KR870000138B1 - Automatic direction finder - Google Patents

Abstract

The appts. comprises a pair of loop antennas disposed so that their directivities are orthogonal to each other. A goniometer includes a pair of search coils perpendicular to each other, each search coil producing an output. At least one low frequency oscillator produces a low frequency signal or signals, and at least one modulator receives the low frequency signal to modulate at least one of the outputs from the search coils. A nondirectional vertical antenna produces an output which is then phase shifted. A device combines the modulated signals with the phase shifted signal, the combined signal is then amplified and detected.

Description

Auto direction finder

1 is a block diagram showing the configuration of a first embodiment of an automatic direction finder according to the present invention;

2 is a block diagram showing the configuration of a second embodiment of an automatic direction finder according to the present invention;

The present invention relates to an automatic direction finder for use in ships, vehicles and aircraft.

In general, an automatic direction detector including an orthogonal loop antenna circuit in which a goniomer is inserted is known. In this automatic detector, the output of the goniometer is modulated with a low frequency signal, and the modulated signal The output of the vertical antenna is combined with the secon signal over 90 ° (phase shift). The synthesized signal is then amplified and detected by the receiver: the detected signal is supplied to the drive coil of the servomotor, and at the same time the modulated low frequency signal is applied to the excitation coil of the servomotor. The servo motor is mechanically coupled to the goniometer to indicate the position of the goniometer's pointer in the direction of the incoming electromagnetic waves.

Quadrature loop antennas are known to use a pair of modulators to generate two outputs that are each modulated with two low frequency signals of the same frequency having a phase difference of 90 ° to each other. The modulated signals are synthesized into a single signal with a signal with the output of the vertical antenna greater than 90 °, and the synthesized signal is amplified and detected by the receiver and then filters a filter that filters all frequency components except for the modulation frequency. Will pass. Then, the phase of the reference frequency signal for the modulation low frequency is compared with the phase of the output frequency of the filter, thereby generating a phase difference angle signal used to indicate the direction of the receiving electromagnetic wave.

The prior art direction finders as described above have several disadvantages. Specifically, when the direction detectors are installed in a ship or the like, there are many obstacles such as a mast or a stay around the antenna, which disturbs electromagnetic waves. In particular, as the frequency to be measured approaches the VHF band, the high-frequency grounds of the vertical antenna and associated components used for sense determination become less stable. Therefore, the amplitude and phase of the signal in the vertical antenna substantially changes the direction of the incoming electromagnetic waves due to the influence of the mast and the stay, resulting in inaccurate sense determination resulting in increased error.

Accordingly, a main object of the present invention is to provide an improved automatic direction finder which eliminates the above problems. According to the invention, as in the prior art device, the output of the vertical antenna and the outputs of the loop antenna are used together in the initial measurement step. However, in the final step of indicating the measured angle, the direction of the incoming electromagnetic wave is measured without using any vertical antenna with defects in phase and amplitude as mentioned above.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, an automatic direction detector according to an embodiment of the present invention includes a pair of loop antennas (1) and (2) arranged in directions perpendicular to each other; A pair of stator coils 3 and 4 of the goniometer disposed at right angles to each other; A pair of search coils 5 and 6 arranged at right angles to each other; A 90 ° phase shifter 9; And a switching device 10 for supplying an output to the synthesis circuit 11. Usually, the output of the phase shifter 9 is connected to the synthesis circuit 11, but after the initial measurement, the output of the phase shifter 9 is disconnected from the synthesis circuit 11 and the output of the search coil 6 Is connected to the synthesis circuit (11). The control signal for this operation is generated by the level comparator 15 described later. The output of the synthesis circuit 11 is connected to the receiver 12. The automatic direction detector of the present invention also includes a low frequency amplifier 14 whose detector 13 and output are connected to a drive coil of the servomotor 17, which is mechanically mounted to the goniometer. Directional instructions 18 are mechanically coupled to the servomotor 17. The low frequency oscillator 16 generates an AC signal of 135 Hz supplied to the excitation coil of the servo motor 17, for example. The output of this oscillator 16 is applied to a balance modulator 7 connected to the output side of the search coil 5 of the goniometer to modulate the output of the goniometer. The output of this balance modulator 7 is connected to the synthesis circuit 11.

