JPH02180435A - Squelch circuit and multimode receiver equipped with the squelch circuit - Google Patents

Abstract

PURPOSE:To accurately operate even for a weak input signal by detecting a noise component out of an IF signal and intermittently controlling a demodulated signal. CONSTITUTION:Since the noise component is small when the signal intensity of a received FM radio wave is strong, an FMw noise signal (f) is small, and a noise detected signal (k) is also small. Therefore, the noise detected signal (k) is smaller than a squelch operation level (m), and a squelch actuating signal (n) is not outputted. Since the noise component becomes larger when no signal component exists in the received FM radio wave, the FMw noise signal (f) is large, and the noise detected signal (k) is also large. Therefore, the noise detected signal (k) is larger than the squelch operation level (m), the squelch actuation signal (n) is outputted, and an FMw demodulated signal (d) is interrupted in an AF signal intermitter 55 and never drives a speaker 7. Thus, the title squelch circuit, which can execute a squelch operation even for the weak input signal and has high sensitivity, can be obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a receiver for FM radio waves containing signals in the audio frequency band and signals above the audio frequency band.

[Conventional technology]

As for the squelch for FMn mode (narrowband FM reception mode), a noise squelch circuit is used for boat fishing as shown in FIG. 10kHz from the output signal from the demodulator
z~20kHz noise component is detected, amplified and detected, and used as a squelch signal. This is a method that takes advantage of the fact that when there is no input signal, the noise in the 10kHz to 20kHz band decreases as the input signal becomes stronger, and blocks the harsh noise that occurs when there is no signal.Noise squelch It is called , and the operating point can be set even for very weak signals. And FMw mode (wideband FM reception mode)
The squelch for boat fishing is as shown in Figure 3. A part of the signal is extracted from the IF amplification circuit that amplifies the intermediate frequency signal (IF multiplied signal), and a level detection circuit generates a signal proportional to the input signal strength. This is a method of intermittent low frequency signal (AF multiplied signal) and is generally called S meter squelch as it is proportional to the input signal strength. In the case of a multi-mode receiver having modes, a single squelch level setting knob is provided so that it can be used in both modes.

[Problem to be solved]

However, in FM stereo broadcasting, etc., the noise squelch of the FMn mode receiver has the disadvantage that the pilot signal interferes and does not work properly, and the S-meter squelch generally has good squelch operation sensitivity. In other words, the S-meter squelch has the disadvantage that it does not work unless the input signal is strong to a certain extent.In addition, in the case of a multi-mode receiver, there are two types: a noise squelch for FMn mode and an S-meter squelch for FMw mode. If you combine the squelch circuits and share the squelch level setting knob in each mode,
Since the squelch operating point and the position of the knob differ depending on the mode, there is a problem that it is difficult to use. When receiving FM stereo broadcasting, the output of the FMw demodulator shown in Figure 3 is used up to a very high frequency band, as shown in Figure 4, and this signal is used as it is at 10K.
When connected to a noise squelch circuit that detects noise components in the Hz to 20kHz range, the problem is that the signal components in this frequency range are mistakenly recognized as noise, and the AF multiplied signal output is erroneously cut off even if there is a received signal. There is a point. Therefore, it has been desired to realize a noise squelch circuit that can use a single squelch level setting knob at the same position and that can operate accurately with FMw mode signals and even with weak input signals.

