JP2868869B2 - FM-CW fish finder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fish finder for detecting a school of fish by transmitting an ultrasonic signal into the sea, and particularly uses an ultrasonic signal of FM-CW.
It relates to an FM-CW fish finder.

[Prior Art] Conventionally, a fish finder has been essentially used in fields such as fisheries.

A conventional fish finder transmits a short-duration pulse signal as ultrasound to the sea, and detects the presence or absence of a fish shoal using reflected waves.

Therefore, in the conventional device, the detection distance and the detection sensitivity are determined by the power of the transmission pulse signal, and the distance resolution is determined by the pulse width.

[Problems to be Solved by the Invention] This property of a conventional fish finder has been an obstacle in securing a detection distance, detection sensitivity, and distance resolution, and configuring a small and inexpensive device.

First, in order to execute detection at a longer distance and detection at a higher sensitivity, it is necessary to use a high-output transmitter. In this case, the configuration of the transmitter has become large and the price has been expensive.

In order to ensure high distance resolution, the pulse width may be reduced. However, when the pulse width is narrow, the detection distance and the detection sensitivity decrease.

Among such problems, characteristic problems are solved in principle by adopting a signal based on FM-CW (FM continuous wave). FM-CW is known as a technique related to target detection in the field of radar and the like, and performs frequency analysis to obtain information related to detection from a received signal. When a school of fish is detected using an ultrasonic signal of FM-CW, since a pulse signal is not used, there is no limit to the detection distance and the distance resolution due to the pulse signal power and pulse width.

However, simply applying FM-CW to a fish finder causes a problem of a complicated device configuration and high price for a reason different from the case of a pulse signal.

That is, in order to secure the depth to be detected (measurement depth) from a shallow depth to a deep depth, it is necessary to widen the frequency range related to the measurement of the received signal, and also to increase the resolution of the frequency analysis. In other words, in order to obtain a sufficient display resolution at a shallow depth and to sufficiently secure a measurement bandwidth at a deep depth, a device having a high resolution and a wide measurement frequency width is required as a frequency analyzer. . A frequency analyzer having such performance generally has a complicated configuration and is expensive.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an FM-CW type fish finder that can use a simple and inexpensive frequency analyzer.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a measurement depth changeover switch for switching and setting a measurement depth, and a signal having a frequency change rate inversely proportional to the set measurement depth. Signal generator to generate and FM from signal from signal generator
-Transmitting underwater as a CW ultrasonic signal, receiving and detecting a reflected wave from a school of fish, etc., and transmitting and receiving means for obtaining a beat signal, and attenuation included in the beat signal caused by the ultrasonic signal propagating in the sea An equalizer that compensates for the reflection depth according to the measurement depth, a frequency analyzer that determines the reflection intensity-depth relationship for the received signal equalized by the equalizer, and a reflection intensity-depth relationship depending on the measurement depth that is set. And a display for displaying the captured fish school.

According to a second aspect of the present invention, the apparatus further includes means for variably setting characteristics of attenuation compensation by the equalizer in accordance with selection of a measurement depth.

A third aspect of the present invention is characterized in that a means for offsetting the beat signal by a predetermined frequency is provided.

[Operation] In the present invention, the measurement depth is set by the measurement depth switch. Further, a signal is generated by the signal generator. This signal is a signal having a frequency change rate inversely proportional to the set measurement depth. This signal is transmitted into the sea as an ultrasonic signal of FM-CW by the transmitting / receiving means.

The transmitted ultrasonic signal is reflected by a school of fish or the like, received by a transmitting / receiving means, and a beat signal is obtained by detection. The beat signal is supplied to an equalizer. The equalizer compensates for the attenuation of the received signal included in the beat signal according to the measured depth. Here, the attenuation to be compensated is caused by the propagation of the ultrasonic signal in the sea.

Further, a reflection intensity-depth relationship is obtained from the relationship between the reflection intensity and the frequency component for the equalized received signal by the frequency analyzer. The obtained relation is taken in by the display according to the measurement depth, and information on the school of fish is displayed based on this relation.

