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Title:
UNDERWATER COMMUNICATIONS
Document Type and Number:
WIPO Patent Application WO/1997/026551
Kind Code:
A1
Abstract:
An underwater communications device (10), wherein each device includes: a signal receiver, a signal transmitter, a transducer (12) associated with the signal receiver and with the signal transmitter, and having a first field of view; a controller for operating the signal receiver and the signal transmitter in at least first and second operative modes, wherein in the first mode, the transducer (12) is operative to receive output signals from the signal transmitter and to transmit output signals to the second device; a mode selector, associated with the controller, for selecting modes of operation; and selectably operable signal blocking apparatus (14) having a second field of view, and associated with the transducer (12), for blocking signals emanating from the second device from outside the second field of view, thereby to prevent their impinging on the transducer (12).

Inventors:
Kantor
Benjamin, Taratuta
Aba, Gozlan
Ely
Application Number:
PCT/IL1997/000020
Publication Date:
July 24, 1997
Filing Date:
January 14, 1997
Export Citation:
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Assignee:
AQUA ACOUSTIC LTD
Kantor, Benjamin Taratuta Aba Gozlan Ely
International Classes:
G01S1/72; G01S3/805; H04B11/00; H04B13/02; (IPC1-7): G01S3/80; H04B11/00
Foreign References:
US3940575A
US4862278A
US3986161A
US5010529A
Download PDF:
Claims:
CLAIMS
1. An underwater communications device to be carried by a diver underwater and for communicating with at least one second, similar device underwater, wherein said device comprises: signal receiver means; signal transmitter means; a transducer associated with said signal receiver means and with said signal transmitter means, and having a first field of view; control means for operating said signal receiver means and said signal transmitter means in at least first and second operative modes, wherein in said first mode, said transducer is operative to detect incoming signals from the second device, and to provide corresponding output signals to said signal receiver means, and in said second mode, said transducer is operative to receive output signals from said signal transmitter means and to transmit output signals to the second device; selector means, associated with said control means, for selecting modes of operation; and selectably operable signal blocking means having a second field of view, smaller than said first field of view, and associated with said transducer, for blocking energy of signals emanating from the second device from outside said second field of view, thereby to prevent their impinging on said transducer, and not preventing incoming signals emanating from the second device within said second field of view from impinging on said transducer.
2. A communications device according to claim 1, wherein said signal blocking means comprises a sleeve member mounted in association with said transducer for movement between nondeployed and deployed positions, and wherein, when said adjustable member is in said nondeployed position, it does not prevent signals of said predetermined type originating from the entire first field of view to impinge on said transducer, and when said adjustable member is in said deployed position, it is operative to prevent incoming signals of said predetermined type and originating from outside said second field of view, from impinging on said transducer.
3. A communications device according to claim 2, wherein said transducer is omnidirectional, and wherein said movement of said sleeve member converts signal reception of said device from omnidirectional signal reception to unidirectional signal reception.
4. A communications device according to claim 2, and also comprising a housing for said signal receiver means, said signal transmitter means, said transducer and said control means, said housing being watertight when submerged in water to at least a predetermined maximum depth.
5. A communications device according to claim 4, wherein said transducer is an ultrasonic transducer, and said adjustable member is operative to block ultrasonic signals.
6. A communications device according to claim 5, wherein said adjustable member has an ultrasonic energy absorbent construction.
7. A communications device according to claim 5, wherein said adjustable member has an ultrasonic energy reflective construction.
8. A communications device according to claim 1, wherein said selector means also comprises: means for selecting a signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined signal output; and means for selecting a search mode, wherein said control means activates said receiver means to detect said predetermined signal output from the at least one second device; and wherein said communications device also comprises sensible output means associated with said control means and said signal receiver means, for providing, when said device is operated in said first mode, a predetermined sensible output in response to a signal output emanating from the second device in response to the second device being operated in said signal transmission mode.
9. A communications device according to claim 8, wherein said device defines a signal detection axis along which incoming signals are detected most clearly, and wherein, when said device is in said search mode, said sensible output means is operative to provide a sensible output of intensity which increases in accordance with the degree of angular coincidence of the signal detection axis with the transducer of the second device from which the signal output emanates, and in accordance with the proximity of said transducer to the second device transducer.
