US2093080A - Teletypewriter system - Google Patents

Description

sept. i 4, 1937.

J. L. HYSKO ET AL -'I"'r:I..E:TYPEw!lITERl SYSTEM Filed Oct. 6,- 1934 6 Sheets-Shed 1 J.L HYS/(0 /N VEN TORS IY. IKK. LARGE By NUIWiOi ATTORNEY Sept. 14, 1937-.- J. L HYsKo s1- Al.

TELETYPEWRITER SYSTEM 6 Sheets-Sheet 2 Filed Oct. 6, 1934 .INN

'v lMill- Arron/ver sept. 14, 1937. J. AL HYSKQ, n AL 2,093,080

TELETYPEWRITER SYSTEM -bwl'lw ATTRNEV Sept. 14, 1937. J. L HYsKo E-r Al. 2,093,080

' TELETYPEWRITER SYSTEM Fund oct'. 61954 s sheets-sheet 5 FIG. 7

ATTORNEY /NI/E'NTORS: W. V.l(. LARGEl Patentecllsept. 14, 1937 d v v n UNITED sTATEs PATENT OFFICE 'rammawarraa SYSTEM John L. Hysko, Brooklyn, and Wayne V.'K. Large, Hollis, N. Y., and Charles C. Munro, East Orange, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y.. a corporation of New York Application October 6, 1934, Serial No. 747,138

23 Claims. (Cl. lill-nii)V 'Ihis invention relates to teletypewriter comtelephone exchange omces to the oflice at which munication circuits whereby exchange service the subscriber's line terminatesand thence to an may be rendered to one or more subscribers at oscillator-modulator-demodulator circuit at the outlying points from the nearest teletypewriter subscribers oilce which may,y by suitable arswitching point over available telephone lines to rangements, be connected to an ordinary sub- 5 the subscribers or subscribers., station or stascribers telephone line in lieu of his telephone tions. subset. 1

An object of the invention is to provide circuit At the teletypewriter switching circuit, aiack arrangements whereby teletypewriter subscribis connected to a conductor, lead or line extendnetwork by circuit arrangements which are tem. Means are provided whereby supervisory economically feasible. conversations between the teletypewrlter and the Among the subsidiary objects are to provide telephone toll operators relative to putting transmission of teletypewriter signaling impulses through a teletypewriter call proceed to the tel'-Y sisting in part of a teletypewriter network and in but when the operator at the teletypewriter ex,- part of a telephone network and to provide suchange switching point-plugs a teletypewriter pervisory and disconnect signals in connection cord circuit into the teletypewriter trunk theretherewith. at, the telephone toll line circuit is seized for the Various other features and objects will appear transmission of the voice frequency carrier waves 9 Y from the general statement of the nature of the modulated in accordance with teletypewriter s18- invention and the detailed descriptionof the naling impulses to the outlying subscriber. Opoperation of the various parts thereof. eration of the toll circuit for. the purpose of call- Preliminarily to a detailed description, assume ing therethrough to establish a teletypewriter` scriber, who, in the general case, may represent the oscillator-modulator-demodulator circuit so v a plurality of subscribers in the same general that the filaments are heated upand the circuits locality but not necessarily upon the same local prepared for communication without delay. telephone exchange, said subscriber or sub- Circuit arrangements and equipment in acscribers being located so far from the nearest cordance with an embodiment of the invention o teletypewriter exchange. switching point that it is are disclosed in the appended drawings wherenot expedient to extend individual teletypein: writer trunk lines to them. At a suitably. near Fig. -1 indicates an arrangement of sheets of teletypewriter exchange switching point, which, the drawings showing how the principal figures in the general case, 'may be a regular teletypeare to be'put together to make a complete sys- 35 writer exchange provldedwith toll line equiptem; ment, such as is disclosed in the patent of Iiane- Fig. 2 discloses an arrangement of sheets of Locke, No. 1,979,273, .granted Nov. 6, 1934, or the drawings to make a modied complete sysf similar apparatuslocated at a suitably modified tem; telegraph test board, there is provided a switch- Fig. 3 is a diagram showing the general outo ing pointfrom which theoutlying subscriber line of the system: may be given teletypewriter exchange -service Y Fig. 4 is a simplified circuit arrangement of the over telephone lines. The telephone lines may osciilator-modulator-demodulatorunit which is extend through the local telephone exchange connected at times in a telegraph trunkchannel adjacent the subscriber and then through one between a direct current telegraph line and the or more telephone toll exchanges, if necessary. voice frequency telephone system;

At the teletypewriter switching point is a tele- Fig. 5 is a simplified diagramvof the operating typewriter jack circuit extending to a normally circuits of a teletypewriter trunk terminating idle circuit consisting of an oscillator, a moduequipment; v f w latorand dcmodulator equipment, which will Fig. 6 is a simplified diagram of atrunk conherein on Aoccasion be called a teletypewriter cartrol circuit; y rier'v terminal circuit. 'I'he carrier channel Fig. 7 is a simplified .diagram of the remote therefrom extends to multiple jacks at a telesubscriber's equipment land circuits; phone toll board through a teletypewriter con- Fig. 8 is asimplified circuit diagram of a modu trol circuit and thence through any number of ified form of circuits and apparatus at a tele- 1o ers may be connected up to a widely extended ing, in general, to a teletypewrit'er exchange sys- 1.0. l'

15 by modulated carrier current over circuits conephone toll board circuit over a voice circuit l5 5 a teletypewriter exchange network land a subcommunicationcircuit energizes the filaments of 25' ytelegraplhaortion. being in and of itself subtypewriter switchboard, this apparatus in the stantially identical "with equipment utilizable for ordinary teletypewriter communication through switchboards over lines not employing carrier frequencies.

