JPS6123903Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a receiver for receiving audio multiplex broadcasting.

As is well known, the TV audio multiplex broadcast receiver is
A multiplex composite signal in which a main channel signal in a band from 0 KHz to 15 KHz, a sub channel signal in a band from 16 KHz to 47 KHz, and a control signal at 55.125 KHz are combined is received, and the main channel signal and sub channel signal are respectively After demodulating, during stereo broadcasting, the matrix circuit is operated by the 982.5Hz AM signal included in the control signal to generate the main channel signal (sum signal L of the left audio signal and right audio signal).
+R) and the sub-channel signal (difference signal L−R between the left audio signal and the right audio signal),
It obtains left and right audio signals, and is included in the control signal when broadcasting different programs, for example in two languages.
The configuration is such that either one or both of the main channel signal and the sub-channel signal is output as is as the main channel audio signal or the sub-channel audio signal under control using a 922.5 Hz AM signal. By the way, in such TV audio multiplex broadcasting, the SN ratio of the sub-channel signal is lower than that of the main channel signal, and especially when the input electric field strength is low, the SN ratio of the sub-channel signal decreases significantly, and therefore When receiving program broadcasts on the subchannel, high-frequency noise may become noticeable and may be unpleasant to the ears. Also, since the main channel signal and sub-channel signal are added and subtracted even when receiving stereo broadcasting, the high-frequency signal is lower than when receiving monaural broadcasting (main channel signal only) due to the low SN ratio of the sub-channel signal. Noise increases, and this tendency becomes particularly noticeable when the input electric field strength is low. This idea was made in view of the above circumstances, and in a multiplex broadcast receiver having a main channel signal, a sub-channel signal, and a control signal, each output path of the matrix circuit constituting the multiplex broadcast demodulation circuit is A frequency characteristic variable circuit is individually inserted, and when the matrix circuit is in an operation mode in which a sub-channel signal component appears on its output side and the received electric field strength of the multiplex broadcast wave is less than a predetermined value, the frequency characteristic variable circuit is inserted. In this way, when the matrix circuit is in an operation mode in which the component of the sub-channel signal appears on its output side, that is, in the stereo operation mode and the different program operation mode, By operating the frequency characteristic variable circuit when the electric field strength level is low, it is possible to achieve the optimum reception condition by suppressing high-frequency noise when receiving stereo broadcasts and receiving different program broadcasts. .

Hereinafter, embodiments of this invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram for explaining the basic principle of the receiver of this invention, schematically showing the latter part of the multiple signal demodulation circuit of the receiver, particularly the part after the matrix circuit. In Figure 1,
FM demodulated main channel signal and also FM
The demodulated sub-channel signal is input to a main channel signal input terminal 1A and a sub-channel signal input terminal 1B of the matrix circuit 1, respectively. This matrix circuit 1 is
When receiving stereo broadcasting, the sum signal L+ of the left channel audio signal L and the right channel audio signal R
The main channel signal which is R and the sub channel signal which is the difference signal LR are added and subtracted to output the addition result of both signals to the left output path 2L, that is, the left channel audio signal L of stereo broadcasting, and the right channel signal Outputting the result of subtraction of both signals, that is, the right channel audio signal R of stereo broadcasting, to the output path 2R,
On the other hand, when receiving a different program broadcast, the switching operation is performed so that the main channel signal is output as is to the left output path 2L without performing addition or subtraction as described above, and the sub channel signal is output as is to the right output path 2R. It is said to be composed of However, in reality, a different type program output switching circuit (not shown) is inserted on the output side of the matrix circuit 1 to appropriately switch between the left output path 2L and the right output path 2R. Both output systems 2L and 2R as appropriate during program broadcasting.
It is possible to output only the main channel signal from , or to output only the sub-channel signal from both output paths 2L and 2R, or even to output the main channel signal from one path and the sub-channel signal from the other path. It is usually configured so that Furthermore, the left side output system 2L and the right side output system 2R each include a frequency characteristic variable circuit 3L that can change the frequency characteristics in the system.
3R is inserted, so each output path 2
The L and 2R signals are transmitted through these frequency characteristic variable circuits 3.
It is output from the left audio output terminal 4L and the right audio output terminal 4R via L and 3R. These frequency characteristic variable circuits 3L and 3R are controlled according to the operation mode of the matrix circuit 1 constituting the multiplex broadcast demodulation circuit and the received electric field strength of the receiver. In other words, the frequency characteristic variable circuit 3
L and 3R determine the optimum reception condition depending on whether the matrix circuit 1 is in stereo operation mode, heterogeneous program operation mode, or monaural operation mode, and on the magnitude of the received field strength of multiplex broadcast waves. It changes the frequency characteristics of the output signal in response to the signals applied to the control input terminals 9, 9 so that The collector emitter of a transistor ₈ and a resistor _R2 are connected in series to the ground circuit of a capacitor _C1 of a low-pass filter 7 consisting of a resistor R1 and a capacitor _C1 , and a diode D is connected to the base of the transistor 8. ₁ and control input terminal 9 via resistor R ₃
It is sufficient to connect the bias resistor _R4 . Here, the frequency characteristics of the low-pass filter 7 may be set so that the cut-off frequency is approximately 15 KHz, as shown by the solid line in FIG. 3, for example. Note that the broken lines in FIG.
The frequency characteristics of R are shown. When using the frequency characteristic variable circuits 3L and 3R as described above, a low level signal is applied to the control input terminal 9 under normal conditions, that is, when the SN ratio is relatively good and there is little noise in the high frequency range. In a receiving state where the ratio is poor and noise in the high frequency range is noticeable, a high level signal is applied to the control input terminal 9. If you do this,
Under normal conditions, the transistor 8 is not conductive, so the low-pass filter 7 does not operate, so the input terminal 5
The input signal is output to the output terminal 6 as it is. On the other hand, in a reception state where the signal-to-noise ratio is poor and high-frequency noise is noticeable, the transistor 8 becomes conductive and the low-pass filter 7 operates. The signal is output from the output terminal 6 in a state in which high-pitched noise is removed, and therefore a good reception condition is obtained. FIG. 4 shows the basic configuration of a circuit for controlling the frequency characteristic variable circuits 3L, 3R, and a reception mode switching circuit 13 is connected to the control input terminals 9, 9 of each frequency characteristic variable circuit 3L, 3R. and the field strength level detection circuit 10 are connected via an AND gate 12, and furthermore, the 982.5Hz detection circuit 11A and the 922.5Hz detection circuit 11B of the multiplex control signal detection circuit 11 are connected to the input side of the reception mode switching circuit 13. The output side of is connected.

