DE1566867B2 - Method and device for underwater echo sounding - Google Patents

Description

The invention is based on a method for underwater sound and on universal application during all stages of a cruise.

It is here z. B. to consider the voyage of a supertanker. Such ships have one very large draft, for which hardly any port has been designed. Most of the time it has to be as close to the coast as possible be anchored in order to discharge the cargo by means of a pipeline ending at a buoy. To as possible The ship's guides also have a special way of getting far into the harbors or the coast Technology developed to drive over individual silt or sand banks with keel contact. Here However, the sea floor must be free of stones and the keel or the ship floor must not be closed Cut deeply so that the propeller's advance is still sufficient, the increased resistance to movement to overcome. It is clear that such, at the limit of what is just possible lying maneuvers can only be carried out if perfect measurement results about the water depth below the keel and statements about the nature of the seabed are available to the ship's command.

On the other hand, the other stages of a voyage include seas of shallower depth, such as the North Sea and the Baltic Sea, and the oceans are also navigated with very great water depths. A distance range from a few centimeters to one or more kilometers, that is to say a distance ratio of 1:10 ⁵ , must therefore be precisely recorded by an echo sounder system.

But the problem also arises in fishing, very different distances due to echo sounding capture. Once a school of fish is said to be horizontal in a fjord, then again in a shallow one Shelf Sea (e.g. North Sea) and also in the ocean.

The range of an echo sounder is, however, both towards large distances and in relation to limited distances so that existing echo sounder systems are not used during all stages of a Cruise are applicable. However, this is made possible by the invention.

According to the method according to the invention, at least two solder pulses are generated with respect to their beginning of different duration and frequency sent out simultaneously or almost simultaneously, with a higher one Frequency the shorter duration is to be assigned. Furthermore, those reflected from the underwater objects are reflected Echo pulses received separately in time and amplified separately in time. But here are all reception channels except the one for the highest frequency from the beginning of the plumbing period disable or switch off. Furthermore, the blocked or switched off reception channels are then in the sequence of falling frequencies controlled by a clock during the course of the soldering period to open or turn on, and finally the echoes of different frequencies are spatial in the correct time consecutively on a common display area.

It is known per se (German patent specification 1017 054), two plumbing with different Perform frequencies at the same time. However, this is about the separate recording of dense fish standing above the seabed as well as individual layers of the seabed. Except the other The task at hand are these ground plumbing on the same underwater object or in close proximity Directed underwater objects should therefore receive during the entire plumbing period. In contrast the invention divides the soldering period into sub-areas and one for each of these sub-areas own sound frequency and solder pulse duration assigned, with the initial part with the highest Frequency and the shortest solder pulse duration and the

ίο last subrange with the lowest frequency and the longest solder pulse duration must be provided.

As a result, each individual sub-area can be optimally explored, and still appears on the writing surface contiguous for the entire soldering period. It is also ensured that the individual sub-areas the records to be assigned do not interfere with one another. For example, is great for a Range, a low sound frequency is required because this means that the solder pulse is less attenuated, as well as a longer solder pulse, because this means that a smaller bandwidth of the amplifier can be used, whereby the noise voltage drops. However, this results in a for extremely short distances Too long zero sound, which is already longer than the distance to be recorded, and the settling times the individual parts of the echo sounder are too large, so that no longer acceptable misdirections arise in the ad. On the other hand, the limit of the shortest soldering distances can be reduced to a few Push down centimeters when using high sound frequencies. Then he can too The zero sound to be recorded can be kept short enough, and the noise voltage hampers despite the then not required larger bandwidth.

A two-fold subdivision of the entire lot period already results in a satisfactory expansion of the distance range that can be detected by the plumb system to both sides, so that all stages a ship voyage, especially a super tanker or fishing vessel, can be closely monitored can.

The method according to the invention is expediently carried out with a division the control or switching pulse program that effects the soldering period. Appropriately is a with the To use display device synchronous clock to trigger another pulse generator. This pulse generator generates the control or switching pulse program, which according to the invention consists of soso there is a lot of consecutive control or switching pulses, such as different frequencies and the total duration of which corresponds to the plumbing period. Also is the first impulse this control according to the invention: · 'and switching pulse program to open the receiving channel for the to use the highest frequency or the blocking of the other receiving channels and the following one in time Impulse for successive opening of the following channels in frequency or the blocking of the other reception channels whose frequency is currently not to be made ready for display.