[Means for Solving the Problems] The present invention has been made in view of the above problems, and the squelch circuit according to the present invention is capable of receiving FM radio waves including signals in the audible frequency band and signals above the audible frequency band. The apparatus is equipped with AM detection means for detecting the IF multiplied signal AM and outputting an AM detection signal, and signal intermittent means for controlling the demodulated signal intermittently using the AM detection signal. In the multi-mode receiver according to the present invention, the multi-mode receiver is a receiver of FM radio waves including signals in the audio frequency band and signals above the audio frequency band.
a noise squelch circuit comprising a noise detection circuit that detects a noise component from a 1F signal and outputs a noise signal; and a signal intermittent means that controls a demodulated signal intermittently using the noise signal; a squelch circuit having the above configuration; and both squelch circuits. A measure was taken to provide a switching circuit. Further, a sensitivity matching circuit may be provided to match the signal levels of both squelch circuits. [Function] According to the squelch circuit according to the present invention, the [' signal extracted from the IF amplifier etc. in the FM radio wave receiver has
Internal noise is included when there is no signal or when there is a weak signal, but this includes not only the FM component but also the AM acid component, so when this is detected by AM, the resulting AM detected signal will mainly contain noise components. . That is, when the FM signal component is small, the noise signal component is large (so the AM detection signal becomes strong), and when the FM signal component is large, the noise signal is small, so the AM detection signal becomes weak (so this AM detection signal becomes weak). By performing intermittent control of the signal using the detection signal, squelch operation can be performed.Furthermore, according to the multi-mode receiver of the present invention, the noise component is detected from the demodulated signal and the noise signal is detected. The noise squelch circuit includes a noise detection circuit that outputs a signal, a signal intermittent means that controls the demodulated signal intermittently using the noise signal, a squelch circuit having the above configuration, and a switching circuit for both the squelch circuits. By switching both squelch circuits at the same time as switching, it is possible to perform the optimal squelch operation in each mode.Also, by matching the signal levels of both squelch circuits to almost the same level using a sensitivity matching circuit, each time the reception mode is switched, There is no need to adjust the squelch level.

【Example】

The present invention will be explained in detail below based on the drawings. FIG. 1 is a block diagram of an embodiment of a squelch circuit according to the present invention. In the drawing, 1 is an FMw mode receiving section, 2 is an FMn mode receiving section, and 3 is an FMw mode receiving section.
4 is an AM detection circuit, 5 is a noise squelch circuit, 6 is an AF amplifier, and 7 is a speaker. In the FMw mode receiving section 1, the received signal a and the local oscillation signal S from the local oscillator 11 are mixed in the mixer 12, and the generated signal is