The multiplex control signal detection circuit 11 detects a 55.125KHz multiplex control signal included in the multiplex composite signal, and further detects a 982.5Hz or 922.5Hz AM signal included in the 55.125KHz multiplex control signal. It is usually a matrix circuit 1.
It can also be used to control the switching operation of the auxiliary channel and squelch control of the sub-channel demodulation path. Here, if the broadcast signal mode from the broadcast station is monaural broadcast, the received radio waves do not include a multiplex control signal, and therefore both the 982.5 Hz detection circuit 11A and the 922.5 Hz detection circuit 11B detect the AM signal. do not. On the other hand, if the broadcast signal mode from the broadcast station is stereo broadcast,
A multiplex composite signal including a 55.125KHz multiplex control signal is input, and this multiplex control signal includes a 982.5Hz multiplex control signal.
Since AM signal is included, 982.5Hz detection circuit 11A
operates and outputs a stereo broadcast reception state detection signal. Furthermore, if the broadcast signal mode from the broadcast station is heterogeneous program broadcasting, a multiple composite signal including a 55.125 kHz multiple control signal is input, and this multiple control signal includes a 922.5 Hz AM signal. The 922.5Hz detection circuit 11B operates and outputs a different program broadcast reception state detection signal.

The receiving mode switching circuit 13 is for selecting the receiving mode of the receiver from among a stereo broadcast receiving mode, a different program broadcast receiving mode, and a monaural broadcast receiving mode, and controls the matrix circuit 1 according to the selected receiving mode. The receiving mode switching circuit 13 is usually configured to perform both manual switching of the receiving mode and automatic switching for automatically selecting the receiving mode according to the detection signal from the multiplex control signal detection circuit 11. The receiving mode switching circuit 13 also normally switches between the left output path 2L and the right output path 2R, particularly when a different program is selected, to appropriately select a state in which either or both of the main channel signal and the sub-channel signal are received, but this path is not shown here.

Here, the multiplex control signal output circuit 11
When a stereo broadcast reception state detection signal is obtained by detecting a 982.5Hz AM signal, and the reception mode switching circuit 13 selects the stereo broadcast reception mode, the matrix circuit 1 enters the stereo operation mode, and the matrix circuit 1 switches to the stereo operation mode. A state is reached in which the left channel audio signal L and the right channel audio signal R appear on the left and right output paths 2L and 2R of the circuit 1, respectively. In this stereo operation mode, the reception mode switching circuit 13 outputs a signal capable of controlling the variable frequency characteristic circuits 3L and 3R to the operating state. For example, the frequency characteristic variable circuits 3L and 3R are
In the configuration shown in the figure, the reception mode switching circuit 13 outputs a high level signal. On the other hand, when the multiplex control signal output circuit 12 detects a 922.5 Hz AM signal and outputs a different program broadcast reception state detection signal, and the reception mode switching circuit 13 selects the different program broadcast reception mode. , the matrix circuit 1 enters the different program operation mode, and the left and right output paths 2 of the matrix circuit 1
A state is reached in which the main channel signal, the sub-channel signal, or both appear on L and 2R. In this heterogeneous program operation mode, the reception mode switching circuit 13 outputs a signal, for example, a high-level signal, which can control the variable frequency characteristic circuits 3L and 3R to the operating state.

After all, when the matrix circuit 1 is in an operation mode (stereo operation mode and different program operation mode) in which the component of the sub-channel signal appears on its output side, the reception mode switching circuit 1
3 outputs a signal capable of controlling the frequency characteristic variable circuits 3L and 3R to an operating state, for example, a high-level signal. In addition, in operation modes other than the above, the frequency characteristic variable circuit 3 is switched from the reception mode switching circuit 13.
A signal that can control L and 3R into an operating state is not output. That is, when using the variable frequency characteristic circuits 3L and 3R of FIG. 2, for example, the output of the reception mode switching circuit 13 is at a low level.

On the other hand, the electric field strength level detection circuit 10 detects the signal strength at an intermediate frequency amplification stage (not shown) of the receiver, and when the signal strength level becomes less than a predetermined value, the frequency characteristic variable It is configured to output a signal capable of controlling the circuits 3L and 3R into an operating state, for example, a high-level signal. When the signal strength level is a high level exceeding a predetermined value, the output of the field strength level detection circuit 10 is a signal that does not put the frequency characteristic variable circuits 3L and 3R into an operating state, for example, a low level signal.

In the configuration shown in FIG. 4 as described above, when the matrix circuit 1 is in an operation mode in which the component of the sub-channel signal appears in its output, that is, in the stereo operation mode or the different program operation mode, and the electric field strength is When the level is below a predetermined level, the control input terminals 9, 9 of the frequency characteristic variable circuits 3L, 3R are input from the AND gate 12.
A signal for controlling the frequency characteristic variable circuits 3L, 3R to the operating state, for example, a high level signal, is added to the frequency characteristic variable circuits 3L, 3R.
The low pass filter 7 operates, and the output path 2L,
The high frequency range of the signal in 2R is cut, reducing high frequency noise.

FIG. 5 shows the overall configuration of a multiplexed signal demodulation circuit of a receiver according to an embodiment of the present invention to which the basic configuration shown in FIG. 4 is applied. signal (for main carrier)
(obtained by performing FM detection) is applied to an amplifier 16, and a sub-channel signal included in the multiplexed composite signal is extracted by a bandpass filter 17 having a frequency characteristic of 31.5KHz±15KHz.
It is demodulated by an FM demodulator 19 through an amplitude limiting circuit 18, and is applied to a low-pass filter 22 with a cut-off frequency of 15 KHz through a de-emphasis circuit 20 and a squelch circuit 21.
2 is applied to the sub-channel signal input terminal 1B of the matrix circuit 1. The main channel signal included in the output of the amplifier 16 is applied to a low-pass filter 25 with a cutoff frequency of 15 KHz via a de-emphasis circuit 23 and an amplifier 24, and from the output terminal of the filter 25 to the main channel signal input terminal 1A of the matrix circuit 1. added to. On the other hand, a 55.125 KHz multiplex control signal is taken out from the stage before the aforementioned bandpass filter 17, and is applied to the AM detector 27 via the band amplifier 26, where an AM signal of 982.5 Hz or 922.5 Hz is taken out. Then, the 982.5Hz AM signal is detected by the 982.5Hz lead filter 28, and the rectifier circuit 29
It becomes a DC voltage and is applied to the control circuit 30, and then passes through the reception mode switching circuit 13 to the matrix circuit 1.
control. That is, when a 982.5 Hz AM signal indicating that a stereo broadcast is being received is detected and the stereo broadcast reception mode is selected in the reception mode switching circuit 13, the matrix circuit 1 switches between the main channel signal and the sub channel signal. Control is performed to add and subtract channel signals to create a stereo reception state. On the other hand, the 922.5Hz AM signal taken out from the AM detector 27 is detected by the 922.5Hz lead filter 31, converted into a DC voltage by the rectifier circuit 32, applied to the control circuit 33, and passed through the reception mode switching circuit 13. Controls the squelch circuit 21. In other words, a 922.5 Hz AM signal indicating that a different program broadcast is being received is detected, and the reception mode switching circuit 13 selects the different program broadcast reception mode and selects the subchannel signal program as the program to be received. If not, squelch circuit 2
1 to shut off the subchannel signal path.

