SIGNAL MULTIPLEXER FOR SONAR

The invention lies in the field of SONAR (acronym for SOund NAvigation and Ranging) equipment, and more particularly deals with sonars composed of two parts linked together by a cable responsible for ensuring the exchange of signals.

Sonars are devices that use the properties of sound propagation in water to detect and locate underwater objects. They are used in particular in the field of defense for the detection of submarines or mines.

Sonars are often made up of two parts:

a first so-called emergent part, generally located on board surface equipment such as a boat or an aircraft. By emerged part is meant the fact that it is not intended to be immersed in water. This does not make it incompatible with use in an underwater building, such as a submarine. This part carries out at least the generation of the power signals emitted by the submerged part of the sonar and of a signal allowing the power supply of the submerged part. It also includes the electronics necessary for the exchange of communication data with the submerged part. Advantageously, it can have the digital electronics necessary for the analysis of the signals acquired by the submerged part for the detection of sources;

- a second part called submerged because it is intended to be submerged to transmit sonar signals underwater. This part is mainly made up of acoustic transducers allowing the transmission and reception of underwater signals. It also includes the electronics necessary for the acquisition of submarine signals, their digitization and their transmission to the emerged part.

FIG. 1 represents an example of a two-part sonar for the detection of submarines, when on board a helicopter. The emerged part of the sonar is positioned inside the helicopter 101, while the submerged part 102 is under the sea, at depths that can reach a few hundred meters. The two parts are connected by an electric carrier cable 103. This cable is wound around a winch placed on board the helicopter making it possible to raise / lower the submerged part of the sonar, and to keep it in position. The cable 103 is armored, that is to say that its structure is reinforced so as to support the weight of the submerged part and its own weight. The length of the cable can reach a few hundred meters. As an illustration, Thaïes is developing a Sonar called Sonar Flash,

The electric carrier cable therefore maintains the submerged part of the sonar, and serves as a support for the transmission of electrical signals. Three types of signals are generally transmitted between the two parts of the sonar:

- signals to be transmitted, analog signals of high power.

These signals are generated by the emerged part, and are intended to be emitted by the acoustic transducers of the submerged part.

By way of illustration, in the case of Sonar Flash, the signals emitted have a power of 10 kW at a voltage of 2500 V rms in alternating,

- an electrical supply signal, ensuring the supply of electrical energy for the submerged part of the sonar. This signal is usually a direct current signal or a low frequency alternating signal (50 Hz to 400 Hz),

- a bidirectional signal allowing the transmission of communication data between the two parts of the sonar, transmitting among other things in one direction the management and control / command data of the submerged part, and in the other direction information on the state of the submerged part of the sonar and the digitized acquired signals.

The helicopter-hoisted sonars of the state of the art, such as the Sonar Flash, for example, use a coaxial electric carrier cable as a medium for the transmission of the various signals. They are transmitted successively over the cable, which is thus shared in time between the different functions. However, such time multiplexing leads to cuts on each of the signals, in particular on the power supply signal. Equipment dedicated to ensuring the continuity of the signals, such as energy storage devices (batteries) for the power supply signal, must then be implemented in the submerged part. Active power switching elements, such as power relays, must also be implemented in the submerged part and constitute sources of unreliability. All this has repercussions on the mass and the volume of the submerged part, and therefore on the diameter of the power cable, as well as on the volume and mass of the assembly. It is therefore desirable to have a solution which makes it possible to reduce the mass and the volume of the submerged part, while improving its reliability.

In addition, the average rate of the signal carrying the communication data is limited as a function of the time resources allocated to it. Progress in terms of miniaturization of components and

the increase in computing power for signal processing means that sonars are carrying more and more sensors. The requirements for the quantities of data transported then increase accordingly. It is therefore necessary to find a solution making it possible to increase the average bit rates of this signal.

The problem posed is therefore threefold: to lighten the device, increase its reliability and increase the bit rate allocated to the signal carrying the communication data.

