JP3124119B2 - Receiving machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver in which a notch filter circuit is automatically turned on when it is determined that a received signal contains a beat signal.

[0002]

2. Description of the Related Art A notch filter circuit is known as a circuit for removing a beat signal included in a received signal. In this method, the beat signal is detected, and the notch frequency is made to match this frequency by automatic tracking, thereby removing the beat signal from the intermediate frequency signal and eliminating the beat sound from the reproduced sound.

[0003]

Conventionally, the above-described notch filter circuit has a structure in which a user listens to a sound reproduced from a receiver and determines whether or not a beat signal exists.
The ON / OFF control of the notch filter circuit must be performed manually. For this reason, when a continuous beat signal is present, the operation becomes complicated.

The present invention has been made in view of the circumstances of the related art, and provides a receiver in which the notch filter circuit is automatically turned on when the presence of a beat signal is detected. Aim.

[0005]

In order to achieve the above object, a receiver according to the present invention includes a single antenna and a part of a received signal received by the antenna through a wide band filter and a notch filter circuit. A first demodulation circuit which makes a first demodulated signal in the first demodulation circuit, and a second demodulation circuit which makes a part of the received signal a second demodulated signal in the second demodulation circuit via a narrow band filter. A detection system for detecting, from the levels of the first and second demodulated signals, that the level of the received signal of the target reception frequency is high and the level of the received signal of the transmission frequency of another station nearby and the level of disturbance noise are low. Means, said second
And a control means for controlling ON / OFF of the notch filter circuit in accordance with signals from the detection means and the fluctuation detection means. .

In the receiver of the present invention, the first demodulation signal is converted by a first demodulation circuit into a single antenna and a part of a reception signal received by the antenna via a noise blanker and a notch filter circuit. A first reception system, a second reception system in which a part of the reception signal is converted into a second demodulation signal by a second demodulation circuit via a narrow band filter, and a noise detection signal of the noise blanker. Detecting means for detecting from the level of the second demodulated signal that the level of the received signal of the target reception frequency is high and the level of the received signal of the transmission frequency of another station nearby and the level of disturbance noise are low; Fluctuation detecting means for detecting that there is no level fluctuation of the demodulated signal;
Control means for controlling ON / OFF of the notch filter circuit according to signals from the detection means and the fluctuation detection means may be provided.

The receiver according to the present invention comprises: a reception system which converts a reception signal received by an antenna into a demodulation signal through a noise blanker and a filter having a narrower bandwidth and a notch filter circuit; Detecting means for detecting that the level of the received signal at the target reception frequency is high and the level of the received signal at the transmission frequency of another station nearby and the level of disturbance noise are low from the noise detection signal of the blanker and the level of the demodulated signal; A fluctuation detecting means for detecting that there is no level fluctuation of the demodulated signal; and turning on the notch filter circuit in accordance with signals from the detecting means and the fluctuation detecting means.
/ OFF control means.

[0008]

According to the first aspect, the first demodulated signal obtained in the first receiving system is a signal of a target reception frequency and another station located near the signal in accordance with the bandwidth of the wide band filter. And the disturbance noise of the transmission frequency is superimposed. Further, the second demodulated signal obtained by the second receiving system passes through a narrow band filter, so that a received signal of only the target receiving frequency can be obtained. Therefore, it can be determined from the levels of the first and second demodulated signals whether or not the signal at the target reception frequency is strong and the other signals are weak and the reception situation is such that a sufficient S / N ratio can be obtained. . And sufficient S / N
If the level of the second demodulated signal is constant in a good reception situation where a ratio can be obtained, it can be determined that a beat signal exists. Therefore, the beat signal can be reliably removed by controlling the notch filter circuit to be ON by the control means.

According to a second aspect of the present invention, the noise detection signal of the noise blanker is obtained by superimposing a signal of a target reception frequency, a reception signal of a transmission frequency of another station in the vicinity thereof, and disturbance noise. It is. Thus, from the level of the noise detection signal and the level of the second demodulated signal, it can be determined whether or not a reception state in which a sufficient S / N ratio can be obtained, as in the case of the first aspect. If the reception state is such that a sufficient S / N ratio can be obtained and the level of the second demodulated signal is constant, it can be determined that a beat signal exists, and the notch filter circuit can be turned on.