In the known automatic direction detector, the search coil 6 is not used, and the abnormal phase 9 is always connected to the synthesis circuit 11 by the switching device 10. The operation principle of the well-known part except for the novel configuration according to the present invention is considered to not need to be described.

The level comparator 15 compares the level of the intermediate frequency of the receiver 12 with the level of the demodulation wave of the detector 13. If the level of the intermediate frequency is 0 or if the level of the frequency component of the demodulation wave having the same frequency as the output of the low frequency oscillator 16 exceeds the specified level even if there is an intermediate frequency, the comparator does not generate any control signal. The output of the phase shifter 9 is applied to the synthesis circuit 11. On the other hand, if the level of the intermediate frequency is greater than zero and the level of the demodulated low frequency component is smaller than the specific level, the level comparator 15 supplies a control signal to the switching device 10. As a result, the output of the phase shifter 9 is not transmitted, and the search coil 6 is connected to the synthesis circuit 11 instead of the phase shifter 9.

The switching operation and initial and final measurement steps performed by the device are as follows. When no electromagnetic wave is supplied, the level comparator 15 does not generate any control signal and waits for the electromagnetic wave to arrive, as in the conventional automatic direction detector. When the signal wave is received, the output of the vertical antenna is transmitted to the synthesis circuit 11 via the phase shifter 9. In addition, the output of the search coil 5 is applied to the synthesis circuit 11 via the balance modulator 7. The synthesized signal is amplified by the receiver 12 and detected by the detector 13, for example, into a signal having a frequency equal to a modulation frequency of 135 Hz. This signal is amplified in the amplifier 14 to rotate the servomotor 17 and then rotates the gonio motor in the aural nwl direction. As the goniometer approaches the direction of minimum sensitivity, the output level of 135 Hz from detector 13 decreases. This output level is detected by the level comparator 15. If the output level is less than a certain level indicating that each position lies within ± (20-30) ° at minimum sensitivity, the initial measurement is complete. The level comparator 15 then generates a control signal that replaces the output of the phaser 9 and the output of the search coil 6 to enable final measurement. By doing in this way, it is possible to avoid the influence of the vertical antenna causing the micro error in the direction measurement. When no subsequent wave is received, the level comparator 15 stops generating control signals. This returns the device to the initial measurement state where the vertical antenna is used. If the level comparator 15 is configured to have a suitable time constant, it is noteworthy that the apparatus is free from any obstacles in detecting intermittent waves such as telegraph waves.

With regard to the signal voltage derived from the search coil 6, the goniometer is in the minimum sensitivity direction as soon as the initial measurement is completed, so that the search coil 6 is in the maximum sensitivity direction. In addition, the coils 5 and 6 are wound at right angles to each other in a fixed arrangement with respect to the phase of the signal of the search coil 6. Therefore, in the initial measurement, the goniometer indicates the actual orientation without the uncertainty of 180 ° even though the search coil 5 generates an error. In addition, as a natural result, this signal is in phase with the signal above 90 ° of the vertical antenna output.

In this embodiment, even though the output of the search coil 6 is connected to the synthesis circuit 11 via the switching device 10, the output of the search coil 6 is permanent without passing through the switching device 10. It may also be directly connected to the synthesis circuit (11) This another configuration is not shown in the drawings but will be described in detail how it operates.

The output of the search coil 6 will be in phase or out of phase with the output of the phase shifter 9, depending on the orientation of the incoming electromagnetic wave. And the output voltage will also change. However, in the initial measurement, if the output of the abnormal phase 9 exceeds the maximum output of the search coil 6 to some extent, the output phase of the search coil is independent of each position of the search coil relative to the direction of the incoming electromagnetic wave. Is always in phase with the output of the ideal phase 9. Thus, whether the search coil 6 is isolated or connected to the synthesis circuit will result in the same operations in the initial measurement. After completing the initial measurement, the same final measurement is made according to the above embodiment. Therefore, we will no longer discuss these measurements.

