JPS6127228Y2 - - Google Patents

Description

[Detailed explanation of the invention] This invention is applicable to the MW (AM medium wave) band, for example.
Regarding the improvement of a multi-band radio receiver that can receive multiple bands such as the LW (AM long wave) band,
In particular, it is an object of the present invention to provide a multi-band radio receiver that is devised so that when receiving broadcast waves within one band, a receiving circuit for the other band does not have an adverse effect.

Conventionally, a multi-band radio receiver as shown in FIG. 1 is known. In FIG. 1, 1 is a primary coil for MW, 2 is a secondary coil for MW which is wound on the same ferrite as the primary coil 1, and 3 is a MW antenna tuning circuit together with the primary coil 1. Variable capacitance diode for MW, 4 is the above MW
The primary coil for LW is wound around the same ferrite core as the primary coil for LW, 5 is the secondary coil for LW, and 6 is the primary coil for LW along with the primary coil 4 for LW.
7 is the variable capacitance diode 3 for MW, which constitutes the antenna tuning circuit for
A tuning voltage input terminal 8 is used to apply a tuning voltage in common to the variable capacitance diode 6 for LW, and 8 inputs the received signal obtained to the secondary coil 2 for MW via a capacitor 9 and a diode 10. The signal obtained from the secondary coil 5 for LW is transferred to the capacitor 11
and a signal output terminal which is taken out via the diode 12, and 13 is the diode 10 for the MW.
This is a changeover switch for supplying a bias to one side of the LW diode 12 and outputting a signal via the diode 10 or 12 supplied with the bias to the output terminal 8.

In the circuit shown in FIG. 1, when receiving broadcast radio waves in the MW band, first the movable terminal of the changeover switch 13 is switched to the terminal a side. Then, the MW diode 10 becomes conductive, and the broadcast radio waves tuned by the MW antenna tuning circuit pass through the MW secondary coil 2, the capacitor 9, and the diode 10 to the output terminal 8.
is derived. Similarly, when receiving broadcast radio waves in the LW band, switch the movable terminal of the changeover switch 13 to the terminal b side, make the LW diode 12 conductive, and transmit the broadcast radio waves tuned by the LW antenna tuning circuit to the LW antenna tuning circuit. It is sufficient to lead out to the output terminal 8 via the secondary coil 5, capacitor 11, and diode 12. The tuning frequency of the MW antenna tuning circuit and the LW antenna tuning circuit is determined by variable capacitance diode 3 for MW and variable capacitance diode 6 for LW, respectively.
is determined by the change in the capacitance of , that is, the change in the tuning voltage applied to the tuning voltage input terminal 7.

The circuit shown in FIG. 1 operates as described above.
Although it is possible to switch and receive broadcast waves in the MW band and LW band, it has various drawbacks. First, the first
In the circuit shown in the figure, the antenna coil is wound around the same ferrite bar, and the LW band (approximately
145KHz~365KHz) and MW band (535KHz~
1605KHz) are close to each other, one antenna tuning circuit has a M
They have the disadvantage that they influence each other due to coupling and the like, leading to a decrease in Q, resulting in a decrease in sensitivity.

Furthermore, the conventional circuit shown in FIG. 1 has the disadvantage of deteriorating spring characteristics. Because the antenna coils for MW and LW are wound around the same ferrite core, M-coupling occurs, and during reception of the MW band, the received radio wave signal of the LW band tuned by the LW antenna tuning circuit and its The harmonics are the M
The signal is supplied to the MW antenna tuning circuit via coupling, and is led out to the output terminal 8 via the capacitor 9 and diode 10 together with the received radio wave of the MW antenna tuning circuit. Similarly, during LW band reception, the MW tuned by the MW antenna tuning circuit
The received radio waves and harmonics of the band are supplied to the LW antenna tuning circuit via the M coupling, and are led out to the output terminal 8 via the capacitor 11 and the diode 12 together with the received radio waves of the LW antenna tuning circuit. Therefore, the relationship between the harmonics of the LW band that become unnecessary signals when receiving MW, the local oscillation frequency for MW, and its harmonics, the MW signal that becomes an unnecessary signal when receiving LW, the harmonics of the MW signal, and the local oscillation frequency for LW. Also, the spring characteristics deteriorate due to the relationship with harmonics of the local oscillation frequency.

