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Publication numberUS3435407 A
Publication typeGrant
Publication dateMar 25, 1969
Filing dateJun 24, 1966
Priority dateJun 29, 1965
Publication numberUS 3435407 A, US 3435407A, US-A-3435407, US3435407 A, US3435407A
InventorsJean Bertheas
Original AssigneeCsf
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High speed system for processing long range sonar pulses
US 3435407 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

March 25, 1969 1 J. BERTHEAS 3,435,497

HIGH SPEED SYSTEM FOR PROCESSING LONG RANGE SONAR PULSES Filed June 24, 1966 Sheet of 3 TRANSMTTER RECEIVER D15 PERSWE NETWORK FIGJI March 25, 1969 J. BERTHEAS 3,435,407

HIGH SPEED SYSTEM FOR PROCESSING LONG RANGE SONAR PULSES Filed June 24, 1966 Sheet 2 of 3 arch 25 1969 J. BERTHEA HIGH SPEED SYSTEM FOR PROCESSING LONG RANGE SONAR PULSES Filed June 24, 1966 Sheet United States Patent 3,435,407 HIGH SPEED SYSTEM FOR PROCESSING LONG RANGE SUNAR PULSES Jean Bertheas, Paris, France, assignor to CSF Compagnie Generale de Telegraphic, a corporation of France Filed June 24, 1966, Ser. No. 560,340 Claims priority, applicrtzio mFrance, June 29, 1965,

Int. Cl. G01s 9/66 US. Cl. 340-3 8 Claims ABSTRACT OF THE DISCLOSURE Long-range sonars operate at a transmission frequency of a few kilocycles per second, and have a high radiation energy and a comparatively long listening period. In order to obtain a satisfactory signal-to-noise ratio without impairing the accuracy in localizing the target, the transmitted pulse is linearly frequency-modulated so that it may be of several tenths of second. This time interval is means of a suitable dispersive network.

However, when applied to long-range sonars, the pulse compressing technique meets with many difficulties, because the dispersive lines actually used as compression networks do not permit, as is known, of the desirable compression rates at frequencies of some kc./s.

On the other hand, with the long ranges of the sonar, the listening period between two successive transmissions may be of several tenths of second. This time interval is wasted if the received signals are treated separately in a plurality of decoding channels. In the present day technique, the problem is of dealing rapidly with compressed pulse sonar signals with a duration of some hundred milliseconds, a recurrence period of some tenths of seconds and a center frequency of some kilocycles. This processing can be made with a dispersive line of reasonable size and operating at higher frequencies with pulses whose length cannot normally exceed ten milliseconds.

According to the invention there is provided an information processing system for time multiplexing a plurality of simultaneously available variable sequences of N information items, said sequences being periodically repeated, said system comprising: means for recording said items at a first speed and playing them back at a second speed, said second speed being at least N times higher than said first speed; means for sequentially operating said recording and playing-back means in respective synchronism with said sequences; said recording means having at least N inputs for respectively collecting said N information items; said playing-back means having at least N outputs for reading said information items; switching means having at least N inputs, respectively connected to said playing-back means outputs, and one output; and means for sequentially connecting said switching means output to said switching means inputs for sequentially providing said information items at said switching means outputs.

For a better understanding of the invention and to show how the same may be carried into effect, reference will be made to the drawings accompanying the following description and in which:

FIG. 1 is a diagram of a long-range sonar system using frequency compression;

FIG. 2 shows the oscillograms of frequency modulated wave pulses at the input and at the output of a dispersive network;

FIG. 3 is a diagram of a system according to the invention; and

FIG. 4 is a diagram explaining the operation of the system according to the invention.