Furthermore, in the example shown in FIG. 5, the left output path 2L and right output path 2R of the matrix circuit 1 are provided with frequency characteristic variable circuits 3 and 3, respectively, as described above.
L and 3R are inserted, and the outputs of these frequency characteristic variable circuits 3L and 3R are respectively connected to an amplifier 34.
The signal is supplied to the left audio output terminal 35L and the right audio output terminal 35R via L and 34R. And each frequency characteristic variable circuit 3L, 3
R has a frequency characteristic that is determined by the frequency characteristic switching circuit 36.
It is configured to be controlled by the reception mode switching circuit 13 and the electric field strength level detection circuit 10 described above. That is, the frequency characteristic switching circuit 36 has two states: a state in which the low pass filters 7 (see FIG. 2) of the frequency characteristic variable circuits 3L and 3R are forcibly operated, and a state in which the low pass filters 7 are also forcibly inoperative. This frequency characteristic switching circuit 36 is used to select one of three states: and a state in which operation/non-operation of the low-pass filter 7 is automatically controlled depending on the reception state.
When the automatic control state is selected in , the signal from the field strength level detection circuit 10 and the signal from the reception mode switching circuit 13
frequency characteristic variable circuit 3 (including a signal corresponding to the reception mode set to 3 and a signal corresponding to the broadcast mode applied from control circuits 30 and 33).
L and 3R are controlled. In other words, if the input electric field strength of the broadcast radio wave is lower than a certain level, and the broadcast mode is stereo broadcast or different program broadcast, and the receiver is receiving it, it is the stereo broadcast reception state or the different program broadcast reception state (however, In this state, if the sub-channel signal is output only in the frequency variable circuit of the system), that is, if the matrix circuit 1 is in an operation mode such that the component of the sub-channel signal appears on its output side. , the low-pass filters 7 of the variable frequency characteristic circuits 3L and 3R are controlled to be in an operating state.

FIG. 6 shows the main parts of a more specific example of the embodiment shown in FIG. 5, and FIGS. FIG. 7 shows a switch operation section, that is, a switching operation section provided on the panel side of the receiver, and will be described first with reference to FIG.

FIG. 7A shows the reception mode switching operation section 37, which can be operated by rotating its operation knob 37A.
Auto position P ₁ automatically changes the reception mode according to the broadcast signal mode of the broadcast signal, monaural position P ₂ forces the reception mode to monaural broadcast reception, and forced reception mode to stereo broadcast reception. _{and a} different program position _P4 for forcibly setting the reception mode to _a different program broadcast receiving state. Note that this receiving mode switching operation section 37 is one of the switching switches 37S ₁ to 37S ₆ used in the circuit shown in FIG.
is operated in conjunction with each position _P1 to _P4 . FIG. 7B shows a left output switching operation section 38 and a left output switching operation section 38 for selecting whether to set the left output and the right output to the main channel signal program or the sub channel signal program, respectively, while receiving a different program broadcast. This shows a right output switching operation section 39, and these output switching operation sections 38 and 39 can be set to a main channel signal program selection position Pm and a subchannel signal program selection position Ps by swinging their respective operation levers 38A and 39A. It is configured so that it can be switched to Note that these left side output switching operation section 38 and right side output switching operation section 39 are the changeover switches 38S ₁ , 38S ₂ ; 39S ₁ , 39 among the changeover switches used in the circuit of FIG.
This is what operates _S2 . Furthermore, FIG. 7C shows a frequency characteristic switching operation unit 40 for directly controlling each low-pass filter 7 of the variable frequency characteristic circuits 3L and 3R. By operating the lever 40A, there is an on position Pon where the low pass filter 7 is forcibly set to the operating state, and an off position Poff where the low pass filter 7 is forcibly set to the non-operating state.
and a variable position Pval that can automatically change the low-pass filter 7 into an operating state or a non-operating state depending on the reception state. Note that this frequency characteristic switching operation section 40 is
Of each changeover switch used in the circuit shown in the figure,
The changeover switches 40S ₁ and 40S ₂ are operated in conjunction with each other.

Next, the specific example shown in FIG. 6 which is controlled by each of the switching operation units 37 to 40 described above will be explained. The main channel signal and the sub channel signal are outputted from the main channel signal input terminal 1A and the sub channel signal input terminal 1B, respectively. Left side output terminal 1L and left side output line 2L of input matrix circuit 1
Between the input terminal of the variable frequency characteristic circuit 3L,
A changeover switch 37S 1 operated by the reception mode changeover operation unit 37 and a changeover switch 38S ₁ operated by the left output changeover operation unit ₃₈ are inserted, and also the right output of the matrix circuit 1 is inserted. Between the terminal 1R and the input end of the variable frequency characteristic circuit 3R of the right output path 2R, there is a changeover switch 37S2 operated by the reception mode switching connection section ₃₇ and a right output switching operation section 39. A changeover switch _39S1 is inserted. That is, the changeover switches 37S ₁ and 37S ₂ have their respective movable contacts connected to the left output terminal 1L and the right output terminal 1R of the matrix circuit 1, and the changeover switches 37S 1 and 37S 2
The contacts of auto position P ₁ , monaural position P ₂ and stereo position P ₄ of 7S 1 and 37S ₂ are connected to the input sides of frequency characteristic variable circuits 3L and 3R, respectively, and the different program position _{P 4} of changeover switch 37S ₁ is connected to the input side of frequency characteristic variable circuits 3L and 3R, respectively. The contacts are connected to the main channel signal program selection position Pm of the changeover switches 38S ₁ and 39S ₁ , and the different program selection position of the changeover switch 37S ₂ .
The contact of P ₄ is connected to the sub-channel signal program selection position Ps of the changeover switches 38S ₁ and 39S ₁ ,
The movable contact sides of the changeover switches 38S ₁ and 39S ₁ are connected to the input ends of the variable frequency characteristic circuits 3L and 3R, respectively. Amplifiers 34L and 34R are provided between the frequency characteristic variable circuit 3L of the left output path 2L and the left audio output terminal 35L, and between the frequency characteristic variable circuit 3R of the right output path 2R and the right audio output terminal 35R, respectively. is inserted.