[0010] In the third aspect,
The noise detection signal of the noise blanker contains more reception signals and disturbance noise of the transmission frequency of another station near the target reception frequency than the demodulation signal obtained through a filter having a narrower bandwidth. Thus, from the levels of the noise detection signal and the demodulated signal, it can be determined whether or not a reception state in which a sufficient S / N ratio can be obtained, as in the case of the first aspect. Then, the presence of the beat signal can be determined from the fluctuation state of the level of the demodulated signal, and the notch filter circuit
N / OFF control can be performed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the receiver according to the present invention will be described below.
This will be described with reference to FIGS. FIG. 1 is a block circuit diagram of an embodiment of the receiver of the present invention, FIG. 2 is a flowchart for explaining the operation of the fluctuation detecting means of FIG. 1, and FIG. 3 is an operation of the control means of FIG. It is a flowchart explaining.

First, the structure will be described with reference to FIG. 1
The received signal received by the antenna 10 is amplified by the high frequency amplifier circuit 12 and provided to the first mixer 14, where it is mixed with the first local oscillation signal from the first local oscillation circuit 16. The frequency-converted signal output from the first mixer 14 is supplied to a first intermediate frequency amplification circuit 18, and a first intermediate frequency signal having a predetermined frequency is extracted and amplified, and supplied to a distributor 20. The divider 20 divides the first intermediate frequency signal into two, one of which is, for example, 20 KH
z is applied to a broadband filter 22 having a bandwidth of z, the other being a narrowband filter 2 having a bandwidth of, for example, 3 KHz.
4 given. Note that the bandwidth of the narrow band filter 24 is included in the bandwidth of the wide band filter 22.

The first intermediate frequency signal that has passed through the broadband filter 22 is applied to a second intermediate frequency amplifier circuit 26 where it is amplified and applied to a second mixer 28. Means 30 are provided. The second mixer 28 is supplied with a second local oscillation signal from a second local oscillation circuit 32, and converts a second intermediate frequency signal obtained by frequency-converting the first intermediate frequency signal into a notch filter circuit 34. , And to the first demodulation circuit 38 via the amplification circuit 36, and the first demodulation signal is output. This first demodulated signal is amplified by the low frequency amplifier circuit 40 and
2 is output as audio. A part of the first demodulated signal is provided to the first level comparator 44.

The first signal having passed through the narrow band filter 24 is
The intermediate frequency signal is supplied to a third intermediate frequency amplifier circuit 46 and amplified, and the amplified output is supplied to a second demodulation circuit 48 to output a second demodulated signal. This second demodulated signal is supplied to a second level comparator 50 and a fluctuation detecting means 52.
Given to.

The first and second level comparators 44,
The signals output from 50 are applied to AND circuits 54, respectively, and the output of the AND circuits 54 is applied to control means 56. Further, the signal output from the fluctuation detecting means 52 is given to the control means 56. Further, a signal output from the control means 56 is supplied to the notch filter circuit 34, and the notch filter circuit 34 is ON / OFF controlled. The first and second level comparators 44 and 50 and the AND circuit 54 form detection means.

It should be noted that a wideband filter 2 is
A first reception system is constituted by a path leading to the first demodulation circuit 38 via the second demodulation circuit 2, and a second reception path is constituted by a path leading from the antenna 10 to the second demodulation circuit 48 via the narrow band filter 24.
Are configured.

Here, the first level comparator 44 is connected to the first level comparator 44.
And compares the demodulated signal level with the first reference value, and outputs a signal when the first demodulated signal level is lower than the first reference value. The second level comparator 50 compares the level of the second demodulated signal with a second reference value, and outputs a signal when the level of the second demodulated signal is higher than the second reference value. I do. Therefore, the AND circuit 54 outputs a signal when the level of the first demodulated signal is low and the level of the second demodulated signal is high, that is, when the level of the received signal at the target reception frequency is strong, When the level of the received signal of the transmission frequency and the level of disturbance noise are low, a signal is given to the control means 56.

