JP2008294742A - Multiplex broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid deterioration in receiving performance of a first receiving part or generation of abnormal noise which are caused by the interference of the local oscillation frequency of a second receiving part with the first receiving part without increasing a cost when the first receiving part and the second sub receiving part use the same local oscillation frequency band. <P>SOLUTION: This multiplex broadcast receiver comprises: the first receiving part (main tuner 1) for receiving sound; the second receiving part (sub tuner 2) for receiving data multiplexed on the sound; and a control part 7 for performing mute control of the sound received by the first receiving part (main tuner 1) just before a condition is established, on which the local oscillation frequency of the second receiving part (sub tuner 2) causes interference in the first receiving part (main tuner 1), and shifting the second receiving part (sub tuner 2) to the next receiving state out of the condition on which the interference occurs during mute control. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multiplex broadcast receiving apparatus capable of automatically switching and receiving a data broadcast program such as traffic information as necessary in addition to a radio broadcast program, such as an RDS (Radio Data System) receiver. .

  In a multiplex broadcast receiving apparatus including a plurality of receiving units (tuners) of the first receiving unit and the second receiving unit including the RDS receiver described above, each receiving unit uses the same local oscillation frequency band In some cases, the local oscillation frequency of the second receiving unit interferes with the first receiving unit, the reception performance of the first receiving unit deteriorates, and abnormal sound is generated in the reproduced sound by the first receiving unit. is there.

For example, in an RDS receiver that performs voice reception at the first receiving unit and confirms the reception state of the alternative frequency at the second receiving unit, when receiving the alternative frequency at the second receiving unit, the second reception is performed. The local oscillation frequency of the unit and the frequency of ± 200 kHz before and after that cause interference with the first receiving unit, and may generate beat noise in the audio output.
The occurrence of beat noise is accompanied by a change in the tuning voltage when the second receiver changes the frequency. At this time, the change in the tuning voltage is damped, and the fluctuation range of the local oscillation frequency corresponding to the fluctuation is the first. It is generated by interfering with one receiving unit. In order to solve this, a technique is known in which the tuning voltage is changed stepwise to reduce the occurrence of damping, and the local oscillation frequency of the second receiver is prevented from interfering with the first receiver. (See Patent Document 1).

  Further, as described above, in a receiver having two tuners, when a program that the viewer desires to receive exists on the same frequency channel, the local transmission frequencies output from the two tuners interfere with each other. There is also known a technique for switching the pass characteristic of the signal distribution circuit in the preceding stage of the tuner according to the contents of the received signal in order to cause the deterioration of the reception performance.

Japanese Patent Laid-Open No. 11-251940 JP 2003-347948 A

However, according to the technique disclosed in Patent Document 1 described above, when the reception frequency change of the second reception unit straddles the reception frequency of the first reception unit, although temporarily, the second reception unit It is an unavoidable problem that a local oscillation frequency and a frequency of ± 200 kHz before and after the local oscillation frequency interfere with the first receiving unit.
Further, according to the technique disclosed in Patent Document 2, when the local transmission frequency interferes with the first receiving unit and the second receiving unit, the output of one receiving unit is separated by the signal distribution circuit, The operation of one receiving unit stops. Therefore, it is impossible to switch and view the two systems of receiving units as necessary. The technique disclosed in Patent Document 2 is a technique in which an antenna distribution circuit exists and an antenna path is assumed to wrap around.

On the other hand, reception ICs designed for FM multiplexing and RDS reception are currently on the market, and the intermediate frequency used in the audio reception tuner on which this reception IC is mounted is usually 10.7 MHz. In addition, 15 MHz, 21.7 MHz, etc. can be selected and used as the intermediate frequency.
The frequency band used in FM multiplex broadcasting in Japan is 76.0 MHz to 90 MHz. If the intermediate frequency is 15 MHz, the minimum value of the local oscillation frequency is 91.0 MHz. On the other hand, the frequency band used in RDS broadcasting popular in Europe is 87.5 MHz to 108.0 MHz. If the intermediate frequency is 21.7 MHz, the minimum value of the local oscillation frequency is 109.2 MHz. . In this way, by shifting the local oscillation frequency to a band outside the broadcast frequency, the local oscillation frequency is prevented from interfering with the reception frequency of the audio reception tuner.

