JPH0360391B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a simple direction finding device for measuring the arrival direction of radio waves mainly in the VHF/UHF band.

[Conventional technology]

As a direction finding device by antenna switching,
A portable Doppler type direction finder in the VHF/UHF band created by the applicant (patent application filed in 1983).
-263178, JP-A-61-139770)
No. 050930, Utility Application No. 162679 (1987), (Utility Application No. 162679)
No. 050931 and Utility Model Publication No. 173080 (Sho 62-173) are presented. These devices have a reception indicator placed between the two doublet antennas that instructs the meter to output the detected Doppler shift amount obtained by alternately switching the outputs of the two spaced doublet antennas. Furthermore, the applicant converts the detection output of the Doppler shift amount into an audio frequency signal,
He proposed a method for determining direction based on changes in the tone (Utility Application No. 61-050932 and Utility Model Application No. 163775-1983).

[Problem that the invention seeks to solve]

The above-mentioned direction finder proposed by the present applicant has two doublet antennas arranged parallel to each other with a distance between them on an axis connecting the antenna centers, and receives radio waves arriving in a direction perpendicular to the axis to detect both antennas. The induced signal has zero phase difference, but this method takes advantage of the fact that the maximum phase difference occurs with respect to received radio waves arriving in the axial direction. In other words, if you switch the antennas using a low frequency signal and alternate the two antenna reception signals and guide them to the phase detection section via the selection amplifier, there will be a phase difference between the two antenna reception signals at the time of antenna switching, so the switching will occur. A phase difference signal containing low frequency components is obtained. While measuring this phase difference signal, the antenna is rotated to determine the direction of the radio waves. The same principle applies to the idea of changing the timbre of an audio frequency signal.

In the direction finder described above, in order to quantitatively grasp the phase difference signal, the phase-detected signal is filtered with a bandpass filter centered on the antenna switching frequency, and then a synchronous rectifying circuit and A phase difference voltage is obtained via a smoothing circuit. Although it is possible to obtain an accurate phase difference voltage in this way, a synchronous rectifying circuit, a phase adjustment of a synchronizing signal for synchronizing the synchronous rectifying circuit, a bandpass filter, etc. are required.

An object of the present invention is to provide a new direction finding device that is further simplified and eliminates the need for synchronous rectification.

[Means for solving problems]

The present invention delays each received signal of two omnidirectional antennas arranged in parallel with an interval l and one of the received signals by a delay time equal to or less than the time required for a radio wave to propagate over a distance l. a receiving means for obtaining the delayed signal as a received output signal; a switching means for outputting a signal obtained by switching each of the received output signals in a specific order as a switched received signal; and a switching means for detecting the switched received signal. and an audible sound output means for obtaining an output obtained as an audible signal based on a phase difference of the received output signal at each point of the switching included in the signal obtained by the switching. Then, as a direction finding operation, first, with only the two received signals of the antenna being switched, the direction in which the radio waves arrive is detected by the change in the audible output obtained by rotating the antenna, and the center of the antenna is moved in that direction. Lay out the axis line to connect. Next, switching is performed in a predetermined switching order including the two received signals and the delayed signal, and the sense of the radio wave arrival direction is determined based on whether the tone of the auditory output changes compared to the state in which only the two received signals are switched. do.

[Effect]

The principle of the present invention will be explained with reference to FIGS. 2 and 4. Assume that two antennas A and B are arranged with an interval l as shown in FIG. 2a. As the direction of radio wave arrival, the axial direction connecting the antenna centers is α, and the direction in which the radio waves arrive with an angular difference of θ with respect to this direction is β. β(θ=±π/
In case 2), the phase difference between the radio waves received by antennas A and B is zero, and when α and α are in opposite directions, the phase difference reaches the maximum value φ ₀ . If the phase difference in the β direction is φ, φ=lcosθ/λ=φ ₀ cosθ (1) where λ is the wavelength. In Figure 2b, the α direction is θ=0 ⁰
, |φ| is illustrated with respect to the arrival direction θ of the radio wave.

When the antenna is at a position θ _i with respect to the radio wave arrival direction, a phase difference signal with an amplitude of |φ(θ)|θ=θ _i is detected. This detection signal is repeatedly generated at the antenna switching period. Since switching is performed at a frequency of decreasing audible frequency, the phase difference signal can be heard as a sound with many harmonics having the switching frequency as a fundamental wave. The amplitude value |φ(θ)| of the phase difference signal is recognized as the magnitude of the amplitude of the sound. rotate the antenna,
By finding the maximum or minimum sound point, the direction of arrival of the radio waves can be detected. When finding the minimum sound point, find the direction perpendicular to the direction connecting the antenna centers (θ = 90°,
270°) is the direction of arrival of the radio waves. Since △|φ(θ)|/△θ is large near the minimum sound point, the arrival direction of the radio wave can be determined with high accuracy.

