JPS6262094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver for a wireless microphone. Wireless technology that can completely eliminate transient noise that occurs when the switch is opened or closed.
This invention relates to a microphone receiver.

Wireless microphones are generally turned on and off using a built-in oscillator power switch, but after the power switch is turned on, it takes time for each part of the circuit to reach a steady state, so this transient During this period, radio waves with a carrier frequency that deviates from the specified frequency are emitted, and when the switch is turned on or
Transient noise is transmitted when off. When such radio waves are received by an FM receiver, DC components and transient noise appear in the output of the detector or demodulator, generating large noise.

In order to prevent the occurrence of such noise, a receiver equipped with a squelch circuit as shown in FIG. 1 has conventionally been used. To explain the receiver of FIG. 1, a signal received by an antenna 2 is amplified by a high frequency amplifier 4, mixed with a signal supplied from a local oscillator 8 by a mixer 6, and converted into an intermediate frequency signal. . The intermediate frequency signal is amplified by an intermediate frequency amplification section 10 and detected by a wave detector 12, and the audio signal is supplied to a low frequency amplification section 18 via a switch section 16 of a squelch circuit 14. Low frequency amplification section 18
The output of is supplied to the speaker 20.

On the other hand, the signal taken out from the intermediate frequency amplification section 10 is supplied to a rectifier circuit 25 made up of diodes 22 and 24 of the squelch circuit 14 and rectified. The rectified signal passes through a first time constant circuit 29 consisting of a capacitor 26 and a resistor 28 to the transistor 3.
Hysteresis circuit 3 configured by 0,32
3. The output of the hysteresis circuit 33 is supplied to the switch unit 16 via a second time constant circuit 37 consisting of a resistor 34 and a capacitor 36.

FIG. 2 shows the relationship between the operating time of the squelch circuit 14 and the control voltage generated at its output point A. When the power switch of the wireless microphone, which is a transmitter, is turned on at _t1 , the resistor 34 and capacitor 36 The output voltage increases exponentially due to the action of the second time constant circuit 37 consisting of. When the voltage at the output point A reaches the on level Vi ₂ at t ₂ , the switch section 16 is turned on and the audio is broadcast. In this way, by the time the switch section 16 is turned on, t ₁
Since there is a delay between −t ₂ (usually 0.2 to 0.3 seconds),
Transient noises that occur between when the wireless microphone is turned on and when broadcasting starts are completely blocked and are never broadcast.

However, when the switch of the wireless microphone is turned off at _t3 , the voltage at the output point A decreases relatively rapidly due to the action of the first time constant circuit consisting of the capacitor 26 and the resistor 28, but still slightly decreases. However, due to the hysteresis characteristic of the hysteresis circuit 33, the switch section 16 is turned off at time _t4 when the off level _Vi1 , which is lower than the on level _Vi2 , is reached. Therefore, when the switch of the wireless microphone is turned off, the gain of the amplifier increases significantly during the period _t3 to _t4 (usually 2 to 3 milliseconds) until the switch section 16 of the squelch circuit 14 turns off. The problem was that it produced a lot of noise.

In addition, in the circuit of FIG. 1, the first time constant circuit 29
The reason why a variable resistor is used as the resistor 28 is to adjust the squelch levels Vi ₂ and Vi ₁ for the antenna input, and the reason why the hysteresis circuit 33 is used is when the wireless microphone is carried around and the electric field strength is somewhat high. This is to prevent the squelch circuit itself from turning on and off frequently when the change occurs.

The present invention uses a simple method of providing a delay circuit with an appropriate delay time between the detector 12 and the switch section 16 of the squelch circuit 14 to prevent wireless communication that could not be blocked by conventional squelch circuits. - It is an object of the present invention to provide a wireless microphone receiver that can completely block the noise generated when the microphone is switched off.

