JPH01212926A - Audio output control circuit for receiver - Google Patents

Abstract

PURPOSE:To receive 2 signals or over with nearly equal strong electric field at the same time and to output an audio signal even when a squelch circuit judges the presence of noise by turning on a switching circuit regardless of the presence or absence of a signal of the squelch circuit when an electric field level of a reception signal from a slave station is a predetermined value or over. CONSTITUTION:A level detection circuit 26 is added to an output side of a 2nd IF amplifier 10. The output of the 2nd IF amplifier 10 is detected and smoothed by the level detection circuit 26, a DC voltage is outputted across a resistor 25, compared with a preset voltage by a comparator circuit 27, a transistor(TR) 34 is turned on by the output of the comparator circuit 27 when the level is a setting level or over and a switching TR 17 is turned off. That is, the TR 17 is forcibly turned off regardless of the presence or absence of the signal output from a squelch circuit 16 and the audio signal sent from a discrimination circuit 11 and a BPF 12 is fed to an output amplifier 18. When the electric field level of a reception signal is low, the output of the comparator circuit 27 is OV, the TR 34 is turned off and the presence or absence of the squelch signal controls ON/OFF of the TR 17.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is an audio system for a receiver that prevents malfunctions when a base station receives audio signals from multiple slave stations at the same time, such as in a taxi radio. This relates to an output control circuit.

"Prior Art" Conventionally, a receiver for a base station such as a taxi radio has a circuit configuration without the chain line portion in the figure.

That is, when a signal from a slave station is received by the antenna (1), it is amplified by the RF amplifier (2), and the first signal is amplified by the mixing circuit (3).
It is mixed with the oscillation signal of the local oscillation circuit (4), passes through a BPF (band pass filter) (5) to obtain a first IF (intermediate frequency) signal, and is amplified by a first IF amplifier (6).

This first IF signal is further mixed with the oscillation signal of the second local oscillation circuit (8) in the mixing circuit (7), and B P F (9)
A second IF signal is obtained through the second IF signal.
The signal is inputted to a discrimination circuit (11) via an amplifier (10).

This discrimination circuit (11) changes from FM to AM, and the BP
Sent to F (12). The output of the discrimination circuit (11) is also sent to a squelch circuit (16) consisting of a B P F (13), an amplifier (14), and a detection circuit (15). When the noise level is below a certain value, the transistor (17) as a switching circuit is turned off, so the output of the B P F (12) is output from the output amplifier (1).
8) and the sound is output from the speaker (19).

[Problems to be Solved by the Invention] However, in the conventional circuit, when two or more signals with substantially equal strong electric fields are simultaneously received at the base station, the audio signal demodulated by the discrimination circuit (11) is output from the squelch circuit (16). ), that is, the squelch circuit (16) detects it as a noise demodulated output, and the transistor (17)
is turned on, then B is output from the discrimination circuit (11).
The audio signal sent via P F (12) is not output to the output amplifier (18), therefore.

It becomes impossible to even understand whether the slave station is responding to a call from the base station.

An object of the present invention is to obtain a circuit that determines whether or not a signal with an electric field of a certain level or higher is received, and when the electric field is 1 strong, turns off the switching circuit and outputs audio regardless of the presence or absence of the squelch circuit signal. It is something to do.

"Means for Solving the Problems" The present invention has the following features: 1. Receiving signals from a plurality of slave stations, obtaining an intermediate frequency signal using an intermediate frequency circuit, and demodulating into an audio signal using a discrimination circuit. In a receiver that controls audio output to a speaker using a squelch circuit and a switching circuit,
a level detection circuit that detects the intermediate frequency signal to detect an electric field level;

The device includes a comparison circuit that compares the output of the level detection circuit with a preset value, and a gate circuit that controls the switching circuit using the output of the comparison circuit.

