Retrievable buoy

[57] ABSTRACT

A retrievable, submersible buoy is disclosed which is anchored at an underwater location and includes an explosive charge release mechanism which releases the buoy from its anchor in response to a remotely actuated recall signal. The buoy may be anchored by an inflatable bag that becomes buried in the sea bed and is filled so as to be buoyant in response to actuation of the explosive charge release mechanism, or by connection through a lanyard line to an underwater structure which connection is released in response to actuation of the explosive charge release mechanism. A recall transmitter located above water actuates a plurality of sound sources, such as explosive charges which provide a series of mechanical signals in a predetermined time sequence to provide a coded recall command, and the buoy includes a receiver which receives these mechanical signals and when the properly coded recall command is received actuates the explosive charge release mechanism to release the buoy and cause it to ascend.

Claims, 14 Drawing Figures

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PATENTEDMAR271973

3,722,014

SHEET 1 OF 5

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ATTORNEYS

PATENTEDMAR27I973

3,722,014

SHEET 2 OF 5

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PATENTEDMAR27I973

SHEET 3 OF 5

3,722,014

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ATTORNEYS

PATENTEDMAR27I973

3,722,014

SHEET U OF 5

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Jack 0. Uill.

David 5. Fridge, Jr.

Vaughn R. Dibble, Jr.

INVENTORS

BY

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ATTORNEYS

PATENTEDMAR27I973

3,722,014

SHEET 5 GF 5

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Jack O. Hill

David 5. Fridge. Jr.

Vaughn R. Diddle, Jr.

INVENTORS

<img file="US3722014A_D0011.tif" />

<img file="US3722014A_D0012.tif" />

ATTORNEYS

3,722,014

RETRIEVABLE BUOY

This invention relates to submersible marker buoys and in one of its aspects to a retrievable, submersible buoy in which a remotely actuated explosive device is employed to cause the buoy to rise from an underwater location. Another aspect of this invention relates to a system for recalling such a buoy by use of a coded recall command including a series of distinctly coded signals, and to a recall transmitter and recall receiver which may be used in such a system for respectively transmitting and receiving such signals.

In the past, retrievable marker buoys have been used to mark underwater locations without the need of a surface buoy. These retrievable buoys generally included instrumentation and were released from their underwater mooring in response to a remotely generated recall signal which was usually a single signal of a predetermined frequency. However, such buoys generally employed mechanical release devices, such as a solenoid operated release latch, and such devices do not have the reliability needed for use for extended periods at underwater locations.

Also, the use of a single recall signal of a specified frequency has not been entirely satisfactory since spurious signals of that frequency or multiplies thereof can recall the buoy. Attempts have been made to reduce the possibility of false recall by requiring a recall signal of a relatively high level signal, as compared to ambiant noise, but doing so results in lessening of the recall range of the buoy.

It is thus an object of this invention to provide a retrievable, submersible buoy in which a release mechanism which does not utilize a mechanical latch is used to separate the buoy from an underwater mooring in response to a remotely generated recall signal.

Another object of this invention is to provide such a buoy in which the release mechanism for the buoy includes an explosive charge actuated by receipt of a buoy recall command.

Another object of this invention is to provide a retrievable, submersible buoy in which the recall command for recalling the buoy includes a series of distinct signals generated from a remote location.

Another object of this invention is to provide such a buoy in which the recall command is coded by having predetermined time intervals between the distinct signals comprising the recall command.

Another object of this invention is to provide a remotely actuated recall transmitter for generating and transmitting such a coded recall command to a submerged buoy.

Another object of this invention is to provide a buoy recall receiver adapted to be mounted in a submerged buoy and responding to receipt of only the properly coded buoy recall command to actuate the buoy release mechanism.

Another object of this invention is to provide such a recall receiver in which a sequence of interval timing signals is generated in response to receipt of the first of a series of distinct signals comprising the buoy recall command, and an output signal for actuating the buoy release mechanism is generated only upon coincidence of the sequence of interval timing signals and pulses generated by the receipt of the remainder of the coded signals comprising the buoy recall command.

