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Publication numberUS3234468 A
Publication typeGrant
Publication dateFeb 8, 1966
Filing dateNov 8, 1961
Priority dateNov 8, 1961
Publication numberUS 3234468 A, US 3234468A, US-A-3234468, US3234468 A, US3234468A
InventorsBryant F Craig
Original AssigneeAmalga Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Conelrad warning device
US 3234468 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Filed Nov. 8, 1961 United States Patent O 3,234,468 CQNELRAD WARNING DEVHCE Bryant F. Craig, Ariington, Tex., assigner to Amalga Corporation, Dallas, Tex., a corporation of Texas Filed Nov. 8, 1961, Ser. No. 150,946 7 Claims. (Cl. S25-466) This invention relates to a radio warn-ing device and more particularly to a radio receiver warning device for developing and delivering an audible warning of an impending national emergency.

More specifically, the present invent-ion relates to an electronically actuated signal decoding apparatus, the `operation of which is dependent upon the reception of radio frequency signals transmitted pursuant to and in accordance with the standard CONELRAD warning system.

The instant apparatus may be used in application where lan alerting signal of the predetermined CONELRAD code actuates one portion only of the apparatus which in turn causes a standard superheterodyne transistorized radio receiver to be actuated so as to render a signal reproducing device operative and thereby result in Aan audible announcement of an impending national emergency.

The instant `apparatus may be also used in conjunction with the predetermined NEAR code which is transmitted over pre-existing power transmission lines and networks.

Various radio warn-ing systems and devices have been known for many years. None, however, are particularly suited for use in conjunction with standard CONELRAD warning signals and many of the prior devices require complicated equipment and expensive circuit components. The present invention avoids these difficulties by p-roviding a simplified, inexpensive unit usable in civilian, industrial or governmental sites to give an audible indication of an emergency and which unit is particularly suited for use in conjunction with standard CONELRADv warning alerts.

Further, most of the heretofore known radio warning systems relied principally upon the fact that, in the event of a national emergency, modulation of the `broadcast carrier frequency of standard transmitting stations would cease, thereby causing signalling means, such as lights, buzzers, bells, etc., to be actuated. Such systems, however, are not practical or effective since Ithere are often circumstances when standard transmitting stations transmit only a carrier wave for short periods of time. It is apparent therefore, that under such conditions, systems operating on the above-mentioned principle would emit false alarms.

Still further, since it is obviously desirable to quickly alert the populace and instruct lthem on the proper course of action to be taken in the event of a national emergency, many of the heretofore known systems have suggested the use of centrally located loudspeakers. However, an obvious disadvantage, regarding centrally located loudspeakers, is that a sizeable portion of the populace may not hear the emergency because of the-ir physical location in respect to the loudspeaker.

Yet still further, most of the heretofore known radio warning systems and devices required specic and cumbersome procedures for attachment thereof to existing superheterodyne radio receiver-s commonly found in civilian, industrial and governmental sites. Such arrangements were often objectionable in that the normal operation or use of the radio receiver was impaired or the cost for connecting the device or system to the radio receiver was considerable.

Yet still further, most of the prior known radio warning systems or devices were unreliable, ineffective, and inefficient in performing the function intended should the commonly available 110 volts, 60 cycle, alternating cur- ICC rent power supply be disconnected. That is to say, the receipt of a warning of an impending disaster, or the like, was not perfected in the event that conventional alternating current power commonly available in this coun-try were to be disconnected for one reason or the other.

In addition, the heretofore known radio warning systems have required the continuous operation of the entire Warning device, Whereas, the device and principles of the present invention permit conventional superheterodyne trans-istorized radio receivers to be uniquely modified so as to receive and respond to CONELRAD alerts and yet not require the continuous full operation of the apparatus, thereby resulting in a noticeable economy of operation.

While the present invention may be used in a variety of civilian, industrial and governmental applications, the principle of operation makes it particularly useful for the unattended reception and reproduction of CONEL- RAD code signals. Accordingly, the present invention may be used for civil defense purposes by the gener-al public, by operators of Iradio broadcasting equipment and by commercial, industrial or amateur services which are presently Irequired by law to have available CONELRAD responsive equipment in order that radio broadcasting, except for civil defense purposes, may be discontinued during a national emergency.

