US2102983A

US2102983A - Telegraph system

Info

Publication number: US2102983A
Application number: US12364A
Authority: US
Inventors: Gilbert S Vernam; Frederick G Hallden
Original assignee: POSTAL TELEGRAPH CABLE CO
Current assignee: POSTAL TELEGRAPH CABLE CO; POSTAL TELEGRAPH-CABLE Co
Priority date: 1935-03-22
Filing date: 1935-03-22
Publication date: 1937-12-21
Anticipated expiration: 1954-12-21

Description

Dec. 21, A1937.

G. S. VERNAM ET AL LEGRAPH SYSTEM Filed March 22, 1935 2 Sheets-Sheet l DeC- 2l, 1937- G. s. VERNAM ET Al. 2,102,983

TELEGRAPH SYSTEM Filed March 22, 1935 2 Sheets-Sheet 2 lf/ ASE) 0 0 SL (AC. BELL) (SLOW OPERATING AND 5L 0W RE L EASE) 7:- 101e. y l mms mvmrons.- maf/e592. vmun Patented Dec. 21, 1937 UNITED STATES PATENT QFFCE TELEGRAPH SYSTEM- Application March 22,

20 Claims.

rI'his invention rel-ates to telegraph Systems and more particularly to a polar ysimplex telegraph system, namely a system for transmitting polar telegraph signals in either direction over a line f circuit, in one direction at a time, and without employing the usual duplex balance.

Such a polar simplex telegraph system may be used for manual signalling by means of the ordinary Morse code, but it is intended primarily 1U for operating telegraph printers or teletypewriters of the start-stop type over line circuits whose transmission characteristics are such that they are not Suitable for high speed operation by the ordinary neutral or make and break method 115 of signalling, and where the polar half-duplex system cannot be used because of the excessive cost of the equipment required and the lack of trained repeater attendants for balancing the duplex terminal sets and repeaters.

One of the objects of the invention is to provide a system without duplex balance for transmitting polar signals under the control of a printer keyboard or tape transmitter at any one station on a line, and for receiving such signals on f, polar relays and causing them to actuate recording printers at any one or at all other stations on the line for the purpose of inter-communication.

Another object is to provide a telegraph Sysg, tem suitable for operation over long line circuits, having considerable resistance and capacity and which may be subject to interference from telegraph cross-fire or power line induction, without requiring reduction in sending speed or continual f 3:, readjustments of relays or duplex balance to compensate for varying weather conditions.

Another object is to provide a system suitable for way wire circuits, having three or more stations in series with the line, without requir- .1;, ing costly and complicated repeaters at the intermediate stations.

Another object is to provide a system suitable for way-wire lines having a main station located in the central telegraph oilice at a rela- .;,7 tively large city, where a supply of direct current is available, and h-aving one or more way stations in smaller cities where only an alternating current supply is available.

A further object is to arrange the system so if.) that the local direct current required at each way station is reduced to a minimum, so that it may be supplied by a small motor-generator or rectifier, and so that all local power may be Switched off at the Way stations when they :.5 are not actually in use for sending or receiving 1935, Serial No. 12,364

messages. This results in considerable savings in the cost of power and power supply equipment and reduces the cost of maintaining the motorgenerator or rectifier.

Still another object is to provide a Simple and reliable method of selectively calling any way station by means of a code of bell signals, the bells being arranged to operate independently of, and to be unaiected by, the polar telegraph;

signals. The bell signals are also arranged to operate even though the printer motors are stopped and the local power supply is switched off.

Another object is to arrange the system so that the circuit can be linked at the main station to a duplex set or carrier'ch-annel terminal toy extend the circuit for direct printer operation to any distance, without changing the method of polar simplex operation to the way stations.

Another object is to provide a break feature, to permit any operator to interrupt the sending station and obtain control of the circuit, which is positive in action, and, as compa-red with other systems, is less affected by line capacity and leakage. This break feature is also arranged to operate in the same manner when the circuit is extended over a polar duplex or ca-rrier circuit.

Another object is to provide a system in which no preliminary operation of break keys or 'foot switches is required before sending, the operation of the printers and their keyboards being eX- actly the same as on an ordinary closed line circuit using neutral or half-duplex transmission.

Another object is to `arrange the system so that line battery is always connected to the line at in the accompanying drawings, wherein:

Fig. 1 shows the circuit of the main station, including rthe method of extending the Circuit over a duplexed line; and

Fig. 2 shows the circuit of a way" station and indicates how one or more additional way stations may be connected in series with the line.

Uil

To show the complete system, Fig. l should be placed to the right of Fig. 2. The line DL shown near the bottom of Fig. l extends to a half duplex set at a distant point and the leg or loop or" this set connects to a start-stop printer. As the details of such sets and printers are well known, and as these details are not part of this invention, they have been omitted from Fig. 1.

In the drawings, certain of the relays are designated to indicate that they are polarized, slowto-release, or slow-operating. As is well known, relays may be made sloW-to-release or slow-tooperate by equipping them with copper slugs surrounding part of the core. The slow-operating relays have slugs at the armature end of the core, which make them slow-to-release as well as slowto-operate.

Main station equipment Referring to Fig. 1, the equipment at the main station MS consists essentially of a group of relays connected with the polar simplex line SL and associated with the printer set P and the duplex set D. The printer set P includes the keyboard contacts K, the printer line magnet LM and printer driving motor PM, which in this case may be a direct current motor with the usual centrifugal governor for maintaining its speed substantially constant. The printer set P is normally associated with the polar simplex set relays through the contacts of switching key SK, but if this key is operated, the printer is disconnected and the duplex set D is connected in its place for the purpose of extending the circuit over duplex line DL.