To increase the rate of the signal carrying the communication data, it would be possible to have several transmission lines in parallel within the cable, one per type of signal, instead of a single transmission line. This would eliminate the power switching and energy storage devices from the submerged part. However, by increasing the number of transmission lines, the section of the cable and its mass would increase, which would pose the problem of the size of the reel necessary to wind the cable over its entire length, as well as the problem of the mechanical stresses exerted on it. the cable and the reel. This solution is therefore not suitable, in particular when the sonar is on board a helicopter.

In order to respond to the problem posed while solving the problems raised by the prior art, the invention proposes to continuously and simultaneously transmit all the signals (power supply, transmissions and communication data) by combining the various signals, each type of signal using its own frequency band. Such a combination is not considered in the prior art because it amounts to transmitting on the same medium heterogeneous signals having very different characteristics: high power signals, such as signals intended to be transmitted by the submerged part and of which the voltage can reach several thousand volts and the power several tens of kilowatts, with signals of lower power, such as the signal carrying the communication data.

In order to mix the various signals transmitted on the power transmission cable, the invention proposes to implement, on the one hand, combining means and, on the other hand, means for separating the signals. A practical example of the implementation of such a device, optimized so as to reduce the mass and the volume of the second part of the sonar, is given in FIG. 3 and described in detail.

To this end, the invention relates to a sonar comprising a first part and a second part connected by a power carrier cable configured to mechanically support the second part and allow the two parts of the sonar to exchange signals. The signals transmitted include:

- a unidirectional signal called power supply signal, by which the first part transmits a power supply to the second part, analog unidirectional signals called signals to be transmitted, transmitted by the first part to the second part with a view to their transmission in the form acoustic waves, and

- a bidirectional signal carrying communication data exchanged between the two parties.

In the sonar according to the invention, the first part comprises signal combining means, configured so that the power supply signal, the signals to be transmitted and the signal carrying communications data are transmitted simultaneously and in frequency bands. different on the power cable. In addition, the second part comprises separation means allowing the recovery of each of the signals transmitted over the power-carrying cable, one or more acoustic emission transducers (Tr), and tuning / adaptation means (L1) of the transducer or transducers. emission acoustics.

Advantageously, the power carrier cable comprises a single transmission line.

In one embodiment, the combining means comprise components configured to couple the signals to be transmitted with the power supply signal. These components can advantageously comprise a transformer configured to raise the voltage of the signals to be transmitted and to couple them with the power supply signal. They can also include components configured to guide the propagation of signals towards the power carrier cable. In one embodiment, the components configured to guide the propagation of signals to the power carrier cable include:

an inductor configured to pass the power supply signal and the signals to be transmitted and to restrict the propagation of the signal carrying the communications data, said inductor being connected between on the one hand the power-carrying cable, and on the other hand elements generating the signals to be transmitted and generating the power supply signal, and

a filter configured to pass the signal carrying the communications data and to restrict the propagation of the power supply signal and of the signals to be transmitted, said filter being connected between the power transmission cable and a signal generator carrying the communications data.

Advantageously, the separation means comprise an inductor configured to both separate the power supply signal from the other signals transported by the power carrier cable and to perform the tuning / adaptation of the acoustic transducer (s). In one embodiment, this inductor is mounted in parallel with the acoustic transducer (s) and is connected between the power carrier cable and a capacitor with which it is mounted in series, the electrical supply signal being recovered at the terminals of said capacitor.

Advantageously, the inductance is configured to allow the electrical supply signal to pass and to restrict the propagation of the signal carrying the communications data and the signals to be transmitted.

In one embodiment of the sonar according to the invention, the separation means comprise:

an inductor configured to allow the signals to be transmitted to pass and to restrict the propagation of the signal carrying the communications data, said inductor being connected between the power-carrying cable and the acoustic transmission transducer (s), and

a filter configured to pass the signal carrying the communications data and to restrict the propagation of the power supply signal and the signals to be transmitted, said filter being connected between the power carrier cable and the modulation / demodulation element of the signal carrying the signals communications data.

