JPH043697B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromagnetic wave detector, which detects only electromagnetic waves of a target frequency without malfunction even in an environment where there are interfering electromagnetic waves such as swept waves or pulsed noise. This invention relates to an electromagnetic wave detector that detects electromagnetic waves.

[Background of the invention]

In crime prevention alarm systems such as home security systems that are becoming popular these days, electromagnetic waves are often used to detect abnormalities, and because they are particularly sensitive, leakage of electromagnetic waves from the local oscillators of other electromagnetic wave detectors is a problem. It is susceptible to interference electromagnetic waves such as (sweep waves) and pulse noise, and may frequently malfunction. Therefore, you may end up turning off the switch out of annoyance, and it may end up being completely useless when you actually need it.

On the other hand, in the case of reverse detection of radar waves for speed detection, in addition to the leakage electromagnetic waves from the swept local oscillator of the electromagnetic wave detector of other cars, there is Pulse noise is a particular problem, and unless these are eliminated, it will not be practical.

As a solution to this problem, it may be possible to provide a narrow band filter, but it is impossible to suppress the noise passing within this band, and it is not very useful for swept waves.

[Purpose of the invention]

An object of the present invention is to provide an electromagnetic wave detector that can selectively detect only electromagnetic waves of a predetermined frequency even in an environment where there are interfering electromagnetic waves such as swept waves from local oscillators of other devices and pulsed noise from cars etc. It is to provide.

[Summary of the invention]

In order to achieve the above object, the present invention includes a mixer, a detector for detecting the output of the mixer, a low frequency amplifier with an amplification degree that makes full swing even when the detector output is in the absence of a signal, and an output of the low frequency amplifier. A first switching circuit that is controlled, a current source that is turned on and off by the first switching circuit, a capacitor that is charged by the current source, and discharges the capacitor at a predetermined period or every time the charging voltage of the capacitor reaches a predetermined value. The voltage across the capacitor is maintained by the second switching circuit and the first switching circuit, which normally supplies a swept local oscillation signal to the mixer by the voltage across the capacitor, and remains open when a continuous electromagnetic wave of a predetermined frequency is input. Supply only local oscillation signals with frequencies corresponding to
The present invention proposes an electromagnetic wave detector consisting of a VCO and a pulse width detection circuit that detects only signals with a pulse width of a certain value or more from the low frequency amplifier and activates an alarm or the like.

In the present invention, the charging current to the capacitor is switched using the white noise from the detector when there is no signal input, and the voltage across the capacitor controls the voltage controlled oscillator (VCO) to sweep the local oscillation frequency. When a signal with a predetermined frequency is input within the band, charging to the capacitor is stopped and the sweep is stopped, and when a signal with the predetermined frequency is input continuously, it is detected as a pulse with a width of a certain value or more. Issue an alarm, etc. On the other hand, in the case of leakage electromagnetic waves from the sweep local oscillator of other electromagnetic wave detectors or pulse-like noise from cars, etc., only narrow pulses are output to prevent alarms from malfunctioning. Therefore, an electromagnetic wave detector capable of selectively detecting only electromagnetic waves of a predetermined frequency is obtained.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of an electromagnetic wave detector according to the present invention. In the figure, 1
is an antenna, 2 is a first mixer, 3 is a first local oscillator (fixed frequency), 4 is a first intermediate frequency amplifier, and 5 is a first mixer.
is a second mixer, 6 is a second intermediate frequency amplifier, 7 is a detector, 8 is a low frequency amplifier, 9 is a pulse width detection circuit, and 10 is an alarm. 11 is a low frequency amplifier 8
a switching circuit controlled by the output of 12;
is a current source that is turned on and off by the switching circuit 11; 13 is a capacitor that is charged by the current source 12; 14 is a switching circuit that is turned on and off by pulses from the pulse generator 15 to discharge the capacitor 13; This is a VCO whose oscillation frequency is controlled and which supplies a sweep frequency local oscillation signal to the second mixer 5.

In the electromagnetic wave detector configured in this manner according to the present invention, the electromagnetic waves entering from the antenna 1 are
It is mixed with the fixed frequency local oscillation signal from the local oscillator 3 by the first mixer 2 to become a first intermediate frequency, which is amplified by the first intermediate frequency amplifier 4 and enters the second mixer 5. In the second mixer 5, the first intermediate frequency and
The sweep frequency second local oscillation signal from the VCO 16 is mixed to form a second intermediate frequency, which is amplified by the second intermediate frequency amplifier 6 and detected by the detector 7. The output of the detector 7 is greatly amplified by the low frequency amplifier 8 to the extent that the white noise when there is no signal swings full in the form of a pulse. The amplified detection output turns the switching circuit 11 on and off. Here, an example is shown in which one end of the switching circuit 11 is connected to a power supply line and the other end is connected to a resistor 12 to constitute a current source. Preferably, it is a constant current source. When the switching circuit 11 is turned on and off, the capacitor 13 is intermittently charged by the current source 12. Since the white noise when there is no signal is random noise as shown in FIG. 2A, the voltage across the capacitor 13 increases in a random stepwise manner as shown in FIG. 3. Fourth
The figure is an enlarged view of the voltage waveform in FIG. 3.