  However, even when the intermediate frequency is changed, the local oscillation frequency of the voice receiving tuner and the local oscillation frequency of the data receiving tuner are the same, and there is a problem that the reception performance is deteriorated when interference occurs. Some (for example, 107.0 MHz + 10.7 MHz = 96.0 MHz + 21.7 MHz) When the intermediate frequency is other than 10.7 MHz as described above, the filter component for generating the intermediate frequency is a general filter for 10.7 MHz. Compared to the above, there are problems that it is expensive and the characteristics of the filter parts themselves are poor, leading to a deterioration in reception performance. Ideally, it is desirable that the intermediate frequency can be used at 10.7 MHz.

  This invention is made in order to solve the above-mentioned subject, and when the 1st receiving part and the 2nd sub receiving part utilize the same local oscillation frequency band, it is 2nd to the 1st receiving part. Provided is a multiplex broadcast receiving apparatus capable of avoiding deterioration in reception performance of the first receiving unit or generation of abnormal noise caused by interference of local transmission frequencies of the receiving unit without increasing the cost. For the purpose.

  In the multiplex broadcast receiving apparatus according to the present invention, a first receiving unit that receives audio, a second receiving unit that receives data multiplexed in the audio, and the first receiving unit, Immediately before the condition that causes the local oscillation frequency of the second receiving unit to cause interference is established, the audio received by the first receiving unit is subjected to mute control, and during the mute control, the second receiving unit And a control unit that makes a transition to a next reception state that deviates from the condition in which the interference occurs.

  According to this invention, when the first receiving unit and the second receiving unit use the same local transmission frequency band, the local transmission frequency of the second receiving unit interferes with the first receiving unit. It is possible to provide a multiplex broadcast receiving apparatus capable of avoiding the deterioration of the reception performance of the first receiving unit and the occurrence of abnormal noise without requiring an increase in cost.

Embodiment 1 FIG.
1 is a block diagram showing an example of an internal configuration of a multiplex broadcast receiving apparatus according to Embodiment 1 of the present invention. Here, an RDS receiver is exemplified as the multiplex broadcast receiving apparatus.
As shown in FIG. 1, the RDS receiver includes two tuners, a main tuner 1 and a sub tuner. The main tuner 1 corresponds to a first receiving unit that performs audio reception. For example, it corresponds to a second tuner that receives, for example, TMC (Traffic Message Channel) data superimposed on the sound received by the main tuner 1. The sub-tuner 2 also has a function of performing an in-band frequency search and creating a broadcast wave that can be received in the area as a receivable broadcast frequency list (RDS network list).

  The sound signal received by the main tuner 1 is converted to an intermediate frequency by the detection unit 3 and subjected to synchronous detection. The demodulated sound signal is supplied to the control unit 7 constituted by a microcomputer or the like and the mute circuit 8. Is done. Data relating to the receiving station and the like decoded by the RDS decoder 5 is also supplied to the control unit 7. On the other hand, data such as TMC received by the sub-tuner 2 is synchronously detected by the detector 4 and supplied to the controller 7 via the RDS decoder 6.

Here, when the main tuner 1 and the sub tuner 2 use the same intermediate frequency, that is, the same local oscillation frequency, the local oscillation frequency of the sub tuner 2 interferes with the main tuner 1 to cause deterioration in reception performance or generation of abnormal noise. May cause. For example, the conditions (1) to (3) listed below can be considered.
(1) When the local oscillation frequency of the sub-tuner 2 matches the reception frequency of the main tuner 1, the leakage of the local oscillation frequency of the sub-tuner 2 flows into the antenna input of the main tuner 1. (2) The same frequency is received As a result, the local oscillation frequency becomes the same, and the leakage of the local oscillation frequency of the sub tuner 2 interferes with the local oscillation frequency of the main tuner 1.
(3) Interference occurs when the local oscillation frequency of the sub-tuner 2 matches the image frequency of the reception frequency of the main tuner 1 (the image frequency on the unnecessary side among the frequencies generated by multiplying the input signal by a certain frequency).