Therefore, in the present invention, the measurement frequency width is constant regardless of the measurement depth. In addition, since the frequency is analyzed by the same frequency analyzer regardless of the measurement depth, the display resolution is always the same. As a result, a simple and inexpensive frequency analyzer can be used adaptively according to each measurement depth.

In claim (2), the characteristics of the equalizer are variably set according to the selection of the measurement depth. Therefore, the function of changing the attenuation compensation characteristic of the equalizer according to the measurement depth is easily realized.

Further, in claim (3), the frequency of the beat signal is offset by a predetermined frequency. Therefore, by setting the offset amount, the frequency of the beat signal can be set to a frequency that can be easily handled by the equalizer or the frequency analyzer and that can simplify the configuration.

EXAMPLES Hereinafter, preferred examples of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an FM-CW fish finder according to one embodiment of the present invention.

The device shown in this figure is a device for transmitting and receiving ultrasonic waves of FM-CW into the sea, and therefore includes a transmitter 10 and a receiver 12.

The transmitter 10 and the receiver 12 are composed of, for example, piezoelectric elements. The transmitter 10 is an FM-CW supplied from the transmitter 14.
, And transmit the FM-CW ultrasonic waves into the sea. On the other hand, the receiver 12 receives the reflected wave of the ultrasonic wave emitted from the transmitter 10 from a school of fish, converts it into an electric signal, and outputs it.

A signal generator 16 is connected to a stage preceding the transmitter 14.
In front of the signal generator 16, a measurement depth switch
18 is connected.

The measurement depth switch 18 sets the measurement depth to 50 m, 10
This is a switch for selectively setting any one of 0 m and 200 m. Therefore, for example, when the user wants to detect a school of fish up to 50 m, the switch 18 is operated to set it to 50 m.

The signal generator 16 generates a signal whose frequency F changes linearly from f1 to f2. FIG. 2 shows the output characteristics of the signal generator 16. That is, the signal emitted by the signal generator 16 is a signal whose frequency F changes linearly from f1 to f2 in a sweep time of a length corresponding to the measurement depth. If the measurement depth set by the measurement depth switch 18 is xs, the sweep time is the time for the ultrasonic wave to reciprocate at the measurement depth xs, that is, 2 * xs / c. Here, c is the speed of sound in the sea.

Considering the frequency change rate of the output signal of the signal generator 16, this rate is proportional to the reciprocal of the sweep time. Therefore, it can be said that the signal generator 16 outputs a signal whose frequency change rate is inversely proportional to the measured depth xs. This signal is supplied to a transmitter 14 and also to a mixing amplifier 20 described later for mixing the received signal.

The transmitter 14 performs frequency modulation of a carrier having a predetermined frequency based on an output signal of the signal generator 16. Since the output signal of the signal generator 16 is a signal whose frequency changes as described above, the signal obtained by the transmitter 14 is an FM-CW signal. This signal is supplied to the transmitter 10.

When an ultrasonic wave of FM-CW is emitted from the transmitter 10 and a reflected wave from a school of fish is received by the receiver 12, the received signal is supplied to the mixing amplifier 20. The mixing amplifier 20 is supplied with a signal from the signal generator 16, and this signal is
This is a signal before one sweep time, and is a signal having the same modulation frequency as the received signal. Therefore, the signal to be received and
Detection is performed by mixing the signal from the signal generator 16 and the signal in the mixing amplifier 20, and a component relating to the presence of the school of fish contained in the received signal is obtained as a beat signal. The mixing amplifier 20 amplifies the beat signal and supplies it to the equalizer 22.

The frequency ΔF of the beat signal increases when the distance D to the object related to the reflection of the ultrasonic wave is large, and decreases when the distance D is small. The range that this frequency can take depends on the frequency range of the output signal of the signal generator 16, and is constant regardless of the measurement depth. The intensity of the beat signal increases as the reflection intensity increases (that is, when the distance D is smaller), and decreases as the reflection intensity decreases.

By the way, the reception intensity A of the ultrasonic wave by the receiver 12 has a relationship represented by the following equation with the distance D due to the attenuation of the ultrasonic wave in the sea.

