JPS6317366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an interference wave removal device for eliminating single-frequency interference waves existing in or near the reception frequency band in a receiver having a relatively wide reception frequency band, and particularly to This is intended to ensure that it will not be affected even in a temporary state of disconnection.

For example, in a Loran C receiver, radio waves from a Detsuka navigation device, so-called Detsuka radio waves, may be present in the vicinity of its receiving frequency band. While a mobile object equipped with a Loran-C receiver is moving, it passes through areas where the frequencies of the Detsuka radio waves differ, so when the Detsuka radio waves are removed by the Loran-C receiver, if it enters an area where the frequencies of the Detsuka radio waves differ. It is necessary to readjust the narrow band stop filter used to remove deep radio waves. Since the stopband of the narrowband stopband filter is very narrow, it requires time and skill to operate in order to correctly match the center frequency of the stopband with the center frequency of the interfering wave. It was very tedious to adjust the narrow band stop filter each time the device entered the range.

From this point of view, it has been proposed to automatically match the center frequency of a narrowband blocker that blocks interference waves with the frequency of the interference waves. However, in the case where the interference wave is an intermittent signal, for example, and the interference wave is temporarily interrupted, the control output of the control circuit that detects the deviation between the center frequency of the narrowband stopper and the interference wave frequency is If the normal state is greatly confused and the blocking center frequency of the narrowband blocker is controlled by such an erroneous detection output, the blocking center frequency of the narrowband blocker will be temporarily stopped each time the blocking wave is cut off. is no longer possible, and it is necessary to perform control again to match the center frequency of the narrow band stop filter with the frequency of the interfering wave. Even if everything is done automatically, it requires time, and if the blocking frequency is manually controlled so that it almost matches the frequency of the interference wave, then it is automatically made to match exactly. requires the operator to perform each operation.

The object of the present invention is to change the blocking center frequency of a narrowband blocker that blocks the interference waves without being affected even if the interference waves are temporarily cut off. An object of the present invention is to provide an interference wave removal device that can maintain the state immediately before the interference wave removal device.

According to this invention, a narrowband rejection filter is inserted in the reception signal path, each signal on the input side and output side of the narrowband rejection filter is branched and taken out, and from these two signals, the narrowband rejection filter is sent to the control circuit. The deviation between the center frequency of the wave generator and the frequency of the intended interference wave is detected. The output of the control circuit is held by a holding circuit, and the center frequency of the narrow band stop waver is set by the output of the holding circuit. In this way, the center frequency of the narrow band stop filter is automatically made to coincide with the frequency of the target interference wave.

Furthermore, the signals on the input side and output side of the narrowband rejection filter are amplified and rectified by first and second level detectors, and their levels are detected. When the center frequency of a narrowband blocker correctly matches the target interference frequency, the level at the input side of the narrowband blocker is high when the interference wave is input, but the level at the output side is low. It becomes significantly smaller. However, even if the frequency of the interference wave matches the rejection center frequency of the narrowband stopper, if the interfering wave is interrupted temporarily, the difference in signal level between the input side and the output side of the narrowband stopper will be small. Become. Therefore, by comparing the levels detected by the first and second level detectors with a comparator, it is possible to detect the intermittent state of interference waves, and when the interference waves are interrupted, the control circuit detects Prevent the signal from being supplied to the holding circuit. In other words, a switch is inserted in the path of the detection signal that reaches the holding circuit from the control circuit, and when noise etc. is applied to the narrow band stopper, that is, when the interference wave is cut off, the output of the comparator turns off the switch. To prevent the output detected by the control circuit from being given to the holding circuit. Furthermore, the first
When the inputs of the second level detector both reach a fairly low level, the signal from the first level detector detecting the level on the input side is transferred to the second level detector detecting the level on the output side. These level detectors are configured to be smaller than the output of the comparator so that in such a state, the output signal of the control circuit is not supplied to the holding circuit.

Next, an embodiment of the interference wave removal device according to the present invention will be described with reference to the drawings.