Also, since submerged marker buoys may be left unattended at underwater locations for long periods of time, and such buoys are necessarily operated by batteries, another object of this invention is to provide such a buoy recall receiver wherein battery drain is kept at a relatively low amount during standby periods prior to receipt of a proper recall command, or during periods of receipt of spurious noise signals.

On occasions a submerged marker buoy may become buried in the ocean bed and unless additional buoyancy is provided for the buoy it may not rise to the surface of the water when released. Thus, another object of this invention is to provide a retrievable, submersible buoy which includes an inflatable buoyancy member which is inflated in response to actuation of the buoy release mechanism to impart sufficient buoyancy to the buoy to cause it to ascend even if buried in the sea bed.

These and other objects, advantages and features of this invention will be apparent from the following description taken with reference to the accompanying drawings, wherein is shown the preferred embodiments of the invention:

FIG. 1 is a pictorial representation of a submerged market buoy and surface apparatus for recalling the buoy to the surface;

FIG. 2 is an assembly view of a preferred form of a submersible buoy utilizing this invention;

FIG. 3 is an isometric view partly in section of such a buoy when assembled;

FIG. 4 is an isometric view of another form of buoy utilizing this invention;

FIG. 5 is a sectional view of the release mechanism of this invention taken at 5—5 of FIG. 3;

FIG. 6A is a partial perspective and partial sectional view of another form of retrievable buoy of this invention;

FIG. 6B is an exploded view at 6 of FIG. 6A;

FIG. 7A is a block diagram of the preferred form of buoy recall transmitter of this invention;

FIG. 7B is a schematic of an explosive cap firing circuit used in the transmitter of FIG. 7A;

FIG. 8 is a block diagram of a preferred form of buoy recall receiver of this invention;

FIG. 9 is a block diagram of one form of interval timing circuit used in the recall receiver of FIG. 8;

FIG. 10 is a schematic diagram of the turn-on and turn-off circuits employed in the receiver of FIG. 8;

FIG. 11 is a schematic diagram of one form of a timing circuit employed in the receiver of FIG. 8; and

FIG. 12 is a timing diagram showing the pulse shapes at various points in FIG. 8.

Referring to the drawings, in FIG. 1 a retrievable, submersible buoy 20 is illustrated as connected to a sub-sea structure or anchor 21 through a mooring line of lanyard 22. A buoyancy member 23 is connected to the top of buoy 20 and imparts a positive buoyancy to buoy 20, causing buoy 20 to rise to the surface of the water when it is released from line 22.

At the surface of the water, a buoy recall transmitter 24 is shown as including a source 25 of distinct signals, which when actuated in a proper sequence by transmitter 24, sends a coded recall command to buoy 20. As hereinafter described, buoy 20 includes a buoy recall receiver which actuates a release mechanism for separating buoy 20 from line 22 when the proper buoy recall command is received.

3,722,014

The details of a preferred form of buoy 20 are shown in FIGS. 2 and 3. As illustrated, buoy 20 is preferably made by telescoping together several cylindrical sections to form an elongated cylindrical buoy. This construction permits each section of the buoy to form a separate functional part of the buoy which can be separately stored and then coupled together to form the complete buoy. For example, the upper section 26 includes a hydrophone (now shown) which forms part of the recall command receiving means. The hydrophone is encased in epoxy or similar material, and responds to mechanical signals transmitted through the water to convert these signals to electrical signals. Connected to section 26 is a second section 27 which includes an electronics package 28 also encased in epoxy, and this electronics package forms the remainder of the recall command receiver for buoy 20. The electrical signals from the hydrophone are conducted through suitable connectors 29α and 29b to the circuits of electronics package 28. Buoy section 27 is also connected to another cylindrical section 30 in which a battery package 31 may be encased in epoxy. The electronics package 28 of section 27 is electrically connected to battery package 31 through suitable connectors 32α and 32b. The bottom section of buoy 20 is illustrated as a release squib 33 including a buoy release mechanism 34, which preferably includes an explosive charge as hereinafter described. The batteries of section 30 and the electronics of section 27 are connected to release mechanism 34 of squib 33 through suitable connectors 35a and 35b. An eye hook 36 to which buoyancy member 23 may be connected is shown at the top of section 26, and anchoring line 22 is releasably connected to release squib 33.