Way station equipment Referring to Fig. 2, the way station WS has a group of relays, a printer set P' withits keyboard contacts K', line magnet LM and motor PM. This motor is preferably an alternating current motor either of the synchronous type or a series motor with governor. The necessary direct current for the relays is supplied by motorgenerator MG. A rectier with suitable *filters may be substituted for this motor-generator, if desired.

One or more additional way stations may be connected in series with the line.V One such station WS is shown schematically, but its detailed circuit is not shown as it is the same as station WS. The outgoing line SL is grounded after extending through the set at the last way station.

The circuits at both stations are' shown in the idle condition. The power switch PS at the way station is open, so that the printer motor PM and the motor-generator MG are both shut 01T, and no local current is used at the way station. The power switchrPS at the main station is in the on call position, the printer motor PM being shut of and the signal relay SR connected so that it can operate in response to an incoming call. The main station can also call any of the way stations, operating the single stroke bells, as SB, even though the local power is switched oil at the way stations.

Polar simplex operation-general In this polar simplex system, polar (-l-) and signals sent from one'station are received by polar relays connected in series with the line at other stations, and the circuit connections can be reversed automatically so that a station formerly receiving can send back to a station that was formerly transmitting. While sending polar signals from one terminal station, the line is grounded at the other terminal station; and while sending polar signals from an intermediate station, the line is grounded at both terminal stations.

in the normal, idle condition, negative battery is connected to the line at the main station and the line is grounded at the terminal way station. When the main station sends, its pole changer PC transmits spacing and marking signals over the line, through the way stations in series, to ground. When a way station sends, its pole changers PCA and PCB connect the negative generator terminal to the line toward the main station and the positive terminal to the line toward the terminal way station and ground, to send spacing signals, and they reverse the generator terminals to send marking signals. The first spacing signal transmitted from any way station causes relay RS at the main station to disconnect the battery and connect the line to ground. Relay SS' at the way station also operates at this time to connect the marking contact M of the pole changer PCA to the generator. These relays, RS and SS', are arranged so that they remain energized as long as transmission continues rom the way station, but they release shortly after transmission stops, thus automatically restoring the circuit to its normal idle condition, with negative batteryconnected to the line at the main station and with the generator effectively disconnected from the line at the way station. It should be noted that the direction of the marking and spacing current impulses in the line and through the polar line relays at each station is the same regardless of which station is sending.

Main station circuits-idle condition Referring to Fig. l in the idle condition certain circuits are normally closed at the main station MS-as follows:

1. A circuit from the grounded battery through keyboard contacts K, break key BK, contacts l and 2 of switching key SK and through the windings of the sending control relay SC and pole changer PC to ground, to hold these two relays energized.

2. From negative main line battery MLB through contacts I l and l2 of receiving switching relay RS, marking contact and tongue of PC, upper windings of line relay L and break relay B,

contacts

22 and 23 of calling relay C, line rheostat LR and over the line SL to the way station (Fig, 2), through the rectifier R and signal relay SR', calling key CK', contacts 5l and 52 of power relay PR and over outgoing line SL and in a similar manner through any additional way stations as WS to ground at the terminal way station, The current in this circuit holds the tongues of relays L and B against their marking contacts and holds the signal relay SR at each way station energized. Because of the rectier the current through the SR relay is always in the same-direction and the relay will remain energized as long as current in either direction ows over the line. The purpose of the rheostat LR is to Vadjust the line current to a normal operating value so the equipment will he adaptable for operating over lines of different lengths and resistances.

A circuit through holding rheostat HR and the lower or holding winding of relay B in a j direction to hold the tongue against the marking Cil contact. This current is-adjusted to about 11/2 times the strength of the line current.

4. From negative main line battery MLB through contacts il and.V `|2 of relay RS, bias rheostat BR,

contacts

26 and 25 of sending switching relay SS and through the lower or `bias winding of relay'Lfto ground.r The bias rheostat BR is adjusted so that the current `through the bias winding of relay L is slightly less than the normal current through the'v line winding. The difference in these two currents should-be just suflicient to hold the relay tongue against its marking contact in spite of induced interfering currents in the line.

A circuit through the winding of break `control relay BC and the marking contact and tongue of relay B, holding BC energized.

6. A circuit through the winding of holding lrelay I-I and contacts I8 and I1 of relay RS to hold relay H energized.

7. From -grounded battery through printer line magnet LM, contacts 6 and 'l of switching key SK, marking contact and tongue of relay L and contactst and 35 of relay BC to ground, holding magnet LM energized.

Calling the main station `To Vcall the main station, the operator at any way station switches the local power 'on his set and operates the brake key BK momentarily or depresses any keyA on the printer keyboard, which, as will be explained later, transmits and -1- signals to the line., The rst spacing vsignal reduces the line current to a low value, as negative potential applied to line SL from the way station generator opposes the negative main line battery applied to the line at the main station. If the line battery Voltage at the main station is equal to the generator voltage yat the way station and there is no leakage to ground from the line conductor, the line current will drop to zero, but if there is leakage or if the main station voltage is higher than that at the way station, `the vline current from the main station will bre-.considerably reduced, but not to zero. In either case, the current in the lower or bias winding of relay L will overcome the line current through the upper winding and operate the relay tongue to the spacing contact. Relay G will operate over a circuit from negative main line battery through contacts Il and l2 of RS. winding of relay G and resistance GR in parallel, ycontacts. 2| and 20 of RS, spacing contact and tongue of L, and contacts 35 and 35 of BC to ground. Relay CiV ycloses an obvious circuit for operating the signal relay SR, which locks itself through its contacts '44 and 45, lights the lamp signal LS and operates a vibrating call bell or `buzzer VB. This bell or buzzer may be common to several main station sets similar to set MS, but connected Vto dierent line circuits. The bell indicates that a call is being received over one of these lines and the lamp signal s-hows which line. Relay RS will also be energized at this time, but its function will be described later.