In the sonar according to the invention, the power supply signal can be included in a portion of the spectrum ranging from 0 to 400 Hz, the signals to be transmitted can be included in a portion of the spectrum ranging from 1 kHz to 200 kHz and the signal carrying the communication data can be included in a portion of the spectrum greater than 200kHz.

In one embodiment of the sonar according to the invention, the signal carrying the communication data is modulated by a zero-mean modulation. Advantageously, the modulation uses orthogonal frequency division multiplexing, or OFDM (acronym for Orthogonal Frequency Division Multiplexing, or orthogonal frequency division multiplexing).

DESCRIPTION:

The invention will be better understood and other characteristics and advantages will appear better on reading the description which follows, given without limitation, and thanks to the appended figures among which:

• Figure 1 shows an example of a hoisted sonar composed of two parts,

"FIG. 2 represents an embodiment of a sonar according to the invention,

• Figure 3 shows an advantageous embodiment of a sonar according to the invention.

Hereinafter, when the same references are used in different figures, they designate the same elements.

FIG. 2 represents an embodiment of a sonar according to the invention comprising two parts 201 and 202 separated and connected by a power carrier cable 203. The sonar has a first part 201, called the emerged part, intended to be carried on board the vessel. a building such as a ship, an aircraft or a submarine, and a second part 202, called the submerged part, intended to be immersed in water. The electric carrier cable 203 provides a mechanical support function for the second part 202, and a signal transmission function between the two parts 201 and 202 through the same transmission line, including:

a power supply signal 210. This signal is intended to ensure the operation of the submerged part of the sonar. It is generally a continuous signal, but can equally well be an alternating signal having a frequency of a few tens of Hz. The signal can be generated without distinction by the emerged part 201 of the sonar when it has storage means. energy (batteries), or supplied by an external power source to which the sonar is connected;

signals to be transmitted 211. These are electrical signals intended to be transmitted underwater by the submerged part of the sonar in the form of acoustic waves. These signals are high power signals transmitted at High Frequency (typically, from kHz to a few hundred kHz). The signals to be transmitted 211 convey a high power which can reach several tens of kilowatts. In order to limit the intensity of the current of the signals to be emitted 211, the voltage can then exceed several thousand volts. The signals to be transmitted are generated by the first part of the sonar, then transmitted to the second part of the sonar which emits them using acoustic transducers; and

a bidirectional communication signal 212. The data transmitted on the downlink (that is to say from the emerged part 201 of the sonar to the submerged part 202) essentially correspond to configuration data, while the data transmitted over the upstream path (i.e. from the submerged part of the sonar to the emerged part) correspond mainly to the acoustic signals acquired, amplified and possibly digitized by the submerged part of the sonar, as well as to data on the state of this part. The quantities of

data transmitted on the upstream channel and on the downlink channel of the bidirectional signal carrying the communication data are therefore not symmetrical, the flow requirement being greater on the upstream channel than on the downlink channel. The emerged part 201 of the sonar has the electronics necessary for the generation (modulation, coding) and the reception (demodulation, decoding) of the signal carrying the communication data. The uplink and downlink channels can share the same spectral resource, according to methods known to those skilled in the art such as TDD (acronym for Time-Division Duplex, or duplex by time separation), or each have a frequency band specifically dedicated, according to known methods such as FDD (acronym for Frequency-Division Duplex, or duplex by frequency separation). They are transmitted on higher carrier frequencies than signals 210 and 211.

The emerged part 201 of the sonar may also have computing means enabling it to analyze the signals acquired by the submerged part of the sonar.