FIG. 3 shows buoy 20 with sections 26, 27, 30 and 33 telescoped together. Buoy 20 may be enclosed in a cylindrical housing 37.

A tag line 38 is preferably wound around section 30 of buoy 20. One end of tag line 38 is secured to buoy 20 and the other end is secured to anchoring line 22. Thus when buoy 20 is released from anchor line 22 and ascends, tag line 38 unwinds, but leaves buoy 20 attached to line 22.

When housing 37 is mounted over buoy 20, a clearance or annulus 39 is formed between the inner wall of shell 37 and the outer wall of squib 33, and tag line 38 passes through this annulus to anchoring line 22. Means is provided to clear annulus 39, in response to the release of buoy 20 from anchoring line 22, of obstructions or encrustations which may form due to exposure to the sea. This means is illustrated in FIG. 3 as a wiper line 40 connected to anchoring line 22 and wrapped in one wrap substantially about the periphery of release squib 33. Thus, when buoy 20 ascends, wiper line 40 is pulled through annulus 39 to clear it of obstructions prior to unwinding of tag line 38.

The details of release squib 33 and the preferred form of buoy release mechanism 34 are shown in FIG. 5. Release mechanism 34 preferably includes a threaded female receptacle 41 which forms an opening in the bottom of squib 33 into which a threaded male connector 42 is connected. One end of anchoring line 22 is connected to a male connector 42, and this connector is made of plastic or similar material which fractures in response to an adjacent explosive charge. Receptacle 41 is closed at its other end by threaded member 43 which includes an explosive material such as an explosive powder. An expansion chamber 44 is formed in receptacle 41 between male connector 42 and member 43, and chamber 44 is filled with grease or other material which expands in response to an explosive charge to cause connector 41 to fracture, releasing squib 33 from anchoring line 22. The powder in member 43 is ignited through a primer 45 which is connected to a source of electrical current through connector 35b.

In FIG. 4, another form of buoy 20 is shown in which a buoyant section 46 which may contain styrofoam or other buoyant material is connected to buoy 20 and becomes an integral part thereof, so that the buoy will ascend without need of an auxiliary buoyancy member 23. In this embodiment the elongated body of the buoy acts as an antenna, and the range of the recall command is increased.

FIGS. 6A and 6B show another form of retrievable buoy of this invention in the position it would assume during ascent to water level. Release squib 33 is replaced with a section 47 including an inflatable bag 48 mounted on one end, and in this embodiment at least the bag of buoy 20 is adapted to be buried at a sub-sea location, whereby it provides a large surface which acts to anchor in the buoy. Bag 48 is mounted through flanges 49 to section 47 and the interior of bag 48 communicates with the interior of section 47 through an opening 48α. A source of pressurized gas, such as a CO₂ bottle 50, is mounted in section 47 and surrounded by packing 47α and a normally closed valve 51 connects the outlet 52 of bottle 50 to the interior of bag 48. The buoy release mechanism of this invention in this embodiment includes an explosive charge device 52 for opening valve 51 to permit bag 48 to be charged with gas and become buoyant. Valve 51 includes a rupture disk (not shown), and explosive charge device 52 includes a primer 52 which is electrically connected to the electronic circuit 28 of buoy 20. Explosive powder is placed in the valve 51 housing, and this powder is ignited in response to an electrical output signal from circuit 28. When ignited this powder causes the rupture disk to rupture thus breaking the seal between bottle 50 and the interior of bag 48. The buoy of FIG. 6 includes the same electronics and buoy recall code receiver as the buoy of FIG. 2, and as with explosive release mechanism 34 described with respect to the buoy of FIG. 2, primer 53 is ignited in response to receipt of an electrical signal of sufficient magnitude from the receiver means.