A comprehensive view of the various components ofthe system may be gained by considering each principal component circuit thereof and its principal functions.

'I'he teletypewriter trunk carrier circuit or oscillator-modulator-demodulator circuit accomplishes' the following functions:

(1) The generation of carrier current of a suitable fixed frequency in the voice range.

(2) Modulation'of the carrier current in accordance with printer signals supplied by the teletypewrlter switching equipment connected to and associated with the telegraph 'switching point, which carrier current is to be transmitted over telephone lines to the outlying subscriber.

(3) Demodulationof carrier current received over telephone lines from the outlying subscriber.

(4) Repetition of the signal impulses, resulting from the demodulation, into the teletypewriter switching equipment looking towards the teletypewriter exchange network.

(5) Transmission of break signals through the circuit in either direction.

The carrier teletypewriter trunk control circuit` accomplishes the following functions:

(1) 'Ihe production of a visible indication of an outgoing call at the telephone toll switchboard. v

(2) The giving of a visible and audible indication of `an incoming call.

(3) Switching from telephone communication to telegraph communication.

(4) The production of suitable supervisory signals at the toll switchboard;

(5) 'I'he reception ofY incoming signals when the teletypewriter cord circuit is connected into circuit.

(6) Suitable terminationof the carrier telegraph circuit when the telephone network part of the system is used for telephone communication.

(7) Closure of the filament heating circuit of the carrier oscillator-modulator-demodulator equipment whenever the telephone circuit is uti lined at the telephone toll switchboard.

(8) Production of signal to the teletypewriter switching operator in case of an erroneous disconnect made by the telephone toll operator.

'I'he carrier teletypewriter trunk Jack circuit performs the following functions:

(1) Givesa suitable: signal proceeding from telephone toll operator.

(2) Provides a talking channel to the telephone toll switchboard.

(3) Provides switching and supervisory facilities for teletypewriter communication.

(4) Distinguishes between the lengths of spacing impulses used for supervision on the teletypewriter circuits.

(5) Furnishes supervisory signals back to the telephone toll operator.

The subscribers set circuit performs the following functions:

(1) Operates as a switching and interconnecting instrumentality to connect the subscribers teletypewriter vset to his local telephone office.

(2) Permits the subscribers station operator to call the teletypewriter operator by teletypewriter signals. to transmit and receive teletype- ,ooaosc writer signals and to send recall or disconnect signals to the teietypewriter operator.

(a) Permits the subscribers station operator' to operate his station locally without interfering circuit direct current impulses suitable for operating the teletypewriter.

(5) Provides a suitable source of carrier frequency current preferably different from that used for reception and modulatesA this carrier current in accordance with the teletypewriter impulses.

(6) Furnishes power through suitable circuit arrangements to operate the subscribers set and the teletypewriter.

Fig. 3 is a block diagram of the system with the several parts labeled. 'I'he object of the equipment is to enable a subscriber at the extreme left of the system of Fig. 3 to communicate telegraphically withca subscriber at the extreme right over a path leading to his nearest telephone exchange.

Systems in accordance with the invention may assume a variety of forms. In one form the teletypewriter call for communication with an outly ing subscriber. or vice versa from the outlying subscriber for connection to a teletypewriter network. is assumed to arrive over or to the terminating point of a suitable telegraph line, which terminating point constitutes a station commonly known in telegraph parlance as a telegraph test board. With some modification the equipment at such a board is organized to perform the additional functions'necessary to constitute a component part of a system to extend the call to the outlying subscriber. Such modified test board circuits are shown at the central portion of Fig. 5. Let the telegraph subscribers station 50| of Fig. 5 represent any subscriber upon a telegraph line however extended and which through one or more teletypewriter exchanges or not ultimately terminates at the jack 502. A suitable signal lamp, not shown, is associated with jack 502 in accordance with test board practice for informiiig the telegraph test board operator that a call is awaiting on the line connected to the jack $02. #It may be considered that the call arrives at the test board over another circuit from another subscribers station connected to the test board by a circuit of the same kind that leads to subscribers station 10|., The telegraph operator plugs an operators teletypewriter circuit into the jack 502 and inquires telegraphically what is desired. The desired information may be received from a subscriber at station SII or from an intermediate operator. We shall -suppose that the call is for the subscriber at the station of Fig. 7 having a telegraph equipment III assoclable with a line which terminates at his nearest telephone oillce in a jack and supervisory lamp which is in all respects similar to a telephone line except that it has a line lamp of a special color for the information of the operator. (The call might be 'for any other subscriber having similar equipment.)