To answer such a call, power switch PS is moved lfrom the on call .to 4the foperate position, which starts the printer motor PM and releases relay SR, extinguishing the lamp and `stopping the'bell or buzzer. The main station set is now ready for receiving or sending messages.

C'alling from 'main station To call a way station, the calling key or push button VCK is depressed and released slowly several times to send the code call for the station desired. This operates relay C over an obvious circuit. Relay C opens the line SL, releasing the signal relay SR at each way station and thereby tapping the single-stroke call bell SB at each way station. Relay C also connects a compensating resistance CR to relay B to maintain the continuity of the line circuit of the main station set and prevent the release of relay L while calling the way station.

It should be noted that an alternating current relay may be substituted for slow-release relay SR and its rectilier R. The arrangement shown, however, has theadvantage that it introduces less resistance into theline as a more sensitive relay, having a comparatively low resistance winding, may be used and the slow-release type relay used will hold up reliably during all printer signals.

Way station circuitsswitching on and o1? Local power at a way station may be switched on to answer a call from the main station, to call the main station, or to listen in f on the line to determine whether it is busy before calling. In any case this is done by closing power switch PS (see Fig. 2) which applies alternating current to the printer motor PM and to thel motor-generator MG. The motor-generator starts and supplies direct current to the following circuits:

l. From the positive generator terminal through the winding of holding relay HA, contacts t@ and ci of holding relay HB to the negative generator terminal, energizing relay HA. The operation of the

contacts

53 and 64 of relay HA breaks a short circuit around the winding of relay SC extending by way of contacts 18, 19 of SC and 'll, l2 of SS.

2. From the positive generator terminal through the windings of pole changer relays PCB and PCA and sending control relay SC' contacts l2 and ll of sending switching relay SS', break key BK and keyboard contacts K i to the negative generator terminal, operating relaysPCB, PCA and SC'. Relay SC at its contacts i6 and 'll' opens a short circuit including contacts 513, 55 of PR around the winding of relay PR.

3. From the positive generator terminal through resistance RP, contacts 8l and 82 of power switch PS, winding of power relay PR to the negative generator terminal. It should be noted that, as above stated, relay PR is normally short-circuited through its contacts 54 'and 55 and contacts Tl and l5 of relay SC', and that relay PR, therefore, cannot operate until after relay SC and the pole changers PCA and PCB have operated. This prevents the pole changers from transmitting a spacing signal to the line while the set is being switched on and also pre-- vents relay SS from operating at this time (as

contacts

55 and 56 cannot close until after contacts i5 and 'H open).

4. From the positive generator terminal through printer line magnet LM', tongue and marking contact of line-break relay LB, break key BK', and keyboard contacts K to the negative generator terminaljoperating line magnet When relay PR operates, the line circuit is extended through both windings of relay LB in series, over a circuit extending from contacts y5| and 53 of PR through the upper winding of LB, tongue and marking contact of PCA, lower winding of LB, Vcontacts 'I5 and'HI of relay SS and over the outgoing line SL to ground. As the lower' contacts of relay PR are of the makebefore-break type, this action takes place without interrupting the line circuit or otherwise interfering with signals that other stations may be sending, except to cause a very slight reduction in line current due to the added resistance of the windings of relay LB. If signals are passing over the line at this time, relay LB will respond to these signals and repeat them into the printer magnet LM over circuit 4 described above. The printer P will, therefore, record any messages passing over the line.

If the printer indicates that the line is busy the power should be switched off by opening switch PS'. This will release power relay PR immediately and switch the incoming line circuit directly through to the outgoing line. .The other relays which were operated over the four circuits described above will remain operated for a brief interval while the voltage of the generator is dying down. It is obvious, therefore, that the act of switching the power off at a way station will not interfere with signals passing over the line between other stations.

Transmission and reception ai main station Assuming that the power switch PS (Fig. l) has been operatedY to start the printer motor PM, signals may be sent from the keyboard K to actuate relays SC and PC over a circuit previously traced. The rst open or spacing impulse from the keyboard will release these two relays and relay SC will close an obvious circuit for operating sending switching relay SS. Relay PC will transmit a spacing impulse from positive main line battery MLB to the line through the upper windings of relays L and'B. Relay B will not respond as it is held by current throughV its holding winding that is stronger then the normal line current (except that it may be momentarily operated by surges due to line capacity, the effect of which will be described later). Relay L will respond to the outgoing signals, however, and the first time its armature touches its spacing contact, relay G will be operated over a circuit previously traced. In this case, signal relay SR will not operate, as its circuit is open at switch PS. Relay RS will operate, however.