Inflatable bag 48 also includes a vent hole 48b which includes a check and relief valve 48&lt;? in it. Valve 48b permits fluid above a certain pressure to escape from the bag, but prevents water from entering the bag through hole 48b. If the bag has water in it, this water will be expelled upon inflation of the bag to increase the buoyancy of the bag. With bag 48 attached and inflated, buoy 20 has sufficient buoyancy to ascend and meter out an anchor cable from a spool (not shown) which may be connected between buoy 20 and an underwater structure.

The system for remotely calling buoy 20 is illustrated in FIGS. 7-12. A preferred form of transmitter 24 is shown in FIG. 7 in which a plurality of sound sources, such as blasting caps, are actuated in a timed sequence

3,722,014 to provide a buoy recall code comprising a plurality of distinct signals. Transmitter 24 includes a source of periodic pulses such as oscillator 54 which puts out a sine wave signal at a relatively high frequency, for example, 7680 cps. The frequency of oscillator 54 is preferably controlled by a tuning fork (not shown) and is very stable. The output of oscillator 54 is connected to a seven stage countdown counter 55 which divides the 7680 cps input signal to obtain a relatively low frequency 60 cps signal at the output of counter 55, and on line 56.

An arming switch 57 connects oscillator 54 to a power supply 58, and a “fire” switch 59 is connected to actuate counter 55. When it is desired to transmit a buoy recall code, switch 57 is first actuated, starting oscillator 54. Switch 57 is also connected between power supply 58 and three blasting caps 60, 61 and 62, each of which are fired by the charge on a firing capacitor CF, such as shown in FIG. 7B for blasting cap 60. Actuation of arming switch 57 also places voltage on each of capacitors CF so that these capacitors begin to charge. The normally closed contacts 63α of a relay 63 are connected across caps 59, 60 and 61 and prevent these caps from being inadvertently fired while capacitors CF are being charged. Relay 63 is actuated by fire” switch 59, and when sufficient time has elapsed for capacitors CF to charge to a sufficient value to fire caps 60, 61 and 62, this switch can be closed. Counter 55 is also connected to switch 59, and actuation of this switch causes a 60 cps output at line 56. Cap 60 is fired at this time, and a predetermined timing sequence for the firing of caps 61 and 62 begins.

Line 56 is connected to the input of an eight stage binary divider 64 in which each of the eight stages has two outputs equivalent to one of a binary “ 1 ” or binary “0.” A reset but 65 is connected through additional normally closed contacts 63b of relay 63 to power supply 58, and bus 65 applies a reset voltage to the eight stages of divider 64 until relay 63 is actuated. When relay 63 is actuated all the stages of binary divider 64 which had previously been held in reset to their binary “1” states are changed to a binary “0” state upon generation of the next input pulse from line 56. Coincident with all stages of binary counter going to zero, a pulse from stage 8 is conducted to cap 60 to cause it to be fired. The firing of cap 60 provides the first of a series of distinct mechanical signals which in the embodiment described comprise the buoy recall command.

Two AND gate circuit 65 and 66 are connected to the outputs of each of the binary stages of divider 64. Gates 65 and 66 each have eight inputs, and each input is connected to one of the binary “1” or binary “0” output terminals of each stage of binary divider 64, and the manner in which these gate inputs are connected determines the time intervals between firing of cap 60 and cap 61, and between firing of cap 61 and cap 62. When all the stages of binary divider 64 have a binary “1” output, a total count of 255 is provided which represents 255 pulses from line 56 after start of a counting cycle. The firing of caps 61 and 62 can be set to occur at different time intervals, represented by a count of up to 255 pulses from line 56. However, of these 255 time intervals it is preferred that the first 60 be ignored since a 60 cps control pulse is being used, and that multiples of 60 (120, 180 and 240) also be ignored. Thus, with these exceptions the timing intervals between firing of cap 60, 61 and 62 can be at a count of anywhere from 61 to 255, and the number of code combinations is great.

