Emergency airplane locating transmitter

Abstract

A bracket mounted, portable airplane emergency locating transmitter manually or automatically actuated for transmitting radio distress signals with voice capabilities which is automatically actuated by a predetermined gravitational force along the flight axis of the aircraft.

Description

BACKGROUND OF THE INVENTION

This invention pertains to apparatus manually or automatically actuated to transmit on civilian and military international distress frequencies of 121.5 MHZ and 243.0 MHZ distress signals.

Heretofore, devices of the above type have failed to serve the dual plane mounted and portable uses so that distress signals could not be properly transmitted and clearly picked up by search parties. The former devices also lacked durability on impact to prevent damage to the transmitter and were complex and costly to produce, thereby placing them outside of small plane owners' use.

SUMMARY OF THE INVENTION

In accordance with the invention claimed, an improved portable or bracket-mounted airplane locating device is provided which has both automatic distress tone and voice modulation capabilities and is automatically or manually operable, depending on how the selector switch is set.

It is, therefore, one object of this invention to provide an improved device for locating a downed aircraft.

Another object of this invention is to provide apparatus for identifying a plane crash site and thereby reduce the rescue time.

A further object of this invention is to provide an immediate radio signal on a given frequency at the moment of impact.

A still further object of this invention is to provide a downed plane transmitter that is self-contained and may be bracket-mounted and operated with a fixed external antennae or portably used with a telescoping antenna, and which requires little maintenance for long periods of time.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

BRIEF DESCRIPTION OF THE DRAWING

The present invention may be more readily described by reference to the accompanying drawings, in which:

FIG. 1 is an exploded, partially broken-away perspective view of a portable or bracket-mounted airplane locating device incorporating the features of this invention;

FIG. 2 is a perspective view of the portable device shown in FIG. 1 with the portable telescopic antenna mounted in position;

FIG. 3 is a schematic illustration of the circuitry embodied in the airplane locating device shown in FIG. 1;

FIG. 4 is a wiring diagram of the transmitter; and

FIG. 5 is a modification of the remote control feature shown in FIGS. 1-4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings by characters of reference, FIG. 1 discloses a downed or crashed airplane locating device 10 comprising a housing 11 having a detachably mounted back 12 which is formed for fitting into an airplane-mounted bracket 13. An antenna 14 is shown for being received and retained by a connector 15 mounted on the face or front 16 of housing 11.

The housing 11, as viewed in FIG. 1, comprises a compartment 17 containing four batteries 18A-18D, a compartment 19 containing a printed wiring board (PWB) 22 and an auxiliary compartment 23 in which is mounted an impact switch 24. A partition 25A in back 12 and a similar partition 25B in housing 11 separates the battery compartment 17 from compartment 19 and auxiliary compartment 23.

On the front 16 of housing 11 are mounted in addition to antenna connector 15 a master switch 26, a microphone jack 27, a remote control jack 28, a "power on" indicator 29, and an impact switch reset button 30. Detachably mounted back 12 and associated neoprene gasket 90 are normally held in position against the rear side of housing 11 by six screws, two of which, namely screws 32 and 33, are shown. The screws pass through clearance holes 34, 35 and 36 in back 12 and turn into threaded holes (not shown) in the rear of housing 11. An integral carrying handle 37 is provided at the top of housing 11.

Airplane-mounted bracket 13 is normally secured to the frame of the airplane and is employed to hold the airplane locating device 10 in place. For proper operation of impact switch 24, the mounting position for bracket 13 should be such that arrow 38 shown on face 16 of housing 11 is pointed in the direction of flight. Bracket 13 is made from a flat piece of sheet metal formed into a flat rectangular pocket-like center section 39 for receiving and supporting housing 11 and more particularly the rear surface of cover 12. Its wrap-around top flange 40 formed by two right angle bends 42 and 43 passing under handle 37 causes the tab formed by bend 43 to fit over the top edge 45 of surface 16 of housing 11. Side flanges 46 and 47 of mounting bracket 13 are bent to secure the sides of housing 11 and prevent its lateral motion. A lower flange 48 comprising a first flat surface 49 extending at a right angle to center section 39 and a second flat surface 50 extending laterally thereto in a plane parallel to center section 39 bears against a lower edge 53 of back 12 and serves in cooperation with top section 40 to prevent longitudinal motion of housing 11. Surface 50 is a mounting surface for retainer clip 54, and when clip 54 is placed over surface 50 of section 48, fastener 56 by engaging with mating part 57 of fastener 56 grips lower extension 58 of housing 11 to firmly capture and retain housing 11 within bracket 13. A plastic ring 59 loosely secures clip 54 to bracket 13 when clip 54 is not secured by fastener 56. Clip 54 is thus prevented from being lost or misplaced when not in use.

