US2349586A - Inverse neutral telegraph repeater concentration group switching - Google Patents

Description

MW 23 3944- A. R. BoNoRDEN ET AL f 2I34958' INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP S'WITCHING Filed Oct. 24, 1940 6 Sheets-Sheet 1 JAL/(RE CEA ARGE n/.I/.L MMAR ALL WJ j ATTORNEY 2,349,5@6 INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING 6 Sheets-Sheet 2 MW 23 39ML A. R. BONORDEN ET Al.

Filed oct. 24, 1940 mSvNN BONORDE/v KOOS A TTORA/EV May 23, w44 A. R. BONORDEN ET A1. 2,349,586

INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING Filed oct. 24. 1940 e sheets-sheets EAS T LINE P. V. /fOOS /NI/ENTORSI J.A.KREC`EK W VLA/PG E TAMARS AL By A INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING 6 Sheets-Sheet 4 23, W44 A. R. BoNoRDl-:N ET AL Filed oct. 24, 1940 QOL QS SE May 23, T944. A, R, BONORDEN ET AL 2,349,586

INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING Filled oct. 24, 1940 e sheets-sneeze 5y W MA ALL g l Z C? ATTORNEY RVAVA APJWT /N VE N TORS Patented May 23, 1944 UNITED STATES PATENT OFFICE INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING New York Application October 24, 1940, Serial No. 362,548

21 Claims.

This invention relates to telegraph systems and more particularly to telegraph systems wherein private branch lines are associated together, in local, state-wide, or nation-wide networks on a semipermanent basis as distinguished from a telegraph exchange switching system.

An object of this invention is the improvement of arrangements for associating telegraph circuit elements, such as lines and station loops in telegraph networks on a semipermanent basis, in order to facilitate additions to and subtractions from the network and to facilitate the'substitution of new circuit elements for existing circuit elernents, as Well as the testing of the various circuit elements in telegraph networks.

The operation of telegraph systems wherein private telegraph lines are associated together into networks which remain interconnected for indefinite periods has heretofore been characterized by a lack of flexibility. That is to say,` the addition to the network, or the subtraction from the network of telegraph lines or station loops, or the substitution in the network of one telegraph line or station loop for another, re-

quired compensatory adjustments of one or more of the telegraph repeaters in the network, because the repeaters were arranged in series and the current in the various repeaters was affected when the resistance was changed as the network was altered. Furthermore, added repeaters had to be adjusted to provide the proper polarity as well as type of operation, such as half or full duplex operation.

To overcome this diiiiculty, a new type of telegraph repeater was devised, which provides what is known as the inverse neutral type of transmission on the drop side, for use primarily in service where private telegraph lines were associated in networks on a semipermanent basis. The operation of such inverse neutral repeaters is described in Patents 2,056,277, F. S. Kinkead et al., October 3, 1936, 2,069,224, G. C. Cummings, February 2, 1937 and 2,069,251, F. S. Kinkead, February 2, 1937.

When circuit elements of a private line network appear in a telegraph oiice in which the new inverse neutral repeater is used, as described in the above-mentioned patents, each telegraph station loop and telegraph line is connected into what is known in the art as a concentration group through its own individual inverse neutral repeater. The drop sides or legs of all of the line repeaters and station loop repeaters are interconnected through a common point, which is otherwise known as the hub of the concentration group. From this common point or hub, the leg of each line repeater and station loop repeater extends in series through the armature and marking contact of a receiving relay and through the winding of a sending relay to negative battery common to all repeaters. This common battery has its positive terminal grounded. No current flows through the various legs of a concentration group during the marking condition. For the spacing condition, the armature of the receiving relay in a partcular leg is actuated to engage with a grounded contact. This causes current to ilow through each of the other legs toward and through the hub point to ground through the single spacing contact. A sending relay having a winding in series in each of the other legs is energized to transmit the spacing signal to the circuit connected to each of the other legs in the same concentration group.

For the full duplex condition two independent hubs are provided, as it is impossible to transmit in two directions simultaneously through a single hub. The transmission in each set of connected legs is otherwise the same as for the half duplex condition.

