US2436824A - Radio paging for vehicles - Google Patents

Description

` March 2, 1948. R, K POTTER RADIO PAGING FOR- VEHICLES Filed Dec. 22, 1944 3 Sheets-Sheet -1 .wv N/W 1 nl, m. l |11 .E A

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' March 2, 1948. R, K POTTER RADIO ,PAGING FOR VEHICLES 3 Sheets-Sheet 2 Filed Dec.

EN Si Qml /NVE/vrof? RK. POTTER ATTORNEY March 2, 1948. R. K. POTTER RADIO PAGING FOR VEHICLES 5' Sheets-Sheet 5 Filed Dec. 22, 1944 an m m N MPM wK/Z. EN .R v v1 mN present invention operates as follows.

Patented Mar. 2, 1948 2,436,824 v l mimo PAGING Foa VEHICLES Ralph K. Potter,

Bell Telephone Laboratories,

Morristown, N. J., assignor to Incorporated.

New York, N. Y., a corporation of New York Application-December 22, 1944, Serial No. 569,347 12 Claims. (Cl. Z50-6) This invention relates in general to communication systems and in particularto radio systems in which a single radio transmitting station can selectively signal any one of a plurality of subscribing units. v

The need has been-recognized for a Simple and inexpensive method of communication to enable drivers of vehicles en route from one point to another to be apprisedk of awaiting messages. Such a service is especially adapted for :use by buses and trucks traveling over extendedroutes and by professional persons Such as doctors or salesmen obliged to make a series of consecutive calls in their private'vehicles. -Howeven the system herein disclosed conceivably has many other uses. While radio calling or annunciator Systems of the type disclosed in an article entitled Radio telephone signallingfby Charles S. Demarest, Milton L. Almquist, and Lewis M. Clement, Journal of the American Institute of Electrical Engineers, volume 43, March 1924, have been employed in ship to ship and ship to shore communication, and Similar systems have been utilized for train dispatching and air-transport communication, the apparatus used for these purposes is in general somewhat expensive and cumbersome for the typeof service primarily envisioned by the applicant.

`It is therefore theprincipal object of this invention to provide ya simple means for radio paging of vehicles whereby conventional broadcast program receiving equipment is utilized at least in part for call reception by subscribing units. Y

Another object of this invention is to provide an inexpensive means whereby one of a plurality of subscribing stations may be selectively signalled by the calling transmitter.

A. still further object of this invention isto prow/idea method for increasing the number of subscribing units which can be served with facility by a single call transmitting" unit without appreciably increasing the cost and size of the transmitting equipment. Y

Additional objects will be apparent upon consideration of the following specification.

In a preferred embodiment, the system ofthe A message for a, calling service subscriber is communicated to an operator at thetransmitter station. The operator then selectively signals the designated vehicle subscriberstation whereupon some signal device, such as a lampor a bell, referred to variously hereinafter as, an announcing device or signal annunciator operates to notify Y the subscriber that a message awaits him. vThereupon he may communicate with the calling transmitter station by telephone jat his'earliest convenience to learn the message.

. Certain phrases and terms as 4used hereinafter 1 y in the specification and claims will be defined as follows. y

The phrase calling carrier frequency refers to oscillations preferably but not necessarily of an order of frequencies which is the same as or higher than that of the conventional broadcast range; while the phrase modulating frequencies refers to frequencies of the order of 15 kilocycles or less.V

Message translator refers to any device such as a loud Speaker or an ink recorder connected tothe audio stage of a conventional high frequency receiver whereby the audio modulations of carrier frequency there detected and amplified are translated rinto such a form as to convey meaning to a receiving operator. l VMobile unit refers to any body which may be moved with facility from one place to another. .The phase selector unit or selector mechanism refers to mechanisms of a type Well known in the art whereby one of a plurality of local units may be signalled in preference to the others byvirtue of the fact that the local circuits contain uniquely placed contacts each of which is engaged at a dierent instant during a Stated time interval by contactors or arms moving synchronously in all of the localunits. The selector arm usually but not necessarily moves in rotary fashion about an axis, an attached brush engagingcontacts fixed at desired points on a dial.

