JPH0330111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a simple direction finding device with a simple structure.

``Prior art'' Methods for measuring the direction of arrival of radio waves can be roughly divided into three methods: a method that determines the direction of arrival of radio waves by determining the arrival time difference of the radio waves, a method that uses the Doppler effect, and a method that uses the directional characteristics of a directional antenna. There is.

In the early days, this system received the same radio waves using two omnidirectional antennas and two receivers that amplified and extracted the high frequency signals induced by these two omnidirectional antennas. This method has been used to determine the direction of arrival of radio waves from the orientation of the antennas by measuring the phase difference of the signals and aligning the lines connecting the antennas in the direction where the phase difference is maximum.

In this method, accurate direction measurement is difficult if the phase characteristics of the two receivers do not match completely, and if the phase characteristics of the receivers do not match each other over a wide frequency band, the received signal An error will occur depending on the frequency.

It is extremely difficult to match the phase characteristics of two receivers over a wide band. For example, in the method for this reason,
As disclosed in Publication No. 23-734, two omnidirectional antennas are connected alternately to one receiver, and the phase of the received signal output from the receiver is displayed on a cathode ray tube in the direction in which the radio waves arrive. There is an idea to try to measure it. In this method, for example, 31 omnidirectional antennas are arranged in a ring, and the group of omnidirectional antennas arranged in the ring is connected to one frequency modulation receiver using a rotary switch that rotates at about 40 revolutions per minute. Doppler effect occurs in the received signal when the antenna is switched in the direction of suppressing radio waves and in the direction of escaping from the direction of arrival of radio waves, and the frequency fluctuation caused by the Doppler effect is extracted by frequency discrimination. This method uses the signals to issue propeller-shaped direction instructions to the cathode ray tube to determine the direction in which the radio waves are arriving.

This Doppler system is not suitable for mobile use because it requires a large number of antennas to be arranged in a ring shape with a large diameter. For this reason, the method is generally put into practice. As a simple device using this method, a device called a meter-indicating route indicator method has been put into practical use.

This route finding method combines the receiving characteristics of a directional antenna such as a loop antenna and an omnidirectional antenna such as a whip antenna to obtain cardioid characteristics, as seen in, for example, Japanese Utility Model Application Publication No. 57-164479. The minimum sensitivity position is the position where the same reception level can be obtained in any of the antenna switching states, and the direction of arrival of the radio waves can be determined by the orientation of the loop antenna at that time.

In systems other than the navigation method, the directional antenna must be rotated, so a rotating coupler such as a slip ring or a gonion meter is required, resulting in a large device. In particular, automatic direction finding devices that have a sense determination means and automatically measure the arrival direction of radio waves in all directions are large-scale devices, and are mainly used at fixed stations or mounted on ships and automobiles, but are not suitable for portable devices. It has become completely unsuitable.

``Problems to be Solved by the Invention'' As mentioned above, the apparatus of the above method is large, and it is difficult to make it portable. In the other method, the direction measuring method disclosed in Japanese Patent Publication No. 23-734 uses a cathode ray tube as a display, which makes it difficult to make it portable.

The present invention aims to improve the above method and provide a simple direction finding device which can be used satisfactorily even as a portable device.

``Means for Solving the Problems'' The simple direction finding device according to the present invention includes: A) two omnidirectional antennas arranged at a predetermined interval; B (C) a phase detector that generates a signal that is amplified by the receiver and is proportional to the phase difference of the received carrier signal; and (D) a signal that is phase-detected by this phase detector. Two synchronous detectors perform synchronous detection using a reference signal that is synchronized with the switching of the antenna switch; and a double-oscillation type indicator that indicates the relationship between.

"Operation" When the direction connecting the two omnidirectional antennas is perpendicular to the radio wave arrival direction, the phases of the carrier signals of the radio waves induced in the omnidirectional antennas are in the same phase.

On the other hand, if the direction connecting the two omnidirectional antennas matches the direction in which the radio waves arrive, the carrier signals of the radio waves induced in the two omnidirectional antennas will have a phase difference corresponding to the distance between the two antennas. .

This invention utilizes this principle to perform direction finding.

For this purpose, the carrier signals induced in the two omnidirectional antennas are switched at regular intervals and fed to one receiver, and the received signal is phase-detected. For this phase detection, for example, a commonly used FM detector can be used. By applying the phase-detected signal to two synchronous detectors and performing synchronous detection using a reference signal synchronized with antenna switching, the signal is proportional to the phase difference between the signals induced from each synchronous detector to the two omnidirectional antennas. , it is possible to obtain a voltage with a polarity determined by the direction of the antenna. This voltage is used to drive an indicator to display the relationship between the antenna and the direction of arrival of radio waves.

