JPH0210674Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention relates to the improvement of multi-band radio receivers, especially for the MW (medium wave) band of AM broadcasting.
The present invention relates to a multi-band radio receiver that can switch reception between LW (long wave) bands. (b) Prior Art As shown in FIG. 1, a multi-band receiver is known which receives multi-band signals by switching the coils used. The multi-band receiver shown in Figure 1 is described in the "Frequency Synthesizer Technical Data Collection" published by Daiichi International Co., Ltd. on January 5, 1978.
As described on page 211, the first and second coil sections 2 are installed after the radio frequency amplification circuit 1.
and 3, and a tuning circuit consisting of first and second variable capacitance diodes 4 and 5.
Therefore, the connection midpoint between the primary coil 2a of the first coil part 2 and the primary coil 3a of the second coil part 3 is
It is connected to the power supply (+B) via the first switching diode 6, resistor 7 and switch 8,
The connection midpoint between the secondary coil 2b of the first coil section 2 and the secondary coil 3b of the second coil section 3 is connected to the power supply (+B) via the second switching diode 9, the resistor 10, and the switch 8. It is connected.
In addition, the first and second variable capacitance diodes 4 and 5
A tuning control voltage Vt is applied to , and the capacitances of the first and second variable capacitance diodes 4 and 5 are set by the voltage Vt. Now, in the receiver shown in Fig. 1, if you want to receive the first band, turn on switch 8 and turn on the first band.
and forward bias the second switching diodes 6 and 9. Then, the first and second switching diodes 6 and 9 are turned on, and the middle point of the connection between the primary coils 2a and 3a and the middle point of the connection between the secondary coils 2b and 3b are short-circuited to ground, so that the second coil section 3 becomes inoperative, the tuning frequency of the receiver is determined by the first coil section 2 and the first and second variable capacitance diodes 4 and 5, and reception of the first band is achieved. Next, when receiving the second band lower than the first band, the switch 8 is turned off, and the first and second switching diodes 6 and 9 are turned off. In that case, since the inductance of the first coil section 2 is sufficiently smaller than the inductance of the second coil section 3, the tuning frequency of the receiver is determined by the inductance of the second coil section 3 and the first and second variable capacitance diodes 4. and 5, and reception of the second band is achieved. As mentioned above, the multi-band receiver of FIG.
Since the reception band is switched depending on whether or not the second coil section 3 for the band is short-circuited, a multi-band receiver with a simple configuration can be provided. however,
During reception of the second band, the first coil section 2 is not short-circuited and is normally arranged, which has the disadvantage of deteriorating spurious characteristics due to stray capacitance and the like. Furthermore, since the multi-band receiver shown in FIG. 1 is of a single tuning type, it has the disadvantage that a difference in sensitivity occurs within the reception band, making it impossible to obtain good reception characteristics. (c) Purpose of the invention The present invention was created in view of the above points, and by making each tuning circuit of a multi-band radio receiver a double tuning type and devising a band switching circuit, The present invention aims to provide a multi-band radio receiver with good characteristics. (d) Structure of the invention The multi-band receiver according to the invention includes a first tuning circuit of a double tuning type for the first band, a second tuning circuit of the double tuning type for the second band, and a second tuning circuit of the double tuning type for the second band. a first short-circuiting means for short-circuiting a third coil section of the second tuning circuit when receiving the first band; a second short-circuiting means for short-circuiting a fourth coil section of the second tuning circuit when receiving the first band; third shorting means for shorting the first coil portion of the first tuning circuit when receiving two bands;
and fourth shorting means for shorting the second coil section of the first tuning circuit when receiving the second band. (E) Embodiment Figure 2 is a circuit diagram showing an embodiment of the present invention.
11 is a receiving antenna, 12 is for radio frequency amplification.