:The calling apparatus in a, preferred embodiment comprises a source of radio-frequency carrier oscillations which are fed from a transmitter onto an antenna as a Series of pulses, the duration and timed relationship of Which are controlled by a clock-driven selector mechanism. Removable contact plugs connected to the pulsing means of the transmitter may be inserted into jacks on'the selector dial .s'o that one or many desiredsubscribing stations can besignalled during a particular selector cycle which may be defined as that time interval during which trie selector arm moves from the home position through all the positions on the Selector dial and returns again to the home position. Ina preferred embodiment, the call receiving apparatus may comprisethe conventional broadcast receiving` antenna coupled to a receiver of the type ordinarily employed in automobiles Awhich can be tuned eitherto the broadcast range or to a calling frequency carrier wave. The conventional dash-board clock mechanism furnishes the motive power for operation of the selector which is connected to one optional contact of a two-way switch the common pole of which is connectedto the audio output Y of a conventional receiver and the other optional contact of which is connectedv to a conventional broadcast loudspeaker,V broadly designated in the claims hereinafter'as 'a message indicator or message the clock-driven selector mechanism preparatory to receiving signals from the calling system. A

plug electrically connected to an an n uriciatorV device is fixed at a predetermined position on the subscribers selector dial, 'Aft'er the tsub-` scriber tunes his broadcast receiver tothe calling carrier frequency and operates 'the switch cutting ofi the loud-speaker or other message indicator, the rst received pulse of calling carrier frequency initiates operation of the selector mechanism. When that particular subscribers station is called, a second carrier frequency pulseV is received at that instant when the selector arm at'that 4station engages the contact plug, causing a signal device to operate indicating a call.

It is therefore 'significantthataccording to this invention only the'functionswitch, theselector, and the clutch with its clutch'mechanismneed be added to the conventional car `dasli-board radio and clock equipment to enable vany'particular vehicle'to'b'ecome a participating member of the calling system.

Inv one embodimentof the invention, acentral transmitting unit of carrierifrequency isprovided with apparatus for simultaneously'sending out signals of several diiferent audio modulations. To each 'audio'circuia aseparate select-or'unit vis connected, Vso that `such a transmitting station is thus' enabled toserve several times as "many subscribers Vas can conveniently'be' accommodated'in a selective signalling or annunciator system utilizing pulses of carrier frequency Without audio frequency modulation A tuned-circuit placed vin each subscribers selectorcircuit causesthat particularcircuit when connected to itsirespectivejbroadcast receiverto be responsive to only' one of theaudio frequenci'e sent out by the calling transmitter.

The 'invention will be 'better understo'od'from' a study of the detailed description of 'several embodiments of the features'thereof as'given hereinafter and'by reference'to the accompanying drawings, in'which:

Fig. `1 'is a schematic diagram of apreferre'd embodimentA of a calling system for vehicles shwing` a typical call transmitter 'and call receiving unit;

Fig. '2Ashows schematically alternative selective signalV receiving means which mightibe in'- corporated in a`v calling'system in 'accordance with the invention; Y

Fig. 2B is a side elevation of the clock-driven selector mechanism of Fig. vZ'Ashowing in detail lead Wires 2 from the oscillator and the lead wire 2a to the transmitter in response to energization ofthe electromagnet 5. "En'erg'ization' yof the electromagnet"5whichis electrically connected to the .battery 6 and the ground connection 'I is controlled by the clock-driven selector mechanism 8.

Theselectgr;mechanism 8 operates as follows.