When the minimum sound point is found in this way,
At this time, the axis connecting the centers of antennas A and B is 90°
(Either ± is acceptable) If the direction is rotated, that direction becomes the arrival direction of the radio waves or the opposite direction. Therefore, to determine the sense, antennas A and B
Switching is performed including each received signal of , and a signal C obtained by delaying the received signal of one antenna (here, antenna A) by a delay circuit. Considering the phase relationship between the above signals, there are two cases related to the arrival direction of the radio waves. To explain with reference to FIG. 4, the positions of antennas A and B are determined, and the arrival directions of radio waves are expressed as D(α) and D(β). now,
When the distance of the delay circuit delay time l is the time t, which is equal to the propagation time of the radio wave, and when the signal C is expressed from the phase as the antenna position, as shown in Figure 4, in the case of D(α), C(α) and has the same phase as antenna B. If D(β) then C(β)
become.

Therefore, if the switching order is ABACABACA..., the phase difference signals at the switching times C, A, B, A, C... in Fig. 5 will be as shown in Fig. 5 a, b, and D
It differs depending on the (α) direction and the D(β) direction. D
In the case of the (α) direction, signal C is phase-identical to the signal of antenna B. Therefore, in the previous operation, only antennas A and B were switched, and when the antenna was rotated 90 degrees, the maximum audio signal with the switching frequency as the fundamental wave was heard as a sound of a magnitude corresponding to the amplitude of the phase difference signal. Then, even if the antenna and the delayed signal ABC are changed in the switching order described above to determine the sense, no change is observed in the audio signal.
However, in the case of the D(β) direction, in addition to the component whose switching frequency is the fundamental wave, a frequency component of 1/2 of the fundamental wave is included, so these components are Due to the passband characteristic of the selective amplifier 14 shown in FIG. 1, the output 15a of the FM detector 15 has different tones, as shown in FIG. 5 a' and b'. Here, Fig. 5 a' shows the case where only antennas A and B are switched, and Fig. 5 b' shows the antenna and delayed signal.
This is the case when ABC is switched.

From the above, it is possible to determine the sense of the direction of arrival of radio waves by judging from the tone when changing the direction of the central axes of antennas A and B to match the direction of arrival of radio waves and then adding delay signal C. .

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Figure 1 is a circuit block diagram, in which omnidirectional antennas 10 are arranged in parallel with an interval of less than 1/2λ of the wavelength of the highest frequency of the direction-finding radio waves.
A delay circuit 11 connected to A, 10B and antenna 10A and providing a phase delay is switched and connected to a selection amplifier 14 in a switch 12. This switching is
This is done electronically by the output of an oscillator 13 with a period in the audio frequency range. The switching order is such that in the first step of determining the minimum sound point, ABAB, . . . are performed at regular intervals, so that the received signals of the antennas 10A and 10B are alternately guided to the selection amplifier 14. The selective amplifier 14 selectively amplifies the incoming radio waves to a constant amplitude,
The output 14a is used as a frequency detector (FM detector using a PLL detector, etc., hereinafter simply referred to as FM detector).
15 for FM detection. The output waveform of the selection amplifier 14 is as shown at 14a in FIG. 3, and the output waveform of the FM detector 15, that is, the phase difference signal is as shown at 15a' in FIG. Since the received radio waves change at the time of switching between the antennas 10A and 10B and their phases differ, this phase difference signal is generated. The phase difference signal uses the repetition frequency of the switch 12 as a fundamental wave and contains many harmonics, so when listened to directly through the speaker 17, it can be heard as a click-like sound. By removing a portion of the harmonics with the reduction pass filter 16, the click sound can be changed into a more audible sound.

Note that when the radio wave is an FM modulator, the FM detector 15 demodulates the frequency modulation component and detects the phase difference component generated by switching the antenna. Although it is superimposed on the signal, it can be distinguished and recognized as voice. In the case of AM modulated waves, only the phase difference signal generated by switching is input to the speaker 17. If you want to know the call status at this time, you can use the selective amplifier 14 to guide the signal before the amplitude limiting operation for FM detection to the AM detector 18, detect it, and input it to the speaker 17.