For stationary reception, if the reception frequencies of the main tuner 1 and the sub tuner 2 meet these conditions (1) to (3), it is possible to avoid the interference problem as a reception prohibited frequency for the sub tuner 2. However, it is impossible to avoid the interference problem in a situation where these conditions are passed by changing the setting of the reception frequency of the sub tuner 2.
For this reason, in the multiplex broadcast receiving apparatus according to Embodiment 1 of the present invention, the main tuner 1 is connected to the control unit 7 immediately before the condition that causes the local transmission frequency of the sub-tuner 2 to interfere with the main tuner 1. Mute control of the received audio is performed, and during the mute control, the sub-tuner 2 has a function of transitioning to the next reception state that deviates from the condition that causes interference, so that the reception frequency of the sub-tuner 2 is reduced. It is intended to solve the problem when passing through the condition where the problem occurs. Details will be described below. Reference numeral 8 denotes a mute circuit for muting the audio signal output from the detection unit 3 under the control of the control unit 7, and reference numeral 9 denotes a reproduction circuit for reproducing audio and data.

FIG. 2 is a block diagram showing the function of the internal configuration of the control unit 7 shown in FIG. As shown in FIG. 2, the control unit 7 includes a main control unit 70, a storage unit 71, an interference condition monitoring unit 72, a modulation degree monitoring unit 73, a mute control unit 74, a zero cross determination unit 75, The frequency setting control unit 76 and the timer monitoring unit 77 are configured.
The main control unit 70 performs mute control on the audio received by the main tuner 1 immediately before the condition in which the local transmission frequency of the sub tuner 2 causes interference in the main tuner 1, and during the mute control, the sub tuner 2 serves as a control center for realizing a function as the control unit 7 that makes a transition to the next reception state that deviates from a condition in which interference occurs, and performs sequence control of each functional block 71 to 77 described later.

The storage unit 71 stores in advance a condition that causes local oscillation frequency of the main tuner 2 to interfere, and a modulation degree determination threshold value when the mute control unit 74 described later performs mute control of audio output. Here, since the above-mentioned conditions are fixed, the ROM is stored, and the threshold value is stored in the RAM to be variable as will be described later.
The interference condition monitoring unit 72 monitors the reception frequency of the sub-tuner 2 to determine whether or not the interference condition stored in the storage unit 71 matches, and when it matches, changes the setting of the reception frequency of the sub-tuner 2. It has a function of holding and setting to a standby state. Further, the modulation degree monitoring unit 73 determines the average value of the modulation degree within a predetermined period of the received audio output by the main tuner 1, and the determined modulation degree and the modulation degree determination threshold value stored in the storage unit 71. And has a function of controlling the mute controller 74. The mute control unit 74 also determines that the modulation level monitoring unit 73 determines that the modulation level of the audio received by the main tuner 1 is lower than the modulation level threshold for a certain period of time (hereinafter referred to as low modulation level) while the sub tuner 2 is in the standby state. A function of driving the mute circuit 8 to mute the audio output.

The zero-cross determining unit 75 follows the instruction from the modulation degree monitoring unit 73 or the instruction from the main control unit 70, and the mute control unit 74 during the low modulation degree period near the zero-cross point or near the zero-cross point of the received voice waveform by the main tuner 1. Start mute control by.
In addition, the frequency setting control unit 76 sets the reception frequency setting by the sub-tuner 2 during the mute control of the audio output by the mute control unit 75 as a reception frequency candidate that is out of the condition for causing the interference stored in the storage unit 71. Has a function to change the setting.