Such a design, it is also possible at the same time, already in use or in the Equipping existing echo sounder systems in accordance with the invention. Other advantages of the invention are explained on the basis of the exemplary embodiments shown in the figures. It demonstrate

Fig. 1 and 2 examples of subdivisions according to the invention of a solder period,

(Fig. 3 shows a block diagram of an inventive Echo sounder system,

F i g. 4 shows a monostable multivibrator for use as the pulse shaper of FIG. 3 and

F i g. 5 shows another embodiment.

In the diagrams of Fi, g. 1 and 2, the sound propagation time t is plotted on the abscissas. A plumb period extends from the beginning t _{0 of} a transmission pulse to the beginning t ₀ * of the following transmission pulse. Lines A to F show a division of the plumb period into three time segments according to the invention, each of which is to be explored separately with plumb pulses of different lengths and different frequencies. These time segments correspond to distance segments in the water.

In row C, 1 shows a transmission or solder pulse of medium duration, about 2 m / sec, and medium frequency, about 30 kHz, as is commonly used. The choice of these two dates represents a compromise by means of which a large distance range can be covered. This distance range is extended considerably by the invention both towards short distances and towards long distances. A first section (line B) extending from t _t to t ₂ is plumbed by a very short solder pulse 2, about 0.05 m / sec long, of high frequency, about 150 to 200 kHz. It becomes clear that the time t _v from which echoes can already be recorded would still lie within the normal, at least ten times longer plumbing pulse 1, so that in principle, with the usual plumbing (line C), such short distances can never be explored, As with the transmit pulse 2. A shortening of the solder pulse 1 is not possible because a certain length is necessary in order to be able to store the sound energy necessary for the generation of sufficiently strong echoes with the possible energy density in the sound wave packet sent into the water. On the one hand, this is easier with the solder pulse 2 because of its much higher frequency and, on the other hand, it is also not necessary to the extent that it is not intended to sound out larger distances; it can be grown at very close distances or shortened in length. The end of the plumbing pulse 2 or the earliest possible reception start of echoes at the time t _t , which coincides with it, corresponds to a plumbing distance of approximately 4 cm with a plumbing pulse duration of 0.05 m / sec.

In contrast, a transmission pulse 1 is about 2 m / sec in duration - if it is to reach far enough, it is possibly even longer to choose - forty times as long and could therefore only from a minimal distance from 150 cm. In practice, however, this distance is postponed even further because of the normal pulse 1 acting for great distances because of its great strength post-oscillation - revibration— that have yet to subside. This can normally only be done with a minimal amount of solder of 200 cm can be expected. But this is a lower distance limit for supertankers is way too high. Such ships have to be under water in ports with only a few centimeters drive the keel or even with soft mud banks with ground contact. For example is the port Hamburg in this way, and if the tidal wave is exploited at the same time, for essential larger tankers can be reached than when using the usually without precise knowledge of the true distance and the nature of the seabed, the required safety distance between the keel and the seabed is driven.

The two transmission pulses not only need to differ in their length and frequency, but also are expediently also sent out with a different energy content, with the for near Solder pulse 2, imaginary distances, needs to have a significantly smaller amplitude.

The two soundings by means of the frequencies Z ₁ and Z ₂ work together as follows: The beginning of the two solder pulses 1 and 2 are sent out simultaneously. The receiver for Z _{1 is} to be blocked for the transmission time i _o -i _t. Furthermore, from the shortest transmission pulse 2, z. B. from its generator to derive a write voltage for the zero mark on the common display area. The selective receiver for Z ₁ is opened for the time t _t -t ₂ . The easiest way to do this is by means of an opening pulse 3 (line B), which is applied, for example, as an additional positive control voltage to the grid of an amplifier tube which is otherwise permanently blocked by means of a negative DC bias. The solder pulse 1 of the second, far away frequency / ₂ , which still extends considerably into the opening time t _x -t ₂ - for reasons of space, the difference cannot be shown to scale in the drawing - but cannot generate any voltage _{in the selective input of the receiver for Z 1 and} therefore do not bother.
On the other hand, the selective receiving amplifier for Z _{2 is} ^{only opened a} b h and protected against interference from its own strong transmit pulse 2. In addition, the better resolution due to the shorter duration of the solder pulse 2 during the time t _t -t _{2 is} not spoiled again by recordings that originate from the significantly longer and therefore significantly poorer resolving solder pulse 1.