'seY

When the transmitting operator presses the key 9 '-causin'gthelgroundfconnection I0 to be engaged, 1b

electromagnetl 'and the battery I2 to ground "connection r I3. Thus energized, the electromagafcircuit'isicllpleted through the windings of the net I rIA actuates its movable solenoid core constituting part of the clutch I5 thus mechanically :coupling clock shaft I4 to the selector arm I6. Rotation 'of the *cl'ck shaft |14 rby the clock mechanism I l whichfis" l`ele ctr'ially connected to theI battery I9 and theground Econnection 2i), causes the selector armto "movev around the selector dial. When the brush I 6a on 'the selector arm I6 engages thejc'onducting ring 22, the circuit Vof the electromaghet I l is connected through the resistor 24,`ring `22, brushl Ia and selector arm I6 tothe -groundconnection 23, thus causing lectro'rnagnetl IIto remain energized after release ofthev key S'by'th'e operator. This locks the selector arm I6 in engagement with the clock shaft I4 for the `duration ofthe cycle, i. e., until brushv Ia, disengages ring 22, so'that said selector arm continues to m've around the selector dial. The first lstep through which selector army I6 moves after motion `thereof has 'been initiated brings it into' engagement with contact 25 which is permanently connectedthrough the lead Z to the winding of 'electromagnet 5. Connection through thevselector arm I6 tothe ground contact 23 causes the' electromagnet to be momentarily energized thus'actuating the armature 4to close the circuit 2-2a'whereby a pulse of carrier frequency oscillations is transmitted. As the selector arm 'I6 moves 'o'n' around the dial, it males electrical contact with-'whichever of the plugs 21 are Dlaced in the J`acl s'.?8,r each of which represents a different subscribing station inthe selector lcyc'le. IVS/'hen'ftle selector arm IS contacts a givenplugfZ'Ijwhich has been previously placed inthe corresponding'jack 2 8, the circuit is closed from the ground' contact -23 through the brush I-Sa. and plug 21 connecting wire 29, the windings of thef l'exgtromaety 5, and the battery 6 -'to ground'l. As Latthe'initial step, the electromagnet 5-'is"again 'energized whereby the armature'4 is actuated to closethe 'circuit' 2- -2c tr thus )causing pulses of carrier frequencyoscillations to Vbe transmitted fat desired instants in the selector cycle, corresponding :to particular subscribing stations to be called.

mechanical means for "coupling 'the selector mechanism to 'the'driving'shaft ofthe clock; and

Fig. 3 is a schematic 'diagram of a modified calling system in which the calling carrier frequency is modulated according toseveral'distinct audio frequencies. Y

A typical vehicle calling system according to the inventi-on may, asA shown'in Fig. 1 of the drawings, embody the follo'wingfeatures. Carrier frequency oscillations are supplied from the radio frequency oscillator I,'which may be of any well-known type, through 1a circuit 2-'2a to the radio transmitter 3 from which the oscillations `are fed onto the'transmittingantenna' 3a.

The transmittedcarrier' vfrequency oscillations are pulsed by means of "an armaturellwhich I'I'l'aksand breaks 'contactwbetween" one of the `One embodiment 'of a'` call receivingf'apparatus for subscribers as shown schematically inFig. 1 opeates'asfollws. 'A pulse'ofcarrier frequency received bythe I'anter'ina v"30 passesto ground through thepr'imary 3| of the transformer 33 thereby inducing anelectromotive 'force inthe transformer second-aryy 32. 4The tuning means 34, which may compriseeither a single variable' con- `denser or ablock of condensers in series and/ or parallelarrangernent, may be varied over a range that includes the callingca'rrier frequency in addition to the conventional ;broadcastrange of frequencies. The incorning signal to'which the 4circuit 32-i34 is tunedM passes' into the receiver"35, whichjrnaybe of rany "well-known type, but is preferably"a typeS/'liitable for 'use ina conventionalZdashY-board car'radio .,unfit. .'Iheidirect current output'froni'the adiode'tector lo1 thereceiver 35 83 to the loud-speaker or' other message translating unit 42. This is the condition for ordinary broadcast reception.