FIG. 1 shows a simplified diagram of a long range sonar. It comprises a transmitter-receiver 1 supplying a hydrophone array 2. Array 2 transmits ultrasound waves which are frequency modulated and are radiated according to a broad radiation lobe, such as that traced in dotted lines. A hydrophone receiver array 3 is coupled to the transmitter-receiver 1 by a plurality of channels to which correspond respectively the reception lobes 4, 5, 6, 7, 8, 9 and 10 arranged in fan shape. For the sake of clarity the lobes are shown as clearly separated from each other, although in actual practice they are very close to each other. Targets 11 and 12 are assumed to lie in the zone explored by the sonar and reflect wave trains towards the hydrophone group 3. The latter transducer converts them into reception signals which propagate along the corresponding channels towards the transmitter-receiver 1. Each of these signals is applied, after amplification, to a dispersive network 13, which compresses it and supplies compressed pulses by means of which the targets can be displayed in an azimuth-distance presentation, on an indicator 14. At regular intervals, the group 2 radiates a frequency modulated wave pulse which is propagated towards the targets 11 and 12 from which it is reflected towards the group 3. The channels corresponding to the lobes 5 and 8 are the seat of reception signals which, after amplification, are available at the input of the dispersive network 13. In FIG. 2 is shown at (a) the frequency modulated wave pulse transmitted by the transmitter-receiver 1 and applied to the input of the dispersive network 13; and at (b) the same signal is shown after compression, i.e. at the output of this network. In known systems, this information processing must be effected separately for each receiving channel, which requires a plurality of channels according to FIG. 1. More particularly, it is necessary to provide as many dispersive networks as there are lobes in the reception diagram of the hydrophone array 3. This becomes prohibitive when a great accuracy in the angular localization is desired, without sacrificing the distance measurement accuracy. In order to overcome this drawback, the invention provides a device for multiplexing in time the reception signals so as to process them successively in a single compression channel. This also results in a much better utilization of the listening time and of the compressing system.

FIG. 3 shows a diagram of a long-range sonar according to the invention. It comprises a transmission hydrophone array unit 2 and a reception hydrophone array unit 3 with m aligned transducer elements. These elements are connected to a pre-amplifier unit 15 whose outputs supply m inputs of a receiving channel formation matrix 16. This matrix, which is of a known type, comprises phase-shifters and an interconnection which makes it possible to obtain at its N outputs the decoupled reception signals respectively incoming from N directions, to which correspond the lobes 4, 5, I O of FIG. 1. Amplifiers 17 assure the further amplification of these signals which are made available at the N outputs 4 to 10. A set of twoposition change-over contacts 18 switches the preformed channels either to a first assembly 19 of N-magnetic recording heads, or to a second similar assembly 20. The said recording heads 19 and 20 are, respectively associated with magnetic drums 21 and 22 carrying N erasable tracks and at least one prerecorded track on which the acoustic pulse to be radiated has been recorded once for all. The drums 21 and 22 are driven in uniform rotation by high speed motors 27 and 28 and low speed motors 29 and 30. Electromechanical clutches 23, 24, 25 and 26 permit the selection of one or the other rotational speed for each drum. The reading out of the tracks recorded on the drums is made by means of reading heads 31 and 32 with regard to the pre-recorded track, and head groups 33 and 34 with regard to the other tracks.

The reading system is completed by a set of rotating switches 36, 37 and 38, whose respective sliders are driven by a common reducer 35 at half the slow rotational speed of the drums. The switch 38 has two fixed contacts which are respectively connected to the outputs of the reading heads 31 and 32 associated with the pre-recorded tracks.

The slider of the switch 38 supplies the amplifier 39 connected to the power stage 43 of the sonar transmitter.

The slider of the rotary switch 37 supplies the receiver amplifier 40. The switch 37 has two groups of N contacts. The contacts of each group are respectively connected to the reading heads of groups 33 and 34.

The switch 36 has its slider permanently connected to a supply (not shown) and has two contacts. Through its contact A it controls the clutches 23 and 26 and contacts 18 to bring them into position A. Through its contact B it controls the clutches 24 and 25 and contacts 18 to bring them into position B.

A mixer 41 receives the signals coming from a local oscillator 42 and from the amplifier 40. The resulting signal is applied to the dispersive network 13 which compresses it. After detection by the detector 44, the compressed signal is applied to the indicator 14 whose angular and radial sweeps are synchronized with the rotation of the switch 37 by means of a control input 45.

Since the operation of the device of FIG. 3 is cyclic, it will be assumed that the process is started when the slider of the switch 36 starts engaging its contact A. FIG. 4(a) shows diagrammatically the two states A and B which are successively provided according to whether the slider of switch 36 engages its contacts A or B. During the phase A, the switch 38 connects for a time interval the reading head 31 to amplifier 39. The drum 21 rotates at high speed, and the pre-recorded track supplies a linearly frequency modulated signal which is applied to the transmitter, comprising the amplifiers 39 and 43 and the hydrophone array 2. An ultrasonic wave train is radiated as shown at (b) in all directions of the zone covered by the sonar. During the same time interval T, the drum 22 rotates at slow speed and the recording heads 20 are connected to the receiver hydrophone array 3, through the pre-amplifiers 15, the matrix 16, the amplifiers 17 and the contacts 18 which are in position A.