The present invention avoids the above set forth diii culties by providing a simplified and inexpensive unit usable in civilian, industrial or governmental sites to develop and deliver an audible indication of a national emergency and which device is particularly suited for use in conjunction with the standard CONELRAD system as well as the standard NEAR system.

Copending application Serial No. 123,469, now Patent No. 3,121,841, tiled July 12,1961, in the names of Craig and McCartney, discloses a Warning device in the form of a small portable transistor radio receiver. rl`he present invention relates to a Warning device of the type disclosed in said copending application but is of simpler and more inexpensive construction, making it more economical for mass production and mass utilization.

It is therefore a primary object of the present invention to provide a novel radio warning device capable of civilian, industrial and governmental use.

Another object of the present invention is to provide a unique system for developing and delivering audible warnings of a national emergency.

Still another object of the present invention is to provide a simplified receiving unit for civilian, industrial or lgovernmental use for developing audible Warnings of a national emergency.

Yet still another object of the present Iinvention is to provide an inexpensive radio warning device particularly suited for use in conjunction with the existing CONELRAD warning system.

A further object of the present invention is to provide a novel radio warning device which is capable of delivering an audible Warning of a national emergency notwithstanding the destruction or discontinuance of conventional A.C. power supply commonly used by radio receivers in this country.

A still further object of the present invention is to provide a unique Warning device which is capable of receiving `the CONELRAD signal code and 'et does not require the continuous full operation of the apparatus there-by resulting in economy of operation.

A yet still further object of the present invention is to provide a novel Warning device whereby the CONELRAD emergency signal code alctuates a portion of the device which in turn causes the receiver port-ion of the device to lne-actuated thereby giving an audible warning of an impending national emergency.

An additional object of the present invention is to provide a warning device wherein a continuously operating, unattendedresponding circuit thereby is responsive Vtofthe-CONELRAD signal code and which circuitauto- Vmatically'actuates an alertirigcircuit thereby resulting in an audibleiwarningfof an impendingnationaldisaster. A still additionalo'oject of 4-the `presentlinvention isto provide a novel emergency warning device particularly suited for use in conjunction with Athe existing CONEL- :RAD warning system which issirnple in. construction, economical to manufacture, and highly reliable vin performing the function intended.

These and further objects and advantages :of the invention will be'more apparentupon reference tothe following specification, claims and. appended drawing wherein: :The single `gure of the drawing .ishaxdetailed circuit diagram of the novel portion of the radio warning device ofthe present invention.

,While-the present `invention is described in conjunction with,l and is particularly' suited for usewith, the existing VCONELRAD radio warning system.-the present inventionhas ;utility in conjunction with `other emergency warning purposes such -as general broadcast information,

rrtornado,hurricane and other weather warnings, police and ',iire warnings,and other, emergency warnings.

Injthe event of an enemy bomber or missile attack, it is well known thatthe general public Vwill have very little `warning andwill' have `onlyashort time to, -takeycover,

4 via leads 22 and 24 and the contacts 28 and 30 of a rst re1ay26 to a speaker 32.

The audio signal developed at the primary of transformer is also delivered by way of lead 34 and contatcs 36 and 38 `of a seoondrelay 40 to the base electrode of an NPN junction transistor 42. The signal is then coupled by vresistor 43pand capacitor 44 to parallel resonant circuiti which is connected tothe base electrode of a transistor 42.

Connected to the `actuating coil of relay 26 by way of resistor 48, is a double pole double throw switch 50.

Switchit) yis provided with a parallel swinger 52 and two While conventionalair raid warning `sirens to vsome p extent provide a useful general warning system,'they have many undesirable features, amongwhich may be listed the high expense of installation Aand upkeep, along with the periodic disturbance and annoyance to the public when the .sirens are tested or inadvertently turned on.

The novel warning `device of the present invention Y may be incorporated in a small container inthe form of 'hour day on an automatic basis so that it does, not depend on-the owner having his radio turned lon and `will operate to warn the owner even during the nightwhen most are asleep.