For example, gate 65 is connected to provide an output at the receipt of 167 pulses on line 56 after start (represented by the binary number 11100101), and gate 66 is connected to provide an output at the receipt of 219 pulses on line 56 after start (represented by a binary number 11011011). The output of gate 65 is conducted to the firing circuit for cap 61 to cause it to provide the second of the series of distinct mechanical signals of the buoy recall command, and the output of gate 66 is conducted to the firing circuit of cap 62 to cause it to be fired to provide the third of the series of distinct mechanical signals of the buoy recall command.

The firing circuit for cap 60 is shown in FIG. 7B; the firing circuits for each of caps 61 and 62 being identical to the circuit of FIG. 7B. Cap 60 is connected at one terminal 60 to ground through a charging capacitor CF, and the other terminal 68 of cap 60 is connected to power supply 58 through a resistor 60 and the contacts of switch 57. As previously noted, when arming switch 57 is closed, capacitor CF charges through the normally closed contacts 63α of relay 63 which are connected across cap 60. An SCR 70 is also connected through its power electrodes between terminal 68 and ground, and when SCR 70 conducts, it provides a discharge path for capacitor CF, through cap 60. However, “fire” switch 59 must be closed, and thus, the contacts of relay 63 opened for this to occur; otherwise, the discharge path for capacitor CF would be through these contacts. Thus, when both switches 57 and 59 have been actuated, cap 60 is ready to be fired upon conduction of SCR 70.

The command pulse for firing cap 60 is applied to the gate of SCR 70 through a diode 71 and a terminal 72. The command pulse for firing cap 60 is obtained from stage 8 of binary divider 64 on coincidence of the first 60 cps pulse after removing the reset of binary divider 64. The outputs of gates 65 and 66 provide the command pulses to fire caps 61 and 62. An order to reduce the likelihood of a spurious signal causing SCR 70 to conduct, an RC filter 73 is connected to the gate electrode of SCR 70.

Thus caps 60, 61 and 62 are fired from transmitter 24 in a predetermined time sequence, and the sound waves from this firing comprises a coded recall command which is transmitted through the water to the submerged buoy 20. A preferred form of of receiving means 28A in buoy 20 for receiving this recall command is shown in FIG. 8. An important feature of this invention is that the buoy recall command includes a series of distinctive signals arranged in a predetermined code sequence, and the buoy recall receiver will act to recall the buoy only upon receipt of the properly coded command. A great number of coded commands can be sent by transmitter 24, and the buoy recall receiver 28A can be made highly selective to respond to only one of these commands. Thus, a large number of submerged buoys 20 can be located in the same general area and a selected one of the buoys can be recalled one at a time without disturbing the other buoys. One

3,722,014 relaxation oscillator having an unijunction transistor Q2 and two RC timing circuits. The first of these RC circuits includes resistors R5, R6 and timing capacitor, C1, and provides the first timing interval prior to actua5 tion of the first timing pulse G. The second of these RC circuits includes resistors R3 and R4 and timing capacitor Cl, and provides the second timing interval when switched into the circuit with unijunction transistor Q2. This switching is accomplished by an SCR Q4 which ¹⁰ changes the charging path for Cl when it is caused to conduct. The gate of SCR Q4 is connected to function as an AND gate and is normally biased or locked off through diodes D6 and D7. However, terminal 83 is _]5 connected to the negative output of window pulse shaper 78, and when this output F goes negative in response to generation of the first window pulse, one leg of the bias applied to the gate of SCR Q6 is removed. D6 is connected to the output of interval.

