|Publication number||US2566121 A|
|Publication date||Aug 28, 1951|
|Filing date||Apr 8, 1948|
|Priority date||Apr 8, 1948|
|Publication number||US 2566121 A, US 2566121A, US-A-2566121, US2566121 A, US2566121A|
|Inventors||Decker Donald P|
|Original Assignee||Decker Donald P|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Referenced by (11), Classifications (12)|
|External Links: USPTO, USPTO Assignment, Espacenet|
A115283 1951 D. P. DECKER Y2,566,121
RADIO OPERATED FIRE ALARM' FiledV 'April 8, 1948 2 Sheets-Sheet 1 Aug. 28, 1951y Y y D. P. DECKER 2,556,121
v .RADIO OPERATED FIRE: ALARM Filed April s, 1948`Y E 2' sheets-sheet 2 4m?? 25 l AAW l 1152?: l v 43; 44,-. 4 24 4|..-
i A 4? y 25 EEA-ADAE' L E f '44@ 44 lf5 Y /A REEIVER F .9 Aw-4 'Q 4'/ Flc-mo 5 25 22 1 /NvEA/rof? DONALD E DECKER ATTORNEYS Patented Aug. 2'8, 1951 UNITED STATES PATENT OFFICE 2,566,121 Immo oPERATEn FIRE ALARM Donald P. Decker, Belmont, Mass. Application April 8, 1948, Serial N o. 19,663
6 Claims. l
This invention relates to electrical nre detection and alarm apparatus and particularly to an automatic nre alarm system of the radio operated type comprising a plurality of self-contained, local station, nre detector and nre alarm signal transmitter units located at positions of maximum lire hazard in the protected property, each of which units is so constructed as to generate a signal carrier whenever iire conditions originate in its vicinity, and a central station radio receiver tuned to the same frequency as the signal carrier generated by the transmitter units, said receiver having provision for sounding a nre alarm signal.
Fire detection and alarm equipment hitherto available for use by owners of private residences, smaller business properties, and rural buildings may be identied under two general classifications, namely, (1) wired-in types of central station systems and (2) local alarm units principally operated by clockwork mechanism or dry batteries.
The wired systems are the most highly rated protection and while they have widespread use among the larger commercial properties, the expense associated with their installation has precluded any appreciable use by smaller type property owners. The local alarm devices are inherently limited, as their name implies, and despite lower costs, have also failed to gain extensive use.
The net result of this situation is the almost total absence of ilre detection and alarm devices in the majority of smaller residential, rural, and business properties.
Authentic statistics reveal that each year the property losses from flre in the United States increases. A` total loss of $700,000,000 has been estimated for. the year 1947. Of the lives lost each year by flre at least two-thirds are casualties in res occurring in residences and apartments.
The present invention is intended to render available to the smaller property owner, a simple, low cost. plug-in type of re detector and radio operated rm alarm signal transmitter unit which affords a standard of protection coinparable to the more expensive forms of wired-in iire alarm systems, but which can be installed in a building by simply plugging the apparatus into the electric light wiring system of said building in the same way that most electrically actuated household appliances are installed, thereby eliminating the necessity of any special wiring for such installation.l
It is recognized that the general public is accustomed to the use of a wide variety of plug-in devices such as electric irons, toasters, electric clocks, radios, etc. from which fact it is highly probable that a plug-in type of re detector and radio operated fire alarm should be favorably regarded and result in a wider use oi such fire detection equipment by a` large number of the owners of smaller type properties which are now exposed to re hazards.
A primary object of the invention is to provide an improved and simplified form of re detector and alarm of the class described whose installation consists simply in connecting a plurality of re detector and radio operated firm alarm signal transmitter units and a radio receiver-alarm unit into the -120 volt alternating current electric light wiring system by screw-in or plugin means at convenient wall plug outlets or light sockets throughout the protected property, said installation thereby being readily accomplished by a layman, Without need for expensive skilled assistance or special wiring.
lA further object of the invention is to provide aplug-in compact form of radio operated :lire alarm signal transmitter unit which is powered from the standard 110-120 volt alternating current electric light wiring system, said unit being so constructed that when rendered operative by an excessive rise in temperature it transmits a carrier signal over the wiring network of said electric light system to a receiver-alarm unit which is plugged into said system at any con-l venient wiring outlet thereof in a protected property.