, Referring now to the drawing, the device of the present invention, generally indicated at lil, includes the front end of a conventional superheterodyne transistorized radio receiver lindicated by the dashed box 12. The entire device takes the'form of a small portable transistor radio receiver as more fully described in said copending application Serial No. 123,469, now Patent No. 3,121,841. Recalling that the radio receiver includes, inter alia, conventional rstyand second detector stages (not'shown), and that the output from the second detector ofthe radio receiver is applied to terminal-14 and passes through a pair of audio amplier stages including PNP'junction transistors 16 and 18. The audio signal is then inductively coupled through audio transformer 420 and delivered fpairsof stationary contacts54 and 56. When swinger52 is moved.V to.v engage .contactsl54, the switch is ina first position, hereinafter referredto asthe ALARM position; and when the swinger 54 is moved to engage contacts S6,

Connected to the lower stacouplesthesignalinthe collector circuit of `transistor 42 to the base electrode of transistor 16 so as to provide regeneration and enhancing of the volume of the signal reproduced by speaker 32.

Ajsecond switch 60 isprovided which, when -in theopen position, `asshown inthe drawing, permits the receiver to .betuned to any radio carrierfrequency. or preferably tunes y.thereceivertolthe mostl powerful l-ocalabroadcast station.

.'driawing, there is shown a plug 62foriinsertioninto the conventional A.C. p oweroutlet-comrnonly availablejn this country vso as to, provide. the 60 cycle, 11-0 volt voltage i supply for the-l device. Blug l62.is coupled to a-lament i transformer;64, which1steps ,down the "110. volt supply so that;,approximatelyvr 1l volts is availableat junction 66.

The .A C.,voltage,is rectiiiedin rdkioclepand passes/through the ltercircuit ,comprisingresistorvfltl and parallel ca- `.lector electrode of .transistorl is.connected to a resistor '.92 wh1ch develops. andndeliversthe .transistoroutput sigt supplyline, 82..v1a.v the energizing coil. of relay lltland lead 10.0. y The .output of, transiston energize-s the `energizing .coll of relay40, and .causes lthe contacts of that .relayx to pacitors 72and f'7 4. A, second diode-276,isolates the AC.

- powersupplyy from ay 9,volt;sta ndby battery 78. vNegative lpotentialis supplied from junction 66 by wayof lead 80 v tonegative supply line Slandpositive potential is supv pliedfrorn :the opposite side of transformer.y 64 by Way-of 45y lead 84 to positive supply line; 36.

Theyconventional automatic .volume control voltage dev veloped in the superheterodynereceiverv is applied toterrrnnal 2S-,and hence to` the base .electrode` of NPN junction transistorftl. Theemitter electrode of transistor .90.is connected toinegative supply lineZ Vvial-cad 91. The colnal by way of capacitor 94 and resistor 196 `tofthe -base electrodeofPNP junctiontransistor. The collector electrode..of..transistor-.98 is connectedto the negative close therebycoupling the output signal of transistor 18 4to, the base `electrode of transistorflz via resistor 43 and capacitor44.

CYCLE OF OPERATION .lr1.;.operation, ,fthe/alarm device 10 is plugged into the A.C. power outlet commonly available in this country and `remains.,sile nt until a CONELRADcode signal is transduring or after an attack, the A.C. power should fail, the

-ldiscontinu/ance of negative 11 volts,potential at junction 66 permits battery 78 to feed into the load wthrough diode *'76 .and automatically take overV as the power supply f or the device. Diode 'p76 operates somewhat like a relay perm1tt1ng9 volt batteryf to be inoperative or have full shelf life until the A.C. power is removed for any reason. When the A.C. pow-er is disconnectedfor any reason, such as, the plug 62 being removed from the wall outlet, battery 78 automatically furnishes current to the load. However, so long as the A.C. power is connected to the device, the battery 78 will be isolated from the device by diode 76 and only a very low current in the micro-amp region is drawn during standby or isolation period.

The alarm device may be initially tuned to one of the stronger local stations so that the CONELRAD code signal will be received at any time it is sent from the local broadcast station. Therefore, the switch 50 must be in the ALARM position with swinger 52 engaging stationary contacts 54.

During a CONELRAD alert, the regular local broad cast station transmission is replaced by the CONELRAD cod-e signal which ultimately results in a 1000 c.p.s. modulation of the broadcast station carrier. This 1000 cycle signal actuates the device of the present invention and connects speaker 32 in the circuit so that the 1000 cycle signal can be reproduced so that the owner of the device may hear a loud audible tone through the speaker 32. This audible tone is greatly amplified by the regenerative circuit including capacitor 58. Once the owner of the device is alerted by this audible tone, he can then move manual switch 50 from the ALARM position to the LISTEN position, i.e., swinger 52 engaging stationary contacts 56. This movement of switch 50 disconnects the regenerative feedback loop from the circuit so that the device now functions as a simple radio receiver tunable to any local broadcast station frequency so that any instructions or information that may he broadcast by the local station can be heard and heeded.