Next, the operation of the fluctuation detecting means 52 will be described with reference to FIG. First, the fluctuation detecting means 52 has a function of sampling the second demodulated signal at a period of, for example, 1 ms,
It has a function of storing them and a function of calculating them. When the second demodulated signal is newly sampled, its level is read (step), the level sampled and stored earlier is read from the storage means (step), and the difference between the two levels is calculated (step). . Then, the magnitude of the absolute value of the difference obtained by this calculation is compared with an appropriate reference value (step). If the absolute value of the difference is smaller than the reference value, it can be determined that the previously sampled level is substantially equal to the newly sampled level and there is no change in the level of the second demodulated signal. Is output (step),
Return to step. If the absolute value of the difference is larger than the reference value in the step, it can be determined that the level of the second demodulated signal has changed, and the process returns to the step without outputting any signal to the control means 56. .

Here, when it is determined by the fluctuation detecting means 52 that the level of the second demodulated signal is substantially constant, the received signal of the target reception frequency is either a beat signal or white noise. is there.

The operation of the control means 56 will be described with reference to FIG. First, it is determined whether there is a signal from the detecting means, that is, a signal from the AND circuit 54 (step).
If there is a signal from the detecting means, it is next determined whether there is a signal from the fluctuation detecting means 52 (step). Here, if there is a signal from the detection means, it is clear that the reception situation is in a state where the S / N ratio is excellent, and the reception signal of the target reception frequency is not due to white noise. And
If there is a signal from the fluctuation detecting means 52, it can be determined that a high-level beat signal exists at or near the target reception frequency. For this reason, if there is a signal from the fluctuation detecting means 52 in the step, the control means 56 outputs a signal to the notch filter circuit 34 to make it ON control (step), and returns to the step. If there is no signal at least in the step, no beat signal is present and no signal is output from the control means 56 to the notch filter circuit 34, and the notch filter circuit 34
FF control is performed (step), and the process returns to the step. The control means 56 is configured to be able to hold the ON control of the notch filter circuit 34 for a time slightly longer than the sampling cycle of the fluctuation detecting means 52.

With such a configuration and its operation, the receiver of the present invention can reliably determine the presence or absence of a beat signal, and the notch filter circuit 34 is automatically turned on / off.

Further, another embodiment of the receiver according to the present invention will be described with reference to FIGS. FIG. 4 is a block circuit diagram of another embodiment of the receiver of the present invention, FIG. 5 is a flowchart for explaining the operation of the fluctuation detecting means of FIG. 4, and FIGS. 6 is a flowchart illustrating first to third operations of the level comparator. 4, the same or equivalent circuit blocks as those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

First, the structure of another embodiment will be described with reference to FIG. 4 differs from FIG. 1 in that a noise blanker 60 is provided in place of the broadband filter 22 in FIG. 1 and that the noise detector 6 is provided in place of the first demodulated signal.
2 is supplied to a level comparator 70 as a detecting means. In the noise blanker 60, one of the first intermediate frequency signals divided by the divider 20 is supplied to a noise gate 64 and a noise amplifier 66. The first intermediate frequency signal is amplified by the noise amplifier 66 and provided to the noise detector 62, and the noise detector 62 outputs a noise detection signal. And
This noise detection signal is supplied to a level comparator 70 and also to a gate control circuit 68 having a threshold value. The pulse noise included in the noise detection signal is extracted by the gate control circuit 68, and the noise gate 64 is turned ON / OFF according to the extracted pulse noise, and the pulse noise is removed through the noise gate 64. The first intermediate frequency signal is supplied to the second intermediate frequency amplifying circuit 26.
Given to. Further, the second demodulated signal is output from the level comparator 7.
0, and a signal output as a result of comparing the level of the noise detection signal with the level of the second demodulated signal by the level comparator 70 is supplied to the control means 56.

