JPS5918759Y2 - squelch circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to improvements in squelch circuits.

FIG. 1 shows an example of a squelch circuit in a conventional radio device with a tone squelch, such as that disclosed in Japanese Patent Publication No. 17450/1983.

In the figure, 1 is an antenna, 2 is a high frequency amplifier, 2' is an intermediate frequency amplifier, 3 is a detection circuit, 4 is a low frequency amplifier, and 5
is a speaker.

On the other hand, as a noise squelch circuit, a high-pass filter 6, a noise amplifier 7, and a detection circuit 8 are provided, and as a tone squelch circuit, a tone amplifier 9 and a tone squelch band filter 10 (for example, a specified frequency of 67 to 250 .3H
z) and a detection circuit 11 are provided, and the output of the detection circuit 8 is connected to a switch circuit 13 via a squelch volume resistor 12.

The output of the detection circuit 11 is connected to this switch circuit 13, and the low frequency amplifier 4 is connected to the switch circuit 13.
muting is performed.

As described above, the conventional squelch circuit uses both a tone squelch and a noise (or carrier) squelch, which has the drawbacks that the circuit configuration is complicated and expensive, and the squelch operation range is relatively narrow.

In order to improve the drawbacks of the conventional circuit, the present invention is characterized in that it is configured to be controlled only by a tone squelch circuit, and will be described below with reference to embodiments shown in the drawings.

In the embodiment shown in FIG. 2, the same reference symbols as in FIG. 1 indicate the same circuits, and 14 is an AGC circuit connected between the intermediate frequency amplifier 2' and the tone amplifier 9;
15 is a selection switch, 16 is a high-pass filter, and 17 is an inverter circuit.

In the above configuration, if an input signal containing the tone signal of the own station is received, this input signal is amplified by the tone amplifier 9 and then passed through the selection switch 15 (the selection switch 15 is now switched to the upper side). After passing only the predetermined band signal, the tone signal of the own station is detected by the detection circuit 11, and the detection output activates the switch circuit 13 to The muting of the frequency amplifier 4 is canceled and sound is output from the speaker 5.

On the other hand, if a tone signal different from that of the local station or an input signal that does not include a tone signal is received, that signal is removed by the tone squelch bandpass filter 10, so the switch circuit 13 does not operate. Since muting is applied to the low frequency amplifier 4, no sound is output from the speaker 5.

In this case, it is not possible to vary the squelch operation level by simply detecting the presence or absence of a tone signal, so A
The GC circuit 14 applies AGC to the tone amplifier 9.

In this way, the input level of the bandpass filter 10 can be controlled according to the received signal level, and the detection output of the detection circuit 11 can be made linear with respect to the received signal, as shown by curve a in FIG. , the squelch operation range can be widened.

That is, as shown in FIG. 3a, since the range of change in the antenna input until reaching the switching level can be widened, the squelch operation range can be widened.

If you want to operate as a noise squelch, select switch 15.
What is necessary is to switch it to the high-pass filter 16 side.

As is clear from the above explanation, according to the present invention, when implemented in a radio device with a tone squelch, for example, there is no need to provide a noise squelch (or carrier squelch) circuit.
Since control can be performed using only the tone squelch circuit, the circuit configuration can be simplified and costs can be reduced.

Moreover, AGC is applied to the tone amplifier according to the input signal,
By operating the switch circuit so that the detection output varies with respect to the input signal, it is possible to make the squelch variable over a wider range than the conventional squelch operation range (FIG. 3b).

It is also easy to operate it as a noise squelch.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional squelch circuit in a tone squelch radio, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing its operating characteristics.

Claims (1)

[Scope of utility model registration request] a tone signal amplifier; and A that generates an output signal according to the input signal level and controls the gain of the tone signal amplifier.
A GC circuit, a tone squelch bandpass filter and a noise squelch highpass filter provided in parallel with each other, a detection circuit provided in common to these bandpass filters and highpass filter, and this detection circuit. a switching circuit controlled by the circuit, and a selection switch provided in the tone signal amplifier to switch its output to a high-pass filter for tone squelch or a high-pass filter for noise squelch, and for switching the selection switch. 1. A squelch circuit characterized in that the squelch circuit is configured to mute a low frequency amplifier of a radio device by controlling a switching circuit according to an output signal from a detection circuit.