It is presently contemplated by Civil Defense authorities that sometime after the initial warning, all local broadcast stations will discontinue transmission on their regular broadcast frequencies and various stations throughout this country will commence broadcasting over the CONELRAD frequencies. When this happens, it is possible for the owner of the device to close switch 60 so that the device is automatically tuned to the CONEL- RAD frequency whereby additional information and in structions may be heard. It will be recalled that when switch 60 is closed, it automatically connects a capacitor across the RF input coil (not shown) so as to automatically tune the receiver to either the 640 or 1240 c.p.s. CONELRAD frequency.

The CONELRAD recognition or control circuit in the device of the present invention operates off the conventional AVC receiver with the AVC voltage signal supplied to the base electro-de of transistor 90. The CONEL- RAD signal code is characterized by a standard broadcast station carrier being (l) OFF `5 seconds, (2) ON 5 seconds, (3) OFF 5 seconds, (4) ON with a 1000- cycle modulating tone superimposed thereon and (5) ON indelinitely with audio modulation of instructions and information. During normal operation of the local broadcast station, the negative AVC voltage supplied t0 the base electrode of transistor 90 maintains the transistor in a non-conducting state. Transistor 98 is likewise normally non-conductive with capacitor 94 normally charged through the lower portion of resistor 92 to the positive potential of the power supply.

During the rst 5 second interval of the CONELRAD code, i.e., carrier OFF, the AVC voltage at terminal 88 rises and the potential at the base electrode of transistor 90 also rises suficiently to permit transistor 90 to conduct. Conduction of transistor 90 lowers the potential at the base electrode of transistor 98 and thereby permits capacitor 94 to partially discharge through transistor 90. However, during this first 5 second interval of the CONELRAD code, capacitor 94 does not discharge suiiiciently to permit transistor 98 to conduct. During the second 5 second interval of the CONELRAD code,

i.e., carrier ON, capacitor 94 tends to recharge through resistor 92 but the time constant of resistor 92and capacitor 94 is such that during this second 5 second interval, capacitor 94 does not charge to its initial voltage level but rather to some lower intermediate voltage level. During the third 5 second interval of the CONELRAD code, i.e., carrier OFF, capacitor 94 again discharges through transistor but to a suiicient level so as to permit transistor 98 to conduct near the end of this third 5 second interval of the CONELRAD code. Capacitor 94, in conjunction with resistors 96 and 92, acts in the manner of an integrator so that transistor 93 will conduct for approximately one or two seconds during the fourth interval of the CONELRAD code, i.e., carrier ON with the modulating tone now superimposed thereon.

Conduction through transistor 98 passes suicient current through the coil of relay 40 to energize this relay and close the contacts thereof.

The closing 0f relay 40 momentarily delivers the audio signal, i.e., the 1000 cycle tone, at the primary of transformer 20 to the base electrode of transistor 42. Resonant circuit 46 has a bandwidth or" approximately 100 to c.p.s. on either side of 1000 -c.p.s. and discriminates against all other signals. This 1000 cycle tone is rectified in transistor 42 and smoothing capacitor 43, and energizes the coil of relay 26 so as to close the contacts of that relay.y The coil of relay 26 receives suiiicient -current from the power supply via the series circuit including lead 84, the coil of relay 26, reistor 48, contacts 54 and 52 of switch 50, and lead 55 to the negative potential line 82 so as to retain the contacts of'relay 26 closed even after the 1000 cycle tone disappears. This latter power supply current is insuiiicient to draw the Icontacts of relay 26 in but is suiiicient to hold the contacts of relay 26 in after it has been closed by current conduction through transistor 42. The closing of relay 25 places the speaker 32 across the secondary of transformer 20 so that the audible tone can be reproduced thereby.

The subsequent movement of the switch 50 from the ALARM position to the LISTEN position disconnects feedback capacitor 5S and relay 25 from the device and places the speaker 32 directly across the secondary of transformer 20. When switch S0 is in this position, the receiver may he removed from the wall outlet and carried about as a portable transistor radio so that instructions transmitted by the local broadcast station can be fheard. Accordingly, switch 60 may then be closed and the device automatically tuned to one of the two CONEL RAD frequencies.