"Embodiment" FIG. 1 shows an embodiment of the present invention. 1A in the diagram
and 1B each indicate an omnidirectional antenna. Although this example uses a doublet antenna, a vertical antenna may also be used. The arrangement interval L between these two omnidirectional antennas 1A and 1B is selected to be a value shorter than at least 1/2 wavelength of the target radio wave. The above actual arrangement interval L is determined based on the practicality of the target radio wave frequency, for example, 150M.
If it is around Hz, L = about 40 to 50 centimeters is selected.

Omnidirectional antennas 1A and 1B are matching boxes 2A and 2
It is connected to the antenna switching circuit 3 via B. This antenna switcher 3 uses a rectangular wave signal PA selected to have a frequency of, for example, about 60Hz output from an oscillator 4.
Two omnidirectional antennas 1 by (Fig. 2D)
A and 1B are connected alternately to the receiver 5.

As the receiver 5, a receiver including a phase detector 6 at the final stage can be used. For example, a frequency discriminator can be used as the phase detector 6. Therefore, the receiver 5 can be an FM receiver. The demodulated output of the frequency discriminator is amplified by a low frequency amplifier 7, and is applied to an acoustic transducer 8 such as a speaker or earphone, so that the received signal can be heard as sound.

On the other hand, the phase detection output signal of the phase detector 6 is given to a low pass filter 11. This low-pass filter 11 extracts a signal with a frequency determined by the antenna switching period. In other words, when switching the antenna, the carrier signal phases 1A and 1B (Fig. 2A) change,
Direction signals SN ₁ and SN ₂ (second
B) is taken out by a low-pass filter 11, unnecessary frequency components are further removed by a band-pass filter 12, and azimuth signals _S1 and _S2 (FIG. 2C) are obtained by a phase adjustment circuit 13. These direction signals S ₁ and S ₂ are generated by two synchronous detection circuits 14A and 14B.
give to

The synchronous detection circuits 14A and 14B are supplied with reference signals P _A and P _B (FIG. 2, D and E) having mutually opposite phases from the oscillator 4, and synchronously detect the direction signals S ₁ and S ₂ separately. The phase adjustment circuit 13 adjusts the phases of the reference signals P _A and P _B for synchronous detection so that the phases of the azimuth signals S ₁ and S ₂ match.

By synchronous detection, positive and negative polarity detection signals P _F and P _G are obtained as shown in FIG. 2 F and G. The detected signals P _F and _PG are smoothed by smoothing circuits 16A and 16B, and the smoothed output voltages are amplified by DC amplifiers 17A and 17B as required, and are provided to an indicator 18. In this example, the indicator 18 is a double-oscillation type meter whose pointer indicates the zero point at the center when no current is applied. The output voltages of the DC amplifiers 17A and 17B change with respect to the rotation angle θ of the antennas 1A and 1B while maintaining completely opposite relationships as shown in curves A and B shown in FIG. It is applied to one and the other terminals of the swing type indicator 18. In the double-oscillating indicator 18, when the two terminals are at equal potential, the pointer points to zero at the center. Therefore, in this example, when the line 21 connecting the antennas 1A and 1B is at 90° and 270° with respect to the direction of arrival of the radio waves, the indicator 18 indicates zero,
Indicator 1 when one terminal is positive and the other is negative potential
8, the pointer swings in the positive direction, for example, and when a negative voltage is applied to one terminal and a positive voltage is applied to the other terminal, the pointer swings in the negative direction. Therefore, two DC amplifiers 17A and 17B
indicates the polarity and amount of potential difference of the output. Indicator 1
A variable resistor 19 connected in series with 8 is a variable resistor provided to calibrate the indication of the indicator 18.
That is, the indicator 18 is adjusted so as to indicate the central zero point when the amplitudes of the azimuth signals SN ₁ and SN ₂ are zero.

"Operation of Example" As shown in Figure 3, omnidirectional antennas 1A, 1
When the angle θ formed by the line 21 connecting B and the arrival direction 22 of the radio wave is θ=90° or 270°, the phases of the received signals induced in these omnidirectional antennas 1A and 1B will be in the same phase. Therefore, even if the antennas 1A and 1B are switched by the antenna switcher 3, the phases of the carrier signals given to the phase detector 6 are the same, so when the antennas 1A and 1B are switched from the phase detector 6, the azimuth signal SN is sent to the phase detector 6. ₁ , SN ₂ does not occur. As a result, the indicator 18 indicates the central zero point. Indicator 1
The degrees θ in which 8 indicates the zero point are angles of 90° and 270°, as shown in FIG.