Antenna 14, which may be of a telescopic configuration, is equipped with a twist-lock connector 62 that mates with antenna connector 15 on housing 11. Two snap clips 63A and 63B are provided on the side of housing 11 to hold antenna 14 when it is not in use. The clips expand to snap over the outer cylindrical surface of the antenna to hold it in place.

FIG. 2 shows antenna 14 mounted by means of connector 62 to housing 11 and detachably mounted back 12 in position on housing 11.

The simplified schematic of FIG. 3 shows the electrical relationships between physical parts illustrated in FIG. 1. A transmitter 64 is assembled on printed wiring board 22 of FIG. 1. Other parts shown in FIG. 3 which are identified by the same numerals in FIG. 1 are antenna connector 15, impact switch 24, microphone jack 27, remote control jack 28, light-emitting diode (LED) power-on indicator 29 and batteries 18A-18D. A resistor 60 connected in series with LED power-on indicator 29 limits current through the diode when voltage is applied thereacross. Transmitter 64 delivers modulated radio-frequency signals to antenna 14 via antenna terminal 69 when negative input terminal 65 and positive input terminal 70 are connected to the negative and positive terminals 71 and 72, respectively, of series-connected batteries 18A-18D. Positive terminal 72 of batteries 18A-18D is permanently wired to transmitter terminal 70. When master switch 26 is in the ON position, negative battery terminal 71 is connected directly through switch 26 to transmitter terminal 65. When master switch 26 is in the OFF position, battery terminal 71 is not connected to transmitter 65 and the transmitter does not operate. When master switch 26 is in the AUTO position, connection between battery terminal 71 and transmitter terminal 65 can only be made through switch 26, and thence through impact switch 24 or remote cabin control switch 28 to terminal 65. If either of these switches (24 or 28) is closed, the transmitter will operate. When battery voltage is applied across terminals 65 and 70 by any of the means described above, current will flow through resistor 70 and light emitting diode 29, and diode 29 will emit light, indicating the transmitter 65 is energized and should be delivering modulated radio frequency signals to antenna 14 via terminal 69 and antenna connector 15. For operation in the automatic mode, switch 206 is moved to the AUTO position. Impact switch 24 will normally be open, but the impact of a crash by the airplane will close impact switch 24 to complete the circuit between battery terminal 71 and transmitter terminal 65, thereby initiating operation of the transmitter. Following closure of impact switch 24, the impact switch may be reset to the open condition by depressing reset button 30. Impact switch 24 is of the well known type offered to the market by Technar, Inc., and sold by them as an acceleration sending switch. Details of this switch are shown in a copending application filed by the same applicants as this application and entitled "Airplane Crash Locating Device", Ser. No. 389,967 filed Aug. 20, 1973.

When master switch 26 is in the automatic mode, the pilot of the airplane may wish to operate the transmitter even though no crash has occurred. He may be out of fuel and contemplating an emergency landing in a remote area or he may wish to test the operation of the device. A remote switch accessible from the pilot's position in the aircraft and connected by means of an electrical cable to remote control jack 28 may be closed by the pilot to accomplish this purpose.

The signal delivered by transmitter 64 is automatically modulated by a sweep frequency multivibrator. Alternatively, voice modulation may be employed by means of a microphone connected at jack 27.

The circuit diagram for transmitter 64 as shown in FIG. 4 includes a crystal oscillator 73, a modulator 74, an output amplifier 75, a relaxation oscillator 76 and a stable multivibrator 77. The transmitter is powered from batteries 18A-18D, which are connected to positive input terminal 70 and negative terminal 65.