Here, the noise detection signal includes, in addition to the reception signal at the target reception frequency, a reception signal due to a transmission frequency of another station nearby and disturbance noise. Therefore, the level of this noise detection signal and the narrow band filter 2
The reception status of the receiver can be determined by comparing the level of the second demodulated signal consisting of only the reception signal of the target reception frequency after passing through Step 4.

In such a configuration, the operation of the fluctuation detecting means 52 will be described with reference to FIG. First, a newly sampled level (step) and a previously sampled level (step) are read at a period of, for example, 1 ms, and a ratio between the two levels is calculated (step a). Then, it is determined whether or not this ratio is substantially "1" (step a). In this step, if the ratio is substantially "1", it can be determined that there is no level change in the second demodulated signal, a signal is output to the control means 56 (step), and the process returns to the step. If the ratio is not substantially "1" at the step, it can be determined that the second demodulated signal has a level fluctuation, and the process returns to the step without outputting any signal to the control means 56. The operation of the fluctuation detecting means 52 may be any of the operations shown in FIGS. 3 and 5 as long as it is possible to determine whether or not the level of the second demodulated signal fluctuates.

Next, a level comparator 70 as a detecting means
Will be described. First, the first operation of the level comparator 70 shown in FIG. 6 calculates the difference between the levels of the noise detection signal and the second demodulated signal (step), and determines whether the difference is smaller than a reference value. (Step). If the level of the noise detection signal is equal to the level of the second demodulated signal only when the level of the noise detection signal is only the reception signal of the target reception frequency, the difference calculated in the step will be different from the target reception frequency included in the noise detection signal. In accordance with the level of the received signal. If the difference is smaller than the reference value, it can be determined that the S / N ratio of the reception status is good.
Therefore, when the difference is smaller than the reference value in the step, a signal is output to the control means 56 (step), and the process returns to the step. If the difference is larger than the reference value in the step, the beat signal cannot be accurately determined due to the presence of a signal having a strong transmission frequency of another station, or it is considered that white noise is being received. Return to the step without sending a signal to the means 56.

The second level comparator 70 shown in FIG.
Will be described. In FIG. 7, first, a quotient obtained by dividing the level of the second demodulated signal by the level of the noise detection signal is calculated (step a), and it is determined whether or not this quotient is larger than a reference value (step a). The quotient becomes smaller as the level of the signal other than the target reception frequency included in the noise detection signal is higher. Therefore, if the quotient is larger than the reference value, it can be determined that the reception status is good. Therefore, when the quotient is larger than the reference value in step a, a signal is output to the control means 56 (step), and the process returns to step a. If the quotient is smaller than the reference value in step a, the process returns to the step without outputting a signal to the control means 56.

Next, the third operation of the level comparator 70 shown in FIG. 8 will be described. In FIG. 8, first, the difference between the level of the noise detection signal and the second demodulated signal is calculated (step), and the quotient obtained by dividing the level of the second demodulated signal by the difference is calculated (step b). It is determined whether the value is larger than the reference value (step a). Here, if the quotient is large, a signal is output to the control means 56 (step),
Return to step. If the quotient is smaller than the reference value in step a, the process returns to the step without outputting a signal to the control means 56.

Still another embodiment of the receiver according to the present invention will be described with reference to FIG. 9 that are the same as or equivalent to those in FIG. 4 are denoted by the same reference numerals for the circuit blocks, and redundant description will be omitted.

9 differs from FIG. 4 in that the distributor 20, the narrow band filter 24, the third intermediate frequency amplifier circuit 46, and the second demodulator circuit 48 in FIG. 4 are omitted, and the first intermediate frequency The first intermediate frequency signal output from the amplifier circuit 18 is provided to the noise gate 64 and the noise amplifier 66 of the noise blanker 60, and the first intermediate frequency signal passing through the noise gate 64 is narrower than the noise blanker 60. 4 and the first demodulated signal output from the first demodulation circuit 38 is supplied to the low frequency amplification circuit 40. In place of the second demodulated signal in
It is provided to the fluctuation detecting means 52 and the level comparator 70 as the detecting means. Further, the control means 56
When the notch filter circuit 34 is turned on, the notch filter circuit 34 is automatically turned off after an appropriate predetermined time has elapsed.
The F control is set so that the presence or absence of a beat signal can be determined again.