A further object of the invention is to provide a form of radio operated lire alarm signal transmitter unit having novel features of design and installation which enable it to be manufactured and sold at moderate prices to owners of small type residences, rural or business properties, which hitherto have been largely unprotected because of the relatively high cost of available wired-in alarm systems.
Another object of the invention is to provide a radio operated fire alarm signal transmitter unit which includes a vacuum tube oscillator having a normally open heater circuit that is closed by a self-contained thermostatic re detector assembly associated with said vacuum tube, thereby rendering the vacuum tube oscillator operative to transmit a carrier signal whenever a fire condition originates in the vicinity of said transmitter unit.
Another object ol the invention is to provide a form of thermostatic switch assembly which constitutes an integral part of a radio operated re alarm system transmitter unit but which has means for its simple disconnection from the cas.- ing of said transmitter unit so that adjustment of the thermostatic switch or substitution of one switch for another can be easily made, thus facilitating the ready nter-changeability and use of a wide; choiceorucommercially available approved types ofi thermostatic switches accordingv to the option of a user or t t the protection requirements of a given type of property.
Another object of the invention isv to `provide a radio operated fire alarm signal transmitter unit having means for the extension of. itslthermo-.
static switch circuit to various thermostatic switch units located outside the'casin'g of said*` transmitter unit when it is installed, for example.; in a large cellar or attic area where conventional re protection practices require 4an extended coverage by a numb" of tlermostatic switches in a parallel al- "circuit with the switch contained in the housing ofA said` transmitter u-nit.
Another Object! onf the invention iS to provide a selfcontained, forni of? radio operatedv iirm alarm signal transmitter unit having' simple means embodied' therein for thepl'iysical location of said unit at higl'iposi't'ions with respect toroom ceilings in the protected property,` accordance with` conventionah therrnostaticV coverage practices for alarm. s' temsof the class. described'.
Mothercare@ er me intenties is to provide arado operated fire alarm signal transmitter unit of such comp t'size andiorn a's to be capable of inconspouousinstallation without sacrinc' thereby of' effectiveness is. operation or its ability' to meet thestandardjs' required' by super visor'y' agencies with respect to devices' of' this: kind. i
Another obect of the invention is" to' provide a radioY operated fire alarm signal transmitter unit and a radio receiver alarm unit' having means' incorporated in both units for the simple' test of their operative condition. 1'
A final objectI of the invention is to provide a radio operated firm ala'frn'fi` transmitter unit having meansl for avoiding the possibility of false alarms occurring asa result of spurious radio free quency signals originati-ng outsidefcf the pro-f tected property". v
For a more detailed. understanding of the invention, reference: is made to the. accompanying drawings showing al preferred form'. thereof in which: L
Fig. 1 is a vertical sectional view of the transmitter unit. t
Fig. 2 is a section onthe line 2-v;2, Fig. 1.
Fig. 3 is a section on the line 3*'3, Fig. 1. y
Fig. 4 is a sectional View of an alternate form of casing end cap incorporating a standard male plug for connection with an electric light system standard socket. u
Fig. 5 is aviewshowing installation of a transmitter unit by attachment to a standard electric light ceiling fixture. Y
Fig. 6y isavie'w showing installation or a transmitter unit by suspension` from the ceiling mould ing of aroom. y
Fig. 7 yis a view showing installation of a transmitter unit to a standard electric light system junction box.
Fig. 8 is a perspective view of a terminal mounting strip used Vin the transmitter unit.
Fig. 9 is a 'Schematic Wiring diagram Showing a typical installation employing a plurality of transmitter units.
Fig. 10 is a circuit diagram of the radio transmitter.
Fig. 11 is a circuit diagram of the preferred form of receiver-alarm unit.
For convenience I have used the reference character T to indicate the transmitter units and the reference character R to indicate the receiver unit. I f
- As.V stated above the instal-lation of a re alarm system embodying this invention in a protected property involves simply the operation of plugging. in one or more transmitter units and a ren ceivr' unit into various wiring outlet fixtures of the electric lighting system of said property, the transmitter units naturally being located at points of maximum lire hazard.
'I his is illustrated in Fig. 9 which shows a schematic wiring diagram for a building or pro tested property and in which di. illustrates the main wires 0i'. the lighting .system with the conventional cut-oi switch'V iia' and fuse boi;l 42',V and 43 indicates a plurality ofbranch wiring cii'lcuits,` each of which is providedlwith one or more outlet boxes 44 to which .1"arr'1p`s,` fans, radios or other household appliances' are customarily connected.