Relay SS will lock itself through its contacts 3I and 3E)l and through contacts I5 and I4 of RS to ground. With relays SS and RS both energized, negative main line battery is now connected' to the marking contact of the pole changer PC through contacts 2l, 26, I3 and I2. Rheostat BR is now short-circuited by contacts I3 and I2 of RS, Vand the lower or bias winding of relay L is open at contact 25 of SS. The bias current is, therefore, removed from relay L and .it will operate as an unbiased polar relay in re- I9 and 20 to theV being transferred to the spacing contact Aof relay L, and itY remains operated as long -as signals are being transmitted to Aactuate relay L. The condenser CX connected to relay H acts to prolong the impulses through the winding of Yrelay H by allowing the current to continue after the tongue of relayL leaves its spacing contact, while the condenserV charges. Relay H remains operated, therefore, as long as relay L responds to printer signals, but it will release about onehalf second after relay L stops with its tongue against its marking contact. Relay H provides a locking circuit for relay RS through the contacts of relay H and contacts I6 and I1 of relay RS, so that relay RS is no longer dependent upon the contacts of relay G, which releases shortly after relay RS operates. It is obvious, therefore, that relays SS and RS will remain energized as long as signals are transmitted from the keyboard, but will release successively, (relay RS iirst and then relay SS) a short interval after transmission stops. Y

When signals are transmitted from a way station, the rst spacing impulse reduces the line current by opposing the negative main line battery, as previously described, thus allowing the bias winding of relay L to operate its tongue to the spacingV contact. This grounds the line through relay G and its shunt resistance GR and operates relay G, as previously described. Relay G operates relay RS, which transfers the circuit of relay H to the spacing contact of relay L in the same manner as for outgoing signals. Relay G releases, as its circuit is now open at contact 2I of YRS but relay RS is held energized by relay H, which remains operated as long as relay L is actuated by incoming signals. As relay- RS is operated and relay SS is not operated, the line circuit SL now extends through the upper windings of relays B and L, tongue and marking contact of PC, contacts I2 and I3 of RS,

contacts

26 and 25 of SS and lower winding of L to ground. It should be noted that the line relay now has no bias, as the negative battery circuitV is open at contact I I of RS and the rheostat BR is shortcircuited by contacts I2 and I3. With both windings of relay L in series it will be more sensitive to receive the polar signals from the distant way station. Relay L will repeat the incoming line signals through its marking contact M to printer magnet LM, causing it to record the incoming messages. Relays H and RS will remain energized until transmission stops from the way station, after which they will release and restore the main station circuit to its normal condition with negative battery connected to the line and the biasing circuit applied to the lower winding of relay L.

1 Transmission and reception at way station Referring to lig.v 2, with the power switch PS clo-sed, relays PR, HA, SC', PCA, PCB, SR' and printer magnet LM are normally energized as previously described. Relay LB is held energized by the line current from the main station so as to hold its tongueagainst its marking contact. When signals are transmitted by the main station pole changer PC, as previously described, signal' relay SR' remains energized but polar relay LB responds toY the signals, repeating them into the printer magnet LM' so that printer P records the incoming messages.

When the way station keyboard K' is operated, the rst open or spacing impulse releases relays PCA, PCB and SC and the printer magnet LM'. Relay PCA connects the negative generator terminal to line SL, through the upper winding of relay LB, while relayPCB connects the positive terminal of the generator over outgoing line SL' to ground, thus sending a negative impulse over the line SL to operate relayL at the main station, as previously described. Relay SC, upon releasing, closes a circuit from the negative generator terminal through its contacts 'it and 1T, cont-acts 55 and 5t of PR, contacts 58 and 5l of HB and through the winding of sending switching relay SS to the positive generator terminal, operating relay SS. Contacts 73 and 'l5 of SS connect the lower winding of relay LB to the positive generator terminal instead of to the outgoing line and ground. Contacts 72 and 'ifi' of SS' connect the contacts of relay LB in series between the keyboard contacts K and the winding of relay SC, so that the contacts of relay LB now control relays SC', PCA and PCB as well as the printerv magnet. This change is for the purpose of controlling the break,` as will be described later.

Relay SS establishes a locking circuit for itself f1, through its contacts 68 and es', through contacts 65 and 6T of relay HA and through the winding 'of relay HB tothe negative generator terminal.

As relay SC' is now released, a direct circuit for energizing relay SS' now exists through contacts f 51 and 58 of HB,

contacts

56 and 55 of P R and contacts ll and l@ of SS to the negative generatorterminal, so that the winding of relay HB is now short-circuited and'relay HB does notl yet operate. Relay SC operates, however, when the next closed or marking impulse is transmitted v from keyboard contacts K', and relay SC then opens, at its contacts 16 andil, the short circuit' around relay HB, so that relay HB now operates in series with relay SS', over the circuit previously traced through contacts t8, 69, t5 and Si.

' The original operating circuit forV relay SS is now open at contact 5l of HB, and the circuit of relay HA instead of extending directly to the negative generator terminal through contacts @El and 6I of relay HB, now extends through contacts 59 and 58 of relay HB, contacts 5t and 55 of PR to contact 'El of SC'. Relay HA, therefore, receives an impulse of current through contacts 'il' and lof relay SC' every time a spacing impulse is transmitted from, keyboard contacts K'. As relay HA is of the slow-release as well as slowoperate type, it will remain energized as long as signals are transmitted from the keyboard. Condenser CX acts to prolong the impulses through relay HA, in the same manner as condenser CX at the main station. Relays SS', HA and HB, therefore, remain energized as long as signals are transmitted from the keyboard K'.

