US2143000A - Telegraph system - Google Patents

Description

Jan. l0, 1939. w. w. CRAMER Er A1. 2,143,000

TELEGRAPH SYSTEM Filed April 14, 1937 B Sheets-Sheet l `Ian. 10, 1939. ww CRAMER ET AL 2,143,000

TELEGRAPH SYSTEM Filed April 14, 1937 8 Sheets-Sheet 2 POLAR/25o WWCRAMER /NVE/VTORS A 7' TORNE V Jan. 10, 1939. w, wa CRAMER AL 2,143,000 TELEGRAPH SYSTEM Filed April 14, 193'? 8 Sheets-Sheet 3 HlI 'Hl' WW CRAMER /NVE/vToRs- KEF/TCH ATTORNEY Jan. l0, 1939. w. w. CRAMER Er AL 2,143,000

y TELEGRAPH SYSTEM Filed April 14, 1937 8 Sheets-Sheet 4 los f\,

FIG. 4

. WW CRAMER /NVE/vToRs. KEF/TCH ATTORNEY Jan. 10, 1939. w, w, CRAMER ET AL 2,143,000

TELEGRAPH SYSTEM Filed April 14, 1937 8 Sheets-Sheet 6 POLA RIZE WWCRAMER /Nl/ENmRs KEF/TCH By y ATTORNEY W. W. CRAMER El' AL TELEGRAPH SYSTEM Jan. 10, 1939.

Filed April 14, 1937 N I N H" www 8 Sheets-Sheet 7 WW CRA/HER KEF/TCH A T TOR/VE V Jan. 10, 1939. W w, CRAMER ET AL 2,143,000

.TELEGRAPH SYSTEM- Filed April 14, 1937 B Sheets-Sheet 8 POLAR/Z50 PGLARIZE A TTORNEY POLAR/IED emma Jn. 1o, :ses

UNITED STATES PATENT OFFICE TELEGBAPH BYBTEH application anni 14, mi, semi No. ucm' 16 Claims.

This invention relates to avcommunication system for transmitting signaling impulses over long telegraph lin'es-or telegraph channels of -composite toll lines and more particularly to a telegraph system for connecting an outlying telegraph subscribers station to a central switching station over a long telegraph line or composite toll scribed and the novel features thereof claim'ed. in a copending patent application of W. W.'

Cramer, Serial No. 104,959, med-October 10, 1936, Patent No. 2,131,870, issued Oct. 4,1938.

This improved transmission system permits the extension of the long telegraph lines and composite toll lines from a transmitting standpoint to such an exten't that the existing supervisory signaling arrangementshave been found to be inadequate. v

It is an object of this invention to provide improved circuit arrangements for extending the supervisory range to take advantage of the extended transmission range provided by the transmitting system described in said copending appication.

Another object of this invention is to provide means for transmitting all of the supervisory signais between an outlying subscriber and the central exchange over such long telegraph lines as are employed between the local subscribers and 35 the central exchange.

A further object of this invention is to provide terminal apparatus for these long telegraph, or composite toll lines at the central exchange, which will cooperate with the same switching or cord circuits as employed for interconnecting local subscribers.

Another object of this invention is to provide supervisory circuit arrangements in which the supervisory signals at the ends of the line are positively and continuously controlled from the other end of the line.

Still another -object of this invention is to provide supervisory circuit arrangements for long direct current or low frequency telegraph channels 50 which require intermediate repeaters so that the same supervisory information may be transmitted between the subscribers stations located at the ends of these long circuitsand the central exchange as is transmitted between local sub- 55 scribers stations and the central exchange.

` to the central exchange over the telegraph chan- Another object of this invention is to adapt the telegraph transmitting system described in said' copending application tor use'over sections by a multi-section subscribers line circuit and at the same time provide means for transmitting supers -visory signals over this same circuit by arranging 4the .line section for full duplex operation.

Other objects and features of this invention relate to improved circuit arrangements at the ysubscribers station, improved trouble indicating farrangements, as weil as improved supervisory circuits.

4The novel features oi' these improved circuit arrangements set forth in the claims appended hereto, may be more readily understood from the -following description when read with reference to the attached drawings in which:

Fig. 1 shows the apparatus and circuit arrangements at the outlying subscribers station Fig. 2 shows the terminal equipment of the long tollline at the central station;

Fig. 3 shows atypical cord circuit;

' Fig. 4 shows an operators circuit for cooperating with the cord circuit shown in Fig. 3;

Fig. 5 shows a local subscribers line circuit and station equipment;

Figs. 6, 7 and 8 show equipment at an intermediate repeater point and the terminal equipment at the central exchange for a long multi-section subscribers line circuit; v

Fig. 9 shows, in block form, the manner in which Figs. 1, 2, 3, 4 and 5 may be arranged to illustrate a typical connection between a local subscriber and an outlying subscriber connected nel of a single-section toll line; and,

Fig. 10 shows, by means of a block diagram, the manner in which Figs. l, 6, 7, 8, 3, 4 and 5 should be arranged to illustrate a typical connection between a local subscriber and an outlying subscriber connected to the centralexchange over a telegraph channel of a long multi-section toll line. i

GENERAL DESCRIPTION stantially independent oi the leakage resistance, or changes in the leakage resistance, ot the toll lines. This is accomplished by providing the proper transmitting potentials at the two ends i' the long line and by employing the correct biasing current for the receiving relays at each end oi the line. When these factors are correctly proportioned with respect to the distribution oi the line resistance and leakage resistance, the sum of the marking and spacing current received at each end of the line remains constant and substantially independent o! the leakage resistance of the line. The biasing current of the receiving relays is then adjusted to be onehalf the magnitude of the sum of the received marking and spacing currents but in a direction to oppose the magnetic eiiect of the sum of these currents on the relay. Under these conditions, the bias of the telegraph signaling impulses is substantially independent of the leakage resistance of the line.

The term bias as applied to the signaling impulses in this specification indicates a lengthening of one of the signal impulses or conditions, and the shortening of another signaling impulse of condition. For example, marking bias means that the marking impulses or pulses are lengthened and that the spacing impulses or pulses are shortened, whereas spacing bias indicates that the spacing pulses are lengthened and the marking pulses are shortened. Thus, signals having greater bias are less satisfactory for operating receiving apparatus than are signals having less bias. Consequently, the biased signals are poor in quality.

Acommon cause of this lengthening and shortening of the various signal impulses is due to the fact that the magnitude of the two pulses of the current conditions are unequal, or differ by different amounts from a fixed reference or biasing current adjustment of the receiving apparatus. For a marking bias, the marking current is greater, or diiers by a greater amount from a reference or fixed biasing current than a spacing current, whereas for spacing bias, the spacing current is greater or differs from a given reference current by a greater amount than the marking current.

However, in accordance with the transmission arrangement shown in this speciilcation and claimed in the above-identified copending application, when the sum of the marking and spacing currents remains substantially constant and independent of variations of the leakage resistance of the line both currents will always be of substantially the same magnitude or diiIer from a given reference current by substantially the same amount.

The term marking" and spacingas used in this specication, diil'erentiate two line or signaling conditions transmitted from each end of the line to the other end of the line. These terms are also used to designate the positions of relays and other apparatus during these signaling condltions.

The term marking is used to designate the line or signaling condition employed during the time no intelligence or signaling impulses are being transmitted over the system but the transmission circuits oi' the system are fully established, connected and energized and properly connected to suitable circuits so that it is ready to transmit the signal impulses when the transmitting apparaus at either end of the line is operated. The

term "spacing" designates the other signal or line condition.

This improved transmission system permits extension oi thetelegraph lines beyond'the limit maintain a constant current owing in the line` at all times. Another disadvantage is that it is dimcult. if not impossible, to distinguish beween break signals and supervisory signals transmitted over the system.

