US2357840A - Regenerative telegraph repeater - Google Patents

Description

-Sept. 12, 1944. w. B. MARTIN REGENERATIVE TELEGRAPH REPEATER Filed Feb. 25, 1941 lNvx-:NToR I BY W t ATTORNEY un. N Il Il Ille.. QN lw. :mu llo Y NL A PatenteclxSept. l2, 1.944

UNITED STATES PATENT ,OFFliC-l" REGENE'RATIVE TELEGRAPH REIR Wade nMartin, Westwood; N. J.,'aeei,e,m r fc American Telephone andTelegraph' Company, a corporation of New York I Y v Application February 25, 194i, semina. 380,440 Claims. (01.178-71) j This invention relates to' telegraph systems and particularly to an improved type'of regenerative telegraph repeater.

Regenerative repeaters of 'the type heretofore employed have been characterized by the'use of distributors for' 1re-spacing the received signal impulses prior to` retransmitting them over the line. Not only are the` frst cost and the main' tenance charges'of such distributors fairly high but also they are subject to" the limitation that they can be used for only one transmission speed and a fixed number of pulses per signalY combination.

I have found that by replacing such distributors by an arrangement of vacuum tubes it is possible not only to, materially reduce the first cost and the charges upon such repeaters, but also to readily' adapt the repeater to any desired speed, and. any desired number of pulses per signal combination.

This invention resides in such a repeater characterized by the use of two vacuum tubes one of which, together with its associated relay, serves as a character length timer; and the other vacu'um tube, together with its relay', serves to control the spacing of the several impulses embraced Within the signal character. In this repeater the receiving relay, upon the receipt of thespacing impulse constituting the first' impulse of the signal character, operates twoother relays, one of which removes the grid biasing voltage from' the vacuum tube that forms part of the characterlength timing device; and the other relay removes the grid biasing' voltage'from the vacuum tube that forms part of the pulsing circuit. The pulsing circuit continues'to operate until seven pulses have `been created whereupon its operation is stopped as the result of the flowv of space current throughthe vacuum tube that forms part ofthe character-length timing circuit. Those pulses serve to operate a locking relay which, in turn, controls the sending relay of the repeater and thereby insures the retransmission of the signal character free from distortion.

This invention willv be clearly understood from the following description, when read in connection with the attached drawing of which Figure l shows' schematically the embodiment of the invention in a circuit for transmitting the signals in one direction; Fig. 1a is a graph indicating the relativeA time of operation of the several relays; andr Fig. 2 shows the circuit arrangement for two-way transmission between stations.

