JPS6331966B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a tone squelch device that allows the detection output of a receiver to be passed to a speaker only when a predetermined tone signal is included in received radio waves. .

Prior Art In a simple wireless system for business use, in order to enable multiple groups to share a carrier frequency of, for example, 150 MHz, the modulated signal in the transmitted radio wave is set to 67 Hz, for example, as shown in Figure 5, in addition to the audio signal. ~
Out of a total of 33 tone signals with a band of 250.3 Hz, one tone signal, for example, a 250.3 Hz tone signal, is assigned to group A, and the other group B is assigned, for example, a 67 Hz tone signal, and the receiver side In this case, only while detecting a pre-assigned tone signal, the audio cutoff switch is controlled on and off so that the detected output is passed to the speaker. In this way, group A
Group B turns on the audio cutoff switch and takes out the audio from the speaker only when a 250.3Hz tone signal is detected, and Group B turns off the sound cutoff switch when receiving a 250.3Hz tone signal.
If a 67Hz tone signal is used, the operation is the opposite of the above, so you will not be able to hear the conversations of other groups, and although it will not be possible to use multiple groups in the same area at the same time, you will not be able to hear the conversations of other groups. No more audio interference.

FIGS. 6 and 7 are block diagrams showing examples of the configuration of conventional tone squelch devices, with FIG. 6 showing an analog type one and FIG. 7 showing a digital type one.

In FIG. 6, radio waves received by an antenna 1 are input to a receiving section 2, from which a detected output is extracted. This detected output is guided to a speaker 4 via a sound cutoff switch 3 and is also input to a bandpass filter 5. band pass filter 5
The center frequency of the filter is set so as to pass only the tone signal previously assigned to the receiver. For example, if the receiver is of group A, the center frequency is set to 250.3Hz. The output of the bandpass filter 5 is the rectifier circuit 6
The tone signal is then rectified. This rectified output is applied as a control signal to the sound cutoff switch 3, and when the rectified output reaches a predetermined level or higher, the sound cutoff switch 3 is turned on.

On the other hand, in FIG. 7, instead of the bandpass filter 5 and rectifier circuit 6, a lowpass filter 7 that extracts only the tone signal band component (67 to 250.3Hz) from the detected output and the output of the lowpass filter 7 are used. a waveform shaping circuit 8 that shapes the pulse waveform;
A frequency measuring means 9 for measuring the frequency of the output pulse of the waveform shaping circuit 8, and a determining means 10 for determining at each predetermined period whether or not the measured frequency matches a tone frequency previously assigned to the receiver. ,
Each time the determination means 10 determines that the measured frequency matches the tone frequency range, it is re-triggered, and when it is re-triggered, it outputs an ON signal for a predetermined period of time, for example, 3 seconds, and the sound cut-off switch 3 is activated.
It is composed of an on-signal generating means 11 that turns on the on-signal.

Such a conventional tone squelch device has the following features.

In the case of analog type (Figure 6) Since the bandpass filter 5 is a fixed single wave type, in the case of multitone type, bandpass filters of as many types as the number of tones are required, realizing a tone squelch device without adjustment. difficult to do. Recently, there have been some bandpass filters that use switched capacitor filters to achieve multi-tone and no adjustment, but switched capacitor filters are still expensive.

Audio malfunctions occur.

Usually 600-700Hz for men, 700-700Hz for women
It has a voice spectrum of 800Hz, but if you bring your mouth close to the microphone and speak in a low and loud voice, it will also contain many frequency components of 300 to 400Hz. When this low frequency component of 300 to 400 Hz increases, the original tone signal becomes smaller due to the blocking phenomenon, which may cause the tone squelch to malfunction and close the sound cutoff switch 3 unnecessarily (this is called a sound malfunction).

Noise causes malfunction.

Even when the radio is in a no-signal state, the output from the detection output (white noise) contains a spectrum of 67 to 250.3Hz, which is a tone signal component, so the tone squelch malfunctions and the audio cutoff switch 3 does not need to be opened. (This is called a noise malfunction).

In case of digital type (FIG. 7) By changing the frequency information given to the discriminating means 10, a multi-tone type can be easily realized.

Due to the same reasons as the digital type, noise malfunctions occur with the same probability.