A = 20 log (2D) + α (2D) This relationship is shown in FIG. As shown in this figure, the reception intensity A decreases as the distance D increases. Note that the relationship in FIG. 3 changes depending on the sea area and the reflection coefficient of the reflecting object.

Accordingly, the intensity of the beat signal changes by switching the measurement depth xs. For example, the reception intensity A is a value in the range of A0 to A1 when the measurement depth xs is set to 50 m, and A0 when the measurement depth xs is 100 m.
A value in the range from A2 to A2, and a value in the range from A0 to A3 in the case of 200 m. The intensity of the beat signal output from the mixing amplifier 20 also takes a value corresponding to this.

The equalizer 22 is a means for eliminating such a change in intensity, that is, for assuring attenuation of ultrasonic waves caused by propagation in the sea.

Specifically, the equalizer 22 includes, as shown in FIG.
The beat signal is attenuated by the attenuation amount ρ corresponding to the frequency ΔF and the measurement depth xs. The horizontal axis in FIG. 4 is the frequency ΔF, and the vertical axis is the attenuation ρ.

For example, when the measurement depth xs is set to 50 m, the amount of attenuation ρ is the range of change in reception intensity A0−A1 as the frequency ΔF increases.
To 0 in a manner similar to P0 to P1 in FIG. Similarly, when the measurement depth xs is 100m or 200m, A0-A2
Or from A0-A3 to 0, respectively from P0 in FIG.
It changes analogously to P2 or from P0 to P3. Equalizer 22
Attenuates the output of the mixing amplifier 20 by such an attenuation amount ρ characteristic. The operation of switching the attenuation amount ρ characteristic according to the measurement depth xs is performed according to the operation of the measurement depth switch 18.

As a result of such attenuation, the output of the equalizer 22 is a signal having no difference in signal strength depending on the measurement depth xs. In other words, in this embodiment, no matter which measurement depth xs the measurement depth changeover switch 18 is set, it is possible to obtain from the equalizer 22 a signal from which the intensity difference caused by attenuation in the sea has been eliminated. it can.

The output of the equalizer 22 is connected to a frequency analyzer 24. The frequency analyzer 24 performs a frequency analysis on the equalized signal supplied from the equalizer 22.

FIG. 5 shows an example of an analysis result by the frequency analyzer 24.

What is obtained by the analysis by the frequency analyzer 24 is the relationship between the reflection intensity S and the frequency ΔF of the beat signal, that is, the relationship between the reflection intensity and the beat frequency. The frequency analyzer 24 obtains a reflection intensity-beat frequency relationship based on the equalized intensity of the beat signal and the frequency ΔF. Beat signal frequency ΔF
Has a one-to-one correspondence with the depth associated with the reflection, which can be converted to a depth. Therefore, the frequency analyzer
By 24, the reflection intensity-depth relationship is determined.

The relationship shown in FIG. 5 is a relationship when two fish schools R1 and R2 exist up to the measurement depth xs. For example,
The reflection intensity S of the fish school R1 having a low frequency ΔF (thus existing at a short distance) is strong, and the reflection intensity S of the fish school R2 having a high frequency ΔF (thus existing at a long distance) is weak.

Further, the resolution of the analysis of the frequency analyzer 24 is, for example,
If the sweep frequency width f2-f1 is 1 kHz, the distance resolution is 10 Hz / 1 kHz * xs = xs / 100.

The relationship determined in this way is stored in the display memory 26, and is displayed on the display 28.

That is, the display memory 26 stores the relationship between the reflection intensity and the depth. Specifically, for example, the horizontal axis in FIG. 5 is associated with a series of addresses in the display memory 26, and the reflection intensity S corresponding to the addresses is stored. Each time the sweep in the signal generator 16 is repeated, the storage address in the display memory 26 is sequentially set to a different address.

The information stored in the display memory 26 in this manner is
It is displayed on the screen of the display 28 according to the set measurement depth xs. FIG. 6 shows an example of the display screen.

