JPH0946248A - Tone squelch circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate futile transmission time by providing a tone detection means, first and second tone signal voltage conversion means, a holding means, a comparison means and a control means turning on tone squelch by compared output. SOLUTION: When a radio wave is received, a tone signal is detected by a detector 4 through a limitter 2 and BPF 3. When the detected tone signal is less than a threshold, sound is not emitted from a radio machine, and sound is outputted when it is more than the threshold. A microcomputer 5 reads the level of an analog signal outputted from an integrator 6. The level is compared with a maximum value level Vm stored in a memory 7. When the read value has the level larger than an initialized maximum value, the stored maximum value Vm is rewritten into the read value and it is held. When the read value is that less than A-bit which is previously decided from the maximum value Vm, the microcomputer 5 recognizes that the tone signal is not detected, on- controls squelch and insulates the sound output of the radio machine.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to CTCSS (Conti
tone squelch circuit using tone signals of a nuous tone-ontrolled squelch system.

[0002]

2. Description of the Related Art Conventionally, in a wireless device or the like, a CTCSS frequency is added to voice as a sub audio signal and transmitted.
In the tone squelch circuit using the tone signal of CTCSS, which opens the squelch only when the CTCSS frequencies of the own station and the partner station match, the tone signal is detected based on the circuit configuration of FIG.

In FIG. 4, a demodulated output obtained by demodulating a radio wave received by a radio device or the like is input from an input terminal 1 to a limiter 2,
The output of the limiter 2 is input to the bandpass filter 3,
Only the tone signal of the desired CTCSS contained in the demodulated output is taken out. The tone signal obtained from the bandpass filter 3 is detected by the detector 4 and converted into a DC voltage. The DC voltage from the detector 4 is input to a microcomputer (hereinafter referred to as a microcomputer) 5, and the microcomputer 5
Checks whether the DC voltage from the detector 4 is lower or higher than a predetermined threshold value (Ref1), and if it is low, L (low) level indicating non-detection of the tone signal, and if high, the tone signal. It is recognized as a digital value of H (high) level that indicates the detection of, and when it is at the L level, the squelch is controlled to be turned on and the voice output of the radio is cut off. Output the machine sound. The circuit configuration described above has the advantages of being relatively simple and low in cost.

[0004]

However, the above circuit configuration has a problem that it takes time to detect the tone signal due to the delay time of the bandpass filter 3 and the detector 4. Further, when the threshold value (Ref1) is lowered, there is a problem that the detection time of the tone signal is shortened but the non-detection time is delayed.

The object of the present invention is to solve the above-mentioned problems and to provide C
An object of the present invention is to provide a tone squelch circuit that can reduce the non-detection time of the tone signal of TCSS.

[0006]

A tone squelch circuit according to the present invention comprises a tone signal detecting means for detecting a tone signal included in a demodulated output of a received radio wave, and a tone signal from the tone signal detecting means into a DC voltage. First tone signal voltage converting means for converting, second tone signal voltage converting means for converting the tone signal from the tone signal detecting means into a DC voltage, and DC voltage from the second tone signal voltage converting means Of the first tone signal voltage converting means and the holding means for holding the maximum value of the above, and the output of the holding means is compared with the second threshold value. The tone squelch is turned off by a comparison means and a comparison output from the comparison means between the output of the first tone signal voltage conversion means and the first threshold value, and The output of the holding means and comparing the output of the second threshold value is made of a control means for turning on the tone squelch.

The first tone signal voltage converting means is a detector and the second tone signal voltage converting means is an integrator. Further, the first and second tone signal voltage converting means may be integrators. The second threshold value is set to a value larger than the first threshold value and smaller than the maximum value held by the holding means by a predetermined value.