In order to condition the apparatus to receive calls from the calling transmitter, the tuning means 34 is tuned vto the calling carrier frequency of transmitter 3 and the switch 31 is positioned to close contacts 38 and 39 thereby' cutting off the loud-speaker 42, and connecting the audio detector of the receiver 35 to the clockdrivenselector mechanism 48. Received calling carrier signals then pass from the antenna 30 through the transformer' 33, the tuned circuit 32-34 to the receiver 35, and the resulting space current from the detecting circuit passes by Way' oflthe -switch31and the Winding of the electromagnet 43 to ground 44. "An alternate path to ground 44al through the condenser-44h is provided to shuntalternating current remaining in the output of the-receiver 35 away from the windings ofI the magnet 43. The electromagnet 4'3 should be understood to'be of a -marginal type responsive to direct current such that any minute current which mayrow in the absence of calling signals Awill be insuicient to energize the relay,4

but the increased current occurring upon detection will exceed the margin and operate the relay. vThus energized, the electromagent 43 actuates the armatures 45 and 41, thereby connecting the ground 45 throughthe connecting Wire 49, to the circuit ofthe electromagnet 50, which is connected to the battery 5l and ground 52. The

electromagnet 50--is then caused to -actuate its movable solenoid core which constitutes part of the clutch 53 thereby mechanically coupling the clock shaft 54 to the selector arm 58. l As in the transmitter apparatus described hereinbefore, rotation ofthe clock shaft 54 which is electrically connected through the battery 51 to ground 59, causes the selector arm 58 to move around the selector dial. As soon as the brush 58a on the selector arm 58 contacts the ring 60, the ground.'

6| is applied through the resistor 62 'to the circuit of the'electromagnet 5D, thereby causing the electromagnet 50 to remain energized after the cessation of the initial calling pulse which energizes the electromagent 43, and thus locking the clutch 53' in operation for the duration of the selector cycle, i. e., until brush 58 rdisengagesi ring 68. The selectork arm 58 moves around the selector dial untilV it engages the annunciator contact plug 82 which is iixed in an appropriately positioned jack 8l. Each subscribing station has a unique position on the dial. In the particular subscribers unit being called the second pulse of calling carrier `frequency received through the antenna-*30, passes through the transformer 33, the tuned circuit 32-34 and into the receiver 35. The direct current output,

which is then taken from the audio detector of the receiver 35, passes through contacts 38 and 39 of switch 31, and the windings of the electromagnet 43 to ground 44, thus causing the electromagnet 43 to be energized at the instant when the arm 58 is in engagement with the plugv contact 82. The armature 45 ls actuated completingv thelclin'g circuitof the electromagnet 5|);l 'andv the armature 41 rlsactuated completing a circuit from 'the'ground Gl'through the selector arm 58,' the contact82, the-windings of theelectromagnet the loud-speaker 42 through the audio amplier s4; andv the battery 65 tigrounu s6. Energiza-l tion of 'the electromagnet 64' actuates the arma.- ture 61 to close circuit'from the ground 18 through lthe signal lamp 69, armature 61, and

.thebattery 65 to ground 66, thus causing the signal lamp-69 to light. Simultaneously, the armature 68 is actuated to'apply the ground contact 10through the normally closed contacts of key' -1I and armature 68 to the circuit of the Yelectromagnet 64, causing it 'to vremain energized after the cessation of the pulse, and thereby locking the signal lamp 69 in operation. Depressing the'key 1| will disconnect the ground v10 from the circuit of the electromagnet 64, thereby deenergizing it-and causing the signal lamp 69 to bey extinguished,

It will be apparent that each of the various receiving stations which are to be called will have its annunciator energizing selector contact 82 at a position individual to and characteristic of that Consequently, a.

-provided as will "aiford the necessary selective factor Which'is, of course, dependent yupon the diiference in lthe time interval occasioned by passing from a selector contact position tothe nearest adjacent one. A particular advantage vof the system l.is that additional mobile stationsV may be' added by the vuse of apparatus identical with that used at the other mobile stations eX- cept for the position of the contact 8| to which the lead .to the annunciator circuit is connected.