10. A communications device according to claim 9, wherein said sensible output means comprises: audible output means for providing an audible signal to the person carrying said device; and a visual output means, for providing a visible signal to the person carrying said device.
11. A communications device according to claim 8, wherein said means for selecting a signal transmission mode comprises means for selecting an alarm signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined alarm signal output; said means for selecting a search mode comprises means for selecting an alarm signal search mode, wherein said control means activates said receiver means to detect said predeterrnined alarm signal output from the at least one second device; and wherein said sensible output means associated with said control means and said signal receiver means is operative to provide, when said device is operated in said first mode, a predetermined sensible output in response to an alarm signal output emanating from the second device in response to the second device being operated in said alarm signal transmission mode.
12. A communications device according to claim 11, wherein said means for selecting an alarm mode comprises a manually operated switch.
13. A communications device according to claim 12, wherein said means for selecting an alarm mode also comprises automatic means, responsive to at least one predeterrnined condition, for selecting said alarm mode.
14. A communications device according to claim 8, wherein said means for selecting a signal transmission mode comprises means for selecting a beacon signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined beacon signal output; said means for selecting a search mode comprises means for selecting a beacon signal search mode, wherein said control means activates said receiver means to detect said predetermined beacon signal output from the at least one second device; and wherein said sensible output means associated with said control means and said signal receiver means is operative to provide, when said device is operated in said first mode, a predetermined sensible output in response to a beacon signal output emanating from the second device in response to the second device being operated in said beacon signal transmission mode.
15. An underwater communications system which comprises a plurality of similar, intercommunicating portable underwater communications devices, of which at least one is carried underwater by a person of one or more people underwater, each carrying one of said devices, wherein each said device comprises: signal receiver means; signal transmitter means; a transducer associated with said signal receiver means and with said signal transmitter means, and having a first field of view; control means for operating said signal receiver means and said signal transmitter means in at least first and second operative modes, wherein in said first mode, said transducer is operative to detect incoming signals from the second device, and to provide corresponding output signals to said signal receiver means, and in said second mode, said transducer is operative to receive output signals from said signal transmitter means and to transmit output signals to the second device; selector means, associated with said control means, for selecting modes of operation; and selectably operable signal blocking means having a second field of view, smaller than said first field of view, and associated with said transducer, for blocking energy of signals emanating from the second device from outside said second field of view, thereby to prevent their impinging on said transducer, and not preventing incoming signals emanating from the second device within said second field of view from impinging on said transducer.
16. A system according to claim 15, wherein said signal blocking means comprises a sleeve member mounted in association with said transducer for movement between nondeployed and deployed positions, and wherein, when said adjustable member is in said nondeployed position, it does not prevent signals of said predetermined type originating from the entire first field of view to impinge on said transducer, and when said adjustable member is in said deployed position, it is operative to prevent incoming signals of said predetermined type and originating from outside said second field of view, from impinging on said transducer.
17. A system according to claim 16, wherein said transducer is omnidirectional, and wherein said movement of said sleeve member converts signal reception of said device from omnidirectional signal reception to unidirectional signal reception.
18. A system according to claim 16, and also comprising a housing for said signal receiver means, said signal transmitter means, said transducer and said control means, said housing being watertight when submerged in water to at least a predetermined maximum depth.
19. A communications device according to claim 18, wherein said transducer is an ultrasonic transducer, and said adjustable member is operative to block ultrasonic signals.
20. A communications device according to claim 19, wherein said adjustable member has an ultrasonic energy absorbent construction.
21. A communications device according to claim 19, wherein said adjustable member has an ultrasonic energy reflective construction.