In this figure, the numerical value displayed on the vertical axis indicates the depth, and particularly the one shown at the bottom is the measured depth xs related to the setting. The schools of fish R1 and R2 are displayed in alignment with the scale on the vertical axis according to the depth related to the reflection. The display mode is a mode in which the luminance is changed or the color is changed according to the reflection intensity S, for example.

Each time the sweep by the signal generator 16 is repeated, the display is shifted leftward. In this way, the school of fish
The movement of R1 and R2 is displayed over time.

As described above, according to the present embodiment, the frequency change rate is set by the signal generator 16 according to the measurement depth xs, and the measurement depth
Since the attenuation characteristic of the equalizer 22 is set according to xs, it is possible to perform frequency analysis with the same frequency width and display with the same resolution regardless of the measurement depth. In comparison, the peak transmission power can be reduced. Further, since a fish finder using FM-CW can be realized by the frequency analyzer 24 having a simple and inexpensive configuration, it is possible to detect a fish shoal using FM-CW with a device having a simple and inexpensive configuration.

In the above description, the equalizer 22 and the frequency analyzer 24
The description has been given of the case where the frequency ΔF of the beat signal handled by the above is from 0 to f2 to f1, but the equalizer 22 or the frequency analyzer
To simplify the configuration of 24, the frequency ΔF of the beat signal may be offset by an appropriate frequency. The configuration for the offset can be easily configured by a technician in the same technical field as the present application.

[Effects of the Invention] As described above, according to the present invention, a signal equalized according to the measurement depth is subjected to frequency analysis.
Frequency analysis can be performed with the same frequency analyzer regardless of the measurement depth. This makes it possible to obtain a fish finder using FM-CW with a simple and inexpensive configuration regardless of the measurement depth of the display resolution.

According to claim (2), since the characteristics of the equalizer are variably set according to the selection of the measurement depth, the function of changing the attenuation compensation characteristics of the equalizer according to the measurement depth can be easily realized. it can.

According to the third aspect, since the frequency of the beat signal is offset by a predetermined frequency, the configuration of the equalizer or the frequency analyzer can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an FM-CW fish finder according to one embodiment of the present invention, FIG. 2 is a characteristic diagram of a signal generator, and FIG. 3 is a relationship between reception intensity and distance. FIG. 4, FIG. 4 is an attenuation characteristic diagram of the equalizer, FIG. 5 is an output diagram of the frequency analyzer, and FIG. 6 is a display screen diagram. 10 ... Transmitter 12 ... Receiver 14 ... Transmitter 16 ... Signal generator 18 ... Measurement depth changeover switch 20 ... Mixed amplifier 22 ... Equalizer 24 ... Frequency analyzer 28 ... Display xs: Measurement depth ρ: Attenuation S: Reflection intensity ΔF: Beat signal frequency R1, R2: Fish school

Continuation of the front page (56) References JP-A-51-75468 (JP, A) JP-A-62-27681 (JP, A) JP-A-2-171683 (JP, A) Actually open JP-A-61-3488 (JP) , U) Japanese Patent Publication No. 50-7939 (JP, B1) Japanese Patent Publication No. 36-13498 (JP, B1) Japanese Patent Publication No. 36-13288 (JP, B1) Japanese Patent Publication No. 48-17110 (JP, B1) 36-3094 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 15/34

Claims (3)

(57) [Claims] 1. A measurement depth changeover switch for switching and setting a measurement depth; a signal generator for generating a signal having a frequency change rate inversely proportional to the set measurement depth; Transmitting and receiving means as an ultrasonic signal into the sea, receiving and detecting a reflected wave from a school of fish, etc. to obtain a beat signal, and measuring the attenuation included in the beat signal caused by the propagation of the ultrasonic signal in the sea and measuring the depth. An equalizer that compensates according to the following conditions; a frequency analyzer that obtains a reflection intensity-depth relationship for the received signal equalized by the equalizer; An FM-CW type fish finder comprising: a display for displaying; 2. An FM-CW type fish finder according to claim 1, further comprising means for variably setting characteristics of attenuation compensation by an equalizer in accordance with selection of a measurement depth.
-CW fish finder. 3. The FM-CW fish finder according to claim 1, further comprising means for offsetting a beat signal by a predetermined frequency.