JP3157281B2 - 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 which is automatically controlled to an optimal setting according to the state of a received signal.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No. Hei 3-187623 discloses a technique for selecting one of a plurality of IF band filters incorporated in a receiver in accordance with the state of a received signal. Briefly describing this technology, the tuning frequency of the receiver is shifted to a predetermined range above and below the target reception frequency by the user, and the transmission frequency of the other station is shifted to the vicinity of the target reception frequency from the level of the received signal obtained by the shift. The presence / absence of a signal is determined, and if a signal of a transmission frequency of another station exists, a narrow-band IF band filter is selected, and if not, a wide-band IF band filter is selected.

[0003] This technique is excellent in that a conventional user listens to a demodulated output of a target reception frequency from a receiver and automatically switches and selects an IF band filter based on the user's judgment. It is. Then, the distortion due to the intermodulation can be removed by automation.

[0004]

In the above prior art, the presence of a signal of a transmission frequency of another station is determined by the level of a received signal of only that frequency. The IF band filter is not selected by a relative comparison between the level of the received signal of the other station and the level of the received signal of the transmission frequency of another nearby station. As a result, even if the level of the reception signal of the target reception frequency is relatively considerably higher than the level of the reception signal of the transmission frequency of another station, if the reception signal of the transmission frequency of the other station exceeds a predetermined level, the narrow band The IF band filter is selected, and the sound quality is unnecessarily deteriorated. Also, the level of the reception signal at the target reception frequency and the level of the reception signal at the transmission frequency of another station are relatively similar in magnitude, but if both levels are small, a wideband IF band filter is selected, There is a problem that intermodulation is easily caused.

The present invention has been made in view of the circumstances of the related art, and has been developed in consideration of the level of a reception signal including a signal of a transmission frequency of another station close to a target reception frequency obtained through a wide band filter and a narrow band. A receiver that performs a relative comparison operation with the level of a received signal of only a target reception frequency obtained through a filter and automatically controls an optimal setting state according to a reception situation based on the calculation result. The purpose is to provide.

[0006]

In order to achieve the above object, a receiver according to the present invention comprises a single antenna and a wideband filter and a variable bandwidth filter for converting a part of a signal received by the antenna. A first demodulation signal through a first demodulation circuit through a first demodulation circuit, and a second demodulation circuit through a second demodulation circuit through part of the received signal through a narrowband filter. And a comparison operation means for comparing the level of the first demodulated signal and the level of the second demodulated signal and controlling the bandwidth of the bandwidth variable filter based on the operation result, It is provided with.

[0007] Further, the receiver according to the present invention provides a single antenna and a part of a received signal received by the antenna as a first demodulated signal by a first demodulation circuit via a wide band filter and an AGC. A first receiving system including means, a second receiving system for converting a part of the received signal to a second demodulated signal by a second demodulation circuit via a narrow band filter, and a first receiving system for the first demodulated signal. A comparison operation means for comparing a level with the level of the second demodulated signal and controlling a time constant of the AGC means based on the operation result may be provided.

The receiver according to the present invention is configured such that a first demodulation circuit performs a first demodulation on a single antenna and a part of a received signal received by the antenna via a noise blanker and a variable bandwidth filter. A first receiving system that is a signal, a second receiving system that makes a part of the received signal a second demodulated signal by a second demodulation circuit via a narrow band filter, and a noise detection signal of the noise blanker And a comparison operation means for comparing the level of the second demodulated signal with the level of the second demodulated signal and controlling the bandwidth of the bandwidth variable filter based on the operation result.

In the receiver of the present invention, 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. A first receiving system including AGC means;
A second receiving system in which a part of the received signal is converted into a second demodulated signal by a second demodulation circuit via a narrow band filter; a level of a noise detection signal of the noise blanker; Comparison operation means for comparing the level with the level and controlling the time constant of the AGC means based on the operation result.

[0010]

[Operation] Since the second demodulated signal obtained in the second receiving system passes through a narrow band filter, a signal of only the target receiving frequency can be obtained, but the first demodulated signal obtained in the first receiving system is obtained. Is a signal obtained by superimposing a signal of a target reception frequency and a signal of a transmission frequency of another station in the vicinity thereof in accordance with the bandwidth of the bandwidth variable filter. Therefore, by controlling the bandwidth of the bandwidth variable filter based on the result of relatively comparing the levels of the first and second demodulated signals, the signal of the transmission frequency of the other station near the target reception frequency is obtained. If the level is relatively large, the bandwidth is narrowed to improve the clarity of the demodulated output of the target reception frequency, and if the level is relatively small,
By increasing the bandwidth, the sound quality of the demodulated output at the target reception frequency can be improved.