In such a configuration, the noise detection signal includes a signal other than the target reception frequency and disturbance noise as compared with the first demodulated signal due to a difference in bandwidth. Therefore, by comparing the level of the noise detection signal with the level of the first demodulated signal, it is possible to determine whether the reception state is good, and it is possible to determine the presence or absence of the beat signal from the presence or absence of the level fluctuation of the first demodulated signal.

In the embodiments shown in FIGS. 1, 4 and 9, the detecting means may be any means as long as the receiving condition can be determined from two signals having different bandwidths.
Further, as shown in FIGS. 2 and 5, the fluctuation detecting means 52 may be any means as long as the presence or absence of the level fluctuation can be detected. The sampling cycle of the fluctuation detecting means 52 is not limited to the 1 ms cycle.
Further, in the embodiment shown in FIG. 9, the input of the fluctuation detecting means 52 may be a noise detection signal output from the noise detector 62.

Further, in the description of the above embodiment, the fluctuation detecting means 52, the control means 56 and the level comparator 70
Of course may be incorporated in a one-chip microcomputer or the like, and may of course be constituted by discrete components. And DS
It can also be configured using a P (digital signal processor). In the above embodiment, the case of single mode reception has been described. However, in the case of having a multi-mode switching function, the wideband filter 2 is used in accordance with the reception mode.
2 and the pass band width of the narrow band filter 24 may be appropriately controlled.

[0034]

As is clear from the above description, the receiver of the present invention has the following special effects.

First, in the receiver according to the first aspect, the presence / absence of a beat signal can be reliably determined from the reception state and the presence / absence of a level change of the received signal. When the presence of the beat signal is determined, the notch filter circuit is used. Since automatic ON control is performed, manual operation by the user is not required, and the operation becomes extremely simple.

Also, in the receiver according to the second aspect,
As in the receiver of the first aspect, the ON / OFF control of the notch filter circuit is automatically performed according to the presence or absence of a beat signal, so that the operation is simple. In addition, the noise detection signal of the noise blanker is used to determine the reception status, and is suitable for a receiver having a noise blanker.

In the receiver according to the third aspect, similarly to the receivers according to the first and second aspects, the ON / OFF control of the notch filter circuit is automatically performed, and the operation is simple. In addition, since the reception state and the like are determined from the level of the noise detection signal of the noise blanker and the demodulated signal obtained through a filter having a narrower bandwidth than this, the reception state other than the reception system for reproducing the sound is determined. This does not require a receiving system used only for this purpose, has a simple circuit configuration, and can be applied to a receiver having a noise blanker with a simpler configuration.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an embodiment of a receiver according to the present invention.

FIG. 2 is a flowchart illustrating an operation of a fluctuation detecting unit in FIG. 1;

FIG. 3 is a flowchart illustrating an operation of a control unit in FIG. 1;

FIG. 4 is a block circuit diagram of another embodiment of the receiver of the present invention.

FIG. 5 is a flowchart illustrating an operation of a fluctuation detecting unit of FIG. 4;

FIG. 6 is a flowchart illustrating a first operation of the level comparator in FIG. 4;

FIG. 7 is a flowchart illustrating a second operation of the level comparator of FIG. 4;

FIG. 8 is a flowchart illustrating a third operation of the level comparator in FIG. 4;

FIG. 9 is a block circuit diagram of still another embodiment of the receiver of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Antenna 12 High frequency amplifier circuit 14 1st mixer 18 1st intermediate frequency amplifier circuit 20 Divider 22 Broadband filter 24 Narrow band filter 26 2nd intermediate frequency amplifier circuit 28 2nd mixer 34 Notch filter circuit 38 1st Demodulation circuit 44 First level comparator 46 Third intermediate frequency amplification circuit 48 Second demodulation circuit 50 Second level comparator 52 Fluctuation detecting means 54 AND circuit 56 Control means 60 Noise blanker 62 Noise detector 64 Noise gate 70 level comparator

