JP3214918B2 - 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 the time constant of the AGC means 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 technique, 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 another station near the target reception frequency is obtained from the level of the received signal obtained by shifting. The presence / absence of the signal is determined. If a signal of the 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-mentioned prior art, the clarity of the demodulated output of the target reception frequency is improved or the sound quality of the demodulation output of the target reception frequency is improved according to the state of the received signal. However, no improvement has been made with respect to a change in the volume of the demodulated output due to fading or disturbance noise.

The present invention has been made in view of the above prior art, and controls the time constant of the AGC means according to the state of a received signal, thereby fading or controlling the volume of a demodulated output due to a signal other than the target reception frequency. It is an object of the present invention to provide a receiver in which a change in the frequency is suppressed.

[0006]

In order to achieve the above object, in a receiver according to the present invention, a reception signal received by an antenna is demodulated by a demodulation circuit via a high frequency amplifier circuit, a noise blanker, and an intermediate frequency amplifier circuit. In a receiver for controlling at least one gain of the high frequency amplifier circuit and the intermediate frequency amplifier circuit by an AGC means which receives the output signal of the intermediate frequency amplifier circuit as an input while providing a demodulated signal, the gain of a noise amplifier is added to the noise blanker. Noise controlling noise
C means is provided, and a period detecting circuit detects an amplitude variation period of a control signal of the noise AGC means, and the control means controls a time constant of the AGC means according to the amplitude variation cycle.

The time constant of the AGC means may be controlled by the control means such that the time constant is reduced as the amplitude fluctuation cycle is longer and is increased as the amplitude fluctuation cycle is shorter.

The time constant of the AGC means can be switched between three levels, large, medium and small, and the control means reduces the time constant when the amplitude variation cycle is longer than a first predetermined cycle. When the period is shorter than the first predetermined period and shorter than the second predetermined period, the time constant is increased. When the amplitude fluctuation period is between the first and second predetermined periods, the time constant is set to medium. It can also be configured to do so.

[0009]

[Operation] The noise detection signal of the noise blanker includes a target reception frequency and a transmission frequency of another station in the vicinity thereof and a wide band signal such as disturbance noise. The control signal of the noise AGC means includes the noise detection signal. Smoothed, showing the overall amplitude variation of the wideband signal. When the amplitude fluctuation period of the control signal of the noise AGC means is, for example, 2 seconds or more and the period is long, it can be determined that fading has occurred. When the amplitude fluctuation period is particularly short, a high-level pulse is used. It can be determined that sexual disturbance noise is present. Therefore, by appropriately controlling the time constant of the AGC means in accordance with the amplitude fluctuation period, it is possible to suppress a change in the volume of the demodulated output due to an adverse effect such as fading or pulse noise.

If the time constant of the AGC means is made smaller as the amplitude fluctuation period becomes longer and is made longer as the amplitude fluctuation cycle becomes shorter, the change of the sound volume can be reduced by the fast AGC control with respect to the gradual change of the received signal amplitude such as fading. It is possible to suppress the disturbance noise of the pulse by the slow AGC control so that the sound volume of the demodulated output does not change due to the disturbance noise of the pulse.

If the AGC means has three stages,
Particularly fast or slow AGC control can be achieved only for fading or pulsed disturbance noise.

[0012]

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 a receiver according to the present invention, and FIG. 2 is a diagram showing a relationship between an amplitude variation period by the control means of FIG. 1 and a time constant of the AGC means.

In FIG. 1, a received signal received by an antenna 10 is amplified by a high-frequency amplifier circuit 12 and provided to a first mixer 14, and a first local oscillation signal from a first local oscillation circuit 16 and Mixed. This first mixer 14
Is output to a first intermediate frequency amplification circuit 18, a first intermediate frequency signal of a predetermined frequency is extracted and amplified, and is applied to a noise gate 22 and a noise amplifier 24 of a noise blanker 20. Can be The first intermediate frequency signal that has passed through the noise gate 22 is
Only a signal of a predetermined frequency is extracted and amplified by the intermediate frequency amplifying circuit 26, and supplied to the second mixer 28, and a part of the signal is supplied to the AGC means 30. The second mixer 28 is supplied with the second local oscillation signal from the second local oscillation circuit 32, is supplied with the frequency-converted second intermediate frequency signal to the demodulation circuit 34, and outputs the demodulated signal. Is done. This demodulated signal is amplified by the low-frequency amplifier 36 and output from the speaker 38 as a low-frequency signal.

