JP2001069018A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a radio receiver provided with a squelch circuit not affected by an unnecessary radio wave. SOLUTION: The radio receiver that controls a squelch operation with a noise component included in a detection output, is provided with a medium and high frequency noise extract means 30 that extracts a medium high noise component in an audio signal included in the detection output, a low frequency noise extract means 40 that extracts a low frequency noise component in the audio signal included in the detection output, and a control means 21 that interrupts an output of the audio signal when at least either of the medium and high frequency noise component extracted by the medium and high frequency noise extract means and the low frequency noise component extracted by the low frequency noise extract means reaches a prescribed level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver, and more particularly to a radio receiver having a squelch circuit.

[0002]

2. Description of the Related Art In a radio receiving apparatus, an RF (radio frequency) signal obtained by receiving a radio wave of a desired frequency is detected by a detector to obtain an AF (audio frequency) signal. When there is no feeling (when there is no signal), only noise is output as the AF signal. In order to prevent this state, the output of the AF signal is stopped by the squelch circuit.

In a conventional squelch circuit, an RF signal received by a radio receiver or the like is detected by a detector to obtain an AF signal, and then a middle to high frequency noise component in the AF signal is removed by a band pass filter of about 7 kHz to 30 kHz. The noise is extracted, only the mid-high frequency noise component is obtained through an amplifier, and input to the noise detection circuit, and a DC voltage proportional to the noise amount is extracted from the noise detection circuit.

Then, a DC voltage proportional to the amount of noise is input to an analog port of a microcomputer (microcomputer), and ON / OFF of squelch is controlled according to the level.

Thus, in the squelch-on state where no RF signal is sensed, control is performed to cut off the AF signal on the input side of the AF power amplifier, and the sound output from the speaker is turned off. In the squelch-off state when an RF signal is sensed, the AF signal is controlled to pass through the input of the AF power amplifier, and the AF signal obtained by detection is output from the speaker.

[0006] Such a squelch circuit is generally used in a radio receiving apparatus that performs FM detection. This is because the audio frequency band used in the FM detection circuit is not affected.

[0007]

In recent years, clock frequencies of various computer devices have been increased, and unnecessary radiation has been increased. There are also strong radio waves such as pagers. These radio waves and their harmonic components (hereinafter collectively referred to as unnecessary radio waves) are close to the frequencies used for wireless communication. Unwanted radiation from the computer device and radio waves from the pager are modulated with digital data (pulses).

[0008] The inventor of the present application has found that when the radio receiving apparatus receives and detects the above unnecessary radio wave, low frequency noise caused by a relatively low digital pulse is output.

When such unnecessary radio waves are detected, low-frequency noise caused by low-frequency digital pulses is obtained. Therefore, an AF signal having a relatively high frequency such as when no RF signal is detected is detected. It is not included in the output. As a result, the squelch circuit opens even though it is not the desired AF signal (squelch
(OFF state), low-frequency noise caused by digital pulses resulting from detection of unnecessary radio waves is output at a high volume from the speaker. Therefore, an object of the present invention is to realize a wireless receiving device including a squelch circuit that is not affected by unnecessary radio waves.

[0010]

According to a first aspect of the present invention, there is provided a radio receiving apparatus for controlling a squelch operation by using a noise component included in a detection output. Mid-high frequency noise extracting means for extracting the mid-high frequency noise component, low-frequency noise extracting means for extracting the low-frequency noise component in the audio signal included in the detection output, and mid-high frequency noise extracted by the mid-high frequency noise extracting means Control means for interrupting the output of the audio signal when at least one of the component and the low-frequency noise component extracted by the low-frequency noise extraction means reaches a predetermined level. It is a receiving device.

According to the present invention, when the squelch operation is controlled by the noise component included in the detection output, the middle and high frequency noise component and the low frequency noise component in the audio signal included in the detection output are extracted. When at least one of the extracted middle and high frequency noise components and the low frequency noise component reaches a predetermined level, the output of the audio signal is controlled to be cut off.