22. A system according to claim 15, wherein said selector means also comprises: means for selecting a signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined signal output detectable by the other of said plurality of devices; and means for selecting a search mode, wherein said control means activates said receiver means to detect said predetermined signal output from said other of said plurality of devices; and wherein said communications device also comprises sensible output means associated with said control means and said signal receiver means, for providing, when said device is operated in said first mode, a predetermined sensible output in response to a signal output emanating from the second device in response to another of said plurality of devices being operated in said signal transmission mode.
23. A system according to claim 22, wherein said device defines a signal detection axis along which incorning signals are detected most clearly, and wherein, when said device is in said search mode, said sensible output means is operative to provide a sensible output of intensity which increases in accordance with the degree of angular coincidence of the signal detection axis with the transducer of said other device from which the signal output emanates, and in accordance with the proximity of said transducer to said transducer of said other device.
24. A system according to claim 23, wherein said sensible output means comprises: audible output means for providing an audible signal to the person carrying said device; and a visual output means, for providing a visible signal to the person carrying said device.
25. A system according to claim 22, wherein said means for selecting a signal transmission mode comprises means for selecting an alarm signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined alarm signal output; said means for selecting a search mode comprises means for selecting an alarm signal search mode, wherein said control means activates said receiver means to detect said predetermined alarm signal output from said other device; and wherein said sensible output means associated with said control means and said signal receiver means is operative to provide, when said device is operated in said first mode, a predetermined sensible output in response to an alarm signal output emanating from the second device in response to said other device being operated in said alarm signal transmission mode.
26. A system according to claim 25, wherein said means for selecting an alarm mode comprises a manually operated switch.
27. A system according to claim 26, wherein said means for selecting an alarm mode also comprises automatic means, responsive to at least one predetermined condition, for selecting said alarm mode.
28. A system according to claim 22, wherein said means for selecting a signal transmission mode comprises means for selecting a beacon signal transmission mode, wherein said control means activates said transmitter means to transmit a predetermined beacon signal output; said means for selecting a search mode comprises means for selecting a beacon signal search mode, wherein said control means activates said receiver means to detect said predeterrnined beacon signal output from the said other device; and wherein said sensible output means associated with said control means and said signal receiver means is operative to provide, when said device is operated in said first mode, a predetermined sensible output in response to a beacon signal output emanating from said other device in response to said other device being operated in said beacon signal transmission mode.
29. A communications device which comprises: signal receiver means for receiving environmentborne communications signals of a predetermined type; a transducer for detecting incoming signals of said predetermined type and for conveying the detected signals to said signal receiver means, and having a first field of view; and selectably operable signal blocking means having a second field of view, smaller than said first field of view, and associated with said transducer, for blocking energy of incoming signals of said predeterrnined type originating from outside said second field of view, thereby to prevent their impinging on said transducer, and not preventing incoming signals of said predetermined type originating from within said second field of view from impinging on said transducer .
30. A communications device according to claim 29, wherein said signal blocking means comprises a sleeve member mounted in association with said transducer for movement between nondeployed and deployed positions, and wherein, when said adjustable member is in said nondeployed position, it does not prevent signals of said predetermined type originating from the entire first field of view to impinge on said transducer, and when said adjustable member is in said deployed position, it is operative to prevent incoming signals of said predetermined type and originating from outside said second field of view, from impinging on said transducer.
31. A communications device according to claim 30, wherein said transducer is omnidirectional, and wherein said movement of said adjustable member converts signal reception by said device from omnidirectional signal reception to unidirectional signal reception.
32. A communications device according to claim 29, wherein said housing is watertight when submerged in water to at least a predetermined maximum depth, and the incoming signals are waterborne.
33. A communications device according to claim 32, wherein said transducer is an ultrasonic transducer, and said adjustable member is operative to block ultrasonic signals.
34. A communications device according to claim 33, wherein said adjustable member has an ultrasonic energy absorbent construction.
35. 5 A communications device according to claim 33, wherein said adjustable member has an ultrasonic energy reflective construction.
Description:
UNDERWATER COMMUNICAΗONS