` A modified embodiment of a receiving unit, according to the invention, is shown in Fig. 2A of the drawings. Y Members identical in structure and function lwith corresponding members of the system of Fig. '1' will be designated by correspondingl reference characters. As in Fig. 1, the carrier frequency' signal is received by the antenna 38, vfrom which it passes through `the transformer 33 andtuning means 34 to the radio frequency stage'of the receiver 35. The amplied,

detector signal is conducted from the audio.

detector ofthe receiver 35 to the common terminal 38 of the double-throw switch 31. As in Fig. ljwhen the apparatus is utilized for ordinary broadcastreception, the switch 31 is positioned to connect points 38 and 40, thereby coupling 83 and the transformer 4I to the audio detector of the receiver 35.

' When the tuning means 34 is tuned tothe calling carrier frequency and the switch 31 is positioned to engage contacts 38-39 thus cutting olf the amplifier 83 and the loud-speaker 42 and electrically coupling theV clock-driven selector mechanism 48 to the-receiver 35, -the apparatus is in condition to receive calling signals as follows. An initial pulse of calling carrier frequency is received by the antenna 30 and passed through the transformer 33 and the tuned circuit 32-34 to the receiver 35'where it is amplified and detected. Current from the audio detector of the receiver 35then passes through contacts 38 and 39 of the switch 31, through the windings of the electromagnet 43 `to ground 44. The electromagnet 43' ris of a marginal type as described with reference to the apparatusorFig. 1. Y e

'j' The mechanicalarrangement utilized for coupling the selector mechanism to the drive shaft in Fig. Z'is aftype'offriction clutch well known 'onerof the jacks 8l annunci.

in the art. ts operation "Will-beV better underflstood by .reference to Fig. 2B of thedrawings.y

When the selector mechanism 48' is notin opa eration, the clock shaft 54 driven bythe; clock mechanism 55 rotates carrying with-it the collars 18 and 11a, and the spring.; '|65` attachedthere-k between. The spring 16 acts through al splinerto maintain a sliding frictionalcontact between the` matching surfaces ofthe rotating collar 11a andA the collar 11b Whicliv remains -xedas longv as the. arm 14 isl held `in positionpby the latch-ing ar;-

plete rotation with the 'shaft 54, carrying with` it the stop arm 14 and thecontactarm58. When the arm 14' returns to its start-ing point itl is again latched in position by thearmaturev 1 3.

The removable contact plug. 82- is. inserted in calling service. As the contact arm`58fmoves around the selector dial, it. en'gagesthefcontact plug 82 during the course,oftherotation-. VIn.

the particular subscribingV unit which. is being called, a second pulse of calling.l carrier frequency is received bythe antenna SIIVampliiied and detected by the receiver at the-instant when the contact arm 58 engages theI contact plug 82; The detector output from the; receiver-35vthen in a position 'assignedY uniquely to each particular lsubscriber by the passes through the'l contacts V38 and 39 of' the` switch 31 and by way of `the lead 96fthrough the` relay 43 to ground 44; Current'also `passesover a parallel path by way. of the conducting Wire 95 through the brush 86 whichA rides onthe shaft 54', whereby electricalcontact established with the contact arm 58' closing.theicixcuit through the plug 82; The relay 64' Whichis: of the marginal type,yis1 energized, actuating the relay armature 68', thereby closingthe circuit from the power source 51?, andcausingthe lamp 69' to be lighted and locked in operation. The lamp ,69' may be extinguishedgby depressing the key 1I thereby breaking the circuit to the bat-Y tery 51..

As stated in the description ofFig, 1 above,

the number of receiving stations which may bek selectively called by a single transmitter depends on the number of individual.contact` positions which may be 'accommodated with thevrequired degree of selectivity in a single selector cycle.

vInorder to make `it possible -for a-'sin'gle trans-` mitter to accommodate a lar-ger number oi'sub-` scribers than wouldI be possible`K by use ofthe systems described withreferenceto Figs. l4 an ld.2` of the drawing, another embo'di'mentof the in;

vention employs audio `frequency modulation "l" the tined carrier frequency `pulse'sw s'nt' out by. the calling service' transmitter; t Y