Thus, when the desired radio wave cannot be received, the squelch is turned on by the middle and high frequency noise component.
When an unnecessary radio wave is received, the squelch is turned on by a low-frequency noise component.

As a result, it is possible to realize a radio receiving apparatus having a squelch circuit which is not affected by unnecessary radio waves. It is preferable that the low-frequency noise extracting means extracts a low-frequency noise component equal to or lower than the audio frequency.

By extracting the low-frequency noise component below the audio frequency in this manner, it is possible to reliably avoid a situation in which low-frequency noise caused by a digital pulse resulting from detection of unnecessary radio waves is output from a speaker at a large volume. can do.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a radio receiving apparatus according to an embodiment of the present invention will be described in detail. Note that the wireless receiving device of the present embodiment may be a single wireless receiving device, or may be a transmitting / receiving device (transceiver) in which a wireless transmitting device and a wireless receiving device are integrated. In the following description, a wireless receiver that receives the frequency-modulated RF signal to which the present invention is applied will be used as a specific example of the embodiment.

<Configuration of Radio Receiving Apparatus> In FIG. 1, reference numeral 10 denotes an antenna for receiving a radio wave, 11 denotes an RF amplifier for amplifying a received RF signal, and 12 generates a local oscillation signal for performing frequency conversion. Local oscillator (OS
C) and 13 are frequency converters for mixing the received signal and the local oscillation signal to generate an intermediate frequency signal (IF signal).
Is an IF amplifier that amplifies the IF signal, and 15 is an IF amplifier that amplifies the IF signal.
F which detects M and demodulates AF (audio frequency) signal
M detector, 16 is a de-emphasis circuit that attenuates the high frequency component of the AF signal emphasized by pre-emphasis at the time of transmission, 17 is an AF preamplifier that amplifies the AF signal to a certain level, and 18 is an AF preamp by a squelch control signal described later. AF switch for blocking or passing signals, 1
Reference numeral 9 denotes an AF power amplifier that amplifies the AF signal to a level at which the speaker 20 is driven.

Although a single superheterodyne radio receiving apparatus has been described here, the present invention is not limited to this, and a double superheterodyne, triple superheterodyne, or another type may be used.

Reference numeral 21 denotes a medium-to-high frequency noise extracting means 30 which will be described later.
When at least one of the middle and high frequency noise component extracted by the above and the low frequency noise component extracted by the low frequency noise extracting means 40 described later reaches a predetermined level, the AF switch 1
8 is a microcomputer as control means for setting 8 in a cutoff state.

Reference numeral 30 denotes a medium-to-high range noise extracting means for extracting a medium-to-high range noise component in the AF signal included in the detection output, and includes the following 31 to 33. 31 is 7 kHz to 30
A band-pass filter (BPF) that passes a middle-high-frequency noise component of about kHz, an amplifier amplifies the middle-high-frequency noise component that has passed through the BPF 31, and a rectifier 33 that rectifies the amplified middle-high-frequency noise component to generate a middle-high-frequency noise component. This is a detector that generates a voltage corresponding to the amplitude and applies the voltage to the microcomputer 21.

Reference numeral 40 denotes a low-frequency noise extracting means for extracting a low-frequency noise component in the AF signal included in the detection output, and includes the following 41 to 43. 41 is a low-pass filter (LP) that passes low-frequency noise components of about 100 Hz or less.
F) and 42 are amplifiers for amplifying the low-frequency noise component passing through the LPF 41, and 43 is rectifying the amplified low-frequency noise component to generate a voltage corresponding to the amplitude of the low-frequency noise component and apply it to the microcomputer 21. It is a detector. Note that the upper limit of the pass frequency of the LPF 41 is not limited to 100 Hz.
z or 200 Hz.