The action of the on-signal generating means 11 can reduce audio malfunctions. That is, since the on-signal generating means 11 continues to turn on the sound cutoff switch 3 for, for example, 3 seconds after detecting the tone signal as described above, the sound malfunction will not occur unless the cause of the sound malfunction continues for 3 seconds. In general, the low audio spectrum that causes audio malfunctions rarely lasts for more than 3 seconds, so
The above configuration can reduce audio malfunctions. However, because of this configuration, the voice cutoff switch 3 remains on for about 3 seconds after the call state changes from a call state to a non-call state, which has the disadvantage that noise is generated from the speaker 4 during this time. be.

Problems to be Solved by the Invention The present invention aims to solve the above-mentioned drawbacks of the conventional tone squelch device, which is easy to implement in a multitone system.

Means for Solving the Problems In order to solve the above problems, the present invention, as shown in FIG.
Sound cutoff switch 2 inserted in the path leading to
1, a low-pass filter 22 that extracts only tone signal band components from the detection output, a waveform shaping circuit 23 that shapes the output of the low-pass filter 22 into a pulse waveform, and a frequency that measures the frequency of the output pulse of the waveform shaping circuit 23. The measuring means 24, the determining means 25 which determines at predetermined intervals whether or not the frequency measured here matches a tone frequency previously assigned to the receiver; On-signal generating means 26 which is re-triggered every time it is determined that the tone frequency range matches the tone frequency range and outputs an on-signal for a predetermined time when re-triggered, and a high-pass filter 27 which extracts only high-frequency noise band components from the detected output. and a rectifier circuit 2 that rectifies the output of the high-pass filter 27.
8, and gate means 29 for applying the on signal to the audio cutoff switch 21 to turn it on only when the output of the rectifier circuit 28 is below a predetermined level.
and constitute a tone squelch device. Note that if a predetermined period of time has not elapsed since the last determination by the ON signal generating means 26 and the gate means 29 that the frequency measured by the determining means 25 matches the tone frequency range, and the output of the rectifier circuit 28 is at a predetermined level. A means is configured to turn on the audio cutoff switch 21 only in the following cases.

Operation If a tone signal assigned to the own receiver is present in the detection output of the receiver, the determining means 25 determines this and sends an on signal to the gate means 29. If the detected output does not contain a noise component, the gate means 29 applies an on signal to the audio cutoff switch 21 to turn it on, so that reproduced sound is extracted from the speaker 20. Even if the cause of the audio malfunction occurs, the ON signal generating means 26 continues to output the ON signal for a predetermined period of time, for example, 3 seconds from the time when the determining means 25 determines that a tone signal is included, so that the cause of the audio malfunction is detected. No audio malfunction will occur unless it lasts for more than 3 seconds. In addition, when the call is interrupted, the high-pass filter 27 and the rectifier circuit 28
When the noise is detected, the gate means 29 immediately stops sending out the on signal, so the audio cutoff switch 21 is quickly turned off and no unnecessary noise is emitted from the speaker 20.

Embodiment FIG. 2 is a block diagram of essential parts showing an example of the hardware configuration of the tone squelch device of the present invention.
In the figure, 30 is an antenna, 31 is a receiving section, and a detection output is extracted from this receiving section 31. The detected output is guided to a speaker 33 via an audio cutoff switch 32. The detection output is also input to a low pass filter 34 and a high pass filter 35. The low-pass filter 34 extracts only the tone signal band component (67 to 250.3Hz) from the detected output, and its output is input to the waveform shaping circuit 36, where it is shaped into a pulse waveform of "1" and "0". be done. This pulse is input to the input port IN1 of the microprocessor (MPU) 37. Further, the high-pass filter 35 extracts only high-frequency noise band components (80 to 100 kHz) from the detected output, and its output is input to a rectifier circuit 38 and rectified. Therefore, the output level of the rectifier circuit 38 increases or decreases depending on the magnitude of the noise, and this analog level is converted into a digital value by the A/D converter 39 and input to the input port IN2 of the MPU 37. The MPU 37 has an internal ROM and a RAM, and processes information from the input port as described later, and generates a signal from the output port OUT to turn on and off the audio cutoff switch 32.