Having-received the information the telegraph operator plugs into the jack IN an operators cord circuit III equipped with a telephone. Upon doing this ground upon the upper spring of the jack is supplied over the lead TK to relay A. The

relay A operates and supplies batteryto the lamp 60| which lights. The relay T also operates over the lead .TK which connects the leads T and R to the telephone toll operator who plugs her cord circuit into the jack 603 and connects her telephone set 602. The telegraph operator then. passes orally to the'telephone toll operator the information concerning the wanted subscriber who puts the call through the' line 600T, 500E, which line may include none or any number of telephone exchanges 604. The last operator calls the subscriber at the set 10| by the ringer 102 in the manner common in telephone practice. If the subscriber is upon a magneto exchange the switches SW will be closed upon the points M1 which may be assumed to be closed in the case of a magneto exchange to connect magneto gen# erator 100M to` the line. "Upon the ringing of the bell the subscriber is informed that he *isV wanted for a teletypewriter communication. 'I'he 2o operation of the switch 1|0 to the fon position by thesubscriber will actuate the relay 1li and perform other functions which Awill be herein- .after described. Actuation of thev relay 1H connects the input circuit of the amplier tube |06 through the lower contact of the relay 100S which is normally in its lower position. The subscribers apparatus will then be connected to the line to his telephone exchange to receive telegraphically modulated voice frequency current through repeating coil 105.

Meantime the telegraph operator has placed a telegraph repeating cord into the jacks 502 and jack 505 and thereafter pulled out the telephone cord from. the jack 504. Relay T releases. Ground is then supplied over the upper spring of the jack 505-to the lead Sl which closes a holding circuit for the relay A. In operating, the relay 'A had previously operated the relay Slvover an obvious circuit. When the telephone operator plugs into the jack 503 the relay S operated thereby locking up the relay SI over the front contact of the relay S to ground on the upper inner contact of relay A. The relay LF operated and closed the filament circuit of the three tubes of the oscillator-modulator-demodulator circuit of Fig. 4. This allows the laments to become heated so that by the time thev subscriber at station 10| answers the tube circuit is ready for communication. 'I'he subscribers at stations and 10| are now connected for telegraph communication by means of their respective teletypewriter machines over the circuits connecting them including the circuits of Fig. 4.

Oscillator-moduZator-demodulator set between telegraph and telephone Zines Fig. 4 includes the sending oscillator tube 400T, an amplifier vtube 400Aand a detector tube 400D. When the filaments are heated by a circuit FC which is closed when the` relay LF is actuated the oscillator generates current of a suitable frequency in the voice range, for example 690 cycles per second. When a teletypewriter machine lin the operators circuit ora telegraph repeater 508 is plugged into the jack 505 battery is applied to one of thewindings of the polar relay 400 over a path from the tip of the jack 505 to the normal selector contact 506, the relay 500L and conductor TL and winding of relay 400 through the other directly to the jack 505 is operated to producea winding of relay 400 to ground. This current spacing impulseupon the line the relay 400 .is

`actuated back to its lower position. Alternating current of 690 cycle frequency is therefore impressed upon a telephone line tov represent spacing impulses and no current on the telephone line represents marking impulses. This current isreceived in the demodulating circuit of the subscriber provided with machine 10| as will be i'urther discussed hereinafter. When signals are not being transmitted by the relay 400 it is ai'. a standstill in the upper position and received impulses of alternating current of a suitable diifexj-4 l ent frequency, for examplef-1640 cycles per 'sec-- out on the line may be reflected back into the carrier terminal equipment due to imperfect balance at repeater points and for possible other reasons. If the time of return of the reflected currentshould be suillciently long after 'the sending of the current into the line the part of the current sent during the spacing interval would be received when the relay 400 was connected to the receiving -circuit during the marking interval. False operation might thus result and in order to prevent such false-operation the input circuit is tuned or otherwise suitably provided wlth a i'llter 0F to prevent the passage of` current of the frequency of 690 cycles per second but to pass freely received current of the frequency of 1640 cycles per second. i

Reception and transmission by outlying subscriber Alternating current arriving at the station of the subscriber having the teletypewriter 10| is transformed by the repeating coil 105 and supplied, through a circuit 108 tuned to 690 cycles per second, to the input circuit of a five-'electrode tube 106 of a conventional type by means of .which the energy is amplified and impressed upon copper-oxide or other suitable full wave rectifying devices 101 from which direct current lis supplied to operate the relay B.. The relay 100B is normally in the upper position when the subscribers circuit is energized for operation lbut spacing impulses represented by carrier current upon the line cause its 'armature to be actuated downwardly. Marking impulsesv energize the printer magnet PM over an obvious circuit u nder the control of the relay 100R and spacing impulses cause its release, thereby're'cording the received signals upon the teletypewritr machine. For the purpose of sending the oscillator 100T is normally producing oscillations lof 1,640 cycles per second. `When the teletypewriter sending contacts SC are opened current .will iiow through the left-hand winding of relay 100S and operate the relay armature to its spacing contact. This During the sending process ai portion of the carrier current seni;