FIELD OF THE INVENTION The present invention relates to signal communications devices.

BACKGROUND OF THE INVENTION

Many different types of communicatior-S device, including those which enable location of a particular person or object, are known. In the area of personal underwater cornmunications, these devices are of key significance, due to the fact that the environment is hostile in terms of human survival In particular, the underwater environment is hostile in terms of the necessity of a diver to carry a supply of air, in the absence of artificially supplied breathable air underwater, and also in terms of the elevated pressures present at increased depths. Both of these factors require the presence of a communications channel which can be used by a diver in distress.

As opposed to on-land corrununications, however, which utilize, inter alia, both optical and acoustic energy in the range of human perception, the use of these types of energy is very limited underwater as human-detectable transmissions of both types of energy are very distorted underwater. In view of this, various systems and devices have been developed so as to enable divers in distress to be located and rescued as quickly as possible.

An indication of the state of the art is found in US Patent No. 4,563,758. This patent describes an underwater communicator service which permits acoustic communication between two divers carrying the device. Communication is provided by means of a voice synthesizer cooperating with a transducer. A selector associated with a computer allows a diver to send a signal to the transducer of another diver's device, and so as to be provided as a spoken output via the voice synthesizer. Various warning systems may also be incorporated in the device so as to warn the diver carrying the device of various hazards, such as elevated depth, lack of air, and so on.

There is also known an acoustic search device, described in PCT application No. WO 91/15781. This uses reflected acoustic energy to scan an underwater search area and to display the search area on a screen viewed by a diver wearing the device.

An underwater homing and navigation system, entitled "DiveTracker™ Sport," marketed by Desert Star Systems of 2370 Highway 1, Moss Landing, CA 95039-006, USA, employs an omnidirectional-directional transmitter, located on a boat or another selected site, and a unidirectional receiver, worn by a diver. While the system enables navigation by divers, as the portion of the system worn by the diver is a receiver only, it does not allow communication directly between divers, nor does it permit tracking of divers. Desert Star Systems also markets a further, software driven product, that operates as a personal dive computer and communicator, and employs separate omnidirectional-directional sonar transducers, a directional sonar transducer, and a sonar transceiver. Neither of these products provides specifically for location of a disabled diver in distress, and both represent highly complex systems, which are very expensive.

SUMMARY OF THE INVENTION

The present invention seeks to provide an underwater communications device for use by a diver, which is characterized by its operating in plural modes, serving as a panic button and as a means of locating a diver, and, optionally, as a beacon or marker, and as a means of homing in on a beacon. The present device is further characterized by its use of a single transducer in both omnidirectional and unidirectional modes, for the above purposes.

There is thus provided, in accordance with a preferred embodiment of the invention, an underwater communications device, and an underwater communications system which includes a plurality of such devices, of which at least one is carried underwater by a person who may be one of a group of people underwater, each carrying one ofthe devices, wherein each the device includes: a signal receiver; a signal transmitter; a transducer associated with the signal receiver and with the signal transmitter, and having a first field of view;

a controller for operating the signal receiver and the signal transmitter in at least first and second operative modes, wherein in the first mode, the transducer is operative to detect incoming signals from the second device, and to provide corresponding output signals to the signal receiver, and in the second mode, the transducer is operative to receive output signals from the signal transmitter and to transmit output signals to the second device; a mode selector, associated with the controller, for selecting modes of operation; and selectably operable signal blocking apparatus having a second field of view, smaller than the first field of view, and associated with the transducer, for blocking signals emanating from the second device from outside the second field of view, thereby to prevent their impinging on the transducer, and not preventing incoming signals emanating from the second device within the second field of view from impinging on the transducer.

Additionally in accordance with a preferred embodiment of the invention, the signal blocking apparatus includes a sleeve member mounted in association with the transducer for movement between non-deployed and deployed positions, and wherein, when the adjustable member is in the non-deployed position, it does not prevent signals ofthe predetermined type originating from the entire first field of view to impinge on the transducer, and when the adjustable member is in the deployed position, it is operative to prevent incoming signals of the predetermined type and originating from outside the second field of view, from impinging on the transducer.

Further in accordance with a preferred embodiment of the invention, the transducer is omnidirectional, and wherein the movement ofthe sleeve member converts signal reception of the device from omnidirectional signal reception to unidirectional signal reception.

Additionally in accordance with a preferred embodiment of the invention, the transducer is an ultrasonic transducer, and the adjustable member is operative to block ultrasonic signals.