timer 79 and when the first interval timing pulse G is received, this leg of the lockout bias is overcome, and SCR Q6 conducts, causing Cl to be charged now through resistors R3 and R4 to begin a second interval timing cycle. Also the voltage H at terminal 80A 25 changes from a high first level to a lower second level as shown in FIG. 12. Prior to the switching of Q6 the charging path for Cl is through diode D2 and resistors R5 and R6, and transistor QI which is connected in the voltage path for R3 and R4 is biased off. When Q6 con³® ducts, the voltage across D2 is lowered, and QI conducts to permit charging of Cl through R3 and R4. The values of the RC circuits for a particular buoy receiver are selected to provide timing intervals corresponding to the intervals between the three signals of the proper ³⁵ buoy recall command for that buoy.

If the second timing interval begins, indicating receipt of the second of the signals of the recall command, then the third such signal, when received, will ₄₀ generate another output pulse C from circuit 76 which will in turn generate a second 100 ms window pulse E. If the second timing pulse G occurs during this window pulse, indicating receipt of the third signal of the recall command in proper sequence, then an output pulse J is generated by a final contact circuit 83 which is connected to squib 33 to fire the explosive squib charge. First contact circuit 83 is connected to terminal 80A and responds to the voltage H, and is connected to respond to squib timing pulse G and the second window pulse F. Circuit 83, like second level circuit 80, preferably includes an SCR functioning an an AND gate with its gate electrode locked off except upon receipt in coincidence of window pulse E and second timing pulse G during the time that voltage H is in the second level.

Several other circuits may be included in buoy recall receiver 31A in order to greatly reduce the chances of a false recall of buoy 20, and to reduce battery drain * during periods in which signals other than the recall 6® command are being received. The outputs of window pulse shaper 78, interval timer 79 and second level circuit 80 are all connected to a turn-off circuit 84, a preferred form of which is shown in FIG. 11. As shown ₆₅ turn-off circuit 84 includes an SCR Q7 which is connected to tum-on circuit 77 to turn it off under proper circumstances. The gate electrode of Q7 has multiple inputs and is normally biased or locked off. An input 85 basic transmitter can be used, and different code boards plugged in to recall different buoys. Also, because of the coded recall command used and the highly selective receiver 28A, the likelihood of a false recall by spurious noise is greatly minimized.

In the preferred form of receiver 28A illustrated, the buoy recall command is received by a hydrophone 74 which converts the mechanical signals received to electrical signals shown as the waveform A in FIG. 12. The received signals are amplified and clipped in an amplifier-clipper 75 to provide the pulses shown as B in FIG. 12, and these pulses are conducted to a pulse shaper circuit 76, which is preferably a one-shot multivibrator. A short duration square wave pulse, shown as pulse C in FIG. 12 is provided at the output of pulse shaper 76, and pulse C is conducted to a turn-on circuit 77 and a window pulse shaper circuit 78. The buoy recall receiver includes an interval timer circuit 79, a second level circuit 80 and a reverberation lockout circuit 81 all of which, in addition to window pulse shaper 78, are turned off during standby periods and prior to generation of pulse C, because line 82 is maintained at a voltage level above effective ground. As shown in FIG. 11, turn-on circuit 77 includes a switching device, such as an SCR Q5, and a transistor Q6 connected between a source of voltage from batteries 31 and line 82. The output of pulse shaper 76 is connected to the gate of SCR 05, and upon receipt of pulse C, Q5 conducts to lower the voltage in the base of transistor Q6 and lower the voltage at line 82 to an effective ground and thus renders the circuits connected to it operative. The voltage on line 82 is shown as the voltage level D in FIG. 12. When this occurs, interval timer 79, which is shown in detail in FIG. 10, begins its timing cycle by, for example, changing a timing capacitor Cl.