In FIG. 1, a received signal is amplified from an input terminal 11 through a preamplifier 12, and a narrow band rejection filter 13 removes interference waves.The output from which the interference waves have been removed is amplified by a postamplifier 14, and then passed through an output terminal 15. A processing device 16, such as a Loran C signal processing device, is provided. Signals on the input side and output side of the narrow band stop filter 13 are branched and supplied to the control circuit 17 . In the control circuit 17, a deviation between the blocking center frequency of the narrow band blocking filter 13 and the frequency of the target interference wave is detected. This detected deviation is supplied to a holding circuit 19 through a switch 18, which will be described later, and is held there. The holding signal is given to the narrow band stop waver 13 as its stop center frequency control signal. Narrowband stopper 1
3 is configured as a notch filter, for example, and includes variable capacitance diodes 21,
22 are provided, and these variable capacitance diodes 2
1 and 22 are controlled by a control signal from a holding circuit 19 to control the blocking center frequency.

In the control circuit 17, for example, a signal on the input side and a signal on the output side of the narrowband rejection filter 13 are taken out through bandpass filters 23 and 24, respectively, and the outputs of these bandpass filters 23 and 24 are outputted in phase. The comparator 25 compares the phases, and the phase comparison output is used as the output of the control circuit 17. The pass center frequencies of the bandpass waveforms 23 and 24 are made to substantially match the rejection center frequency of the narrowband waveform stopper 13, and these bandpass waveforms 23 and 24 have wave characteristics that are approximately equal to each other. This narrow band stopper 1
For example, some of the components of these bandpass waveformers 23, 24 are controlled so that the rejection center frequency of 3 is controlled by the output of the holding circuit 19, and the center frequencies of the bandpass waveforms 23, 24 are also controlled. The variable capacitance diode is controlled by the output of the holding circuit 19, and the change characteristics of the center frequency with respect to the control signal are made to be similar to the characteristics of the narrow band stop filter 13.

The phase frequency characteristic of the narrow band stop filter 13 is the second
As shown by curve 66 in the figure, the phase rapidly advances by approximately 90 degrees at frequencies higher than the center frequency o, and the phase rapidly shifts by 90 degrees at frequencies lower than the center frequency o. In other words, the phase changes rapidly within the range o-△ to o+△. On the other hand, bandpass waver 2
3 and 24 are configured as a single-peak tuning type consisting of a tuning circuit of a coil and a capacitor, for example, and their phase frequency characteristics gradually advance in phase on the side lower than the center frequency o, as shown by curve 67 in Fig. 2, and the phase becomes higher. The phase gradually lags on the side. Therefore, between the frequencies △o-△ and o+△, the phase of the outputs of wave generators 23 and 24 follows curve 6.
It is almost determined by the characteristics of 6. Therefore, by detecting the phases of the outputs of these wave generators 23 and 24 with the phase comparator 25, it is possible to detect the deviation between the center frequency o of the narrow band rejection wave generator 13 and the frequency of the interference wave. In other words, if the frequency of the interference wave is higher than the blocking center frequency o, the output of the wave generator 24 will be in phase, and if the frequency of the interference wave is lower, the output of the wave generator 23 will be in phase. .

In this invention, the signals on the input side and the output side of the narrowband rejection filter 13 are branched, and their respective levels are detected by a level detector. In this example, the outputs of the bandpass waveformers 23 and 24 are supplied to level detectors 26 and 27, respectively, to detect their respective levels, and the outputs of the level detectors 26 and 27 are compared in magnitude by a comparator 28. The switch 18 is controlled by the comparison output of the comparator 28.