<Operation of Wireless Receiving Apparatus> (1) When a target radio wave of a sufficient level is received: The radio wave received by the antenna 10 is amplified by the RF amplifier 11 as an RF signal. Then, the amplified RF signal is mixed with the local oscillation signal from the local oscillation unit 12, and is converted into an IF signal having an intermediate frequency corresponding to the difference frequency between the frequency of the RF signal and the frequency of the local oscillation signal. .

Here, since the received radio wave is of a sufficient level and is a target radio wave, the IF signal is amplified while its amplitude is limited by the IF amplifier 14. Then, the IF signal is FM-detected by the FM detector 15, and the AF signal is demodulated.

In this state, a constant level AF signal is output. Here, the main component of the AF signal is an audio signal, and the signal is distributed at about 300 Hz to 3 kHz. For this reason, there is almost no signal component detected by the middle and high frequency noise extraction means 30 and the low frequency noise extraction means 40.
Therefore, the microcomputer 21 controls the AF switch 18 to a passing state (a squelch-off state).

The AF signal from the FM detector 15 is attenuated by the de-emphasis circuit 16 in the high-frequency component of the AF signal emphasized by the pre-emphasis at the time of transmission, and is returned to a flat frequency characteristic. Furthermore, A
The F signal is amplified to a certain level by the AF preamplifier 17, passes through the AF switch 18, and is amplified to a level for driving the speaker 20 by the AF power amplifier. Then, a sound corresponding to the AF signal is output from the speaker 20.

(2) When the target radio wave cannot be received or when the weak radio wave is received: When the target radio wave cannot be received or when the weak radio wave is received,
In the RF amplifier 11 and the IF amplifier 14, the function of automatic gain adjustment (not shown) does not work, and each amplifier operates at the maximum gain.

For this reason, the AF signal demodulated and demodulated by the FM detector 15 is mainly composed of noise components in the middle and high frequencies. Therefore, 7 kHz passed through the BPF 31
The middle-high band noise component of about 30 kHz is amplified by the amplifier 32 and rectified by the detector 33 to be applied to the microcomputer 21 as a middle-high band noise component voltage.

The microcomputer 21 responds to the fact that the mid-high frequency noise component has reached a predetermined level, and
8 is turned off (squelch-on state). Thereby, the AF signal is cut off on the input side of the AF power amplifier, and the sound output from the speaker is stopped.

(3) When a target radio wave has not been received and an unnecessary radio wave has been received: Here, the "unwanted radio wave" means an unnecessary radiation from various computer devices, a radio wave for a pager, or , These harmonic components,
It means a component containing a component modulated by a pulse signal.

As described above, when the target radio wave is not received and the unnecessary radio wave is received, the antenna 10
The unnecessary radio waves received by the RF amplifier 11
Amplified by Then, the amplified RF signal is mixed with the local oscillation signal from the local oscillation unit 12, and is converted into an IF signal having an intermediate frequency corresponding to the difference frequency between the frequency of the RF signal and the frequency of the local oscillation signal. . This IF signal is amplified while its amplitude is limited by the IF amplifier 14. Then, the IF signal is FM-detected by the FM detector 15, and the AF signal is demodulated.

In this state, an AF signal whose main component is a pulse-like low-frequency component due to detection of unnecessary radio waves is obtained. This pulse-like low frequency component (low frequency noise component)
Has a main component below the audio frequency (300 Hz to 3 kHz). For this reason, 10
The low-frequency noise component below 0 Hz is amplified by the amplifier 42,
The voltage is rectified by the detector 43 and becomes a low-frequency noise component voltage, which is applied to the microcomputer 21.

The microcomputer 21 receives the notification that the low-frequency noise component has reached a predetermined level, and controls the AF switch 18 to a cut-off state (squelch-on state). With this control, the microcomputer 21 cuts off the AF signal on the input side of the AF power amplifier and stops the sound output from the speaker.