It will be apparent from the foregoing that the device of the present invention is low in cost, rugged in construction, and requires very little maintenance. The use of a standby storage supply provides economy in that the life of the battery in conjunction with the present invention is near the shelf life thereof.

It is further apparent from the above that the present invention provides a simple and inexpensive radio receiver alarm device of a size comparable to a portable transistorized radio'receiver. The alarm system is operative both day and night and can be preset to a local station so that any time the CONELRAD alert is transmitted, the receiver is automatically energized and broadcasts a 1000 cycle CONELRAD tone as an audible sound to awaken sleeping household occupants or to draw the attention of occupants to the fact that an alert is being given. Also, through the manual switches 50 and 60, it is possible to switch the receiver from the ALARM position to the LISTEN position wherein the speaker 32 is normally driven Without regeneration. When switch 50 is in this LISTEN position, the unit may be removed from the A.C. power outlet and carried around as a portable transistor radio automatically tuned to the preset local station. As soon as the connection is broken to the A C. power outlet, battery 78 immediately is cut into .the circuit and supplies the operating voltages for the device. Further, the closing of switch 60 connects a suitable trimming capacitor to the receiver of the device and automatically tunes the RF stage of the receiver to the CQNELRAD frequencies so that the device then constitutes a portable transistorized radio tuned to the CONELRAD frequencies for receiving the CONELRAD code signal.

From the foregoing it will be seen that this invention is uniquely adapted to obtain all of the ends and objects hereinbefore set forth together with lother advantages which are obvious and which are inherent to the device.

It will be understood that certain features and subcombinations are .of utility and may be 4employed without reference to other lfeatures and subcombinations. This is contemplated by and is within the scope of the appended claims. i

It is to be -understood that the device of the present invention may be readily modied so as to be responsive to any code signal which maybe adopted by governmental authorities for the purpose of notifying the ,populace of an imminent and impending emergency without departing from the scope of the invention. Accordingly, the hereinabove described CONELRAD signal code systemV is merely exemplary of one of the presently adopted YCivil Defense systems to which the device of the present invention is responsive and should not be construed as restricting .or limiting. By Way ofV example, the device of the present invention may be modified to be responsive to a signal code system which .utilizes power -transmission lines or ltelephone lines as the means yfor linking the signal between the transmitter and the receiver. A system of the latter type has been adopted by Civil Defense Authorities and is commonly lreferred to as the NEAR warning system. Thus, ya modification of the device of the present invention so as to be responsive Ito the NEAR signal code is clearly contemplated and requires only minor circuit changes.

vIt is to be further understood that the parameters of the regenerative feedback circuit (5d-58) are preferably designed so as to drive the rear-end of the transistor radio (1S-Z0) into oscilla-tion so that the audio tone (1000 c.p.s.) reproduced by the speaker 42 will continue until the 4switch 44 is moved to the LlSTEN position. Of

course, it is not necessary that the rear-end of the radio without departing from the spirit or essential character- -istics thereof. The present embodiment is therefore to `be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoingdescription, and all `changes which come within the rneaning and range of equivalency of Ythe claims are4 therefore lintended to be embraced therein.

What is claimed and desired lto be secured by United States Letters Patent is:

i. A warning device for receiving a transmitted signal code comprising: aradio receiver having second detector circuit, an AF circuit and an AVC circuit, said AVC circuit .developing an AVC signal in accordance with said signal code, a speaker, a first relay actuated switch for connecting said AF circuit to said speaker, a first relay actuating control circuit for actuating said first switch, a second relay actuated switch for .connecting the output of said AFfcircuit to said first control circuit, a second relay actuating control circuit for actuating said second switch, said second relay actuating control circuit connected to receive said AVC signal and including a norinaliy charged storage means, a normally open .discharge switch and a first normally open actuating switch, said discharge switch opening and closing in accordance with the signal code developed by said AVC circuit, lsaid storage means partially discharging through said discharge switch upon each closure of said discharge switch, said first actuating switch closing upon the discharge of said storage means to a predetermined voltage level thereby actuating said second relay actuated switch whereby the output of said AF circuit is coupled to said first control circuit, said first control circuit, upon receipt of said AF output, operating to actuate said first relay actuated switch to connect said AF circuit to said speaker, and a regenerative feedback circuit coupled between the output and input of said AF circuit, said first relay actuated switch, upon actuation in response to said first control circuit, rendering said regenerative feed-back circuit operative.