It may be observed, therefore, that in the use of inverse neutral repeaters the legs of the various repeaters, when joined in a concentration group, are all connected in parallel. One end of each leg is joined at the common electrical point or hub. The other end of each leg terminates in battery of the same potential and magnitude for marking. Any repeater when sending toward the hub connects ground to the hub point and transmits signals simultaneously to all other legs in the concentration group. The signals are open and close or neutral signals, as they are known in the art, but they are inverted from the usual, in that the marking signals are rio-current signals and the spacing signals are current signals, hence the term in- Verse neutral.

When each loop leg and each line leg is terminated in its own individual inverse neutral repeater, it becomes electrically, for the purpose of connection into a concentration group, an independent unit. Since each repeater leg of a line or loop radiating from the hub point termihates in battery of the same polarity and magnitude for the marking condition, so that no current iows for this condition, and since, electrically, ground is connected, as a practical matter, directly to the hub point for the spacing condition, the current conditions in any leg when it is receiving from the hub, are unaffected by the addition or subtraction of another leg to the concentration group or by the substitution of a different leg for any leg forming part of a concentration group. When transmitting toward the hub, the only eifect is a change in magnitude of spacing current in the transmitting leg, from the single spacing contact to the hub point, as the number of connected legs is changed.

When the circuit elements of private telegraph line networks are arranged so that each includes its own inverse neutral telegraph repeater and becomes, for the purposes of association into a network, an electrically independent unit, it is possible to terminate the legs of line repeaters and loop repeaters in a switchboard and to make such changes in private line concentration groups as may be necessary, simply by a switching or patching operation at the switchboard, without the necessity for making poling or current adjustments in the leg side of the various repeaters in the concentration group to accommodate such changes. As will be shown later, the type of operation, viz. half or full duplex, of any line repeater is automatically effected at the time the repeater is patched.

In one of its major aspects, therefore, this invention is a switching system for inverse neutral telegraph repeater circuits, adapted to exploit the inherent characteristic of inverse neutral repeaters that, for the purpose of association in concentration groups, each telegraph line or loop leg. equipped with an inverse neutral repeater, is electrically an independent unit.

In this invention, control circuits are arranged to adapt inverse neutral repeater circuits, as used in semipermanent concentration groups, so that they may be controlled at telegraph switchboard positions. To this end, telegraph line circuits extending to telegraph central offices in distant cities are equipped with inverse neutral repeaters and their legs are extended through leg multiple iack circuits which provide a jack appearance within reach of each attendant in the line-up of switchboard positions. This makes every telelgraph line facility available, through the medium of a jack outlet, to every switchboard attendant in the switchboard line-up. The line side of the line repeater circuit isadjusted once for all, so as to provide the optimum signaling conditions Since the leg of each line circuit in the board is equipped with an inverse neutral repeater, and is, therefore, an independent entity electrically, it may be used to communicate with the distant central oiice as a separate facility. Or it may be added to a network without the necessity for compensatory adjustments on the leg side.

In this invention, an appearance of a particular private line network may include a number of station loops, extending from various points in the local area where one of the switchboard lineups of this invention is assumed to be located, into the switchboard. Each of the local station loops will have an independent inverse neutral loop repeater connected to it. Each leg of such loop repeater will be terminated in a particular position in the board in a group of three jacks which will be termed hereafter loop concentration jacks. All of the ,jacks associated with loop circuits which are to be formed into a pai'- ticular concentration group will appear, preferably side by side, at some one position in the switchboard line-up, so that the loop circuits may be administered by an attendant at that position. The loop jacks may be multipled to a second position, so that at times, a second attendant may supervise the concentration group. The line circuits, the repeater legs of which, as has been pointed out, are multipled throughout the board, must be interconnected to the loop circuits so that the concentration group may be extended to other portions of the network appearing in switchboards in distant Cities as required. This is done by selecting the proper line facilities from the entire group which are multipled throughout the board and extending the leg of each one which is required into a group of three other jacks, termed line concentration jacks, each group of jacks being individual to a line circuit at the particular position where the .concentration group is to be administered. The legs of each of the loop and line repeaters which are to be associated in a particular concentration group, after passing through its individual group of jacks at a particular attendants position, are all joined in a common electrical point which becomes the hub of the concentration group.