In Fig. 1, A represents a teletypewriter' station I eaters overure- 1meL1 to a distant Station B (represented all?" the' right-handelde* f*` the flgllie) which isada'pted to receive those signal'ch'ar-j acters and to" translate trl-ern into' printed messages a manner that is well understoodby lse 'fainiliar W'tll' the' art'. The transmitting and receiving'apparatus may `beef anywell known type such as that disclosed in Penders Electrical Engineers'I-Iandb'oo vo'l. V, 3rd ed., section l1, pages 23 a1`d124' (published Je'hri Wiley 8i Sons 1936) Between those` stations' is are'generative repeater, the purpose of 'which is t0' rC'eiVe the impulses, representing a signal character, to prop= eily SpaCe and rplifyths'e' iIiplIlS'S andtd tel-A transmit them to the' distant; receiving station. The line LL is adapted' to'r be' ote'd t the re" rpea'tei by' inserting tfl plug' l `in tlfi jack 2, In like manner the lifl Iii, Xfen'dirig t6 the distant receiving station l,V is clr'leiedt the repeater by inserting the JJy 3 tl' jack' 4. The yjack 2 is conneted to the lip'p' vvidilg` of. relay C. The IWE' iviillli,` is`l tfl biasing' Winding 0f .the relay, has Colfieid tlieeli a battery 5 and a suitable resistano'f.' fIh tongue of relay C is (notitie-Glied dllcti 'l to the Lipper iii/"irid-A ing cf relays Ded Eend' isn als@ ccnnected by conductor 8 with the upper' winding' o'f relay G andthe lWr Wiidingof relay F'. ITli upper windings of relays DMS-indv E are' the' Operating windings cf those relays and the lower windings are the locking widins that serve to prevent the lIrioveint Off the lorlg'liesv f tls' relays until ltain tiIIil-g oprations hai/"el taken'plac, vvlich will later be nre fully des'eribed.' Th tongue of relay G has connected therewith'a bat-` tery 9 that serves to charge the condenser" l0 when the tongue is upon its I`r`n`arling contact; and tolockV relays F and Gkvvhen the At`or`lg'u'e vis upon its spacing contact. `The tngle of relay F serves toconnect the potentiometer Il tothe' condenser I2` when the arr'nature of F is up its marking contact. 'Trie lcwer wridingjc'f ,relay G is connected between the battery I3 and the plate ofthe Vacuum tube Tl. 4The grid f that tube is connected te tire condenser lo and also to the battery 9,- the voltage of which is such that when applied to the 'grid it will prevent the liow of currentv through the space in the tube.Y When the battery 9 is disconnected from'tle' condenser lll the latter Will discharge thiu'gil tli resistance i4' and the battery'l l5, which are SprpUrtioled als .t0 fix' the time f dishaifge alt a Adeflnite gure is the' ptinmm timejc-f trans` mission fone character' atthe selected speed, all f Whih Will b Iie lllly des'ribed herein-2' connected to the plate of T2 and also to the condenser I6. 'I'he tongue of that relay is connected tothe battery I'I. When that tongue moves to its marking contact it will charge the condenser I2 and when it moves to its spacing contact it will serve to cause a ow of currentV through the locking windings ofrelays D,"E 'and Fior the purpose of controlling the actionV of those relays. y

VThe manner in which this circuit functions for the re-spacing and re-transmission of the impulses that go to make up a teletypewriterV character is as follows:

Let it be assumed that the tongues of the various relays are in the postions shownin the figure. Current will ow from the positive ter- Y minalof battery I8, associated with the marky ing contact of relay C, thence over conductor 'I and through the upper windings of 'relays D and E to ground at 2 8. The windings of those relays, and of all the relays of this drawing are so poled thatiwhenthe positive pole of a battery is connected ,to the lower numbered terminal of a winding,the tongue of the relay will either move or tend to move toward or remain upon the marking contact'of that relay. If the negative pole of a battery is connected to the lower'numbered terminal, the tongue willmove or tend to move toward or remain uponthe spacing contact of the relay.Y Since the positive poleofbattery I8 is so connected that current will flow in the direction from the lower numbered terminalsto the' higher numbered terminals of the upper windings of relays D andY E,V the tongues of those relays will remain on' the marking contacts."

'Current from battery I8 will also flowVover conductor 8 and through theY upper winding of relayV G and the lower winding of relay lF to ground. ,Since the direction of owis from the lower numbered to the' higher numbered terminal of each winding,`the tongues of those relays will remain on their marking contacts. Considering relay G, battery 9 will apply a voltage to the condenser III the magnitude' of which is such as to prevent the flow of current from the plate to` the filament of the tube T1 to the grid of which the condenser is connected. Accordingly noV current will flow through the lower winding connected to the higher numbered terminal of those lower windings of relays D and E the tongues of these relays will thereby be locked in the position shown upon the marking contacts.