Furthermore, 982.5Hz detection circuit 11A (982.5Hz in Figure 5)
The output of the Hz lead filter 28, rectifier circuit 29, etc.) is applied to one input terminal of the AND gate 41, and the other input terminal of the AND gate 41 is connected to a 55.125KHz multiplex control. The output side of a control signal level detection circuit 42 that detects the level of a signal is connected. This control signal level detection circuit 42 may be provided, for example, near the AM detector 27 in the circuit shown in FIG.
Further, in this example, a configuration may be adopted in which a detection signal is output when the level of the multiplex control signal is equal to or higher than a certain level. Also, 922.5Hz detection circuit 11B (fifth
922.5Hz lead filter 31 and rectifier circuit 32 in the diagram
etc.) is applied to one input terminal of an AND gate 43, and the output side of the control signal level detection circuit 42 is connected to the other input terminal of this AND gate 43. There is. The output terminals of these AND gates 41 and 43 are each connected to the input terminal of an OR gate 44, and the output terminal of this OR gate 44 is connected to one input terminal of an AND gate 45. The other input terminal of the AND gate 45 is connected to the output terminal of a field strength level detection circuit 10' which outputs a high level detection signal when the field strength of the received input of the broadcast radio wave is below a certain level. Also, the output terminal of this AND gate 45 is the control input terminal 4 of the opening/closing gate 46, which will be described later.
6a. Note that the output terminal of the AND gate 41 described above is connected to the reception mode switching operation section 3.
the third changeover switch 37S ₃ operated by 7;
is also connected to the auto position _P1 contact. This changeover switch _37S3 has its movable contact connected to the control input terminal 1C of the matrix circuit 1, and the contact at the stereo position _P3 of this changeover switch _37S3 is connected to the positive voltage power supply terminal +B. has been done.

On the other hand, the opening/closing gate 46 has a positive voltage power supply terminal +
B and the auto position _P1 of the fourth changeover switch _37S4 operated by the reception mode changeover operation section 37.
It is inserted between the contact point of The contacts at the stereo position _{P 3 and the contacts at the different program position P 4 of this switch 37S 4 are directly connected to the positive voltage power supply terminal +B, and the movable contact of this switch 37S 4 is connected to} the frequency characteristic switching operation described above. It is connected to the contact point of the variable position Pval of the changeover switches 40S ₁ and 40S ₂ operated by the section 40. The ON position Pon contacts of these changeover switches 40S ₁ and 40S ₂ are each connected to the positive voltage power supply terminal +B, and the movable contacts of these changeover switches 40S ₁ and 40S ₂ are connected to the reception mode switching operation section, respectively. 3
It is connected to the movable contacts of the fifth and sixth changeover switches 37S ₅ and 37S ₆ operated by the switch 7. And the auto position P ₁ of the changeover switch 37S ₅ ,
The contacts at the monaural position P ₂ and the stereo position P ₃ are directly connected to the control input terminal 9 of the frequency characteristic variable circuit 3L of the left output path 2L, and the contact at the different program position P ₄ is connected to the left output Changeover switch 38S ₂ operated by the changeover operation section 38
The left output system 2L is connected to the left side output system 2L through the contact point and movable contact piece at the sub-channel signal porogram selection position Ps.
It is connected to the control input terminal 9 of the variable frequency characteristic circuit 3L. On the other hand, the auto position P ₁ , monaural position P ₂ and stereo position P ₃ of the changeover switch _37S6
Each contact is directly connected to the control input terminal 9 of the variable frequency characteristic circuit 3R of the right output path 2R, and the contact at the different program position _P4 is connected to the changeover switch 39S operated by the right output switching operation section 39. It is connected to the control input terminal 9 of the variable frequency characteristic circuit 3R of the right output system 2R through the contact point and movable contact piece at the sub-channel signal program selection position Ps of _{No. 2} .

Next, the operation method and action of the specific example shown in Figs. 6 and 7 will be described. First, when the frequency characteristic switching operation unit 40 is set to the off state Poff, the change-over switches _40s1 and _40s2 are in the off state. As a result, regardless of the operation of the reception mode switching operation unit 37 and the output switching operation units 38, 39, a positive voltage signal, i.e., a high level signal which operates the low pass filter 7 of the frequency characteristic circuits 3L, 3R, is not applied to the control input terminal 9 of the frequency characteristic variable circuits 3L, 3R. As a result, the low pass filter 7 does not operate, and therefore the frequency characteristics of the left and right output paths 2L, 2R do not change and the treble range is not cut.