From this state, a line 21 connecting antennas 1A and 1B
and the direction of arrival 22 of the radio wave is 90° or
A slight deviation from 270° causes a difference in phase between the signals induced in antennas 1A and 1B. As shown in Figure 5, this phase difference is maximum when θ = 0° (360°) or 180°, and the peak values of the direction signals P _F and _PG maintain a relationship of opposite polarity and reach a maximum. Become. At this time, when the antenna 1A is in the front and the antenna 1B is in the rear with respect to the direction of arrival of the radio wave, the polarity of the azimuth signal shown in FIG. 2B is
Assuming that SN ₁ and SN ₂ are obtained, when the positions of antennas 1A and 1B are reversed, the polarities of azimuth signals SN ₁ and SN ₂ are reversed, SN ₁ is inverted to negative, and SN ₂ becomes a positive azimuth signal. Change. Therefore, antennas 1A and 1B
By predetermining the polarity of phase detection, the switching timing of antennas 1A and 1B, the timing of synchronous detection, and the polarity of the terminal of indicator 18 in a predetermined relationship, the arrival of radio waves is determined by the direction indicated by indicator 18. Can determine direction. As shown in FIG. 5, the angle .theta. at which the indicator 18 indicates the maximum point of +V is an angle of 0.degree., and the angle .theta. degrees at which the indicator 18 indicates the maximum point of -V is an angle of 180.degree.

In other words, the direction signal SN ₁ generated at the timing of switching from antenna 1A to antenna 1B is converted into direction signal S ₁ through a low-pass filter, and this direction signal
_S1 is synchronously detected by the synchronous detection circuit 14A, and the DC voltage obtained by smoothing the synchronous detection output signal P _F is sent to the indicator 1.
8 to the positive terminal (+) and antenna 1B.
Direction signal SN ₂ generated when switching from to 1A
Pass through the low-pass filter 11 in the same way and obtain the direction signal.
_S2 , synchronous detection is performed by the synchronous detection circuit 14B, and the synchronous detection output signal P _G is sent to the negative terminal (-) of the indicator 18.
When the antenna 1A approaches the radio wave arrival direction, the signal induced in the antenna 1A leads the signal induced in the antenna 1B in phase. At this time, from antenna 1A to 1B
If the positive direction signal SN ₁ is generated from the phase detector ₆ at the timing when switching to It will be done. Also, at this time, a signal of negative polarity is output from the synchronous detection circuit 14B, and this signal is applied to the negative terminal (-) of the indicator 18, so that the pointer of the indicator 18 swings in the positive direction. Therefore, in this case, when the indicator 18 swings in the positive direction, it can be seen that the antenna 1A is approaching the radio wave source, and the direction of arrival of the radio waves can be determined. By determining in advance the relationship between the switching timing of the antennas 1A and 1B and the synchronous detection timing of the synchronous detection circuits 14A and 14B and the polarity of the terminal of the indicator 18, the indicator 18
The direction of arrival of the radio wave can be determined by the direction of the deflection.

"Effects of the Invention" As described above, according to the present invention, a pair of omnidirectional antennas 1A and 1B, an FM receiver 5, a low-pass filter 11, a band-pass filter 12, a phase adjustment circuit 13, and a synchronous detector are provided. 14A,1
4B, smoothing circuit 16A, 16B, amplifier 17A,
17B, an indicator 18, etc., the entire device can be made small and lightweight. Therefore, for example, as shown in FIG. 6, the antennas 1A and 1B can be stored in a box-shaped bag 23 called an attache case or the like. It is necessary to consider the arrangement of the circuits of the receiver 5 and other parts so that they are located approximately in the center of the antennas 1A and 1B to reduce mutual influence. By attaching the indicator 18 near the handle 24 of the bag 23, direction finding can be performed while carrying the bag 23. In addition, the bag 23 is provided with a terminal for outputting an acoustic transducer 8 such as an earphone, if necessary, and in this case, the indicator 18 is attached with, for example, the positive direction pointing toward one end of the bag 23. If the pointer is configured so that when it swings in a positive direction, that direction is determined to be the arrival direction of the radio waves, it is convenient because the user can intuitively know the direction of arrival of the radio waves from the direction indicated by the indicator 18. Furthermore, if necessary, the bag 23 is provided with an output terminal for outputting an acoustic transducer 8 such as an earphone, so that it is possible to listen to audio content at the same time as direction finding.

