JPH09219656A - Tone squelch circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the detection time of the tone squelch signal contained in analog signals. SOLUTION: The analog input signal of the reception signal, etc., of a simple radio receiver is inputted in the band-pass filter 11 whose center frequency is set to the basic frequency of a tone squelch signal, a tone squelch signal TS is extracted and the basic frequency is made twice by performing a full- wave rectification for the signal TS in a full-wave rectifier circuit 12. After this basic frequency is amplified by a limiter 13 and an amplitude limit is performed for the frequency, a multiplication tone squelch signal RS' with high accuracy is extracted by a band-pass filter 14 set to the center frequency of high-order number and twice as many as the basic frequency of the tone squelch signal. This signal RS' is supplied to a squelch signal detection circuit 15, this signal is threshold processed and the tone squelch signal is detected by the presence or absence of the binary signal. As a result, the tone squelch signal is detected for the detection time which is about the half of that of a conventional example.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tone squelch circuit for detecting a tone squelch signal used when a plurality of wireless stations jointly use a single frequency, such as a simple radio, and want to communicate with a specific wireless station.

[0002]

2. Description of the Related Art A tone squelch circuit of this type is, for example, a simple radio, in which one frequency is shared by a plurality of radio stations, and therefore unrelated radio stations may be received. Is a circuit having a function of automatically disconnecting a call of a wireless station that is not related to the selection, and is also called a CTCSS circuit.

As a conventional tone squelch circuit, there is one having a configuration shown in FIG. 3, for example. That is, the tone squelch circuit receives the analog reception signal received by the wireless receiver, and first extracts the band including the tone squelch signal from the analog reception signal and the band pass filter 1 to roughly extract the band. With the limiter 2 that amplifies the tone squelch signal and limits the amplitude, the second band-pass filter 3 that extracts the tone squelch signal from the output signal of the limiter 2 with higher accuracy, and the second band-pass filter 3 The extracted tone squelch signal is converted into a binary pulse signal by comparing it with a predetermined threshold voltage by the comparator 4a, and a predetermined high frequency pulse signal is generated during the period from the rising of this pulse signal to the rising of the next pulse. By counting with the counter 4b, based on the count value, a specific toe And a squelch signal detection circuit 4 for detecting the presence or absence of the squelch signal.

[0004]

However, in the above-mentioned conventional tone squelch circuit, the frequency of the input tone squelch signal is as low as 67 Hz to 205.4 Hz, and in order to detect this tone squelch signal with high accuracy. Since it is necessary to configure the second bandpass filter 3 with a filter having a high Q value, the detection time for detecting the tone squelch signal must be 200 msec or more, and the tone squelch signal can be detected early. There is an unsolved problem that you cannot do it.

Therefore, the present invention has been made by paying attention to the unsolved problem of the conventional example, and an object thereof is to provide a tone squelch circuit capable of shortening the detection time of the tone squelch signal.

[0006]

In order to achieve the above object, a tone squelch circuit according to the present invention is a tone squelch circuit for inputting an analog signal and detecting the tone squelch signal, wherein the tone squelch signal is extracted from the analog signal. A signal extraction circuit, a multiplication circuit for multiplying the fundamental frequency of the tone squelch signal extracted by the tone squelch signal extraction circuit, and a multiplied tone squelch signal extraction circuit for highly accurately extracting a tone squelch signal obtained by multiplying the fundamental frequency from the output signal of the multiplication circuit. And a squelch signal detection circuit that binarizes the multiplied tone squelch signal extracted by the multiplied tone squelch signal extraction circuit to detect a specific tone squelch signal.