Further in accordance with a preferred embodiment of the invention, the mode selector also includes:

apparatus for selecting .a signal transmission mode, wherein the controller activates the transmitter to transmit a predeterrnined signal output detectable by the other ofthe plurality of devices; and apparatus for selecting a search mode, wherein the controller activates the receiver to detect the predeteπr ned signal output from the other of the plurality of devices; and wherein the communications device also includes sensible output apparatus associated with the controller and the signal receiver, for providing, when the device is operated in the first mode, a predetermined sensible output in response to a signal output emanating from the second device in response to another ofthe plurality of devices being operated in the signal transmission mode.

Additionally in accordance with a preferred embodiment of the invention, the device defines a signal detection axis along which incoming signals are detected most clearly, and wherein, when the device is in the search mode, the sensible output apparatus is operative to provide a sensible output of intensity which increases in accordance with the degree of angular coincidence of the signal detection axis with the transducer ofthe other device from which the signal output emanates, and in accordance with the proximity ofthe transducer to the transducer ofthe other device.

Further in accordance with a preferred embodiment of the invention, the signal transmissions are alarm signals transmissions, and the search mode is an alarm signals search mode.

In accordance with a further embodiment of the invention, the signals transmissions may also include selectable beacon transmissions, indicating the location of a device acting as a marker, and the search mode may be a beacon signals search mode.

There is also provided, in accordance with a further embodiment ofthe invention, a communications device which includes signal receiver apparatus for receiving environment-borne communications signals of a predetermined type; a transducer for detecting incoming signals of the predetermined type and for conveying the detected signals to the signal receiver apparatus, and having a first field of view; and selectably operable signal blocking apparatus having a second field of view, smaller than the first field of view, and associated with the transducer, for blocking energy of incoming signals

of the predetermined type originating from outside the second field of view, thereby to prevent their impinging on the transducer, and not preventing mcorning signals of the predetermined type originating from within the second field of view from impinging on the transducer .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated form the following detailed description, taken in conjunction with the drawings, in which:

Fig. IA is a schematic side view of a diver-to-diver communications device, constructed in accordance with a preferred embodiment of the invention, in an omnidirectional operational mode;

Fig. IB is a partially cut-away side view of the device seen in Fig., IA, in a unidirectional "search" mode;

Fig. 2 is a block diagram representation ofthe device ofthe present invention;

Fig. 3 is a pictorial illustration showing the device ofthe present invention in use as a panic button and search device; and

Fig. 4 is a pictorial illustration showing the device ofthe present invention in use as a beacon and navigational aid.

DETAILED DESCRIPTION OF THE PRESENT INVENTION Referring now to Figs. IA and IB, there is seen a communications device 10 for a diver, constructed and operative in accordance with a preferred embodiment of the present invention. As will be appreciated from the following description, device 10 is a multi-operational underwater communications device, which is intended to be carried by each diver of a group of divers, and which is operative in a plurality of modes, serving as a panic button and as a means of locating a diver. Optionally, device 10 may also be constructed so as to be selectably operable as a beacon or marker, and as a means of

homing in on a beacon. It will be appreciated that the uses as a panic button and as a beacon, in which quasi-continuous pulsed signals are emitted, are generally similar to each other, as are the modes in which a diver, carrying the device, locates either a diver in distress or a beacon location, by using the communications device 10 to home in on the signal source.

In order to provide the described multiple functions in a single device, whose size and cost are kept to a minimum, and in absolute independence from a surface station, the device is provided with a single transducer 12. The transducer 12 is preferably an ultrasonic transducer, having an operating frequency in the range 30-100 kHz, and which can be driven by appropriate receiver or transmitter circuitry, in accordance with the mode of operation selected. The transducer 12 is omnidirectional, and therefore, in order to facilitate omnidirectional signal transmission, omnidirectional reception, and unidirectional searching by device 10, in accordance with the present invention, there is also provided an adjustable, ultrasonic transmission energy blocking sleeve, referenced 14. When deployed, sleeve 14 masks the transducer, thereby to convert the device into a unidirectional device, having a predetermined limited field of view, defined by the sleeve. Typically, transducer 12 is ofthe piezoceramic cylinder type.