[0008]

The CTCSS tone signal is detected and non-detected separately, and the tone signal is detected when the tone signal level included in the demodulated output becomes equal to or higher than the first threshold value. The squelch-off control is performed based on the non-detection, and the non-detection of the tone signal is performed when the tone signal level included in the demodulation output becomes equal to or lower than the second threshold value. Since the second threshold value is set to a value smaller than the maximum value of the detected tone signal by a predetermined value, the non-detection time becomes shorter than that of the conventional circuit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the tone squelch circuit of the present invention will be described below with reference to FIGS. 1 is a block diagram, FIG. 2 is a waveform diagram of a tone signal, and FIG. 3 is a flow chart for explaining the operation of the circuit of FIG. In FIG. 1, a demodulated output of a radio wave received by a wireless device or the like is input to an input terminal 1, and a limiter 2 causes limiting.
After that, the desired CTCSS with the bandpass filter 3
Take out only the tone signal of. Here, the tone signal obtained from the bandpass filter 3 is branched and input to the detector 4 and the integrator 6. Both outputs are captured by the microcomputer 5,
The output from the detector 4 is used for detecting the tone signal, and the output from the integrator 6 is used for not detecting the tone signal.

That is, the tone signal included in the demodulated output of the received radio wave is detected by the detector 4 and converted into a DC voltage, which is input to the tone detection input port of the microcomputer 5.
As shown in the waveform diagram of the tone signal shown in FIG. 2, when the DC voltage level becomes higher than the predetermined threshold value (Ref1) at the time t1, the microcomputer 5 makes the DC voltage level at the time t1. Is recognized as an H (high) level digital value indicating the detection of the tone signal, and the squelch is controlled to be off to output the voice of the wireless device. The tone signal included in the demodulated output of the received radio wave is integrated by the integrator 6 and converted into a DC voltage, which is input to the tone non-detection input port of the microcomputer 5. The microcomputer 5 A / D (analog / digital) converts the analog signal (DC voltage) input to the tone non-detection input port into a corresponding digital signal, and stores the maximum value of this digital signal in the memory 7.

At time t2 in FIG. 2, the amplitude of the tone signal included in the demodulated output of the received radio wave begins to decrease, and the A / D conversion value of the output of the integrator 6 in the microcomputer 5 reaches its maximum value at time t3. An L (low) level indicating non-detection of a tone signal indicates that a threshold value (Ref2) smaller than Vm (digital value) by a predetermined A bit (for example, A = 14 bits) is reached. Then, the microcomputer 5 controls the squelch to be turned on at time t3 to cut off the voice output of the wireless device.

By the way, in the conventional circuit of FIG. 4, the detection and non-detection of the tone signal is carried out by comparing the DC voltage level from the detection circuit 4 with the threshold value (Ref1), so that the tone signal is not detected. The detection is as shown in FIG.
Time t at which the DC voltage level from the detection circuit 4 decreases from its maximum value Vm to a threshold value (Ref1) or less.
At 4, the microcomputer 5 recognizes it as an L (low) level, and the microcomputer 5 controls the squelch to be turned on and cuts off the voice output of the wireless device. Therefore, in the conventional circuit of FIG. 4, the non-detection time of the tone signal is the time T2 = t4−t2 until the amplitude of the tone signal decreases from the maximum value Vm to the threshold value (Ref1). In the circuit of the present invention shown in, the time from the maximum value Vm to the threshold value (Ref2) T1 = t3-t
2, and T1 is shortened by T3 = T2-T1.

Next, the operation of the tone squelch circuit of the present invention will be described with reference to the flow chart shown in FIG. When CTCSS is set in the wireless device (step S1), the bandpass filter 3 cutoff frequency is set to the frequency of the tone signal set in CTCSS (S2). When the radio receives radio waves (S3), the tone signal is detected by the wave detector 3 via the limiter 2 and the bandpass filter 3 (S4). (The threshold level to be detected is preset.) At this time, if the tone signal detected by the detector 4 is below the threshold level (Ref1), no sound is output from the wireless device, and the threshold signal is not output. If it is equal to or higher than the drive level (Ref1), sound is output from the wireless device (S5). Next, the level of the analog signal output from the integrator 6 is read by the microcomputer 5 (S6). Then, the level of the analog signal is compared with the initially set maximum value level Vm stored in the internal memory 6 of the microcomputer 5 (S7).