The system Vof Fig; s which i'scresigneditb `sndrtaneously transmit 'a number "of V"ep'arate signals. each having thesamecarrier Three different audio frequency' signals `from a modulating circuit of :s'ometype well'knowniinn l l equn'cy but a different audio modulation', operatesas follows.:

the art with a carrier frequency oscillator andy conventional transmitter such asare indicated separately as elements. lIV and 3v of Fig. 1; The functionA of the band- pass filters 88A, 88B and 88C is' to prevent the transientsproduced by the operation of the relays. from being transmitted and possibly ycausing false operation. Before being fed into the transmitting unit 9|, the three different audio 4signals are pulsed by means of `armatures 4A; 4B and 4C which are responsive to electromagnets 5A, 5B and 5G, respectively. The energiza-tion of electromagnets 5A, 5B and 5C vis controlled` in each case by means of a corresponding separate selector unit 8A; 8B or 8C,

. each of which operates :in the .manner described hence, the number of. separate systems to be usedv in anyV particular calling system, need not be limited to three as shown in the foregoing example, but may be any number which can be operated conveniently from a singletransmitter.

The calling receiver inthe audio modulated calling system shownin Fig. 3 operates as follows: Assume that the tuned circuit 32, 34 is tuned tothe calling carrier frequency and the switch l31 is positioned to close contacts 38 and 39 so that the message translator 42 is disconne'cted from the receiver 35. An initial pulse of audio modulated calling carrier frequency energy isreceived by the antenna 30, and passed through the transformer 33 and the tuned circuit 32, 34 tothe receiver 35 where it is detected. The audio detector output of the receiver 35, the amplitude of which varies in accordance with the modulating audio frequency of the received calling carrier pulse then passes throughthe amplifier 83', the contacts 38 and 39 of the switch 31, and into the tuned circuit 91 which comprises the condenserA |09 and the inductance 99 in parallel. The tuned `circuit 91 is an audio frequency selective device which corresponds in its resonance frequency to one of the` modulating vfrequencies of the audio generators 81A, 81B or 81C. If the modulating frequencyof the received calling carrier signal issuch that the tuned circuit 91 is responsive-thereto, the output of the rectier 918 `energizes the electromagnet 43, 4,which repre-A and received at that instant when the selector arm 58 is in engagement Vwith contact 82 in jack 8l again energizes the relay 43. This 'causes the signal lamp lt'o light as described with reference to Fig. l.

Bymeansofthe system'de'scribed with reference to Fig. 3, the transmitting operator can call simultaneously a number of differentsetsof subscribers. corresponding to the number of audio modulated-frequencies@sent outfby the transmit-g ter, inasmuch as each subscribingiselector unit contains a tuned circuit responsive to one of the several audio modulating frequencies of the transmitter.

Although the invention of the applicant has able contactor, a message translator, a constant-L ly operating motor, an announcing device, means responsive to a first pulsed signal received by said radio receiver for causing the selector to mechanically connect the movable contactor to the motor, meansresponsive tb a second pulsed signal received by said radio receiver at a predetermined interval after the preceding signal to enable the motor-driven movable contactor of the selector to actuate the announcing device and means whereby the selector or the message transf.

lator may be alternatively connected to said output terminals.

2. Radio call receiving apparatus lfor a mobile unit comprising a radio receiver, a loud-speaker,

a clock, and a signal annunciator device the env,

ergization of which is controlled by the clock, and means for alternatively'connecting the radio receiver to the loud-speaker or to the annunciator device whereby either radio broadcast program messages or an annunciator signal individual to.'u

the particular mobile unit may be had from the same radio receiver according to which apparatus is connected thereto.

3. An annunciator system for a mobile station comprising a radio receiver having output termi-i nals, said radio receiver tunable to a range of frequencies including a calling carrier frequency, a loud-speaker, selective call receiving means, an annunciator apparatus, a motor, and means for connecting the radio receiver output terminals to the loud-speaker or to the selective receiving means alternatively, said selective receiving means responsive to one impulse of calling frequency carrier Waves received by said receiver to connect itself to the motor and to a second properly timed impulse of waves of the same carrier frequency received by said receiver to actuate said annunciator device to announce a call.