Crystal oscillator 73 is a transistorized version of the well known plate tuned plate vacuum tube oscillator in which a piezoelectric crystal serves as the series tuned circuit for the grid. In oscillator 73, piezoelectric crystal 78 acts as a series tuned LC circuit in the emitter base circuit of oscillator transistor 79.

Piezoelectric crystals are commonly used in oscillator circuits of this type because of their ability to control with a great deal of accuracy the frequency of the oscillator. When excited electrically, the crystal tends to vibrate at its resonant frequency, which is determined by its dimensions and other mechanical properties. In the presence of such mechanical vibrations, electrical signals are produced across the opposite faces of the crystal. The equivalent electrical circuit drawn between these two opposite crystal faces comprises a first capacitor connected directly from one face to the other and in parallel with the first capacitor, a series network including a second capacitor, an inductor and a resistor. The first capacitor represents the shunt capacitance between the two faces and its capacitance is much greater than that of the second capacitor so that the resonant frequency is determined almost entirely by the second capacitor and the inductor.

In the case of the preferred embodiment of this invention, the resonant frequency of the crystal is 121.5 Mhz. A first terminal 82 of crystal 78 is connected in parallel with resistor 95 to emitter 83 of transistor 79. Resistor 93 is the collector resistor for transistor 79 providing a stabilized operating impedance for the tuned collector circuit comprised of inductor 88 and capacitors 87 and 89.

Capacitors 87 and 89 and inductor 88 comprise a tuned circuit in the collector circuit of transistor 79. This tuned circuit is adjusted by adjusting the value of inductor 88 to set its resonant frequency near the crystal frequency. Resistors 85 and 92 and bypass capacitor 91 establish the operating point voltage for the amplifier portion of the oscillator and RF ground of the base circuit necessary for a common base configuration. The network comprising resistors 95 and 96 and capacitor 97 sets the desired DC and AC emitter impedance to ground. The combined resistances of both resistors 95 and 96 constitute the DC resistance, while only resistor 95 is effective as an Ac resistance because of the shunting of resistor 96 by capacitor 97. Resistor 98 acts as a power divider to adjust the R-F signal level to modulator 74 and feed back through crystal 78 to transistor 79. Resistors 99 and 144 act as a DC divider network to appropriately adjust the DC bias of transistor 142.

Relaxation oscillator 76 comprises an oscillator stage including unijunction transistor 101, resistors 102, 103 and 104 and capacitor 105, and an amplifier stage including transistor 106 and resistors 107, 108, 109 and 110.

Unijunction transistor 101 in the oscillator stage has an emitter 111, a first base 112 and a second base 113. The impedance between emitter 111 and base 112 is high until emitter voltage exceeds a given fraction, typically five-tenths to seven-tenths of the voltage impressed from base 113 to base 112. When this fraction of the base-to-base voltage is exceeded, the impedance from emitter 111 to base 112 drops abruptly to a very low value. The term commonly employed to identify the fraction of base-to-base voltage at which the drop in emitter-to-base impedance occurs is "the intrinsic standoff ratio." The very low emitter-to-base impedance is sustained only so long as the emitter-to-base current is sustained above the critical "valley current" (typically 1 to 10 milliamperes) for the device.

In the relaxation oscillator 76 of FIG. 4, the initial base-to-base (113 to 112) voltage is essentially equal to the battery voltage present at positive input terminal 70 relative to negative input terminal 65, the latter being at ground potential. Battery voltage in the preferred embodiment is approximately 7.2 volts. Assuming an intrinsic standoff ratio of 0.6, capacitor 105 will be charged exponentially by a current flowing through resistor 104 to a voltage equal to (7.2 .times. 0.6) 4.32 volts, whereupon the emitter-to-base impedance of unijunction transistor 101 will drop abruptly to a very low value, allowing capacitor 105 to discharge quite rapidly, the discharge current flowing from the upper plate 110 of capacitor 105 to emitter 111, to base 112 through resistor 103 to ground. Resistor 103 limits the discharge current. When the discharge current falls below the valley point current of unijunction transistor 101, the emitter-base impedance returns to its very high level and capacitor 105 again begins to charge exponentially as before. The discharge time interval is typically very short compared with the charging interval and the resultant voltage waveform across capacitor 105 is thus a sawtooth waveform with a relatively slow and nearly linear rising portion and a relatively steep and abrupt falling portion. The period of the sawtooth waveform across capacitor 105 is approximately equal to the product of the value of the resistance of resistor 104 times the value of the capacitance of capacitor 105.