Let it be assumed that the next impulse of the signal character transmitted over the lineV L1 is an open or spacing impulse. That will cause the tongue of relay C to move to itsspacing contact and that, in turn, will connect the negative pole of battery 35 to the conductors 'Il and 8 and a current will flow through the windings connected to those conductors in av direction opposite to that previously described. Since the negative pole of battery 35 is connected to the lower numbered terminals I9 and 2I of the upperV windings of relays D and E, the tongues of those Y relays vwould move to their spacing contacts if of relayG which is connected to the plate ofthe tube T1. VConsidering relay F, the voltage Vof the Y potentiometer II will be appliedto the condenser I2, lthe magnitude Aof, which will depend uponthe setting of vthe potentiometer. That voltage may be of the order of 30 volts and it is suilicient,

when applied tothe grid of T2, to prevent transto the marking'contact of that relay, and through the lower windings of` relays E and D, shunted by the resistances'29 'and 30, to ground at 28. This current is of higher value than that flowing in the upperwindings. Since the negative pole isn they were free to do so but they are prevented for the time being by the effect of the current f from battery II that flows through thelowerv windings of relays D and E. 1 Current from the negative pole of battery35 will also flow through the upper winding of relay G and the lower winding of relay F. Sincethe lower numbered terminals of those windings are connected. to a negative pole, the tongues of the relays will be moved to their spacing contacts. Considering relay G, the movement of its tongue disconnects the battery 9 from the condenser I0 which there- Y upon begins to discharge through the circuit lof I4 and I5. The rate of discharge depends upon the circuit constants, which are varied to values dependent upon the selected optimum rspeed of transmission of the system. If the rate of transmission be assumed to be 60 words per minute, the time .of discharge of the condenser would be .one-sixth of a second. During that period of time one teletypewriter character consisting of a start impulse, five code signal impulses, anda stop impulse, would be transmitted through the Y repeater and during thek course of such transmission those impulses would be subjected to the control mechanism of the repeater so that when retransmit-ting to station B they would be properly spaced to effect the correct result in the teletypewriter receiver at that station. Y

Considering relay F, the flow of current from battery 35 through its lower winding causes its tongue to move tothe spacing position and both relays, F and G, would be locked in Vthat position by current from battery 9. Resistancesfa: and y are so proportioned that the. currentinthe locking windings of relays; F and G willreinain inV a spacing directionregardless of the position of the armature of relay C but the value of the current will be twice asgreat, when relayCs armature is on its spacing contact thanV when it is on" its marking contact. VThis is to prevent the operation of relay G while relayC is on its spacing contact. The movement ofthe tongue of relay F to its spacing'position disconnects the potentiometer. II Vfrom the condenser I2 and permits that condenser to discharge. .By proper proportioning of its circuit that condenser will discharge in 11 milliseconds and thereupon current will llow throughA the lowerwinding of relay H which is connected tothe plate of the tube T2. "'The'direction of flow through that winding is jsuchas to lcauseftheltongue of the relay to move to its marking contact. That operation connects battery I'I to thel ,condenser I2 and since the magnitude` of the voltage of that battery is very much greater than that of the potentiometerv I I, being ofthe orderV of volts, the condenser I2 will take an appreciably great- 'er'charga In fact, condenserr I6 has been provided in order that condenser I2 may acquire its full charge. As soon as that has occurred, the flow of current through the tube T2 and consequently through the lower winding of relay H ceases, and the tongue of that relay drops back to its spacing contact.