When the level of the signal of the transmission frequency of another station nearby is relatively large with respect to the signal of the target reception frequency, it is expected that an interference signal from the other station exists. Therefore, if the level of the first demodulated signal is relatively larger than the reference value by the comparison operation than the level of the second demodulated signal, the AGC means is used to suppress the level fluctuation of the first demodulated signal due to the interference signal. By controlling the constant to be small, the response speed of the AGC control is increased, and the level fluctuation due to the interference signal of the first demodulated output can be suppressed.

The noise detection signal of the noise blanker provided in the first reception system is a signal in which a signal of a target reception frequency and a signal of a transmission frequency of another station in the vicinity thereof are superimposed. Accordingly, by setting the bandwidth of the bandwidth variable filter based on the result of relatively comparing the level of the noise detection signal and the level of the second demodulated signal, the clarity of the demodulated output according to the reception situation Or sound quality can be improved.

If the level of the noise detection signal of the noise blanker is relatively higher than the level of the second demodulated signal by the comparison operation, the time constant of the AGC means is advanced to increase the level of the first demodulated output by the interference signal. Fluctuations can be suppressed.

[0014]

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, and FIG. 2 is a diagram for explaining the relationship between the bandwidths of the wide band filter and the narrow band filter of FIG. 3 is a flowchart illustrating different operations by the comparison operation unit in FIG. 1.

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. In addition, as shown in FIG. 2, 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 wideband filter 22 is applied to a second intermediate frequency amplifier circuit 28 via a variable bandwidth filter 26 and amplified, and is applied to a second mixer 30. And part of it is AG
C means 32. This second mixer 30 includes:
The second local oscillation signal from the second local oscillation circuit 34 is provided, and the second intermediate frequency signal obtained by frequency-converting the first intermediate frequency signal is provided to the first demodulation circuit 36, and the first A demodulated signal is output. This first demodulated signal is amplified by the low-frequency amplifier circuit 38 and output from the speaker 40 as a low-frequency signal. Further, a part of the first demodulated signal is provided to the comparison operation means 42 constituted by a microcomputer or the like.

The first signal passing through the narrow band filter 24 is
The intermediate frequency signal is supplied to a third intermediate frequency amplifier circuit 44 and amplified, and the amplified output is supplied to a second demodulation circuit 46 to output a second demodulated signal. The second demodulated signal is provided to the comparison operation means 42.

As will be described later, the comparison operation means 42 performs a comparison operation on the levels of the first and second demodulated signals, controls the bandwidth of the bandwidth variable filter 26 on the basis of the operation result, and controls the AGC means. 32 time constants are controlled. The bandwidth variable filter 26 is not limited to the one in which a plurality of filters having different bandwidths are connected in parallel and one of them is switched and selected by the signal of the comparison operation means 42. The passband tuning circuit, the IF WIDTH circuit, etc. It may be used. Also, the AGC means 32
The AGC signal is supplied to the first and second intermediate frequency amplifier circuits 18 and 28 with a time constant based on the signal from the comparison operation means 42 according to the level of the intermediate frequency signal.

A first receiving system is constituted by a path from the high-frequency amplifier circuit 12 to the first demodulation circuit 36 via the wide-band filter 22, and a second reception system is formed from the high-frequency amplifier circuit 12 via the narrow-band filter 24. The path to the demodulation circuit 46 constitutes a second receiving system.

Next, referring to FIG.
Will be described. First, the difference between the levels of the first and second demodulated signals is calculated (step), and the difference is compared with a reference value (step). By the way, the first
Since the demodulated signal includes a signal of the target reception frequency and a signal of a transmission frequency of another station in the vicinity thereof, it is at a higher level than the second demodulated signal of only the target reception frequency. And, a small difference between the levels of the first and second demodulated signals means that the level of the signal of the transmission frequency of another station close to the target reception frequency is small and the interference signal is small. Also, a large level difference means that the level of the signal of the transmission frequency of another station in the vicinity is high, and that there is a large amount of interference signal and intermodulation occurs. Therefore, if the difference is smaller than the reference value in the step, a filter having a wider bandwidth of the bandwidth variable filter 26 is selected or controlled so that the bandwidth is expanded (step). Furthermore, A
Increase the time constant of the GC means 32 (step), and return to the step. If the difference is larger than the reference value in the step, a filter having a narrow bandwidth of the bandwidth variable filter 26 is selected or the control is performed such that the bandwidth is reduced (step). Further, the time constant of the AGC means 32 is reduced (step), and the process returns to the step. If the difference and the reference value are almost the same in the step, the bandwidth of the bandwidth variable filter 26 is left as it is (step), and the time constant of the AGC means 32 is also left as it is (step). Return.