If the reception mode switching operation unit 37 is set to the auto position _P1 , the output of the AND gate 41 is applied to the control input terminal _1C of the matrix circuit 1 via the changeover switch 37S3. Therefore, if the broadcast signal mode is stereo broadcast, 982.5
Since the 982.5 Hz AM signal is detected by the Hz detection circuit 11A, if the control signal detection circuit 42 detects that the level of the multiplexed control signal is above a certain level, the AND gate 41 The matrix circuit 1 is set to perform addition and subtraction by the output of Changeover switch 37S ₁ , 37S ₂
via the auto position P ₁ contact (changeover switch 38
S ₁ , 39 (without passing through S ₁ ), left and right output lines 2L, 2
R, left and right audio output terminals 35L, 35
Output from R. Also, the reception mode switching operation section 3
7 is set to the monaural position _P2 , no signal is applied to the control input terminal 1C of the matrix circuit 1, so the matrix circuit 1 does not perform addition or subtraction, and its input is directly sent to the left and right output terminals 1L, 1.
R, and passes through the monaural position P ₂ contact of the changeover switches 37S ₁ , 37S ₂ (changeover switches 38S ₁ ,
39S ₁ ) to the left and right output lines 2L and 2R. Further, if the reception mode switching operation section ₃₇ is set to the stereo position _P3 , a positive voltage signal, that is, a positive voltage signal is sent to the control input terminal 1C of the matrix circuit 1 from the contact point at the stereo position P3.
A high level signal is added that causes the matrix circuit 1 to perform addition and subtraction operations. Therefore, if the transmitted radio wave is a stereo broadcast, the left and right audio outputs are output from the left and right output terminals 1L and 1R of the matrix circuit 1, respectively. are obtained, and these outputs pass through the contacts at the stereo position P ₃ of the changeover switches 37S ₁ , 37S ₂ (changeover switches 38S ₁ , 3
_9S2 ) is added to the left and right output lines 35L and 35R. On the other hand, if the reception mode switching operation section 37 is set to the different program position _P4 , the control input terminal 1C of the matrix circuit 1 is set to the monaural position.
As in the case of P ₂ , no signal is applied to operate the matrix circuit 1, so the main channel signal and the sub channel signal are output from the left and right output terminals 1L and 1R, respectively, and the main channel signal is output from the changeover switch. 37S ₁ different program position
The main channel signal of the changeover switches _38S1 and _39S1 is applied to the contact of the program selection position Pm through the contact point of _P4 , and the subchannel signal is applied to the contact point of the changeover switch 38S1, 39S1.
The sub-channel signal is applied to the contacts at the program selection position Ps of the changeover switches 38S ₁ and 39S ₁ via the contacts at the different program position P ₄ of 7S ₂ . Therefore, by appropriately operating the left output switching operation section 38 and the right output switching operation section 39, the changeover switches 38S ₁ and 39S ₁ are switched.
By switching, the main channel signal or the sub-channel signal can be outputted to the left output system 2L and the right output system 2R as appropriate. As mentioned above, the operation of the matrix circuit 1 controlled by the changeover switch _37S3 and the operation of the matrix circuit 1 from its left and right output terminals 1L and 1R to the left and right audio output terminals 35 are controlled by the changeover switch 37S3.
For operation up to L and 35R, frequency characteristic variable circuit 3
The same applies to each of the following cases, except for the operations of L and 3R.

On the other hand, move the frequency characteristic switching operation section 40 to the on position.
When set to Pon, positive voltage power supply terminal +
The positive voltage signal (high level signal) from B passes through the on-position Pon contacts of the changeover switches 40S ₁ and 40S ₂ and their movable contacts to the changeover switches 37S ₅ and 40S 2 .
37S Joins the movable contact piece of ₆ . Here, if the reception mode switching operation unit 37 is set to auto position P ₁ , monaural position P ₂ or stereo position P ₃ , the above-mentioned high level signal is switched to selector switch 37S ₅ , 37S ₆
Frequency characteristic variable circuit 3L,
The signal is applied to the control input terminal 9 of the signal path 3R, and the low-pass filter 7 operates to cut out the high frequency range of the signals of the signal paths 2L and 2R. Further, when the reception mode switching operation section 37 is set to the different program position _P4 , the above-mentioned high-level signal passes through the corresponding contacts of the changeover switches _37S5 and _37S6 , and is then applied to the changeover switches _38S2 and _39S2. The sub-channel signal is added to the contact at the program selection position Ps. Therefore, for example, the left output switching operation section 38 and the right output switching operation section 3
If either one or both of 9 and 9 are set to the sub channel signal program selection position Ps, the output path 2 corresponding to the set side
A high level signal is applied to the control input terminal 9 of the L or 2R frequency characteristic variable circuit 3L or 3R via the changeover switch 38S ₂ or 39S ₂ ,
The low-pass filter 7 operates to cut out the high frequency range, and the main channel signal program selection position
Since no high-level signal is applied to the control input terminal 9 of the frequency characteristic variable circuit 3L or 3R of the output path 2L or 2R on the side set to Pm, the low-pass filter 7 on that side does not operate. Here, since the changeover switches 38S ₁ and 39S 1 operated by the respective output changeover operation units 38 and ₃₉ are also inserted in each of the output paths 2L and 2R, the main channel signal is ultimately transmitted. The low-pass filter 7 does not operate in the output path, and the low-pass filter 7 operates in the output path to which the sub-channel signal is transmitted, thereby cutting out the high frequency range.

In addition, the frequency characteristic switching operation section 40 can be moved to a variable position.
When set to Pval, the reception mode switching operation section 37 is set to auto position P ₁ , monaural position P ₂ , stereo position, and different types. Different operations are performed depending on the case set in program position _P4 , so each case will be explained individually below.

First, in the case where the frequency characteristic switching operation section 40 is set to the variable position Pval as described above, and the receiving mode switching operation section 37 is set to the auto position _P1 , the positive voltage power supply terminal +B is set by the opening/closing gate 46. Since the circuit from the output circuits 2L, 2R to the control input terminals 9 of the frequency characteristic variable circuits 3L, 3R is opened and closed, the operation of the frequency characteristic variable circuits 3L, 3R is controlled by opening or closing of the gate circuit 46. will be controlled. If the broadcast signal mode of the broadcast radio waves is stereo broadcasting, the multiplexed composite signal includes a 55.125KHz multiplexed control signal, and the 982.5Hz detection circuit 11A detects a 982.5Hz AM signal from this multiplexed control signal. A detection signal is output from the 982.5Hz detection circuit 11A. At this time, if the level of the multiplexed control signal is higher than a certain level, a detection signal is also output from the control signal level detection circuit 42, thereby obtaining the output of the AND gate 41, and the output signal is passed through the OR gate 44 to the AND gate. It is applied to one input terminal of gate 45. In this state, if the received input electric field strength is below a certain level, a detection signal is output from the electric field strength detection circuit 10'.
Since it is applied to the other input terminal of the AND gate 45, the output of the AND gate 45 is obtained, which closes the opening/closing gate 46, and the positive voltage (high level signal) from the positive voltage power supply terminal +B opens/closes. Gate 46, changeover switch 37S ₄ , 40S ₁ , 40
Frequency characteristic variable circuit 3 via S ₂ , 37S ₅ , 37S ₆
It is added to the control input terminals 9 of L and 3R, and the low pass filter 7 operates. After all, when the broadcast signal mode is stereo broadcast, the low-pass filter 7 operates to cut out the high frequency range when the multiplex control signal level is above a certain level and the input electric field strength is below a certain level. On the other hand, even if the broadcast signal mode is stereo broadcast, if the level of the multiplex control signal is low or the input electric field strength is high, the opening/closing gate 46 remains open, and therefore the low pass filter 7 does not work. Note that when the level of the multiplex control signal is low, it is usual to prevent the matrix circuit 1 from operating by using an additional circuit (not shown). In addition, when the broadcast reception mode is program broadcast, the 922.5Hz detection circuit 11B detects a 922.5Hz AM signal from the multiplexed control signal.
Since the detection signal is output from the 922.5Hz detection circuit 11B, if the level of the multiplex control signal is above a certain level, the output signal of the AND gate 43 is obtained.
The output signal is applied to one input terminal of an AND gate 45 via an OR gate 44. Here, if the received input electric field strength is below a certain level, a detection signal is output from the electric field strength detection circuit 10' and that signal is applied to the other input terminal of the AND gate 45, so that the output of the AND gate 45 is obtained. , the opening/closing gate 46 is closed, and the frequency characteristic variable circuits 3L, 3R
A high-level signal is input to the control input terminal 9 of the low-pass filter 7, and the low-pass filter 7 operates. After all, even when the broadcast signal mode is a different program broadcast, if the level of the multiplex control signal is above a certain level and the input electric field strength is below a certain level, the low-pass filter 7 operates to cut out the high frequency range. On the other hand, if the multiplex control signal level is low or the input electric field strength is high, the opening/closing gate 46 will not close and the low-pass filter 7 will not operate. Furthermore, when the broadcast signal mode is monaural broadcasting, neither the 982.5Hz detection circuit 11A nor the 922.5Hz detection circuit 11B outputs a detection signal, so the opening/closing gate 46
does not close, so the low pass filter 7 does not operate.

