JPS6237564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is used, for example, in a Loran C receiver to remove interference waves such as Detsuka radio waves existing within or near the receiving band, and the removal frequency, that is, the blocking frequency, is changed. The present invention relates to a variable narrow band stop waver which can be used to

In receivers with relatively wide receiving frequency bands, so-called notch filters, as shown in Figure 1, were used to remove single-frequency interference waves existing within or near the receiving band. . This wave generator is a capacitor of the same capacity 1
1 and 12 are connected in series, a resistance element 13 is connected in parallel with this series connection, both ends of this parallel connection are terminals 14 and 15, and capacitors 11 and 12 are connected in series.
The connection point is grounded through a series circuit of an inductance element 16 and a variable resistance element 17, that is, connected to a common potential point. When the signal input from terminal 14 that resonates with capacitors 11, 12 and inductance element 16 and the same component that has passed through resistance element 13 cancel each other out at terminal 15, the frequency component will be blocked. The level of the resonance component is adjusted by the variable resistance element 17 so that these cancellations occur.

In the variable narrow band stopper, capacitor 1
The blocking frequency is changed by adjusting either the capacitors 1 and 12 or the inductance of the inductance element 16. In this case, even if the variable resistance element 17 is adjusted at one point such as the center of the variable range of the stopping frequency, and the stopping frequency is changed, the variable resistance element 17
No adjustments were made.

In this conventional variable narrow band stopper,
Particularly when the variable range of the blocking frequency is widened, sufficient blocking (attenuation) cannot always be obtained at the ends of the variable range. That is, for example, the resistance value of the variable resistance element 17 is adjusted so that the amount of attenuation is maximum at the center frequency f ₀ of the variable stop band, and the resistance value of the variable resistance element 17 is left unchanged.
When only the stopping frequency is changed by ±Δf with respect to the center frequency f ₀ , the amount of attenuation at the stopping frequency becomes smaller as the stopping frequency moves away from the center frequency f ₀ as shown in FIG. Therefore, if the range of variation of the stopping frequency is widened, the desired amount of attenuation cannot be obtained at both ends of the variable range.

As a result of investigating the cause of this, it was found that the effective resistance of the inductance element 16, such as a coil, changes depending on the frequency as shown in FIG _.
As the distance from capacitor 1 increases in Fig. 1,
It was found that this is because the level difference between the frequency component that passed through the resistor element 13 due to resonance and the same frequency component that passed through the resistor element 13 becomes large. Therefore, by re-adjusting the resistance value of the variable resistance element 17 each time the stopping frequency is changed, a variable narrowband transducer with sufficiently large attenuation over a wide frequency band can be obtained, but it is cumbersome to make such adjustments each time. It is.

An object of the present invention is to provide a variable narrow band stopper that can obtain sufficient attenuation in the variable stop frequency band without having to perform complicated operations such as adjusting variable resistance elements each time the stop frequency is changed. There is a particular thing.

According to the present invention, a compensating capacitor is inserted in series with the inductance element of a conventional narrow band stopper, and the impedance of the compensating capacitor is set to a sufficiently small value so as not to affect the stopping frequency. Moreover, the frequency characteristic is almost opposite to the frequency characteristic of the effective resistance of the inductance element. In other words, the sum of the impedance of the compensation capacitor and the effective resistance of the inductance element is made to be approximately constant within the range of change in the blocking frequency.

For example, as shown in FIG. 4 with the same reference numerals assigned to parts corresponding to those in FIG. 1, a compensating capacitor 18 is connected in series with the variable resistance element 17. The impedance of this compensation capacitor 18 is the capacitor 1
The impedances of the capacitors 11 and 12 are sufficiently small compared to the impedances of the capacitors 11 and 12, and the resonant frequency characteristics of the resonant circuit made up of the capacitors 11 and 12 and the inductance element 16 are not substantially affected. Furthermore, as shown in FIG. 5, the frequency characteristic curve 19 of the impedance of the compensation capacitor 18 changes almost inversely to the frequency characteristic curve 21 of the effective resistance of the inductance element 16, and the sum of these impedances and resistances changes along the frequency axis. They are made to be almost parallel. Since the frequency characteristic of the compensation capacitor 18 is generally not a straight line but a curve, this curve 19 intersects the frequency characteristic curve 21 of the effective resistance at two points as shown in FIG. It is preferable to set the frequency to be near both ends of the range f ₀ −Δf and f ₀ +Δf, and adjust the variable resistance element 17 at one of the crossing points so that the amount of attenuation becomes maximum at that frequency.