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/10 H04B 1/26

Claims (9)

(57) [Claims] 1. A first receiving system in which one antenna and a part of a received signal received by the antenna are converted into a first demodulated signal by a first demodulation circuit via a wideband filter and a notch filter circuit. A second demodulation circuit converts a part of the received signal into a second demodulated signal via a narrow band filter by a second demodulation circuit.
From the reception system and the levels of the first and second demodulated signals, it is detected that the level of the reception signal of the target reception frequency is high and the level of the reception signal of the transmission frequency of another station nearby and the level of disturbance noise are low. Detecting means, fluctuation detecting means for detecting that there is no level fluctuation of the second demodulated signal, control means for controlling ON / OFF of the notch filter circuit in accordance with signals from the detecting means and fluctuation detecting means; A receiver comprising: 2. A first receiving system wherein one antenna and a part of a received signal received by the antenna are converted into a first demodulated signal by a first demodulation circuit via a noise blanker and a notch filter circuit. A second demodulation circuit converts a part of the received signal into a second demodulated signal via a narrow band filter by a second demodulation circuit.
From the level of the noise detection signal of the noise blanker and the level of the second demodulated signal, the level of the reception signal of the target reception frequency is high and the level of the reception signal of the transmission frequency of another station and the level of the disturbance noise are in the vicinity thereof. Detecting means for detecting a low level, fluctuation detecting means for detecting that there is no level fluctuation of the second demodulated signal, and turning on / off the notch filter circuit in response to signals from the detecting means and fluctuation detecting means.
Control means for performing FF control. 3. A receiving system for converting a received signal received by an antenna into a demodulated signal by a demodulation circuit via a noise blanker, a filter having a narrower bandwidth and a notch filter circuit, a noise detection signal of the noise blanker, Detecting means for detecting that the level of the received signal of the target reception frequency is high from the level of the demodulated signal and the level of the received signal and the disturbance noise of the transmission frequency of another station in the vicinity thereof is low, and there is no level fluctuation of the demodulated signal. A receiver comprising: a fluctuation detecting means for detecting the change; and a control means for controlling ON / OFF of the notch filter circuit according to signals from the detecting means and the fluctuation detecting means. 4. The receiver according to claim 1, wherein said detecting means determines that a level of said first demodulated signal or said noise detection signal is lower than a first reference value. A receiver configured to determine that the level of the second demodulated signal or the demodulated signal is higher than a second reference value. 5. The receiver according to claim 1, wherein the detecting means comprises a level of the first demodulated signal or the noise detection signal and a level of the second demodulated signal or the demodulated signal. And a receiver configured to determine that the difference from the reference value is smaller than the reference value. 6. The receiver according to claim 1, wherein said detecting means controls a level of said second demodulated signal or said demodulated signal to a level of said first demodulated signal or said noise detection signal. A receiver configured to determine that a quotient divided by is greater than a reference value. 7. The receiver according to claim 1, wherein said detecting means determines a level of said second demodulated signal or said demodulated signal from a level of said first demodulated signal or said noise detection signal. Is subtracted to obtain a difference between the two, and the second demodulated signal or the level of the demodulated signal is divided by the difference to determine whether a quotient is greater than a reference value. 8. The receiver according to claim 1, wherein the fluctuation detecting means samples the level of the second demodulated signal or the demodulated signal at a predetermined cycle, and samples and stores the level first. A receiver configured to determine that a difference between the sampled level and the newly sampled level is less than a reference value. 9. The receiver according to claim 1, wherein the fluctuation detecting means samples the level of the second demodulated signal or the demodulated signal at a predetermined cycle, and samples and stores the level first. A receiver configured to determine that a ratio of the sampled level to the newly sampled level is within a predetermined range centered at one.