provides two paths for theilow of the alternating current from the oscillator 100T. One path is through the high resistance 1I2 which will supply alternating current to the receiving amplifier tube 1.06 and thence to'operate the printer magnet PM in the same manner as it is operated for received signals, in consequence of which the transmitted message is printed locally upon the subscriber's machine. The principal portion of the energy of the transmitted carrier wave is induced into the line circuit through the repeating 0011.105 and conveyed through the telephone .network to the oscillating-modulating-demodu- 20 connected in shunt to the series combination of the left-hand winding and a resistance with the result that the current in thegleft-hand winding drops to about three milliamperes while the current in the right-hand winding becomes about l25 thirty-three milliamperes. The direction of these currents through the windings is such as to actuate the amature of the relay to its marking contact and thus connect the line circuit directly to the input circuit of the receivingv amplifier through the selective network 108.

If the subscriber wishes to operate his local teletypewriter equipment for test or practice purposes and at the same time be ready to receive a call, the key 'IMK is operated. This prevents 35 relay 1li from operating and leaves the local circuit readyy for operation and his line circuit ready for ringing.

Preparation for call by outlying subscriber The method by which the subscriber at station 10| originates a call or prepares his circuit for receiving a call will now be discussed. Assuming that the subscriber wishes to make a call he puts the switch H into its on position.` The relay '|09 operates and locks up over a circuit from a v blade of switch 1in through a resistance, windmon alternating current source.

ing of relay '|09 and back to ground of the com- The motor of the set 10i is started into operation over an obvious circuit and the relay 1li operated over a circuit extending from the positive side of the rectifier H2 through the relay 1H, left-hand winding of relay 100s and back to ground. The filaments of the oscillator tube and amplifier tube '|06 are directly energized from transformers connected to the alternating current source. The

1640 cycle current produced by the oscillator isV supplied to the line through the upper contact of the relay NIS-when the said upper contact is closed. Actuation of the relay 'HI closes the ring side R of the line to the repeating coil 1li and likewise lights a line lamp at the central omce in the manner customary in telephonepractice. In order to indicate to the telephone operator that this is a teletypewriter call.- the' line lamp may be of a special color or `the operator may be specially instructe'd or directed through other means. The telephone toll operator estab lishes communication with the teletypewriter op-A erator (in the case of a call from the outlying subscriber) in' the following manner:

The telephone toll operator .plugs her cord I circuit into the :lack l and rings on the circuit toward the teletypewriter operator with alcommon in telephone practice. This actuates the relay GMAC which in turn releases the relay 605 and operates the relay 6 08 which locks up to ground on the upper spring of jack 4IM and lights the teletypewriter toll lamp 508. The teletypewriter operator plugs her telephone cord circuit 5M into the jack 5M. This removes ground from the locking winding of the relay 80B which releases and extinguishes'lamp 506. Aand T operate. In operating, the relay A operates the relay Sl and the relay LF. The relay LF closes a circuit which lights the illaments of the tubes 400T, 400D and 400A. The relay Si locks up under control of the relay A. The relay T transfers the leads T and R. to the talking jack 504 and places a terminating impedance inreleases the relay T but the relay A is held operated through its secondary winding and ground over the lead SI. The telegraph operator then receives from the calling subscriber at thersta- -tion infomation as to the party with which the subscriber at said station wishes to communicate. The telegraph operator plugs into The relays the jack 502 which is connected to a line extend- The subscribers then communicate by teletypewriter;

Recalling the teletypewriter operator from the telephone toll position If the telephone toll operator wishes to recall the teletypewriter operator, she may do this by ringing upon the circuit with her ringing key. The relay GMAC operates and lights the lamp 506 which stays lighted because the relay 608 locks up when no telephone set is in jack 504.

When communication between the subscribers ends, the teletypewriter operator will be informed by a disconnect signal on the line connected to jack 502 or by'other means as will be hereinafter described and will remove the plug from jack M5. When the teletypewriter cord is taken down from jack 505, the circuit relay A releases which places battery on the ring conductor SMR and ground on the tip conductor SIIIT `which lights the usual cord supervisory lamp (not shown) in the toll telephone operators cord circuit. Such supervisory lamps and operating circuits therefor are disclosed in numerous patents and are well known to those skilled in the art. The voperator takes down the cord circuiti!! which clears the telephone circuit in the usualmanner.

tor conversion unit of Fia. 4

Fig. 4 comprises the oscillator tube 0T and its associated circuits. the detector 400D and the amplier "IA with an input filter 0F tuned to pass the carrier frequency to be received and to exclude the carrier frequency to be transmitted. The polar sending relay l normally stands on its marking contact during the opera- 75 ternating ringing current in' the usual manner --tive condition of the circuit and the relay IR amg likewise normally stands on its marking contact. The polar relay 400 is controlled from the teletypewriter or teletypewriter circuit connected to the jack 50B-over a path extending from the tip 5 of the plug. tip of the loop, contact 500, relay 0001.., lead TL to the right-hand winding of relay 400, and thence to positive battery on the contact of relay 400R'. When the teletypewriter interrupts the path just traced during a spacing l impulse, the relay 400 is actuated to its spacing contact and high frequency currentv is applied Ithereover to the tip and ring T, R of the voice frequency channel. Thus voice frequency carrier waves are transmitted to the line, the carrier l waves being on the'line for spacing signals and on the line for marking signals.