The pulse generator 15 generates a narrow pulse as shown in FIG. 5 at a constant cycle or under conditions such as when the voltage of the capacitor 13 reaches a constant voltage, turns the switching circuit 14 on and off, and turns the capacitor 13 on and off. discharge the voltage. Therefore, capacitor 1
The voltage across 3 becomes a sawtooth wave as shown in Figure 3,
Make the VCO 16 output a swept frequency local oscillation signal.

On the other hand, the detection output amplified by the low frequency amplifier 8 is also input to the pulse width detection circuit 9. The pulse width detection circuit 9 outputs a signal only when a pulse with a time width of a certain value or more is input. Therefore, the lower limit of the pulse width to be detected is set so that no signal is output in the case of white noise resulting from the detection output when there is no signal or the detection output having a narrow width of pulse-like noise. Only when a pulse with a width equal to or greater than this lower limit is received, the alarm device 10 is activated and an alarm is issued.

Now, if the second local oscillator 16 simply sweeps, even if electromagnetic waves are received, only a pulse-like output will appear as shown in FIG. 2B. However, in the case of this circuit, when an electromagnetic wave is received, the switching circuit 11 is turned off by the detection output, and charging of the capacitor 13 is stopped, as shown in FIG. Reception continues until the received signal deviates out of the band due to frequency fluctuations in the electromagnetic wave being received, or until a reset pulse is issued from the pulse generator 15. Therefore, the width of the detected output is substantially expanded as shown in FIG. 2C, and the output pulse of the low frequency amplifier 8 becomes a wide pulse as shown in FIG. 7. This wide pulse can pass through the pulse width detection circuit 9, becomes the pulse shown in FIG. 8, and operates the alarm 10.

Here, the reason why the width of the detected output is substantially expanded as shown in FIG. 2C will be explained in more detail. FIG. 9 is a circuit diagram showing an example of the configuration of a known AM detector using a diode as a detection element. In the figure, C1 is a coupling capacitor, D1 is a detection diode, resistor R1 and capacitor C2 are a low pass filter, and R2 is a load resistor. Assuming that the detection diode D1 is an ideal diode, when a carrier-only signal, that is, a CW wave, shown in FIG. 10 is input from the input A, a half-wave rectified signal as shown in FIG. A signal with a different waveform can be obtained. When this is passed through a low pass filter consisting of resistor R1 and capacitor C2, a negative voltage is generated at output B. The magnitude of this negative voltage corresponds to the magnitude of the carrier wave. Therefore, when an (AM) signal in which the carrier wave is amplitude modulated is input to input A as shown in Fig. 12, the output B is as follows.
A negative voltage as shown in FIG. 13 is generated.

In this embodiment, since the VCO 16 sweeps the frequency of the local oscillation signal, an envelope signal corresponding to the normal band characteristics appears at the output of the second intermediate frequency amplifier 6, as shown in FIG. When this envelope signal is input to input A in FIG. 9, the detected output has the waveform shown in FIG. 2 C above.

On the other hand, if the received electromagnetic wave is a sweep signal or a pulse signal with a narrow width, even if the sweep by the VCO 16 is stopped according to the output of the low frequency amplifier 8, the detection time is short, and at most Only a waveform like that shown in FIG. 2B is output. Therefore, the wide pulse shown in FIG.
Since no signal is sent to the alarm circuit 10, there is no possibility of a malfunction as an alarm.

In this embodiment, when a signal is input, a negative detection output is obtained from the detector 7, and accordingly, the low frequency amplifier 8, pulse width detection circuit 9, and alarm 1
0 and the switching circuit 11 operate, but by setting the logic levels in the opposite direction, when a signal is input, a positive detection output is obtained from the detector 7, and these circuit parts operate accordingly. Needless to say, you can do it as well. 15th
The figure is a circuit diagram showing an example of the configuration of an AM detector for this purpose. Note that even if the output of the AM detector shown in Fig. 9 is used, if the output of the low frequency amplifier 8 is inverted, the logic level will be set in the opposite way.
It will be easily understood that an operation equivalent to that of the circuit shown in FIG. 15 can be realized.