As shown in FIG. 2, the automatic direction detector according to the second embodiment of the present invention includes a pair of loop antennas 31 and 32 arranged at right angles. Each output from each loop antenna is fed to balanced modulators 33 and 34, respectively, and modulated with signal " a " and signal " b " generated from low frequency oscillator 35. Signal "a" and signal "b" have, for example, a frequency of 135 Hz and have a phase difference of 90 degrees with respect to each other. Each output of the loop antenna is also applied to polarity controllers 36 and 37 that operate to control the polarity of radio frequency signals by receiving the output of control signal generator 38. The sense circuit for initial measurement, which consists of an ideal group that makes the output of the antenna of the omnidirectional antenna 39 by more than 90 °, generates an output that is applied to the switching circuit 41. The switching circuit 41, the outputs of the modulators 33, 34 and the polarity controllers 36, 37 are all applied to the synthesis circuit 42, the output of which is applied to the receiver 43 for amplification. And demodulated. The demodulation signal having a low frequency of 135 Hz is applied to the level detector 45 and the phase detector 46 through a narrowband filter passing only signals having the frequency. When the output of the filter exceeds a predetermined level, the level detector 45 opens the switching circuit 41 to operate the control signal generator 38 after a short time of about 0.5 seconds has elapsed. To generate a signal.

The phase detector 46 is also supplied with a suitable low frequency signal having a fixed phase, such as the phase reference signal of the oscillator 35. The output signal of the phase detector is not only applied to the display device 47 such as the cathode ray tube or the digital phase indicator 47 that displays or indicates the wave direction of arrival, but also to the signal generator 38.

In operation of the FIG. 2 apparatus, when the level detector does not generate any signal, the switching circuit 41 is closed, and the signal generator 38 is a loop antenna 31 of polarity controllers. Inhibiting signal " 0 " is supplied to the two polarity controllers 36 and 37 to prevent operation by the output of the 32. In this initial measurement phase, when the device is started up, the outputs of the loop antennas 31, 32 are modulated by signals " a " and " b " . At the same time, the output of the vertical antenna 39 is modulated by a signal " a " and a signal " b " respectively having a phase difference of 90 [deg.]. At the same time, the output of the vertical antenna 39 is applied to the synthesis circuit 42 via the 90 ° phase shifter 40 and the switching circuit 41. The synthesized signal is then applied to the receiver 43 where the low frequency components of the output of the oscillator 35 are demodulated, and then the noise components in the narrowband filter 44 are completely removed. Next, the output of the filter 44 is detected in phase by the phase detection circuit 46 so that the coming propagation direction can be displayed on the phase display device 47. It will be appreciated that the operations in these initial measurements have been performed in a conventional manner.

After the initial measurement operations have been completed, the level detector 45 after the slight delay, such that the switching circuit 41 is opened and the output of the vertical antenna 39 does not emit any signal for subsequent steps. Generate a Control Signal At the same time, the output of the detector 45 is applied to the control signal generator 38. Here, the signal generator applies one of two signals to the output side of the phase detector 46 to the polarity controllers 36 and 37. That is, it becomes the direction of the electromagnetic wave as shown in the table below. Specifically, if signal " 1 " is applied to both controllers 36 and 37, generator 38 causes signals to have the same polarity as the output of loop antennas 31 and 32. do. On the other hand, if signal "-1" is applied, generator 38 will transmit signals of opposite polarity.

[table]

If the control relationship is maintained, the radio frequency signals transmitted from the polarity controllers 36 and 37 are in phase with the signal passing through the phaser 40 after leaving the vertical antenna 39 irrespective of the direction of the incoming electromagnetic wave. Becomes Thus, even if the received electromagnetic waves from the antenna 39 are disturbed after completion of the initial measurement, inputs in phase with the output of the phase shifter 40 can be obtained from the loop antennas 31 and 32. Thus, in the final measurement, it is not necessary to use a vertical antenna 39 whose input phase of the antenna is adversely affected by disturbances caused by surrounding objects or other similar phenomena. As a result, an azimuth value having a small error can be obtained.

For example, suppose that the initial measurement contains an error of ± 10 °. Then, when the electromagnetic wave arrives in a direction near any one of 0 °, 90 °, 180 °, and 270 °, the polarity controllers 36, 37 each have a wrong signal " 1 " You may receive "-1". However, as will be apparent from the following description, it does not affect the respective phases of the synthesized signals applied from the polarity controllers 36 and 37 to the synthesis circuit 42.