The sawtooth waveform just described is applied by means of resistors 107 and 108 acting as a voltage divider to the base 114 of transistor 106. Transistor 106, having resistor 110 connected between its emitter 115 and ground, reacts in the manner of a high input impedance DC coupled amplifier in which the voltage gain is a function of the current gain of transistor 106 and the ratio of collector resistor 109 and emitter resistor 110. A sawtooth current waveform thus flows in collector resistor 109 and voltage waveform at collector 116 of transistor 106 is thus an inverted sawtooth waveform with the characteristics of the waveform produced at the emitter of transistor 101 and previously described.

Stable multivibrator 77 is commonly employed to produce a rectangular wave voltage at its output terminal 117. The two transistors alternately switch ON and OFF, the first turning ON as the second turns OFF and then at the next switching time, the first turning off as the second turns on. In the switching operation, the transistor turning off is aided by the transistor turning on and the transistor turning on is aided by the transistor turning off. Assume, for example, that transistor 118 is initially off and transistor 119 is initially on. The right hand terminal 121 of capacitor 120 is held essentially at ground potential by virtue of its connection through diode 122 and thence through saturated transistor 119 to ground. The left hand terminal 123 of capacitor 120, by virtue of the charge remaining on capacitor 12, is still negative with respect to ground, and is thereby sustaining transistor 118 in its off condition by holding its base 124 at a negative potential relative to ground. This charge on capacitor 120 and the negative potential at base 124 are steadily being reduced, however, by a charging current flowing from collector 116 of transistor 106 through resistor 130 into terminal 123 of capacitor 120. At this same time, capacitor 126 is being charged toward battery voltage applied at terminal 70 of transmitter 64, the charging current flowing through resistor 127, capacitor 126 into base 128 of transistor 119 and from emitter 129 to ground, thereby aiding in sustaining the on condition of transistor 119. At some point in time, the charging current to capacitor 120 will raise the base 124 of transistor 118 to a sufficiently positive potential (approximately 0.6 volts) to supply a base drive current into base 124 and thereby switch transistor 118 to the on condition. As transistor 118 turns on, its collector 131 moves quickly to a very low potential barely above ground, and by virtue of its connection through diode 132 it also drives the left-hand terminal 133 of capacitor 126 to a voltage only slightly more positive than ground. Because the right-hand terminal 134 is at this time substantially negative with respect to the left-hand terminal 133 as the result of the charging current that had been flowing through capacitor 126 during the previous interval, right-hand terminal 34 and hence base 128 of transistor 119 are now substantially negative with respect to ground and transistor 119 is thereby switched to and sustained in the off condition.

The conditions of the previous interval are not reversed such that a charging current through resistor 135 and capacitor 120 into base 124 now holds transistor 118 in the on condition while a current flowing from collector 116 of transistor 106 through resistor 136 into right-hand terminal 134 of capacitor 126 reduces the charge on capacitor 126 and gradually raises the voltage at base 128 of transistor 119 from an initially negative value toward the slightly positive value necessary to switch transistor 119 on and thereby initiate the succeeding interval.

It has been noted that each interval is terminated when the charging current through resistor 130 or 136 has raised base voltage of the off transistor 118 or 119 to a sufficiently positive level to switch the off transistor to an on condition. This condition will be produced relatively sooner or later, depending upon the voltage present at collector 116 of transistor 106.

It has been shown previously that the voltage present at collector 106 is of an inverted sawtooth form beginning at an initially high value and falling slowly toward a minimum value. During the initially high value, the charging of capacitor 123 or 126 through resistor 130 or 136, respectively, will occur rather rapidly and the intervals described above relating to "on" and "off" periods of transistors 118 and 119 will be relatively short, i.e., the switching frequency will be relatively high. As the initially high value of the sawtooth wave decays, the switching frequency also decays until the sawtooth wave switches abruptly from its minimum value and the switching frequency of the astable multivibrator simultaneously jumps abruptly to its highest rate.