The first intermediate frequency signal is amplified by a noise amplifier 24, detected by a noise detector 40, and converted into a noise detection signal. This noise detection signal is supplied to a noise AGC means 42 and a gate control circuit 43 having a threshold. Then, the control signal output from the noise AGC means 42 is given to the noise amplifier 24 to perform gain control, and the period detection circuit 4
4 given. Further, the pulse noise included in the noise detection signal is extracted by the gate control circuit 43, and the noise gate 22 is output in accordance with the extracted pulse noise.
Are turned on / off, and the first intermediate frequency signal from which the pulse noise has been removed through the noise gate 22 is supplied to the second intermediate frequency amplifier circuit 26.

An example of the cycle detection circuit 44 includes an edge detection circuit 46 and a frequency / voltage conversion circuit 48.
The rising edge or the falling edge due to the amplitude fluctuation of the control signal output from the noise AGC means 42 is detected, and a pulse is output from the edge detection circuit 46 for each edge.
Outputs a DC voltage signal. A DC voltage signal corresponding to the amplitude fluctuation period is supplied to the control means 50, and the control means 50 supplies the AGC means 30 with a time constant control signal for controlling the time constant. And the AGC means 30
The time constant controlled by the time constant control signal, the high frequency amplifier circuit 12 and the first
And the gains of the second intermediate frequency amplifier circuits 18 and 26 are appropriately controlled.

By the way, fading is a spatial phenomenon that affects a wide range near a target reception frequency, and causes a uniform amplitude fluctuation regardless of the strength of a radio wave or a modulation method. For this reason, when fading occurs, the noise detection signal including the target reception frequency and the signal of the transmission frequency of another station in the vicinity thereof is affected, and the noise detection signal is smoothed and output from the noise AGC means 42. Are also affected by amplitude fluctuations. Moreover, the amplitude fluctuation due to fading has a long cycle, for example, 2 seconds or more. If strong pulsed disturbance noise is present, the control signal of the noise AGC means 42 varies in amplitude in a short cycle.

Therefore, the period of the amplitude fluctuation is detected by the period detecting circuit 44 from the amplitude fluctuation of the control signal of the noise AGC means 42, and the control means 50 responds to this amplitude fluctuation by the control means 50 in FIG.
The time constant of the AGC means 30 is controlled as shown in FIG. In other words, the longer the amplitude fluctuation period, the higher the degree of fading, and the smaller the time constant of the AGC means 30, so as to suppress the change in the volume of the demodulated output with respect to the fluctuation in the amplitude of the received signal. Also, the shorter the amplitude fluctuation period, the higher the degree of the presence of pulsed disturbance noise.
By increasing the time constant of the C means 30, the gain of the AGC means 30 is prevented from being affected by the peak level of pulse noise or the like.

As described above, by controlling the time constant of the AGC means 30 in accordance with the amplitude fluctuation period of the control signal output from the noise AGC means 42 of the noise blanker 20, the influence of fading, pulse noise and the like is obtained. Even in the receiving situation, the receiver is automatically adjusted to the optimal setting state, the change in the volume is suppressed, the audibility is excellent, and the operation is extremely simple.

FIG. 3 is a flowchart showing another operation by the control means 50 of FIG. In the operation shown in FIG. 3, the AGC means 30 shown in FIG. 1 is configured so that the time constant can be freely switched between three stages of large, medium and small. First, a DC voltage signal corresponding to the amplitude fluctuation cycle detected by the cycle detection circuit 44 is supplied to the control means 50 (step), and this DC voltage signal is compared with a first reference value to determine that the amplitude fluctuation cycle is, for example, 2 It is determined whether it is extra long, such as longer than a second (step). Here, if the amplitude fluctuation period is particularly long, it is because fading has occurred, and the time constant of the AGC means 30 is set to a small value (step), and the process returns to the step. If the amplitude fluctuation cycle is not particularly long in the step, the cycle detection circuit 44
Is compared with the second reference value to determine whether the amplitude variation period is particularly short or not (step). Here, if the amplitude fluctuation period is particularly short, it is because pulse disturbance noise is present, and the time constant of the AGC means 30 is set to a large value (step), and the process returns to the step. If the amplitude fluctuation period is not particularly short in the step, the time constant of the AGC means 30 is set to medium (step), and the process returns to the step.