In the present invention, the tone squelch signal is extracted from the analog signal input by the tone squelch signal extraction circuit, converted by the multiplication circuit into a multiplied tone squelch signal having an integral multiple of the fundamental frequency of the tone squelch signal, and multiplied again. The tone squelch signal extraction circuit extracts the multiplied tone squelch signal with higher accuracy, and supplies this to the squelch signal detection circuit, whereby this circuit detects the tone squelch signal. Here, since the multiplied tone squelch signal extraction circuit extracts the multiplied tone squelch signal obtained by multiplying the fundamental frequency of the input tone squelch signal, its pulse period when binarized by the squelch signal detection circuit is 1 of the conventional pulse period. / Multiplying number, and the detection time of the tone squelch signal can be shortened to about half or less of the conventional time.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a tone squelch circuit of the present invention. A tone squelch circuit 10 is a first tone squelch signal extraction circuit to which an analog input signal including a tone squelch signal received by a wireless receiver is input. Bandpass filter 11
Having. The bandpass filter 11 has a center frequency of the tone squelch signal ranging from 67 Hz to 205.
The frequency of the tone squelch signal to be selected is set to 4 Hz, and only the desired sine wave tone squelch signal can be extracted from the input analog input signal.

The tone squelch signal TS output from the bandpass filter 11 is supplied to a full-wave rectification circuit 12 as a multiplication circuit. In this full-wave rectifier circuit 12,
Full-wave rectification of the tone squelch signal TS to set the fundamental frequency to 2
A multiplied tone squelch signal RS to be multiplied is output. Then, the multiplied tone squelch signal RS of the full-wave rectification circuit 12
Is supplied to the limiter 13. The limiter 13 amplifies the input multiplied tone squelch signal RS and limits the amplitude.

The output LS of the limiter 13 is supplied to a third bandpass filter 14 as a multiplied tone squelch signal extraction circuit having a high Q value and a center frequency set to twice the fundamental frequency of the tone squelch signal, and this band LS is supplied to this band. The pass filter 14 extracts the tone squelch signal RS 'whose fundamental frequency is doubled with high accuracy. Then, the multiplied tone squelch signal RS ′ extracted by the bandpass filter 14 is input to the squelch signal detection circuit 15.
In the squelch signal detection circuit 15, the multiplied tone squelch signal RS 'is input to one input side and the threshold signal TH is input to the other input side, and the amplitude of the multiplied tone squelch signal RS' is set to a predetermined value while the amplitude is equal to or higher than the threshold signal TH. Level 2
A comparator 15a that outputs a pulse signal PS having a value, and a counter that counts a pulse signal having a higher frequency, for example, 10 kHz to 100 kHz in the period from the rising of the pulse signal PS output from the comparator 15a to the rising of the next pulse. 15b and a counter 15b
The tone squelch detection signal DS is output when the count value of is within a predetermined range.

Next, the operation of the above embodiment will be described with reference to the time chart of FIG. Now, when the analog reception signal received by the simple radio receiver is input to the bandpass filter 11 of the tone squelch circuit 10, the bandpass filter 11 shifts the analog reception signal to its center frequency as shown in FIG. Only the corresponding desired sinusoidal tone squelch signal TS is extracted, supplied to the full-wave rectifier circuit 12, full-wave rectified by the full-wave rectifier circuit 12, and the fundamental frequency shown in FIG. 2B is doubled. The multiplied tone squelch signal RS is output.

This multiplied tone squelch signal RS is supplied to a limiter 13, which amplifies the multiplied tone squelch signal RS as shown in FIG. 2 (c) and obtains an amplitude-limited output signal LS. The output signal LS is output to the bandpass filter 14. In the bandpass filter 14, the output signal LS of the limiter 13 is converted into the signal shown in FIG.
As shown in (3), the multiplied tone squelch signal RS 'which is twice the fundamental frequency is extracted with higher accuracy.