'I'he preferred method of supervising is to open the line circuit at the subscriber's station to indicate an idle line condition. However, as the line becomes long, the eil'ect of earth potential, interference. cross-fire and leakage resistance becomes greater so that the usual methods employed at the central ofilce for recognizing an open line condition at the subscriber station were found to be unsatisfactory.

In accordance with this invention the outlying subscriber's station is arranged to connect substantially equal positive and negative sources of potential to the subscriber's line in accordance with the impulses to be transmitted while at the central station ground and a source of potential are connected to the line extending to the subscriber's station. The ground is applied to the line at the central station for the marking condition and a source of potential which aids the marking pote'ntial at the subscriber's line is connected to the line at the central station during the spacing condition transmitted therefrom. By thus reversing the ends oi' the line from that described in the above-identified copending application it is possible to distinguish at the central ofilce between both the marking and spacing signaling conditions and conditions applied at the subscriber's station and an open line or idle condition at the subscriber's station.

In addition a neutral relay and a polarized relay are connected in series with the line at the central station in addition to the usual receiving relay employed to receive the signaling or telegraph current impulses. The neutral relay is adjusted to release when the line circuit at the subscriber's station is open for any appreciable period of time. This relay, however, is designed to remain operated as long as either the marking or the spacing current conditions are transmitted from the subscriber's station. It has been found impossible, however, to design a relay to meet these conditions and also remain operated during the time the marking and spacing signal conditions are transmitted in rapid succession from the subscribers station. It has also been found impractical to maintain a slow release relay operated from the contacts of this relay during the time signaling impulses .are being transmitted to or from the subscriber's station. Consequently, a second, or polar relay, is also connected in series with the line at the central exchange. This relay is arranged to alternately charge and discharge the condenser through the windings of a. third or alternating current relay. This alternating current relay will thus be maintained operated as long as signaling impulse are transmitted over the system because the polar relay follows the signaling impulses and alternately 7s charges and discharges or reverses the charge on the condenser through the windings of the third relay. During the time no signals are being transmitted'to or from the subscriber's station but the line circuit is closed or potential applied to thell'ne at the subscriber's station, the polar relay will be maintained on one oi' its contacts so that'the alternating current relay will release. To prevent this, the neutral relay which operates at these times is arranged to close a direct current circuit through the windings oi' the alternating current relay and thus maintain it operated at this time. It has been found necessary to make the polar relay somewhat less sensitive than the receiving relay so that it will not respond to interference and cross-nre received from other circuits during the time the circuit in question is idle. This prevents a false operation of the supervisory apparatus at the central station.

In the case oi multi-section subscribers' lines, the line section between the subscriber and the first repeater point is substantially the same as the single-section line. 'Ihe line section between repeater points and between a repeater point and the central station is arranged for full duplex operation. As pointed out in the above-identified copendin'g application, the improved transmission circuit described therein was not arranged for full duplex operation because the self-compositing feature which renders the bias` of the transmitted signal substantially independent of the leakage resistance or changes of the leakage resistance of the line cannot be obtained for full duplex operation. 'However, a circuit arrangement, shown lnFig. 7, providesffull duplex operation as required over the intermediate sections'and the section nearest the central exchange. During the normal transmission of signal impulses over the line, the signal impulses are transmitted in only one direction at a time. During these times the*` circuit is arranged to be self-compensated. However, when it is desired to transmit supervisory or break signals over the line in the reverse direction at a time when signaling impulses are being transmitted in one direction, the system will not be fully self-compensated. At these times it is usually desired to interrupt the transmission for some reason or other, hence the reduced quality of the transmission circuit is of small importance.

In addition, it is to be understood that the long toll, or telegraph line may include open wire sections, entrance cable sections, cable sections, as well as terminal and intermediate composite sets. These lines may also include suitable noise suppression and shaping coils and networks, as well as other circuit elements usually employed in long telegraph lines or composite toll lines.

In order that the invention can be more readily understood, the operation of the single-section line when the toll subscriber originates a call will be described rst. The operation of a single-section line when the central exchange operator calls the subscriber will next be described, and then the operation of the multi-section line under these respective conditions will be described. It is to be understood, however, that the following description with reference to the attached drawings illustrate only a typical circuit arrangement in which this invention may be employed. In addition to the particular switchboard and circuits described, this invention may be used equally well with other types of switchboard, as, for example, single-section switchboards which do not have any multiple jacks, switchboards which have simple cord circuits which do not includa repeaters, automatic switching systems, as well sssmall lprivatebranchcxchaniresystems.

Smau: Lim: Sparrow Idle condition Reference will now be made to Film1. 2, 3, 4, and 5 arranged as` shown in Fig. 9. With the exception oi sending relays 22 and 2l and the receiving relay II at the subscrlber's station, the

relays ot the single line section are shown in Figs. n

1. 2, 3. 4, and 5 in their normal positions. These relays remain in these-positions during the time the circuit is idle. Relays Ii, 22, and 23 at the subscribers station may. however, be on their spacing contacts during the idle condition.

Key i3 is normally in the position shownin Fig. 1. Key i3 is provided to enable the printing equipment 44 at the subscrlber's station to be testing locally. When key I2 is operated to the.

opposite position from the position shown. line Il is connected directly to ringer 40 and relay 31 through condensers 39 andv Il, respectively. This permits the central exchange operator to call the subscriber during thetimehis equipment is belng tested or adjusted. In the opposite position key i3 also connects the right-hand winding of relay 22 and left-hand winding of relay 22 directly across a rectiiier 24, thus maintaining these relays in their marking position. Key i3 in its opposite positionvalsoconnects transmitting contacts 34 of the printer equipment 44 directly in series with printer magnet 32 of printer equipment 44, thus permitting the local operation of this equipment for test purposes.

However, as stated above, test key i3 is normally maintained in the position shown and permits the operation of the system as will be described hereinafter.

At the central ofllce the relays of the terminal equipment are shown in their normal positions. 'I'he term "normal position or normal is used to indicate the position assumed by the relays when the circuit is idle. Relays 5l and 52 are maintained on their marking contacts by current flowing in a circuit from ground vconnected toA Subscriber originates a call 'I'he subscriber originates a call by operating the power switch 36 at the subscribers station. The operation of switch 36 completes a path from the source of power 43 through its right-hand make contacts for energizing the printer motor 33, rectifier 24 and relay I4. Relay I4 in operating closes the circuit from line Ii extending from the central station through recall key I2, test key i 3, contacts of relay i4, resistance l5, upper Winding of relay i6, resistances I'l and 2l and noise suppressing choke coil i9 through the armature and contact of relay 22, rectifier 24, armature and contacts of relay 23,`through choke coil 25 to ground 238. The energized rectifier 24 supplies a source of potential between its terminals and thus in series between ground 288 and line Il extending to the central exchange. Rectiiler 24 on becoming energized also causes current to ilow through the lower biasing winding oi receiving relay i8 and the biasing and operating windings of relays 22 and 23. The biasing winding oi relay 22 is the lett-hand winding while the biasing winding oi relay 22 is the right-hand winding. The operating windings are the other windings oi these relays. Resistances 28 and 48 as well as k46 control the value oi the biasing currents.

Line il which extends to the central exchange may include the various types of lines and equipment mentioned above which are usually employed or associated with telegraph lines or telegraph channels or composite toll lines.