It also has means 213 allowing the combination of the different signals. The function of these means is to ensure that the supply signal 210, the signals to be transmitted 211 and the communication data simultaneously use the same transmission medium in the power carrier cable 203, in this case a single transmission line such as than a coaxial cable, without endangering the equipment responsible for generating each of these signals. Simultaneously means the fact that each signal can be transmitted continuously, without being interrupted by the other signals.

The submerged part 202 is configured to transform the signals to be transmitted 211 that it receives from the first part 201 into acoustic waves emitted in the water, and to receive the acoustic waves propagating in the water. To this end, the second part therefore comprises acoustic transducers, some being configured to transmit and others being configured to acquire acoustic signals. Acoustic transducers are most often piezoelectric elements whose electrical behavior is mainly capacitive. The implementation of a tuning / adaptation network of acoustic transducers (in English matching) makes it possible to minimize the power losses on the signals to be transmitted.

The second part 202 also comprises the electronics necessary for the amplification of the signals acquired by the acoustic transducers operating in reception, their possible digitization, and their transmission to the emerged part 201 of the sonar.

Finally, the submerged part 202 of the sonar also has means 223 for separating the various signals. These separation means make it possible to separately recover a power supply signal 220, signals to be transmitted 221 and communication data 222.

The device according to the invention therefore allows more flexible operation than the devices of the state of the art because all the signals to be transmitted on the cable are available at all times, transparently and without interruption. It thus has many advantages, including:

- all the signals take the same transmission line, which makes it possible to control the diameter and the mass of the power-carrying cable 203. A single coaxial cable or a twisted pair can thus act as a transmission line,

- the device does not require the implementation of electromechanical switching elements (such as a power relay) in its submerged part, which reduces its volume, its

mass, its cost, nor to synchronize the signal transmission and the switching elements, which improves the reliability of the system and simplifies it. The control circuitry can then be removed from the submerged part,

the temporal continuity of the electrical supply signal 220 is ensured, the submerged part then being able to dispense with the use of energy storage elements (batteries), which reduces its volume, its mass, its cost, and improves its reliability,

the temporal continuity of the communication data 222 is ensured, which makes it possible to increase the quantity of data transported, and therefore the number of acoustic sensors of the submerged part,

all of the above advantages make it possible to reduce the mass and the size of the submerged part of the sonar, and therefore its hydrodynamic performance, as well as the size of the power carrier cable, as well as that of the reel necessary to wind it.

The signal carrying the communications data can equally well take the form of an analog or digital signal. Any modulation / coding scheme can be used. Advantageously, the sonar uses zero-mean modulation so as not to have a DC component. Indeed, such a component would be superimposed on the supply signal. Again advantageously, it implements error correcting codes, in order to improve the quality of the transmission on a cable where the electrical performances can prove to be low and are subject to variability, in particular due to the length of the cable, its coiled / unrolled state, or its aging. Advantageously, the communication signals are modulated according to an orthogonal frequency division multiplexing technique, such as, for example, OFDM modulation. Indeed, such a modulation scheme makes it possible to achieve very high bit rates for a given spectral occupation, and is compatible with the use of error correcting codes making it possible to improve the quality of the transmission. OFDM also has very high flexibility in adapting the spectral resource, which makes it possible to dynamically adapt the allocation of the frequency resource to the two directions of transmission.

An example of implementation of the invention consists in placing, in each of the parts of the sonar, filtering elements adapted to each of the transmitted signals, allowing on the one hand their combination without interference, and on the other hand their separation. More precisely, according to one embodiment, these elements can be a low-pass filter for the power supply signal, a band-pass filter for the signals to be transmitted, and a band-pass or high-pass filter for the signal. carrying the communication data. These filters can be designed based on networks of resistors, inductors and capacitors. However, when it comes to power electronics, the components must withstand very high power levels and voltages at low frequencies (a few hundred kilohertz), which imposes a significant volume and mass. Among the components used in the filters, the inductors generally form the greatest contribution in terms of volume and mass, which then has repercussions on the dimensioning of the cable 203 and of the associated drum. In addition, these components are very expensive. It is therefore necessary to limit their number, in particular in the submerged part of the sonar.