The multiplied tone squelch signal RS 'extracted by the bandpass filter 14 is input to the squelch signal detection circuit 15. This squelch signal detection circuit 15
Then, the multiplied tone squelch signal RS 'input by the comparator 15a is compared with the threshold signal TH, and this comparator 15a is compared.
Then, as shown in FIG. 2 (e), the amplitude of RS 'is equal to the threshold signal T
A pulse signal PS having a low level when it is less than H and a high level when it is at least the threshold signal TH is output, and this pulse signal PS is input to the counter 15b to count.
When the count value is within a predetermined range, FIG.
As shown in (f), the tone squelch detection signal SD having a high level indicating that the tone squelch signal has been detected is output.

When detecting another tone squelch signal having a different frequency, the center frequencies of the bandpass filter 11 and the bandpass filter 14 may be changed accordingly. As described above, according to the above-described embodiment, after the tone squelch signal TS is separated and extracted from the input analog signal, the full-wave rectifier circuit 12 doubles the basic frequency to output the multiplied tone squelch signal RS, which is output. Band-pass filter 14 after waveform shaping by limiter
The squelch signal detecting circuit 15 binarizes the extracted tone squelch signal RS 'with high precision, binarizes the extracted tone squelch signal RS', and detects the presence or absence of the tone squelch signal based on the binarized signal. Therefore, the pulse period of the binarized pulse signal in the squelch signal detection circuit 15 is 1/2 as compared with the conventional example, and therefore the count-up time of the counter 15b is approximately 1/2 of the conventional example. The detection time until the tone squelch detection signal DS is inverted to a high level can be shortened to about 1/2.

Moreover, in the above embodiment, since the full-wave rectification circuit 12 is applied as the multiplication circuit, there is an advantage that the basic frequency of the tone squelch signal TS can be doubled with a simple structure. In the above embodiment, the case where the full-wave rectification circuit 12 is applied as the multiplication circuit has been described, but the present invention is not limited to this, and a voltage isolation type or a current isolation type using a varactor diode or the like is used. A multiplication circuit may be applied to multiply the fundamental frequency of the tone squelch signal by an integer multiple of 3 or more. In this case, the center frequency of the multiplied tone squelch signal extraction circuit for extracting the multiplied tone squelch signal RS 'is multiplied. It suffices to set the frequency according to the number, and thereby the detection time can be further shortened to 1/3 or less of the conventional example.

[0016]

As described above, according to the tone squelch circuit of the present invention, the basic frequency of the tone squelch signal extracted from the analog signal is multiplied by the multiplication circuit, and the multiplied tone squelch signal extraction circuit is extracted from the multiplied tone squelch signal. Since it is configured to detect a tone squelch signal by extracting a more accurate multiplied tone squelch signal with the squelch signal detection circuit and binarizing the extracted multiplied tone squelch signal, By multiplying the pulse period of the binarized signal in the squelch signal detection circuit, it is possible to obtain the effect that the detection time required to detect the tone squelch signal can be shortened to about 1/2 or less of that in the conventional example. .

[Brief description of drawings]

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

FIG. 2 is a time chart used to explain the operation of the embodiment of FIG.

FIG. 3 is a block diagram showing a conventional tone squelch circuit.

[Description of Reference Signs] 10 tone squelch circuit 11 bandpass filter (tone squelch signal extraction circuit) 12 full-wave rectifier circuit (multiplier circuit) 13 limiter 14 bandpass filter (multiplied tone squelch signal extraction circuit) 15 squelch signal detection circuit 15a comparator 15b counter

Claims (1)

[Claims] 1. A tone squelch circuit for inputting an analog signal and detecting a tone squelch signal, wherein a tone squelch signal extracting circuit for extracting a tone squelch signal from the analog signal and a fundamental frequency of the tone squelch signal extracted by the tone squelch signal extracting circuit are multiplied. A multiplying circuit, a multiplying tone squelch signal extracting circuit for extracting a tone squelch signal obtained by multiplying a fundamental frequency from the output signal of the multiplying circuit with high accuracy, and binarizing and specifying the multiplied tone squelch signal extracted by the multiplying tone squelch signal extracting circuit. And a squelch signal detection circuit for detecting the tone squelch signal of 1.