By the control of the bandwidth of the variable bandwidth filter 26 by the comparison operation means 42 and the control of the time constant of the AGC means 32, the receiver is automatically set to an optimum setting state according to the reception condition of the target reception frequency. Is controlled. In addition,
It is needless to say that the order of the step and the step may be reversed.

Referring to FIG. 4, comparison operation means 42
The second operation will be described. The difference between the operation shown in FIG. 4 and the operation shown in FIG. 3 is that the level of the second demodulated signal is first divided by the level of the first demodulated signal instead of the steps in FIG. The quotient is compared with a reference value (step a). If the quotient is larger than the reference value in step a, the bandwidth of the bandwidth variable filter 26 is increased (step), the time constant of the AGC means 32 is increased (step), and the process returns to step a. If the quotient is smaller than the reference value in step a, the bandwidth of the bandwidth variable filter 26 is reduced (step), the time constant of the AGC means 32 is reduced (step), and the process returns to step a. And step a
If the quotient and the reference value are substantially the same, the bandwidth of the bandwidth variable filter 26 is left as it is (step), and AG
The time constant of the C means 32 is also kept as it is (step),
Return to step a.

In the operation shown in FIG. 4, regardless of the magnitude of the received signal strength at the target reception frequency, the signal at the target reception frequency is relatively compared with the signal including the transmission frequencies of other nearby stations. Thus, it is possible to determine the reception status, and it is suitable for receiving a target reception frequency having a weak reception signal strength. Note that, in step a, the first demodulated signal may be divided by the second demodulated signal, and the condition leading to step in step a may be changed.

Further, referring to FIG.
The third operation will be described. The operation shown in FIG.
4 is different from step a in FIG. 4 in that first, the difference between the levels of the first and second demodulated signals is calculated (step), and the level of the second demodulated signal is calculated in steps. Divided by the difference (step b),
The quotient is compared with a reference value (step a). The operation after step a is the same as the operation in FIG.

In the operation shown in FIG. 5, in step b, the ratio between the reception signal of the transmission frequency of another station near the target reception frequency and the reception signal of the target reception frequency is calculated. Regardless of the magnitude of the signal strength, it is possible to determine a more accurate reception situation.

Further, the fourth operation of the comparison operation means will be described with reference to FIG. The operation shown in FIG. 6 is applied to a configuration in which the bandwidth variable filter 26 can change between two bandwidths, wide and narrow, and the time constant of the AGC means 32 can be switched between two, large and small. . First, the first
It is determined whether the demodulated signal is below a predetermined level (step). If the first demodulated signal is equal to or lower than the predetermined level in this step, it is next determined whether the second demodulated signal is equal to or higher than the predetermined level (step). If the conditions are satisfied in both of these steps, it can be determined that the received signal strength of the target reception frequency is high and the reception signal strength of the transmission frequency of another station is low. Therefore, a filter having a wide bandwidth is selected by the variable bandwidth filter 26 (step), the time constant of the AGC means 32 is switched to a large value (step), and the process returns to the step. If any one of the steps does not satisfy the condition, it can be determined that the received signal strength of the transmission frequency of another station is large, and a filter with a narrow bandwidth is selected by the bandwidth variable filter 26 (step), and the AGC is performed. The time constant of the means 32 is switched to a small value (step), and the process returns to the step.

The operation shown in FIG. 6 can be realized by a simple comparison means by appropriately setting the predetermined level for comparing the first and second demodulated signals with each other.