As illustrated in Fig. 9` one ofthe `transn'iittei' units 'I embodying my invention is plugged, i'nt Y outlet boxes 44' and will preferably' be solocated that when it is aetuatechitsA alarm signal will" be most readily-heard thro uglfrout'V theV property. Y In many larger residences, th'eg second iloor hallway Vis likely toxbelthe most' suitable location for the' alarm signal.
The* transmitter T which 1 p'erfer't usee'm bodies a vacuum tube which is so wired as' to form an oscillator circuit designed to produce oscillations of the desired wave length, theA power circuit of said tube being connected through a thermostatic switch to the electric light wiring system 4I, 43 'of the protected property as villustrated Fig'. 9, and the oscillator circuit of' said Atube being coup-led tol said wiring' system so that the carrier signal sent out from the` transmitter unit is transmitted over the wires ofthe electric light System to the i'eceiVrYR. y
Fig. l shows d preferred form 'of transmitter unit which comprises a casing 2 preferably cylindrical in form and constructed from 'plastic material or corrosioneresistant light material such. as aluminum, within which is housed the vacuum tube l0 and the elements associated therewith that produce the Y oscillator circuit shown in Fig. 1'0.
The' cylindrical casing 2 is closed at Yone end by a base member 4 of insulating. material which is shown las screw threaded into the end of the y casing as indicated at 3 'thereby `making a dust tight closure for said. end of the casing..y The* the base 4, the assembly thus 4formed can. ben
screwed as a unit into 'the Vend of the casing.
The socket 8 'is shown as Vmoi'udted on the base 4 by Vmeans of screws II which extend through' holes with which the mounting plate I2 of the socket 8 is provided, said screws being screw threaded into the top of the base 4 and carrying spacer sleeves I3 which position the socket 8 a: suitable distance above the base to provide room between the socket and the base for the condensers E, 9 coil 5, resistor 1, etc.
The base 4 together with the socket supporting screws Il thus forms a chassis for the tube and its associated parts. i i Y The type of tube employed in this particular embodiment of the invention is a 117 N7GT, a rectifier beam power amplifier with a heater I4 designed for operation directly across a 110- 120 volt alternating current circuit. The rectifier portion of the tube is not used as will be seen from the wiring diagram Fig. 10. Tubes of other types may be employed with circuit modifications according to the tube characteristics.
Inductance coil 5 of the tube circuit is shown as mounted on a screw I5 carried by and rising from the base 4, said screw extending through the coil mounting cylinder I6 and the latter being clamped in place by two nuts Il. A terminal mounting strip I3 having two connection lugs I9 affording support for wiring leads from the coil 5 and condenser 6 is shown as being mounted on the upper end of the screw I5.
The condensers 6 and 9 and the resistor 'I may be mounted on the base 4 in any suitable way, preferably by connecting the wire leads or terminals thereof to the proper wiring terminals 20 of the socket 3 and the connection lugs I9 of strip I8.
The wiring is partially omitted from Fig. 1 in order not to confuse the drawing, but the circuit connections are fully shown in Fig. 10.
The base 4 is provided with a pair of wiring connections 2i, 2id to which are connected the two wires 22, 23 of a standard line cord 26 by which the transmitter unit is connected to the electric light wiring system of the protected property, said line cord being provided with the usual plug connection 25 adapted to be plugged into any suitable outlet 44 of said wiring system.
The base 4 is also provided with another pair of wiring connections 9| and 92 which will be referred to later.
In order to protect the wiring connections 2|, 2m, SI and S2, and to provide a finished appearance to the end of the transmitter unit, I propose to employ the end cap 2E which is secured to the base il by screws 21 and which is provided with a bushing 28 of insulating material through which the line cord 24 extends.
The base 4 is so made that its screw threads 3 are on the upper portion only thereof, the lower portion 29 of said base portion projecting beyond the lower end of the casing 2. The edge portion 3|! of the cap member 25 embraces said lower portion 29 of the base 4 and is flush with the casing 2.
Means are preferably provided to conceal the screws 21 so as to prevent loosening of said screws and discourage any unauthorized manipulation thereof, and for this purpose there is shown a plate 3| which overlies the end of the end cap and covers the screws, said plate being held in place by a nut 32 screw threaded to the bushing 28.