For reception from the outlying` station the receiving circuit is connected to the line through 0 negative battery is impressed upon conductor TL.

Because the conductor 'I L is connected to nega- ,tive battery at its other end, the telegraph circuit'is eiectively open thereby causingthe telegraph repeater to transmit a spacing impulse 3" through the circuit connectecf to the jack 502.

The battery polarities connected ,to relay 400B.

and the line at the repeatermay be selected and the windings of relay 400 arranged in" accordance with any well known repeater practice.

40 During sending by actuation of the relay 400, a portion of the carriercurrent sent out upon the line may be reectedback into the sending circuit due to imperfect balance at repeater points and to other possible causes. Where the time of return of the reflected current is appreciable due to transmission delay in the circuits, a part of this reflected current may arrive after-the beginning of a marking interval during which the receiving circuit is connected to the line by the sending relay. If this reiiected current reaches the detector, false operation of the receiving relay 400B might occur which would produce Vverrors at both the sending and receiving teletypewriter instruments. This is one of the reasons for the inclusion of the i'llter circuit 400F-which` is designed to pass'current of the frequency of 1640 cycles per second produced by the oscillator 100T but to attenuate and suppress current of the frequency of 690 cycles per second produced by the oscillator 400T.

As stated before, the receiving relay 400B. has on its spacing contact battery of the same polarity as that-which is applied to the other end of the circuit to which the lead TL isconnected and 05 upon its marking contact is battery of the'oppo-A site sign.

As will be readily seen, a break signal can be transmitted in either direction from the break key upon the teletypewriter instrument or by other suitable means. If printing telegraph signal impulses are being transmitted to Vthe out.- -lying station the outlying station may send '-a break signal by impressing carrier current on the line continuously for one or two seconds. This causes the receiving relay 400B. to be operated to its contacta't any time the sending relay 400 is on its marking contact. When this occurs. it is impossible for thev sending relay to be operated from marking to spacing and hence the receiving relay remains on its spacing contact as long as the continuous carrier current is being received. During this condition current in the circuit connected to lead TR remains zero whether the loop is open or closed and the break signal is transmitted to the circuit connected to Disconnectina the subscribers station To disconnect, a subscriber at the station 1Il|` operates the switch 'H0 to the oil position.

This will bring up the supervisory signal at the teletypewriter operators position in the manner hereinafterf described. By leaving the switch 1I0 in the "oil" position, the thermal element will function in approximately ten seconds and shunt the relay 10| Vafter' which all power is cut oil at ythe subscribers station and the circuit is turned to normal.

Incoming call at outlying subscribers station In the case of anincoming call, ringing current' from the switchboard at the outlying teiephone -oillce will operate the ringer 102 which will call the attention-of the station operator. The operator ,will operate the switch 1i0 to the ,on position which will energize rthe station equipment in the same manner as -when a subscriber at station 10| makes a call.

Operation of subscrbers circuit fm' recalling 0r disconnecting Assume-that a complete communication circuit has been set up and that the subscriber at station 50i is in communication with the subscriber at station 10|. The subscriber at station 10i wishes to recall the teletypewriter operator to remedy a line trouble or for some other-reason. The station operator operates the switch 1I0 to the "oiT position momentarily and then back to the "c in position. The re1ay109 remains locked by the switches in the "oi position but the relay 1li is operated-while the switch is in the off position and locks up in series with the contacts of relay 100. The thermal element 1H is thus energized and after a predetermined time which -we may assume tobe ten seconds. the thermal :isl

element is operated to close its contact. 'Ihis shunts the relay which releases and the relay 1i! which releases.

'operation of the teletypewriter trunk jack circuit The operation Just describedwill place continuous carrier current upon the line for approximately ten seconds which will actuate the circuit devices oi' Fig. 5 to produce a supervisory signal at the teletypewriter operators position. y'I'he operation by which this takes place will now be described:

the present case, five seconds. Upon reception of a spacing signal from the operator at the statio n 1li, the relay 5001. (Fig. 5) releases. Onethe circuit closes, the relay MIL reoperates which I reason why this is desirable is that the telegraph network may include exchanges whereat seven and ten second break signals may' produce automatic recall and disconnect signals, respectively. Ground is removed from the relay BML which also releases but it is a slow release relay vand upon normal signaling impulses it does not release before relay "IIL reoperates. In the case of a long spacing signal, relay 5ML releases and battery is put on a rotating magnet ROT in series with interrupter IIIII which operates at 120 in,- terruptions per minute. On the first step of the rotary switch, the contact lll is opened and contacts 508 and WIA 'which are the ofi-normal contacts of the switch are closed. The brush of bank 2 upon the third step of the switch supplies negative battery of signaling voltage over the brush through the winding oi' relay 5ML to the lead 'I'L which replaces the battery normally supplied for the telegraphrepeater and provides battery to release the circuit when the marking condltion is restored. If the circuit is held opened for tive seconds or more, the brush of bank I steps to the tenth point and supplies battery through relay WIC toward jack i" at the. telegraph operators position. The relay IIIIC, upon operating, operates the relay IMD if a cord is plugged into the lack l or the jack Wl. The relay D locks up over contacts on the Jack l if a cord is plugged into the jack SI5 or the jack 501 and the telegraph lamp Bit is lighted. When reoperates the relay IIIL. The circuit is then closed to the release magnet RLS from battery over the back contacts, of relay IML. In the meantime, the relay "DE has operated from battery on the make contact of relay NIL and it locks up under control of the relay "ID from battery over the upper make contact of. relay 500D, inner make contact of relay 500E to ground on jack lill or 501 over a contact of jack 509.