When the tongue was oil its spacing contact current ceased to flow through the locking windings of relays D and E and consequently the tongues of those relays were permitted to move to their spacing contacts.' Upon the return of the tongue of relay H to its spacing contact current will flow from battery I1 over conductor 21 and through the upper winding of relay F and the lower, locking windings of relays D and E. The polarity of the battery and the direction of flow of current through those windings is such as to hold the tongue of each relay upon its spacing contact. It is to be noted that the movement of the tongues of relays D and E to their spacing contacts occurs 11 milliseconds after the movement of the tongue of relay C to its spacing contact, under the influence of the spacing impulse received from station A. Furthermore, it is to be noted that the tongues of relays D and E will stay upon their spacing contacts until they are released after a predetermined length of time by the movement of the tongue of relay H from its spacing contact. Relay I-I will operate seven times during the interval of time of one-sixth of a second in which relays F and G remain locked by the current from the battery 9 while the tongue of G is on its spacing contact and, as shown in Fig, la., each operation of relay I-I occurs at an interval of 22 milliseconds. The movement of the tongue of relay H from its spacing contact disconnects the battery |1 from the circuit of the locking windings of relays D and E once in each 22 milliseconds and permits the tongues of those relays to move at those instants of time (and at those instants only) to that contact toward which they are influenced by the current in the operating windings. By means of this arrangement the eiTect of distortion of an incoming signal upon the outgoing signal from such a repeater is entirely removed unless such distortion was of such magnitude as to be equal to or greater than one and one-half times the length of a normal impulse. In such abnormal instances it is essential to take other steps to remove the cause of such distortion from the line.

At the end of the period of one-sixth of a second condenser I0, associated with tube T1, will have completely discharged and current will 110W through the lower winding of relay G and through the electron path of the tube. Relay C should have reached its marking contact,

`thus reducing the current in the upper windings of relay G to a lower value than that in the lower windings. The instant the tongue of relay G leaves its spacing contact the current in the upper winding of G and the lower winding of F changes from spacing to marking. The magnitude of that current is such as to cause the tongue of relay G to move to its marking contact. That will not only charge the condenser and cut oil a further flow of current through the tube but it will also unlock relay F by cutting oir current through its lower Winding. If the tongue of relay D is on its marking contact, the tongue of relay F will accordingly fall back to its marking position. If the tongue of relay D is on its spacing contact, relay F will remain locked to spacing by current through its upper winding until it is unlocked by the next operation of relay H. The circuit is then in condition to receive the next signal character and to properly re-space its impulses.

The arrangement of the repeater for handling traliic in both directions is shown in Fig. 2. In view of the two-way character of this repeater it is necessary to have receiving, locking and sending relays at each endI and also a preempting relay to give control of the repeater to that station which first begins transmitting a signal character through the repeater. With the tongue of relay IE upon its marking contact, current will flow from battery |00, through a circuit which includes conductors IOI, |02, resistance |03, winding |04 of relay 5, and winding |05 of relay 4 to ground. At the same instant the tongue of relay IW is upon its marking contact and current will flow from the battery |06 over a circuit that includes conductors |01, |08, resistance |09 and the windings |04 and |05 to ground. Those circuits, just traced, have a portion in common, namely, that which includes the windings |04 and |05. At the junction point of those circuits is connected a battery ||0 in series with a resistancel I. Resistances |03, |09 and I are of equal value. The direction of the current owing through windings |04 and |05 will depend upon the poling of the batteries |00, |06 and 0. Since the poling of battery I0 remains xed, the elect upon relays 4 and 5 of the current owing through windings |04 and |05 will depend upon the position of the tongues of relays IE and IW. With both tongues upon their marking contacts current will ilow through windings |04 and 05 from a lower numbered to a higher numbered terminal (indicated upon the drawing by L and H, respectively), which will cause the tongues of relays 5 and 4 to move to or remain upon their marking contacts, as indicated. Since the junction points ||2 and I I3 are at the same potential, no current will flow through the circuit connecting those points which includes the winding ||4 of rela-y 1 and resistances I I5 and IIB. Since no current is owing in any winding of relay 1, its armature may rest on either contact. With the tongue of relay 4 on its marking contact, condenser II1, associated with the tube T11, will be charged by the flow of current fromvthe battery ||8 through the marking contact of vthe relay. The voltage of that battery is sumcient, when applied to the grid oi T11, to cut off electron emission through the tube. At the same time the condenser IIS, associated with the tube T12, will receive a charge from the potentiometer |20 through the marking contact of relay 5. The voltage on that potentiometer is relatively lower than that of the battery |2I so that the charge received by the condenser II9 will be less than that received from battery |2I.

