JP3148589B2 - Tone squelch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a CTCSS (Conti
The present invention relates to a tone squelch circuit using a tone signal of a continuous tone-ontrolled squelch system.

[0002]

2. Description of the Related Art Conventionally, in a radio device or the like, a CTCSS frequency is added to speech as a sub audio signal and transmitted.
In a tone squelch circuit using a CTCSS tone signal, the squelch opens only when the CTCSS frequencies of the local station and the counterpart station match, a 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 or the like is input from an input terminal 1 to a limiter 2,
The output of limiter 2 is input to bandpass filter 3,
Only the desired CTCSS tone signal contained in the demodulated output is extracted. The tone signal obtained from the band pass 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,
Checks whether the DC voltage from the detector 4 is lower or higher than a predetermined threshold value (Ref1). If the DC voltage is low, the L (low) level indicating non-detection of the tone signal. Is recognized as a digital value of H (high) level indicating detection of the signal, and in the case of L level, the squelch is controlled to be on to cut off the audio output of the radio, and in the case of H level, the squelch is controlled to be turned off and the radio is controlled. Output the sound of the machine. The above circuit configuration has the advantage of being relatively simple and low in cost.

[0004]

However, the above circuit configuration has a problem in that it takes time to non-detect a tone signal due to the delay time of the bandpass filter 3 and the detector 4. Also, 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.

[0005] An object of the present invention is to solve the above-mentioned problems and to provide a C
An object of the present invention is to provide a tone squelch circuit capable of shortening the non-detection time of the tone signal of the TCSS.

[0006]

A tone squelch circuit according to the present invention comprises a tone signal detecting means for detecting a tone signal contained in a demodulated output of a received radio wave, and a tone signal from the tone signal detecting means being converted into a DC voltage. A first tone signal voltage converting means for converting, a second tone signal voltage converting means for converting a tone signal from the tone signal detecting means into a DC voltage, and a DC voltage from the second tone signal voltage converting means. And comparing the output of the first tone signal voltage conversion means with a first threshold value, and comparing the output of the holding means with a second threshold value. Comparing means for turning off tone squelch by comparing the output of the first tone signal voltage converting means with a 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.

[0007] 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 conversion 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 detection and non-detection of the tone signal of the CTCSS are performed separately, and the detection of the tone signal is performed when the level of the tone signal included in the demodulated output becomes equal to or higher than the first threshold value. Squelch-off control based on the squelch control, and non-detection of the tone signal is performed when the tone signal level included in the demodulated output becomes equal to or less than the second threshold value, and squelch-on control is performed based on the non-detection. 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 is shorter than that of the conventional circuit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the tone squelch circuit of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram, FIG. 2 is a waveform diagram of a tone signal, and FIG. 3 is a flowchart for explaining the operation of the circuit of FIG. In FIG. 1, a demodulated output of a received radio wave from a wireless device or the like is input to an input terminal 1 and limited by a limiter 2.
After that, the desired CTCSS by the bandpass filter 3
Extract 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 taken into the microcomputer 5,
The output from the detector 4 is used for detecting a tone signal, and the output from the integrator 6 is used for non-detection of a 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.
When this DC voltage level becomes higher than a predetermined threshold value (Ref1) at time t1, as shown in the waveform diagram of the tone signal shown in FIG. 2, the microcomputer 5 sets the DC voltage level at time t1. Is recognized as an H (high) level digital value representing the detection of a tone signal, and squelch is turned off to output the sound 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 converts the analog signal (DC voltage) input to the tone non-detection input port into a corresponding digital signal by A / D (analog / digital) conversion, and stores the maximum value of the 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 starts to decrease, and in the microcomputer 5, the A / D converted value of the output of the integrator 6 reaches its maximum value at time t3. An L (low) level indicating non-detection of a tone signal indicates that the state becomes equal to or smaller than a threshold value (Ref2) smaller than Vm (digital value) by a predetermined A bits (for example, A = 14 bits). Then, the microcomputer 5 controls the squelch to be ON at time t3 and cuts off the audio output of the wireless device.