Further, another embodiment of the receiver according to the present invention will be described with reference to FIGS. FIG.
It is a block circuit diagram of another embodiment of the receiver of the present invention,
FIGS. 8 to 10 are flowcharts for explaining different operations by the comparison operation means in FIG. 7, 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. 7 differs from FIG. 1 in that a noise blanker 50 is provided in place of the broadband filter 22 in FIG. 1 and a noise detector 5 is provided in place of the first demodulated signal.
2 is supplied to the comparison operation means 42. In the noise blanker 50, one of the first intermediate frequency signals divided into two by the distributor 20 is provided to the noise gate 54 and the noise amplifier 56. The noise amplifier 56 amplifies the first intermediate frequency signal and supplies the amplified signal to the noise detector 52, which outputs a noise detection signal. Then, the noise detection signal is supplied to the comparison operation means 42 and to a gate control circuit 58 having a threshold value. Then, the gate control circuit 58 extracts pulse noise having a magnitude equal to or larger than the threshold included in the noise detection signal, and turns on / off the noise gate 54 in accordance with the extracted pulse noise.
F, the first intermediate frequency signal from which the pulse noise has been removed through the noise gate 54 is applied to the bandwidth variable filter 2.
6 given.

Here, the noise detection signal includes, in addition to the reception signal of the target reception frequency, the reception frequency of another station nearby and the reception signal due to disturbance noise. Therefore, the level of this noise detection signal and the narrow band filter 2
By comparing the level of the second demodulated signal consisting only of the reception signal of the target reception frequency through the step 4 with the receiver, the receiver can be set to a setting state according to the reception state, similarly to the receiver shown in FIG. It is possible.

The first operation of the comparison operation means 42 in FIG. 7 for comparing the level of the noise detection signal with the level of the second demodulated signal will be described with reference to FIG. First, a difference between the level of the noise detection signal and the level of the second demodulated signal is calculated (step), and the bandwidth of the bandwidth variable filter 26 is appropriately adjusted and set according to the difference (step). , The time constant of the AGC means 32 is appropriately adjusted and set.

In this operation, the variable bandwidth filter 26 and the AGC means 32 are controlled according to the received signal strength other than the target reception frequency included in the noise detection signal, and the received signal strength other than the target reception frequency is strong. In addition, the bandwidth is narrowed, the AGC time constant is reduced, the clarity is improved, and the influence of the intermodulation due to the interference is eliminated, so that the fluctuation of the demodulation output does not occur. If the received signal strength other than the target reception frequency is weak, the bandwidth is expanded and the AGC time constant is increased, thereby improving the sound quality.

Referring to FIG. 9, the second operation of the comparison operation means 42 in FIG. 7 will be described. First, a ratio between the level of the noise detection signal and the level of the second demodulated signal is calculated (step a), and the bandwidth of the bandwidth variable filter 26 is appropriately adjusted and set according to the ratio (step a). The time constant of the AGC means 32 is appropriately adjusted and set according to this ratio.

The third operation of the comparison means 42 in FIG. 7 will be described with reference to FIG. First,
The difference between the level of the noise detection signal and the level of the second demodulated signal is calculated (step), and the ratio between the second demodulated signal and the difference obtained in the step is calculated (step b). The bandwidth of the bandwidth variable filter 26 is appropriately adjusted (step a), and the time constant of the AGC means 32 is appropriately adjusted and set according to the ratio.

In another embodiment of the receiver of the present invention shown in FIG. 7, a noise blanker 50 is used in place of the wideband filter 22 of the receiver shown in FIG. It is suitable to be applied to a receiver provided.

Still another embodiment of the receiver according to the present invention will be described with reference to FIG. 11, the same or equivalent circuit blocks as those in FIG. 7 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 11 differs from FIG. 7 in that FIG.
, The distributor 20, the narrow band filter 24, the third intermediate frequency amplifier circuit 44, and the second demodulation circuit 46 are omitted.
Is supplied to the noise gate 54 and the noise amplifier 56 of the noise blanker 50, and the first demodulated signal output from the first demodulation circuit 36 is This is to be provided to the low frequency amplifier circuit 38 and the comparison operation means 42. Note that the maximum bandwidth of the bandwidth variable filter 26 is the noise blanker 5
At 0, it is set narrower than the bandwidth in which the noise detection signal is detected.

In such a configuration, as compared to the first demodulated signal due to the difference in bandwidth, the noise detection signal is used to transmit a greater number of transmission frequencies of other stations near the target reception frequency and the received signal due to disturbance noise. May include. Therefore, by comparing the level of the noise detection signal with the level of the first demodulated signal, the receiver is automatically set to the optimum setting state according to the reception state, similarly to the receiver shown in FIGS. Can be switched.