The receiver for the second frequency is expediently only opened at t ₂ . How long it stays open depends on how many other frequencies are still used. If you are satisfied with a total of two frequencies - this already results in considerable advantages, especially for the supertanker trip - then you will allow the opening to f ₀ * (line G) to utilize the solder pulse sequence. In the case of further and lower frequencies, the amplifier for Z ₂ closes at the beginning of the next frequency. Another frequency Z _{3 is} assumed in FIG. 1.

The frequency Z ₃ does not begin until time t ₃ , when the echoes originating from the pulse 1 would already be too weak or too noisy. Before this, the sounding with the frequency Z _{2 is} ended by means of the control pulse 4. The remainder of the plumbing period is sounded out by means of the very long, about 10 to 20 m / sec, plumbing pulse 5 at a very low frequency, about 10 kHz. As a result, the normal range, which is approximately at t ₃ , is pushed out a little further. 6 is the opening pulse (line F) for the gain channel relevant _{for the last frequency Z 3.} This achieves the oversized ranges, which are particularly interesting for horizontal plumbing, so that the ship's course is aligned in good time

can be made out to a far ahead Catch school of fish with the trawl.

The three control pulses 3, 4, 6 simultaneously demonstrate the division of the display area as they do each of the echoes of a frequency can be described one after the other. Through this inventive division the soldering period or the soldering distance in partial areas, which are preferably connected to one another, on the one hand, the entire area is considerably expanded and, on the other hand, each sub-area is optimally explored; because close distances or long distances can best be dealt with with very different Record properties of the solder impulses. So for great distances a low frequency, long plumb pulses because of the lower attenuation in the water and to lower the Aimed for a smaller noise bandwidth; while, on the other hand, a short solder pulse at short distances is necessary because otherwise the plumbing times fall within the duration of a longer transmission pulse would. But then a large bandwidth is required and, because of the small amount of the Sound wave to traversed interference volume can also be recorded. Therefore, with the invention Division of the plumb period not just an area expansion, a shift in the front and rear limit, but a division on the recording surface such that the At short distances the resolution increases and at long distances the signal / noise ratio increases is improved.

However, the invention is not limited to the division shown, but is capable of even more diverse designs, in particular an even more extensive division than into three sub-areas is advantageous, although a single division, i.e. the division into two sub-areas, already achieves significant advantages. So it is enough z. B. for supertankers, add a front sub-area corresponding to plumbing / ₂ , while an additional rear sub-area corresponding to plumbing / _{3 is} interesting for horizontal plumbing. It is also pointed out that the timing of the F i g. 1 does not claim to be true to scale.

Furthermore, it is not necessary for the transition between the individual sub-areas to abruptly adjoin one another, as in FIG. 1 drawn, but it can also run into one another, as shown in FIG. 2 represents advantageous. During a transition time t ₄ -t ₅ , the sounding of the shorter frequency / _{4 is} falling and the sounding of the normal frequency / _{5 is} increasingly and simultaneously effective on the display surface. It is also not necessary, as shown in FIG. 2 drawn, the decrease and increase times coincide. Another variant is in connection with the in F i g. 3 illustrated echo sounder explained.

Here, 11 denotes a display device. A writing device is shown, albeit the invention can also be used advantageously for cathode ray display devices. 12 is an electrically sensitive recording paper that moves gradually from left to right after each plumbing is passed over a metal, earthed desk 13. Runs across this indexing device a pen 14 over the recording paper to which the electrical writing voltage is applied. The stylus is carried by a continuously revolving, non-conductive belt 15 and grinds with its other End on a busbar 16. The spatially adjacent recordings of the plumbing period result the so-called echogram on the recording paper 12.

According to the invention, the individual soldering periods are now divided. In the case of the echogram, this results in a horizontal division of stripes, of which in FIG. 3 an example with two strips A and B is drawn. The echogram strip A is sounded out by means of a high frequency of approximately / * = 180 kHz and the other echogram strip B is sounded out at a commonly used frequency / = 30 kHz or is described by the echoes that arise during sounding. Here, the zero line 17 is recorded solely by the very short high-frequency transmission pulse. The fact that the two echogram strips A and B overlap somewhat serves primarily to simplify the circuit. In addition, the floor contour 18 is accentuated in the overlap area due to the higher frequency of the writing voltage increased by the floor echoes. The overlap area is also suitable for adjustments.