  The timer monitoring unit 77 performs time monitoring under the control of the main control unit 70, and a low modulation degree period of the received voice by the main tuner 1 that is lower than the modulation degree determination threshold within a predetermined time (first period). Is not obtained, the modulation degree determination threshold value stored in the storage unit 71 is increased stepwise to generate a signal that serves as a trigger for the mute control unit 74 to perform mute control. Further, when a low modulation degree period of the received voice by the main tuner 1 lower than the modulation degree determination threshold is not obtained within a predetermined time (second period), the mute control unit 74 forcibly performs mute control. Generate a signal to trigger. That is, the time (period) monitored by the timer monitoring unit 77 is an elapsed time after the modulation degree determined by the modulation degree monitoring unit 73 becomes equal to or less than the modulation degree determination threshold value stored in the storage unit 71. Is also used to monitor the elapsed time when the frequency change of the sub tuner 2 is suspended and the current status is waited.

3 and 4 are flowcharts showing the operation of the multiplex broadcast receiving apparatus according to the embodiment of the present invention. Here, the mute control of the reception frequency output of the main tuner 1 and the frequency setting operation of the sub tuner 2 are performed. Shown in the center.
Hereinafter, the operation of the multiplex broadcast receiving apparatus according to the embodiment of the present invention shown in FIGS. 1 and 2 will be described in detail with reference to the flowcharts of FIGS.

First, when the main control unit 70 reproduces the sound received by the main tuner 1 by the reproduction circuit 9, the current reception frequency of the sub tuner 2 (the current reception frequency set by the frequency setting control unit 76) is the use frequency. It is determined whether or not the band edge (upper and lower limit frequencies) of the band (step ST301 in FIG. 3). Here, when it is determined that it is not a band edge (step ST301 “No”), it is further determined whether or not a change in reception frequency setting (next candidate frequency) by the frequency setting control unit 76 interferes with the main tuner 1. (Step ST302). Here, the determination of the presence / absence of interference is performed by determining whether the interference condition determination unit 72 matches the candidate frequency set by the frequency setting control unit 76 with the condition for causing the interference problem stored in the storage unit 71 in advance. This is possible by monitoring.
If it is determined that the interference problem does not occur (step ST302 “NO”), the frequency setting unit 76 sets the next candidate frequency for the sub-tuner 2 and starts a frequency search (step ST303). The above operation is repeatedly executed unless there is an instruction to turn off the power (step ST304 “No” in FIG. 4). As soon as there is a power-off instruction (step ST304 “Yes”), the frequency search operation of the sub-tuner 2 is terminated.

On the other hand, if it is determined in step ST301 that the current reception frequency is a band edge (step ST301 "Yes"), or if it is determined in step ST302 that the next candidate frequency interferes with reception by the main tuner 1 ( In step ST302 “Yes”), the main control unit 70 temporarily suspends the change of the current reception frequency of the sub-tuner 2 to enter the current standby state (step ST305), and simultaneously starts the standby time measurement timer by the timer monitoring unit 77. (Step ST306).
On the other hand, the modulation degree related to the received audio output of the main tuner 1 is always determined by the modulation degree monitoring unit 73, and within the elapsed standby time monitored by the timer monitoring unit 77 (step ST307 “Yes”), the storage unit If it is determined that the low modulation degree period is equal to or less than the modulation degree determination threshold stored in 71 (step ST308 “No”), the timer monitoring unit 77 further starts a low modulation degree duration measuring timer. Thus, the duration of the low modulation degree is measured (step ST309).

  Here, if the low modulation degree continues for a certain period of time (step ST310 “Yes”), the modulation degree monitoring unit 73 estimates that the low modulation degree will continue for a while thereafter. 77 is activated to set a certain mute operation permission period (step ST311 in FIG. 4). If the modulation degree lower than the modulation degree determination threshold does not continue for a certain period (step ST310 “No” in FIG. 3), the low modulation degree duration measuring timer is reset and the process returns to step ST307. (Step ST312).