As transistors 118 and 119 of the multivibrator 77 alternately switch from off to on in a periodic manner, the voltage present on collector 131 of transistor 118 as well as the voltage at collector 117 of transistor 119 is a rectangular wave. During the "on" condition of transistor 118, for example, collector 131 of transistor 118 is essentially at ground potential, while during its "off" condition its collector 131 is pulled up to battery voltage by pull-up resistor 137, which is connected between collector 131 and positive battery terminal 70. Similarly, collector 117 of transistor 119 is essentially at ground potential while transistor 119 is on and it is essentially at battery voltage during the off period of transistor 119 by virtue of the connection of pull-up resistor 138 between collector 117 and positive battery terminal 70. Note that diode 132 is reverse-biased when transistor 118 is off so that collector 131 of transistor 118 is isolated from the voltage drop appearing across resistor 127 as a result of charging current to capacitor 126. Collector 117 of transistor 119 is similarly isolated during the off period of transistor 119 by the then reverse-biased diode 122.

Modulator 74 has a first input terminal 100 which receives the 121.5 Mhz output of oscillator 73, and a second input terminal 139 which receives the rectangular wave output of the multivibrator 77 as taken from collector 117 of transistor 119. Modulator 74 includes two transistors 142 and 143, five resistors, 144, 145, 146, 147 and 148, a coupling transformer 149, three capacitors 152, 153, and 154, and an output terminal 155.

In the operation of modulator 74, the signal received from oscillator 73 at modulator input terminal 100 is transmitted to output terminal 155 when transistor 142 is biased in its active region, but the signal from oscillator 73 is not transmitted to output terminal 155 when transistor 142 is biased in its off condition. The bias condition of transistor 142 is produced by the action of transistor 143 in response to the signal it received from input terminal 139.

Thus, for example, assume that the instantaneous voltage at input terminal 139 is essentially zero volts. The base of transistor 143 is held substantially at ground potential by a base voltage applied through resistor 148 to base 156 and transistor 143 is held substantially at ground potential by a base voltage applied through resistor 148 to base 156 and transistor 143 is thus held "off." Resistors 145 and 146 act as a voltage divider network connected between positive battery input terminal 70 and ground and the divider terminal 157 is substantially more positive with transistor 143 off than the DC value of the signal present at modulator input terminal 100. By virtue of the connection of divider terminal 157 to the emitter 158 of transistor 142 and the connection of base 159 of transistor 142 to input terminal 100, emitter 158 is accordingly more positive than base 159 and transistor 142 is thus biased in the off condition so that the signal from oscillator 73 is not transmitted to output terminal 155. Assuming now that the signal at input terminal 139 is positive, a base drive current flows through resistor 148 into base 156, turning transistor 143 on. When transistor 142 is turned on, the voltage at terminal 157 is substantially more negative than when transistor 142 is off, and emitter 158 of transistor 142 is no longer positive with respect to base 159. The input signal from oscillator 73 is now transmitted via transistor 142 and coupling transformer 149 to output terminal 155. The RF signal appearing at output terminal 155 has thus been shown to be modulated on and off by means of the rectangular wave signal appearing at input terminal 139 as received from multivibrator 77.

Capacitor 152 is selected to be resonant with the inductance of transformer 149, thereby becoming a parallel resonant circuit at the RF frequency. Capacitor 153 is an RF bypass for emitter 158.

Transmitter 64 is also designed to permit voice modulation as an alternate mode of operation. Microphone jack 27 provided for this purpose has a signal terminal 162, a grounding terminal 163 and a chassis ground terminal 164. When a microphone is plugged into jack 27 and pressing the "talk" button of the microphone connects terminal 163 to ground, transistor 119, by virtue of the connection of its base 128 to grounding terminal 163, is held in an off condition so that the multivibrator 77 becomes inoperative. The signal from the microphone installed in jack 27 is now transmitted via coupling capacitor 154 to the base 156 of transistor 143 and the microphone signal thus drives transistor 143 over a range spanning the conductive to non-conducting states of transistor 143, thereby controlling the bias condition of transistor 142 and accordingly modulating the signal from oscillator 73 at the audio-frequency rate produced by the microphone. Resistor 165 and diode 166 supply voltage to the microphone through jack 27.