On the opposite end of the casing 2 from that carrying the base 4 is mounted a thermostatic switch device 33 by which the operationV of the transmitter unit is initiated whenever fire conditions arise in -the vicinity of the transmitter.
Any suitable type of thermostatic switch, of
which there are many on the market, may be used for this purpose. The thermostatic switch 33 is detachably mounted on the end of the casing so that it can be readily removed for adjustment purposes or so that it can be replaced by another thermostatic switch. For thus detachably mounting the thermostatic element on the casing, I have employed an end cap 33 to which 1 the thermostatic element 33 is detachably mounted, and which in turn is detachably mounted on the casing. The end cap 34 is shown as provided with a skirt 35 which embraces the end of the casing, and it is held in place by attaching -screws- 35.
The end cap 313 is formed with a central opening i to receive the wiring connections 33 of the thermostatic unit, and said end cap 3:3 is also provided with slots 39 adapted to receive `screws liti by which the thermostat unit is secured to the cap.
By removing the screws 33 the thermostat and cap assembly can be readily removed as a unit from `the casing, after which the thermostat can be disconnected from the cap by loosening the screws 4U.
ln assembling the device, the cap and the thermostat element will first be secured together by the screws 43 ,and then the wires 23a of the thermostat circuit may be connected to the wiring connections 38, after which the assembled cap and thermostat may be placed on the end of the casing 2 and secured in position by screws 36.
-As shown in Fig. 10, the thermostat is connected in series with the heater It of the vacuum tube I so that normally the heater circuit is open. Whenever fire conditions arise in the vicinity' of any transmitter unit, the thermostat associated with said unit will become operative to close the heater circuit thereby activating the vacuum tube oscillator circuit and causinggeneration of a carrier signal which is superimposed on the electric light wiring system i3 and actuates an associated receiver alarm unit.
The schematic diagram of Fig. 1l shows the wiring of a preferred form of radio receiveralarm unit. triode 45 of the OA4G type is wired in the conventional manner with its tuned circuit-elements;
(inductance 46 and capacitance 4i) `is in series with a signal device such as alarm bell 60 in acircuit 93. Line voltage in the circuit 54 is controlled by a switch 8|) with neon bulb 69 in a parallel electrical circuit serving as a line voltage indicator.
No special claim is made in connection with the receiver unit as such, hence 'no exact constructional details are shown. However, it will be readily apparent to one conversant with the art, that va small sub-panel supporting the receiver and alarm elements shown in Fig. 11 can be As indicated, a cold cathode gas having Values effecting impedance matching with the`` easily tted into the standard miniature or table type radio receiver cabinetsk thus insuring a receiver-alarm unit whose appearance will not disturbthe decorative scheme. of. the most discriminating property owner. It is further evident that with minor adaptations a radio broadcast receiver and electric clock combination could be offered to the using public with the addition of a radio receiver-alarm for the nre detection. service thereby providing a single unit of mani fold utility.
It is readily apparentthat the plug-in feature of said units aords a wide choice of location for effective installation throughout the protected property. Y
Having located said units, as described, let us assume a fire condition` arises in the proximity of one of the transmitter units' T. The heat from the nre rises and circulates in the Well known manner. The thermostatic. switch assembly incorporated in said' unit T is responsive to the ambient tei'nperatureV and has electrical contacts which close when the rate of rise of said temperature exceeds normal. or when a predetermined temperature, say 165 F. isreached.. This closure of the thermostatic. contacts places the normally open heater circuit I4 of' vacuum.
tube lo across the power line 4I and thus causes the generation of a signal carrier of. a frequency determined by the values of incl-uctance 5 and cap-acitance 6 oi Fig.. 1.0. A frequency should be used, 100 kc. for instance, which` creates a nti-ini-s mum of harmonic. interference With. other portions of the radio spectrum. TheV signal. carrier is superimposed upon the electric. light wiring network 4|, t3, thereby actuating the re-` ceiver-alarm unit regardless of. where said unit is plugged. into said wiring. network.`
The carrier signal impressed onsaid wiring network appears` acrossl inductance 66 and capacitance il ofV Fig. 11. wherein a cold. cathode, gas triode lo type OAlG is wired in the conventional manner so that the addition of the resonant signal voltage across capacitance 41 increases the negative potential peaks on thecathode and thus increases thepotential between the cathode '65 and starter-anode 5B.