In the above description of the embodiment, the comparison operation means 42 performs comparison operation processing by software using a microcomputer or the like. However, the invention is not limited to this, and the comparison operation means may be constituted by discrete parts. Of course, it is also good. And a DSP as a comparison operation means.
(Digital signal processor).
Further, it will be easily understood that the level of the second and third intermediate frequency signals may be compared instead of performing the comparison operation on the level of the first and second demodulated signals. Similarly, instead of comparing the level of the noise detection signal and the level of the second demodulated signal, the level of the signal at the preceding stage of the noise detector 52 and the level of the third intermediate frequency signal may be compared. Further, in the above embodiment, the case of single mode reception is described, but in the case of having a multi-mode switching reception function,
According to the reception mode, the narrow band filter 24 of the second reception system
, The pass band width of the first receiving system is variable.
May be appropriately controlled so as to be narrower than the bandwidth selected in the above.

[0040]

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 level of the received signal at the target receiving frequency is relatively compared with the level of the received signal including the target receiving frequency and the transmitting frequency of another station near the target receiving frequency. If the received signal of the target reception frequency is relatively larger than the reception signal of the transmission frequency of another nearby station, the interference signal is determined. In addition to improving the sound quality by expanding the bandwidth without the existence of the signal, if the received signal of the transmission frequency of another station in the vicinity is relatively large, the demodulation output is reduced by reducing the bandwidth to eliminate the intermodulation due to the interference signal. Improve clarity. As described above, the receiver is automatically adjusted to the optimum setting state according to the reception state, and the operation is extremely simple.

In the receiver according to the second aspect, if the interference signal does not exist, the time constant of the AGC means is increased to reproduce the demodulated output faithfully according to the reception condition, and if the interference signal exists, The receiver is automatically adjusted to the optimum setting state so that the time constant of the AGC means is reduced and the demodulation output of intermodulation due to interference is eliminated, and the operation is simpler.

Also, in the receiver according to the third and fourth aspects, the receiver is automatically adjusted to the optimum setting state similarly to the receivers according to the first and second aspects, and the operation is simple. is there. In addition, since the level of the noise detection signal of the noise blanker is used to determine the reception status, it is suitable for application to a receiver having a noise blanker.

Further, in the receivers according to the eleventh and twelfth aspects, similarly to the receivers according to the first to fourth aspects, the receiver is automatically adjusted to the optimum setting state according to the reception situation. Easy to operate. Moreover, since the level of the noise detection signal of the noise blanker is compared with that of the demodulated signal, a receiving system using a narrow band filter is not required, and it can be applied to a receiver equipped with a noise blanker with a simpler configuration. it can.

[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 diagram illustrating the relationship between the bandwidths of a wide band filter and a narrow band filter of FIG. 1;

FIG. 3 is a flowchart illustrating a first operation by a comparison operation unit in FIG. 1;

FIG. 4 is a flowchart illustrating a second operation performed by the comparison operation unit in FIG. 1;

FIG. 5 is a flowchart illustrating a third operation by the comparison operation unit in FIG. 1;

FIG. 6 is a flowchart illustrating a fourth operation performed by the comparison operation unit in FIG. 1;

FIG. 7 is a block circuit diagram of another embodiment of the receiver of the present invention.

FIG. 8 is a flowchart illustrating a first operation of the comparison operation unit in FIG. 7;

FIG. 9 is a flowchart illustrating a second operation of the comparison operation unit in FIG. 7;

FIG. 10 is a flowchart illustrating a third operation of the comparison operation unit in FIG. 7;

FIG. 11 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 Bandwidth variable filter 28 2nd intermediate frequency amplifier circuit 30 2nd mixer 32 AGC means 36 first demodulation circuit 42 comparison operation means 44 third intermediate frequency amplification circuit 46 second demodulation circuit 50 noise blanker 52 noise detector 54 noise gate

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 1/10 H04B 1/16 H04B 1/26

Claims (12)