To this end, FIG. 3 describes the main elements of a sonar according to an embodiment of the invention, optimized in order to limit the number of elements used. The embodiment presented exploits the large frequency differences which exist between the signals to be transmitted. For this purpose, components playing the role of combination means are implemented in the emerged part. These components are configured so that the power cable 203 has the impedance best suited to the frequency of each of the signals 210, 211 and 212, so that these signals are guided to the power cable 203, thus limiting everything as much as possible. return of these signals to the respective generation elements. Likewise, in the submerged part, components playing the role of separation means are implemented.

Just like FIG. 2, FIG. 3 represents a sonar comprising a first emerged part 201, intended to be loaded on board a ship, an aircraft or a submarine, a second part 202, intended to be submerged under water in order to emit the acoustic signals allowing the detection of targets, the two parts being connected by a power-carrying cable 203 which ensures the maintenance of the submerged part and the transmission of signals between the emerged part and the submerged part of the sonar.

The emerged part 201 comprises a transmitter TX intended to generate the signals to be transmitted. These signals generally have a power of a few kilowatts, modulated in a frequency band ranging from kilohertz, for sonar at very low frequencies, to a few hundred kilohertz, for sonar at high frequencies. The carrier frequency of the signals to be transmitted may be caused to change over time.

The submerged part also comprises a power supply source A1, shown in the figure as a direct current source, and a modem 310, which generates / receives the signal carrying the communication data. Modem 310 also performs

synchronization of the signal carrying the communication data on the uplink and downlink channels. The power source A1 can be a DC or AC power source belonging to the sonar or from an external source to which the sonar is connected.

The emerged part 201 comprises means 213 allowing the combination of the signal 210 delivered by the power supply A1 with the signals 211 delivered by the transmitter TX and the signal 212 carrying the communications data provided by the modem 310.

To this end, in this embodiment, the emerged part 201 comprises a transformer TR1, the role of which is to raise the voltage of the signals to be transmitted, and therefore to adapt the working impedance of the electronics to that of the acoustic transducers in order to limit the power losses of these signals during their transmission over the entire length of the power transmission cable 203. The implementation of the transformer TR1 is not strictly essential, but it makes it possible to considerably improve the transmission of the signals to be transmitted between the first and the second part of the sonar and to couple the power supply signal with the signals to be transmitted.It therefore has a dual role because it increases the voltage of the signals to be transmitted and at the same time contributes to the summation of the electrical supply signal with the signals to be transmitted.

Power source A1 is connected via the secondary of transformer TR1. So that the electrical supply voltage is superimposed with the voltage delivered by the transformer, a capacitor C1 is connected in parallel with the electrical supply source. Without this capacity, the voltage delivered by the transformer would return to the power supply, which would have the effect that the submerged part of the sonar would no longer receive any power supply or signals to be transmitted, and would probably destroy the power supply A1. The capacitor C1 mounted in parallel with the electric power source therefore makes it possible to couple the signals to be transmitted with the electric power supply signal.

The communication data is generated / received by a modem 310, and linked to the other signals through a high pass filter 311 (or band pass). This high pass filter, connected so as to separate the modem 310 from the entry of the cable 203, has a much higher impedance than the entry of the cable at the frequencies of the power supply signal and of the signals to be transmitted. Thus, it makes it possible to prevent the signal coupled with the signals to be transmitted and the power supply signal from returning to the modem 310, which directs it towards the power carrier cable 203 and therefore towards the submerged part 202 of the sonar. Advantageously, the high-pass filter is designed so as to withstand the high voltages of the signals to be transmitted, for example by using components designed to withstand high voltage levels,

An inductor L2 is connected between the cable 203 and the transformer TR1, so as to separate the part carrying out the combination of the signals to be transmitted with the power supply signal, from the part dedicated to the transmission of the signal carrying the communication data. This inductance has a high impedance at the frequencies used by the signal carrying the communication data, so as to prevent this signal from returning to the transmitter and the power supply source, which guides it to the cable 203 and therefore to the submerged part 202 of the sonar. The voltages of the three types of transmitted signals are then superimposed.