It becomes clear that because of the extraordinary possible at the high frequency of 180 kHz Shortness of the plumbing pulse of about 0.1 m / sec and the zero line 17 can be written very narrow, so that the sea floor elevation 19, which is only a few centimeters below the keel, is still flawless can be recorded.

A clock generator 21 runs synchronously with the recorder, indicated by the dashed line 20 Clock provides electrical impulses. These can be generated mechanically by, for example, a Switching cam on the belt 15 actuates an electrical switch contact, which has a short electrical Impulse supplies. Depending on the requirements, the electrical Pulse can be converted into an exact square pulse by a Schmitt trigger. The clock pulse solves both the transmitter 22 for the low frequency / and the transmitter 23 for the high frequency / * at the same time. 24 and 25 are the associated transmission transducers that generate the electrical transmission pulses and convert sound impulses and transmit them into the water. At the same time, the transmitter becomes 23 from the short high-frequency solder pulse a marking voltage for writing the zero mark 17 derived: line 26.

27, 28 are the receiving transducers and 29, 30 are the associated receiving channels. The second receiving channel 29 of medium frequency is to be blocked, according to the strip division B. To obtain the correct time interval, a pulse shaper 31 is arranged between the clock generator 21 and the receiving channel 29. As a result, neither the relatively long transmission pulse - about 2 m / sec duration - nor the correspondingly long echo pulses can interfere with the distance resolution at the beginning of the plumbing period. However, this is a particularly important distance range for supertankers, which extends down to a few centimeters.

Furthermore, the invention is based on the knowledge that the simultaneous transmission of several, in particular the two plumbing pulses are not readily given, although the two transmitters from the same clock. Nevertheless, there are still misconceptions in the

show that can be attributed to different emission are. This is remedied by a pulse shaper 32 to which the clock generator 21 acts between clock generator 21 and transmitter 23 for the higher frequency, for converting the clock pulse for the so much delayed triggering of the transmitter 23 higher frequency that the first full Amplitude of all sound transmission pulses in the water with the first full amplitude of the sound transmission pulse coincide in time with the lowest frequency in the water. This takes into account the fact - which has not yet happened - that a transmitting device for high sound frequencies is bred for rapid settling. Since then If the operation takes place in a pulsed manner, there are also different frequencies in the case of the transmission devices of different frequencies Settling times in which the mechanical vibrations of the converter and the Transfer to the water are to be included, · The invention thus ensures that various The times until the full amplitude of the sound pulse is reached in the water is balanced so that a clear, common reference point is obtained for the measurements.

The coincidence can be precisely adjusted by means of an adjustable design of the delay time of the pulse shaper 32. The overlap area of the bottom echogram strips A and B is used as an indicator for the correct adjustment. In FIG. 3 the leading edge 18 of the sea floor was used. For the adjustment, the handle 33 of the pulse shaper 32 is drawn.

Furthermore, there is the possibility of making a later transmission of the transmission pulse with a lower frequency, which differs only slightly in time, and in particular is precisely defined. This allows z. B. write a more or less sharply separated sharp contour line from the sea floor through the higher frequency. The white band-shaped space in between then highlights the sea surface in the display. This so-called "white line" is an advantageous type of recording known per se, for which separate and different devices are otherwise required (German patent 1136 248). In the present invention, this type of recording can be achieved by the way. It only needs to be changed from the simultaneous transmission of the two transmission pulses to an almost simultaneous transmission. This transition is possible at any time optionally and / or with a great number of gradations, for example by means of the handle 33. D ₁ , D ₃ are isolating diodes in order to prevent the two positive write voltages fed to the busbar 16 from affecting one another.

The program control in the embodiment of FIG. 1 essentially only provides for the blocking of the receiving channel 29 for the lower frequency for a part at the beginning of the plumbing period. Here, the knowledge is used that high sound frequencies have only a limited range under water, so that it is not actually necessary to end the strip A by controlling or switching. If an abrupt limitation of the sub-range for the high frequency is desired, a z. B. over the blocking time of the channel 29 for the lower frequency reaching opening pulse to the normally to be blocked receiving channel 30: line 34.

