JPS6324671Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a squelch circuit in communication transmitters, FM receivers, etc.

Conventionally, communication transceivers, FM receivers, etc. (hereinafter referred to as receiving circuits) have been provided with squelch circuits (also referred to as mute circuits). Squelch circuit 1 is the first
As shown in the figure, a noise rectifier circuit 2, a time constant circuit 3,
and a switching circuit 4. The receiving circuit can receive a channel corresponding to the local oscillation frequency _o (n is ₁ , ₂ , . . . n) supplied to the mixer 7 via the receiving frequency switch 9 (hereinafter simply referred to as a switch). If the selected channel has a signal, the received wave _i is output as an audio signal _p to a speaker (not shown). Furthermore, when there is no signal, the audio signal _p is not output. The level of the received wave _i fluctuates due to fading or the like, and in some cases, the level of the received wave _i may fall below a certain limit value. When the squelch circuit 1 operates in accordance with the state in which the level of the received wave _i falls below the limit value, an audio signal is generated.
Since _{p is} intermittent, squelch circuit 1
A time constant circuit 3 is provided. In a receiving circuit provided with a squelch circuit 1 having a time constant circuit 3, noise outputted from a detector 11 when there is no signal is outputted to a terminal 1a of the squelch circuit 1 via a noise detection filter 13. Noise input to the terminal 1a is rectified by the noise rectifier circuit 2, converted into a DC signal, and output to the time constant circuit 3. The time constant circuit 3 operates the switching circuit 4 according to the progress of the input DC signal. The state in which the switching circuit 4 is activated is called "squelch closed." When the squelch is closed, a control signal is output to the switch 12 via the terminal 1b. Therefore, the switch 12 is controlled and the normally closed contact 12
a opens. Therefore, the noise output from the wave detector 11 is suppressed. In FIG. 1, numeral 5 is an antenna, 6 is a high frequency amplifier, 8 is a local oscillator, and 10 is an intermediate frequency amplifier.

For example, when the first channel is switched to the second channel by the switching operation of the switch 9, the operating state of the squelch circuit 1 does not change if both the first channel and the second channel have a signal or no signal. . When the first channel has no signal and the second channel has a signal, the state changes from "squelch closed" to "squelch open" and audio signal _p is output.

When the first channel has a signal and the second channel has no signal, the state changes from "squelch open" to "squelch closed". In this case, the second channel is selected due to the time constant for preventing malfunction, and the "squelch remains open" temporarily despite the noise being output. Therefore, squelch circuit 1
However, there are drawbacks such as the fact that the noise suppression function is temporarily lost and noise is output to the speaker.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a squelch circuit that can immediately obtain a noise suppression function when the receiving frequency is switched.

The present invention includes a switching point detecting means for detecting the start of switching by the receiving frequency switching means, and a time constant shortening means for shortening the time constant of a time constant circuit for preventing malfunction based on the detection information obtained by the switching point detecting means. The squelch is immediately closed when the receiving frequency is switched from a signal channel to a non-signal channel.

The squelch circuit according to the present invention will be explained below with reference to FIG.

FIG. 2 is a block diagram showing a part of a specific circuit in an embodiment of the squelch circuit according to the present invention.

Components that are the same in FIG. 2 and FIG. 1 are designated by the same reference numerals, so their explanation will be omitted.

In FIG. 2, 14 is a squelch circuit. The squelch circuit 14 includes a switching point detection circuit 15, a time constant shortening circuit 19, a noise rectification circuit 2, a time constant circuit 3,
and a switching circuit 4. Further, the detection changeover device 20 is formed of a rotary type switch having the same shape as the changeover device 9, and has a coaxial structure so as to be interlocked with each other. Child contacts P ₁ , P ₂ of the detection switch 20
...P _o are both connected to ground. When the detection switch 20 rotates, the slider P _s switches between the child contacts P ₁ and P ₂
... P _o contacts, but the structure is such that the plurality of child contacts P ₁ , P ₂ ... P _o do not contact the slider P _s at the same time.
Therefore, when the knobs associated with the switching device 9 and the detection switching device 20 are rotated, the slider P _s is temporarily disconnected from the ground and then connected to the ground again at each step. At this time, the change that occurs in the slider _Ps due to connection and disconnection with the ground is used as detection information for detecting the switching point.

The switching point detection circuit 15 is composed of an amplifier 16, a differentiating circuit 17, and a waveform shaping circuit 18.
When the detection switch 20 rotates and advances one step, the detection information generated on the slider _Ps is sent to the squelch circuit 14.
The signal is input to the amplifier 16 via the terminal 14c.
The amplifier 16 amplifies the input detection information, that is, the ground change, and outputs it to the differentiating circuit 17 as a detection signal. Differentiator circuit 17 differentiates the input detection signal and outputs it to waveform shaping circuit 18 . The waveform shaping circuit 18 shapes the input differential waveform and outputs it to the terminal 15.
output as a drive signal to a.

