JPH11304912A - Echo hearing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regenerate finely changing amplitude information with high fidelity without being affected by frequency shift due to Doppler effect, by mixing a receiving signal with oscillation signals different in frequency, and extracting a difference frequency signal from the two mixed frequency signal. SOLUTION: Mixer circuits 5, 5' mix a receiving signal (a) having a frequency f1 with oscillation signals which are supplied from local oscillator 6, 6' and have different frequencies f3 , f4 , and generates sum frequency signals f1 +f3 and f1 +f4 and difference frequency signals f1 -f3 =F1 and f1 -f4 =F2 . Filter circuits 7 and 7' pass a signal (e) of the difference frequency F1 and a signal (f) of the difference frequency F2 , respectively. A multiplier circuit 11 forms a sum frequency F1 +F2 and a difference frequency F1 -F2 =Fa. By a filter circuit 12, a signal (g) of the difference frequency Fa is only sent to a root circuit 13. An amplitude signal which has been squared by multiplication is returned to the original state. The signal (g) is converted to a signal in an audible bandwidth, and outputted to an amplifier 14. Thereby frequency shift due to Doppler effect is canceled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater detection device for transmitting an ultrasonic pulse into water and detecting the underwater from a reflected signal (echo) of the ultrasonic wave.

[0002]

2. Description of the Related Art The amplitude of the reflected signal from a target varies slightly depending on the type of fish, the seabed, etc., and it is possible to identify the type of target by listening to the change in amplitude. Become.

In order to hear an echo having a frequency as high as tens of KHz or more with the human ear, conventionally, an echo signal is mixed with an oscillating frequency signal lower (or higher) by an audio frequency than the echo signal. The difference frequency signal (beat signal) was obtained as an audible wave signal.

In this method, when the frequency of the exploration ultrasonic signal is increased, the amount of frequency shift due to the Doppler effect increases accordingly.
And the audio frequency band deviates from the upper limit of the audible frequency band.

Therefore, the present applicant avoids the above-mentioned problem by compressing the amount of change in the frequency in "a hearing device in an underwater detector" (Japanese Patent Publication No. 57-25784). FIG. 1 shows a control block diagram thereof. The transmitter / receiver 1 converts the ultrasonic pulse signal of the frequency f0 generated by the transmitter 2 into an ultrasonic wave, emits the ultrasonic wave into water, and receives the echo changed to the frequency f1. The transducer 1 is provided at a constant tilt angle (an angle formed with the horizontal direction), and is turned around the own ship at a predetermined pitch angle by driving a motor (not shown). Exploring the entire surroundings (searchlight sonar). The received echo signal is supplied to the receiver 3, and the amplified received signal (a) is sent to the display 4 to display underwater information and to the mixing circuit 5. In this mixing circuit 5, the received signal is mixed with an oscillation signal of frequency f2 supplied from the local oscillator 6, and the sum frequency
A signal of (f1 + f2) and a signal of difference frequency (f1-f2) are generated. The filter circuit 7 calculates the difference frequency (f ₁ −f ₂ = Δ
f), the amplitude value is clipped below a certain level in the next shaping circuit 8, and the difference frequency Δf is divided by 1 / N in the frequency dividing circuit 9 to obtain the frequency f.
It is converted (that is, compressed) into the signal (b) of a. This frequency f
The oscillation frequency f2 of the local oscillator 6 and the frequency division ratio 1 / N of the frequency dividing circuit 8 are set so that a becomes an audible wave frequency.

The above-mentioned received signal (a) is also supplied to a detection circuit 10 to perform envelope detection. The detection signal (c) is
A signal (d) in which the amplitude value of the audio signal (b) changes along the envelope waveform by being input to the multiplication circuit 11 and multiplied by the audio signal (b) from the frequency dividing circuit 9 here. Is obtained. The signal (d) is supplied to the speaker 15 through the amplifier 14 so that the echo signal can be heard.

[0007]

As described above, the amplitude of the echo signal varies delicately depending on the target, and the type of the target can be identified by discriminating the delicate change in the amplitude with the sound. If the signal (a) is detected, the whisker-like signal is absorbed by the averaging at the time of detection, and a subtle change in amplitude is lost. There were drawbacks.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an echo hearing device capable of faithfully reproducing information of a subtly changing amplitude without being affected by a frequency shift due to the Doppler effect at all.