Referring now particularly to the drawings, device 10 has a preferably plastic housing which has a front portion 19, a middle portion 20, and a rear portion 22. The housing is typically cylindrical, and is watertight - and thus functional underwater - up to a predetermined submersion depth of 100m or more, in accordance with the strength of the housing. The transducer 12 has a longitudinal axis 18, and is housed in front portion 19 of the housing, this being connected to middle portion 20 of the housing in which electronic circuitry, described below in conjunction with Fig. 2, is housed. The rear portion 22 ofthe housing is configured to contain a battery power source, typically a pair of 9V, 0.12 Ah battery, and has mounted thereon various indicator lamps, referenced 24 and 26. A first indicator lamp 24 provides a visual indication of power, and is operated for a short period after switching the device on, and a second indicator lamp 26 is an ALARM lamp, providing a visual indication of signal reception from the communications device of another diver. An optional beacon signal indicator lamp, referenced 27, is seen in Fig. 2.

An audible output indication of either an alarm transmission from another diver or, when provided, a beacon signal, is provided by a buzzer 28 or the like, located typically at the rear of device 10. A mode selection switch, referenced 30, typically ofthe ring type, is provided for selecting between various operative modes of the device, as described below.

As mentioned above, ultrasonic transmission energy blocking sleeve, referenced 14, is provided for converting the transducer 12 into a unidirectional transducer, having a predetermined limited field of view. Sleeve 14 is mounted onto front housing portion 20 in proximity to the transducer 12, and is typically manually movable between a retracted position, seen in Fig. IA, in which transducer 12 may be used to transmit and receive omnidirectionally; and an extended or deployed position. This position is seen in Fig. IB and, due to the masking or shielding effect provided by sleeve 14, the effective field of view of the device is limited to a very much reduced angular field of view, typically of no more than about 20°. It will be appreciated that use of the device in this unidirectional manner and when in a receiving mode, enables a diver to home in on a communications device from which signals are being transmitted.

As illustrated schematically in Fig. IB, sleeve 14 is formed from a preferably porous material, such as expanded polyurethane, whose pores constitute a gas barrier to ultrasonic signals, thereby to prevent transmission therethrough to transducer 12, of incoming ultrasonic signals impinging on the sleeve. All incoming signals that do not impinge on the sleeve, however, but which impinge directly on the front end portion 19 of the housing, however, are received by the transducer. It will be appreciated that all such incoming signals that impinge directly on the transducer when the sleeve 14 is in the extended or deployed position, must originate from within the narrow field of view defmed by the sleeve, and therefore provide a good indication of the direction of the alarm signals. This is described in greater detail below, in conjunction with Fig. 3.

It will be appreciated that sleeve 14 may be of any ultrasonic signal blocking construction, which operates either by absorbing or by reflecting ultrasonic signals. A further example of suitable signal blocking constructions, in addition to that shown and described in conjunction with Fig. IB, include the formation of sleeve 14 so as to have a hollow wall construction, wherein the formation of a hollow space between the inner

and outer wall skins prevents transmission therethrough of signals impinging on the sleeve.

Referring now to Fig. 2, it is seen that mode selection switch 30 is connected to a microprocessor-based controller 40, whose function is to operate the device 10 in accordance with a selected mode, as described below. The terms controller and microprocessor are used interchangeably throughout the specification. As seen, the device 10 is powered from a battery power source 42, via power switch 44 and a power supply unit 46. The microprocessor is operative to drive, in accordance with the selected mode, a variable gain amplifier 48 and receiver circuitry 50 connected thereto, and a signal generator 52 and transmitter circuitry 54 connected thereto.

The signal generator 52 is operative, in response to an ALARM mode selection via mode selection switch 30, to generate signals for omnidirectional transmission. In an embodiment ofthe invention wherein these signals may be either alarm signals or beacon signals, the signals are transmitted in a pulsed stream on the same channel, but so as to have different bandwidths, such that a receiving device is capable of distinguishing between them.