Suppose that one electromagnetic wave is coming from the 80 ° direction, but the initial measurement is 100 ° due to disturbance light. If the direction of the incoming wave is 80 ° or 100 °, then the loop antenna 31 in the east-west (EW) direction will have polarity "1" as shown in the above table. If the effect peak value and development intensity of each loop antenna are denoted by "h" and "E", respectively, the output is given as follows.

Eh sin 80 ° = Eh × 0.98... … (One)

If the direction of the vehicle is 80 °, the output of the antenna 32 in the north-south (NS) direction is given as follows.

Eh cos 80 ° = Eh × 0.17... … (2)

If the measurement direction of arrival is 100 ° due to measurement error, the output is given by

Eh cos 100 ° =-(Eh x 0.17)... … (3)

Theoretically, equation (1) + equation (2) = Eh (0.98 + 0.17) = Eh x 1.15 is obtained: whereas in the case of error, equation (1) + equation (3) = Eh (0.98). -0.17) = Eh x 0.81 is obtained from the initial measurement. Thus, it became clear that the normal phase was obtained as long as the measurement error did not exceed 45 ° in the initial measurement.

As will be apparent to a person skilled in the art, various modifications may be made within the scope of the above description. Such modifications, which depend on the ability of a person skilled in the art, form part of the present invention and will be adopted in the following claims.

Claims (4)

Goniometer including a pair of loop antennas (1) and (2) arranged so that their directions are perpendicular to each other, and a pair of search coils (5) and (6) arranged at right angles to each other to generate one output. And receiving the low frequency signal of the low frequency oscillator 16 to modulate the output of at least one low frequency oscillator 16 and one of the outputs of the search coils 5 and 6 for generating a low frequency signal. At least one modulator (7), an omnidirectional vertical antenna (8) for generating one output, an phase shifter (9) for phase shifting the output of the vertical antenna (8), and a modulated signal and phase from the phase shifter In an automatic direction detector comprising means for synthesizing a mutated signal (11) and means (12) for amplifying and detecting the synthesized signal, a control circuit for isolating the vertical antenna after the initial measurement of the direction is completed. Including 10 and in the initial measuring instrument Using both the pair of the loop antenna (1), (2) and a vertical antenna (8) and, in the final measurement detector automatically direction characterized in that to only use the loop antenna. 2. The search coil according to claim 1, wherein the output of one search coil is modulated in the modulator 7 and then the search coil is connected to the synthesis circuit 11, and the other search coil is connected to the synthesis circuit 11 in the initial measurement. Automatic connection characterized in that the search coil described above is connected to the synthesis circuit 11 to perform the final measurement instead of the output of the phase shifter 9 for the vertical antenna 8 after completion of the initial measurement. detector. 2. The synthesizer circuit according to claim 1, wherein the modulator (7) is connected to only one of the search coils wound at right angles to each other in the goniometer and the output of the phase shifter (9) to the vertical antenna (8) in the initial measurement. Connected to the vertical direction detector in order to isolate the vertical antenna. The method according to claim 1, further arranged between the antenna of one of the pair of loop antennas (1), (2) / (31), and (32) and the synthesis circuit (11) / (42). And a pair of polarity controllers 36 and 37 for generating opposite polarities, wherein the at least one low frequency oscillator 16 generates an output having a phase difference of 90 ° to each other. Oscillator 35, wherein the at least one modulator 7 is disposed between the loop antenna and the synthesis circuit 11/42 to output the output from each loop antenna to the output from the low frequency oscillators. And a pair of modulators 33 and 34 respectively modulating, and in this case, the phases of the outliers 9 and 40 for the omnidirectional vertical antennas 8 and 39 only in the initial direction measurement. Outputs and modulated outputs from modulators 33 and 34 are used and then the outlier 9/40 is isolated Control the polarity controller 36, the detector automatically direction, characterized in that means for causing (37) to determine the output polarity of the loop antenna according to each quadrant of the initial measurement to the selective for the last measurement.

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