According to this configuration, within the variable range of the blocking frequency, the level of the frequency component that has passed through the resonant circuit of the capacitors 11 and 12 and the inductance element 16 and that of the same frequency component that has passed through the resistance element 13 are approximately the same. A large amount of attenuation can be obtained with respect to the stop frequency in this variable frequency band. For example, if the compensation capacitor 18 is used under the same conditions as shown in Figs. 1 and 2, the attenuation characteristics at the stop frequency will become as shown in Fig. 6, resulting in an attenuation of approximately 40 dB or more in the variable band. The amount was improved by about 10 dB compared to the case shown in Figure 2.

As described above, according to the present invention, a large amount of attenuation can be obtained without adjusting the variable resistance element each time in the variable band, so that unnecessary frequency components can be sufficiently removed in this band. Furthermore, the range of changeable stopping frequencies can be widened.

Because of these features, the variable narrow band stopper of the present invention can be applied, for example, to automatically remove deep radio waves in a Loran C receiver. An example will be explained with reference to FIG.

In FIG. 7, the received signal is amplified from the input terminal 31 through the preamplifier 32, the interference wave is removed by the narrow band rejection filter 33 of the present invention, and the output from which the interfering wave has been removed is amplified by the postamplifier 34. Via an output terminal 35 it is supplied to a processing device 36, such as a Loran C signal processing device. The signals on the input side and output side of the narrow band stop filter 33 are branched and supplied to the control circuit 37 . Control circuit 3
At step 7, a deviation between the blocking center frequency of the narrow band blocking filter 33 and the frequency of the target interference wave is detected. This detected deviation is supplied to a holding circuit 39 through a switch 38 and held there. The holding signal is given to the narrowband rejection filter 33 as its rejection center frequency control signal.

The narrow band blocking filter 33 has the same configuration as shown in FIG. 4, and variable capacitance diodes are used as the capacitors 11 and 12. and the blocking center frequency is controlled. This control voltage is applied to the connection point between the variable resistance element 17 and the compensation capacitor 18, and is applied to the diodes 11 and 12.

In the control circuit 37, for example, the input side signal and the output side signal of the narrowband rejection filter 33 are taken out through the bandpass waveformers 41 and 42, respectively, and the outputs of these bandpass waveformers 41 and 42 are outputted in phase. The comparator 43 compares the phases, and the phase comparison output is used as the output of the control circuit 37. The pass center frequencies of the band pass wave generators 41 and 42 are made to substantially match the rejection center frequency of the narrow band stop wave generator 33, and the wave characteristics of these band pass wave generators 41 and 42 are approximately equal to each other. . This narrow band stopper 33
For example, some of the components of the bandpass waveforms 41 and 42 may be controlled so that the rejection center frequency of the bandpass waveforms 41 and 42 is controlled by the output of the holding circuit 39 and the center frequencies of the bandpass waveforms 41 and 42 are also controlled. A variable capacitance diode is used, and the variable capacitance diode is controlled by the output of the holding circuit 39, and the change characteristics of the center frequency with respect to the control signal are similar to the characteristics of the narrow band stop filter 33.

The phase frequency characteristic of the narrow band stopper 33 is as follows:
As shown by curve 66 in the figure, the phase rapidly advances by approximately 90 degrees at frequencies higher than the center frequency _f0 , and the phase rapidly lags 90 degrees at frequencies lower than the center frequency _f0 . . In other words
The phase changes rapidly within the range of f ₀ −Δf to f ₀ +Δf. On the other hand, bandpass waveforms 41 and 42
For example, it is constructed as a single-peak tuning type consisting of a tuning circuit of a coil and a capacitor, and its phase frequency characteristics gradually advance in phase on the side lower than the center frequency f ₀ and as shown by curve 67 in Figure 8, and on the higher side The phase gradually lags. Therefore the frequency
Between f ₀ -△f and f ₀ +△f, the phase of the outputs of wave generators 41 and 42 is almost determined by the characteristics of curve 66. Therefore, these wave devices 41, 42
By detecting the phase of the output with the phase comparator 43, it is possible to detect the deviation between the center frequency f ₀ of the narrowband rejection filter 33 and the frequency of the interference wave.
In other words, if the frequency of the interference wave is higher than the blocking center frequency f ₀ , the output of the wave generator 42 will be in forward phase, and if the frequency of the interference wave is lower than the blocking center frequency f 0 , the output of the wave generator 42 will be in forward phase.
The output of is in the forward phase.