It should also be noted that the bottom echo 18 of the higher frequency can be written more prominently, especially for the overlap zone of the two strips A and B , if it is used in a differentiated form. For this purpose, the demodulated received voltage is to be fed through one or more IC elements, the time constant of which is so small that. not the entire echo signal is transmitted via the coupling capacitor C, but essentially only the parts of the large rise, so z. B. the ground contour. The circuits to be made for the transmit and receive channels are common technology and are therefore not shown in detail. Also in the more detailed explanations of the pulse shapers 31, 32 - z. B. monostable multivibrators - these are standard circuits, the further explanation of which is unnecessary, but they should be shown in FIG. 4 will be briefly described.

In FIG. 4, the pulse shaper 31 is represented by a monostable multivibrator formed by means of the two npn transistors T ₁ and T _2. The line 35 coming from the clock 21 (FIG. 3) initially leads via a network that _{differentiates the key pulse C 1} and the resistors, thus converting it into a needle pulse that coincides with its leading edge, also by means of the diodes D ₄ and D. _{5 is} freed from the negative components, in particular the trailing edge, in order to open the negatively biased, locked base of T _1. Then a negative pulse can be taken by means of the line 36, which is used to block the receiving channel 29 35 '(Fig. 3), and by means of the line 34 a temporally coincident positive pulse that can be used to open the receiving channel 30 . The time constants that determine the pulse duration of the monostable multivibrator are selected in such a way that they correspond to the desired subdivision of the plumbing period.

For the pulse shaper 32, the principle of FIG. 4 use, as it was indicated for the pulse shaper 31, only the dimensioning is to be chosen significantly different, so that much shorter pulses result. Furthermore, for other uses for triggering the transmitter 23, the output pulses must be differentiated. To this end, the output is to be followed by the i? C element C ₂ , R ₂ , as shown in FIG. 4 is shown on the left. If, as shown, the negative output pulse is used - earlier line 36 - _{a positive trigger pulse results after the diodes D 6} , D ₇ , the timing of which corresponds to the rise of the negative output pulse of the monostable multivibrator. This derived positive trigger pulse is thus delayed compared to the original positive trigger pulse (input 35 or 37). This delay can be varied by an adjustable change in the time constant of the monostable multivibrator, for example by means of the resistor R _1. This is because the point in time of the tilting back, that is to say the temporal position of the trailing edge, is determined.

If the positive output pulse is assumed (line 34), the _{polarity of the diodes D 6} , D ₇ must be reversed, and an inverting stage is required to get off the falling trailing edge of the positive

009 544/207

Output pulse to gain a positive trigger pulse again. .

The invention is in no way restricted to the embodiments of FIG. 3; Fig. 5 therefore shows a Another exemplary embodiment: Here, a common receiving amplifier is used for at least two frequencies. This one needs at least one Switching stage 40. The following stages can, for example, be designed as .RC amplifiers. It is useful to tune at least one level of this to all frequencies simultaneously but discretely. :.

In the example of FIG. 5, an oscillating circuit L ₃ , C ₃ , which is tuned to the lowest frequency, is short-circuited in the switching stage by a transistor T ₁ to one part, e.g. the oscillating circuit coil, whereby the switchover to the higher frequency takes place Switching transistor T ₁ is of the npn type and its emitter-collector path lies _{parallel to one part, the resonant circuit coil L 3.} At the base, it is permanently blocked by means of a negative bias voltage and is only used for one part of the time that can be assigned to the higher frequency The soldering period is opened by the positive switching or control pulse. With this measure, the two frequencies are alternately amplified .:

The further amplifier stage 41 is "arranged on both frequencies gain, although of course these two frequencies arrive in sequence. For this purpose, two of the respective frequency" for the simultaneous but discrete parallel tuned resonant circuits L _4, C ₄ and Lj ,: C ₅ provide in series so that there is enough resonance for each frequency to get enough voltage. Nevertheless, compared to a broadband or AC amplifier, there is the possibility of obtaining optimal signal-to-noise ratios through a suitable choice of bandwidth - a small bandwidth for the low frequency and a large bandwidth for the high frequency.

Finally, the output voltage is sent to the output amplifier stage 42 and from this to the recorder 43 fed. 44, 45 are selective amplifiers or just simple separators for the two frequencies for decoupling the two receiving transducers 27, 28. Ohmic resistances are sufficient for this, and one consisting of two resonant circuits in series is shown Crossover.