4. An automobile radio announcersystem for announcing to an occupant of an automobile that i120 selector mechanism provided with a clutch, means for disconnecting said message translator from said receiver' and connecting said selector mechanism in its stead, means for engaging said selector mechanism-with the driving mechanism of said motor, vmeans for retaining said selector mechanism in said engagement for a designated 1 time interval, a signal device connected to said selector mechanism, and means responsive to a calling signal received by said receiver at a predetermined time in said time interval to actuate ,y said signal device.

his attention is desired comprising a radio broadcast receiver having output terminals and a loudspeaker electrically connected thereto, a selector having a movable contactor, a clock having a rotating shaft, an annunciator, means for disconnecting the loud-speaker circuit from the output terminals of the receiver and connecting the selector in its stead, means responsive to a calling signal received by the receiver yfor connectingthe selector contactor to the shaft and responsive to a second calling signal received at a predetermined interval after the first for causing the selector contactor to energize the annunciator.

5. In a radio calling system, a call receiving device comprising in combination a radio receiver, a message translator connected thereto, means for tuning said receiver to desiredincoming carrier frequencies; including the calling carrier frequency, a continuously operating motor, al driving mechanism connectedthereto, a

6. In a radio calling system, a calling means including a transmitter, said transmitter comprising in combination a source of carrier frequency oscillations, a continuously operating motor, a driving Vmechanism connected thereto, a selector mechanism provided with a clutch, means to actuate said selector clutch to cause said selector mechanism to be connected to said driving mechanism, means for retaining said selector mechanism connected with said driving mechanism for a designated time interval, pulsing means controlled by said selector mechanism to enable carrier frequency pulses to be transmitted at desired instants in said time interval; a plurality of call receiving means each of which comprises in combination a radio receiver, means for tuning said receiver to desired incoming carrier frequencies including the calling carrier frequency, a message translator connectedfto said receiver, a continuously operating motor, a driving mechanism connected thereto, a selector mechanism provided with a clutch, means for disconnecting said message translator from said receiver and connecting said selector mechanism in its stead, means operative upon reception of an initial calling frequency pulse to cause said selector mechanism to engage the driving mechanism of said motor, means for retaining said selector mechanism in saidengagement for the desired time interval, a signal device connected to said selector mechanism, means to cause said signal device to respond to a calling signal received at a predetermined time in said time interval.

'7. In a radio callin'gsystem, a call receiving device comprising in combination a radio receiver, a message translator'connected thereto, means for tuning said receiver to desired incoming carrier frequencies including a calling carrier frequency, a continuously operating motor, a driving mechanism connected to said motor, a selector mechanism comprising a selector dial, a'removable contact positioned at a predetermined point thereon, a selector arm rotatable'to engage said means responsive to an initial pulse of calling -frequency vreceived by said receiver to actuate said selector clutch to cause said selector mechanism to engage the driving mechanism of said motor, means for retaining' said selector mechanism in said engagement for the desired time interval, a signal device connected to said contact on said selector dial,I and means responsive to -a calling signal received by said receiver at a predetermined time in said selector cycle to actuate said signal device.

8. In a radio calling system, a calling means including a transmitter, said transmitter comprising; in combination 'a source of carrier frequency oscillations, a selector mechanism com- 11 prising a selector dial, removable contact plugs positioned thereon, a selector arm rotatable to engage said contacts in succession, clutching means connected to said selector mechanism,fa

continuously operating motor, a driving mechanism connected thereto, means to actuate said selector clutch for connecting said selector mechansm to said driving mechanism, means for retaining said selector. connected to said driving mechanism for a desired ytime interval, means connected to said contact plugs to enable pulses of carrier frequency to be transmitted at desired instants in said selector cycle; Va plurality of call receiving means each comprising in combination a radio receiver, means for tuning said receiver to a desired calling carrier frequency, a continuously operating motor," a driving mechanism connected' thereto, a selector mechanism comprising a selector dial, a removable contact plug positioned at a predetermined point thereon, a selector arm rotatable to engage said contact at a predetermined time in the cycle of rotation of said selector, a clutch connected to said selector mechanism, means to actuate said selector clutch to engage the driving mechanism of said motor, means for retaining said clutch in said engagenient for the desired time interval, a signal device connected to said contact plug on the selector dial, and means responsive to` a calling signal received by said receiver at a predetermined time in said selector cycle to actuate said signal device.