The transmitted radiation is reflected by the targets 11 and 12, located, for example, in the lobes and 8 of FIG. 1, and one obtains in the receiving channels 5 and 8 signals delayed by A and A, respectively. These signals are shown in FIG. 4 at (c) and (d) respectively. Obviously, their delay with respect to the starting of the radiated pulses measures the distance between the targets and the sonar system. Their position among the receiving channels corresponds to the direction of the reception. These signals are recorded on the drum 22, whose tracks pass at low speed past the heads 20.

When the slider of the switch 36 has completed a halfrevolution, the state A is abruptly replaced by the state B; the speeds of the drums change and change the heads which receive the signals. The drum 22 now assumes the rapid rotation-a1 speed which is at least N times higher than the slow speed, where N is the number of receiver channels to be multiplexed. It follows that each of the tracks, which have received a recording during the preceding phase, passes N times the reading heads 34. The reading time for the recorded information changes from T to T/ N and all frequencies of the spectrum of the read out signal are multiplied by N. Since the switch 37 advances by one step, i.e. by one contact for each revolution of the drum 22, the slider delivers successively the recorded signals corresponding to the receiving channels 4, 5, 6, 7, 8, 9 and 10. FIG. 4 shows at (c) the reading signals available on the slider of the switch 37. Due to the fact that the drum rotates N times faster than during the transmission phase, the time is divided by N. These signals appear with their respective delays with respect to the beginning of each cycle corresponding to the respective distances of the targets from the sonar. The succession of the channels corresponds to a sweep or scan of the space by the lobes of the hydrophonic unit 3 and this scanning is repeated in the indicator 14 in synchronization with the switching action of the switch 37 The succession of the channel signals is equivalent to a signal received from a unique lobe in azimuthal scanning with a transmitted pulse whose frequency and duration are respectively multiplied and divided by N, and which propagates in a medium whose sound velocity is N times the sound velocity inlwater.

The multiplexed signals delivered by the switch 37 are amplified by the amplifier 40; they are mixed in the mixer 41 with the signal of the local oscillator 42 before reaching the dispersive network 13 where they are successively compressed. The operation introduces a time delay T which is shown at (f) in FIG. 4, showing the compressed signals after having been detected by the detector 44. These signals are applied to the indicator 14 and modulate the scanning beam in accordance with the angular and distance location of the targets.

By way of a non-limitative example, the invention may be applied to a sonar with a range of 10 km., a transmission frequency of 5 kc./s. and 20 receiver channels The listening period is 113.3 seconds and the transmitted pulses will be linearly frequency modulated in a 500 c./s. band with a duration of 200 ms.; a compression rate of 100 is provided.

The recording speed will correspond to one revolution in 13.3 seconds and the reading speed will amount to 20 revolutions during the same time. The read out signal will therefore have a center frequency of 100 kc./s., a duration of 10 ms. and a modulation band of 10 kc/s.; it will be located in an interval T/N equal to 0.66 second. The compression of the said signal will be effected by means of an acoustic line having a center frequency of 25 kc./s., which requires a frequency change by means of a kc./s. oscillator. The line, described in a copending application for a Dispersive Acoustic Lines, Ser. No. 554,785 filed Apr. 25, 1966 by P. Tournois and assigned to the same assignee, can be used. The signal compressed by such a line has a duration of ,uS. and undergoes an envelope detection, before it is applied to a visual display system which traces in polar coordinates 20 lines in 13.3 seconds.

Without thereby departing from the invention, the information may also be processed by means of a single magnetic drum, used alternately for recording and reading. However, with two drums and the alternating of the functions of recording and reading, no information is lost.

The system of the invention has also other advantages: the decoding and the processing of the signals are effected by means of a single receiving channel whatever the number of reception channels; the manufacture of the dispersive network is made easier, due to the use of an accelerated time scale; the presentation of the information on a cathode ray tube indicator and their subsequent transmission at a distance are simplified, due to multiplexing.

Another modification of the system according to the invention consists in providing an additional track wherein a local oscillation is recorded. This arrangement shown in FIGURE 3 in dashed lines permits a substantial compensation of any flutter, i.e. fluctuations in the speed of the drums. The arrangement comprises a stable oscillator 46, recording heads 47 and play-back heads 48 which are alternately coupled to the input of mixer 41 by means of a switch 49. This track can receive the recording of the stable oscillator 46 during the slow passage in order to supply from the heads 48 a correctly multiplied frequency during the fast passage phase. The improvement obtained by the use of the above mentioned additional track is a substantial reduction of the flutter arising in the frequency supplied by mixer 41; this reduction results from the fact that mixer 41 supplies the difference between two frequencies which are subjected to the same amount of flutter.

Of course the invention is not limited to the embodiment described and shown which is given solely by way of example.

