JPS60194832A - Squelch circuit - Google Patents

Abstract

PURPOSE:To adjust the operating point at a district of a wide range from a low electric field to a high electric field by using a noise detection output to switch a power supply of a carrier detector and using a carrier detection output to change over a switch of a demodulation signal. CONSTITUTION:The amplitude of an intermediate frequency (IF) band input signal IFIN is limited (1) and demodulated with frequency discrimination (2). The demodulated signal is applied to a BPF4 when a switch SW3 is closed and a demodulation output signal AF is outputted. On the other hand, an HPF5 amplifies the demodulation signal and passes through noises of a high frequency. The noise is rectified (6), inputted to a power supply SW7m and it is turned on when a rectified output 6 is smaller than a prescribed value, and a power is applied to a BPF8. The BPF8 amplifies an IF and closes the SW3 to pass the demodulation signal. The output is rectified (9), inputted to the SW3 and it is closed only when the value is larger than a prescribed value to pass the demodulation signal. The operating point is adjusted by variable resistors VR1, VR2. Thus, the squelch is adjusted over a wide range from a high electric field to a low electric field to attain a plesant reception.

Description

DETAILED DESCRIPTION OF THE INVENTION (11) Technical Field of the Invention The present invention relates to a squelch method for a single radio device, and particularly to a squelch circuit having a wide squelch adjustment range.

(2) Background of the technology With a single radio using FM modulation, when there are no incoming radio waves or when the received electric field is low, the noise in the demodulated signal increases and it becomes difficult to separate the signals, so a switch is installed to open and close the demodulated signal. A squelch circuit is provided that closes this switch when the received electric field is high and opens this switch when the received electric field is low. Since a single wireless device is often used while moving, a squelch circuit is desired that can widely change the squelch setting point depending on the radio wave condition.

(3) Prior Art and Problems Conventionally, squelch methods include a noise detection method and a carrier detection method.

The noise detection method detects high-frequency noise components in the demodulated signal, opens the demodulated signal switch when the detected output is above a predetermined value, and closes when the detected output is below the predetermined value, and the received electric field is low. This is effective when there is a relatively large amount of noise, and when the received electric field is high, that is, when there is relatively little noise, the predetermined value is set to a low value, so the high-frequency components of the audio signal are treated as noise. The disadvantage is that the switch is detected and opened (audio malfunction).

The carrier wave detection method is a method in which a carrier wave converted to an IF (intermediate frequency) is detected, and a switch is closed when the detection output is above a predetermined value and opened when the detection output is below a predetermined value. In other words, it is effective when the received level of the carrier wave is relatively high, and when the received electric field is low, that is, when the received level of the carrier wave is relatively low, the predetermined value is set to a low value, so noise is detected as a signal. The disadvantage is that the switch closes when the switch is closed.

Therefore, the squelch setting range for both types was narrow.

(4) Object of the Invention An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a squelch circuit having a wide adjustment range by combining a noise detection method and a carrier detection method.

(5) Structure of the Invention According to the present invention, the above-mentioned object is to provide a wireless communication receiver with means for detecting noise in a demodulated signal, means for detecting m-wave transmission, and switching on and off of a power source for the carrier wave detection means. This is achieved by providing a squelch circuit having the characteristics described above, which has means for opening and closing the demodulated signal, and opening and closing the power supply according to the noise detection output.

(6) Examples of the invention Examples of the present invention will be described below.

In the embodiment of the present invention, the power supply of the carrier wave detection circuit in the IF band is switched on and off based on the detection output of the demodulated signal noise detection circuit, and the demodulated signal is switched on and off based on the detection output of the carrier wave detection circuit.

The figure is a block diagram of a squelch circuit according to an embodiment of the present invention.
In the figure, 1 is a limiter (LIM), 2 is a frequency discriminator (DISC), 3 is a switch (SW), 4 is a first band filter, 5 is a high-pass filter, 6 is a first rectifier, and 7
is a power switch, 8 is a second bandpass filter, 9 is a second rectifier, IFIN is 1. AFOUT is a demodulated output signal, Vcc is a power supply voltage, VRI and VH2 are variable resistors, and crt and CF2 are terminals.

In the city, the IF band input signal IFIN is amplitude limited by a limiter 1 and then demodulated by a frequency discriminator 2. If the switch 3 is closed, this demodulated signal is band-limited by the first bandpass filter and then becomes the demodulated output signal AF 0L.
Output as TT.

The high-pass filter 5 amplifies the demodulated signal and passes high-frequency noise. This noise is rectified by the first rectifier 6 and input to the power switch 7.

The power supply voltage Vcc is output to the second bandpass filter 8 only when the input to the power switch 7 is smaller than a predetermined value. The second bandpass filter 8 amplifies the IF band large input signal and passes the carrier wave converted to the IF band. This carrier wave is rectified by the second rectifier 9 and input to the switch 3.

Switch 3 closes to allow the demodulated signal to pass only when this input is greater than a predetermined value.

The high-pass filter 5 and the first rectifier 6 constitute a noise detector, and the degree of amplification in the high-pass filter 5 is changed by a variable resistor VRI to isometrically adjust a predetermined value. The second bandpass filter 8 and the second rectifier 9 constitute a carrier wave detector, and the variable resistor R2 controls the amplification level of the second bandpass filter 8. When this squelch circuit is used in a high electric field, the noise The predetermined value of the detector is set to a relatively high value so that the power switch 7 is always closed, and squelch is mainly performed by the carrier wave detector, and when used for a low electric field, the predetermined value of the carrier wave detector is set to a relatively high value. The switch 3 is closed while the power supply voltage Vcc is being supplied at a relatively low level, and the squelch is mainly performed by opening and closing the power switch 7 by the noise detector.

Furthermore, in a low electric field, the squelch may be performed only by the noise detector by connecting the terminals CP1 and CF2.

(7) Effects of the Invention As described above, according to the present invention, the power supply of the carrier wave detector is opened and closed by the noise detection output, and the switch of the demodulated signal is opened and closed by the carrier wave detection output. This has the great effect of being adjustable.

4. Detailed description of the invention The figure shows a squelch circuit according to an embodiment of the present invention.

In the drawings, 1 is a limiter, 2 is a frequency discriminator, 3 is a switch, 4 and 8 are bandpass filters, 5 is a high-pass filter, 6 and 9 are rectifiers, and 7 is a power switch.

Claims (1)

[Claims] A wireless communication receiver includes means for detecting noise in a demodulated signal, means for detecting a carrier wave, means for opening/closing a power supply for the carrier wave detecting means, and means for opening/closing a demodulated signal, and a means for detecting the noise. A squelch circuit characterized in that the power source is opened and closed depending on the output direction, and the demodulated signal is opened and closed depending on the output direction of the carrier wave detection.