"Operation" When the electric field level of the received signal from the slave station is above a certain value, the detection level of the intermediate frequency signal is higher than the set value, so
It is output from the comparison circuit and sent to the switching circuit via the gate circuit. Then, the switching circuit is turned off regardless of the presence or absence of the squelch signal, and the audio signal is sent from the discrimination circuit to the speaker to output audio. This means that even if two or more received signals with the same electric field level are received at the same time and the demodulated audio signal becomes noise, the squelch circuit will not operate and audio will be output, and the slave station will not respond to the request from the base station. It turns out that there is.

When the electric field level is low, the output of the level detection circuit is lower than the set value and the comparison circuit does not operate.

The squelch circuit operates and cuts off audio output when there is a noise signal.

"Example" Hereinafter, one embodiment of the present invention will be described based on the drawings.

In the present invention, a circuit surrounded by a chain line is added to the output side of the second IF amplifier (10) of the illustrated circuit described as a conventional example. That is, a capacitor (2G) and a detection diode (21) are connected to the output side of the second IF amplifier (10).
) (22), smoothing capacitor (23), resistor (25
), and the output side of this level detection circuit (26) is connected to the input side of a comparator circuit (27). A constant voltage circuit (28), resistors (29) (30), and a voltage setting variable resistor (31) are coupled to the negative input terminal of the comparator circuit (27). Also, on the output side of this comparison circuit (27), resistors (32) (33
), the emitter of this transistor (34) is grounded, and the collector is coupled to the squelch output terminal and the base of the switching transistor (17).

In the above configuration, the output of the second IF amplifier (10) is detected and smoothed by the level detection circuit (26).

A DC voltage is output across the resistor (25) and compared with a preset voltage in a comparison circuit (27). When the signal received from the slave station has an electric field level higher than a preset level, the output of the comparator circuit (27) becomes the power supply voltage,
Turn on transistor (34). Therefore, the switching transistor (17) is turned off. This means that
Regardless of whether the signal detected as a noise signal is output from the squelch circuit (16), the switching transistor (17) is forcibly turned off. Therefore, the audio signal sent through the discrimination circuit (11) and BPF (12) is sent to the output amplifier (18), and the audio is output from the speaker (19).

When the electric field level of the received signal is low, the comparator circuit (27
) becomes Ov and the gate transistor (34)
is turned off. Therefore, the switching transistor (17) is turned on or off depending on the presence or absence of the squelch signal. That is, when noise occurs, the transistor (17) turns on and cuts off the output of the audio signal.

"Effects of the Invention" Since the present invention is configured as described above, when a request from a base station is received from slave stations all at once, even if two or more signals with substantially equal strong electric fields are received at the same time, the squelch circuit Even if it is judged as noise, the level detection circuit forcibly turns off the switching circuit and outputs the sound. Therefore, the inconvenience of not knowing whether or not the slave station is responding to a request from the base station is resolved. Of course, the squelch circuit operates normally when weak electric field noise is detected.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the audio output control circuit of the receiver according to the present invention. (1)...Antenna, (10)...Second IF amplifier, (11)...Discrimination circuit, (16)...Squelch circuit, (17)...Switching transistor, (1
8)...Output amplifier, (19)...Speaker, (
26) Level detection circuit, (27) Comparison circuit, (28) Constant voltage circuit, (34) Gate transistor. Applicant Fujitsu General Ltd.

Claims (2)

[Claims] (1) Receive signals from multiple slave stations, obtain an intermediate frequency signal using an intermediate frequency circuit, demodulate it to an audio signal using a discrimination circuit, and control the audio output to the speaker using a squelch circuit and a switching circuit. In the receiver, a level detection circuit detects the electric field level by detecting the intermediate frequency signal, a comparison circuit compares the output of this level detection circuit with a preset setting value, and the output of this comparison circuit An audio output control circuit for a receiver, comprising a gate circuit for controlling the switching circuit. (2) The audio output control circuit for a receiver according to claim 1, wherein the level detection circuit comprises a diode for detecting the intermediate frequency signal and a smoothing capacitor for the detected signal.