Relay LB is so connected that marking signal-sl are transmitted through both windings in series,

in a direction to hold its tongue against its marking contact. Spacing signals are transmitted to line only through the upper winding of LB, but, while spacing signals` areV being transmitted, the

L. lower winding is. connected across the generator The I When transmission of signals from keyboard K stops, relays SC, PCA and PCB come to rest energized, transmitting marking (-1-) potential to the line SL toward the main station. The circuit of relay HA is now open at contact Tl of relaySC. After about one-half second, rrelay HA releases and opens the circuit of relay HB at contact 6l, after first establishing a holding circuit for relay SS through'v contacts 68, 69, t5 and 66, resistance RH,`and contacts t2 and 5l of HB. After a further intervalV of about one-half second, relay HB releases, opening the locking circuit for relay SS at contacte?, causing the release of relay SS and re-operating relay HA through contacts El and Gil. As two slow-release relays, HA and HBfmust release in succession to release relay SS', while only oneslow-release relay, H (Fig. l), releases to cie-energize relay RS, relay RS will always release before relay SS',

if the relays are properly adjusted. Therefore,

marking batteryV will be applied to the line lat the main station before marking (-I) potential is removed from the line at the "way station, and a double strength marking current will flowl over the line momentarily whenever the way station stops sending. This serves no useful purpose, but it is important not to allow relay S tor release before relay RS, as this would ground both ends of the line at the sameA time, reducing the'line current to zero and possibly releasing relay L at kthe main station and the SR' relays at all "Way" stations, tapping the signal bells.

If the "way" station operator, after sending part of a message, should hesitate' long enough to allow relays HA, HB and SS to release and should then start to send before relay HA had re-operated, relay SS mightY operate at a time when its locking circuit is open. To 'prevent relay SS from releasing, and thus interfering with the next marking impulse, a circuit is lestablished from the negative generator terminal through keyboard contacts K', key BK', contacts 63 and 64 of HA and contacts l@ and 73 of SC to relay PCA, thus short-circuiting relay SC so that it cannot operate until after relay HA operates. The operating circuit vfor relay SS' through contacts 'il and 'i6 of relay SC' remains closed, therefore, until relay HA operates and establishes the locking circuit for vrelay SS' through contacts 65 and 6l.

Breaking To break or interrupt transmissiorrfrom another station, it is only necessary to momentarily depress break key BK or BK', or to depress any key on the printer keyboard, several times in succession, using preferablya key which transmits more spacing than marking impulses such as the lo-lank" key or space bar. the spacing signals so transmitted coincide with spacing impulses from the other station, the double strength spacing current in the line will operate relays LB and B to their spacing contacts, overcoming the holding veffect of the currents through rheostats HR and HR".

Referring to Fig. 2, as relay SS. is operated while transmitting from the way station, relays SC, PCA and PCB as well as printer magnet As soon as a LMY will be released, as their circuits are open at the contacts of relay LB. As long as the double strength spacing current exists in the line, the tongue of relay LB will remain against its spacing contact a-nd spacing current will be transmitted from the way station pole changers PCA and PCB. Release of printer magnet LM' stops the printing and gives a denite indication of the break at the way station.

Referring to Fig. 1, relay B applies ground through its spacing contact and through contacts 29 and 28 of relay SS to the winding of pole changer PC, short-circuiting the pole changer and preventing itA from re-operating. The spacing current from the` main station continues, therefore, as long as relay SS` remains operated. Break control relay BC releases after a short interval, as its operating circuit is now open at the marking contact of relay B. Relay BC applies an additional ground to the pole changer circuit and removes ground from the tongue of relay L, thereby opening the circuit of relay H which releases after a short interval and releases relay RS. Relay RS opens the locking circuit of relay SS at its contact l5, but signals from the keyboard K repeated through contacts 4I and 42 of relay SC will hold relay SS operated. TheV printer magnet circuit is held open at the marking contact oi relay L to indicate the break to the main station operator.

When the main station operator stops sending on the keyboard, relay SC remains energized and,

after a brief interval, relay SS releases, openingY at its contacts 28 and 29 the short circuit around pole changerPC. Pole changer PC will operate and connect marking battery to the line. The reduced line current will permit relays B and LB to close their marking contacts, operating relay BC at the main station and relays SC',

VPCA and PCB as well as the printer magnet LM at the way station. If the way station operator has stopped sending, relays HA, HB and SS' will release and relay HA will re-operate, as y previously described, restoring the circuit to its normal receiving condition. As the main station operator has also stopped sending, relay L will also operate, closing the main station printer magnet circuit. The main station circuit is now restored to normal and either station may transmit.

Calling from one way station to another Although it is expected that the trafc handled will be chiefly between the main station and the way stations, there may be occasional messages to be transmitted from one way station to another. The calling key CK has been provided to enable one way station to call another. This is done by operating the break key BKand, while holding it operated, depressing and releasing the calling key CK slowly several times to send the code call of the desired station.Y

Operating the break key releases relays SC', PCA and PCB and operates relay SS as previously described, and transmits a spacing signal which causes relay L to operate relay G and relay RS at the main station, thus connecting the main station end of the line to ground. Operating calling key CK', while the break key is held depressed, releases relay SR at each way station, and taps the bells in the same manner as when the main station calls. After calling, the break key is'released to restore the circuit to its normal idleV condition.

Transmission from one way stationY to another As previously explained, the directions of cur- Vrent flow over the'linefor marking and spacing signals are the same regardless of whether the signals originate at a main station or at one of the way stations. It is obvious, therefore, that any way station can receive Vand record the messages sentV from any other way station, if the local power is switched on.

When aV way station operator operates the keyboard continuously and rapidly, the switching relay RS remains energized, and the line remains continuously grounded at the main station, with the main line battery disconnected. If the way station operator sends in a slow or hesitant manner, however, relay RS may release and apply negative battery to the line occasionally. This does not affect the proper operation of the printers at the main station or at the sending way station, as the-bias current is re-applied to line relay L whenever relay RS releases, and the printer magnet LM at the sending way station is operated directly over a local circuit by the signals from the keyboard contacts K'.