The operator observes the lighted lamp lll and challenges on the circuit by plugging a monitoring teletypewriter circuit into the jack tilt. 'I'his releases the relays IIID and IMIE and extinguishes the lamp Bil. The operator then challenges upon the circuit and in the case of a recall signal she receives the necessary information transmitted from the subscribers teletypewriter. In the case of a disconnect signal there will be no answer upon the circuit and the circuit will be pulled down and released.

In a modified circuit arrangement which is preferred for use if the outlying subscriber or subi scrlbers are sumciently near to a teletypewriter exchange, a circuit arrangement in accordance.

with Fig. 8 will replace that of Fig. 5. Fig. 8 con- -sists .of two parts, namely.- a cord circuit and 'a line terminating circuit. The cord circuit is essentially in accordance with the disclosure of the above mentioned Patent 1,979,273, to which reference is made for a full disclosure. The line terminating equipment appears at the exchange as a trunk circuit termination especially ldentliled to the operator. This line termination includes a talking jack l and'a teletypewriter jack lll.

In Figs. 1, 2, and 3 of said application there are disclosed forms of subscribers' lines and line terminating equipment which are understood to be 'a part of the exchange and to or from which connections may be made to communicate with a Il subscriber whose station includes the apparatus 10|. It will also be understood that the exchange includes trunk lines of the type referred to'in said application for connecting to a subscriber through other exchanges. ('I'he subscribers lines are not shown herein inasmuch as they are fully disclosed in said application.) The particular exchange disclosed in said application is illustrative of exchanges at which lead- TL may terminate.

Operation ,fof incoming call When a telephone toll operator receives a request for teletypewriter service from a distant telephone operator, she will insert the trunk and toll cord 602 into the jack Atill and ring on the N circuit. This will operate the relay OMAC which the relays T and A in the trunk control circuit.' The relay T connects the tip and ring of the trunk to the` talking jack 8M. The operators may then converse and the' teletypewriter operator secures the calling subscribers numberfrom the originating telephone operator. The teletypewriter operator then inserts the answering plug of the teletypewriter cordcircuit into the Jack I and thereafter takes down the cord that is plugged into the jack Ill. This releases the relay BIIIS which removes ground from the lead TK and allows the relay T to release. The trunk is then in ycondition for telegraph communication. When the teletypewriter cord is plugged into the telegraph line, the relay LS operates from ground over the sleeve of the cord and Jack of the telegraph line over the lead lill. It will be noted that the sleeve ofthe answering plug is grounded.

'I'he operation of the relay LS places ground on thconductor Si to maintain the relay A operated an hold the trunk circuit in a condition for telegraph communication. The busy lamp BSY is maintained lighted by relay LS. The operator now operates the monitoring or listeningI key IIIIK and places her teletypewriter instrument in the cord circuit for communication with the subscriber having a teletypewriter 10i. 'I'he call is then completed to a called line by the answern ing Jack in the same manner as teletypewriter calls are completed by means ofthe system disclosed in the application of Lane and Locke above referred to. If the telephone toil operator wishes to recall the teletypewriter operator she can ring on the circuit which operates the relayv IAC in the' trunk control circuit and causes the lamp l to be lighted.` With a cord plugged into the telegraph toll line the lamp Il. is lighted over the locked-up relay m. `It will be assumed that the telephone toll operator goes into the circuit with her monitoring key operated in order to avoid mutilating the telegraph signals. When a disconnect signal is received over the telegraph` toll line and the teletypewriter cord, the operator will take down the teletypewriter cord. Removal of the teletypewriter cord will release the relay LS which in turncauses the relay A in the trunk control 'circuit to release which lights the usual cord circuit supervisory lamp (not shown) selectorwill arrive in a predetermined time, for` lease of relay LS extlnguishes 'the busy lamp .BSY. The telephone toll operator then takes down the cord from the associated jacks in accordance with customary routine. In case the toll operator disconnects in error,

the relay S in the trunk control circuit will re-.