Next, when the frequency characteristic switching circuit 40 is set to the variable position pval and the reception mode switching operation section 37 is set to the mono position _P2 , the switch _37S4 is turned off and, as a result, no positive voltage is applied to the contacts of the variable position Pval of the switch _40S1 , _40S2 . Therefore, no operation signal (high level signal) is applied to the control input terminal 9 of the frequency characteristic variable circuits 3L, 3R, so that the low pass filter 7 does not operate and the treble range of the signal is not cut off.

In addition, in the case where the frequency characteristic switching circuit 40 is set to the variable position Pval and the reception mode switching operation section 37 is set to the stereo position _P3 , a positive voltage (high level signal) from the positive voltage power supply terminal +B is applied. is the changeover switch 37S ₄ , 40S ₁ and 40
It is applied to the control input terminal 9 of the left and right frequency characteristic variable circuits 3L, 3R via S ₂ , 37S ₅ and 37S ₆ , and thereby the low pass filter 7 is operated, and the left and right signal paths 2L, 2R are Cuts the high frequency range of the signal.

On the other hand, the frequency characteristic switching circuit 40 is set to the variable position Pval.
In addition, the reception mode switching operation section 37
In the case where is set to the different program position P ₄ , the positive voltage (high level signal) from the positive voltage power supply line +B is switched via the changeover switches 37S ₄ , 40S ₁ and 40S ₂ , 37S ₅ and 37S ₆ The sub-channel signal of the switches 38S ₂ and 39S ₂ is applied to the contacts at the program selection position Ps. Therefore, when the left output switching operation unit 38 is set to the sub-channel signal program selection position Ps (that is, when the sub-channel signal is output to the left output path 2L), the left output switching operation section 38 is set to the sub-channel signal program selection position _Ps . A high level signal is applied to the control input terminal 9 of the variable frequency characteristic circuit 3L of the output path 2L, and the low pass filter 7 operates to cut out the high frequency range of the sub channel signal.
9 is set to the sub-channel signal program selection position Ps (that is, when the sub-channel signal is output to the right output path 2R), the frequency characteristics of the right output path 2R are changed via the changeover switch _39S2 . A high level signal is applied to the control input terminal 9 of the circuit 3R, and its low pass filter is activated to cut out the high frequency range of the sub channel signal.
Of course, when both output switching operation units 38 and 39 are set to the sub-channel signal program selection position Ps (when outputting sub-channel signals from the left and right output lines 2L and 2R), the left and right output lines 2
A high level signal is applied to the control input terminals 9 of the L and 2R frequency characteristic variable circuits 3L and 3R, and the respective low pass filters 7 operate. In addition, when one or both of the output switching operation units 38, 39 are set to the main channel signal program selection position Pm, the output systems 2L, 2R on that side
Of course, the frequency characteristic variable circuits 2L and 2R do not operate.

FIG. 8 shows the main part of another specific example of this invention. In the specific example of FIG. 8, the left and right output terminals 1L, 1 of the matrix circuit 1
R to left and right audio output terminals 35L, 3
Frequency characteristic variable circuits 3L, 3R and amplifier 3 are connected to the left output paths 2L, 2R leading to 5R, respectively.
4L and 34R are inserted, and the frequency characteristic variable circuits 3L and 3R are respectively connected to a resistor _R1 and a capacitor, similarly to those shown in FIG.
A low pass filter 7 consisting of C ₁ and a transistor 8 that turns on and off this low pass filter 7
and a resistor R ₂ connected to this transistor 8,
It is composed of R ₃ and R ₄ . Each resistor R ₃ on the control input side of these frequency characteristic variable circuits 3L, 3R has a forward-direction diode D ₁₁ , D _{12 with an on-position contact S 1a of} the first frequency characteristic changeover switch S ₁ .
The off-position contact _S2b of the second frequency characteristic switching switch _S2 linked to the first frequency characteristic switching switch _S1 is connected via diodes _D21 and _D22 in opposite directions. and the mode selector switch _S3 's upper position contact
S _3b are connected via forward diodes D ₃₁ and D ₃₂ , respectively, and the sub-channel-sub channel position contact S _4b of the different program output changeover switch S ₄ is connected via forward diodes D ₄₁ and D ₄₂ . and the right output line 2R.
Control input side resistance R ₃ of variable frequency characteristic circuit 3R
is connected to the main channel-subchannel position contact _S4c of the different program output changeover switch _S4 via a forward diode _D43 . Here, the first frequency characteristic switching switch _S1 and the second
The switch _S2 has on-position contacts _S1a and _S2a that forcibly turn on the variable frequency characteristic circuits 3L and 3R.
and the off position contact S _1b which is forced into the off state,
S _2b and auto-position contacts S _1c and S _2c that can be automatically turned on or off depending on the reception status
The movable contact piece of the first switch _S1 is connected to the positive voltage power supply terminal +B via a resistor _R5 ,
The movable contact piece of the second switch _S2 is grounded. The mode changeover switch _S3 also has a monaural position contact _S3a for setting the monaural broadcast reception state.
and an auto-position contact _S3b that can be automatically set to a stereo broadcast reception state or a different program broadcast reception state depending on the broadcast signal mode, and the movable contact will be described later. The output terminal of the AND gate 49 is connected to the output terminal of the AND gate 49. Further, the dissimilar program output changeover switch _S4 connects the main channel-main channel position contact _S4a , which sets the main channel signal to be output from the left and right audio output terminals 35L and 35R in the dissimilar program broadcast reception state, and the left and right main channel position contacts S4a. The sub-channel position contact S _{4b sets the sub-channel signal to be output from the audio output terminals 35L and 35R on both sides, and the sub-channel position contact S 4b} outputs the main channel signal from the left audio output terminal 35L and outputs the sub-channel signal from the right audio output terminal 35R. It is configured to be switched between the main channel and the sub-channel position contact _S4c , which sets the channel signal to be output, and its movable contact is connected to the output terminal of an AND gate 50, which will be described later. There is. In reality, a changeover switch (not shown) linked to the different program output changeover switch _S4 is inserted into the left and right output paths 2L and 2R, and the switch is used to change over the channels output from the respective audio output terminals 35L and 35R.