Further, the predetermined frequency of the target signal is a carrier frequency, and it goes without saying that it does not matter whether the radio wave format is AM, CW, FM, or the like. In the case of CW waves, referring to FIG. 10, FIG. 11, and FIG. 14, the case can be considered almost the same as the case of the above AM detector. FIG. 16 is a diagram showing the S-curve characteristics of a well-known FM detector. Various types of FM detectors, such as quadrature detectors and ratio detectors, are widely used. Most circuits show S-shaped characteristics as shown in Figure 16 when the horizontal axis shows the input frequency and the vertical axis shows the detection output.
This is generally called the S-curve characteristic. By using the characteristic below the center of this S curve, it is possible to open the first switching circuit 11 and stop the sweep of the VCO 16, and the control operation of the VCO 16 can produce the same result as in the case of the AM detector described above. can get. Furthermore, even if the characteristics above the center of the S curve are used, if the output of the low frequency amplifier 8 is inverted, the logic level will be set in the opposite way, compared to when the characteristics below the center of the S curve are used. It will be readily understood that equivalent effects can be achieved.

Note that the object controlled by the pulse width detection circuit is not limited to an alarm device, and may be any other sequence circuit.

〔Effect of the invention〕

According to the present invention, charging of the capacitor is regulated using white noise from the detector when there is no signal, the voltage across the capacitor is used to sweep the VCO, and when a signal of a predetermined frequency is input within the band, the capacitor is charged. When charging is stopped and the sweep is stopped, and a signal of the specified frequency is input continuously, it is detected as a pulse with a width exceeding a certain level and an alarm is issued, while the sweep local part of other electromagnetic wave detectors is In the case of electromagnetic waves leaking from an oscillator or pulse-like noise from cars, etc., it is possible to prevent alarms from malfunctioning by outputting only narrow pulses, making it possible to selectively detect only electromagnetic waves of a predetermined frequency. An electromagnetic wave detector is obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of an electromagnetic wave detector according to the present invention, Figure 2 is a waveform diagram of the detector output, Figure 3 is a diagram showing changes in the voltage across the capacitor when there is no signal, and Figure 4 is a diagram showing the change in voltage across the capacitor when there is no signal. Figure 5 is a diagram showing an example of the output waveform of the pulse generator, Figure 6 is a diagram showing the state in which the voltage across the capacitor is held when the desired signal is input, and Figure 7 is a diagram showing the state in which the voltage across the capacitor is held when the desired signal is input. A diagram showing the output waveform of the low frequency amplifier corresponding to the holding state in Figure 6,
Fig. 8 is a diagram showing the output waveform when the pulse width detection circuit activates the alarm, Fig. 9 is a circuit diagram showing an example of the configuration of a well-known AM detector using a diode as a detection element, and Fig. 10. ~Figure 14 is Figure 9
A diagram showing waveforms for explaining the operation of the AM detector, FIG. 15 is a circuit diagram showing an example of the configuration of the AM detector when used with the logic level set opposite to that of the AM detector in FIG. 9, Figure 16 is a well-known FM
It is a figure showing the S curve characteristic of a wave detector. 1... Antenna, 2... First mixer, 3... First local oscillator, 4... First intermediate frequency amplifier, 5...
...Second mixer, 6...Second intermediate frequency amplifier, 7...
...Detector, 8...Low frequency amplifier, 9...Pulse width detection circuit, 10...Alarm, 11...Switching circuit, 12...Current source, 13...Capacitor,
14... Switching circuit, 15... Pulse oscillator, 16... Voltage controlled oscillator (VCO).

Claims (1)

[Scope of Claims] 1. An electromagnetic wave detector that selectively detects only electromagnetic waves of a predetermined frequency in an environment where there are interfering electromagnetic waves such as swept waves and pulsed noise, which includes: a mixer; a detector that detects the output of the mixer; , a low frequency amplifier with an amplification degree that swings full even when there is no signal, a first switching circuit that is controlled by the output of the low frequency amplifier, a current source that is turned on and off by the first switching circuit, and a current source that is turned on and off by the first switching circuit. a second capacitor that discharges the capacitor at predetermined intervals or each time the charging voltage of the capacitor reaches a predetermined value;
It corresponds to the voltage across the capacitor held by the switching circuit and the first switching circuit, which normally supplies a swept local oscillation signal to the mixer by the voltage across the capacitor, and remains open when a continuous electromagnetic wave of a predetermined frequency is input. an electromagnetic wave detection circuit comprising a VCO that supplies only a local oscillation signal of a certain frequency, and a pulse width detection circuit that detects only a signal with a pulse width above a certain level from the low frequency amplifier and activates an alarm, etc. vessel.