[The F signal C is amplified by the IFF width circuit 13 and demodulated by the FMw demodulator 14 to generate an FMw demodulated demodulated signal band. Further, a noise signal e is obtained from the IFF width circuit 13, and A
The FMw noise signal signal ratio is output from the M detection circuit 4. In the FMn mode receiving section 2, the received signal g and the local oscillation signal from the local oscillator 21 are mixed in the mixer 22, the generated IF signal is amplified in the distortion IFF width circuit 23, and the signal is sent to the FMn demodulator 24. demodulate and wait for the FMnMn demodulated signal. The noise detection circuit 8 detects the FMnMn demodulated signal
n noise signals q are obtained. In the mode switching unit 3, the squelch operation changeover switch S2 outputs either the FMw noise signal ``or the FMn noise signal q to the noise amplifier 51 of the noise squelch circuit 5, and the demodulation signal changeover switch Sl outputs either the FMw noise signal `` or the FMn noise signal q to the noise amplifier 51 of the noise squelch circuit 5. The demodulation signal band MnMn demodulation signal delay is output to the AFF signal interrupter of the noise squelch circuit 5.The squelch operation changeover switch S1 and the demodulation signal changeover switch S2 are controlled by a mode setter 31. By the sensitivity matching circuit 32, the FMW noise signal f and the FM
Adjust the level of n noise signal q. In the noise squelch circuit 5, the mode switching section 3
The FMw noise signal (or FMn noise signal q) outputted from the noise amplifier 51 is amplified by the noise amplifier 51 and detected by the noise detector 52 to output the noise detection signal k. In the squelch controller 53, the operation level setter 54
The squelch operation level m set in is compared with the noise detection signal, and when the latter exceeds the former, the squelch operation signal n is output, and when the latter does not exceed the former, the squelch operation signal n is not output. When the squelch activation signal n is manually input to the AFF signal interrupter 55, the FMw demodulation signal d or the FMnMn demodulation signal output from the mode switching unit 3 is paused, and if the squelch activation signal n is not input, the output from the mode switching unit 3 is The output FMw demodulated signal d or FMnMn demodulated signal is waited for. The AF multiplied signal that has passed through the AFF signal interrupter 55 is amplified by the AFF width circuit 6, drives the speaker 7, and is output as an audio signal. In the above configuration, the squelch operation in the FMw reception mode will be described below. When the signal strength of the received FM radio wave is strong, the noise component is small, so the FMw noise signal f is small and the noise detection signal is also small. Therefore, since the noise detection signal is lower than the squelch operation level m and the squelch operation signal n is not output, the FM
The demodulated demodulated signal band W passes through the FF signal interrupter 55 and drives the speaker 7 via the AFF width circuit 6. When there is no signal component of the received FM radio wave, the noise component becomes large, so the FMw noise signal f is large and the noise detection signal is also large. Therefore, the noise detection signal is higher than the squelch operation level m, and the squelch operation signal n is output, and the FMw demodulated signal d is cut off by the AF signal interrupter 55 and does not drive the speaker 7. According to the present invention, since the squelch operation is performed in this manner, it is possible to obtain a highly sensitive squelch circuit that can perform the squelch operation even in response to a weak input signal. Next, the squelch operation in the FMn reception mode will be explained. When the signal strength of the received FM radio wave is strong, the noise component is small, so the FMn output from the noise detection circuit 8
The noise signal q is small, and the noise detection signal is also small. Therefore, since the noise detection signal is lower than the squelch operation level m and the squelch operation signal n is not output, the FM
The n demodulated signal passes through the AF signal interrupter 55 and drives the speaker 7 via the AF amplifier circuit 6. When there is no signal component of the received FM radio wave, the noise component becomes large, so the F output from the noise detection circuit 8
The Mn noise signal q is large, and the noise detection signal is also large. Therefore, the squelch operation signal n, which is higher than the squelch operation level m, is output as the noise detection signal, and the F M n demodulated signal j is cut off at the AF signal intermittent 2355 and does not drive the speaker 7. A mode setting device 31 in the mode switching section 3
By setting , the above-mentioned FMw reception mode and FMn reception mode can be switched. In this way, according to the multi-mode receiver of the present invention, the predetermined squelch operation can be switched in conjunction with the mode switching, so that the optimal squelch operation can be performed in each mode, resulting in high performance. The effect is that a multi-mode receiver with high performance can be provided. In addition, the operation level setter 54 is set to FMw reception mode and FM
Since it can be used in common for n reception modes, it is possible to simplify the structure of the receiver, especially the structure of the operation panel. Further, the sensitivity matching circuit 32 allows both the noise signals f,
By adjusting the signal levels of q to be almost the same, there is no need to adjust the squelch operation level m every time the mode is switched, so that an effect of extremely improved operability can be obtained. [Effects] As described above, according to the squelch circuit according to the present invention, it is possible to provide a squelch circuit that is highly sensitive and operates reliably even when the input signal is weak. Further, according to the multi-mode receiver according to the present invention, by switching to a predetermined squelch operation in conjunction with mode switching, it is possible to perform an optimal squelch operation in each mode. This has the effect of providing a receiver. Furthermore, since a single knob for setting the squelch level can be used in common for each mode, it is possible to simplify the structure of the receiver, especially the structure of the operation panel. In addition, by matching the signal levels of both squelch circuits to almost the same level using a sensitivity matching circuit, there is no need to adjust the squelch level each time the squelch circuit is switched, resulting in extremely improved operability. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the squelch circuit according to the present invention, and FIG. 2 is a block diagram of an embodiment of the squelch circuit according to the present invention.
Figure 3 is a block diagram of a conventional squelch circuit for FMw mode (wideband FM reception mode), and Figure 4 is a block diagram of a conventional squelch circuit for FMw mode (wideband FM reception mode).
It is a frequency spectrum distribution diagram of M stereo broadcast radio waves. 3...Switching circuit, 4-AM detection means, 5...Squelch circuit, 8...Noise detection circuit, 13.23-IF amplifier, 32...Sensitivity matching circuit, 55-...Signal Intermittent means, e... noise signal f/-AM detection signal d, i... demodulated signal.

Claims (3)

[Claims] (1) In an FM radio wave receiver that includes signals in the audible frequency band and signals above the audible frequency band, the IF signal is
A squelch circuit comprising: AM detection means for detecting and outputting an AM detection signal; and signal intermittent means for controlling a demodulated signal intermittently using the AM detection signal. (2) In a multi-mode receiver that is a receiver of FM radio waves including signals in an audible frequency band and signals above an audible frequency band, a noise detection circuit that detects a noise component from an IF signal and outputs a noise signal; A multi-mode reception comprising: a noise squelch circuit comprising a signal intermittent means for controlling a demodulated signal intermittently using a noise signal; the squelch circuit according to claim 1; and a switching circuit for both the squelch circuits. Machine. (3) The multimode receiver according to claim (2), further comprising a sensitivity matching circuit that matches the signal levels of both squelch circuits according to claim (2).