In this embodiment, the signal combining means 213 therefore comprise the capacitor C1, the high-pass filter 311 and the inductor L2.

The electric carrier cable 203 ensures the mechanical maintenance of the submerged part 202, as well as the transmission of the combined signals through a single transmission line.

The submerged part 202 comprises means 223 for separating the signals transmitted over the power transmission cable 203. In the embodiment described in FIG. 3, these means 223 comprise a high-pass filter 320, comparable to the high-pass filter 311, which has a high impedance at the frequency of the power supply signal and at the frequency of the signals to be transmitted, in order to restrict the propagation of the signals to be transmitted and of the power supply signal by attenuating the low frequencies while allowing the high frequency signals to pass . The role of the high-pass filter is to completely block the propagation of the signals to be transmitted and of the power supply signal, however residues of these signals can nevertheless pass through the filter, which is why it is said that it "restricts »The propagation of these signals. It therefore makes it possible to separate the signal carrying the communication data from the other signals. Advantageously, just like the high-pass filter 311 of the first part 201 of the sonar, the high-pass filter 320 of the second part 202 of the sonar is designed so as to withstand the high voltages of the signals to be transmitted. It is arranged between the power carrier cable 203 and a modem 321, hanging from the modem 310 of the emerged part 201, configured to synchronize with the modem 310 in order to generate / receive the signal carrying the communications data. The modem is connected to acoustic reception transducers (not shown) via amplifiers and, where appropriate, analog / digital converters (not shown). Advantageously, just like the high-pass filter 311 of the first part 201 of the sonar, the high-pass filter 320 of the second part 202 of the sonar is designed so as to withstand the high voltages of the signals to be transmitted. It is arranged between the power carrier cable 203 and a modem 321, hanging from the modem 310 of the emerged part 201, configured to synchronize with the modem 310 in order to generate / receive the signal carrying the communications data. The modem is connected to acoustic reception transducers (not shown) via amplifiers and, where appropriate, analog / digital converters (not shown). Advantageously, just like the high-pass filter 311 of the first part 201 of the sonar, the high-pass filter 320 of the second part 202 of the sonar is designed so as to withstand the high voltages of the signals to be transmitted. It is arranged between the power carrier cable 203 and a modem 321, hanging from the modem 310 of the emerged part 201, configured to synchronize with the modem 310 in order to generate / receive the signal carrying the communications data. The modem is connected to acoustic reception transducers (not shown) via amplifiers and, where appropriate, analog / digital converters (not shown). the high pass filter 320 of the second part 202 of the sonar is designed to withstand the high voltages of the signals to be transmitted. It is arranged between the power carrier cable 203 and a modem 321, hanging from the modem 310 of the emerged part 201, configured to synchronize with the modem 310 in order to generate / receive the signal carrying the communications data. The modem is connected to acoustic reception transducers (not shown) via amplifiers and, where appropriate, analog / digital converters (not shown). the high pass filter 320 of the second part 202 of the sonar is designed to withstand the high voltages of the signals to be transmitted. It is arranged between the power carrier cable 203 and a modem 321, hanging from the modem 310 of the emerged part 201, configured to synchronize with the modem 310 in order to generate / receive the signal carrying the communications data. The modem is connected to acoustic reception transducers (not shown) via amplifiers and, where appropriate, analog / digital converters (not shown).