When negative battery is connected to the line at the main station, the next spacing signal from the sending way station reduces the line current substantially to Zero, as previously explained, but does not reverse it. The lin`e relay LB at another way station,.which is receiving, would not respond to such an impulse unless it was adjusted to have a normal spacing bias, which is not desirable. Line relay L, at the main station would respond immediately to such a spacing signal, however, and as soon as its tongue touches its spacing contact, it grounds the line through relay G and its non-inductive shunt GR, which are of comparatively low resistance. The line current reverses as soon as this ground is applied, and the receiving way station line relay there operates. The only noticeable effect of such hesitant sending, therefore, is to cause a slight delay or lag in some of the spacing start irnpulses, which causes a slight reduction in the range of orientation adjustment at the receiving way station printer.

Eects of Zine capacity In the preceding description, the eiect of line capacity was disregarded. Every line circuit will have a certain amount of electrostatic capacity to ground, and if the line includes a considerable Yamount of terminal cable, this capacity will have a noticeable effect on the action of certain relays.

When the polarity of battery connected to the line is changed, as by the release of relay PC, the polarity of the charge on the line conductor must be reversed. The current in the line increases rapidly to a peak value which may be several times the normal steady line current Vand then decreases to this normal'current as the line becomes charged. This current surge is of brief duration and the line current usually decreases nearly to its normal steady Value by the end of a single impulse in the printer code.

With equal line voltages at both stations and no line leakage, the break current will be twice the line current, but with leakage present the outgoing line current will be increased, the incoming current from the distant station will be decreased, and the break current will be less than twice the outgoing steady line current. In any case, the holding currents through rheostats HR andi-IR must be less than the break current so that the break relays can operate as described.

TSI

The peak Value of the current surge into the line at` the beginning of a spacing impulse may exceed the break current, and either the break relays must be arranged so as not to operate on these surges, or else the circuit must be so arranged that if they do operate no bad effect on signal transmission will result.. 1n certain other types of polar simplex systems the former method was used, the circuit being so arranged that part of the surge current was by-passed around the break relay., With this. arrangement, however, the range of adjustment of the break relay is very small. The latter method has, therefore, been used in our system, i. e., the circuit is so arranged that the break relays may operate momentarily on line surges without aifecting signal transmission. f

Holding rheostat HR is adjusted so that the holding current through relay B will be less than the break current, but more than the normal or steady outgoing line current, and suiiciently strong so that the armature of relay B, if operated to its spacing contact by a line surge, will return to its marking contact before the end oi a single spacing impulse in the printer code. As the armature of relay B is lagainst its marking Contact mostv of the time, slow-acting relay BC will` remain operated. Relay B will ground the pole changer circuit momentarily during the rst part of each spacing impulse, but, as relay PC is released at this time,no harm is done as long as relay B removes the ground before the next marking impulse starts. If the way station breaks, howeventhe armature of relay B will remain on its spacing contact preventing relay PC from sending marking impulses and relay BC will then release, as `previously described. If the holding current is nearly as strong as the break current in the line, interfering currents in the line may cause the armature of relay B to chatter on its spacing contact during the break. This willhave no effect, however, as'the circuit controlled by this contact is also grounded by contacts 34 and 35 of relay BC. It is evident that` this arrangement permits a wide range of adjustment of the holding rheostat HR.

The adjustment of rheostat HR at the way station is similar to that of the rhecstat HR at the main station. Relay LB may respond to spacing current surges without aiecting `signal transmission, provided its armature does notremain away from the markingv contact long enough to prevent the sending pole changers PCA and PCB from operatingv at the start of the next marking impulse. When the break current has operated relay LB, as previously described, it can chatter on'its spacing contact without effect, as the spacing contact is not used in this circuit.

In addition to the effect ofA line'capacity on the break relays described, surges may occur at the way station when keyboard transmission stops long. enough to release relay SS. Marking potential is connected to the line through both windings of relay LB before relay SS releases and when it releases the potential is removed and the line is connected to ground. At this time, the line charge is dissipated by current surges in both directions, but principally through the windings off relay LB. This is equivalent to a short spacing impulse which is followed by the steady marking current from the main station battery, i. e., the vline discharge surge may be strong enough to overcome momentarily the marking current in the line which is applied from the main station before relay SS. releases.

Relay LB may open its marking contact cir cuit momentarily as a result of such surges, but at .this time its contacts are short-circuited vthrough contacts 63 and 64 of relay HA and contacts 'i9 and 80 of relay SC. Relay HA is slowacting and does not operate until relay LB has closed its marking contact, so that such surges do not release the printer magnet.

Duplex set connections It may be desired. to extend the circuit from the main station.. to a distant city, so that the distant. city may operate directly with one of they way stations on the polar simplex circuit. The. line circuit tov the. distant city may be operated. by carrier Ytelegraph or by polar duplex, the method of connecting with the polar simpiex set being the same in either case. As shown in Fig. l the. sending and receiving legs of the duplex set are connected to the switching. key SK of the main oiiicey polar simplex set. This key should be operated. The distant end of the duplexr line should terminate in a duplex set (not shown in the drawings) arranged for halfduplex operation with the loop connected to a printer.

When the switching keyv SK is operated, the main station printer P is disconnected from the circuit, printer magnet LM being connected to ground through key contacts i and 5 to hold its circuit closed. lThe marking contact of relay L is connected to the pole changer PC of the duplex set through contacts 'l and 8 of the key, and sending relays SC and PC are connected to the contacts of lineV relay L of the duplex set through contacts 2 and 3 of the switching key. The switching key SK also establishes at its contacts 9 and iii a circuit from duplex pole changer PC to contacts 33 and 4l! of relays SS and SC, so that pole changer PC will remain energized Whenever relay SC is released or relay SS operated, regardless of whether the tongue of line relay L is against its marking contact or not; This prevents pole changer PC from responding to outgoing signals which are repeated by pole changer YPC through the winding of relay L.