What is claimed, is:

1. An information processing system for the time multiplexing a plurality of simultaneously available N variable sequences of information items, said sequences being periodically repeated, said system comprising: means for recording said items at a first speed and playing them back at a second speed, said second speed being at least N times higher than said first speed; means for sequentially operating said recording and playing-back means in respective synchronism with said sequences; said recording means having at least N inputs for respectively collecting said N sequences of information items; said playing-back means having at least N outputs for reading said information items; switching means having at least N inputs respectively connected to said playing-back means outputs and one output; means for sequentially connecting said switching means output to said switching means inputs for sequentially providing said information items at said switching means output; said information items being frequency modulated signals and pulse compression means being coupled to said switching means output for compressing said signals.

2. A system as claimed in claim 1 further comprising display indicator means connected to the output of said pulse compression means; said indicator means having a scanning means and means for operating said scanning means in synchronism with said sequentially connecting means.

3. A system as claimed in claim 1, wherein said recording and playing-back means comprise at least one magnetic drum having at least N erasable tracks; driving means for rotating said drum at either said first or said second speeds; clutch means controlled by said sequentially operating means for coupling said driving means to said drum; said recording means comprising at least N first recording heads respectively associated with said tracks and respectively coupled to said recording means inputs; said playing-back means comprising at least N first play-back heads respectively associated with said tracks and coupled to said playing-back means outputs; said drum effecting a revolution at said first speed within the duration of one of said sequences and at least N revolutions at said second speed within the duration of the next of said sequences.

4. A system as claimed in claim 3, wherein said recording and playing-back means further comprise a second magnetic drum having at least N tracks; at least N second recording heads respectively associated with said tracks of said second drum; at least N second play back heads respectively associated with said tracks of said second drum; change-over means controlled by said sequentially operating means for alternately coupling said first and said second recording head to said recording means inputs; said switching means comprising at least N further inputs respectively connected to said second playback heads; said clutch means including means for further coupling said driving means to said second drum for alternately rotating said drums at said first and said second speeds.

5. A system as claimed in claim 3 incorporated in a long range sonar system comprising a further track on said drum; a further play-back head facing said last mentioned track for supplying a frequency modulated pulse at regular intervals of time; means for radiating said pulse connected to said further play-back head; means for receiving in response to said pulse a plurality of echo signals forming said variable sequences of N information items available in N respective channels corresponding to a plurality of reception directions; display indicator means connected to the output of said pulse compression means for displaying said echo signals in said respective reception directions, said indicator means having a scanning means and means for operating said scanning means in sychronism with said sequentially connecting means.

6. A system as claimed in claim 5, wherein said pulse compression means comprise a mixer having a signal input, a local oscillator input and an output; dispersive delaying means having an input connected to the output of said mixer and an output.

7. A system as claimed in claim 6, further comprising a reference track on said first drum; a further play-back head facing said track, said further play-back head being connected to said local oscillator input and said reference track being pre-recorded.

8. A system as claimed in claim 6, further comprising a reference track on said first drum, further recording and play-back heads facing said reference track; said further play-back head being connected to said local oscillator input and said further recording head being coupled to a constant frequency generator.

References Cited UNITED STATES PATENTS 2,995,725 8/ 1961 Kliever 3403 RODNEY D. BENNETT, JR., Primary Examiner. J. G. BAXTER, Assistant Examiner.

US. Cl. X.R. 34317.2

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2995725 *Jun 10, 1955Aug 8, 1961Honeywell Regulator CoHigh speed sonar scanning apparatus
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3790925 *Jun 19, 1970Feb 5, 1974Electroacustic GmbhEcho-sounding apparatus having a digital intermediate store
US4199246 *Jan 5, 1979Apr 22, 1980Polaroid CorporationUltrasonic ranging system for a camera
US4693940 *Mar 30, 1984Sep 15, 1987Raychem CorporationLaminate and method of preparing same
US6046962 *May 27, 1998Apr 4, 2000Thomson Marconi Sonar SasElectrodynamic transducer for underwater acoustics
US6144342 *Feb 11, 1997Nov 7, 2000Thomson-CsfMethod for controlling the navigation of a towed linear acoustic antenna, and devices therefor
Classifications
U.S. Classification367/105, 367/113
International ClassificationG01S15/10, G01S7/526, G01S1/72, G01S15/42, H03K5/06
Cooperative ClassificationH03K5/065, G01S15/104, G01S1/72, G01S15/42, G01S7/526
European ClassificationG01S1/72, G01S15/42, H03K5/06B, G01S7/526, G01S15/10F1