These peaks start a discharge between the cathode 55 and starterea-node 56. This discharge produces free ions which enable the.V discharge to transfer to the anode 5l since bleeder resistors 53 and SQ are of such-.value as toinsure that sumcient starter-anode. current flows.y The normally open circuit of relay 43 with. protective resistance i9 and condenser 5G is thereupon. closed in turn causing closure of contacts 5lv and 52, thus closing. the normally open` primary circuit of. stepdown transformer 53 and. thus furnishing operating voltage for the alarm device or bell 50 and. sounding the. desired warn ing. that a iire condition. exists.. Extension contacts Si and 92 provide means for an extension of the alarm circuit if sodesired. as hereinafter described.
As is commonly known, the magnitude of the carrier signal voltage required. to actuate the OAllG tube precludes any false alarm caused` by direct radiation from other services inthe. radio spectrum. Furthermore, the. voltage attenuationof. the carrier which. is an inherent characteristic of this type of application acts to limit. its effective use to the wiring. network of av given property. Control of thepower requirements of both receiver-alarm and. transmitter units plus possible use of aline lter or wavel trap could serve,
if necessaryA as additional means to insure the elimination of interference between adjacent installations.
Provision is made for simple tests to indicate the operative condition of the transmitter unitsby means of a test button S3 mounted on thccasing 2 and having contact terminals 64 and: connected in a parallel electrical circuitwithV the thermostatic switch unit as shown ina Fig.
Another similar test button 65 is provided in: the receiver-alarm unit as shown in Fig. 11 with contact terminals 51 and 68 providing means for closure of the. normally open relay contacts 5i and 52 thereby testing the operation of the alarm of Fig. l and in a parallel electric circuit withV contacts 2l and 21a. lt is apparent thatth-ese test provisions provide simple meansv whereby a. layman can check the operative condition ofi a complete system: in a protected property,
One of the most serious obstacles: to thev wide-fr spreadY use of many forms of ther detection and alarm. devices: by own;l
properties has been the objection. to special, eX.-
pensive and possibly unsightly wiring required. The present invention offers advantages of a wired system, but eliminates the need ofV wiring supe iposi'ng a signal carrier on the electric lig-lit wiring network. The compact physical' dimensions oi the radio transmitter unit render possible its eflicient yet inconspicuous mounting in a protected property. It is further evident that through the use of a choice oi basic colors, the transmitter units can be' effectively hare 'ri-ionized with a given room color scheme.
As shown in the transmitter unit can suspended' from the ceiling moulding Q' oi"A room byineans of a hook' lll attached screws' to bosses' i l of casing 2 and having a curved' end which iits snugly over said moulding thus supporting said unit in a horizontal position.A close to the moulding in the least conspicuous manner.. This form of mounting has. two further advan= tages', namely, location of. the thermostatic. switch assembly in. the uppermost area of a. room where, if a fire occurs, the ambien-t temperature most eectively actnates. said switch, and further. the line cord connection from said unit may be conveniently extended close alongside of said moulding to the nearest wall plug outlet. Commerciali-.y available wire clam-ps |2-v may be inserted. under said moulding for. a neat and easy installation and minimum disigure ment of the room decoration scheme.
ln Fig. 5 another method.- of. instal-ling the transmitter unit is shown, using a clamp l3- screwed to bosses il on casing 2 thus aflording, means to attach said unit tothe ordinarily ek.a tended. portion ,of the conduit piping. 'l5 of an electric light ceiling fixture l. Inth-is case as. in Fig. 6, the mounting means insures location of the therinostatic switch, associated with said transmitter, in. an ideal ceiling location in accordance with conventional fire protection practices.
ielectric'light junction box 11 4located ata room ceiling. A mounting plate 13 is substituted 4for cover plate 3l in Fig. 1, and the said unit is fasten ed tothe junction box in the usual manner byu screws 19 fitting into tapped holes of the box 11.* It is apparent that this form of installation has decided advantages in areas such asfcellars or attics and assures conformity with the usual wiring practices.
The transmitter unit may also be constructed to be connected to the electric light wiring system through the medium of an ordinary electric light socket, such a construction being illustrated in Fig. 4 which shows the end cap portion 26 only of the transmitter unit. In this construction the end cap is provided with a tting 8| having a screw threaded shank portion G2 that extends through the enrL cap and the protective plate 3l, said iitting being secured to the end cap by the nut 32.