FET, 13 is an AGC transistor, 14 is a first tuning circuit consisting of a first coil section 15, a second coil section 16, and first and second variable capacitance diodes 17 and 18, 19 is a third coil section 20 and a fourth coil section. Coil section 21 and the first and second variable capacitance diodes 17
and 18; 22 is a first short circuit consisting of diodes 23 and 24 and a capacitor 25; 26 is a second short circuit consisting of diodes 27 and 28 and a capacitor 29; 30 is a diode 31 and 32. and a capacitor 33, 34 is a diodes 35 and 36
and a fourth short circuit 38 consisting of a capacitor 37 and a capacitor 37;
A first switch 39 supplies an operating voltage (+B) to the first and third short circuits 22 and 30 , and a switch 39 operates in conjunction with the first switch 38 to supply an operating voltage (+B) to the second and fourth short circuits 26 and 34 . This is the second switch that supplies (+B). When receiving the first band (for example, the MW band of AM broadcasting), the first and second switches 38 and 39 are switched to the contact a side, and the diodes 23, 24 of the first and second short circuits 22 and 26 are connected. 27 and 28 to put the first and second short circuits 22 and 26 into operation. Then, the first short circuit 22 causes the secondary winding 20b of the third coil section 20 and the primary winding 21a of the fourth coil section 21 to
is short-circuited in an alternating current manner, and the secondary winding 2 of the fourth coil portion 21 is short-circuited by the second short circuit 26 .
1b is short-circuited in an alternating current manner, and the third and fourth coil sections 20 and 21 become independent of the tuning frequency. Therefore, it is received by the receiving antenna 11, and the FET 12
The signal amplified by AGC transistor 13 and level-controlled by AGC transistor 13 is sent to primary winding 2 of third coil section 20.
0a, is led out to the output terminal 40 via the tertiary winding 21c of the first coil section 15, second coil section 16, and fourth coil section 21. At this time, the tuning frequency of the double-tuned first tuning circuit 14 is determined by the inductance of the first and second coil sections 15 and 16 and the capacitance of the first and second variable capacitance diodes 17 and 18. Next, when receiving a second band of a lower frequency band than the first band (for example, LW band of AM broadcasting), switch the first and second switches 38 and 39 to the contact b side, and The diodes 31 , 32, 35 and 36 of the four short circuits 30 and 34 are turned on to put the third and fourth short circuits 30 and 34 into operation. Then, the third short circuit 30 causes the primary winding 1 of the first coil section 15 to
5a is short-circuited in an alternating current manner, and the tertiary winding 1 of the second coil portion 16 is short-circuited by the fourth short circuit 34 .
6c is AC short-circuited. Said first coil part 1
When the primary winding 15a of 5 is short-circuited, the secondary winding 15b is also substantially short-circuited depending on the winding ratio,
When the tertiary winding 16c of the second coil part 16 is short-circuited, the primary winding 16a and the secondary winding 16b are substantially short-circuited according to the winding ratio, and the first and second coil parts 15 and 16 become irrelevant to the tuning frequency. Therefore, the signal obtained at the collector of the AGC transistor 13 is led out to the output terminal 40 via the third coil section 20 and the fourth coil section 21, and the tuning frequency of the double-tuned second tuning circuit 19 is The inductance of the third and fourth coil parts 20 and 21 and the first and second variable capacitance diodes 1
7 and 18.
Note that the first and second variable capacitance diodes 17 and 1
The capacitance of 8 has a value according to the control voltage Vt, and the signal obtained at the output terminal 40 is applied to a subsequent mixing circuit (not shown). (f) Effect of the invention As described above, according to the invention, when receiving the first band, the coil part of the second band is
When receiving a band, the coil section of the first band is short-circuited so that it is not related to the tuning frequency.
This has the advantage that spurious characteristics are improved and unused coils are prevented from adversely affecting the tuning frequency. Further, since the first tuning circuit and the second tuning circuit are substantially independent, there is an advantage that the design is easy even if the first and second tuning circuits are of double tuning type.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional multi-band receiver, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of main drawing numbers, 14 ...First tuning circuit, 1
5, 16, 20, 21...Coil part, 17, 18
... Variable capacitance diode, 19 ... Second tuning circuit, 22 , 26 , 30 , 34 ... Short circuit, 3
8,39...Switch.

Claims (1)

[Scope of utility model registration request] A double-tuned first tuning circuit that receives a first band signal and includes a first and second coil section and a first and second variable capacitance diode;
a double-tuned second tuning circuit that includes a coil section and the first and second variable capacitance diodes and receives a second band signal having a lower frequency band than the first band; In a multi-band radio receiver that receives the first and second bands in common by connecting the primary winding of the first coil part and the primary winding of the second coil part in series, when receiving the first band, a first shorting means for shorting the third coil section; a second shorting means for shorting the fourth coil section when receiving the first band; and a second shorting means for shorting the first coil section when receiving the second band. A multi-band radio receiver comprising: a third short-circuiting means; and a fourth shorting means for short-circuiting the second coil section when receiving the second band.