By the way, the center frequency of the narrow band stop filter 13
When o matches the frequency of the interfering wave, the output of the narrow band stop filter 13 becomes sufficiently small compared to the input. Therefore, the output of level detector 26 is large, and the output of level detector 27 is significantly small. In this state, the output of the comparator 28 becomes high level, the switch 18 is turned on, and the output of the control circuit 17 is supplied to the holding circuit 19. However, when the interference wave is blocked, the narrowband stopper 13 enters the same state as if noise had been input, and the input side and the output side are at almost the same level, so the level detector 26, The output levels of the detectors 27 are almost the same, and in this state, the detection level of the detector 26 on the input side is smaller than the detection level of the detector 27 on the output side. As a result, the switch 18 is turned off, and the output of the control circuit 17 is not supplied to the holding circuit 19. Therefore, the detection signal of the control circuit 17 is not reliable in a state where the interference waves are blocked, but such an erroneous control signal is not supplied to the holding circuit 19, and the holding circuit 19 The control state is maintained, and when interference waves are inputted again, the interference waves can be reliably blocked by the narrow band blocking filter 13.

The level detectors 26 and 27 are configured as shown in FIG. 3, for example. These level detectors 26,2
7 performs amplification and rectification, and for example, in the level detector 26, an operational amplifier 31 and diodes 32, 33 whose one end is connected to the output side thereof, and further between the other end of the diode 32 and the other end of the diode 33 are connected. A resistor 34 is connected, and a connection point between the diode 33 and the resistor 34 is connected to the inverting input side of the operational amplifier 31 to serve as a feedback resistor, and further includes an input resistor 35 and a smoothing circuit that smoothes the output of the diode 32. It consists of 36. These operational amplifier 31, diodes 32, 33, feedback resistor 3
4. An amplification and rectification circuit 37 is configured by the input resistor 35 and the smoothing circuit 36. This amplification rectification circuit 37
An amplification suppression circuit 38 is connected to the signal. That is, the amplification suppression circuit 38 includes a diode 39 and a resistor 4.
1 in series, which is connected across feedback resistor 34.

For example, when the input of the level detector 26 is positive, the output side of the operational amplifier 31 becomes negative and the diode 3
2 is in a cutoff state and rectified output cannot be obtained, but
When the input becomes negative, the output of the operational amplifier 31 becomes positive, the diode 32 operates, and it is supplied to the smoothing circuit 36, where it is half-wave rectified and output. If the input at that time becomes further negative, the amplifier 31
, the level at the input side of the rectifier circuit 36 also becomes high, and the diode 39 of the amplification suppression circuit 38 becomes conductive. Until then, input resistor 3
The gain was determined by 5 and the feedback resistor 34, but
The gain is determined by the input resistor 35 and the parallel circuit of the resistors 34 and 41, and the degree of amplification is reduced. In this way, the degree of amplification is suppressed for large inputs.

Also in the level detector 27, the operational amplifier 4
2, an amplification and rectification circuit 47 consisting of diodes 43 and 44, a feedback resistor 45, a smoothing circuit 46, and an input resistor 50; and an amplification suppression circuit 51 consisting of a diode 48 and a resistor 49.

In the level detectors 26 and 27, the inversion boundary point of the switch 18 shown in FIG. 1 is determined by selecting and setting the resistance values of the input resistors 35 and 50.
In this example, the resistance value of the input resistor 35 is made larger than the resistance value of the input resistor 50. In that case, the resistance values of resistors 34 and 35 are made equal, and the resistance values of resistors 41 and 35 are made equal.
Make the resistance values of 49 equal. For example, when the resistance value of the resistor 35 is made twice the resistance value of the resistor 50, the gain of the level detector 26 becomes 1/2 of the gain of the level detector 27, and therefore, the gain of the level detector 26 becomes 1/2 of the gain of the level detector 27. If the attenuation is, for example, 6dB, that is 2
If it is 1/2, the outputs of the level detectors 26 and 27 will be at the same level when the level on the output side of the narrowband rejection filter 13 is half of the level on the input side of the narrowband rejection filter 13. , the switch 18 is turned on only when the level on the input side of the narrowband rejection filter 13 is greater than twice the level on the output side of the narrowband rejection filter 13, and the switch 18 is turned off when it is less than twice the level on the output side of the narrowband rejection filter 13. .