The signals on the input side and output side of the narrowband rejection filter 33 are branched, and their respective levels are detected by a level detector. That is, the outputs of the bandpass waveformers 41 and 42 are respectively supplied to level detectors 44 and 45 to detect their respective levels, and the outputs of the level detectors 44 and 45 are compared in magnitude by a comparator 46. A switch 38 is controlled by the comparison output of 46.

By the way, the center frequency f ₀ of the narrow band stop filter 33
When the frequency of the interference wave matches the frequency of the interference wave, the output of the narrow band stop filter 33 becomes sufficiently small compared to the input. Therefore, the output of level detector 44 is large, and the output of level detector 45 is significantly small. In this state, the output of the comparator 46 becomes high level, the switch 38 is turned on, and the output of the control circuit 37 is supplied to the holding circuit 39. However, when the interference wave is blocked, the narrowband blocker 33 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 that the level detectors 26, 27 The output levels of the detector 44 on the input side are made to be smaller than the detection level of the detector 45 on the output side in this state. As a result, the switch 38 is turned off, and the output of the control circuit 37 is transferred to the holding circuit 39.
is not supplied. Therefore, the detection signal of the control circuit 37 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 39 and is sent to the holding circuit 39.
9 maintains the previous control state, and when a disturbance wave is inputted again, it is possible to reliably block the disturbance wave by the narrow band rejection filter 33.

In this way, in the Loran C receiver, single-frequency interference waves in or near the band can be removed by the narrow band rejection device of the present invention, and the rejection frequency can be automatically changed to the interference wave as shown in FIG. In this case, it is not necessary to adjust the variable resistance element 17 one by one, and the desired amount of rejection attenuation can be obtained even if the rejection frequency is changed over a wide variable band. In the example shown in Fig. 7, the compensation capacitor 18 also functions as a DC cutoff capacitor for the control signal, and in the Loran C receiver, the resistor 13 in Fig. 4 is 150Ω, and the capacitor 1
1 and 12 are each 100 to 400 pF, the inductance element 16 is 6 mH, and the variable resistor 17 is approximately 10 Ω, the capacitance of the compensation capacitor 18 is
A polyester capacitor of about 0.01 to 0.022 μF is preferable.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional narrow band blocking filter, Figure 2 is a frequency characteristic diagram of the blocking attenuation of the wave generator in Figure 1, Figure 3 is an effective resistance frequency characteristic diagram of an inductance element, and Figure 4 The figure is a circuit diagram showing an example of a variable narrow band blocking device according to the present invention, FIG. 5 is an impedance frequency characteristic diagram of the compensation capacitor 18, and FIG. 6 is a frequency characteristic diagram of the blocking attenuator of the wave device shown in FIG. 4. 7 is a block diagram showing an example of an interference wave removal device using the wave generator of the present invention, and FIG. 8 is a frequency characteristic diagram of the wave generator 33. 11, 12: first and second capacitors, 16: inductance element, 17: variable resistance element, 18:
Compensation capacitor.

Claims (1)

[Claims] 1. The first and second capacitors are connected in series, a first resistance element is connected in parallel to the series connection, and both ends of the parallel connection are used as first and second terminals, and the first and second capacitors are connected in series. A series circuit of an inductance element and a variable resistance element is connected between the connection point and the common terminal, and the impedance of one of the first and second capacitors and the inductance element can be changed. In the variable narrow band stopper, a compensation capacitor is inserted in series with the variable resistance element, and the compensation capacitor has a sufficiently small impedance within the variable frequency band of the narrow band stopper, and has a frequency characteristic. is selected to have a change characteristic that is substantially opposite to the frequency characteristic of the effective resistance of the inductance element.