Output amplifier 75 includes a transistor 167, a coupling capacitor 168, a high frequency bypass capacitor 169, inductors 172 and 173, biasing resistors 174 and 175, tank circuits 176 and 177, and output terminal 178. The combination of inductors 172 and 173 in conjunction with tank circuits 176 and 177 form a ladder network filter for impedance matching of the transmitter to the antenna at the desired frequencies. Bias resistors 174 and 175 establish the desired DC bias condition at the base 183 of transistor 167 so that the output signal from the modulator 74 coupled from terminal 155 through capacitor 168 to the base 183 of transistor 167 produces a pulse of RF collector current in transistor 167 corresponding to each cycle of oscillator voltage passed by modulator 74. The pulses of collector current of transistor 167 flowing through inductor 172 excites tank circuit 176 at the crystal-controlled frequency of 121.5 Mhz produced by oscillator 73 and as modulated by modulator 74. Tank circuit 176 is thus caused to ring or oscillate in synchronism with the oscillator signal at 121.5 Mhz. Inductor 172 provides a path by which synchronizing impulses are supplied to tank circuit 176 and at the same time it provides adequate AC isolation between tank circuit 176 and transistor 167 to permit the substantially sinusoidal oscillation of tank circuit 176. High frequency energy at 121.5 Mhz is coupled to output terminal 178 through inductor 173. The tank circuit 177 is tuned to a resonant frequency of 243 Mhz and it receives current pulses via inductors 172 and 173 as transistor 167 responds to signals delivered by modulator 74. For each impulse received by tank 176, two cycles of oscillation occur therein at its resonant frequency of 243 Mhz. Both the 121.5 Mhz oscillator signal and its 243 Mhz harmonic are thus present at output terminal 178, which is connected to antenna 14.

An improved and exceptionally versatile emergency airplane locating transmitter has thus been described which may be automatically energized on impact or manually energized. The transmitted signal is modulated by means of a specially controlled multivibrator which produces a periodically changing audio distress signal. It is also designed and equipped to permit voice modulated output signals by connecting a microphone to jack 27 on the front of housing 11. The device is equipped with a special mounting bracket so that it may be secured to the aircraft and it is also fitted with a convenient carrying handle for portable use.

A second embodiment of the remote control structure shown in FIGS. 1-4 is shown in FIG. 5, wherein a +12v DC source 190 energizes a bus 191 of the aircraft through a circuit breaker 192, cabin switch 193, remote connector 194, remote disable module 195 and aircraft grounding terminal 196. The disable module 195 and connector 194 are integral parts of the airplane locating device 10. Cabin switch 193 is remotely located in any suitable position for convenient access by the pilot.

The remote control feature in this second embodiment has three operating modes; i.e., AUTOMATIC, REMOTE ON and REMOTE OFF. These three operating modes are determined by the position of the remote cabin switch 193 which has a double pole, double throw, center off configuration.

For automatic operation, cabin switch 193 is set in the "AUTO" position for which no interconnections are made between any of its six contacts, A, B, C, D, E and F. Activation of transmitter 64 of device 100 is thus dependent in this mode upon the operation of inertia switch 24 as in the case of the embodiment shown in FIGS. 1-4 wherein transmitter 64 is energized from the negative terminal 71 of battery 18A-18D through master switch 26 in its "AUTO" position, inertia switch 24 in its closed condition to transmitter terminal 65. The positive terminal 72 of battery 18A-18D is directly connected to the positive transmitter terminal 70.

The "REMOTE ON" mode is employed when an emergency has occurred due to a forced landing and the pilot of the aircraft wishes to activate transmitter 64 manually from the cockpit. In this case, remote cabin switch 193 is set to the "on" position, which closes contacts D and E of this switch. Contacts D and E are connected in parallel with inertia switch 24 through terminals G and H of connector 194, and serve as a manual means of overriding the open condition of switch 24 or as a means for insuring operation when inertia switch 24 should have closed or might have closed due to the impact of a crash landing. In either event, transmitter 64 is energized as in the automatic mode except that the negative battery connection may be made in this case through closed contacts D and E of remote cabin switch 193 rather than through inertia switch 24.