For example, as shown in FIG. 4A, if the interference wave is an intermittent signal, and the signal exists during the Son period and there is no signal during the So period, when such a signal is input, the level detector 26 The output is dotted line 2 in Figure 4B.
During the period when the signal is present as shown in 6a, Son is at a high level, and during the period when the signal is off, So is at a low level. However, the output of the level detector 27 has a small level even during the existence period Son of the signal because the signal is blocked by the narrow band rejection filter 13, and is always at a small level as shown by the curve 27a in FIG. 4B. ing. Therefore, for example, the signal level detection output 26a is the second level detection output 27a.
The switch 18 is controlled so that when it is more than double, the switch 18 is turned on, and when it is less than that, it is turned off. The output of the comparator 28 becomes as shown in FIG.
At this time, the switch 18 is turned on.

For example, as shown in FIG. 4D, if a large noise _N1 is mixed in during the ON period Son of the signal, during the period when this noise _N1 exists, there is a difference in level between the input side and the output side of the narrowband rejection filter 13. becomes smaller, and during that noise period, the output of the comparator 28 becomes a low level as shown as C' in FIG.
Switch 18 is turned off. Therefore, the control circuit 17
The output of the control circuit 17 is supplied to the holding circuit 19 only in a state in which the difference between the interference wave frequency and the blocking center frequency is correctly detected.

The voltage that sets the lowest output level of the operational amplifiers 31 and 42 is applied from the terminal 52 to the resistors 53 and 5, respectively.
However, a resistor 55 is inserted in series with a resistor 53 for the operational amplifier 31 of the level detector 26. When the inputs to the level detectors 26 and 27 are zero or extremely small, the lowest output levels of the operational amplifiers 31 and 42 are set so that the detection level of the level comparator 26 is always smaller than the detection level of the level detector 27. Make it. In this way, the switch 18 is turned off in a state where the output of the comparator 28 is at a low level and the control circuit 17 cannot operate properly.

As the narrow band stopper 13, the curve 6 in FIG.
In addition to the phase characteristics shown in Fig. 6, for example, as shown in Fig. 5, -180° at the center frequency o,
A phase frequency characteristic having a phase frequency characteristic of -360° at a slightly higher frequency and 0° at a slightly lower frequency may also be used. Furthermore, the present invention can also be applied to the case where a plurality of narrow band rejection filters are connected in series and their rejection center frequencies match the frequencies of different interference waves, and in that case, the control circuit 1
7, the level detectors 26, 27, and the comparator 28 can be used in common, and the holding circuit 19 is provided for each narrow band stopper to switch and supply the deviation detection signal to them. Bye.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an interference wave removal device according to the present invention, FIG. 2 is a phase characteristic curve diagram of a narrowband rejection filter, and FIG.
FIG. 4 is a waveform diagram for explaining the operation of the present invention, and FIG. 5 is a diagram showing another phase frequency characteristic of the narrow band stop waver. 11: Input terminal, 12, 14: Amplifier, 13:
Narrowband blocker, 15: Output terminal, 17: Control circuit, 18: Switch, 19: Holding circuit, 26,
27: Level detector, 28: Level comparator.

Claims (1)

[Claims] 1. A narrowband stopper that is inserted in series in the receiving signal path and whose stopping frequency is changed by a control signal, and a center of the narrowband stopper that is determined from the input and output signals of the narrowband stopper. a control circuit that detects a difference between the frequency and the frequency of the target interference signal, and first and second circuits that amplify and rectify the input side signal and the output side signal of the narrow band stopper, respectively, and detect their levels. A level detector, a comparator to which the detection levels from the first and second level detectors are supplied, and a signal corresponding to the frequency deviation from the control circuit is inputted to control the narrowband wave generator. a holding circuit that supplies it as a signal;
a switch inserted between the holding circuit and the control circuit and controlled by the output of the comparator;
An interference wave removal device comprising means for making the output of the first level detector smaller than the output of the second level detector when the inputs of the first and second level detectors are zero.