In order to enable transmission of alarm signals for as long a period as possible, the signal generator 52 is operated by microprocessor 40 to transmit ultrasonic signals having a frequency of 30-100 kHz. In order to save energy, these signals are transmitted as pulses at a predetermined duty cycle, typically 10%, a frequency of 5 Hz, and a pulse peak transmission power of 1.5W. These operating conditions can be expected to provide the described alarm transmission for up to about four hours. Transmitter circuitry 54 receives signals from signal generator 52, and is operative to amplify these signals for transmission via transducer 12, under operating conditions enabling their transmission via the transducer. It will be appreciated that, the higher the power of the transmission signals, the longer will be the transmission range. A typical transmission range is 600m, but this can be any predetermined, suitable range, in accordance with the transmission power and the battery specifications.

The receiver circuitry 50, which includes a plurality of filters and amplifiers in accordance with the preset operating frequencies of the communications device, is operative to receive incoming signals via transducer 12, and to provide them, via the

microprocessor-driven variable gain amplifier 48, and via an analog-to-digital converter 58, to microprocessor 40.

Upon reception of incoming signals, any signals not filtered out by receiver 50, are further analyzed by microprocessor 40, by use of an appropriate algorithm. This further analysis includes bandwidth measurement, and thus a determination as to whether the incoming signals are alarm signals or beacon signals. It will be appreciated that the use of a single channel for transmission of alarm and beacon signals, and wherein these different types of signal are encoded by virtue of having different bandwidths, enables the cost ofthe device ofthe present invention to be kept low.

Device 10 is operative in three basic modes, namely, "standby," "alarm," and "alarm search," and in accordance with a further embodiment of the invention, in two further optional modes, namely, "beacon" and "beacon search."

In the standby mode, sleeve 14 is in a retracted position, such that the transducer can receive omnidirectional incoming transmissions. In the alarm mode, sleeve 14 is maintained in the retracted position, so that transducer 12 is still operated omnidirectionally, but so as to transmit alarm signals. In the search mode, sleeve 14 is deployed or extended over transducer 12, so as to block all incoming signals except for those the narrow field of view defined by the sleeve.

The three basic modes of operation of the communications device of the invention are now described in conjunction with Fig. 3, in which three divers, A, B and C are shown, wherein the device of diver A (device A) is in the standby mode, diver B is in the alarm mode, and diver C is in the search mode.

As shown schematically in Fig. 3, device 10 may be either hand carried, or it may be strapped to an upper part ofthe diver's body. When strapped to the diver's body, the device is connectable to external systems, such as a depth gauge 72 (Fig. 2), and is easily accessible to the diver, so that he can hear an audible alarm indication emitted from buzzer 28, and so that he can easily unstrap the device and hold it in his hand when searching.

In the illustration, diver B is in distress, and moves his mode selector switch 30 (Figs. 1A-2) to the alarm mode, such that device 10 begins to emit alarm signals, omnidirectionally. Divers A and C are seen to be located within reception range of diver

B which, as mentioned above, may be as much as 600m, or more. Upon reception and identification ofthe alarm signals, microprocessor 40 is operative, via suitable drivers 60 and 62 (Fig. 2), to provide both a visual alarm indication, via a suitable lamp 26 (Figs. 1A-2), such as a light emitting diode of a selected color, and also an audible alarm indication, which may be needed to initially alert the diver to the detection of an alarm signal, via buzzer 28 (Figs. 1 A-l).

Diver C is in a search mode, wherein sleeve 14 (Figs. 1A-2) is extended and microprocessor 40 (Fig. 2), upon detection of alarm signals, is operative to deteιτnine the strength of the signals, and to provide output indications to the diver, in accordance therewith. Initially, diver C begins scanning with his communications device omnidirectionally until he again detects an alarm signal, this being indicated to him by means ofthe buzzer 28 and the alarm lamp 26. It will be appreciated that the strength of the signals is affected both by the direction ofthe incoming signals and by the proximity of the signal source. An increase in the strength of the signals detected is indicated by operating the buzzer 28 to provide a louder and/or higher frequency tone and by operating the lamp 26 to flash at increasing frequency. A minimal detection of alarm signals is indicated by a low frequency flashing, such as of 0.5 Hz, while a maximum detection is indicated by a flashing frequency of, for example, 10 Hz.