Current from the marking battery |00 of relay I E? will also flow through the operating windings |22 and |23 of relays 2W and 3W, and since the positive pole is connected to a lower numbered terminal of each relay (indicated by L), the armatures will be upon their marking contacts. At the same ktime current will ow from battery |2I of relay 6 through its spacing contact and thence over the circuit that includes conductors |24, |25, the marking contact of relay 2W and the windings |26 and |21 to ground. Since the nega.- tive pole of battery |2I is connected to the higher marking contacts.

At the same time current will now from the markingbattery |06 of relay IW over conductors |01 and |28 andV through windings'IZS and |30 ofrelays 2E and 3E to ground. Since the positive pole of that battery is connected to the lower numbered'terrninals of windings |29 and |30, the tongues of those relays vwill be held upon their marking contacts and will be locked there by the flow of current from battery I2| of relay 6 over conductor |24, the marking contact of relay 2E and windings I3I and |32 to ground. Relays 2E and 3E are thus locked to marking by current from contacts of relay 6. K

Now, let it be assumed that an open impulse is transmitted from station A. That will open the circuit of winding |33 of relay IE and the tongue ofY that relay will move to its spacing contact under the iniiuence of current through winding Y |34.- A circuit is established from battery |36,

through resistances ||5 and ||6 and winding II4 of relay 1 causing its armature to move to or remain on its spacing contact. Also under this condition there will be two negatively poled batteries, namely, I I and |36, connected to the lower numbered terminals of windings |04 and |05 of relays 5 and 4, and only one positively poled battery, namely, |06. The current through those windings will be reversed in direction and the tongues of those relays will Vmove to their spacing contacts. Current will thereupon flow from battery |42 V(associated with relay IW) through resistance |43, winding I 41 and the left-hand contact of relay 1, through resistance |44, windings |38 and |39of relays 5 and 4,`respective1y, and the spacing contact and battery V| I8 to ground. Resistances |43 and |44 are proportioned so that the direction of current through the lower winding of Y relay IW is reversed, locking it to marking, thus preventing transmission in a W to E direction until the armature of relay 4 returns to its marking contact, as is described hereinafter. The

Vdirection of flow of the current through those windings is such as to lock them upon their spacing contacts. Condenser |I1 will thereupon begin to discharge and its rate of discharge will be assumed to be the same as' in Fig. l, namely, onesixth of'a. second. That time is sufcient to per- Y that given to it by the potentiometer |20.

When the tongue of relay IE'moves to its spacing contact the current through the operating windings |22 and |23 of relays .2W and 3W is reversed, thereby tending to move the tongues of those relays to their spacing contacts. Such movement is'V at that instant prevented by the current in the .locking windings |26 and |21. However, when the tongue of relay 6 moves away from its spacing contact, the current ceases toV iiow through the locking windings |26 and |21 and the tongues of those relays are caused to move to the spacing contacts by virtue of the current in the operating windings. Then, `as soon as the tongue 'of relay 6 returns to its spac- ThereuponV current will ilow through the ing contact the tongues of relays 2W and 3W are locked in their spacing positions by the flow of current over a circuit that includes conductors |24 and |25, spacing contact of relay 2W. Winding |4| of relay 4 and windings |21 and |26 o1' relays 2W and 3W. The spacing impulse is thereupon sent over the line L2 to station B.

In the manner that has been Vdescribedfully in connection with Fig. 1, condenser ||9, associated with the tube T12, willV continue to receive a charge and to discharge at intervals of 22 milliseconds throughout the period of one-sixth of a. second. Accordingly, the circuits of the locking windings |26 and |21 of relays 2W and 3W will be closed and opened at 22 millisecond intervals,

thereby insuring the proper spacing of the signal impulses being relayed fromY the repeater to the station B.