9. In a calling system, a call receiving means comprising 'in combination a radio receiver, a vvmessage translator electrically connected'thereto,

means for tuning said receiver to desired incom-f ing carrier frequencies including the calling carrier frequency, a continuously operating motor,

Va driving mechanism connected thereto, a selector mechanism provided with a clutch, means for disconnecting said message translator vfrom said receiver and connecting said selector mechanism in its stead, electrically selective means connected in circuit with said selector mechanism' and responsive to current of a predetermined audio frequency, means responsive upon reception by said receiver of an initial calling carrier fre- Aquency pulse of the audio-modulating frequency Vto which said selector circuit is responsive to cause said selector mechanism to engage said driving mechanism, means lfor retaining said selector mechanism in said engagement for a desired time interval, a signal device connected to said selector mechanism, and means responsive to actuate said signal device upon reception by said receiver, at a predetermined'time in said "time interval of a calling signal Vmodulated according to the audio frequency `to Which said selector circuit is responsive.

10. In a calling system, a calling means including a transmitter, said transmitter comprising in mechanism, means for retaining each said selector mechanism in said engagement for a desired time interval, means controlled by each said selector mechanism to cause pulses of audio-modulated carrier frequency to be transmitted at deaired instants in said time interval; a plurality '12 of call receiving means each comprising in combinationa radio receiver, a message translator connectedto said receiver, means for tuning said receiver to desired incoming carrier frequencies including the callin-g carrierfrequency, a'continuously operating motor, a driving mechanism connected thereto, a selector mechanism provided with a clutch, means for disconnecting said message translator from said receiver and connecting said selector mechanism in its stead, electrically selective means connected in circuit relationshipA to said selector mechanism and responsive .to one of the modulating audio frequencies of said calling carrier oscillations, means responsive upon reception by said' receiverfof an initial calling frequency pulse of the audio-modulating frequency to whichsaid selector circuit is respon- Vsiveto actuate said clutch to engage the driving mechanism of said motor, means for retaining Vsaid clutch in rsaid engagement for the desired vtime interval, a signal device connected to said selector mechanism, means'responsive to actuate said signal device upon reception by said receiver V at a predetermined time in said time interval of a calling signal vmodulated according to the audio frequency to which said selector circuit is responsive.

11. In a radio calling system comprising in combination a transmitter adapted to send pulsed carrier frequency signals which may be modulated alternatively according to respectively different audio frequencies, a plurality of call receiving units, means for tuning each of said receiving units to desired incoming carrier frequencies including the calling carrier frequency of said transmitter, pulse responsive means connected to each of said receiving units, a signal device connected to each said pulse responsive means, said pulse responsive means adapted to actuate said signal `device only in response to calling pulses of a predetermined time relationship, electrically selective means connected to said pulse responsive means whereby said pulse responsive means responds to pulses of only one of the modulating audio frequencies of said calling carrier frequency signals, and switching means to enable the call receiving equipment including said receiving units and said pulse responsive means to be at least partially utilized for con- `ventional broadcast reception when said receiv- 'receiving means by connection thereof to said motor, and signal controlled means responsive to a second pulsed signal from said receiver following `the first signal byr a predetermined interval for actuating said announcing device.

' RALPH K. POTTER.

REFERENCES 'CITED The following references are of record in the Viile Vof this patent:

UNITED STATES PATENTS Number Name Date 1,464,565 Espenschied v Aug. 14, 1923 2,229,097 Koenig 1- .V Y Jan. 21, 19451

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