At the end of the first timing interval for the buoy recall command and in response to receipt of the second signal of the recall code, a second pulse C is generated from pulse shaper circuit 76, and this pulse is conducted to window pulse shaper circuit 78 which previously was made operative by being effectively grounded through line 82 as described above. Circuit 78 is preferrably a one-shot multivibrator having a rela- 45 tively wide duration output pulse E, for example 100 ms, which is generated in response to pulse C. Meanwhile, assuming that the proper coded command is being received, interval timer 79 completes its first timing cycle and generates a first timing pulse G. If 50 pulse C has been generated at the proper time indicating receipt of the second recall code signal, then the first timing pulse G will fall within the window of pulse E, and the interval timing sequence of receiver 28A will continue in anticipation of receipt of the third signal of the recall command after passage of a second timing interval. If coincidence of pulse G and window pulse E do not occur, then turn-on circuit 84 is turned off as hereinafter described to stop the interval timing sequence.

As shown in FIG. 10, the interval timer 79 is connected to second level circuit 80 which comprises a switching means for switching interval timer 79 to a second timing cycle in response to receipt of the second of the series of recall signals at the proper time. One form of interval timer 79 and second level circuit 80 is shown .in FIG. 10. Interval timer 79 includes a

3,722,014 is connected to reverberation lockout circuit 81, which is described below, and an input 87 is connected to the negative output (pulse F) of window pulse shaper 78. If either pulse F or the output from circuit 85 is applied to the gate of SCR Q7 without the other, then SCR Q7 will conduct and send a pulse L to turn-on circuit 77 causing it to turn off. Another input 88 to the gate of SCR Q7 is connected to the output (pulse G) of interval timer 79, and an input 89 is connected to the positive output (pulse E) of window pulse circuit 78, and if either of these pulses appear without coincidence of the other, SCR Q7 will also conduct pulse L to tum-on circuit 77 causing it to turn off.

Reverberation lockout circuit 81 is preferably a oneshot multivibrator, and is normally biased off by the bias on line 82. When the bias on line 82 is removed in response to the receipt of a pulse C by tum-on circuit 77, lockout circuit 81 puts out a 250 ms pulse (pulse I in FIG. 12) which is conducted to terminal 85 as previously described so that SCR Q7 will not conduct due to the coincidence of pulse I with pulse E. Also, circuit 81 is connected to interval timer 79 and upon generation of the first timing pulse G a second 250 ms lockout pulse I is generated by lockout circuit 81 and conducted to turn-off circuit 81. Upon coincidence of this second lockout pulse I and the positive going trailing edge of pulse E from window pulse shaper 78, the generation of turn-off pulse L by turn-off circuit 81 is prevented.

As noted, the window pulses E and F are generated by pulse C in response to input signals received by hydrophone 74, and the window pulses will cause SCR Q7 to conduct to turn circuit 77 off unless the coincidence referred to above is present. Thus, the receipt of an improperly coded command or other spurious signals will cause such a turn off. The purpose of the 250 ms pulses from reverberation lockout circuit 81 are to prevent this turn off for a predetermined period after receipt of the first and second signals of the recall command so that reverberations from the generation of these signals which might occur during this 250 ms period will not cause the generation of turn-off pulse L.

A recycle delay circuit 90 may also be connected between turn-off circuit 84 and turn-on circuit 77 to apply a bias or lockout signal to tum-on cirtuit 77 which inhibits its turn on until a predetermined period after receipt of turn-off pulse L. This delay period, which may be in the order of 6-10 seconds, prevents recycling of the timing circuits and pulse shaping circuits connected to line 82 until after the delay period so that a continuous noise source, such as a boat propeller, does not cause a continuous drain on the batteries supplying power to receiver 28A. Circuit 90 may be a one-shot multivibrator providing a pulse of the required duration, which pulse applies a lockout bias to the gate of SCR Q5 to prevent its conduction in response to pulses C shaped by pulse shaper 76.