The time point reduction circuit 19 is constituted by a switch circuit having a normally open contact 19a. The time constant shortening circuit 19 operates upon receiving a drive signal from the terminal 15a of the switching point detection circuit 15, and the normally open contact 19a is closed. The normally open contacts 19a are connected to terminals 3a and 3b of the time constant circuit 3, respectively.

Time constant circuit 3 consists of capacitor C ₁ , resistor R ₁ and
Consists of R ₂ . One end of resistor _R1 is terminal 3a
and connected to the rectifier output side of the noise rectifier circuit 2,
The other end is connected together with the terminal 3b to the base of the transistor _Q1 of the switching circuit 4 via a resistor _R3 . A time constant capacitor _C1 is provided between the terminal 3b and the ground. Note that the resistor _R2 connected to both ends of the capacitor _C1 is a resistor for discharging the capacitor _C1 .

Here, the child contact P ₁ and the slider P _s of the detection switching device 20 are in contact with each other, and the local oscillation frequency ₁ related to the first channel is transmitted to the mixer 7 from the local oscillator 8 to the switching device 9. Assume that the data is being sent via . At this time, if the first channel has a signal, the output side of the detector 11 outputs an audio signal _{of 0} or becomes silent, but no noise is generated. Therefore, since no noise-related signal appears on the output side of the noise detection filter 13, the terminal 1 of the squelch circuit 14
A control signal for controlling the switch 12 is not outputted to the switch 4b. Therefore, the switch 12 does not operate, and the audio signal ₀ is output through the normally closed contact 12a, causing the speaker to sound. When the knobs related to the switching device 9 and the detection switching device 20 are rotated by one step to select the second channel, the squelch circuit 1 is switched from the detection switching device 20 to the second channel.
The detection information is sent to the terminal 14c of No. 4. Based on this detection information, the normally open contact 1 of the time constant shortening circuit 19
9a is closed. Therefore, both ends of the time constant resistor _R1 of the time constant circuit 3 are short-circuited. When there is no signal on the selected second channel, a DC signal is output to the output side of the noise rectifier circuit 2, so that the capacitor _C1 is immediately charged by this DC signal.
Therefore, due to the rise in the potential of the capacitor _C1 , the transistor _Q1 of the switching circuit 4 is turned on, and the normally closed contact 12a of the switch 12 is opened. The noise appearing on the output side of the detector 11 is caused by the normally closed contact 12.
By opening a, the signal is cut off, and noise to the speaker is suppressed.

In the above embodiment, a mechanical rotary switch is used as the receiving frequency switching means, but the present invention is not limited to this. Detection of the switching start point can be performed using an electronic receiving frequency switching means such as a frequency synthesizer using a speed lock loop. You can get information.
Furthermore, the switch 12 and the time constant shortening circuit 19 may be formed of semiconductor elements.

The squelch circuit according to the present invention includes a switching point detecting means for detecting the switching start point, and a time constant shortening means for shortening the time constant of a time constant circuit for preventing malfunction based on the detection information obtained by the switching point detecting means. Since the configuration includes the following, it has the feature that the time constant of the time constant circuit can be shortened when switching the receiving frequency. Therefore, there is an effect of reliably suppressing the noise output to the speaker by switching the reception frequency.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional squelch circuit, and FIG. 2 is a block diagram showing a part of a specific circuit in an embodiment of the squelch circuit according to the present invention. In the figure, 1 is a squelch circuit, 2 is a noise rectifier circuit, 3 is a time constant circuit, 4 is a switching circuit, 5
is an antenna, 6 is a high frequency amplifier, 7 is a mixer, 8
is a local oscillator, 9 is a receiving frequency switch (switcher),
10 is an intermediate frequency amplifier, 11 is a detector, 12 is a switch, 13 is a noise detection filter, 14 is a squelch circuit, 15 is a switching point detection circuit, 16 is an amplifier,
17 is a differentiation circuit, 18 is a waveform shaping circuit, 19 is a time constant shortening circuit, and 20 is a detection switch.

Claims (1)

[Scope of utility model registration request] In a receiving circuit provided with receiving frequency switching means and a squelch circuit having a time constant circuit for preventing malfunction, switching time detection means detects the start of switching by the receiving frequency switching means, and detection information obtained by the switching time detection means. Based on the above, there is provided a squelch circuit comprising time constant shortening means for shortening the time constant of the time constant circuit, and configured to prevent malfunctions at the time of switching the receiving frequency.