On the other hand, when the zero-cross point (near zero-cross) of the received audio output of the main tuner 1 is detected by the zero-cross determination unit 75 during the mute operation permission period (step ST314 “Yes”), the main control unit 70 sets the mute control unit 74. The mute control is started, and the mute circuit 8 is controlled to mute the sound (step ST315). If the zero cross point is not detected within the audio mute operation permission period of the main tuner (step ST313 “No”), the process returns to step ST307 in FIG. This zero cross point detection (step ST314) is repeatedly executed during the mute operation permission period (step ST313 “Yes”).
Even when the received audio is muted within the mute operation permission period, it can be determined that there is little sense of sound interruption. At this time, the mute controller 74 controls the mute circuit 8 to receive the main tuner 1. The audio output is muted to avoid occurrence of abnormal noise due to the interference problem, and the reception frequency of the sub-tuner 2 is set as the next candidate during the mute operation permission period (step ST316) and standby The time measurement timer is reset (step ST317). At this time, the reception frequency change of the sub-tuner 2 is set to the next reception candidate frequency without changing to the reception frequency in which the interference problem occurs. The above operations (steps ST301 to ST317) are repeatedly executed unless there is an instruction to turn off the power (step ST304 “No”).

  With the above control, it is possible to avoid setting the reception frequency that causes an interference problem during the mute period and to change the sub tuner 2 to the next reception candidate frequency without causing the user to feel the sound interruption due to the mute control. It becomes possible.

  As described above, once the change of the reception frequency of the sub-tuner 2 is suspended, the modulation degree of the reception sound of the main tuner 1 is determined next. Unlike a talk program that includes a silent period, depending on the content of the broadcast, there may be content that continues to have a high degree of modulation for a long time. In this case, suspension of the reception frequency change of the sub tuner 2 will continue unintentionally for a long time.

  In order to avoid this, when the reception of the sub-tuner 2 becomes standby at the current reception frequency, the timer monitoring unit 77 starts a standby time measurement timer, and within a certain time by the standby time measurement timer. If the received sound of the main tuner 1 continues to be in a state where there is no period for which the low modulation degree is continued for a certain period of time (step ST307 “No” in FIG. 3), the main control unit 70 is stored in the storage unit 71. Control is performed to sequentially change the modulation degree determination threshold that is higher in a stepwise manner (step ST318). Then, the monitoring process of the low modulation degree period is executed by the modulation degree monitoring unit 73 until the modulation degree determination threshold is set to the maximum value or the timeout of the standby time setting timer is detected by the timer monitoring unit 77 (step). ST319 “No”, ST308) When any of the above conditions is satisfied (step ST319 “Yes”), the main control unit 70 activates the mute control unit 74 and forcibly causes the main tuner 1 to operate by the mute circuit 8. Is skipped to the processing after step ST311 so that the received audio output is muted.

This makes it easier to determine that the received voice output of the main tuner 1 has a low modulation degree without setting the modulation degree determination threshold higher than necessary, so that the sub-tuner 2 can wait longer at the current reception frequency. It is possible to avoid continuing the time.
In addition, the timer for measuring the lapse of the standby time is provided with a maximum limit period, and when it exceeds the maximum time period, the mute is forced to proceed to the next processing, so that the sub-tuner 2 can keep the current reception frequency. It is possible to avoid waiting for a short time.

  Further, during the mute operation permission period monitored by the timer monitoring unit 77, the main tuner 1 detects that the voice output waveform of the received voice is zero cross or an extremely low modulation degree corresponding thereto (step ST314 in FIG. 4). By setting this as a trigger for the mute operation, it is possible to reduce and avoid noise and sound discontinuity due to the mute operation. In addition, by satisfying this mute operation condition, even when the modulation degree threshold is increased stepwise as described above, it is possible to perform good mute processing without being affected by the value of the modulation degree determination threshold. become.