2. A warning device in accordance with claim 1 wherein: said first 4control circuit includes a tuned circuit resonant to a, portion of said signal code; said AF circuit delivering said signal code to said rst control circuit under 'the control of saidvsecond control circuit; said tuned circuit being coupled to said first switch through a second normally -open actuating switch; said second actuating switch being operative to close in response to said signal code; and said lfirst switch being actuatedupon closure of said second actuating switch whereby the output of said AF circuit is coupled to saidspeaker.

3. A warning device for receiving a transmitted signal code comprising: a radio receiver havinga second detector, an AF amplifier and an AVC circuit; a speaker; a tuned circuit resonant to one audio frequency of said signal code; a .first normally open relay actuated switch connected between said AF amplifier and said tuned circuit for coupling the audio output of said AF amplifier to ysaid tuned circuit; arsecond normally open relay actuated switch connected between said AF amplitier and said speaker for coupling the audio output of said AF amplifier to said speaker; a first normally non-conducting actuating transistor connected between said tuned circuit and said second switch for .actuating said second switch in response to theaudio output of said Atuned circuit; a normally charged storage capacitor; a normally `open discharge transistor connected between said AVC circuit and said storage capacitor for step-discharging saidsto'rage capacitor to a predetermined voltagelevel in accordance with saidsignai code; a second normally non-conducting 'actuating transistor connected between said storage capacitor and said first switch for actuating said rst switch when said storage capacitor discharges to said predetermined voltage level thereby causing said first switch to connect saidv audio output to said tuned circuit whereby said second switch is caused to connect said audio output to. said speaker for reproduction by said speaker.

4. A Warning device in accordance with claim 3 wherein said device further includes a regenerative feedback capacitor coupled between the output and input of said AF amplifier whereby the actuation of said second switch renders said regenerative feedback capacitor operative.

S. Awarning device in accordance vwith claim 4 wherein 4said device further includes a double pole double throw switch for selectively connecting said second switch to said device and saidffeedback capacitor tosaid'rst actuating transistor; or for disconnecting said second switch from said device and saidfeedback capacitor from the output .of said AF amplifier and connecting said speaker to said AF amplifier.

6. A warning device in accordance with claim 5 wherein said device further includes a switch for selectively connecting tuning means to said receiver, said tuning means automatically tuning said receiver to the CONELRAD frequency.

7. A warning device in accordance with claim 4 wherein: said AVC circuit develops an AVC signal in accordance with said signal code and delivers said AVC signal to said discharge transistor; said AVC signal being of 9 sufficient voltage level to render said discharging transistor conductive whereby said storage capacitor is step-discharged in accordance with said signal code; upon discharge of said storage capacitor to a predetermined voltage level, said second actuating transistor is rendered conductive thereby actuating said first switch; upon actua* tion of said first switch, said output of said AF amplifier is coupled to said tuned circuit; upon receipt of said output of said AF amplifier in said tuned circuit, said first actuating transistor is rendered conductive thereby actuating said second switch; upon actuating of said second switch, said regenerative capacitor is coupled between the output and input of said AF amplifier and said speaker is connected across said AF amplifier whereby the audio output of said AF amplifier is reproduced by said speaker.

References Cited by the Examiner UNITED STATES PATENTS 2,882,390 4/1959 Kum et a1 325-364 3,009,059 1i/1960 straffen et a1 325-364 3,010,098 11/1960 Pomeroy sas-364 10 3,056,086 9/1962 Brauner 325-403 DAVID G. REDINBAUGH, Primary Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2882390 *Apr 15, 1954Apr 14, 1959Aircraft Armaments IncRadio receiver alarm
US3009059 *Dec 23, 1959Nov 14, 1961Sarge Alton EAutomatic emergency alert system
US3010098 *May 25, 1959Nov 21, 1961Pomeroy Circle Ct S IncElectrical warning system
US3056086 *Sep 14, 1959Sep 25, 1962Gen ElectricSquelch circuit
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4039957 *Mar 8, 1976Aug 2, 1977Universal Industries, Inc.Signal activated emergency alarm device
Classifications
U.S. Classification375/312
International ClassificationG08B3/10, G08B27/00
Cooperative ClassificationG08B3/10, G08B27/008
European ClassificationG08B27/00T, G08B3/10