Furthermore, in the specific example shown in FIG. 8, the output terminal of the 982.5 Hz detection circuit 11A that detects the 982.5 Hz AM signal included in the multiplexed control signal in the stereo broadcast mode is connected to one input terminal of the AND gate 47, and 922.5 to detect 922.5Hz AM signal included in multiplex control signal in program broadcast mode
The output terminal of the Hz detection circuit 11B is an AND gate 48
The output side of the first electric field strength detection circuit 10A is connected to the other input terminal of the AND gates 47 and 48 via an inverting circuit 51, and the AND gate The output terminals of 47 and 48 are connected to one input terminal of AND gates 49 and 50, respectively, and the other input terminal of each of AND gates 49 and 50 is connected to the second electric field strength detection circuit 10.
The output side of B is connected, and the AND gate 4
As described above, the output terminals 9 and 50 are respectively connected to the movable contact of the mode changeover switch _S3 and the movable contact of the different program output changeover switch _S4 . Here, the first electric field strength detection circuit 10A and the second electric field strength detection circuit 10B each detect the received input electric field strength from, for example, an intermediate frequency amplification stage of the receiver, and when the input electric field strength is low, a high level signal is detected. A signal is output, and when the input electric field strength is high, a low level signal is output. The configuration may be such that the output of the second field strength detection circuit 10B is set to a value lower than the threshold value of the input field strength at which the output changes from high level to low level. For example, the threshold value of the first field strength detection circuit 10A may be set to 35 dB. The threshold value of the second electric field strength detection circuit 10B may be set to about 60 dB. Each of these field strength detection circuits 10A and 10B may be configured to extract a signal representing the signal strength from an intermediate frequency amplification stage as shown in the figure, and the inverting circuit 51 may be configured to take out a signal representing the signal strength from an intermediate frequency amplification stage as shown in the _figure .
It can be configured using _R9 .

In the specific example shown in FIG.
Switch S ₁ and second switch S ₂ are in the OFF position contact
When set to S _1b and S _2b , the base potential of the transistor 8 of each variable frequency characteristic circuit 3L, 3R becomes the ground potential, and thereby the transistor 8 is controlled to be non-conductive, and the low-pass filter 7 is turned off. It is forced into a non-operating state, that is, a state where the high frequency range is not cut.

On the other hand, when the frequency characteristic switching first switch S ₁ and the second switch S ₂ are set to the ON position contacts S _1a and S _2a , the positive voltage from the positive voltage power supply terminal +B is applied to each frequency characteristic variable circuit 3L, 3R. transistor 8
The transistor 8 becomes conductive, thereby putting the low-pass filter 7 into an operating state, that is, a state in which high-frequency sounds are cut.

In addition, the first frequency characteristic switching switch S ₁ and the second
When the switch S ₂ is set to the auto position contacts S _{1c and} S _2a , the base potential of the transistor 8 of the frequency characteristic variable circuits 3L and 3R is not forcibly set by these switches S 1 and S ₂ . Therefore, the operations of the frequency characteristic variable circuits 3L and 3R are controlled by other conditions. First, let us consider the case where the mode changeover switch _S3 is set to the monaural position contact _S3a .
Since the path leading to R is blocked, regardless of whether the broadcast being actually received is monaural broadcasting or stereo broadcasting (in this case, a detection signal is output from the 982.5Hz detection circuit 11A). The transistors 8 of both frequency variable circuits 3L and 3R are not conductive, so the high frequency range is not cut.
Furthermore, even if the mode selector switch S ₃ is set to the monaural position contact S _3a as described above, if the signal actually being received is a different type of program broadcast, a detection signal is output from the 922.5Hz detection circuit 11B. Therefore, depending on the level of the receiving input electric field strength, a high level signal may be output from the AND gate 50, and therefore, the different program output changeover switch _S4 is set to the subchannel-subchannel position contact _S4b. If set, both frequency characteristic variable circuits 3L and 3R are activated by the above-mentioned high level signal.
may operate, but in reality, if the mode selector switch _S3 is set to the monaural position contact _S3a as described above, only the main channel signal is output from the left output terminal 1L of the matrix circuit 1. Even if the different program output selector switch S ₄ is set to the sub-channel - sub-channel position contact S _4b , no audio output is obtained from the audio output terminals 35L, 35R, and therefore the frequency characteristic variable circuits 3L, 3
It becomes substantially unrelated to the operation of R. Similarly, if the different program output selector switch _S4 is set to the main channel-subchannel position contact _S4c , the above-mentioned high level signal will cause the right output system 2L to
The variable frequency characteristic circuit 3R may operate, but in that case, no audio output is actually obtained from the right audio output terminal as described above, and therefore the operation of the variable frequency characteristic circuit 3R is substantially irrelevant. becomes.