At the central station the line Ii extends through the break contacts of relay 58, the upper windings of relays 5I and 52, noise suppression choke coil 54, winding of relay 55 to ground through the armature and break contact of relay 58. Current iiowing over this line circuit due to the source of potential applied to the line by rectiiler 24 will cause relay 55 to operate. Relay 55 in operating completes a path from battery through resistance 62, through its contacts, winding of relay 51 to ground connected through the armature and marking contact of relay 5i. As pointed out above, relay 5I is maintained upon its marking contact at this time by current flowing through its middle winding. This causes relay 51 to operate, which in turn operates relay 56. Relay 56 in operating transfers the circuit of line il from its back contacts to.

its front contacts and thence Ythrough the armature and marking contact of relay to ground. As pointed out above relay 65 is maintained on its marking contact by current flowing through its lower winding at this time. Relay 56 in operating also connects ground through its lower make contacts and innermost top break contacts of relay 68 to the winding of relay 12. Current flowing in this `path from the battery connected to the other terminal of the winding of relay 12 causes relay 12 to operate, which in turn lights the call lamp 68 and indicating or alarm device 1i. Device 1I may include either or both supervisory and alarm circuits and apparatus.

' Operator answers The operator answers the call by inserting the answering plug 88 in the answering jack 18 associated with the terminal equipment connected to line i I. Jack 18 is shown as a single jack. However, it is to be understood that it as well as lamp 88 may be multipled at various positions of a multi-section switchboard or it may be only a single jack of a. single section switchboard, depending upon the type of switchboard at the central station.

When the operator inserts plug 88 in jack 18 a circuit is completed from ground through the winding of relay 68, sleeve of jack 18, sleeve of plug 83 and winding of relay 84 to battery. Current flowing in this circuit causes the operation of relays 68 and 84. Resistance 248 provides s. shunt for the winding of relay 84 to properly control the potential of sleeve of jack 18 and the currents owing through the windings of relays 68 and 84. The operation of relay 88 extends the transmission circuit from the tip of plug 88 through the tip of Jack 18, the uppermost make contacts of 'relay 68, the upper winding or relay 81, the upper break contacts of relay 88, upper winding of relay 88 to the armsture and contacts ot relay l2. This transmission circuit is completed in the cord circuit shown in Fig. 3 through the upper make contacts oi relay 84. the contacts ot relay 88 through the transmission circuit oi the operators position and teletypewriter circuit to the upper Winding o! the repeater relay 88 and thence to the amature and contacts of repeater relay 8l. The operator usually has key 88 operated at the time she inserts plug 83 in jack 18 so that this transmission circuit is extended through her position equipment. However, if she does not have this key operated at. this time the transmission circuit extends directly to the upper winding oi the repeating relay 88 and is completed through the armature and contacts of relay 8|. Relay 88 in operating completes an obvious circuit through the lower or biasing winding of relay 81. Relay 88 also transfers the ground from the lower make contacts oi relay 58 from its innermost upper break contacts to its innermost up- K per make contacts and the windingsoi relays 58 and 84. This interrupts the circuit through the winding of relay 12 which releases and in turn extinguishes light 88. Relays 58 and 84 are operated by current flowing in the above circuit through their windings. Relay 56 in operating disconnects the above traced circuit through the lower winding of relay 52 and middle winding of relay 5I and connects these windings to the transmission circuit of line Il. These windings are now connected between the transmission circuit line Il and the artificial line 53. It should be noted that the artificial line 58 does not provide any direct current path. No biasing current is required for the receiving relays 5I and 52 be cause they receive positive and negative signal impulse currents of substantially the same magnitude from the subscribers station.

The operation of relay 58 also interrupts the operating circuit oi ringing relay 58 and prepares a circuit for the operation of relay 18 and also connects battery to the upper terminal of condenser 16 through high resistance 18 and the upper break contacts of relay 262. However, ground is connected to the upper terminal of condenser 16 through the marking contact and armature of relay 61 the upper break contacts of relay 283 so that the battery connected through resistance 18 performs no useful function at this time.-

'I'he operation of the relay 84 connects the lower winding of relay 85 to the transmission circuit through jack 18. This relay also completes a circuit in parallel with the contacts of relay 55 through its lower make contacts, condenser and resistance 68.

Transmission circuit Assuming now that the central exchange operator has operated key 88, the transmission path as above traced is now complete between the operators printer equipment |88 (Fig. 4), and the printer equipment 44 at the subscriber's station. Communication signaling impulses may n ow be transmitted from the operator to the subscriber. 'I'he operator in operating the transmitting contacts 242 of her teletypewriter equipment |88 interrupts the transmission circuit through jack 18. This causes the line relay |84 of the operator's position equipment to repeat the signals to the receiving equipment of the operators printer to produce an operators copy. The relay 85 of the terminal equipment shown in Fig. 2 also follows these signal impulses and repeats them to llne II through the transmission circuit above described. It should be noted that relay 66 transmits by connecting ground to line I I for marking signal impulses and connects positive battery to line II for spacing signal impulses. The positive battery connected through the spacing contacts of relay 66 to line I I aids the source of negative potential connected to line II at the subscribers station. As described in the above identitled copending application the prefen'ed ratio of the two currents for marking and spacing conditions respectively is o1' the order of 1 to 3.

To obtain this ratio of currents the potential developed by rectifier 24 is substantially onehalf Athe potential of the source connected to the spacing contact oi relay 36. The current flowing through the lower or biasing winding of the re-4 ceiving relay Il is adjusted to produce substantially one-half the' magnetic e'ect upon relay I6 as is produced bythe sum of the two currents owing through the upper winding of relay I6. However, the magnetic eilect produced by the current flowing `through the lower winding of relay I 6 opposes the magnetic effect of the algebraic sum of two currents flowing through the upper winding' of relay I6. When these yconditions are substantially satisiied as described in said copending application, relay I6 responds substantially equally well to both the marking and the spacing signaling condition independently of the changes of leakage resistance of line II. Relay I6 in responding to the signaling impulses transmitted by the operator repeats them to the printer magnet 32 of the receiving teletypewriter equipment 44 and causes it to record the information transmitted by the operator at the central sation. The operating circuit of the printer magnet 32 may be traced from ground through test key I3, armature and marking contact of relay I6, unilateral conducting device or rectier 3l! in parallel with condenser 3|, winding of printer magnet 32, resistance 45, armature and marking contact of relay 22, rectiiier 24, marking. contact and armature .of relay 23'to ground 238. Rectiiier 24 supplies the current for this path causing the operation of printer magnet 32 in accordance with the signals repeated by relay I6.

yIn the spacing position, receiving relay I6 short-circuits the transmitting contacts 34 and resistance 242. In short-circuiting resistance 242,

relay I6 increases the current through the lefthand winding of relay 23 and the right-hand winding of relay 22 and thus provides an additional load for rectifier 24 during the time relay I6 is on its spacing contact. This extra load compensates for the load on the rectier during the time relay I6 is on its marking contact causing current to flow through the printer magnet 32.

In short-circuiting the transmitting contacts 34 in its spacing position, relay I6 insures the proper reception of a break signal by a transmitting operator at the subscribers station. With the transmitting contact short-circuited it is impossible to transmit signals to line II which might interfere with the reception of the break signal, or to cause signals to be recorded by the receiving printer as home copy.

In response to the information transmitted from the central operator, the subscriber will transmit information regarding the party with which the subscriber wishes to communicate by operating the transmitting contacts 34 of the teletypewriter equipment' 44, The operation of thevtransmitting'contacts 34 opens and closes the circuit through the right-hand winding of relay 22 and left-hand winding of relay 23... Current flowing through these windings is in such a direction as to maintain these relays on their marking contacts. -The current owing through the other windings of these relays is in such a :direction as to cause these relays to be operated and remain upon the spacinglcontacts. However, thev current flowing through the right-handwinding of relay .22 and the left-hand winding of relay 23 overpowers the current-owing through the other windings sothat so long as this current flows these relays remain on their marking contacts. However, when the circuit of these windings is interrupted by the transmitting contacts 34 this current is interrupted .and the biasing windings of these relays cause the armatures to move to their spacing contacts. In moving to the spacing contacts the armatures of relays 22 and 23 reverse the connections of the rectifier 24 to line II whereby a positive potential is now connected between line II and ground 238 instead of negative potential. This causes a spacing impulse to be transmitted over the line I I.