After turn-off pulse L has been generated by turn-off circuit 81, Q7 and Q5 need to be reset by charging of their gate capacitors prior to shaping of any further pulses in circuit 76. Since this reset has a slight delay, an overlap lockout circuit 91 is preferably provided to prevent circuit 76 from shaping pulses so that circuit 77 is inhibited for a preset period sufficient to permit resetting of these SCRs. Circuit 91 may include a diode and an RC circuit connected to the output of turn-off circuit 84 and pulse shaper 76, and its output is shown as pulse N in FIG. 12.

FIG. 9 shows another form of interval timing means such as a binary counter circuit 79α which may be utilized in receiver 28A to provide the first and second interval timing pulses G. The timer 79α of FIG. 9 is identical to the encoder of transmitter 24 which includes the circuits 54, 55, 64, 65 and 66 shown in FIG. 7A. Timer 79α includes a tuning fork oscillator 92, a seven stage countdown counter 93, an eight stage binary divider 94, and two AND gates 95 and 96. The output of gate 95 provides the first timing interval pulse and the output of gate 96 the second timing interval pulse in the same manner in which the second and third fire command pulses for caps 61 and 62 are provided by gates 65 and 66 of transmitter 24, the operation of these circuits being identical. Because of the tuning fork oscillator 92 and since RC circuits and an unijunction transistor is not used, the timer 79α of FIG. 9 is generally more stable than timer 79 previously described. For this reason the width of the window pulses E can be reduced (for example to 60 ms) to decrease even further the likelihood of a false recall of the buoy by reducing the possibility of coincidence of spurious signals. Also, during manufacture of the transmitter and receiver for a specific buoy, identical timing sections can be made for each, and the outputs of binary dividers 64 and 94 connected to their respective gates in an identical manner, thus facilitating manufacture.

In the foregoing description of the preferred form of coincidence circuits of receiver 28A, window pulses E are generated by the second and third of the incoming received signals A and the first and second timing pulses G are generated by completion of an interval timing sequence begun in response to receipt of the first of the series of received signals A comprising a coded command. Coincidence of the first generated permit window E and the first interval timing pulse G cause a first permit pulse which in this case is the second level pulse H¹ which acts to partially arm the gate of final contact SCR by transition of the voltage level H from its first level to its second level. Generation of the second window pulse E completes the arming of the final contact 83 SCR gate so that, in this embodiment, generation of the second timing pulse G within this window causes the final contact SCR to conduct and produce a second permit signal J which fires the squib charge.

Similar coincidence may be provided if the permit windows E are generated in a predetermined timed sequence by an oscillator or clock started in response to the receipt of the first of the series of the received signals A, in which case the window pulses will be the first and second interval timing pulses. Firing of the squib will occur if a series of pulses like pulse C, generated in response to receipt of the second and third of the received signals A, are coincident respectively with a series of the internally generated window pulses.

Because only the circuits 74, 75 and 76 are operative during standby periods before receipt of an incoming signal, and because of the action of turn-off circuit 84 and recycle delay 90, battery drain is kept at a minimum until a buoy recall command is decoded. Thus, it can be seen that the present invention provides

3,722,014 a retrievable buoy which can be located at a submerged location for relatively long periods of time with assurance that it will not discharge its batteries and not be recalled in response to spurious noise signals. Also, when it is desired to recall the buoy, the proper buoy command is transmitted to the buoy, and the range of certainty of recall is greatly enhanced over prior retrievable buoys. The buoy may be modularized for ease of shipment and assembly, and uses highly reliable code generating and recognition circuits. Also, the explosive release mechanism insures complete separation of the buoy from its anchor cable and good reliability.

Also, while the recall transmitter 24 and recall receiver 28A have been described in conjunction with their function to recall a submerged buoy, such a transmitter and receiver could be utilized to perform other functions at inaccessible locations, such as underwater.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.