The connecting together of the individual leg conductors to form the hub may be effected in any convenient manner. In order to reduce the possibility of disconnecting any line or loop inadvertently from a concentration group with which itis normally associated, the individual conductors may be extended to individual punchings on a terminal strip and strapped together with a common soldered connection. When thus assembled, the line circuits and loop circuits in a concentration group each have groups of jacks, individual to each line circuit and loop circuit, all ofwhich appear before a particular attendant in the switchboard line-up who is responsible for the administration of the service. Since, as has been pointed out above, all of the telegraph lines from distant cities, which come into the telegraph office where the switchboard of this invention is assumed to be located, are each equipped with an individual inverse neutral repeater which makes it an independent entity and each line has an appearance, in the form of a multiple jack, within cord reach of each attendant, any idle line in the multiple'may be connected on a temporary basis into a particular telegraph network by a patch from the multiple at the position into one of the concentration jacks at the particular position where the concentration group for that network appears. It is to be understood, of course, that the bank of line leg multiple jacks extending through the switchboard are terminations of circuits which extend to many diiferent cities and it is necessary to select one extending vto the proper destination. This may be determined from reference to the jack designation strip.

The normal network, as required to provide the proper number of telegraph lines to distant cities and the proper number of loops to stations in the local area served by the switchboard of this invention, will be set up in what is essentially a permanent concentration group. Each line and loop leg will be extended through its own individual group of concentration jacks in the switchboard position where the concentration group is to be administered and joined together in a hub, preferably by a soldered connection. The jacks in the various individual line and loop legs provide means for making changes in the network yas required on a temporary basis by means of patches. They also provide means for testing, monitoring, measuring bias, communicating with the attendant. etc., and, in general, permit the complete administration of the various private line networks, the testing and supervision of the elements of a network, the addition of lines or loops, the disconnection of a line or a loop or the substitution of a new line or loop for one forming part of a, network. All of this may be performed by an attendant seated at a' switchboard. As pointed out above, since the leg of each line and loop is equipped with its own'individual inverse neutral repeater, these additions, subtractions and substitutions may be made without the necessity for making any compensating adjustments in the network or in the-individual repeaters.

The invention may be more fully understood from the following description when read with reference to the various associated drawings in which:

Fig. 1 represents two four-wire full metallic telegraph line circuits, equipped with inverse neutral line repeaters, arranged for conversion from full to half duplex operation when connected to full or half duplex concentration groups;

Fig. 2 represents two telegraph station loop circuits equipped with two inverse neutral loop repeaters and two sets of loop concentration jacks, for connecting two local stations into a half duplex concentration group;

Fig. 3 represents two line leg multiple circuits and two sets of line concentration jacks, the last mentioned for use in terminating twoflines arranged for half duplex operation and includes a station calling-in circuit by means of which a station attendant may call an attendant at a service board; f

Fig. 4 represents an idle indicator control circuit for controlling lamps whichmomentarily indicate all idle lines to remotey points, in response to the actuation of a key by an attendant who requires a new line. to enable the attendant to quickly select a line'to la particular distant terminal for connection to a concentration group.

Fig. 5 represents a splitting circuit which is used with a telegraph cord circuit for testing lines before the lines are connected to a concentration group;

Fig. 5A represents a telegraph cord circuit for use in connection with Fig. 5 for testing lines before adding them to a concentration group;

Fig. 6 represents a local station connected through two separate loops to two inverse neutra] loop repeaters and two sets of loop concentration jacks, for use in full duplex operation;

Fig. '7 represents two leg multiple circuits and four sets of line concentration jacks for use in terminating two lines to remote terminals arranged for full duplex operation.

The rectangle Fig. A bearing the-legend Half duplex concentrationgroup indicates the manner in which Figs. 1, 2, 3 and 4 are assembled to form a half duplex-concentration group, comprising two lines to two distant terminals and two local station loops, at the telegraph service board.

The rectangle Fig. B bearing the legend Full duplex concentration group indicates the manner in which Figs. 1, 4, 6 and 7 are assembled to form a full duplex concentration group comprising two lines interconnected through a telegraph service board, as the switchboard of this invention is known to provide full duplex operation between two remote terminals. It shows also a single patrons station in the local area served by the telegraph service board, connected through two loops into the fullyduplex line to provide full duplex operation between the local station and the two remote terminals.