'I'he armatures of relays 22 and 23 in moving to their spacing contacts also tend to reverse the current flowing through the printer magnet 32 at the subscribers station over a circuit traced from ground 238, armature and contacts of relay 23, rectiiier 24, contacts and armature of relay 22, resistance 45, printer magnet 32, unilateral conducting device or rectifier 30, choke coil 23, armature and marking contacts of receiving relay I6 to ground through the contacts of test key I3. The direction of current which would flow through this circuit is opposed by the device or rectifier 30 so that substantially no current ows through printer magnet 32 at this time, thus causing printer magnet 32 to follow the signal impulses transmitted by transmitting contacts 34 to record a home copy of the information transmitted by the subscriber. However, inasmuch as substantially no current flows through the printer magnet 32 it is necessary to provide a compensating load comprising resistances 4'I and 48 across the .terminalsof rectier 24 in order to insure substantially constant voltage under both marking and spacing current conditions. The path of this compensating load may be traced from the negative terminal of rectifier 24 through choke coil 26, resistance 47, arma.- ture and spacing contact of relay 22 to the positive terminal of rectier 24 through coil 21. A similar path may be traced from the positive terminal of rectifier 24 through choke coil 21, resistance 43, armature and spacing contact of relay 23 to the negative terminal of rectifier 24 through choke coll 26.

As pointed out and described in detail in the above identified copending application of Cramer, receiving relay I6 at the subscribers station would not normally follow the signaling impulses transmitted from the transmitting relays 22 and 23. In the arrangement shown in Fig. 1 this is also true. However, it should be noted that the current through the biasing winding of relay I6 is reduced to substantially zero when the transmitting relays 22 and 23 move to their spacing contacts. Normally the current through the biasing winding of relay I6 tends to cause this relay to move to and remain upon its marking contact. The current normally owing through the upper or line winding of relay I6, which is the marking current, tends to operate the armature of relay I to its spacing contact and maintain it on the spacing contact. However. this current under marking conditions is insumcient to overpower the biasing current which, therefore, maintains the relay on its marking contact. When signal impulses are transmitted from the distant station current through the upper or line winding of relay I5 becomes substantially three times as great as the normal current and thus overpowers and overcomes the magnetic effect of the biasing current and causes this relay to move to its spacing contacts. When spacing impulses are transmitted from the subscribers station the line current reverses so that the current through the upper or line winding of relay i5V will tend to hold the relay upon its marking contacts. Hence, the reduction of current through the lower or biasing winding at this time does not permit the relay to leave its marking contact so relay I5 does not follow the signal impulses transmitted from the subscribers station.

The path for the current through the lower winding of relay I5 may be traced from ground through the lower winding of relay I8 and resistance 25 to the negative terminal of rectier 24. During the transmission of spacing current from the subscribers station this terminal of the rectiiier is grounded through spacing and armature contacts of relay 23 to ground 238, thus preventing any current ilow through the lower winding of relay Il. However. during the transmission of marking current from the subscribers station the positive terminal of rectii'ler 2l is grounded through the marking and armature contacts of relay 23 to ground 235, thus including the source of potential of rectifier 2l in the circuit of this biasing winding and causing biasing current to tlow through the lower or biasing winding of relay Il.

During the transmission of the telegraph signal impulses between the subscribers station and the operator, and also during the transmission of signaling impulses to or from the subscriber's station at any other time, relay 51 (see Fig. 2) is maintained operated either from the contacts of relay 55 or by polar relay 5I reversing the chargeV on condenser 53 through resistance I3 and the winding of relay 51. Due to the extended range available with the improved transmission circuit employed and described in the above identified copending application as well as the lower leakage resistance permissible and the higher earth potentials encounteredover the extended range, it has been found impossible to provide a relay similar to relay 55 which will remain operated during the time signal impulses are being transmitted over line Il and at the same time release against the low value of leakage resistance, earth potential', cross-fire, and other interference usually encountered on long telegraph lines or telegraph channels of composited toll lines. In acordance with this invention relay 55 is arranged to release against the low value of leakage resistance, cross-nre and a reasonable value of earth potential when the subscriber removes potential from line Ii. Relay 55 when so adjusted will also operate on the longer signal impulses and the steady state marking and spacing currents received over line Il but may not remain operated during the transmission of telegraph signal impulses. In the specific embodiment of this invention shown in the drawings, marking current or impulses transmitted from the subscribers station is of one polarity and spacing current or impulses transmitted from the subscribers station is of the opposite polarity. Consequently relay 55 is required to close a contact when current of either polarity ilows over the line and through its winding but is required to open its contacts when substantially no current or a very small current is flowing through its winding. Relays of this type are frequently called neutral relays. Consequently relay 55 is referred to in this application as a neutral relay. Relay 5I is arranged to follow the telegraph signal impulses. Inasmuch as the telegraph signaling impulses or currents are of opposite polarity in the embodiment of the invention shown in the drawings relay 5I is a polar relay since it must close one contact on marking impulses and another contact on spacing impulses. This relay has therefore been called a polar relay in this application to clearly distinguish it from relay 55. The essential characteristics, however, of these relays are that relay 5I follow the signaling impulses and that relay 55 close a contact when long impulses of either character are received and these terms neutral and "polar are intended to distinguish these two types of relays but include any relay which function in these respective manners. Relay 5I on its marking position connects ground to the right-hand terminal of the winding of relay 51. When relays 55 and 13 are released the other winding terminal of relay 51 is connected through condenser 53 and lower contacts of relay M to battery connected to the spacing contact of relay 5I. At this time relay 13 is released as it performs other functions. Condenser 53 is charged in the circuit above traced through the winding of relay 51. When relay 5| moves to its spacing position it connects ground to the upper terminal of condenser 63 through the lower make contacts of relay 64 and disconnects ground from the right-hand terminal of the winding of relay 51. Condenser 63 now charges in the reverse direction from battery through the lower contacts of relay 55 over lead 24|, the winding of relay 51, condenser and resistance 53 to ground through the spacing contacts of relay 5I. When relay 5I again closes its marking contact the charge on condenser 53 will be again reversed through the winding of relay 51 as described above. This reversing of the charge of condenser 53 provides in eifect an alternating current for maintaining relay 51 in its operated position during this time. Relay 51 is accordingly arranged to operate and hold operated on alternating current and is some times called an "alternating current" relay. Relay 51 is arranged to hold operated on direct current as are most alternating current relays so that during the time no signal impulses are received over line Il, Vduring which time relay 5I will remain on one or the other contact and thus cause no alternating current to flow through the winding of relay 51, relay 55 will operate to provide a direct current path through relay 51 and thus maintain it operated. It should be noted that the direct current owing through the winding of relay 51 when relay 55 is operated is in one direction when relay 5i is in its marking position and in the opposite direction when relay 5I is in its spacing position. Relay 51 however, operates and remains operated by current iiowing through its winding in either direction so relay 55 will maintain relay 51 operated independently of the position of relay 5| and thus auaooo visory signal indications atthe central switoh,

board, dueto any momentary releases of relay 51 which might occur between the time `either relay I or relay 55 is holding relay 51 operated and the time the other of said lrelays operates and maintains relay 51 operated.

. Relay 5| is provided with a third winding in addition to the two windings similar to the windings of the receiving relay 52. The third or lower winding is connected to the contacts of relay 5I in such a manner that an additional or biasing current flows through this winding in such a direction as to maintain relay 5| on the contact on which it is resting. In other words this winding tendsjo make relay 5I less sensitive than relay 52. This is desirable in order to prevent false operation of relay 5I on cross-fire currents and other interference received during the time the line II is open-circuited at the subscribers station or has no potential connected to it at the subscribers station.