If the read value is at a level higher than the initial set maximum value, the maximum value Vm stored in the memory 7 is rewritten into the read value and held (S8). Reading value is memory 7
If the level is smaller than the maximum value Vm stored in step S9, the process proceeds to step S9. In step S9, the read value is the maximum value V
If the value (Ref2) is equal to or smaller than the predetermined A bits (predetermined number of bits) from m, the microcomputer 5 recognizes that the tone signal is not detected, controls the squelch to be ON, and outputs the voice of the radio device. The output is cut off (S10). Next, in step S11, the value from the integrator 5 is initialized.
(The maximum value rewritten so far is invalidated and set to the initial maximum value.) Further, when the detector 4 is no longer detected during the operation of steps S6 to S11, it is recognized as non-detection of the tone signal, Stop outputting audio from the transceiver. It should be noted that the reference value (Ref2) is set to a value smaller by A bits than the maximum value without setting the maximum value as the comparison reference value (Ref2) because the amplitude of the tone signal varies.
Since it does not become an accurate reference value, the corrected value is used as the reference value, not the maximum value of the actual integration.

[0015]

Although the embodiment of the tone squelch circuit of the present invention has been described above, the present invention is not limited to this, and various modifications can be made. For example, the setting of the non-detection threshold value (maximum value Vm-A bit) of the tone signal may be changed depending on the frequency of the tone signal. Further, the tone signal may be detected using an integrating circuit instead of the wave detector.

[0016]

According to the tone squelch circuit of the present invention, the following effects can be obtained. (1) The circuit configuration is simple, and the non-detection processing becomes faster. (2) Since the non-detection of the tone signal of CTCSS becomes faster, the reverse tone on the transmitting side becomes shorter, and the squelch tail (sounding when the reception ends) does not occur. Thereby, useless transmission time can be omitted.

[Brief description of drawings]

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

2 is a tone signal waveform diagram for explaining the operation of the circuit of FIG.

FIG. 3 is a flowchart illustrating the operation of the circuit of FIG.

FIG. 4 is a block diagram of an example of a conventional tone squelch circuit.

[Explanation of symbols]

 1 Input Terminal 2 Limiter 3 Bandpass Filter 4 Detector 5 Microcomputer 6 Integrator 7 Memory

Claims (5)

[Claims] 1. A tone signal detecting means for detecting a tone signal included in a demodulated output of a received radio wave, and a first tone signal voltage converting means for converting a tone signal from the tone signal detecting means into a DC voltage. Second tone signal voltage converting means for converting the tone signal from the tone signal detecting means into a DC voltage; holding means for holding the maximum value of the DC voltage from the second tone signal voltage converting means; 1
Comparing the output of the tone signal voltage converting means with the first threshold value and comparing the output of the holding means with the second threshold value, and the first means from the comparing means. Of the tone signal voltage converting means of the first and the first
Tone squelch circuit for turning off the tone squelch by a comparison output with the threshold value of the second threshold value, and turning on the tone squelch by a comparison output with the output of the holding means and a second threshold value. . 2. The tone squelch circuit according to claim 1, wherein the first tone signal voltage converting means is a detector.
The second tone signal voltage converting means is a tone squelch circuit which is an integrator. 3. The tone squelch circuit according to claim 1, wherein the first and second tone signal voltage converting means are integrators. 4. The tone squelch circuit according to claim 1, wherein the second threshold value is set to be larger than the first threshold value. 5. The tone squelch circuit according to claim 4, wherein the second threshold value is set to a value smaller than the maximum value held by the holding means by a predetermined value.