[0009]

When a received signal contains a frequency shift Δf due to the Doppler effect, the first frequency conversion circuit (mixing circuit and local oscillator) performs frequency conversion, Contains the frequency shift Δf. Therefore, the received signal is converted into another second frequency conversion circuit.
(The mixing circuit and the local oscillator (the oscillation frequency is different from the first one)) also perform frequency conversion, and if the signal of the difference frequency is extracted from the signals obtained by the two frequency conversion circuits, the frequency shift Δf cancels out. Thus, the influence of the frequency shift Δf due to the Doppler effect is eliminated (claim 2).

If the difference frequency is an audio frequency band,
The signal can be heard as a sound without being detected (claim 3).

It has the elements of claim 2 and claim 3,
In claim 2, an echo hearing device using a filter circuit (12) as means for "using a difference frequency signal (Fa)" is claimed in claim 4.

The amplitude change of the audible sound is returned to a linear characteristic by passing the squared amplitude signal through a square root circuit (14) by signal multiplication (claim 5).

[0013]

FIG. 2 is a control block diagram showing one embodiment of the present invention, and the same reference numerals are given to the same elements as those in FIG. 5 'to 7' are the same as 5 to 7, but the oscillation frequencies of the local oscillators 6 and 6 'are f3 and f4, respectively. The multiplication circuit 11 multiplies the outputs of the filter circuits 7 and 7 ′ with each other, and the filter circuit 12 allows the signal of the difference frequency from the sum frequency signal and the difference frequency signal obtained by the multiplication circuit 11 to pass. , Square root circuit 13. The square root circuit 12 restores the amplitude change of the audible sound to a linear characteristic by returning the amplitude signal squared by the multiplication of the signal, and thereafter supplies the change to the amplifier 14.

The reception signal (a) of the frequency f1 output from the receiver 3 is sent to the display 4 to display the underwater information, while being supplied to the mixing circuits 5, 5 '. In the mixing circuit 5, the received signal (a) is mixed with the oscillation signal of the frequency f3 supplied from the local oscillator 6, whereby the signal of the sum frequency (f1 + f3) and the difference frequency (f1-f3 = F
1) is generated. Similarly, in the mixing circuit 5 ',
The received signal (a) is mixed with the oscillation signal of the frequency f4 supplied from the local oscillator 6 ′, and a signal of the sum frequency (f1 + f4) and a signal of the difference frequency (f1−f4 = F2) are generated.
The filter circuits 7 and 7 'respectively provide difference frequencies F1 and F2.
Pass only the signals (e) and (f),
1 is supplied. Here, the signals (e) and (f) are multiplied by each other, and the sum frequency (F1 + F2) signal and the difference frequency are multiplied.
Although a signal of (F1−F2) is generated, the filter circuit 12 sends a signal (g) of the difference frequency (F1−F2 = Fa) to the square root circuit 13. Therefore, the oscillating frequencies f3 and f4 of the local oscillators 6 and 6 'are selected so that the frequency Fa becomes a frequency in the audible wave band.

Here, F1-F2 = (f1-f3)-(f
As can be seen from 1-f4) = f4−f3 = Fa, the frequency Fa of the audible wave signal (g) does not include the value of the frequency f1 of the echo signal undergoing a frequency change due to the Doppler effect, That is, the frequency shift due to the Doppler effect is eliminated.

For example, when the transmission frequency f0 is 150 KHz, it is assumed that f3 = 140 KHz and f4 = 141 KHz. Here, when there is no Doppler frequency shift, f
Since 1 = 150 KHz, F1 = 10 KHz, F2
= 9 KHz and Fa = 1 KHz. On the other hand, when f1 = 151 KHz due to Doppler frequency shift, F1
= 11 KHz, F2 = 10 KHz, and Fa = 1 KHz.

As described above, the pass frequency of the filter circuit 14
Since (Fa) is constant, the filter circuit 14 can have a narrow band characteristic, whereby unnecessary noise can be cut by the filter circuit 14 and the S / N ratio is improved. Since the pass frequencies of the filter circuits 7 and 7 '(the same applies to the case of FIG. 1) change according to the frequency f1 of the received signal, it is necessary to broaden the band characteristics to some extent. If analog devices are used for these filter circuits, the band characteristics can be arbitrarily changed by changing the parameters.