(57) [Claims] 1. A first reception unit, wherein one antenna and a part of a reception signal received by the antenna are converted to a first demodulation signal by a first demodulation circuit via a wideband filter and a variable bandwidth filter. And a second demodulation circuit for converting a part of the received signal into a second demodulated signal by a second demodulation circuit via a narrow band filter.
And the level of the first demodulated signal and the level of the second
And a comparator for comparing the level of the demodulated signal and controlling the bandwidth of the variable bandwidth filter based on the result of the operation. 2. One antenna and a first reception signal including an AGC means while a first demodulation circuit converts a part of a reception signal received by the antenna into a first demodulation signal via a wideband filter and a first demodulation circuit. System, a second reception system in which a part of the reception signal is converted to a second demodulation signal by a second demodulation circuit via a narrow band filter, a level of the first demodulation signal, and a second demodulation signal. A comparison operation means for comparing the signal level with the signal level and controlling the time constant of the AGC means based on the operation result. 3. A first receiving unit which makes one antenna and a part of a reception signal received by this antenna a first demodulation signal in a first demodulation circuit via a noise blanker and a variable bandwidth filter. And a second demodulation circuit for converting a part of the received signal into a second demodulated signal by a second demodulation circuit via a narrow band filter.
And a comparison operation means for comparing the level of the noise detection signal of the noise blanker with the level of the second demodulated signal and controlling the bandwidth of the bandwidth variable filter based on the operation result. A receiver comprising: 4. An antenna and a first reception circuit including a part of a reception signal received by the antenna, which is converted into a first demodulation signal by a first demodulation circuit via a noise blanker and includes AGC means. A second receiving system for making a part of the received signal a second demodulated signal in a second demodulating circuit via a narrow band filter; and a level of a noise detection signal of the noise blanker and the second receiving system. A comparison operation means for comparing the level of the demodulated signal with the level of the demodulated signal and controlling the time constant of the AGC means based on the operation result. 5. The receiver according to claim 1, wherein said comparing and calculating means calculates a difference between a level of said first demodulated signal and a level of said second demodulated signal, and the difference is a reference value. If smaller, the bandwidth of the variable bandwidth filter is expanded or the time constant of the AGC means is increased. If the difference is equal to a reference value, the bandwidth of the variable bandwidth filter or the time constant of the AGC means is increased. Wherein the control is performed such that the bandwidth of the variable bandwidth filter is reduced or the time constant of the AGC means is reduced if the difference is larger than a reference value. 6. The receiver according to claim 1, wherein said comparison operation means calculates a quotient obtained by dividing a level of said second demodulated signal by a level of said first demodulated signal. If it is larger than the reference value, the bandwidth of the variable bandwidth filter is expanded or the time constant of the AGC means is increased. If the quotient is the same as the reference value, the bandwidth of the variable bandwidth filter or the AGC means is increased. A receiver, wherein a time constant is kept as it is, and if the quotient is smaller than a reference value, control is performed so as to reduce the bandwidth of the bandwidth variable filter or reduce the time constant of the AGC means. 7. The receiver according to claim 1, wherein said comparison operation means calculates a difference between a level of said first demodulated signal and a level of said second demodulated signal, and said second operation is carried out. Calculate a quotient obtained by dividing the demodulated signal by the difference,
If the quotient is larger than a reference value, the bandwidth of the variable bandwidth filter is increased or the time constant of the AGC means is increased. If the quotient is the same as the reference value, the bandwidth of the variable bandwidth filter or the A receiver characterized in that the time constant of the AGC means is kept as it is, and if the quotient is smaller than a reference value, the bandwidth of the variable bandwidth filter is reduced or the time constant of the AGC means is reduced. . 8. The receiver according to claim 3, wherein said comparison calculation means calculates a difference between a level of a noise detection signal of said noise blanker and a level of said second demodulation signal, and according to the difference. A bandwidth of the variable bandwidth filter or a time constant of the AGC means. 9. The receiver according to claim 3, wherein said comparison operation means calculates a ratio between a level of a noise detection signal of said noise blanker and a level of said second demodulation signal, and according to said ratio. A bandwidth of the variable bandwidth filter or a time constant of the AGC means. 10. The receiver according to claim 3, wherein said comparing and calculating means calculates a difference between a level of a noise detection signal of said noise blanker and a level of said second demodulated signal, and calculates the difference between said level and said second demodulated signal. A receiver which calculates a ratio of the second demodulated signal and sets a bandwidth of the bandwidth variable filter or a time constant of the AGC means according to the ratio. 11. A receiving system in which a received signal received by an antenna is converted into a demodulated signal by a demodulation circuit through a noise blanker and a bandwidth variable filter having a bandwidth narrower than a bandwidth in which a noise detection signal is output by the noise blanker. And comparison operation means for comparing the level of the noise detection signal of the noise blanker and the level of the demodulated signal and controlling the bandwidth of the bandwidth variable filter based on the comparison result. Receiver. 12. A demodulation circuit converts a received signal received by an antenna into a demodulated signal through a noise blanker and a filter having a narrower bandwidth than a noise detection signal is output by the noise blanker, and includes an AGC means. A receiving system, a comparison operation means for comparing the level of the noise detection signal of the noise blanker with the level of the demodulated signal and controlling the time constant of the AGC means based on the comparison result;
A receiver comprising: