US2186741A - Telegraph repeater - Google Patents

Description

Jan- 9, 1940- G. s. vl-:RNAM 2,186,741

TELEGRAPH REPEATER Filed 0G13. 27, 1937 3 Sheets-Sheet l lllll @Mum fwn vIvIV ATTORNEY Jan. 9, 1940. Q s VERNAM 2,186,741

TELEGRAPH REPEATER Filed oct.' 27, 1937 s sheets-sheet 2 s KLJ@ INVENTOR G/LBERT 5. VER/YAM ATTORNEY Jan. 9, 1940. G. s. vERNAM TELEGRAPH REPEATER 3i Sheets-Sheet 3 Filed Oct. 27, 1937 Patented Jan. 9, 1940 y 2,186,741 y y i l TELEGRAPH REPEATER y y `.Gilbert S. Vernam, HackensackQN. J., assigner to Postal 'lelegraph-Cablef Company (New York), New York, N.' Y., a corporation of New York Application october, 2r,

'13* Claims.y (Cl. 1785-71) e My invention relates to improvements in telegraph repeaters and particularly to single line or simplex repeaters. l

One objectief my invention is toy design a telegraph `repeater system that will operate athigh .speed and will accurately repeat signals, in either direction, between two single line or loop circuits.

Another object of my invention is to provide a y'repeater circuit with any vassocia-ted switching.

means for cutting the repeater circuit and closingthe line vvcircuit through the associated'relay `winding on'- each side of the repeater, independent oitherepeating contacts of. theother relays, thus stopping the lrepeating of signals 4in both directions.`

It is a further'object of myinvention toestablish a. local test circuit through the repeating.

`contacts of both relays atthe time thatthe repeater circuitA is cut. l It is a further object of my invention to'provide a `repeater for single line operation in which relay locking circuits entirely separate from `the line orloop circuit are provided and used with a relay having separate pairs of make and break' contacts v arranged so that the contacts 4may be adjusted to operate as make-before-break contacts.-

Itv is affurther object of my invention Vto prol .vide-sounder'circuits combined with'the separate relay lockingcircuits so arranged that'the sounder` current decreases and the locking current vfor -each relayincreases upon the-closure of back f contacts of the other relay.` .3 l

vIt isa'further object of my inventiony to providea switching arrangement for separating the sounder and ylocking circuits 'anddisabling the locking circuit of each line relay upon the cutting of the repeater circuit.

both polarized. signals. for printer motor control `or for. operating call indicating signals, e and maille-break signals for regular f' communication. Otherobjectsand features of the' inventionv wiil be presented in the particular vdescription ci my invention made with respect to the ac-v companying drawings, in which:

Fig. yl `discloses a schematic lcircuit of one form l oiV repeater in accordance with my invention,

1937,-.seria1Na 171,205

fOFFICE Fig. Zoillustrate's by way of example a -socalled v half-set. repeater: connection for use with the repeater illustratedinvFig. 1.

Fig. 3 is a schematic .circuit of another embodiment of arepeater` in accordance with'my i;

invention, andl i. 1

. Fig. 4 illustrates an application of the repeaterv shownV in Fig. 3 to agcall.signallingprinter arrangement. y f v Referring more particularly tothe" drawings,

in Fig. 1.r'eferencenumeral II represents a station connected by line I2 through a repeater to line I3, and the telegraph stationfapparatus des-` ignated generally as I4. The switches and relay [..contacts- 'of the repeater circuit are shown in their normal position which theyA assume when the repeater isy connected to aline and no Signals f are being transmitted. Thus, the line I2'is connected through the line relay winding I5 of line yrelay Iii-contact 2 oiA switch element 22 of two position switch 3 which comprises the switch elev,ments n Ila-24. inclusive, the front contact oflne `relayf3I',contact 2 of switch element 2l, to positive battery 33. Line I3 is connected through .contact 2 of switch element 'I2 of two position switch lil, line winding-2l of line relay 3| through contact 2 of switch elements 'II and 'lli` of switch 4, contact-2 of vswitch element 20, the front contact of relayrIE, contact 2-.of switch element I5, e

.Contact 2 of switch; element `69 of switch 4 to battery at 28. Upon the release and operation .of transmitting key I'I, for example, the line .circuit through the linewinding of relay I6 is 4opened*v and closed.- `Relay VI6 willA respond rto vthese signals, opening and closing theline circuit breaking of -this latter line circuit, however, a holding circuit is -established for line `relay `3l from ground-through the holding winding 30 of line relay 3|, contact`2 of switch element I1 `contact 2 of switch element I8, through resistance 35 to battery 25, so that relay. 3|?y remains 35 through thefline winding of relay 3l; `Upon ,4o of switch 3, the back Contact of line relay I6,

energized andthe line circuit connected to trans-j mission line I2 is not broken at theiront contact `of.relay 3|.A g

Similarly, when signals are being transmitted from I4, relay-3l releases, and the opening of its 4iront contactsopens the circuitof line,l2 andl 1 a holding circuit pis established through the back contacts of--relay 3l and contact of switch elen'ientv 24 to establish a holding current through the auxiliary relay `winding 34 oi-.relay IIS'.- The contacts controlled by earl of the line relays vIt and 3l are made iiesik-i and are adjusted so that when the relay releases, the back contacts close before the front contacts open, and when the relay operates the front contacts close before the back contacts open, so as to produce a makebefore-break action and maintain the other line relay energized, so that signals may be repeated by one relay from one station to the other, without efecting the Iother relay.- The line relays with separate contacts arranged for make-before-break operation permit the use of the repeater for repeating between two two-wire loop circuits, or received over either wire of either loop, thus 'permitting the repeater `to be -connected in series with loops of .other repeaters .to

form a 3-way repeater as is well .known in the4 art. This arrangement also permits the Sounders to be operated in a local circuit at the repeater to avoid adding the inductance of the sounder winding in the line or loop circuit.

The operation of the sounder circuit will now be explained. With both line relays operated, as shown in Fig. 1, a circuit exists through the sounder 35, extending from battery through the resistance 36, resistance 31, the winding of sounder 35 to ground. Simultaneously a parallel circuit exists from contacts 2 of switch elementV I8 of switch 3, resistance 38, and the auxiliary winding of line relay 3I to ground. This circuit is arranged with the resistance of the various elements so chosen that the current through the relay winding 30 under these normal conditions is insuiiicient to operate relay 30, but the current rthrough the sounder is sufcient to operate the sounder. A similar circuit may be traced for sounder 39 from battery 25, through resistance 4D associated with element 23 of swtch 3, sounder 33 to ground, and also in parallel therewith through the auxiliary locking winding 34 of relay I 6 in parallel therewith. The current through the locking winding of each of the line relays serves as a biasing current, the springs associated with the armature and relay contacts being strong enough to overcome this biasing current unless the armature is held by a current in the loop circuit. This biasing currentincreases the permeability of the magnetic circuit and makes the operation of the relays more sensitive.

' When one of the line relays, for example relay I6, releases, its back contacts create a short circuit around resistance 38, so that the locking winding 33 of relay 3| is shunted directly across the sounder and its resistance 31. The sounder current therefore decreases, releasing the sounder, and the relay locking current'increases to a value suiiicient to hold relay 3l operated in spite of the fact that the line circuit is now open at the front contact of relay I S. Accordingly, the repeater will operate to repeat the signals as explained above, and simultaneously each sounder will respond to the signals repeated by the corresponding relays. Thus, these Sounders may be used for monitoring the signals at the repeaters. Although, as described above, ordinary Morse telegraph keys and Sounders have been shown, it is clear that the repeater circuits may be used for other types of telegraph apparatus, lforl example, telegraph printers or teletype printers.

It can vbe seen that with the repeater such as described, if trouble conditions should cause either line to go open, the other repeater will also `open its circuit. The quickest method of locating the trouble is to operate a cut -or breaking circuit so that each of the loops through the line relays may operate independently of the other. This will `close the loop that is not in trouble and will permit service over that part of the circuit, until the trouble is cleared.

In order to provide for such a cutting of the circuit, it is only necessary to operate switch 3 so that switch elements I1 to 24, inclusive, are each resting on contact I. This cut circuit may also be used whenever it is desired to prevent the repeater .from repeating signals from one loop to the other, as for example, to shutoff a customers station while his circuit is being lined up. It may also be used for checking the adjustment of the various relays.

The operation of the switch 3 to position I, removes the front contacts of relay 3I from the line circuit I2 and closesthe line through contact I of switch element `2 I directly to battery 33, and similarly it removes the contacts of relay I 6 from line I3 and closes line I3 through contact I of switch element I9 to battery 28, permitting communication over these independent loop circuits without repeatingsignals from either loop to the other. At the same time the shut releasing circuits oi Sounders 35 and 39 are closed through 'the relay back contacts directly to ground, and the biasing circuits through the auxiliary windings of relays I5 and 3l are separately energized through contact -I of switch elements 23 and I8, respectively. Accordingly, the signals from II and I4 may be independently received at the relay station over line relays I6 Aand 3I operating substanl tially in the same way as previously described to energize Sounders 35 and 39. Simultaneously a test circuit is produced from battery 25 through test jack 4I, front contact of relay IB, Contact I of switch element 2B, front contact of relay 3I and contact I of switch element 22 to ground, permitting a test to be made of the relay contacts to determine any faults that may einst therein. By inserting a plug connected to a milliammeter in jack 4I the output signals of either relay may be tested, and the relays may be conveniently adjusted to repeat unbiased signals. I

It is sometimes desirable to connect a single line repeater to the sending and receiving legs of a duplex terminal set so that signals being 'transmitted in either direction over a duplex line may be transmitted or received through the repeater to or from a single Wire line or a single loop circuit. When used in such a connection, the repeater is termed a half-set repeater, and it provides means for furnishing single or halfduplex operation over a duplexed line. In accordance with my invention provisions are made for switching the connections of the repeater illustrated in Fig. 1 to operate as a half-set. To convert the repeater illustrated inl Fig. 1 for half- -ciuplex operation, switch 4 is moved to the left position illustrated in Fig. 1, whereby switch 4 is arranged sothat its various switching elements are on the number I contacts. Thus, connections are lestablished to each of the conductors 50, 5I, 52 and 53 of Fig. 1.

Fig. 2 illustrates the connection of these wires to the sending and receiving legs of a duplex terminal set circuit for operation with the repeater in a half-duplex arrangement. With this arrangement, signals from II are transmitted through the winding of relay I 6 in the same manner as previously described. However, the sending device i4 and line I3 are disconnected from the line winding of relay 3| by the movement of the switch element 12 from contact 2 to Contact I, and the circuit to the line winding 21 of relay SI now extends from contact IOI- of duplex line relay H15 "(Fig. 2), through receiving leg conserve to make and break its front contactsfthus repeating the signals throughthe repeater to receiver I I and simultaneously operating the receiving sounder 39 at the repeater for vmonitoring purposes. a; i

For transmission of signals from II to the duplexv line, the battery connection of thefront contactsjof relay I6 is broken at contact 2 of switch element 69 an dis connected through'contact I, sending legconductor 50and the winding'of pole changer relay |06 topcsitive battery at |01.,` This circuit then extends from battery |01 through the j circuit justvnamed, contact 2 of switch 'element lffrontcontacts ofv relay I6, contact 2 of switch element 20, contact I of switch element 10 and conductor 5I to ground at |08. Associated with relay |06 are two contacts, front contact F being. associated. with a negative battery and back contact B being associated with a positive battery. Contact tongue |09 yisl connected through'a suitable conductor IIO vand inductance III t'o the midpoint of therelay winding of Arelay |05.

Accordingly, signals transmitted from II serve '35 to makeand break the sending leg` circuit at the iront contact of relay I6, thus causing alternate energizing and deenergizing of relay" |064 and operating contact tongue |09 to alternately apply positive and negative signal impulsesto the line I 04 over the winding of relay |05. Since these signals are applied at the midpoint of relay winding vI 05, in accordance with the well known methyod of duplex operation, they will have equal and n opposite effects upon the two windingsof the vpolar relay |05 and accordingly will not affect the contact IIiI. Since the soundercircuit 'and the relay holding circuit are identical with those above described, a repetition of the operation'of these circuits is not considered necessary at this point.

Fig. 3 accordancev with my invention. a conventional printer' circuit is illustrated as the main office printer at 30| enclosed in broken lines, arranged to be connected through a -jack discloses another forni of repeater in vof a switchboard 302, within the bro-ken line block and throughv line 303, to 'the terminal 304 of the repeater. Incoming signals from the printer are applied through a line jack and resistor, line 303, c0ntact'2 of switch element 304, front contacts of relay 3I6,'contact il of switch element 306, the upper winding 3I'i of relay 3I8, contact I of switch element 32|, the lower winding 323 of relay 3I8, contact I of switch element y320, throughr'esistance 320 to negative battery.

Another printer station 330, shown v'at the right of the figure enclosed by broken lines is connected over line 3.3i to terminal T332 of the repeater, and a circuit is established through contact 2 of switch element 300, front contact of re-v In this figure,v

Thus incoming signals' switch element 306,` the back contact of relay 3I8 and resistance 333' to ground at 340, preventing the front contact of relay 3I6.from opening.

Similarly, `when'signals transmitted from 330 the back contact of this relay closes, establishing a circuit from negative battery at 326 through contact I of the switch element 320, winding 323 ofl relay SIB, contact I of switch element 32|, winding SI1 vof relayl 3I8," contact 2 of switch element 335, back Contact of relay Sill, conductor 34|, Contact i of switch element 3I9, conductor 342,'resistance 343, to 'ground at 340, thus establishing a holdingv circuit for relay 3I8, so that it will not open its contacts. The contact springs of relays 3I6 `and 3|8 are madeflexible and adjusted to make-before-break-so that the holding circuitsfor the respective relays ywill be maintained.

Contact switch elements 304 to 3|0, inclusive, are elementsof a single switch for two-position operation indicated generally at 345'and contact operate to open 'the front contact of relay 3I6,

iii).

elements'3i9 to 32| are elements of the-three- 'position switch indicated generally at 346.

With switch 345 in the number two position as shown, and switch 346 in its number one position asv shown, the repeater operates as a straight, through repeater, similar to that illustrated in Fig. 1. -By throwing a switch 345 to the right to establish circuits through the numberv one contacts, a cutcircuit may be established for this re-` peaterg'so that signals incomingth'ereover will not be repeated tothe other line. With the switch thrown to this position signals incoming from 30| traverse the circuit `from terminal 304 through Contact I of switch element 365,' winding 3I1 of relay 3m, contact I of switch element 32|, lower winding 323 of relay 3I8, contact I of switch element 320 and resistance 323 to negative lished extending from positive battery at 326,

test jack 341, contact I cf switch element 304, front co-ntact of relay SIB, contact I ci switch element 306, contact I of lswitch element 301', front Contact of relay 3I8, Contact I of switch element 300, resistance 339 to ground at 300. This produces a test circuit, enabling `the testing'and `adjustment ofthe'separate contacts of the two repeater relays, similar to that described in connection with Fig. l'1. d

In Fig. 3, a motor control circuit for controlling the motor at station -330 from the main oilice station 30| shown. This motor control circuit is established by turning three-position switch 346 to its number three position.` The removal of switch Yelement 32| from the number one contact, removes a short circuit which pre- *viously existedaround polar relay 348, and connects this polarrelay effectively in series between 'zoy windings 351 and 323 of relay 3|8. When the circuit is idle, the plug is removed from the jack at the nia-in oiice and negative current supplied from the main oice switchboard, through the winding of relay 36|, inner contact of the jack, over the line 303 serves to maintain polar relay 34S operated, thus closing the contact 350.

A circuit extending from ground through conductor 353, the' winding of switch relay 334, conductor 354, contact 3 of switch element 322, contact 2 of switch element 3M), conductor 355, contact 350, resistance 324, to negative current supply at 326 serves to energize relay 334 thus closing its front contacts 335, 336 and 331. From the repeater a circuit to station 330 may be traced, from negative battery at 326, through resistance 324, front contact of relay 334, contact arm 335, winding 333 of relay 3|6, through the circuit previously traced to line 33|, through polarized relay 363, motor control relay 365, front contact of relay 363 to ground. Relay 365 being energized operates to hold the motor circuit open.

In order to establish communication by calling from station 330, break key 366 is operated, thus breaking the line circuit and closing it again. This will release and re-operate relay @E6 but relay 3|0 and polar relay 348 will remain energia-ed. The contacts of relay 3i@ will open and close again releasing relay 36| at the main office switchboard, and lighting the lamp 362. When released a contact of relay 36| short circuits its operating winding, so that relay 36| remains released after the line closes. When the cord associated with printer at the main oice is plugged in to the line jack, positive current is supplied to line 303 and relay 348 will be released, also releasing switch relay Insertion of the plug into the jack closes a circuit through a separate Winding on relay 36|, restoring its contacts to normal and also completes a circuit through control relay 336, applying positive battery to printer 30|. Release of switch relay 334 connects positive battery to line 33| from 326 through resistance 333, back contact of 335, the winding of relay 3|6, back through the repeater to line 33| as previously traced, and also connects the positive battery to the locking relay circuit of relay 3 I8 from terminal 326, through the back contact of 331, contact 3 of switch element 3|9, back contact of relay 3|6, contact 2 of switch element 335 to the relay winding of 3H through polar winding of 348, winding 323, as previously traced. This positive current on line 33| operates through the polar relay 333 to release the contacts 364, short circuiting motor relay 365, and closing the motor circuit to start the printer motor. A more complete description of the motor operating arrangement may he found in Patent No. 1,773,952, of, A. F. Connery, issued August 26, 1930.

Relays 348 and 334 remain released while the printer signals are being transmitted through the repeater in either direction. The operation of the repeater in repeating these printer signals is the same as previously described. A resistance 366 is shunted across the winding of relay 3|8 from ground at 340, through resistance 366, contact 3 of switch element 32| to the upper terminal of Winding 323, to reduce the inductive discharge from this relay winding when the circuit is opened at the main oice 36|. Without this shunt circuit the discharge may be suiicient to operate polar relay 348 during the transmission of the signals. When the communication is completed, the plug may be removed at station 30|,

reconnecting negative battery from 302 to the line, thus stopping the station motor by the operation of polar relay 363 and restoring the line to normal.

Although the motor control circuit has been described with a source of both negative and positive direct current supplied at the repeater a single repeater may be installed with a single rectier or motor generator arranged to supply both current polarities at the repeater by reversal of the rectier or generator. In such a case the rectier or generator should not be grounded but both terminals should be connected to the repeater terminals at 326 in Fig. 3. Terminal 351 should then be connected to ground. The connection between ground and Wire 353 should be removed and a connection made from 353 to terminal 369. Then when either terminal of the rectifier or generator is connected through contact spring 335 of relay 334 of the repeater to the station line, the other terminal will be grounded through spring 336 of switching relay 334.

It is sometimes desired to provide a calling system to be operated from the main station for calling several subscribers printer sets so that the desired called station may be connected to the line. In accordance with my invention such a system is indicated generally at 40|, connected through push button switch or break key 402, line 463, polar relay 404 at printer set 405, line 406,.,

repeater 401, line 409, polar relay 408, station printer set 4|0, and a suitable resistance 4| to a negative battery at 4|2.

The repeater station indicated at 401 in Fig. 4 may be a repeater such as that illustrated in Fig. 3, with the switch 346 to the left or No. 3 position or with switch 346 moved to its central or number 2 position. If the line sections are short enough so that they may be operated to ground at one end,that if the first line section may be operated from battery at the main omce to ground at the repeater, and the second section operated from battery at the repeater to ground at the terminal station, then the repeater of Fig. 3 may be used with switch 340 in the No. 3 position, as described above, and the polar signals transmitted over the line used to operate call bells or other signal apparatus to indicate the desired station to be connected. With this arrangement a printer circuit such as shown in Fig. 4 is used. The break-key 402 at station 40| may be operated successively to transmit the code signals indicative of the desired station, and the relay 365 may be arranged to operate a bell instead of closing the motor circuit.

However, the operation of the circuit of Fig. 4 with switch 346 in the No. 2 position is more useful in cases where the lines are long. Negative battery is connected to line 406 from negative terminal at 326 through resistance 31|, contact 2 of switch element 320, winding 323 of relay 3|8, winding of polar relay 348, winding 3|1 of relay 3|8, through the circuit previously traced to terminal 364 and to line 406. The resistance 31| and grounded resistance 343 which is connected to relay 3|8 through contact 2 of switch element 320 form a potentiometer, 'which operate to reduce the negative voltage supplied, below that of the negative battery 436 at the main oice.

In the normal condition current from positive battery is connected to the line at station 40| and flows through relay 348 in a direction to normally maintain its contact 350 open. Interrupting this circuit to call the main station 40| or to transmit printer signals will have no effect, since the relay mally energized relay operatively connected inL b iasing spring'tends to hold the relay contact 350 open. When vthe push button 402 at the main vo mce isoperated a reverse current is impressed on theline from negative battery 430, which current has a reduced strength due to the negative supply which is impressed on the line at the repeater. This reduced current is sucient to operate relay 404 or any other polar relays between themain central station and the relay station, operating the call bell at any of these stations.

` Relay 3l8 will release as this weak currentin its upper winding 3l1 opposes the current through its lower winding 323 and resistance 343, but the reversed current through the line will simultaneously operate relay 348 closing contact 350. Opening of the front contact of relay 3l8 will break the positive line supply on line 409 which formerly was supplied from the positive terminal of. 326 and will impress on the line negative polarity from the negative terminal of 326 through resistance 324, contact 350, conductor 355, contact 2 of switch element 3l0, contact 2 of switch element 322 to terminal 332.

This will impress a negative current on line 409 operating. the Apolar relays 408 and ringing the Abell at station 410, and any other stations which may be interposed in the line. When the pushrbutton 402 is released at the main oilce, positive battery is again connected to the line releasing relay 348 and reoperating the repeater re'- lay 318. These operations may be repeated every timev the push button is depressed, thus ringing the 4bell as many times as desired. Any station may be called by assigning a particular number or code of thecall bells thereto so that when the proper signal is received the printer at that station may be connected to the line.

Instead of repeating the current reversal to operate signal bells at other stations, it may be desired in some cases to use the single stroke bell to vcall the. repeater station only. This may be 'done by opening line 355, Fig. 3, and connect- .ing a signal bell from the part of conductor 355 connected with contact 350 to ground through a suitable resistance. Relay 348 will then respond to current reversal in the main line, but will operate the local .signal bell instead of repeating the reversals over the other line.

vthe line relays 3I6 and 3l8 will operate only to transmit signals through the test circuit and will not in any way affect the transfer of signals between stations on each of the now separate line sections.

While I have described my invention with relation to several specific embodiments thereof, it should be understood that these illustrations are merely intended to describe the principles of operation of my invention and not as a definition of the scope thereof. Any changes and substitution of parts may be made therein within the scope of the appended claims which thereto define Amy invention.

What is claimed is: 1. A repeater system comprising, a. i'irst transmission line, a second transmission line, a nor.

each transmission line, contact means in each line controlled by the relay in the other line, each of said relays being responsive to signal current iiuctuations in the transmission line associated therewith to open and close contacts of said con-` tact means in said other line for repeating sighals thereto, means operative .upon opening of said contacts in either of said lines for maintaining the relay-inthe opened lineenergized during 'the signal current fluctuations, and switching means for disconnecting said contact means from both of said lines and completing the energizing circuit of said relays independent of said contacts for stopping the repeating of said signals from lone line to the other, said switching. means establishing a local lcircuit through both of said contact means upon disconnection of' said contact means from said lines.

2. A repeater system -according to claim l, in,

which said means for maintaining said relays energized comp-rises a local circuit connected to a winding on each of said line relays, and said contact means in each of said lines comprises a' pair of make-before-break contact switches, one ofthe switches of each said pairbeing connected l 3. A repeatervsystem according to claim 1, in

which said means for maintaining lsaid relays energized comprises a local circuit connected to a separate winding on each of said line relays, and further comprising a sounder circuit connected in shunt with each of said separate windings and means for operating said sounder upon operation of said repeating contacts.

4. A repeater system according to claim 1, in which said meansoperative upon opening of the contacts for maintaining the relays in the lines energized,v comprises a local energizing circuit connected to the main relay. winding of saidrelays.

5. A telegraph' system comprising a main ofce telegraph signalling station connected to a first line section, a repeater connected to said -rst line section for repeating signal impulses and telegraph` signalling stations connected to the output of said repeater through a second line section, means at said main ofce for supplying a normal potential to said first line section, a polar neutral line relay in said first line section at said repeater normally energizedrby said normal potential supply, a polar relay in said rst line section at said repeater normally unoperated by said normal potential supply, means in said second line section at said repeater responsive to signal impulses for repeating signals from saidA first line section to said second line section, polar relays in said second line section at each of said telegraph stations, unresponsive to normal repeated signal impulses, means for maintaining a normal potential on said second line` section, means at said main office station for'introducing a current-of polarity opposite to said normal polarity upon said rst line section for op erating said first named polar relay, means in said second line section responsive to operation of said iirst named polar relay for introducing a current of polarity oppositeI to said normally maintained potential on said second line section for energizing said other polar relays, and operating means at said telegraph stations responsive to energization of said pola'r relays.

6. A telegraph system accordingl to claim 5 in 'in the transmission line and the other switch of which said polar relays in said second line section control call signal indicating means.

'7. A telegraph repeater comprising a rst line section, contact means in said line section, a Iirst polar neutral line relay responsive to normal make and break line signals, line signals, having a line winding connected to said rst line section, a polar relay, responsive to polar call signals, having a winding connected to said rst line section, a second line section, contacts means in said second line section controlled by said first polar neutral line relay to repeat said make and break line signals, a second line relay responsive to normal line signals, having a line Winding connected to said second line section, said second line relay controlling repeater contacts in said first line section, and a local circuit controlled by said polar relay operative to supply potential of the polarity of said polar signals to said second` line section, whereby said repeater operates to repeat signals by the operation of said line relays and to translate polar signals by the operation of said polar relay.

8. A telegraph repeater according to claim 7, further comprising back contacts operative with said contactmeans in said rst and second line sections, and another local circuit connecting line relays and said back contacts for maintaining sai-d line relays operated upon the opening of the contacts in the line section connected thereto.

9. A telegraph repeater according to claim 7, in which said local circuit is connected to said second line section, whereby said polar call signals serve to repeat said call signals to said second line section.

'10.A telegraph repeater according to claim 7, further comprising switching means for disconnecting said line contact means from their respective line sections, and completing another local circuit through said contacts responsive to signals on said line section.

l1. A telegraph repeater according to claim '7, further comprising switching means for rendering said polar relay effective or ineffective for operation by polar signals incoming over said first line section.

12. A telegraph repeater system comprising a first line section, a line relay in said rst line section, a second line section, a line relay in said second line section, front contact means in each of said line sections controlled by the relays in the other line section, back contact means controlled by said line relays for closing a holding circuit for the corresponding line relay upon opening of said front contact, a polar relay connected to said rst line section, and switching means movable to alternative switching positions, for rendering said polar relay ineffective in one position, connecting said polar relay to control a call signal indicator in a second position, and connectingsaid polar relay to control telegraph motors in a third position.

13. A telegraph repeater according to claim l2, further comprising a local test circuit and a cut switching means adjustable to two positions, said out switching means in one position connecting said front Contact means in said line sections and in the other position disconnecting said front contacts from said line sections and closing said local test circuit through said front contacts.

GILBERT S. VERNAM.

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