3 and 4 are flowcharts showing an example of processing by the MPU 37. FIG. The MPU 37 executes the process shown in FIG. 3 at predetermined intervals and measures the frequency f of the pulse output from the waveform shaping circuit 36. This frequency measurement monitors the level of input port IN1 and changes the level from a predetermined edge, for example from “0” to “1”.
This is done by measuring how long it takes for the change to occur over multiple pulses and taking the average.

Furthermore, the MPU 37 executes the process shown in FIG. 4 at predetermined intervals. That is, the frequency f measured this time falls within a predetermined frequency range (f _{0 −α} =f _L <f ₀
+α=f _H ), and if so, reset the internal counter CNT to “0”, and if not, count up the internal counter CNT by +1 without resetting the internal counter CNT to “0”. . Next, it is determined whether the value of the internal count CNT has reached a value T corresponding to, for example, 3 seconds in terms of time, and if it has reached it, flag A is set to "0"; if it has not reached it, it Set flag A to "1". Next, the output level of the A/D converter 39 is read from the input port IN2, and it is determined whether or not it is above a predetermined level indicating the presence of noise. If it is above the predetermined level, flag B is set to "0". death,
If the predetermined level is not exceeded, flag B is set to "1". Then, it is determined whether flags A and B are both "1", and if both are "1", that is, 3 seconds have passed since it was determined that the measured frequency matches the predetermined frequency. If the time has not passed and no noise has appeared, turn on the output of the output port OUT, turn on the audio cutoff switch 32, and if either flag A or B is "0", that is, If 3 seconds have passed since the last time the frequency was determined to match the predetermined frequency, or if it is detected that noise has occurred,
The output of the output port OUT is turned off and the audio cutoff switch 32 is turned off.

In order to perform this kind of operation, unless the cause of the audio malfunction continues for more than 3 seconds, the audio cut-off switch 3 is turned off.
2 will not be turned on, thereby effectively preventing audio malfunctions, and since the audio cutoff switch 32 will be turned off immediately when noise appears during the detection output, noise malfunctions will be prevented. Furthermore, if the call ends and there is no signal from the receiving state, noise is detected and the audio cutoff switch is immediately turned off, so unlike conventional methods, when the call ends and there is no signal, the There is no constant noise at all times.

Effects of the Invention As explained above, according to the present invention, a high-pass filter that extracts only high-frequency noise band components from the detected output, a rectifier circuit that rectifies the output of this high-pass filter, and a discriminator that and means for turning on the audio cutoff switch only when a predetermined time has not elapsed since the last determination that the frequency matches a predetermined tone frequency range and the output of the rectifier circuit is below a predetermined level. Therefore, audio malfunctions and noise malfunctions can be prevented, and when the receiving state changes to a no-signal state, the audio cutoff speaker is immediately turned off, thereby preventing unnecessary noise from flowing from the speaker. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram of the present invention, FIG. 2 is a main block diagram showing an example of the hardware configuration of an embodiment of the present invention, and FIGS. 3 and 4 are flowcharts showing processing contents of the MPU 37. FIG. 5 is an explanatory diagram of a tone signal, and FIGS. 6 and 7 are explanatory diagrams of a conventional tone squelch device. 20 and 33 are speakers; 21 and 32 are audio cutoff switches; 22 and 34 are low-pass filters;
3 and 36 are waveform shaping circuits, 35 is a high-pass filter, 37 is an MPU, and 38 is a rectifier circuit.

Claims (1)

[Claims] 1. An audio cutoff switch inserted in the path leading the detected output of the receiver to the speaker, a low-pass filter that extracts only the tone signal band component from the detected output, and a waveform that shapes the output of the low-pass filter into a pulse waveform. a shaping circuit, a frequency measuring means for measuring the frequency of the output pulse of the waveform shaping circuit, and a determination for determining at each predetermined period whether or not the measured frequency matches a tone frequency pre-assigned to the receiver. a high-pass filter for extracting only high-frequency noise band components from the detection output; a rectifier circuit for rectifying the output of the high-pass filter; and means for turning on the sound cutoff switch only when a predetermined time has not elapsed since the determination was made and the output of the rectifier circuit is below a predetermined level.