FIG. 3 shows an embodiment of the receiver according to the present invention.
Components that are the same as those of the conventional receiver shown in FIG. 1 are given the same reference numerals, and explanations thereof will be omitted. A signal delay circuit 38 is inserted in the signal path between the detector 12 and the switch section 16. The delay time of this signal delay circuit 38 is longer than the time t ₃ - t ₄ from when the switch of the wireless microphone is turned off until the switch part 16 of the squelch circuit is opened. Time t ₁ until section 16 closes
-t is set to be shorter than ₂ .

When a delay circuit like the one above is installed in the signal path,
The opening/closing operation of the switch section 16 relative to the audio signal reaching the switch section 16 from the delay circuit 38 becomes relatively quick. Therefore, even if there is a time delay between t ₃ and t ₄ from when the wireless microphone is turned off until the switch section 16 opens, the transient noise will not reach the switch section 16 during this time. This transient noise is never broadcast. Time t ₁ − from when the wireless microphone is turned on until the switch section 16 closes
Since t ₂ is longer than the delay time of the delay circuit 38, there is no worry that transient noise generated when the wireless microphone is turned on will be broadcast by delaying the audio signal.

As described above, according to the present invention, by simply inserting a delay circuit of an appropriate size into the audio signal path, transients at the time of opening and closing of a wireless microphone switch, which could not be prevented by a conventional squelch circuit, can be prevented. can completely block out noise,
Its practical effects are extremely large. Incidentally, there are conventional devices in which a delay circuit is interposed between the detector and the switch section (for example, Japanese Patent Application Laid-Open No. 53-64410
No., 54-11617, 54-77506, 54-104703
In these cases, the delay circuit is provided to determine the timing at which the switch section is opened by supplying a control signal generated by detecting noise caused by fluctuations in the received electric field strength from the output of the wave detector to the switch section.
This is to match the timing at which the output of the detector, which includes noise components caused by fluctuations in received field strength, is supplied to the switch section. Its function is different from that in which the output of the detection section is delayed so that the generated noise arrives after the switch section is opened. In addition, these conventional devices open the switch section to prevent noise caused by fluctuations in received field strength from being supplied to the low-frequency amplifier, so what is being detected is noise. It is an ingredient.
In contrast, in the present invention, in order to prevent the noise generated by turning off the switch of the wireless microphone from being supplied to the low frequency amplifier, the intermediate frequency signal is rectified and smoothed, and the switch section is opened and closed according to the level. There is. That is, the purposes of this invention and those conventionally known are completely different. Depending on the purpose of use of the receiver, the present invention may be applied to a receiver having a squelch circuit without the hysteresis circuit 33.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the structure of a conventional wireless microphone receiver equipped with a squelch circuit, and FIG. 2 shows the receiver of FIG. 1 and the wireless microphone receiver of the present invention shown in FIG. 3. FIG. 3 is a diagram showing changes in the output control voltage of the squelch circuit to explain the operation thereof, and FIG. 3 is a schematic configuration diagram of a wireless microphone receiver according to the present invention equipped with a squelch circuit. 10...Intermediate frequency amplifier, 12...Detector, 1
4... Squelch circuit, 16... Switch section, 38
...Signal delay circuit.

Claims (1)

[Claims] 1. A frequency conversion section that mixes the signal transmitted from the wireless microphone with a local oscillation signal and converts it into an intermediate frequency signal, a detection section that detects the intermediate frequency signal, and a low frequency signal that amplifies the detection output of this detection section. an amplification section; a switch section interposed between the detection section and the low frequency amplification section that closes when a control signal of a certain level or higher is supplied and supplies the detection output to the low frequency amplification section; A rectifying section that rectifies an intermediate frequency signal, a first time constant circuit that smoothes the output of this rectifying section, an amplifying section that amplifies the output of this first time constant circuit, and an input of the output of this amplifying section. a second time constant circuit that generates the control signal and supplies it to the switch section, a delay means is interposed between the switch section and the detection section, and the delay means is connected to the wireless microphone. A receiver for a wireless microphone, characterized in that the delay time is selected to be longer than the time from when the switch is turned off until the control signal becomes smaller than at least the predetermined level.