area around the radio receiver's operating section can be made smaller, and although a few additional parts such as shielded wires and blind diodes are required, the overall cost is lower.

[Brief explanation of drawings]

Figure 1 is a wiring diagram showing the circuit of a conventional sensitivity switching device;
The figure is a wiring diagram showing a circuit of a sensitivity switching device in an embodiment of the present invention. Dl, D,...Diode, R1...
Resistance, S1...Switch, Cl, C2...
...Capacitor.

Claims (1)

[Claims] 1 A series circuit consisting of two diodes, a resistor, and a switch is installed between the high potential section and the low potential section, and a branch from the radio receiver signal line is connected between the two diodes via a capacitor or resistor. and a connection point between the diode and the resistor is grounded via a capacitor.