The signal separation means 223 of this embodiment also comprise two inductors L1 and L3, which have a high impedance at the frequencies of the signal carrying the communication data, and a capacitor C2. The inductance L1 is connected in series with the capacitor C2. The power supply signal A2 is recovered at the terminals of the capacitor C2. The inductor L1 separates the capacitor C2 from the power carrier cable 203. The inductor L3 is connected in series with the one or more

acoustic transducers Tr, which it separates from the power carrier cable 203. The inductors L1 and L3 have a high impedance at the frequency of the signal transmitting the communications data, in order to prevent the propagation of this signal towards the acoustic transmitting transducers Tr and to the components allowing the recovery of the electric power supply A2, that is to say the capacitor C2, and where appropriate the diode D1 and the capacitor C3. Indeed, if in practice the signal carrying the communication data does not interfere with the operation of the acoustic transducers and the power supply, restricting the propagation of this signal to the level of L1 and L3 makes it possible to direct all the power of the signal. transporting the communication data to the modem 321. In addition,

The inductor L1 mounted in parallel with the acoustic transducer (s), the inductor L3, mounted in series with the acoustic transducer (s), and the acoustic transducer (s) which behave like capacitive elements, advantageously form an LC resonator tuned to the frequency. signals emitted by the sonar, so as not to lose power when emitting the acoustic signals. The inductors L1 and L3 therefore form means for tuning / adapting the acoustic emission transducer (s) Tr.

In addition, the inductance L1 is configured to present a sufficient impedance at the frequency of the signals to be transmitted to be able to recover the supply signal alone at the terminals of the capacitor C2.

In one embodiment, the value of the inductance L1 mounted in parallel with the acoustic emission transducer (s) Tr is chosen as a function of the impedance of the acoustic emission transducers at the frequency of the signals to be emitted, so as to what she achieves

mainly the tuning / adaptation of the acoustic emission transducer (s) Tr. The value of the inductance L3 is chosen lower than that of L1, so as not to detune the LC network formed by L1 and the acoustic transducer (s) d 'emission. The role played by the inductor L1 is then twofold: it allows the recovery of the power supply signal by filtering part of the signals to be transmitted and the communication signals, and at the same time contributes to the tuning / adaptation of the acoustic transducers. emission Tr. Using the same inductor L1 to filter the power supply signal and to achieve the tuning / adaptation of the acoustic transducers used for emission,

The inductor L3 does not block the propagation of the supply signal to the acoustic transducer (s) Tr, but these elements are essentially capacitive and do not consume a direct voltage. The power of the supply signal then propagates mainly through L1 to capacitor C2 (and capacitor C3 if applicable).

In this embodiment, the means 223 for separating the signals therefore comprise the capacitor C2, the high-pass filter 320 and the inductors L1 and L3.

The assembly of FIG. 3, in particular the positioning of the inductors L1 and L3, would not be obvious to those skilled in the art. Indeed, the sizing of the two inductors must satisfy a certain number of requirements which may appear contradictory at first glance, namely:

i. L3 must have an impedance much higher than the characteristic impedance of the cable 203 at the minimum frequency used by the signal carrying the communication data, so as not to detune the high pass filter 320,

ii. the impedance of L3 must not be too high at the frequency of the signals to be transmitted, so as not to lose too much power in the acoustic transmission transducer (s),

iii. the impedance of L1 must be much higher than the characteristic impedance of the cable 203 at the minimum frequency used by the signal carrying the communication data, and higher than that of L3 at the frequency of the signals to be transmitted,

iv. the values ​​of L1 and L3 must be chosen so as to achieve the tuning / adaptation of the acoustic emission transducers Tr.

In practice, it is noted that it is possible to determine values ​​of L1 and L3 which satisfy all of the above constraints.

Advantageously, the submerged part 202 can have a diode

D1 and a capacitor C3, arranged so as to filter the power supply signal. This filtering makes it possible to smooth the fluctuations of the electrical supply signal due to the residues of the signals to be transmitted which pass through L1.

The assembly shown in Figure 3 limits to the maximum the number of electronic elements necessary for the implementation of a sonar according to the invention, thus making it possible to reduce its cost, but especially the mass and the volume of the submerged part 202 of the sonar. Of course, the implementation described for the first part 201 of the sonar and the implementation described for the second part 202 of the sonar are independent and can be considered independently.