Thus by jointly controlling relay 51 from the neutral relay 55 connected in series with line II and the polar relay 5I also connected in series with line II it is possible to differentiate between an open line condition at the subscribers station and signaling impulses transmitted over the line during the time the line is closed or potential applied to it at 4the subscribers station. In this manner it is possible to provide reliable supervisory signals at the central exchange.

After the operator at the central station has received all the necessary information she can connect the subscriber to the desired station by inserting the calling plug IUI into the proper jack |39. She will then operate ringing key |08 to call the subscriber and after the called subscriber has answered, the operator may disconnect her circuit by releasing key 89. At this time the outlying subscriber may transmit from the equipment shown in Fig. 1 over line II to a local or other outlying subscriber. A local subscriber is shown in Fig. 5.

The operation of other features of the cord circuit, operators position circuit and local subscribers line and station equipment clrcultsand apparatus need not be described in detail since they operate in their usual manner.

Briey the busy test circuit shown in the operators position circuit of Fig. 4 includes relays II'I, H8, H9, and |20 and-lamps |35 and |23 and indicator |2| and is connected to the tips of both plugs 83 and IIII through the inner lower make contacts of relay 88 and the upper break contacts of relays 84 and 98 to enable the operator to determine if the lines are idle.

Splitting keys II2 and ||3 and relays I l5 and II4 are/provided to enable the operator to communicate with either subscriber connected to the cord circuit without communicating with the other subscriber connected to the cord circuit.

A recall circuit including recall key I|I, relay |24, selector switch |21 having rotary magnet |26 and release magnet |25 is provided to enable the operator to send a. recall signal over a toll line to an operator at a distant central exchange.

Disconnect key 99, relays 95,v |33, |34 and |36, selector switch having contact arms |3| andl32, rotary magnet |29 and release magnet |30 are provided to transmit a disconnect signal over a toll line to a `distant central station operator. Ringing key |69 is likewise provided to ring a 'distantoperaton It is to be understood, that these features may or may not be provided and that other features can be provided when desired. These circuits and features cooperate with the circuits to the outlying subscribers stations in substantiallyv the same manner that they cooperate with local subscriber station circuits and equipment.

Recall Ii' at any time iuring the transmission the outlying subscriber wishes to recall the central exchange operator he may 'do so either by turning on and oi the power momentarily by release and reoperation of key 36 or by momentarily operating recall key I2. Generally, if the central exchange is equipped with a flashing recall feature, recall key I2 is not furnished. However, recall key I2 may or may not be furnished when the ashing recall key is or is not provided at the central exchange. The operation of the recall key or the power switch disconnects the source of potential from line I I at its subscribers station. This will cause the receiving relay 52 as well as polar relay 5| to remain on the contact to which they were last operated and will allow relay 55 to release provided relay 65 is in its marking position. If relay 65 is not in its marking position other circuits described hereinafter function after a given time interval to periodically operate relay 65 to its marking position after which the operation of the circuits is as described below.

yWith relays 5| and 52 remaining on a given contact and relay 55 released, relay 51 will release and release relay 56 which in turn releases relays 58 and 64. When relay 56 releases it connects ground to the ring of jack 'Ill through its lower break contacts and the lower break contacts of relay 262. This ground causes the operation of relay 85 in the cord circuit over the ring of the plug 83 (see Fig. 3). Relay 85 in operating lights the supervisory lamp 86 of the cord circuit. Relay 85 in operating also operates relay 81 which locks operated through its upper make contacts. Then when the subscriber recloses the line either by releasing recall key I2 or by reoperating the power switch 36, potential is again applied to line II which in turn causes relays 55, 51, 56, 58 and 64 to operate. Relay 56 in operating removes the ground from the ring of jack 'I6 and allows relay 85 of the cord circuit to release. The release of relay 85 completes a path from interrupter 93 through the lower make contacts of relay 8l through the lower break contacts of relay 8 5 to lamp 86, which will cause this lamp to flash. Lamp 86 continues to flash until the operator operates key 89 at which time ground from the contacts of the splitting relay ||4 (Fig. 4) is connected to the other side of the winding of relay 81 and causes this relay to release and disconnect the interrupter 83 from lamp 86. In the event that this flashing recall circuit is not provided lamp 86 is controlled directly from the contacts of relay 85. In this case it is necessary for the attendant at the subscribers'station to operate and release the recall key I2 or the power switch 36 as often as it is desired to flash the supervisory lamp 86.

Break signals At any time during the transmission break signais may be `transmitted either by the outlying subscriber to the central exchange or from 4the central exchange to the outlying subscriber. 'I'he outlying subscriber transmits a break signal to the central exchange by operating switch or key |53. This interrupts the circuit including the righthand winding of relay 22 and the left-hand winding of relay 23 and permits the other windings of these relays to operate their armatures to their spacing positions. In their spacing positions relays 22 and 23 connect spacing potential to line I I at the subscribers station and causes relays 5| and 52 at the central station to move to'their spacing positions during the transmission of the next marking impulse to the subscribers station by relay 65. Relay 52 repeats the spacing or break signal over the tip of jack 16 to the operator or the other subscriber connected to the associated cord circuit and prevents the operation of relay 65 to its spacing position by spacing impulses transmitted over the tip of jack from the cord circuit.

When break signals are transmitted from the central exchange to the outlying subscribers station relay 65 is operated to its spacing position and repeats the break signal to line II. At the subscribers station relay I6 responds to the break signal and moves to its spacing position. In its spacing position relay I6 short-circuits resistance 242 and also the transmitting contacts 34 in addition to interrupting the circuit of printer magnet 32. This indicates to the subscriber that a distant operator or subscriber wishes to interrupt transmission and also prevents the transmission of impulses by the subscriber which might interiere with the reception of the break signal.

At the central station relay 61 also responds to the break signals by moving to its spacing position. In moving to its spacing position relay 61 removes the ground connected to the upper terminal of condenser 16 and permits this condenser to start to charge from battery through the high y resistance 16. After an interval of time determined by the constants of condenser 16 and resistance 1l, the potential of the upper terminal of condenser 16 will reach the potential required to initiate a discharge between the control elements of tube 15.- In the preferred embodiment of this invention the constants of condenser 16 and resistance 16 are so chosen that it requires approx# imately 6 seconds to initiate a discharge through tube 15.

When a discharge is initiated between the con-'- trol elements of tube 15, a discharge also takes place between the main anode of tube and the cathode, which causes relay 66 to operate in a circuit from battery through its winding, the inner lower break contacts, of relay 14, the inner upper break contacts of relay 263 to the main anode of tube 15. Relay 66, in operating. connects the transmission circuit of relay 65 to marking battery through the upper make contacts of relay 66 and the upper break contacts of relay 13. Relay 66, in operating, also completes a circuit for the operation of relay 14 from ground through the center set of upper make contacts of relay 63. lower make contacts of relay 66 to battery through the winding of relay 14. Relay 14, in operating, completes a holding circuit for maintaining relay 66 operated from battery through the winding of relay 66, inner lower make contacts of relay 14 to ground through the spacing contacts of relay 61 and interrupts the circuit of the main discharge through tube 15, thus extinguishing this discharge. Relay 14 also connects ground to the upper terminal oi condenser 16 through its upper make contacts and the upper break contacts of relay 263 to discharge condenser 16 and extinguish any remaining discharges between the elements Relay 65 in operating also completes a circuit for the operation of relay 13 from ground through the lower inner make contacts of relay 66, winding of relay 19, source of alternating current 5i and interrupter 62. Relay 16 then follows the interruptions of interrupter 62. Relay 19, in operating, completes a circuit for the operation of relay 13 from ground through its contacts, the lower make contacts of relay 14, lower make contacts of relay 56 to battery through the winding of relay 13. Relay 13, in operating, completes a circuit from the spacing contact of relay 5| to the left-hand winding terminal of relay 51 for holding this relay operated. Relay 13, in operating. also transfers the transmission circuit from the front contact of relay 66 from marking battery to the upper winding of relay 61.