As a generator for. the switching voltage is provided by a contact strip 46 fixed to the housing and having a length that corresponds to the duration of readiness to receive the highest frequency. The same effect can be achieved with the complementary piece 46 a if the voltages - reverse voltage at transistor T ₁ and voltage for the contact - are reversed. 47 is the trigger contact for the transmitter 22, 23. In the event, as shown, that a positive switching pulse is required for the transistor T ₁ , the counter electrode 48 can be carried out jointly with that for triggering the transmitter; otherwise it is to be divided like 47, 46. For example, if you wanted to switch capacitor C _{3 instead of coil L 3} - short-circuit one of two series capacitors through T ₁ - a negative voltage source for a pnp transistor would be required for contact strip 46 because the short circuit of one series capacitor never has a lower frequency results, or it would be the complementary contact strip 46 α to be used with a positive voltage source. .

. The contacts are closed by a contact bridge 49. This is easiest to connect to deni Straps 15 of the pen attached. Of course there are also others, physically separated from the writer, but possible with this synchronized switch. An example is the arrangement of the contacts in the form of a slip ring and the formation of the bridge 49 as a grinder mentioned; the drive can be from one with the recorder common motor, so that the synchronization would be given properly.

Claims (8)

Patent claims: 1. Echosounder method for underwater sound and for universal use for all during of all stages of a voyage: those from extremely small to large values reaching distances, marked by those which are simultaneous with respect to their beginning or almost simultaneous emission of at least two solder pulses of different duration and Frequency, the shorter duration being assigned to a higher frequency, and the time-separated one Reception and the temporally separated amplification of the underwater objects reflected echo pulses, furthermore the blocking or switching off of all reception channels except the one for the highest frequency from the beginning of the plumbing period, furthermore the successive one, from one Clock controlled opening or activation of the blocked or deactivated receiving channels during the expiry of the soldering period in the order of falling frequencies and finally the spatially in the correct time successive display of the echoes of different Frequencies on a common display area. 2. Echosounder method according to claim 1, characterized by the recording of a zero mark on the common display area solely by means of the transmission pulse of the shortest duration. 3. Echosounder system with one transmitting and one receiving channel each for at least two different ones for simultaneous and rectified underwater plumbing, as well as a common display device and a common clock synchronous with the display device for simultaneous Triggering the transmission pulses of different frequencies, in particular to carry out the Method according to Claim 1 or 2, characterized by one to be triggered by the clock generator Pulse generator with as many consecutive control or switching pulses as .different ones Frequencies are used and with a total duration corresponding to the plumbing period this control and switching pulse program, as well as the use of the first pulse of this Control and switching pulse program to open the receiving channel for the highest frequency or the blocking of the other receiving channels and the use of the subsequent pulses for the successive opening of the receiving channels or the Blocking of the other receiving channels whose frequency is currently not ready for display shall be. 4. Echosounder system with two transmit and receive channels with different sound frequencies according to claim 3, characterized by a pulse shaper acted upon by the clock generator (21) (31) for converting the clock pulse into a following and temporally over the first sub-range the blocking pulse extending over the solder period for the lower frequency receiving channel. 5. echo sounder system according to claim 3 or 4, characterized by at least one of the clock generator to be applied pulse shaper (32) for converting the clock pulse into a delayed one Clock pulse for the so much delayed triggering of a transmitter of higher frequency that the first full amplitude of all sound transmission pulses in the water with the first full amplitude of the Sound pulse of the lowest frequency * coincide in time in the water. 6. echo sounder system according to claim 3, characterized by one for at least two frequencies containing a common receiving amplifier, at least one switching stage (40) to be actuated by the switching or control voltage for the assignment of the frequency associated with the respective soldering range and at least one the other frequencies simultaneously tuned amplifier stage (41). 7. Echosounder system with a display device containing a writing strap and after a of the preceding claims, characterized by the arrangement of at least one contact strip (46) with such a length as the length of a sub-spot area assigned to a frequency is equivalent to. 8. echo sounder system according to claim 6, characterized by the common arrangement of resonant circuits fixedly connected to the circuit (L ₄ , C ₄ , L ₅ , C ₅ ) for the individual frequencies, with a bandwidth that decreases with the frequency. 1 sheet of drawings