The tting projects beyond the end cap as indicated at 83 and said projecting portion is made with a sleeve contact 84 constructed to screw into an ordinary electric light socket and also with an end contact 85 insulated from sleeve 84, the circuit wires 22, 23 being connected to these contacts and terminating at contacts 2l and 2id of base 4. When a transmitter unit having the end cap construction shown in Fig. 4 is screwed into an electric light socket, it becomes connected to the electric light wiring system and is in condition to function in case re conditions occur in the vicinity of such electric light socket.
Reference has been made above to the wiring connections 9i, 92 carried by the base l. These wiring connections are connected in parallel with the test button terminals 64, 65 and also with the thermostat wiring connections 38, and they afford means for providing an extension thermostat switch connection by which one or more additional thermostatic switches similar to the thermostat switch 33 can be connected to any transmitter unit T. In some locations, as for instance in an attic or a cellar, it may be desirable to have thermostatic switch devices located at two or three points in the room, and such additional thermostatic switches 33 which are disassociated from a transmitter may be connected to the transmitter through a line cord which is taken through the bushing 28 and connected to the wiring connections 9 i, 92, the opening through said bushing being made large enough for this purpose.
1. A radio-operated iire alarm signaling unit comprising a casing open at opposite ends, a base member of insulating material removably secured to one end of said casing and closing said end, a radio transmitter housed within the casing and mounted on said base member, said base member and transmitter being removable as a unit from the casing, an end cap detachably secured to and closing the other end of the casing, a thermostatic switch element carried by said end cap on the exterior thereof, and means to render the radio transmitter operative to send a radio signal when the thermostatic switch is closed by a rise in the ambient temperature.
2. A radio-operated fire alarm signaling unit comprising a cylindrical casing, a base member of insulating material screw threaded into one end of the casing, a radio transmitter housed ambient temperature.
10 within the casing and mounted on V said base member, said base member and transmitter being removable as a unit from the casing, an end cap detachably secured to and closing the other end of the casing, a thermostatic switch element Vdetachably mounted on theexterior of said end cap, and means to render the radio transmitter operative to send a radio signal'when the thermostatic switch element is closed by a rise in the 3. A radio-operated iire alarm signaling vunit comprising a cylindrical casing, a base member of insulating material screw threaded into one end of thecasing, said base member having a portion projecting beyond the casing end, a radio transmitter housed within the casing and mounted on said base member, the latter and said transmitter being removable as a unit from the casing, a thermostatic switch element detachably mounted on the other end of the casing, means to render the radio transmitter operative to send a radio signal when the thermostatic switch element is closed by a rise in the ambient temperature, an end cap embracing the projecting portion of the base member and having an opening to receive the wire leading to the transmitter, screws connecting said end cap to the base member, and a plate carried by said end cap and both covering said screws and protecting them against unauthorized manipulation. i
4. A radio-operated fire alarm signaling unit comprising a casing open at one end, a base element of insulating material closing said open end, a radio transmitter unit, including a vacuum tube, housed within the casing and mounted on said base element, the latter having a pair of wiring connections for connecting a line cord to the transmitter circuits, a thermostatic switch associated with the transmitter and having contacts which are open at normal room temperature but which close at an elevated temperature and also having a pair of wiring terminals through which said contacts are wired in series with the heater element of the vacuum tube, whereby the circuit of the heater element is normally open but is closed to render said vacuum tube operative by a rise in the ambient temperature, and a second pair of wiring connections on said base element for an extension line cord leading to another thermostatic switch remote from the transmitter, said second pair of wiring connections being connected in parallel with the wiring terminals of the rst named thermostatic switch.
5. A radio-operated iire alarm signaling unit comprising a casing open at one end, a radio transmitter element within the casing and including a vacuum tube and associated radio components, a chassis supporting said tube and radio components, which chassis comprises a base member of insulating material closing said open end of the casing but removable therefrom, posts rising from the base element, a socket element mounted on said posts and paralleling said base element but spaced therefrom, said associated radio components being mounted on the base between the latter and the `socket element, said base together with the chassis and the vacuum tube and associated radio components mounted thereon being removable from the casing as a unit through its open end.
6. A radio-operated fire alarm signaling unit as defined in claim 3, in which the plate carried by the end cap` is larger than said cap and con- 'Y Number wiring system.
DONALD P. DECKER.
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|U.S. Classification||340/288, 455/92, 340/584, 340/538, 340/593, 340/539.1, 340/539.27, 340/538.17|
|International Classification||H04B1/02, H04B1/034|