In such an operation, the AGC means 30 operates with an appropriate time constant in a normal appropriate receiving condition, and only when fading occurs or pulsed disturbance noise is present, the AGC means 30 responds to the receiving condition. The AGC means 30 can operate with a special time constant. Moreover, AGC means 3
Any circuit configuration can be used so long as the time constant of 0 can be switched stepwise, and the time constant can be set arbitrarily without being restricted by the circuit configuration.

The period detecting circuit 44 and the control means 5
0 may be processed by software using a microcomputer or the like, or may be processed by hardware using discrete components. And, needless to say, the configuration may be made using a DSP (Digital Signal Processor). The AGC means 30 only needs to be able to suppress a change in the volume of the low-frequency output from the speaker 38, and may use the high-frequency amplifier 12 and the first and second intermediate frequency amplifiers 18,
It is sufficient if at least one of the 26 gains is controlled.

[0022]

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

The time constant of the AGC means is automatically controlled by judging the receiving condition from the amplitude fluctuation period of the received signal.
A change in the volume of the demodulated output of the target reception frequency is suppressed. Therefore, the operation of the receiver of the present invention is extremely simple as compared with the conventional receiver in which the demodulated output is listened and the time constant of the AGC means is manually switched based on the user's judgment.

The longer the amplitude fluctuation cycle, the smaller the time constant of the AGC means, and the shorter the amplitude fluctuation cycle, the smaller the AGC means.
If the time constant of the means is large, it is possible to reliably suppress the change in the volume of the demodulated output with respect to a gradual change in the amplitude of the received signal, and to prevent the volume from changing due to pulse disturbance noise or the like. it can.

If the time constant of the AGC means can be switched in a stepwise manner, the time constant is particularly small or large only in a bad reception situation such as the occurrence of fading or the arrival of pulsed disturbance noise. Can be easily set, and it is easy to adjust the receiver to the optimum setting state according to the reception situation.

[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 showing a relationship between an amplitude fluctuation period by a control unit of FIG. 1 and a time constant of an AGC unit;

FIG. 3 is a flowchart showing another operation by the control means of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Antenna 12 High frequency amplifier circuit 14 1st mixer 18 1st intermediate frequency amplifier circuit 20 Noise blanker 26 2nd intermediate frequency amplifier circuit 28 2nd mixer 30 AGC means 34 Demodulation circuit 40 Noise detector 42 Noise AGC means 44 Period detection circuit 50 Control means

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-69819 (JP, A) JP-A-6-69818 (JP, A) JP-A-5-335981 (JP, A) JP-A-5-35981 335980 (JP, A) JP-A-3-187623 (JP, A) JP-A-60-62712 (JP, A) JP-A-3-214932 (JP, A) JP-A-60-68729 (JP, U) Japanese Utility Model Application 57-191115 (JP, U) Japanese Utility Model Application 55-165553 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/10 H04B 1/06 H04B 1/16

Claims (3)

(57) [Claims] An AGC receiving a signal received by an antenna through a high frequency amplifier circuit, a noise blanker and an intermediate frequency amplifier circuit to form a demodulated signal at a demodulator circuit, and receiving an output signal of the intermediate frequency amplifier circuit as an input. In a receiver for controlling at least one gain of the high frequency amplifier circuit and the intermediate frequency amplifier circuit by means, a noise AGC means for controlling a gain of a noise amplifier is provided in the noise blanker, and an amplitude variation of a control signal of the noise AGC means is provided. A receiver, wherein a period is detected by a period detection circuit, and a time constant of the AGC unit is controlled by a control unit in accordance with the amplitude change period. 2. The receiver according to claim 1, wherein said A
The receiver is characterized in that the control means controls the time constant of the GC means so as to decrease as the amplitude fluctuation cycle becomes longer and to increase as the amplitude fluctuation cycle becomes shorter. 3. The receiver according to claim 1, wherein said A
The time constant of the GC means can be freely switched between three levels, large, medium and small, and the control means makes the time constant small when the amplitude variation cycle is longer than the first predetermined cycle, and the amplitude variation cycle is the first The time constant is set to be large when the period is shorter than the second predetermined period, which is shorter than the predetermined period, and the time constant is set to be medium when the amplitude fluctuation period is between the first and second predetermined periods. Receiver.