It is evident that any signals from the way station, which operate relay L, will berepeated by relay L over the sending leg to operate the pole changer PC of the duplex set, which will transmit the signals to operate the printer at the distant city. Signals transmitted from the printer at the distant city will actuate the receiving relay L of the duplex set which, in turn, controls the sending relays SC and PC to repeat these signals over the polar simplex line in the same manner as though the signals originated in the main station printer keyboard. Relay SC releases on the first spacing impulse and short-circuits the armature and marking contact of relay L, and then a more permanent short circuit is established by the contacts 32 and 33 of relay SS. This action prevents relay Lrfrom repeating back over the duplex line the signals being transmitted to the way station, as these signals might otherwise interfere with the transmitted signals in the loop 'oi the half duplex set at the distant city.

The operator at the distant city may break the way station by opening his loop or operating his keyboard, and the way station operator may break by operating his keyboard or depressingA his break key. In either case the action is the same as when breaking directly from the (ilA main station printer, i. e., the double strength spacing -current in the line operates the armature of relays B and LB to their spacing contacts and the pole changers at both stations are held released. When relay BC releases, it opens at its

contacts

31 and 38, the sending leg of the duplex set and transmits a spacing signal to break the operator at the distant city.

What is claimed is:

l. A telegraph system comprising a main station and a way station connected by a line circuit, a transmitter anda receiver at each station, a source of current supply at the main station normally connected to the line during all idle periods, a source of current supply at the way station, means responsive to an initial operation of the transmitter at the way station for disconnecting the current supply at the main station and for connecting the current supply at the way station to said line.

2. A telegraph system comprising a main station and a way station connected by a line circuit, a transmitter and a receiver at each station, a source of current supply at the main station normally connected to the line, a source of current supply at the way station, means responsive to an initial operation of the transmitter at the way station for disconnecting the current supply at the main station and for connecting the current supply at the way station to said line and responsive to the cessation of the operation of the way station transmitter to re-connect the mainstation source of current to the line and disconnect the way station source from the line.

3. A telegraph system comprising two separated stations connected by a line circuit, a receiving relay at each station connected in the line circuit, a sending relay at each station having its tongue connected in the line circuit, a source of current at each station, the line circuit at one station being normally connected to the source of current thereat and normally grounded at the other station, a transmitter at said other station, means whereby the sending relay at said other station responds to the initial operation of the transmitter to connect the source of current thereat to said line thereby to transmit a spacing signal over the line circuit.

4. A telegraph system comprising two separated stations connected by a line circuit, a receiving relay at each station connected in the line circuit, a transmitting relay at each station having its tongue connected in the line circuit, a source of current at each station the source at one station being normally connected to the line circuit which is normally grounded through the marking contact of the sending relay at the other station, a transmitter Vat said other station, means whereby the sending relay at said other station responds to the initial operation of the transmitter to'connect the source of current through the spacing contact of the relay to transmit a spacing signal over the line, and means rendered eiective upon the response of the sending relay for disconnecting ground from the marking contact of the sending relay and connecting the source of current of said other station to said marking contact.

5. A telegraph system comprising a main station and a way station connected by a line circuit, a source of signalling current at the main station normally connected to the line circuit and the line circuit being normally grounded at the way station, a source of current at the Way station, a main station receiving relay having a winding connected in the line circuit and provided with a biasing winding, a source of biasing current connected to said biasing winding and poled to oppose the line current, a transmitter at the way station, said receiving relay being responsive to the initial operation of said transmitter, and means at the main station rendered effective by the response of said receiving relay to ground said line at the main station and disconnect the current source therefrom and also to remo-ve current from said biasing winding.

6. A telegraph system comprising two separated stations connected by a line circuit, a receiving relay at each station connected in the line circuit and responsive to received message signals, a transmitting relay at each station having its tongue connected in the line circuit, a source oi current at each station, the source at one station being normally connected to the line circuit which is normally grounded at the other station, a transmitter at said other station, means whereby the sending relay at said other station responds to the initial operation of the transmitter to transmit a spacing signal over the line, and means rendered eiective immediately upon the response of the receiving relay to said spacing signalV to ground the line circuit at said station thereby effectively disconnecting the source of current from the line circuit.

'7. A telegraph system comprising a rst station and a second station connected by a line circuit, a polar receiving relay'at'each station connected in the line circuit, a sending relay at each station having its tongue connected in the line circuit the tongue of the sending relay at the second station being normally grounded through the marking contact thereof,'the spacing contact of the sending relay of the irst station being grounded through a source of potential of one polarity and the marking contact being grounded through a source of potential of the opposite polarity while the tongue of said sending relay normally( rests upon one of its contacts during non-signalling condition, and means for operating the first station sending relay to transmit polar signals over said line to the second station.