The "REMOTE OFF" mode is employed only in the event that the inertia switch 24 has been closed inadvertently and the unit has been activated without need. In this situation, the pilot of the aircraft sets the remote cabin switch 193 to the "off" position, which connects the +12v bus 191 via main circuit breaker 192, contacts B and C of cabin switch 193, and terminal J of remote connector 194 to positive input terminal 197 of remote disable module 195. The negative input terminal 198 of remote disable module 195 is returned via terminal K of connector 194 to aircraft ground terminal 196. A positive 12 volt source is thus contained to positive terminal 197 relative to negative terminal 198 of module 195, and a resulting current flowing from terminal 197 through resistor 199, 4.7 volt zener diode 200 and fuse 201 to negative terminal 198 establishes a +4.7 volt potential at cathode 202 of zener diode 200. The 4.7 volt potential is applied through diode 203 to the junction of resistors 95 and 96, which are serially connected between emitter 83 of transistor 79 and ground in oscillator circuit 73 of transmitter 64. The emitter base junction of transistor 79 is thereby biased to an "off" condition and oscillator 73 is thus disabled. In normal operation, when the "remote off" condition is not set, diode 200 is reverse biased by the positive operating voltage present at the junction of resistors 95 and 96 and the remote disable module 195 has no effect on the normal operation of transmitter 64.

Fuse 201 is incorporated as a fail-safe mechanism which is operated in the event the "remote off" mode has been set and a subsequent crash occurs, in which case it is desirable that the transmitter 64 should be rendered operational. In the event of such a crash it is likely that external fixed antenna 15 will come into contact with the frame of the aircraft. Such a contact making an electrical connection between antenna 15 and aircraft ground causes fuse 201 to open as a result of a fault current flowing from positive battery terminal 72 to transmitter terminal 70 through inductor 181, antenna terminal 178, aircraft frame or ground to ground terminal 196, terminal K of remote connector 194 and fuse 201 to negative battery terminal 71. The resultant opening of fuse 201 effectively removes the +12 volt potential at terminal 197 and the remote disable module 195 is itself disabled and prevented from interfering with the operation of transmitter 64.

Severing or shorting of connections between remote connector 194 and remote cabin switch 193 during a crash also results in fail-safe conditions in that transmitter operation is not thereby prevented.

Loss of the +12 volt source or the opening of the main breaker 192 in the event of a crash will also cancel the effect of the "remote off" condition to allow transmitter operation. Thus, a useful and highly reliable remote control capability is provided.

Although but two embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications of the invention may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

Claims

What is claimed is:

1. An airplane locating device comprising:

a hand-carried portable housing,

said housing comprising a rectangular configuration having a battery compartment at one end, a transmitter compartment between its ends and a handle at the other end,

said housing defining a display plane on its front surface adjacent said transmitter compartment for mounting and exposing to an operator a selector switch and a microphone jack,

a bracket for detachably fitting one face of said housing,

said bracket being fixedly attached to the airplane for holding firmly said device,

switching means mounted in said housing for selectively connecting a battery placed in said battery compartment with a transmitter placed in said transmitter compartment,

said switching means comprising a selector switch and an impact switch,

said selector switch in one position directly connecting the battery in said battery compartment to the transmitter in said transmitter compartment and when in another position connecting the battery through said impact switch to the transmitter,

said impact switch upon closure under given impact forces energizing the transmitter,

a transmitter mounted in said transmitter compartment transmitting periodically changing audio distress signals on civilian and military international distress frequencies,

a microphone jack mounted on said housing for transmitting by said transmitter a voice modulated output signal,

a connector in electrical contact with the output signal of said transmitter for attaching a radiation antenna to said housing, and

means mounted on said housing for resetting said impact switch to its contact open position.

2. The airplane locating device set forth in claim 1 in further combination with:

connector means mounted on said housing for remotely controlling the energization of said transmitter for test purposes.

3. The airplane locating device set forth in claim 1 in further combination with:

a radiation antenna for connection to said connector for broadcasting distress signals generated by said transmitter.