Next, in the operation subsequent to the sense determination, the switch 12 including the output signal C of the delay circuit 11 connected to the antenna A is switched in the switching order shown in FIG.
Switch with ABACABACA…. This latter operation is started after the antenna has been rotated in the previous operation to find the position of the minimum sound point, and the antenna has been rotated ±90 degrees with respect to that direction. When a radio wave arrives from the direction D (α) in FIG. 4, the phase difference signal generated by the switching is as shown in FIG. 5a, and in the case of D(β), it is as shown in FIG. 5b.
This phase difference signal is output as the fifth output 15a of the FM detector 15 due to the passband width characteristics of the selective amplifier 14.
The waveforms will be as shown in Figures a′ and b′. Therefore, if the output 15a of the FM detector 15 is listened to through the speaker 17, a sense judgment can be made based on whether the timbre is different or not. If not different, antenna 10A to 10
If the radio wave arrives at antenna B and the tone is different, the radio wave has arrived from antenna 10B to antenna 10A.

In this embodiment, the delay time of the delay circuit 11 is set to be equal to the time t during which the radio wave is delayed, as explained in the section of the operation, so that the switching time point C→A in FIGS. 5a and 5b, The absolute values of the phase differences from B to A are equal. However, even if the delay time is set to t' less than this, the absolute value of the phase difference at the time of switching will change, but the sign will not change, so
As long as the timbre does not change significantly, the distance l can be made smaller than the time it takes for radio waves to propagate. As mentioned above, the FM detector is capable of both demodulating the frequency modulation component and detecting the phase difference component generated by antenna switching, so that the demodulated signal can also be heard.

In the embodiments described above, the sense determination is made by rotating the antenna after detecting the minimum sound point, but it is also possible to perform the sense determination without rotating the antenna after detecting the maximum sound point. Also, from the beginning
By switching to ABACABAC... it is also possible to detect the direction including sense determination.
In addition to the order described in the embodiments, the switching including the antenna and the delay circuit may be performed in any order as long as the output waveforms shown in FIG. 5 a' and b' are obtained.

〔Effect of the invention〕

As shown in this example, since the receiver listens to the phase difference signal that occurs when the received radio waves are switched at regular intervals as an audio signal, it is not possible to quantitatively obtain the phase difference signal, but the antenna Direction can be determined simply by knowing the timbre change of the audio signal by antenna switching including the delayed signal.

It goes without saying that the present invention enables reliable direction detection regardless of the strength or fluctuation of radio waves, but since there is no need to numerically determine the magnitude of the phase difference signal, synchronous rectification is not required as in the conventional method. Circuit/band filter circuit/
There is no need to create a synchronization signal. For this reason,
The circuit is extremely simple, and by simply using an FM receiver (including a selective amplifier and FM detector) as a receiver, you can listen to its output sound and convert the sound produced by the phase difference component caused by switching to the sound caused by the frequency modulation component. It can be distinguished from others and can perform the function of direction finding.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.
Figure 2a is a diagram showing the relationship between spaced antennas and the radio wave arrival direction, Figure 2b is a diagram showing the phase difference |φ| of the two antennas with respect to the radio wave arrival direction θ, and Figure 3 is a diagram showing the antenna Figure 4 is a diagram to explain the phase relationship between antennas A, B and delayed signal C. Figure 5 is a diagram of antennas A, B and delayed signal for sense determination. FIG. 4 is a diagram of signal waveforms of various parts when switching including C. 10A, 10B...Antenna, 11...Delay circuit, 12...Switching device, 13...Switching oscillator, 1
4...Selection amplifier, 15...FM detector, 16...
...Reducing pass filter, 17... Speaker, 18...
...AM detector.

Claims (1)

[Claims] 1. Each received signal of two omnidirectional antennas spaced apart in parallel on a straight line, and the distance between the received signals of one of the two omnidirectional antennas spaced apart between the two omnidirectional antennas. and a received signal delayed by a delay time or less corresponding to the propagation time of radio waves as a received output signal; and an audible sound output means for obtaining an output as an audible sound signal obtained by a phase difference between the received output signals at each time point of the switching included in the signal obtained by detecting the switched received signal. and direction detection means for detecting the direction of arrival of radio waves based on a change in the audible sound output obtained by rotating the two omnidirectional antennas. 2. The direction finding device according to claim 1, further comprising sense determining means for determining a sense of the radio wave arrival direction based on a change in the tone color of the audible sound output.