8. A telegraph system comprising a first station and a second station connected by a line circuit, a polar receiving relay at each station connected in the line circuit, a sending relay at each station having its tongue connected in the line circuit the. tongue of the sending relay at the i second station being normally grounded through the marking contact thereof, the spacing contact of the sending relay of the rst station being grounded through a source Yof potential of oneV polarity and the marking contact being grounded through a source of potential of the opposite polarity while the tongue of said sending relay normally rests upon one of its contacts during non-signalling condition, means for operating the rst station sending relay to transmit polar signals over said line tothe Vsecond station, the spacing contact of the second station sending relay being grounded through a source of negative potential, means'for operating said second station sending relay to transmit polar signals over said line to the rst station, and means responsive to the initialroperation of said second station sending relay to substitute at the second station a grounded source of positive potential for the ground conpeotedztothe markinaicontact and toI sponsive to variations in .linen current ,but knot redirectly ground that Contact of;A theii'lrststation,

sendi-nsrelay which is normallyieroimded,through a; source of: negative potential.

19.. Aapolarlsimplex telegraph, System confiprising a main station and a way station connected by a line circuit, receiving ands-break; relays connected in the line circuit at both stations, asentiing relay at each station having its tongue connected inv the line oliit, means including groundeclgsourss Ofgrieeaiiveand positive potentials at each station, and connections therefrom to the marking and spacing contacts of the sending relays, whereby the spacing signals initiated at the respective stations are of opposite polarity while the marking signals at the respective stations are also of opposite polarity, the marking and spacing signals initiated at each station being of different polarity, and means for causing the operation of the break relay at the main station upon increase of line current during the spacing interval.

10. In a polar simplex system., a combined polar receiving and break relay having two windings connected in series with the line circuit in combination with a sending relay having a tongue and marking and spacing contacts, means connecting said tongue and one of said contacts between the two windings of said relays and serving normally to connect said windings in series, a resistance element connected across said normally closed contacts one winding of said relay being normally grounded and the spacing contact of the sending relay being normally connected to a source of negative potential, and means for operating the sending relay to move its tongue from the marking to the spacing contact whereby a source of negative potential is connected through the spacing contact, said tongue and one winding of said relay to the line while the other winding of the relay is connected in series with said resistance and thereby serves asa holding winding to prevent the operation of said relay on signal currents. n

ll. A polar simplex telegraph system comprising a main station and a way station connected,

by a line circuit, receiving and break relays connected in the line circuit at both stations, a sending relay at each station having its tongue connected in the line circuit, means including grounded sources of negative and positive potentials at each station and connections therefrom to the marking and spacing contacts of the sending relays whereby the spacing signals initiated at the respective stations are of opposite 'polarity while the marking signals at the respective stations are also of opposite polarity, the marking and spacing signals initiated at each station being of different polarity, means for causing the operation of the break relay at the mainl station upon increase of line current during the spacing interval, and means for locking the way station sending relay to spacing position during the continuance of the increased strength of the telegraph printerv to recordmessage signals, a

second relay traversed by message signals in the line circuit for operating aV call signaLsaid second'y relay being independent of said printer and responsireto, message ,Signal- 13. A telegraph system comprising a mainstation-andy away station interconnected Vby 'a line circuit, asource of currentassociated. with said' circuit, means at s aid stations ,for sending stelegraphA signals over said circuit, rectiflers inl said circuit at the way station,` a slow-actingfrelay'at theway station permanently fed withcurrent, through vvs aid rectiijers, means operable at silllfll.v the mais steilen for. Qontrliieeihie'v O'f Cui-' rent over said circuit and 'a call' signal at the way station controlled by said slow-acting relay.

lli. A telegraph system comprising a main station and a way station interconnected by a line circuit, a source of direct current at the main station connected with said line circuit n and a source oi alternating current at the way station, means at said stations for sending telegraphic messages over the circuit, relays permanently connected with the circuit at said stations responsive to said messages, a slow-acting relay permanently connected with said circuit at the way station, a rectiiier in the circuit on both sides of the connection of the slow-acting relay therewith, a call signal at the Way station controlled by said slow-acting relay, a calling key at the main station, a relay controlled thereby, follow-up contacts for the last-mentioned relay in said circuit, and a resistance connected with the tongue of the last-mentioned relay.

15. A polar simplex telegraph system comprising two stations interconnected by a line, a duplex set at a station, means including a pole changer relay at said station for controlling the operation of said duplex set, a line relay in said line at said station and having contacts for controlling said pole changer relay, means including a sending switching relay at said station for applying signalling currents of different potentials to said line, a polar receiving relay forming part of said duplex set, a sending control relay controlled thereby and -lcontrolling said sending switching relay, a break relay at said station to interrupt transmission over said line', and a shunt aroundsaid contacts of the line relay controlled by contacts of said sending switching, sending control and break relays.

16. A telegraph system comprising two stations interconnected by a line circuit, sending and receiving equipment at each station, a line relay at the first and a line break relay at the second station, each of said relays having two windings, means for connecting both windings of each relay in series during sending from the other station,

and means for energizing one winding for biasing and holding during certain other times# 17. A telegraph system comprising a main station anda plurality of way stations connected in series over a line circuit, transmitting and receiving equipment at each station, means including a power relay at a way station for operatively associating the waystation with theV line circuit, and means for maintaining the continuity of said line circuit at said waystation in all operating conditions of said power relay. Y v

18. A telegraph'system comprising a main station and a way station interconnected by a line circuit, sending and receiving equipment at said stations includingl an electromagnetic telegraph printer and a keyboard at the way station, a break relay at the way station for operatively associating the magnet of said'printer with the line circuit when the way station is receiving messages, and a circuit independent of said relay agita-esa restoration of the system to normal u'pon cessa; tion of the Way station sending.

20, A telegraph system according to claim 15 in which said shunt includes contacts of a break control relay controlled by the break relay, and a slow-acting holding relay at said station controlled by'said contacts of the line relay and con- 'tacts of said break control relay.

GILBERT S. VERNAM. FREDERICK G. HALLDEN.