If the break or spacing impulse is no longer being transmitted over the system at this time. relay 61 operates to its marking contact and releases relay 66 which in turn causes the release of relays 14, 13 and 13. 'Ihis restores the circuit to its normal transmitting condition.

If the spacing or break signal is still being transmitted over the system, relay 13 will transmit long marking impulses to the outlying subscriber at regular periodic intervals and indicate that there is some trouble in the system.

Tube 15 and relays 63, 14, 13 and 13 and their associated circuits by sending long marking impulses over line Il permit an outlying subscriber totransmitrecallordisconnectsignalstothe central exchange in case a long break signal due to trouble or other conditions is transmitted to the subscribers station. Under extreme conditions of line leakage the spacing potential connected to the spacing contact of relay 65 will cause a sumcient current to flow through relay 55 and the leakage resistance of line Il to maintain relay 55 operated independently of the removal of potential from line II by the subscriber in attempting totransmitarecallordisconnectsignaltothe central exchange as described herein. Consequently. it is necessary to remove the spacing potential applied by relay 65 to line I I by operating this relay to its marking position and oonnecting ground to line Il at periodic intervals during the long break or spacing signal to permit thel subscriber to signal the operator at the central exchange at these times. In the preferred embodiment of this invention the marking interval transmitted to the subscribers station is sumciently long to permit the subscriber to cause the 'supervisory lamp to ash several times in case the central exchange equipment is not provided with a ilashing recall circuit.

Disconnect At the termination of transmission between the subscribers connected together through the central exchange the outlying subscriber will stop his machine by releasing the power switch 36. This disconnects power from the teletypewriter motor 33, rectifier 24 and relay I4. Relay I4 will release and connect line Il to ground through ringer 45 and condenser 39 in parallel with condenser 36 and relay 31. This removes all sources of potential from line Il at the subscribers station. A`t the central station, this will permit relay 55 to release provided the transmission circuit through jack 1li is maintained 7s 'contacts or move to these in a marking condition. With this transmission circuit in the marking condition relay i5 is maintained on its marking contact, and thus connects ground to line I I. Consequently the only sources oi potential eii'ective in line Il are earth potential connected to line Il through the leakage resistance of line Il and cross-fire and interference. Relay 55 is arranged to release under these conditions. As pointed out above, relay 5I is made insensitive to any cross-nre and other interference which may be received by line il at this time so that it will remain upon whichever contact it was resting when line il was opened at the subscriber's station. With relay 55 released and relay 5Il remaining on either one of its contacts for a short interval of time relay 51 will release and in turn release relay 55. Relay 55 in releasing connects ground to line Il through its upper break contacts. Relay 55 in releasing also connects ground to the ring ot jack 1I and causes relay 85 in the cord circuit to operate, which lights lamp Il as described above under "Reca However. in this case light Il remains lighted and does not flash. This indicates to the operator that the subscriber has completed the call and turned on his equipment.

The operator will then remove plug 83 from Jack 10. This will allow relay 55 of the terminal equipment shown in Pig. 2 to release which in turn restores the circuit to its normal condition. Relays 5l and 44 previously released when relay 55 released. These relays in releasing cause relays 5l, 52 and l5 to remain upon their marking contacts and remain upon them.

It at the time the subscriber at the outlying station removes the source of potential from line Il or opens line Il relay 65 at the central station is on its spacing contact, potential will be applied to line il at the central exchange. Under extreme conditions of line leakage the current flowingfrom this source of potential on the spacing contact of relay, through the winding of relay 55 and the leakage resistance may be suiiicient to maintain relay 55 operated. This will prevent a disconnect signal from appearing before the operator. At the time the spacing or break signal was applied to or received by the system due to any condition, trouble or otherwise. relay 61 which follows the'signal impulses transmitted over the transmission circuit of jack 1I moves to its spacing contact. In moving to its spacing contact this relay removes ground from theupper terminal of condenser 1.6. 'Ihis permits condenser 15 to start to charge from battery through the upper inner make contacts of relay 58 and resistance 1l. Resistance 18 is of the order of several megohms and is related to the capacity of condenser 56 in such a way that the potential across condenser 16 rises very slowly.

A gaseous conduction tube 15 is provided with three elements comprising a control discharge path and a main discharge path. 'I'he electrodes of the control discharge path are connected across condenser 16 and resistance 11. When a potential across condenser 15 reaches the breakdown potential of tube 15 a discharge starts between the control 'elements of this tube and causes a discharge to now between the main discharge elements of thls'tube. The main discharge then continues substantially independently of the potential across the control discharge elements.

The time constants of the` condenser and resistances 1l and 11 are designed to give the desired time delay. In the preferred embodiment oi' this invention these elements are designed to give a time delay of approximately six seconds. This is the time required after relay 51 moves to its spacing position for the potential across condenser 1l reaches the breakdown potential oi' tube 15. If. during this time relay I1 should be operated by a marking signal to its marking contacts, it will connect ground to the upper terminal of condenser 1I and discharge it so that the charging process will have to start over again when relay 51 again moves to its spacing contact. It relay I1 is so operated, relay l5 will also be operated to its marking position and connect ground to line Il which will permit relay 55 to release and light the disconnect lamp as described above.

If. however, relay l1 remains on its spacing contact for over the entire time interval required to initiate a discharge through tube 15, tube 15 in discharging will cause the relay il to operate. Relay 55 in operating operates relay 14 in a circuit traced from ground through the central upper make contacts of relay Il, the lower make contacts of relay l5 to battery through the winding `of relay 14. Relay 5l, in operating, transfers the circuit through the upper winding of relay 55 from the upper winding of relay 51 to the contacts of relay 1I. It also connects ground to the winding of interrupter relay 14 which is operated from ringing current through condenser Il supplied by generator or source Il. 'I'his rinaing current is periodically interrupted by interrupter I2.

Relay 14 in operating locks relay 55 operated to the ground connected to spacing contacts of relay 51 and interrupts the main discharge path through tube 15 and thus extinguishes the main discharge through tube 15. Relay 14 in operating also connects ground to the upper terminal of condenser 15. and thus discharges it and extinguishes any and ali remaining discharges between the. elements of tube 15. Relay 14 inoperating completes the circuit from the contacts of interrupter relay 15 through the lower make contacts of relay 14, lower make contacts of relay 58 to the winding of relay 13. This relay then follows the operations of relay 19 caused by interrupter 52. When relay operates, relay 13 in turn operates. Relay 13 in operating connects the spacing contact of relay 5| to the left-hand terminal of the winding of relay 51 to hold relay 51 operated during this time. Relay 13 in operating, also removes battery from the upper front contacts of relay 55 and thus transmits the spacing impulses to the subscribers station if the transmission path through jack 10 is still open,

that is, in a spacing condition. During the time relay 19 is released relay 13 will also be released. This will remove the holding circuit connected to the left-hand winding of relay 51. Relayv 13 in releasing at this time also connects marking battery to the front make contacts of relay 65 which will cause relay 55 to be operated to its marking contacts. When relay 65 is in its marking position ground is connected to -line Il which will permit relay 55 to release if the subscriber has attempted to disconnect. Relay 55 in releasing will allow relay 55 to release as described above and light a cord supervisory light 86 in the cord circuit as described above. Relay 55 in releasing connects ground to line Il so that if or be operated to extinguish the supervisory lamp 66 in the cord circuit. When the operator disconnects. relay 60 will be released as described above and in turn releases the other relays so the circuit is restored to its normal condition.