Ground o n the upper make contact of lease. relay A will operate the relay 806 and light the lamp 806. Relay S will not light the lamp outgoing can When a call is received from the teletypewriter network for a subscriber to be reached by a carrier operated loop the teletypewriter operator inserts the plug of thecord of the set 808 in the .lack 804. This operates the relay 800s and causes relays in the trunk control circuit to operate in an obvious manner to connect the leads T and R. of the trunk circuit to the jack 804 and to light the lamp at the toll switchboard. The teletypewriter operator passes verbally the information necessary to identify the called subscriber and the operator then plugs a teletypewriter into the telegraph toll line. Ground over the sleeve of the cord operates .the relay LS which provides holding ground for the relay in the trunk control circuit. For a disconnect in error, the mode of operation is the same as for a call passing in the opposite direction. If a disconnect is received over a line connected to the left end of the cord circuit in Fig. 8, the operator challenges with her teletypewriter. If the call is finished.

she pulls down tle connection ofthe answering plug of the cord or jack 805 which releases the relay LS. The release of the relay LS opens a holding path for the relay A and lights the cord supervisory lamp in the telephone toll operators cord circuit. The telephone toll operator then clears the circuit in the usual manner.

Let us suppose that -a circuit has been set up between two subscribers and that their communication has ended or that the subscriber at the station 10| desires to recall the teletypewriter operator. 'I'he subscriber at station 10|- sends a break signal of ten seconds duration as described. At the teletypewriter operators sta- 'tion of Fig. 8 the relay 800L releases. This pauses the release Aof the slow-acting relay 800E.

which causes energization of the selector rotating magnet ROT whichl steps one step and at the same time the olf-normal contact is closed. The relay 800F releases which operates the relay 800E which again releases the relay 800F. Upon every release of the relay 800E the selector steps for another point. The lead 808 is wired to a terminal of the selector at which the brush of the example, five seconds. Assuming that the chosen time is ve seconds and that the brush reaches the fifth terminal in five seconds then at the expiration of such'time the lead 808 is connected to ground over the selector brush and this establishes a circuit to the ring at the jack, ring of the plug, relay 800B and disonnectlamp 8|0 in parallel through the'lower make-contacts of seeve relays 8H and 8I2 which are closed when the cord is plugged into two jacks, to battery. 'The relay 800B locks up to ground through the key 8i3. When the line closes, the operator connects her teletypewriter machine to her cord circuit and challenges. If the subscriber wishes to recall the operator he answers the challenge and gives the desired information but if there is no answer the operator pulls the plug from the jack.-

When the line closes at the end of the. ten second break the relay v8001i reoperates and the release magnet RLS is operated. This restores the circuit to normal. When the operator pulls the plug from the :lack 800, the'relay LS releases thereby putting out the busy lamp and the circuit of Fig. 8 is returned to normal.

In the fpregoingdescriptlon and in the drawingsnumerous auxiliary devices and features, such as current limitingresistances, fuses, testing jacks, variable featuresaof elements, night alarms. multiple connections to jacks and lamps, spark killers and numerous otherY features employed in commercial practice have been omitted to simplify the description, but it is understood that all such customary features may be used if andy when desired.

What is claimed is: l x

1. A system for giving teletypewriter exchange service to a subscriber equipped with a teletypewriter over an exchange and line network otherwise usable for telephony comprising a line of telephone transmission characteristics extending from said subscribers station to a telephone centrai ofiice, a trunk circuit from an exchange on said exchange network to a teletypewriter switching position, means for intercommunicating by telephone between a teletypewriter operator at the teletypewriter exchange terminus ofk said.

trunk and a telephone operator at the telephone exchange terminus of said trunk, meansunder the control of the operator'at the teletypewriter office for seizing said trunk for teletypewriter communication in combination with anoscillator-modulator-demodulator set operatively connected between said teletypewriter oilice and said trunk when said trunk is so seized and an oscillator-modulator-demodulator set operatively connected between said subscribers teletypewriter and his lineto said telephone central office,l

said oscillator-modulator-demodulator sets each including means for producing oscillations in the telephone frequency range, means for modulating said oscillations in accordance with teletypewriter code and means for detecting modulated oscillations to reproduce teletypewriter code.

In a communication system, a trunk circuit normally terminating at each'end thereof in a jack, an operators telephone set adjacent each jack for connection thereto for telephone communication thereover, another jack adjacent one of said jacks,a plug for insertion into said other jack, a carrier wave source and a modulating device for modulatingthe waves from said source,

relay equipment effective upon the insertion of said plug into said second jack and removal of the telephone set from connection with the adjacent jack to interpose said carrier wave source and said modulating device for modulating the f waves from said sourcebetween said second plug and the jack at the remote end oi said trunk vand to disconnect said one of said jacks from operative connection to said tunk.

3. In a system in accordance with claim 2, trunk terminating equipment adjacent the one of said two jacks terminating the trunk circuit which is adjacent the said other jack, said trunk I terminating equipment including instrumentalities'operable over said trunk to cause the operation of a disconnect signal.

4. A teletypewriter system, comprising a teletypewriter line network `for switched teletypewriter intercommunication, a telephone system, including a. subscribers local office and a'line for teletypewriter communication from said subscriber to said local cnice, a telephone trunk from said oiiice to a teletypewriter switching position, and means including carrier wave sending and receiving devices, said sending devices being under the control of instrumentalities at said teletypewriter switching position for telegraph communication, and means for seizing a termination of said trunk for teletypewriter communication and communicating by telegraphy thereover.