That is, when such an unnecessary radio wave is being received, the conventional squelch circuit cannot cope with it because the middle and high frequency noise components such as when the RF signal is absent are not included in the detection output. Although the state falls into the state (squelch-off state), according to the present embodiment, the state can be controlled to the squelch-on state, and unpleasant low-frequency noise can be prevented from being output from the speaker.

FIG. 2 is a characteristic diagram showing the squelch characteristic of the radio receiving apparatus according to the present embodiment, and shows the frequency of the AF signal and the squelch operation sensitivity. As is apparent from FIG. 2, according to the present embodiment, when a low-frequency noise component included in the unnecessary radio wave is detected, the squelch is turned on so that the output of the AF signal can be effectively cut off. Become.

<Other Embodiments> In the above embodiments, the middle and high frequency noise extraction means 30
And the extracted output of the low-frequency noise extracting means 40 are mixed and input to the port of the microcomputer 21. However, if there is room in the port of the microcomputer 21, the input is independently input to the microcomputer 21. The configuration may be as follows. By doing so, the microcomputer 21 can independently control the middle and high frequency noise components and the low frequency noise components.

Further, in the above embodiment, the extracted output of the middle and high frequency noise extracting means 30 and the low frequency noise extracting means 4
Although the output of the microcomputer 21 is mixed with the extracted output of 0 and input to the port of the microcomputer 21, the configuration may be such that the levels are independently adjusted and then input to the port of the microcomputer 21. By doing so, it is possible to control the middle and high frequency noise components and the low frequency noise components independently.

In some cases, a low-frequency signal of about 80 Hz to 90 Hz is used as a signal for tone squelch superimposed on an audio signal. When the low-frequency noise extraction unit 40 extracts such a signal for tone squelch, the squelch may be turned on and the AF signal may be cut off despite receiving the target radio wave.

Therefore, in the LPF 41, only the frequency used for tone squelch should be prevented from passing.
A circuit for separately detecting the frequency of the tone squelch and notifying the microcomputer 21 may be provided. This allows
Desired control can be performed by distinguishing between low-frequency noise components due to unnecessary radio waves and tone squelch signals.

[0038]

As described above in detail with the embodiment, when controlling the operation of the squelch by the noise component included in the detection output, the middle and high frequency noise component in the audio signal included in the detection output is expressed by: A low-frequency noise component is extracted, and the output of the audio signal is controlled to be cut off when at least one of the extracted middle-high-frequency noise component and the low-frequency noise component reaches a predetermined level. Therefore, when a desired radio wave cannot be received, squelch is turned on by a middle-high frequency noise component, and when an unnecessary radio wave is received, squelch is turned on by a low frequency noise component.
As a result, it is possible to reliably avoid a situation in which low-frequency noise caused by a digital pulse resulting from detection of an unnecessary radio wave is output from a speaker at a large volume.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration of a wireless reception device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating squelch characteristics of the wireless reception device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Antenna 11 RF amplifier 12 Local oscillation part 13 Frequency conversion part 14 IF amplifier 15 FM detector 16 De-emphasis circuit 17 AF preamplifier 18 AF switch 19 AF power amplifier 20 Speaker 21 Microcomputer 31 BPF 32 Amplifier 33 Detector 41 LPF 42 Amplifier 43 Detector

Claims (2)

[Claims] 1. A radio receiving apparatus for controlling a squelch operation based on a noise component included in a detection output, comprising: a medium-high noise extracting means for extracting a medium-high noise component in an audio signal included in the detection output; Low-frequency noise extraction means for extracting low-frequency noise components in the audio signal included in the output; middle-high frequency noise components extracted by the middle-high noise extraction means; and low-frequency noise extracted by the low-frequency noise extraction means. Control means for interrupting the output of the audio signal when at least one of the noise components reaches a predetermined level. 2. The radio receiving apparatus according to claim 1, wherein said low-frequency noise extracting means extracts a low-frequency noise component equal to or lower than an audio frequency.