JPS628604Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a receiving device such as a transceiver, and is designed to reduce the level of residual sound generated from a speaker during so-called standby.

A receiving device such as a transceiver has conventionally been configured as shown in FIG. In the figure, a signal from an antenna 1 is supplied to a frequency mixer 3 through a high frequency amplifier 2, and a locally oscillated signal from a local oscillator 4 is supplied to the mixer 3 to extract a desired intermediate frequency signal. This intermediate frequency signal is supplied to a detection circuit 6 through an intermediate frequency amplifier 5, and an audio signal is extracted.

Further, a DC bias for a noise limiter is grounded through a resistor 14, a resistor 12, a diode 15, and a resistor 16.

Further, the connection midpoint between the resistor 14 and the resistor 12 is grounded by the capacitor 13.

Then, the signal from the diode 15 passes through the capacitor 17 to the fixed contact 18b of the changeover switch 18.
is supplied to Movable contact 18 of this switch 18
d is grounded through a variable resistor 19 and a resistor 20, and a signal from a slider of the variable resistor 19 is supplied to a speaker 22 through a low frequency amplifier 21.
Further, a midpoint between the variable resistor 19 and the resistor 20 is connected to a fixed contact 23b of a changeover switch 23, and a movable contact 23d of this switch 23 is grounded.

Further, a signal with a potential corresponding to the level of the received signal from the intermediate frequency amplifier 5 is grounded through a resistor 24, a variable resistor 25, and a resistor 26, and a signal from a slider of the variable resistor 25 is connected through a capacitor 27. It is grounded and also supplied to the base of transistor 28. The emitter of this transistor 28 is grounded, the collector is grounded through a resistor 29 to a power supply terminal 30, and the collector is grounded through a capacitor 31. Furthermore, a signal from the collector of the transistor 28 is supplied through the diode 32 to the midpoint between the diode 15 and the capacitor 17, and is also supplied to the control terminal of the display signal oscillator 33. The power terminal of this oscillator 33 is connected to the movable contact 34d of the changeover switch 34, and the fixed contact 34c of the switch 34 is connected to the power terminal 34.
Connected to 0. The signal from the oscillator 33 passes through the resistor 35 to the fixed contact 18 of the switch 18.
c.

In this circuit, when the switches 18, 23, and 34 are off (non-operating), the fixed contacts 18a, 23a,
34a. Therefore, the audio signal from the detection circuit 6 is cut off by the switch 18, the power to the oscillator 33 is cut off by the switch 34, and the display signal is cut off by the switch 18, so that no sound is emitted from the speaker 22.

Also, when on (receiving), switches 18, 23, 3
4 are connected to fixed contacts 18b, 23b34b. Therefore, the audio signal from the detection circuit 6 passes through the switch 18 and the variable resistor 19 to the low frequency amplifier 2.
1. The signal is supplied to the speaker 22. At this time, the resistor 20 is switched off through the switch 23, so the audio signal is controlled by the variable resistor 19 from the minimum to the maximum. Furthermore, a signal with a potential corresponding to the level of the received signal from the intermediate frequency amplifier 5 is transmitted to the variable resistor 2.
5 to the transistor 28, the transistor 28 is turned off when the received signal is low level and turned on when the received signal is high level. Then, during the period when the transistor 28 is off, the transistor 28
The collector potential of increases, the diode 32 becomes conductive, and the power supply terminal 30, the resistor 29, and the diode 3
2. The path of the resistor 16 becomes conductive and the audio signal is squelched.

Furthermore, in standby (waiting for reception), switch 1
8, 23, 34 are fixed contacts 18C, 23c, 34
connected to c. Therefore, the power is turned on to the oscillator 33, and the display signal from the oscillator 33 is sent to the switch 1.
8. Low frequency amplifier 21 through variable resistor 19;
The signal is supplied to the speaker 22. At this time, since the resistor 20 is connected in series with the variable resistor 19, the display signal is maintained at a predetermined level even if the variable resistor 19 is set to the minimum value. Furthermore, the collector potential of the transistor 28 is supplied to the oscillator 33, and the oscillation of the oscillator 33 is stopped while the collector potential is at a high potential, so that when the received signal is at a high level, the transistor 28 is turned on and the collector potential is lowered. The oscillator 33 oscillates.

In this way, when the level of the received signal decreases during reception, the audio signal is squelched, and when the level of the received signal increases during reception standby, the speaker 2
A display sound is emitted from 2. Note that the variable resistor 25 is used to set the level of the received signal that generates the squelch and display sound.

However, in this circuit, if the level of the received signal is low during reception standby, the oscillator 33 becomes inactive. In this case, the output end of the oscillator 33 is in a so-called floating state, and noise such as thermal noise is supplied to the low frequency amplifier 21 and speaker 22 through the variable resistor 19. For this reason, when the position of the slider of the variable resistor 19 is set to maximize the volume, a considerable level of so-called after-sound is generated from the speaker 22, which has become a problem.