FIG. 5 is a timing chart showing the operation of the multiplex broadcast receiving apparatus according to Embodiment 1 of the present invention. Here, (a) main tuner audio output waveform, (b) modulation degree determination operation, and (c) timer Each of a set period (duration less than the modulation degree determination threshold), (d) a zero cross detection signal, (e) a mute signal, and (f) a reception frequency of the sub tuner 2 is shown.
The operation of the multiplex broadcast receiving apparatus according to Embodiment 1 of the present invention will be described below with reference to the timing chart of FIG.

  That is, when reproducing the sound received by the main tuner 1 shown in FIG. 5A, if it is determined that the interference problem occurs due to the change of the reception frequency of the sub-tuner 2, here, once, The reception frequency change of the sub-tuner 2 is put on hold, and the current standby state is set. As shown in FIG. 5B, the received audio modulation degree of the main tuner 1 is always compared with the modulation degree determination threshold value. Therefore, the standby state of the sub-tuner 2 is continued without muting. When the average is less than the modulation degree determination threshold, as shown in FIG. 5C, the modulation degree duration measuring timer is started to measure the modulation degree duration. If the low modulation level continues for a certain period, it will be determined that the low modulation level will continue for some time thereafter. Therefore, a certain mute operation permission period (hatched display in the figure) is provided, and within this permission period Even when the received sound is muted, it can be determined that there is little sound discontinuity.

Therefore, as shown in FIG. 5 (e), a mute operation is performed on the received voice to avoid the occurrence of abnormal noise due to the interference problem, and as shown in FIG. 5 (f), The reception frequency of the sub tuner 2 is advanced during the mute period. At this time, the reception frequency change of the sub tuner 2 is advanced to the next reception candidate frequency (fn2) without changing to the reception frequency in which the interference problem occurs. As a basic operation by these operations, it is possible to avoid a reception frequency relationship in which an interference problem occurs during the mute period without a sense of sound interruption due to mute, and to change the sub tuner 2 to the next reception candidate frequency.
Further, during the mute operation permission period, as shown in FIG. 5 (d), it is detected that the zero-cross in the audio output waveform of the received audio by the main tuner 1 or an extremely low modulation degree corresponding thereto is detected, and this is muted. Use as an operation trigger. As a result, noise and sound discontinuity due to the mute operation can be reduced or avoided. In addition, by satisfying the mute operation condition, as described in the flowcharts of FIGS. 3 and 4, even when the modulation degree determination threshold is increased stepwise, the modulation degree determination threshold value is not affected. A good mute operation can be performed.

  As described above, according to the multiplex broadcast receiving apparatus according to the first embodiment of the present invention, when the local oscillation frequency of the sub-tuner 2 causes interference with the main tuner 1, Mute control is performed on the received audio output of the tuner 1, thereby preventing the occurrence of abnormal noise and causing the sub-tuner 2 to transition to the next reception state that deviates from the condition in which interference occurs during the mute operation. According to this, the mute operation for the received sound is performed during a period when the modulation degree of the received sound is lower than the modulation degree determination threshold, so that a sense of incongruity, sound interruption, etc. during the mute operation Can be reduced and avoided.

Further, when the modulation degree determination threshold value for permitting the mute operation is not fixed and the low modulation degree period of the received audio output of the main tuner 1 lower than the modulation degree determination threshold value cannot be obtained within an arbitrary period, an arbitrary period It is possible to easily permit the mute operation by increasing the modulation degree determination threshold value for each and sequentially comparing them. Furthermore, even when the modulation degree determination threshold is increased, if a low modulation degree period of the received voice output of the main tuner 1 lower than the modulation degree determination threshold cannot be obtained within a predetermined period, it is treated as time-out, and forced The modulation degree monitoring process can be limited by performing the mute operation.
Also, when performing mute operation, the mute operation is started at the zero cross point of the main tuner 1 received audio waveform or at extremely low modulation, which is a situation close to it, thereby reducing noise and sound discontinuity due to the start of the mute operation. Can be avoided.