In the above embodiment, the echo hearing device of the present invention is applied to a searchlight sonar. However, it can be applied to, for example, a scanning sonar. As shown in FIG. 3, the scanning sonar is directed from the transducer 1 '(the ultrasonic transducers are arranged in a cylinder as shown in the enlarged view) mounted on the bottom of the ship to the sea floor, When an ultrasonic wave is transmitted in the direction, and the resulting echo is received by the transmitter / receiver 1 ′, a received beam R having a sharp directional angle as shown is formed, and the received beam is maintained at a tilt angle θ. While turning (horizontal scanning), the receiving beam R is a device that scans along the surface of the cone U, and detects echoes from the fish school etc. located on the surface of the cone in order from the closest one. can do.

However, in this scanning sonar,
Even if the echoes from all directions are simultaneously converted into a listening sound, it is difficult to identify them. Therefore, it is preferable to convert only the echoes from the arbitrarily set specific direction into the listening sound.

[0020]

As described above, according to the present invention, the received signal is subjected to frequency conversion in the first and second frequency conversion circuits, and the signal of the difference frequency after both conversions is obtained.
(e) Since the signal (g) of the difference frequency was further obtained for (f), the value of the Doppler frequency shift included in the signal (e) (f) of the difference frequency after the frequency conversion was Because of the cancellation, the effect of the Doppler frequency shift can be completely eliminated. If the difference frequency (g) is an audio frequency band, the signal can be directly heard as a hearing sound without detection,
It is possible to faithfully reproduce even information on subtle amplitude changes. As the filter circuit (14) for obtaining the signal (g) having the above-mentioned difference frequency, a filter having a narrow band characteristic can be used because the pass frequency band may be constant, and thereby unnecessary noise can be removed.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a hearing device used in a conventional underwater detection device.

FIG. 2 is a control block diagram of an underwater detection device employing the present invention.

FIG. 3 is a control block diagram of a scanning sonar employing the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Transceiver 2 Transmitter 3 Receiver 4 Display 5 Mixing circuit 6 Local oscillator 7, 12 Filter circuit 11 Multiplier circuit 12 Amplifier 13 Square root circuit 14 Amplifier 15 Speaker

Claims (5)

[Claims] 1. A listening method for listening to an echo of an ultrasonic pulse radiated into water, wherein the first and second mixing circuits use oscillation signals of different frequencies with respect to a received signal of the echo, respectively. Mixing, selecting a signal of the difference frequency or the sum frequency generated by the mixing, and then multiplying both signals of the difference frequency or the sum frequency with each other; An echo listening method characterized by being provided as a sound. 2. A hearing device for listening to an echo of an ultrasonic pulse radiated into water, wherein an oscillating signal of a frequency f3 is mixed with a received signal of the echo, and only a signal of a difference frequency generated by the mixing is filtered.
(7), further mixes the received signal with an oscillation signal of frequency f4, selects a difference frequency or sum frequency signal generated by this mixing by a filter circuit (7 '), and selects the difference frequency or sum signal. An echo hearing device characterized in that Doppler frequency shift is eliminated by multiplying both signals of the frequency by each other and adopting a difference frequency or sum frequency signal (Fa) generated by the multiplication. 3. A signal (Fa) of the difference frequency or the sum frequency.
Oscillating frequencies f3 and f3 such that
The echo hearing device according to claim 2, wherein the echo bottom is located on the bottom of the ship. 4. A hearing device for listening to an echo of an ultrasonic pulse radiated into water, wherein an oscillating signal of a frequency f3 is mixed with a received signal of the echo, and a signal of a difference frequency or a sum frequency generated by the mixing is mixed. Selected by a filter circuit (7), and furthermore, a frequency f
4 is mixed, and a signal of a difference frequency or a sum frequency generated by the mixing is selected by a filter circuit (7 ').
An echo hearing sound characterized by multiplying both signals of a difference frequency or a sum frequency with each other, and selecting a signal (Fa) of the difference frequency or the sum frequency generated by the multiplication as an audible sound signal by a filter circuit (12). apparatus. 5. The echo hearing device according to claim 4, further comprising a square root circuit for calculating a square root of an amplitude value on an output side of said filter circuit.