Further, according to the present invention, even when the indicator 18 points to the center, it is possible to know the arrival direction (two directions) of the radio waves. In this state, the sensitivity of the pointer to the rotation angle of the bag 23 is high. Therefore, in this state, the arrival direction of the radio waves can be determined with high accuracy.

Ordinarily used direction finding devices are inconvenient in that they are silent when determining the direction of arrival of radio waves, making it impossible to hear the content of the radio waves in this state. On the other hand, in the direction finding device according to the present invention, the reception state of radio waves is maintained no matter where the angle θ between the line 21 connecting the antennas 1A and 1B and the arrival direction 22 of the radio waves is. Therefore, the content of the radio waves can always be heard via the acoustic transducer 8, which is also convenient.

Furthermore, according to this invention, when the direction of the line connecting antennas 1A and 1B is perpendicular to the direction of arrival of radio waves, the direction signals SN ₁ and SN ₂ generated when switching antennas become zero, so listen to the change in sound. You can know the direction of arrival of radio waves (two directions) just by being there. Also, in this state, the direction signals SN ₁ and SN ₂ are at their minimum, making the content most audible.

In the above description, a case was explained in which a double-shake meter with center zero was used as the indicator 18, but the light-emitting elements are arranged in a row, and the one located in the center of the light-emitting elements arranged in one row is called a double-shake meter. It is also possible to use a light emitting element type indicator in which the dotted light emitting element is moved from the center to the positive side and the negative side in response to the zero point indication.

"Other Embodiments of the Invention" In the above embodiments, an example was described in which the simple direction finding device of the present invention was stored in the bag 23, but as shown in FIG. It is possible to create a structure in which the antenna switch 3 is attached, the antennas 1A, 1B and the impedance matching devices 2A, 2B are provided on both sides of the antenna switch 3, and the indicator 18 is placed on the lower end side of the rod 26.

Alternatively, as shown in FIG. 8, two whip antennas 1A and 1B may be attached to the roof of an automobile, and direction detection may be performed using these antennas 1A and 1B. By adopting the structure shown in FIG. 8, it is possible to know the direction of arrival of radio waves according to the direction in which the automobile is traveling.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 1, and FIGS. 3 and 4 illustrate the operation of the invention. 5 is a graph for explaining the operation of the present invention, FIG. 6 is a perspective view showing an example of the external appearance of the direction finding device according to the present invention, and FIGS. 7 and 8 are FIG. 7 is a front view for explaining another embodiment of the invention. be. 1A, 1B: Omnidirectional antenna, 2A, 2B:
Matching box, 3: Antenna switch, 4: Oscillator, 5:
receiver, 6: phase detector, 7: low frequency amplifier,
8: Acoustic transducer, 11: Low pass filter, 1
2: band pass filter, 13: phase adjustment circuit,
14A, 14B: Synchronous detection circuit, 15: Phase inversion circuit, 16A, 16B: Smoothing circuit, 17A, 17
B: amplifier, 18: indicator, 19: variable resistor,
21: Direction of connecting antennas, 22: Direction of arrival of radio waves.

Claims (1)

[Claims] 1. A. Two omnidirectional antennas provided with a predetermined interval; B. Antenna switching that alternately connects these two omnidirectional antennas to one receiver at a predetermined period. C: a phase detector that generates a signal proportional to the phase difference of the received carrier signal amplified by the one receiver; D: detect the two omnidirectional antennas from the detection output of this phase detector; a low-pass filter that extracts an azimuth signal with a switching period; Then, when the line connecting the two omnidirectional antennas is orthogonal to the direction of arrival of the radio waves, a detection signal of the same potential is output, and the line connecting the two omnidirectional antennas coincides with the direction of arrival of the radio waves. At this time, one of the omnidirectional antennas outputs a positive polarity signal in response to the phase difference determined by the distance between the omnidirectional antenna located in front and the omnidirectional antenna located behind with respect to the direction of arrival of the radio wave. , two synchronous detectors, the other of which outputs negative polarity azimuth signals, F two smoothing circuits that smooth the azimuth signals output from these two synchronous detectors, and G smoothed by these two smoothing circuits. The output of one of the above two synchronous detectors is given to one input terminal, the output of the other of the above two synchronous detectors is given to the other input terminal, and the wire connecting the two omnidirectional antennas is connected to the radio wave. When the pointer points to zero in the center and the line connecting the two omnidirectional antennas coincides with the direction of arrival of the radio wave, the pointer swings positively or negatively to indicate the arrival of the radio wave. A simple direction finding device characterized by comprising: a double-oscillation indicator that indicates whether the direction is coming from the front or the rear of a line connecting two omnidirectional antennas.