In addition, according to the multiplex broadcast receiving apparatus according to Embodiment 1 of the present invention described above, the RDS receiver has been described as an example. However, the RBDS (Radio Broadcast) that is not limited to the RDS receiver and is widely used in the United States. The present invention can be applied to all multiplex broadcast receivers having the same configuration such as Data System) and FM multiplex broadcast in Japan.
2 may be implemented entirely by software, or at least a part thereof may be implemented by hardware. For example, the data processing in the main control unit 70, the interference condition monitoring unit 72, and the modulation degree monitoring unit 73 may be realized on a computer by one or a plurality of programs, and at least a part thereof is realized by hardware. May be.

It is a block diagram which shows the internal structure of the multiplex broadcast receiver which concerns on Embodiment 1 of this invention. It is the block diagram which expanded and showed the function of the internal structure of the control part shown in FIG. It is a flowchart which shows operation | movement (1) of the multiplex broadcast receiver which concerns on embodiment of this invention. It is a flowchart which shows operation | movement (2) of the multiplex broadcast receiver which concerns on embodiment of this invention. It is a timing chart which shows operation | movement of the multiplex broadcast receiver which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Main tuner (1st receiving part), 2 Sub tuner (2nd receiving part), 3, 4 detection part, 5,6 RDS decoder, 7 Control part, 8 Mute circuit, 9 Reproduction circuit, 70 Main control part 71 Storage unit 72 Interference condition monitoring unit 73 Modulation degree monitoring unit 74 Mute control unit 75 Zero cross determination unit 76 Frequency setting control unit 77 Timer monitoring unit

Claims (6)

A first receiver for receiving audio;
A second receiving unit for receiving data multiplexed in the voice;
The first receiving unit performs mute control on the sound received by the first receiving unit immediately before the condition that causes the local transmission frequency of the second receiving unit to interfere, and during the mute control. A control unit that causes the second reception unit to transition to a next reception state that deviates from a condition in which the interference occurs;
A multiplex broadcast receiving apparatus characterized by comprising: The controller is
A storage unit in which a condition for causing a local transmission frequency of the second receiving unit to cause interference in the first receiving unit, and a modulation degree determination threshold value for performing mute control of the sound;
The reception frequency of the second reception unit is monitored to determine whether or not the conditions stored in the storage unit are matched, and if they match, the change of the reception frequency of the second reception unit is suspended. An interference condition monitoring unit to be in a standby state;
A modulation degree monitoring unit that determines a modulation degree of the received voice by the first reception unit, and compares the determined modulation degree with a modulation degree determination threshold stored in the storage unit;
When the modulation level monitoring unit determines that the modulation level of the voice received by the first reception unit is lower than the modulation level determination threshold in the state where the second reception unit is waiting, A mute control unit for performing mute control,
During the mute control of the sound by the mute control unit, the frequency setting control unit changes the setting of the reception frequency by the second reception unit to a reception frequency candidate that is out of the condition for causing interference stored in the storage unit. When,
The multiplex broadcast receiver according to claim 1, comprising: The controller is
It has a timer monitoring unit that monitors time,
When the low modulation degree period of the received voice output by the first receiving unit lower than the modulation degree determination threshold is not obtained within the first period monitored by the timer monitoring unit, the read from the storage unit 3. The multiplex broadcast receiving apparatus according to claim 1, wherein the mute control is performed by increasing a modulation degree determination threshold stepwise. The controller is
4. The mute control is forcibly performed when a low modulation degree period of reception audio output by the first receiving unit lower than a maximum value of the modulation degree determination threshold is not obtained. Multiple broadcast receiver. The controller is
If the low modulation degree period of the received voice output by the first receiving unit lower than the modulation degree determination threshold is not obtained within the second period monitored by the timer monitoring unit, the mute control is forcibly performed. 4. The multiplex broadcast receiving apparatus according to claim 3, wherein: The controller is
6. The mute control according to claim 1, wherein the mute control is performed in a low modulation degree period in the vicinity of the zero cross point or in the vicinity of the zero cross point of the received audio output waveform by the first receiving unit. The multiplex broadcast receiver described.

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