In consideration of these points, the present invention is designed to reduce the level of residual sound with a simple configuration. An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, the signal from capacitor 17 is grounded through variable resistor 19, and variable resistor 1
The signal from the slider 9 is supplied to the fixed contact 18b of the switch 18. A signal from the movable contact 18d of this switch 18 is directly supplied to the low frequency amplifier 21. Also, the fixed contact 18b of the switch 18
and the movable contact 18d are connected through a resistor 20. Furthermore, the connection midpoint between the resistor 12 and the capacitor 11 is the fixed contact 36c of the changeover switch 36.
The movable contact 36d of this switch 36
is grounded. The rest of the structure is the same as in FIG.

In this circuit, when the switches 18, 34, 36 are off (non-operating), the fixed contacts 18a, 34a,
36a. Therefore, the audio signal from the detection circuit 6 is cut off by the switch 18, the power to the oscillator 33 is cut off by the switch 34, and the display signal is cut off by the switch 18, so that no sound is emitted from the speaker 22.

Also, when on (receiving), switches 18, 34, 3
6 are connected to fixed contacts 18b, 34b, and 36b. Therefore, the audio signal from the detection circuit 6 passes through the variable resistor 19 and the switch 18 to the low frequency amplifier 2.
1, supplied to the speaker 22. At this time, the resistor 20 is switched off through the switch 18, so the audio signal is controlled by the variable resistor 19 from the minimum to the maximum. Furthermore, a signal with a potential corresponding to the level of the received signal from the intermediate frequency amplifier 5 is supplied to the transistor 28 through the variable resistor 25, so that the transistor 28 is turned off when the received signal is low level and turned on when the received signal is high level. Become. Then, during the period when transistor 28 is off, transistor 2
8 collector potential rises, diode 32 becomes conductive, power supply terminal 30, resistor 29, diode 3
2. The path of the resistor 16 becomes conductive and the audio signal is squelched.

Furthermore, in standby (waiting for reception), switch 1
8, 34, 36 are fixed contacts 18c, 34c, 36
connected to c. Therefore, the power is turned on to the oscillator 33, and the display signal from the oscillator 33 is sent to the switch 18.
The signal is supplied to a low frequency amplifier 21 and a speaker 22 through the signal. At this time, since the variable resistor 19 is connected through the resistor 20, the volume of the display signal can be adjusted with this variable resistor 19, and the resistor 20 is connected in series with the variable resistor 19. , the display signal is maintained at a predetermined level even when the variable resistor 19 is set to the minimum value. Furthermore, transistor 2
8 is supplied to the oscillator 33, and the oscillation of the oscillator 33 is stopped while the collector potential is at a high level. When the received signal is at a high level, the transistor 28 is turned on, the collector potential is lowered, and the oscillator 33 is turned on. 33 is oscillated. Also resistor 1
2 and the capacitor 11, the diode 15 is reverse biased and the audio signal is cut off.

In this manner, also in this circuit, when the level of the received signal decreases during reception, the audio signal is squelched, and when the level of the received signal increases during reception standby, the speaker 22 emits a display sound.
Note that the variable resistor 25 is used to set the level of the received signal that generates the squelch and display sound.

In this circuit, even if the level of the received signal is low during reception standby and the oscillator 33 is inoperative, the input terminal of the low frequency amplifier 21 is grounded via the resistor 20 and the variable resistor 19. Since the output end of the detection circuit 6 is connected to one end of the variable resistor 19, it is also grounded through the output impedance of the detection circuit 6. Therefore, in order to reduce the residual sound level when the oscillator 33 is not operating, and especially to maximize the volume, the present invention uses the variable resistor 19.
A remarkable effect is exhibited when the sliders are located in the same position.

In this way, the squelch during reception and the generation of the display signal during reception standby are performed. According to the present invention, even if the oscillator 33 becomes inactive during reception standby, the squelch circuit is connected to the output terminal of the oscillator 33. This makes it possible to reduce the after-sound level.

Note that the supply point of the signal from the oscillator 33 may be on the fixed contact 18b side of the switch 18. Furthermore, since a low resistance value of the resistor 20 as a signal bypass circuit is sufficient, the switch 18 can be omitted as shown in FIG. 3 if a slight decrease in the detection output due to the resistor 20 is accepted.

Thus, according to the present invention, it is possible to reduce the so-called standby sound level with an extremely simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional device, FIG. 2 is a block diagram of an example of the present invention, and FIG. 3 is a block diagram of another example. 19 is a variable resistor, 20 is a resistor, 21 is a low frequency amplifier, 32 is a squelch diode, and 33 is an oscillator.

Claims (1)

[Scope of utility model registration request] It includes a detection circuit for detecting an audio signal from a received signal, an oscillator that outputs an oscillation signal when the received signal is above a predetermined level, a switch in which a signal bypass circuit is connected in parallel, and a low frequency amplifier. , the output end of the detection circuit is connected to one end of the switch, the input end of the low frequency amplifier is connected to the other end of the switch, and the output end of the oscillator is connected to open the switch. The receiving device is configured such that the input end of the low frequency amplifier is grounded through the output impedance of the resistor and the detection circuit even when the low frequency amplifier is connected to the ground.