JPS60233948A - Electromagnetic wave detector - Google Patents

Abstract

PURPOSE:To detect surely a desired wave by constituting the titled detector that a capcitor whose charging is controlled by a white noise and a VCO is swept by the charge/discharge signal of the said capacitor. CONSTITUTION:The desired wave entering from an antenna 1 is converted into an IF signal by the 1st and 2nd mixers 2, 5 and demodulated by a detector 7. When no signal input exists, a switch 11 is turned on/off by the white noise and the capacitor 13 is charged. The charging voltage of the capacitor is discharged at a prescribed period by a switch 14 controlled by a pulse generator 15. A sawtooth voltage based on the charging/discharging is used as a sweep voltage of the VCO16. When the signal is received as the result of sweep, the switch 11 is turned off. As a result the sweep of the VCO is stopped, the detector 7 generates a wide pulse output to drive an alarm device 10.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] 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 interfering electromagnetic waves such as swept waves and pulse noise are present. 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 ( It is easily affected by interfering electromagnetic waves such as sweep waves) and pulse noise, and may frequently malfunction. Therefore, you may end up turning it off out of annoyance, and 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,
Unless these are eliminated, it will not be practical.

As a solution, it may be possible to provide a narrow band filter, but it is impossible to suppress 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]

The present invention switches the charging current to a capacitor using white noise from a wave detector when there is no signal input, causes a voltage controlled oscillator (VCO) to sweep the voltage across the capacitor, and detects a signal input with a predetermined frequency within the band. If a continuous signal of a predetermined frequency is input, it is detected as a pulse with a constant width, while the sweep local oscillator of the other electromagnetic wave detector In the case of leakage electromagnetic waves from cars or pulse-like noises from cars, etc., only narrow pulses are output to prevent alarms from malfunctioning.

[Embodiments of the invention]

,stomach Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an electromagnetic wave detector according to the present invention. In the figure, 1 is the antenna, 2 is the first
mixer, 3 is the door 1 local oscillator (fixed frequency), 4 is the first
5 is a second intermediate frequency amplifier, 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 switching circuit controlled by the output of the low frequency amplifier 8; 12 is a current source that is turned on and off by the switching circuit 11; 13 is a capacitor charged by the current source 12; The capacitor 13 is turned on by the pulse.
Switching circuit to discharge, J6 is capacitor 13
This is a VCO whose oscillation frequency is controlled by the voltage across both ends of the VCO and which supplies a sweep frequency local oscillation signal to the second mixer 5.

In the electromagnetic wave detector configured as described above according to the present invention, the electromagnetic wave entering from the antenna 1 is transmitted to the first local oscillator 3.
It is mixed with the fixed frequency local oscillation signal from 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 swept frequency box 2 local oscillation signal from the vcoi 6 are mixed, and the second intermediate frequency 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 detected output after amplification turns on and off a switching circuit. 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 for charging. 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 rises in a random stepwise manner as shown in FIG. 3. FIG. 4 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, and turns the switching circuit 14 on and off. The voltage of the capacitor 13 is discharged. Therefore, the voltage across capacitor 130 becomes the sawtooth wave of FIG. 3, causing vCO 16 to provide 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 is
A signal is output only when a pulse with a fixed time width is input. Therefore, the lower limit of the pulse width to be detected should be set so as not to generate a signal in the case of white noise due to the detection output when there is no signal or the detection output with a narrow width of pulse-like noise.

Only when there is a pulse with a width equal to or greater than this lower limit, alarm 1
0 will be activated and an alarm will be issued.

Now, in the case where the second local oscillator 16 simply sweeps, even if electromagnetic waves are received, only a pulse-like output appears 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.
3. Alternatively, reception continues until the received electromagnetic wave deviates out of the band due to frequency fluctuations or until a reset pulse is issued from the pulse generator 15. Therefore, the width of the detected output becomes substantially wider 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 activates the alarm 10.

On the other hand, if the received electromagnetic wave is a sweep signal,
If the pulse signal has a narrow width, even if the sweep by the VCO 16 is stopped in response to the output of the low frequency amplifier 8, the detection time will be short and at most a waveform like that shown in Figure 2B will be output. It is. Therefore, the wide pulse shown in FIG. , will not malfunction as an alarm.

In this embodiment, when there is a signal input, the output of the wave detector 7 decreases, and the low frequency amplifier 8, pulse width detection circuit 9. a binding device 1o1. and switching circuit 11
I explained that it works, but if you set the logic level in the opposite direction, the output of the detector 7 will rise when the signal input is rare.
'It goes without saying that these circuit parts can be made to operate accordingly.

Further, the predetermined frequency of the target signal refers to the carrier frequency, and it goes without saying that it does not matter whether it is a radio wave format such as AM or CW.

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, the charging of the capacitor is regulated by the point and noise from the detector when there is no signal, the voltage across the capacitor is swept to vCo, and when a signal of a predetermined frequency is input within the band, the capacitor is charged. If a continuous signal of a predetermined frequency is input after stopping charging and canceling the sweep, -
While it detects pulses as wide as the footstep and issues an alarm, in the case of leakage electromagnetic waves from the sweeping local oscillator of other electromagnetic wave detectors or pulse-like noise from cars, etc., it only outputs pulses with a narrow width of 5. , alarms, etc. are prevented from malfunctioning, so an electromagnetic wave detector capable of selectively detecting only electromagnetic waves of a predetermined frequency can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of an electromagnetic wave generator according to the present invention, Figure 2 is a waveform diagram of the detector output, Figure 3 is a diagram showing changes in voltage across a capacitor when there is no signal, and Figure 4 is a diagram showing changes in voltage across a capacitor when there is no signal. Figures 1 and 5 show an example of the output waveform of the pulse generator, Figure 6 shows how the voltage across the capacitor is maintained when the desired signal is input, and Figure 7 shows an example of the output waveform of the pulse generator. 6 is a diagram showing the output waveform of the low frequency amplifier corresponding to the state shown in FIG. 6, and FIG. 8 is a diagram showing the output waveform when the pulse width detection circuit fully operates the alarm device. 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, 1
2... Current source, 13... Capacitor, 14... Switching circuit, 15... Pulse oscillator, 16...
Voltage controlled oscillator (VCO). Agent Tatsuyuki Unuma (and 1 other person) Figure 2 (A) 1-CB) (C) Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] (ly) In 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 or pulsed noise, there is a mixer, a detector that detects the mixer's output, and a A low frequency amplifier that fully swings with the detector output when a signal is present, 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 charged by the current source. a capacitor, a second switching circuit that discharges the capacitor, a VCO that sweeps the voltage across the capacitor and supplies a swept local oscillation signal to the mixer, and a VCO that sweeps only the signal with a pulse width of a certain value or more from the low frequency amplifier. When the pulse width detection circuit that detects and activates an alarm etc. is activated and a continuous electromagnetic wave of a predetermined frequency is input, the first switching circuit remains open, the voltage of the capacitor is held at a constant value, and the VCO sweep is stopped. An electromagnetic wave detector characterized in that a pulse width detection circuit receives a wide pulse from a low frequency amplifier and outputs a signal to activate an alarm or the like.