Approximately 1/6 second after the startrwas received by relays IE, 4 and,V 5, condenser ||1 completes its discharge and tube T11 becomes conductive. A current flows in winding |45 which is in a marking direction and of sufficient magnitude to overcome the spacing current in Assuming the 5th pulse to be spacing: Current will flow from battery |2I, through the spacing contact of relay 6, conductors |24 and |25, the spacing contacts of relay 2W and in a spacing direction through winding |4I of relay 4 and similarly through windings |26 and |21 of relays 3W and 2W and their associated bridge resistors to ground, locking relays 4 and 2W and 3W to spacing until they are released by the momentary operation of relay 6 to marking. Y

When the stop pulse, which ls marking. is received, the current in windings |45 and |05 of relay 4 is in the marking direction and of suflicient value to overcome the effect of the current in winding |39 but not sufficient to overcome the combined effects of the currents Vin windings |39 and |46. Therefore relay 4 will remain'` on its spacing contact vuntil the next operation of relay 6 which reduces the current of winding |46 of relay` 4 to zero and allows it to operate to marking.

As soon as the tongue of relay 4 leaves its spacing contact current in windings |39, |38, and |41 of relays 4, 5 and 1 is reduced to zero. VRelay' 1 is completely deenergized. The negative potential through resistance |44 is removed from the lower winding of relay IW and the current in the winding is changed from marking Ato spacing.

The current in windings |04 and |05 now control relays 5 and 4 and they are held on their marking contacts until the balance of potentials on the resistances |03, |09, and I are upset by the operation of either relay IE or IW at some future time.

The operation of relay 5 connects the voltage of the potentiometer to condenser ||9 andthe grid of Tucausing the operations of the tube T12 and associated relay 6 to stop until relayV 5 is again operated to spacing.

The repeater is now closed and waiting for the next transmission. If, before the reception of the next start pulse from the line L1, Lz wishes to send, an open is transmitted to the line which will cause the operation of relay IW to spacing. This will vupset the balance of voltages through resistances ID3, |09, and III and operate relays 4 and 5. Relay 'I will also be moved to its marking contact and relay IE will be locked to marking through paths corresponding to those which locked relay IW. Transmission of an open will ensue, the mechanics of which may be understood from the previous description.

Relay I preempts the distributor for transmission in the direction from which the rst open starting impulse is received and retains it until the tongue of relay 4 returns to its marking contact at the expiration of the period of time of one-sixth of a second hereinbefore described. It will be seen that relays 'I and 4also lock relay IE or IW in the direction opposite to that from which the open impulse comes and such locking is continued for the entire period of each signal character except the stop impulse. For example,v

in transmitting from east to west, after a start impulse is received by relay IE, relay I is moved to or remains on the contact which will allow relay IW to be locked to its marking contact as long as relay 4 is on its spacing contact. All breaking to get control of the repeater must be done during the transmission of the stop impulse.

The transmission of signal characters from station B to station A through the repeater would be carried out in a manner similar to that described hereinbefore in which transmission took place from station A to station B.

Although a speed of 60, and a '7 unit code has been assumed and referred to in the foregoing description, my Ainvention is not limited to that particular speed and code, but may be readily adapted to other speeds and to codes involving other than 7 units. For example, by varying the resistances II, I4 and 36 of Fig. 1 the speed may be made as high as the practical operation of the relays permits, or as low as desired; and the code units may be varied from one to any desired multiple of 1.

The purpose of the batteries I5 and 31, shown in Fig. 1, is to ensure the operation of the tubes T1 and T2 within relatively narrow time limits. As mentioned, hereinbefore, the suppression of the space current in those tubes is accomplished by raising the voltage on condensers Ill and I2 to a negative value above ground potential. As the grid approaches ground potential current begins to flow and its value depends to a degree on the potential of condensers I and I2. Batteries I5 and 31 cause the charges on the condensers to sweep rapidly across the zero to ground potential and thereby ensures the operation of the tubes within relatively narrow time limits.