Calling outlying subscriber In case another subscriber wishes to call an outlying subscriber over a single line section of a long telegraph channel or composited toll linethat subscriber will signal the operator and the operator will insert answering plug 83 in the line jack of that subscriber. For purpose of illustra tion assume that the subscriber located at the station shown in Fig. 5 wishes to call the subscriber whose station equipment is shown in Fig. l. Under these conditions the operator at the central exchange will insert plug 63 in jack |39 connected to the local subscribers line. The operator can communicate to the subscriber shown in Fig. 3 in the usual manner for local calls. Briefly, the local subscriber shown in Fig. 5 will operate the power switch 243 which energizes rectifier |53, motor |58, and relay 244. Relay 244 closes the subscribers line circuit and causes relay |4| to operate. Relay |4| in operating operates relay |42 which in turn causes lamp |44 to operate. In answering the calling subscriber the operator will insert plug 83 in jack |39. This operates relay |40 and permits relay |4| of the subscribers line circuit shown in Fig. 5 to release. Relay 34 of the cord circuit is operated in series with relay |40. The release of relay |4| releases relay |42 which in turn exting'uishes light |44.

With the key 89 of the cord circuit operated as before, the transmission path is completed from the operators teletypewriter equipment |03 to the subscribers teletypewriter equipment 245 located at the subscribers station. If the operator at the central station has received the information from the subscriber located at the station shown in Fig- 5 directing the central station operator to connect the subscribers station shown in Fig. 5 with the subscribers station shown in Fig. l, the operator will insert the calling plug |0| in jack 10. This will cause relays 98 of cord circuit (Fig. 3) and 60 of the terminal circuit shown in Fig. 2 to operate. Relay 66 in operating completes the transmission path from the tip of the jack 10 through the upper winding of relay 61, the upper break contacts of relay 66 and winding of relay 65 to the contacts of relay 52. Relay 66 in operating also closes the biasing circuit of the lower winding of relay 61. A circuit is also completed from ground through condenser 246 and winding of relay 59, inner bottom break contacts of relay 50 to the armature of the upper make contacts of relay 68 to the tip of jack 10.

When the operator operates ringing key |00 of the cord circuit ringing current is connected to the tip of plug |0| which in turn is connected to the tip of jack 10. Relays 65 and 61 may respond to this ringing current but perform no useful function at this time. It should be noted that relay 61 in following the ringing current is in its marking position each cycle long enough to completely discharge condenser 16 and thus prevents a discharge through tube 15. Relay 59, however, will respond to the ringing current from the contacts of key |00. Relay 59 in responding completes an obvious circuit for the operation of relay 263. Relay 263 in operating completes a circuit from ground through the lower break contacts of relay 56, the lower break contacts of relay 262 the lower make contacts of relay 243 to the winding of relay 60. Relay 60 in operating operates relay 50 which is slow release and also connects ringing current to the make contacts of relay 50 which in turn'connects the ringing current to line Ringing current is transmitted over line to the subscribers station and causes ringer 40 to respond to it over a path from line through ringer 40, and condenser 39 to ground.

When the operator inserted plug |0| in jack 10 ground is also connected to the ring of Jack 10 from the lower break contacts oi relay 56 through the lower break contacts of relay 232. Relay 31 in Aoperating in this circuit over the ring of plug |0i connects ground to the circuit of lamp |02, and causes this lamp to light.

When the subscriber answers, the subscriber will operate power switch 36 which will energize rectiiler 24, teletypewriter motor 33 and operate relay |4. Relay |4 will close thesubscribers line circuit as described above and cause relay 55 at the central station to operate which in tum operates relay 51. Relay 51 operates relay 50 which removes ground from the ring of jack 10 and thus allows relay 91 to release and extinguish light |02.

It should be noted that relay 50 in operating interrupts the circuit of relay 55 so that relay '55 can only be operated during time intervals when no ringing current is being transmitted to the subscribers station. In order to prevent false operations of relay 55 as well as relays 5| and 52, relay 50 is made slow in releasing so that when the operator releases ringing key |00 in cord circuit relay 59 will release which in turn releases relays 263 and 60. Relay 60 in turn releases relay 50. However, relay 50 does not release immediately so that relay 60 connects line to ground through resistance 231 during the release time of, relay 50. The release time of relay 50 is sufficiently long to discharge the cable capacity of line so that relay 55 will not be falsely operated when relay 50 releases.

When the subscriber answers, the operation of the system is substantially as described above except that the supervisory lamp |02 of the cord circuit now responds to recall and disconnect signals transmitted from the outlying subscribers station shown in Fig. 1 instead of lamp 66.

Unattended service In cases where it is desired to furnish unattended service to the outlying subscriber and the outlying subscriber doe's not answer after several short rings, the operator at the central station will depress the ringing key |00 for a long interval of time.

At the central exchange relays 59, 263, 60 and 50 operate as described above for attended service and transmit ringing current over line to the subscribers station. However, it should be noted that when relay 263 operates it also connects battery toy the upper terminal of condenser 16 through the center set of its upper make contacts and high resistance 264 and permits this condenser to start to charge. Relay 263 also transfers the main anode circuit of tube 15 to battery through the winding of relay 262, the inner upper make contacts of relay 262 and the inner upper make contacts of, relay 263. At the end of the interval of time determined by the constants oi! condenser 16 and resistance 264, a discharge is initiated between the control elements of tube 15 which causes a discharge beu tween the cathode and main anode oi' tube 15. In the preferred embodimentof this invention these constants are so chosen that it requiresl approximately 9 seconds for the potential o! condenser 16 to reach the value required to initiate va discharge 4through tube 15.

It atl any time during lthis interval the operator releases the ringing key. relays 53, 263, 60 and will release. Relay 263, in releasing, will again complete `a circuit from the upper terminal of condenser 16 to ground through the upper break contact of relay 263 and the marking contact of relay 61. Condenser 13 is discharged in this circuit but will again start to charge rafter the operator again operates ringing key |30.

If. however, the operator maintains the ringing key |00 in thelcord circuit operated during this entire time interval so that relays '53, 253, 66 and 50 remain operated, tube 15 in discharging causes the operation of relay 262. Relay 262, in operating.- lcompletes av lockingv circuit from battery through its windings and upper make contacts to ground through the upper make contacts of. relay 263v and interrupts vthemain discharge circuito! tube 15. Relay 262, in operating, also connects ground to the upper terminal of condenserk16'toldischarge this condenser and extinguishany .remaining 'discharges between the elements o! tube 'l5- Relay 262 in operating interrupts the operatinglcircuit or relay 60 from groundv through' the lower break contacts of relay56 -andlower break contacts of relay 262 and the lower break contacts ofrelay 263 to battery through the winding o1' relay 63. Relay 60 releases and in turn interrupts the operating circuit ofv relay A53 and causes ,this relay to release. As pointed out above. the charge stored in the capacity of line `Ilvis discharged through resistance' 231 during the release time of relay 50. The release of relay 50 connects line il to the upper-windings of relays 5I and 52 and tothe winding ofrelay 55. If the subscribers apparatus has responded as described hereinafter, relay 55 will operate at this time. Relay 262, in operating, also interrupts the circuit from ground through the lower break contacts o1'. relay 56, lower break contacts of relay 262 to the ring of Jack v1li. This permits the release of relay 31 in the cord circuit shown in Fig. 3, which in turn veirtinguishes the s upervisory lamp |02 to indicate to the operator that the called subscriber has answered. The operator will then release ringing key |00. 'Ihis releases relays 59, 263 and 262 as'described above.