CLAIMS

1. Sonar comprising a first part (201) and a second part (202) connected by a power carrier cable (203) configured to mechanically support the second part and allow the two parts of the sonar to exchange signals comprising:

a unidirectional signal called a power supply signal (210, 220), by which the first part transmits a power supply to the second part,

unidirectional analog signals called signals to be transmitted (211, 221), transmitted by the first part to the second part with a view to their transmission in the form of acoustic waves, and

a bidirectional signal carrying communication data (212, 222) exchanged between the two parties,

the sonar being characterized in that:

- the first part comprises means (213) for combining the signals configured so that the power supply signal, the signals to be transmitted and the signal carrying communications data are transmitted simultaneously and in different frequency bands on the power cable ,

- the second part comprises separation means (223) allowing the recovery of each of the signals transmitted on the power transmission cable, one or more acoustic emission transducers (Tr), and tuning / adaptation means (L1) of the or acoustic emission transducers.

2. Sonar according to the preceding claim, wherein the combining means comprise components (TR1, C1) configured to couple the signals to be transmitted with the power supply signal.

Sonar according to claim 2, wherein the components configured to couple the signals to be transmitted with the power supply signal comprise a transformer (TR1) configured to raise the voltage of the signals to be transmitted and to couple them with the power supply signal. electric.

4. Sonar according to one of the preceding claims, wherein the combining means comprise components (L2, 311) configured to guide the propagation of the signals in the direction of the power carrier cable (203).

The sonar of claim 4, wherein the components configured to guide the propagation of signals to the power carrier cable (203) include:

- an inductor (L2) configured to pass the power supply signal (210) and the signals to be transmitted (211) and to restrict the propagation of the signal (212) carrying the communications data, said inductor being connected between d ' on the one hand the power transmission cable, and on the other hand elements for generating the signals to be transmitted (TX) and for generating the power supply signal (A1), and a filter (311) configured to pass the signal carrying the data communications and to restrict the propagation of the power supply signal and the signals to be transmitted, said filter being connected between the power carrier cable and a signal generator carrying the communications data (310).

6. Sonar according to one of the preceding claims, wherein the separation means (223) comprise an inductor (L1) configured to separate the power supply signal from the other signals.

transported by the power carrier cable (203)
contribute to the tuning / adaptation of the acoustic transducer (s).

7. Sonar according to claim 6, wherein the inductor (L1) configured to separate the power supply signal from the other signals and to achieve the tuning / adaptation of the acoustic emission transducer (s) is connected in parallel with the or acoustic transducers (Tr) and is connected between the power carrier cable (203) and a capacitor (C2) with which it is mounted in series, the electrical supply signal being recovered at the terminals of said capacitor.

8. Sonar according to one of claims 6 and 7, wherein the inductor (L1) configured to separate the power supply signal from the other signals and to achieve the tuning / adaptation of the acoustic emission transducer or transducers is configured to pass the power supply signal (220) and to restrict the propagation of the signal (222) carrying the communications data and the signals to be transmitted (221).

9. Sonar according to one of the preceding claims, wherein the separation means (223) comprise:

an inductor (L3) configured to pass the signals to be transmitted (221) and to restrict the propagation of the signal (222) carrying the communications data, said inductor being connected between the power carrier cable (203) and the acoustic transducer (s) d 'emission (Tr), and

a filter (320) configured to pass the signal carrying the communications data and to restrict the propagation of the power supply signal (211) and of the signals to be transmitted, said filter being connected between the power carrier cable and the modulation / demodulation element of the signal carrying the communications data (321).

10. Sonar according to one of the preceding claims, wherein the signal carrying the communication data is modulated by a zero-mean modulation.

11. Sonar according to one of the preceding claims, wherein the modulation of the signal carrying the communication data uses orthogonal frequency division multiplexing.