By the way, in the conventional circuit of FIG. 4, the detection of the tone signal, the non-detection DC voltage level from the detector 4 is performed by comparison with a threshold value (Ref1), non-tone signal The detection is shown in FIG.
DC voltage level from the detector 4 is, time t4 to decrease from its maximum value Vm threshold value (Ref1) below
, The microcomputer 5 recognizes the signal as an L (low) level, and controls the squelch on to cut off the audio output of the wireless device. Therefore, in the conventional circuit of FIG. 4, the non-detection time of the tone signal is a 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, the time T1 from the maximum value Vm to the reduction of the threshold value (Ref2) is T1 = t3-t2.
And the time of 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 a flowchart shown in FIG. When the CTCSS is set by the wireless device (step S1), the cutoff frequency of the bandpass filter 3 is set to the frequency of the tone signal set by the CTCSS ( step S2). When the wireless device receives a radio wave ( step S
3) The tone signal is detected by the detector 4 via the limiter 2 and the band pass filter 3 ( step S4).
(The threshold level for detection is set in advance).
At this time, if the tone signal detected by the detector 4 is equal to or lower than the threshold level (Ref1), no sound is output from the wireless device. If the tone signal is equal to or higher than the threshold level (Ref1), the sound is output from the wireless device. Output ( step S
5). Next, the microcomputer 5 reads the level of the analog signal output from the integrator 6 ( step S6). Then, the level of the analog signal is stored in the internal memory of the microcomputer 5.
7 is compared with the initially set maximum value level Vm stored in step 7 ( step S7).

If the read value is higher than the initially set maximum value, the maximum value Vm stored in the memory 7 is rewritten to the read value and held ( step S8). If the read value is lower than the maximum value Vm stored in the memory 7, the process proceeds to step S9. In step S9, the read value is
If the value (Ref2) is equal to or less than the predetermined A bit (preset bit number) from the maximum value Vm, the microcomputer 5 recognizes that the tone signal is not detected, turns on the squelch, and controls the wireless device. Cut off audio output ( step S
10). Next, in step S11, the value from the integrator 6 is initialized. (The maximum value rewritten so far is invalidated and set to the initial maximum value.) The maximum value is set to the comparison reference value (R
The reason why the reference value (Ref2) is set to a value smaller by A bits than the maximum value without using ef2) is that there is a variation in amplitude depending on the frequency of the tone signal and the reference value is not an accurate reference value. The corrected value is used as the reference value instead of the value.

[0015]

Although the embodiments of the tone squelch circuit of the present invention have been described above, the present invention is not limited to this, and various modifications are possible. For example, the setting of the threshold value (maximum value Vm-A bits) for non-detection of the tone signal may be changed depending on the frequency of the tone signal. Further, the detection of the tone signal may be processed using an integrating circuit instead of the 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 is quick. (2) Since the non-detection of the tone signal of the CTCSS is advanced, the reverse stone on the transmission side is shortened, and the squelch tail (sound of “zapping” at the end of reception) is not generated. Thereby, useless transmission time can be omitted.

[Brief description of the drawings]

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

FIG. 2 is a tone signal waveform diagram for explaining the operation of the circuit of FIG. 1;

FIG. 3 is a flowchart illustrating the operation of the circuit in FIG. 1;

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Limiter 3 Band pass filter 4 Detector 5 Microcomputer 6 Integrator 7 Memory

Claims (5)

(57) [Claims] 1. A tone signal detecting means for detecting a tone signal included in a demodulated output of a received radio wave, a first tone signal voltage converting means for converting a tone signal from the tone signal detecting means into a DC voltage, A second tone signal voltage converting means for converting the tone signal from the tone signal detecting means into a DC voltage; a holding means for holding a 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 threshold value from the comparing means. Output of the tone signal voltage conversion means of
A tone squelch circuit for turning off the tone squelch by a comparison output with the threshold value and turning on the tone squelch by a comparison output between 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 conversion means is a detector,
The second tone signal voltage conversion means is a tone squelch circuit which is an integrator. 3. The tone squelch circuit according to claim 1, wherein said first and second tone signal voltage conversion 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.