While this invention has been described as embodied in particular forms, it is obviously capable of embodiment in other and diierent forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a telegraph repeater, the combination with a receiving relay connected to an incoming line and responsive to signaling impulses thereon a sending relay controlled in part by the said receiving relay and connected to an outgoing line for the transmission of amplified and undistorted signals thereover, a locking relay associated with the sending relay to release the latter relay at prexed time intervals, the said receiving relay being connected to a winding of the said sending relay to operate the latter relay in accordance with the received signaling impulses whenever the said sending relay is released upon the operation of the locking relay at each prefixed interval of time thereby permittin'g the sending relay to transmit a signal impulse of the same polarity, namely marking or spacing, as that received bythe said receiving relay, a pulsing relay adapted to operate the said locking relay at the said prefixed intervals, an electronic timing circuit adapted to cause the pulsing relay to operate at the said time intervals, and a second electronic timing circuit to limit the number of operations of the said pulsing relay.

2. In a telegraph repeater, the combination with a receiving relay responsive to signaling impulses impressed thereon, of a sending relay controlled, in part, by the said Areceiving relay and adapted to impress amplified and undistorted signals upon an outgoing line, a locking relay associated with the sending relay to prevent the operation of the latter relay by the receiving relay except at prefixed time intervals, a pulsing relay having an electronic vacuum tube associated therewith to effect the operation of the said pulsing relay upon each occurrence of an electron discharge within the said tube, the said pulsing relay being arranged to disconnect a source of energy from a winding of the locking relay and the sending relay upon each occurrence of the said discharge whereby the locking relay and the sending relay may be released and permitted to operate under the control of the said receiving relay, a condenser connected to said vacuum tube and adapted to permit the said discharge to occur atl the said prexed intervals, and timing means, having a vacuum tube associated therewith to limit the number of oscillations of the said pulsing relay.

3. In a telegraph repeater, the combination with a receiving relay connected to an incoming line of a sending relay connected to an outgoing line, a locking relay associated with the sending relay, and a pulsing relay having means asso.- ciated therewith to cause it to operate a prexed number of times at prefixed intervals during the time of reception of the impulses constituting a teletypewriter signal, the said locking relay and sending relay each having a plurality of windings, one winding of each relay being connected in series to the armature of thefreceiving relay, and another winding of the said locking and sending relays beingV connected in series with a contact of the pulsing relay, the said pulsing relay having means to connect a source of current to the locking and sending relays whereby those relays may be prevented from operating and also to disconnect the said source from the locking and sending relaysA at prefixed intervals to permit the operation of the latter relays in accordance with the impulses of the received signal.

4. In a telegraph repeater adapted for twoway repetition of signals between an east station and a west station, the combination with an east receiving relay responsive to signals received from the east station, a west receiving relay responsive to signals received from the west station, a pulsing relay having means associated therewith to cause it to operate a prefixed number of times at preiixed intervals during the time of reception of the impulses of a teletype- Writer signal, a sending relay associated `with the east receiving relay but controlled by the west receiving relay to repeat the signal characters from the West station to the east station, the said sending relay having associated therewith a locking relay arranged to be released upon each'operation of the said pulsing relay to per- Vmit the operation ofv the sending relay at the said prefixed intervals of time only, another sending relay associated with, the west station to repeat the signal characters from the Veast station to the West station, the said other sending relay having another locking relay associated therewith also arranged to be released upon each operation of the said pulsing relay to permit the operation of the said other sending relay at the said prefixed intervals of time only,

and a preempting device responsive to the openV starting impulse of a signal character adapted to give control of the repeater to that station permit its discharge at the end of a period of time corresponding to the time-length of an 1m'- distorted teletypewriter character, the said control circuit being'arranged to stop the operation of the said pulsing relay upon the completion of the transmission of each teletypewriter character;

WADE B. MARIIN.k

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