At the subscribers station the ringing current received over line -Il from the central station will operate ringer 40 and will also operate relay 31 through condenser 36 for this entire interval of time. Relay 31 in operating operates relay 4I. Relay 4I is arranged to be very slow in operating and in the preferred embodiment of this invention requires about 8 seconds to operate. If the ringing current remains online Il for at least 8 seconds so that relay 31`maintains the circuit of relay 4| closed `for this entire interval, relay 4l willoperate and in turn operate relay 42. Relay 42 invoperating' locks operated through its lower make contacts, break contacts of power switch 36 and teletypewriter stopcontacts 35. Relay 42 in operating alsoconnects power to theA subscribers lstation apparatus inthe same manner as power switch 36;,1. e., energizes rectifier .24, starts the printer motor .33 and operates re` lay I4. The subscribers station is then ready to record any messages that may be transmitted to it.

When potential is applied to line il from rectiiler 24 by operation oi relay I4 at the subscribers station and relay '56 at the central staltion is released as described above, relay will be operated and in turn cause relays 51, 66, 56 and 54 to operate as described when the subscriber originates a call. The operation oi' relay 56 will prevent reoperation oi' relay 31 oi' the cord circuitat this time and thus indicate to the operator that the subscribers equipment has been started and is ready to receive messages.

It the equipment at the subscribers station does not start u described above no potential will be applied to line Il at the subscribers station and. relay 55 at the central exchange will not operate when relay 53 releases after the operator has released ringing key |63. Under these conditions. relay 31 will again operate when relay 232 releases and thus indicates to the operator that the subscribers equipment did not start whereupon the central exchange operator can again attempt to start the equipment by again operating ringing key |53 for the prolonged interval of time during which the circuits operate as described above.

'I'he operation of 1an unattended subscribers station is similar to that described above 'except -that whenthe transmission of the message is complete va motor stop signal is transmitted to the teletypewriter equipment which causes the operation of contacts 35. The contacts 35 in `operating open alocking circuit ofrelay 42 which in' turndisconnects the station equipment from the-source of power 43 and transmits a disconnect signal to the operator at the central switchboard, thus indicating that the subscribers equipment has returned to normal.

The above-described circuits permit the operator at the central, exchange to both call and start the subscribers equipmentover a long toll line in the same manner that she calls and starts the motor equipment at local subscribers' stations. In addition, the outlying subscriberv cori--l tinuously and positively controls the supervisory signals at the central station. 'I'he outlying subscriber can transmit calling, recall and disconnect signals to the central exchange station at `1 all times and these signals are continuously under the directcontrol ofthe outlying subscriber. These circuits provide the above features and 'at the same time permit the loop and leakage resistance to be extended to the full capabilities of the self-compensating transmitting circuits described in the above identified copending application.

If the outlying subscriber wishes to abandon va call at any time he may do so by releasing power switch 36 which will cause the calling lamp to `be extinguished if the call has not been answered by the central station operator; change the ilashing recall signal to a disconnect signal; or transmit a disconnect signal to the central station loperator in the same manner as a local subscriber transmits and controls these supervisory .signals at the central exchange. Thus it is unnecessary for the operator to do anything merely to restore a circuit to normal or restore any' signal to normal.

It is to be understood that the invention is not limited to the particular type of switchboard circuits shown and described. The terminal circuits may be arranged to cooperatewith any suitable type'A of or other. switching Munn-Lim: Snc'rios General description When the outlying subscriber is beyond the limits of a single-section line, it is necessary to provide intermediate stations or repeater points along the line. Generally, the length of a singlesection line over which the single-line section may operate depends upon the type of line employed. For open wire composite lines the maximum length is around 300 miles, provided the resistance does not exceed 2100 ohms. For simplex open wire lines the maximum length is about 200 miles. For cable lines the maximum length is of the order of 125 miles.

When the subscriber's station is located at a greater distance from the central switching point than the maximum limit of the particular type oi line connected to the subscribers station, one or more intermediate sections is connected between the subscribers station and the central exchange.

The subscribers station circuit is exactly the same as for the single-section line and the line circuit between the subscribers station and the rst repeater point is similar to the single-section line. At the repeater point, however, slightly different terminal apparatus is provided.

Between this intermediate or repeater point and each succeeding intermediate or repeater points, and between the last intermediate or repeater point and the central ofilce, a single full duplex telegraph circuit or channel is required.

At the central oiice ar. additional terminal circuit arrangement is provided to relay both the supervisory and telegraph signal impulses received over the full duplex line to the operator.

The full duplex channel between the intermediate repeater points and between the central exchange and the last intermediate repeater point may be of any suitable type including a grounded open wire full duplex circuit, full metallic full duplex cable or open wire circuits, a full duplex voice frequency carrier telegraph channel or carrier current full duplex telegraph channel. These telegraph channels may be channels of telegraph wires or of composited toll line wires which transmit telephone currents in addition to the telegraph channel currents. The carrier current channels 'may include carrier current ampliers, filters, gain regulators and other equipment usually associated with carrier current lines and channels. As described in this application, a long open wire grounded full duplex telegraph circuit is shown in the intermediate section.

'I'his intermediate section, shown in Fig. 7, is arranged to provide the self-compensating feature described in the above-identified copending application.

In said above-identiiled application a half duplex telegraph system was described, in which signals could be transmitted in either direction, one direction at a time, but not in both directions at the same time. In the intermediate section shown in the multisection line, the circuit has been arranged to provide full duplex operation between the two stations and at the same time provide ior the selifcompensating iesture described in said copending application. so long as the circuit is operated on a half duplex basis. This is the way the circuit is operated to ytransmit telegraph signaling impulses to and from the subscribers station. Telegraph impulses are transmitted over the long line either to or from a subscribers station only in one direction at a time. However, it is necessary for supervisory purposes to provide a iull duplex channel over these intermediate sections. When it is desired to transmit the supervisory signals over the intermediate sections, it is vusually not desirable or necessary to transmit telegraph signaling impulses, so that slight distortion introduced by variation oi the leakage resistance o! the intermediate line section at these times is oi' small importance. The essential requirement is that the line operate substantially independent of the leakage resistance oi the line during the time the circuit is arranged for transmitting telegraph signal impulses either to or from the subscriber's station.

Idle condition Reference will now be made to Figs. l, 6, 7, 8, 3, 4 and 5, arranged as shown in Fig. 10 of the drawings. The operation of Fig. l was described in detail with reference to the single line section and need not be repeated. It should be noted, however, in this case line connected to the subscribers station, shown in Fig. l, terminates in an intermediate circuit arrangement, shown in Fig. 6. The repeater equipment |00, shown in Fig. 7, as well as the equipment shown in Fig. 6, is located at the intermediate repeater point. 'I'his intermediate equipment is connected over line 201 to the central exchange station. The line 201 may be similar to line and include both terminal and intermediate composite sets and other equipment usually associated with long telegraph or toll lines.

The terminal equipment at the central station includes repeater equipment 200, shown in Fig. 7, as well as the equipment shown in Fig. 8.

Equipment is shown in Figs. 6, 7 and 8 in their normal or idle condition with the subscribers station equipment idle and unenergized, and the equipment at the central station in its normal condition and not connected to any cord circuit. At the intermediate station relays |02 and |63 are maintained on their marking contacts by current ilowing from battery through the inner lower contacts of relay |0i, middle winding of relay |02, lower winding ot relay |03, to ground connected through the lower break contacts oi' relay |0|. Relay |02 is maintained in its marking position by current ilowixm from battery through the uppermost break contacts of relay I 11, through the lower winding of relay |02 to ground. Relay |00 is maintained in its spacing position by current flowing through its lower winding in an obvious circuit. Relay 203 of repeater equipment |00 is maintained in its spacing position by current flowing through its lower winding in an obvious circuit. The circuit through the upper winding of relay 203 is interrupted by the uppermost make contacts of relays III and |03. Relay of repeater equipment |00 is maintained in its spacing position by current received over line 201 from the central sta-

Images