The present invention has been developed in view of the above points, and will be described below based on embodiments with reference to the drawings. FIG. 2 shows one embodiment of the present invention, and circuit elements that are the same as those in FIG. 1 are given the same figure numbers and their explanations will be omitted. Therefore, in Figure 2, 14
is the first control transistor whose emitter is grounded,
15 is the collector of the first control transistor 14;
A backflow blocking diode 16 inserted between the cathode of the variable capacitance diode 3 for MW;
17 is a second control transistor whose emitter is grounded; 18 is a terminal between the collector of the second control transistor 17 and the LW variable capacitance diode 6; The bases of the first and second control transistors 14 and 17 are commonly connected to the terminal a of the changeover switch 13 with a resistor inserted between the cathode and the base of the first and second control transistors 14 and 17.

Next, the operation will be explained. Now, in order to receive MW broadcasting, when the movable contact of the changeover switch 13 and contact a are brought into contact, the power supply voltage (+Vcc) is applied as a bias to the MW diode 10, and a signal tuned by the MW tuning circuit is output. available at terminal 8.
At the same time, the power supply voltage is applied to the bases of the first and second control transistors 14 and 17, making the first and second control transistors 14 and 17 conductive. When the first control transistor 14 becomes conductive, its collector becomes approximately at ground potential, and no forced voltage is applied to the MW variable capacitance diode 3. Therefore, the MW variable capacitance diode 3 has a capacitance that corresponds to the tuning voltage applied to the tuning voltage input terminal 7, and the tuning frequency of the MW antenna tuning circuit also has a value that corresponds to the capacitance. On the other hand, when the second control transistor 17 becomes conductive, its collector becomes approximately at ground potential, and the cathode voltage of the LW variable capacitance element 6, which was determined by the tuning voltage applied to the tuning voltage input terminal 7, decreases. Therefore, the capacitance of the LW variable capacitance element 6 increases, and the tuning frequency of the LW antenna tuning circuit shifts to a lower frequency range. By reducing the value of the resistor 18 connected between the cathode of the LW variable capacitance element 6 and the collector of the second control transistor 17, the tuning frequency of the LW antenna tuning circuit becomes small. The value of the resistor 18 may be an appropriate value such that the tuning frequency of the LW antenna tuning circuit is below the lower limit of the LW band, or it may be omitted.

By making the second control transistor 17 conductive and setting the tuning frequency of the LW antenna tuning circuit below the lower limit of the LW band, the LW
The effect of the MW circuit on the MW circuit is almost eliminated, and therefore, drawbacks such as decreased sensitivity and deterioration of spurious characteristics are greatly improved.

Next, reception of LW broadcasting will be explained. When receiving LW broadcasting, connect the movable contact of the changeover switch 13 to contact b. Then, the power supply voltage (+
Vcc) forward biases the LW diode 12,
A signal tuned by the LW tuning circuit is led out to the output terminal 8 via the LW diode 12.
Then the first and second control transistors 14 and 1
7 becomes non-conductive because no voltage is applied to its base, and the LW variable capacitance element 6 is controlled only by the tuning voltage applied to the tuning voltage input terminal 7, and the tuning frequency of the LW antenna tuning circuit is also the same as the tuning frequency. The value depends on the voltage. On the other hand, when the first control transistor 14 becomes non-conductive, the forced voltage applied to the forced voltage input terminal 16 is applied to the cathode of the MW variable capacitance element 3 via the reverse current blocking diode 15. The forced voltage is set to be sufficiently larger than the maximum tuning voltage in the MW band range applied to the tuning voltage input terminal 7, and therefore, the MW
The capacitance of the MW variable capacitance element 3 becomes extremely small, and the tuning frequency of the MW antenna tuning circuit is
It is larger than the upper limit of the MW band.

Therefore, the MW circuit has no influence on the LW circuit, and sensitivity, spurious characteristics, etc. are improved.

As described above, the present invention is useful with many advantages and is practical as it can achieve its purpose with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional multi-band radio receiver, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of main drawing numbers, 1, 2, 4, 5...coil,
3, 6...variable capacitance diode, 14, 17...
control transistor.

Claims (1)

[Scope of utility model registration request] In a multi-band radio receiver using a variable capacitance diode as a tuning element, a first antenna tuning circuit including a first antenna coil and a first variable capacitance diode for receiving a first band signal; a second antenna tuning circuit comprising a second antenna coil and a second variable capacitance diode for receiving a second band signal lower than the first band;
a first forced voltage application means for forcibly setting the tuning frequency of the second antenna tuning circuit below the lower limit of a second band; and tuning of the first antenna tuning circuit when receiving a signal of the second band. A band radio receiver comprising a second forced voltage application means for forcing the frequency to be equal to or higher than the upper limit of the first band.