Meanwhile, set the mode selector switch S ₃ to auto position S _3b.
If the received broadcast is monaural in that state, no detection signal is output from the 982.5Hz detection circuit 11A and the 922.5Hz detection circuit 11B, and therefore both frequency characteristic variable circuits 3L and 3R A high level signal is not applied to the base of transistor 8, and therefore both frequency characteristic variable circuits 3L and 3R do not operate. Also, if the received broadcast is stereo broadcast, 982.5Hz detection circuit 1
A high level detection signal is output from 1A and applied to one input terminal of AND gate 47. Here, if the electric field strength of the receiving input is higher than a certain level _LA , the output of the inverting circuit 51 becomes high level, and as a result, a high level signal is output from the AND gate 47, and this signal is sent to the control input terminal of the matrix circuit 1. 1C and controls the matrix circuit 1 to perform addition/subtraction of the main channel signal and the sub-channel signal (that is, a state in which a stereo output is obtained), and the high level signal is applied to one input terminal of the AND gate 49. . At this time, if the electric field strength of the receiving input is lower than a certain level L _B (however, L _A <L _B ), the second
A high-level signal from the electric field strength detection circuit 10B is applied to the other input terminal of the AND gate 49, and a high-level signal is output from the AND gate 49, thereby causing both frequency characteristic variable circuits 3L,
The transistor 8 of 3R becomes conductive, the low-pass filter 7 becomes operational, and the left and right output paths 2L, 2
The high frequency components of the R signal are cut out. Further, if the electric field strength of the receiving input is higher than the level L _B , the output of the second electric field strength detection circuit 10B becomes a low level, so the output of the AND gate 49 does not become a high level, and therefore the left and right frequency characteristics are variable. The transistors 8 of the circuits 3L and 3R are not conductive, and the low-pass filter 7 is not activated. Note that if the electric field strength of the receiving input is lower than the level _LA , the output of the AND gate 47 will not be at a high level, so the matrix circuit 1 will not operate, and therefore the audio signal will be output in a monaural state. If the received broadcast is a different program broadcast, a high-level detection signal is output from the 922.5Hz detection circuit 11B and applied to one input terminal of the AND gate 48, where the electric field strength of the received input is at the level L _A described above. , the output of the inverting circuit 51 becomes high level, so a high level signal is output from the AND gate 48, and this signal is applied to the control input terminal 1C of the matrix circuit 1 to output the main channel signal of the different program broadcasting and The sub-channel signals are controlled to be output separately, and the high-level output signal of the AND gate 48 is output to the AND gate 50.
is applied to one input terminal of In this state, the electric field strength of the receiving input is at level L _B (where L _B > L
_A ), the second electric field strength detection circuit 10
A high level signal is output from the AND gate 50 in response to the high level signal from B. At this time, if the different program output changeover switch _S4 is set to the main channel-main channel position contact _S4a , the above-mentioned high-level signal will not be applied to both frequency characteristic variable circuits 3L and 3R, and therefore these The low-pass filters 7 of the characteristic variable circuits 3L and 3R are not activated. Furthermore, if the different program output selector switch _S4 is set to the subchannel-subchannel position contact _S4b , the high-level signal described above is applied to the bases of the transistors 8 of both frequency characteristic variable circuits 3L and 3R, and thereby Transistor 8 conducts and each low pass filter 7
is in operation, and the high frequency components of the left and right output path signals, that is, the sub-channel signals, are cut off. And also different program output selection switch
If _S4 is set to the main channel-subchannel position contact _S4c , the above-mentioned high level signal is applied to the base of transistor 8 of frequency characteristic variable circuit 3R of right output path 2R, thereby The low-pass filter 7 of the right output path 2R is activated and the high frequency component of the signal of the right output path 2R, that is, the sub-channel signal, is cut off. Note that if the electric field strength of the received input is higher than the level L _B , the output of the second electric field strength detection circuit 10B becomes low level, so the output of the AND gate 50 does not become high level, and therefore the different program output changeover switch _S4 No matter which position is set, the low-pass filter 7 of each frequency characteristic variable circuit 3L, 3R will not be in an operating state. Further, if the received input electric field strength is lower than the level _LA , the matrix circuit 1, in which the output of the AND gate 48 cannot be at a high level, is in a state of outputting only the main channel signal.

As mentioned above, in the circuit of FIG. 8, when the receiving input electric field strength of the broadcast radio wave is higher than a certain level L _A , the stereo broadcast reception state or the different program broadcast reception state can occur, and the reception input electric field strength is at the level L _B (however, L _B > L _A ), the output path in which the sub-channel signal is involved (i.e., the left and right output paths in the case of stereo broadcasting, and the sub-channel signal is not transmitted in the case of different program broadcasting). The variable frequency characteristic circuit of the output line (on the output side) automatically operates to cut out the high frequency range of the signal, eliminating _high frequency noise. The frequency characteristic variable circuits 3L and 3R will also not operate.

As is clear from the above description, the multiplex broadcast receiver of the present invention can be used in operation modes in which subchannel signal components appear in the output of the matrix circuit, that is, in stereo operation mode and in different program operation mode. In regards to
Moreover, when the received electric field strength level is low, the frequency characteristics of the output path of the matrix circuit can be controlled.
This function cuts these noises when listening to sub-channel broadcast signals of different program broadcasts where the received field strength is low and high-frequency noise is noticeable, or when listening to stereo broadcasts where the received field strength is low and high-frequency noise is likely to occur. Thus, the best reception condition with good output S/N can be obtained.

In the case of the receiver of this invention, the variable frequency characteristic circuit is inserted not at the input side (previous stage) of the matrix circuit but at the output side of the matrix circuit, so the variable frequency characteristic circuit operates in the stereo operation mode. In this case, the separation characteristics of the left and right channel outputs are not adversely affected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining the basic principle of the receiver of this invention, Fig. 2 is a wiring diagram showing an example of a variable frequency characteristic circuit used in the receiver of this invention, and Fig. 3 is a diagram showing the frequency characteristics. A graph showing the frequency characteristics of a low-pass filter used in a variable circuit, Figure 4 is a block diagram showing the basic configuration of an embodiment of this invention, and Figure 5 is a diagram of this invention to which the basic configuration of Figure 4 is applied. 6 is a block diagram showing the overall configuration of a multiplex broadcast demodulation circuit, FIG. 6 is a wiring diagram showing a specific example of the main part of the embodiment shown in FIG. 5, and FIGS. 7A, B, C is a schematic diagram showing the operation part of each changeover switch used in the specific example of FIG. 6;
The figure is a block diagram showing another specific example. 2L...Left side output system, 2R...Right output system, 3L, 3R...Variable frequency characteristic circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] In a multiplex broadcasting receiver that receives multiplex broadcast waves having a main channel signal, a sub-channel signal, and a control signal, each output path of a matrix circuit constituting a multiplex broadcast demodulation circuit is individually provided. A frequency characteristic variable circuit is inserted into the matrix circuit, and the frequency characteristic variable circuit is operated when the matrix circuit is in an operation mode in which a sub-channel signal component appears on its output side and the received electric field strength of the multiplex broadcast wave is below a predetermined value. A multiplex broadcast receiver characterized in that it is configured to control the state.