5. A system in accordance with claim 4, in which the carrier wave sending and receiving .devices are at the junction of the telephone trunk and the teletypewriter network and are connected to means for energizing them preliminarily to` a teletypewriter subscribers connection by devices operative upon seizure of a trunk for voice communication between the teletypewriter operator and the telephone toll operator.

6. In a system in accordance'with claim 4,

devices whereby spacing and break impulses are represented upon the telephone trunk by presence of carrier waves and. marking signals by absence of carrier waves. 7. In a system in accordance with claim 4, a signal at the teletypewriter'operators position, relay controlled devices whereby long impulses transmitted from the subscriber over the telephone network energize said signal.

8. In a system in accordance with claim 4,`

relay controlled devices whereby long impulses transmitted from the subscriber over the telephone network are limited to a predetermined duration at points on said teletypewriter network beyond. the rst teletypewriter switching point.

9. In a system in accordance with claim 4, jack equipment at the teletypewriter operators position and a signal device associated with the multiple thereof showing said trunk connected` with said jack equipment to be busy, and means causing said signal device `to indicate busy when said trunk is seized by a teletypewriter operator for telephone communication and'to continue busy so long as said trunkis continued in use for either telephony or telegraphy.

10. In a system in accordance'with claim 4, a talking cord circuit and a teletypewriter cord circuit at the operators position together with trunk jacks, and means whereby insertion of the talking cord circuit into a jackseizes said trunk for voice communication and then insertion `of a teletypewriter cord circuit into a jack 'seizes said trunk for telegraph communication while maintaining the continuity of said trunk and busy signals.

thereon.` v l A 11. A system in accordance with claim 4 including a call signal device at a subscribers sta- -tion together with a teletypewriter and carrier frequency conversion equipment and a switch for energizing said teletypewriter and equipment,

said switch also acting to remove said signal deceiving tube, and instruments whereby the actu--4 ation of said device to deenergize atleast one of saidoscillator and receiving tube sends a discon# nect signal over said line to a teletypewriter centrai o'illce.

13. A system otherwise in accordance with claim 12 in which actuation of said device for a predeterminedly short period to deenergize at least one of said oscillator and receiving tubes sends a recall signal to a teletypewriter central office operator.

14. A system for communication between subscribers by means including telegraph code sending and receiving devices in which part of the communication circuit is by carrier current of telephone frequency over a telephone channel typewriter subscribers in part by direct current impulses and in part by carrier` waves over a ltelephone trunk, said system" including a cord circuit at a telephone operators position and a connecting link at a telegraph operators-position, a signal device at said telegraph operators position normally non-indicating during tele.-

graph communication, and devices to cause said devicegto give an indication if the telephone operator erroneously disconnects. v

17. A system o1' communication comprising a subscribers station having-a carrier current sup-` ply source, telegraph sending and receiving equipment for modulating said source and adapted to be operated by the current 'products of demodulated received carrier waves. a channel of communication through normal telephone circuits over which said carrier waves may be transmitted, a trunk fromv a switching-position on said telephone circuit to a switching position on a telegraph communication network, devices Fwhereby an operator may operatively connect to said trunk an oscillator-modulator-demodulator circuit and switching equipment whereby direct current impulses from said network may be supplied to said oscillater-modulator-demoduiator circuit for communication in one direction and carrier waves modulated according to direct current impulses supplied from said oscillator-modulator-demodulator circuit for communication in the other direction.

18. A subscriber station includingl a delayed" action thermal device, an operators station including a signal. a line over which said stations are connectable, means for energizing said thermal device, delayed action means for changing the condition of said signal; and interlock means for said delayed action means and said means ing in jacks, means `for connecting said subsets nating current of carrier frequencyby means of said instruments for intercommunication therebetween, means for placing alternating current of carrier frequency continuously upon said line for at least a definite time. and means whereby said disconnect signal is energized thereby.

21. In a communication system, a trunk, means for connecting said trunk to a source of voice waves, means for connecting said trunk to a source of carrier waves, and impedance terminating means connectable to said source of carrier waves as a substitute for the impedance of said trunk upon connection of said trunk to said source of voice waves.

22; A communication system comprising a line and a source of carrier waves, means for applying waves from said source to said line.. means for interrupting the application of said waves. a stepping switch connected to said line to be D controlled by said waves and adaptedto take successive steps in predetermined intervals, and connecting means to cause said switch to step whenever the application of waves from said source to said line is not interrupted for the duration of such predetermined interval.

23. Ina communication system for communicating telegraphically by means of start-stop permutation code teletypewriters over telephone operators cord circuits by carrier waves telegraphically modulated, a source of carrier waves,

circuits for transmitting said waves over a telephone operators cord circuit, a starb-*liep permutation code machine stopping on a closed line condition, and circuits for impressing a no-current condition on said operators circuit concomitantly with and as a result of said closed line condition.

JOHN L. HYSKO. WAYNE V. K. LARGE. CHARLES C. MUNRO.

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