Accordingly, the strongest output indications are provided when the detecting device is closest to the transmitting device, and when the longitudinal axis 18 (Fig. IA), known also as the signal detection axis, of the detecting device, coincides with the transmitting device, i.e. with the communications device of diver B.

Referring now once again to Fig. 2, it will be appreciated that, while, in many situations, a diver in distress is able to manually activate the alarm mode, by means ofthe mode selector switch 30, there also exist situations wherein the diver is incapacitated to the extent that he is unable to operate the mode selector switch.

Accordingly, there may also be provided a chronograph, referenced 70, which is connected to the mode selector-microprocessor circuit, so as to cause microprocessor 40 to operate device 10 in the alarm mode after a set time has passed since the device was activated. Typically, this time corresponds to 80-90% of the time that it should take for the oxygen carried by the diver to be used up. Similarly, the mode

selector-microprocessor circuit may have connected thereto a depth gauge 72, which, upon sensing a depth greater than permitted, activates microprocessor 40 to operate device 10 in the alarm mode.

The two further optional modes, namely, the "beacon" and "beacon search" modes of operation ofthe communications device of the invention are now described in conjunction with Fig. 4. In Fig. 4, there are seen three divers, X, Y and Z, diving in the vicinity of a boat 80 and a cave 82 having an entrance 84. The location of boat 80 is marked by device 10, suspended from the boat below the surface of the water, and operated in a "beacon" mode. Similarly, the location of the cave entrance 84 is also marked by device 10, also operating in a "beacon" mode. The device of diver X is in the standby mode, as described above in conjunction with Fig. 3, and the devices of divers Y and Z are in the "beacon search" mode. The use of device 10 in the scenario of Fig. 4, is described only as far as may be necessary to understand the illustrated scenario, and in as far as it is different from that of Fig. 3.

In the illustration, divers X, Y and Z constitute or form part of a group of divers. They are diving in the vicinity of their boat 80, which is anchored at a location which is located approximately above the entrance 84 of a cave 82. A further diver, such as diver X, may have marked the cave entrance by placing thereat a device 10 and either by activating the device at the time of placement, by means of mode selector switch 30, or by activating it by remote control. As mentioned, the device of diver X is in standby mode. Upon reception and identification of the beacon signals, microprocessor 40 (Fig. 2) is operative, via suitable drivers 63 and 62 (Fig. 2), to provide both a visual beacon locator indication, via beacon lamp 27, which may be a light emitting diode of a selected color, and an audible beacon locator indication, which may be needed to initially alert the diver to the detection of a beacon locator signal, via buzzer 28. Upon inspection of his device, he sees that beacon lamp 27 is flashing, and knows that he is close either to the boat 80 in a generally upward direction, to the cave entrance 84, in a generally downward or lateral direction. Accordingly, in order to home in on either the boat or the cave entrance, he moves his mode selector switch 30 to the beacon search mode.

The devices of both divers Y and Z are already in the "beacon search" mode, wherein sleeve 14 is extended and microprocessor 40, upon detection of beacon signals,

is operative to determine the strength ofthe signals, and to provide output indications to the diver, in accordance therewith. Initially, the divers begin scanning with their communications devices omnidirectionally until beacon signals are again detected, this being indicated to each diver by means of buzzer 28 and beacon lamp 27. It will be appreciated that the strength of the signals is affected both by the direction of the incoming signals and by the proximity ofthe signal source. An increase in the strength of the signals detected is indicated by buzzer 28 operating to provide a louder and/or higher frequency tone and by lamp 27 flashing at increasing frequency. A minimal detection of alarm signals is indicated by a low frequency flashing, such as 0.5 Hz, while a maximum detection is indicated by a flashing frequency of, for example, 10 Hz.

Accordingly, the strongest output indications are provided when the detecting device is closest to the transmitting device, and when the longitudinal axis 18 (Fig. IA), or the signal detection axis, of the detecting device, coincides with the transmitting device, i.e. with the communications devices being used as markers.

It will be appreciated by persons skilled in the art that the scope of the present invention is not limited to what has been specifically shown and described hereinabove, merely by way of example. Rather, the scope of the present invention is limited solely by the claims, which follow.