HALF DUPLEX CONCENTRATION GROUP A half duplex concentration group will first be described.

Figs. 1,-2, 3 and 4 are arranged in relation to each other as indicated in the rectangular block diagram Fig. A, bearing the legend, Half duplex concentration group. As thus arranged, they -constitute a concentration group, comprising two telegraph line circuits and two telegraph loop circuits, together with a calling-in signal circuit and an idle indicator control circuit. The telegraph line and loop circuits are connected together at a telegraph central onice, through a new telegraph facility to be known as a telegraph service board. The'v operation of the fundamental switching circuits of this new board are to be described herein.

From the ofce where the telegraph service board is located, one telegraph line circuit is assumed to extend to a telegraph central office to the east and the second to a telegraph central oice to the west. One loop connects a local telegraph station designated A, of a first patron, in the same local area as that in which the service board is located into the concentration group at the service board. The second loop connects a local telegraph station, designated B, of a second patron, also in the same local area as that in which the service board is located, into the same concentration group at the service board.

The circuits are arranged to form a half duplex telegraphconcentration group. By this is meant, in this instance, that either loop station may send telegraph signals which are transmitted to the other loop station and over the line east and line west simultaneously, or either line may send telegraph signals which are transmitted to each loop andv over the other line simultaneously. It is not possible, however, for any station to receivefrom other stations while it is sending. i

In the description of a half duplex concentration group, apparatus in the circuits for station A and the east line will be designated by numbers only. -The letters B and W will be added to corresponding `apparatus in the circuits for station B and the west line respectively.

The manner in which a loop station transmits to the other loop and to the two lines simultaneously will iirst be described. It will be assumed that loop station A transmits. To do this the shunt 20|, which short-circuits the transmitting contacts-at station A when the circuit is idle, will be opened and the contacts of key 202 will be closed so that the transmitting key 202 may take control of the circuit.

The armature of relay 2|2 is held in engagement with its left-hand or marking contact by the eiect of current flowing from battery ZIB through resistance 2H and the top winding of relay 2l2 to ground. No current liows through the bottom winding of relay 2i2 for this condition as will be explained below.

When the transmitting key 202 is closed, a circuit rnay be traced from ground through positive battery 203, through resistance 25M, through resistance 205, through the bottom winding of reley 206,- through the tip and break contact of jack 201, through the break contact and ring of jack 208, through the variable resistance 226, normal make contacts of call signal key 22T, through the winding of the sounder 209, through the closed contacts of key 202, through the tip and break contact of jack 208, through the break contact and ring of jack 20T, through the top winding of relay 206, through the top winding of polar relay 2|0, through inductance coil 2H, v5 through the armature of relay 2|2, through resistance 2|3, through negative battery 2|4 and back to ground. Positive and negative battery are thus connected'to the two ends of the loop circuit and current flows, for the marking or "lvo closed condition, through the loop circuit. The

eiect of the current flowing through the top winding of relay 2|0 tends to actuate the armature of relay 2|0 to engage with its right-hand or marking contact. It preponderates over the effect of current flowing through the bottom winding of relay 2|0, over a circuit from ground through negative battery 2M, through resistance 2| 3, through the left-hand or marking contact and armature of relay 2|2, through inductance coil 2| through the bottom winding of relay 2|0 and resistance 2|5 to ground, which current tends to actuate the armature of relay 2|0 to engage with its left-hand or spacing contact and the armature of relay 2|0 is thus maintained in engagement with its right-hand or marking contact.

Relay 206 is so arranged that when current flows through both its top and bottom windings, as is the case when the loop is closed, the eiTect in one winding is balanced by the eiect in the other winding and its armature remains in its normal unoperated position as indicated.

When the armature of relay 2|0 is in engagement with its right-hand or marking Contact, it connects negative battery to the hub of the concentration group. The circuit for this may be traced from battery 2| 5, through resistance 2|8, through the bottom winding of relay 2 2, through the right-hand or marking contact yand armature of relay 2|0, through test resistance 2| 9, through the top back contact and armature of relay 220, to conductor 22|. Conductor 22| may be considered electrically as a point which constitutes the hub of the circuit.

Station B is joined into the hub in a corresponding manner. For the marking condition, station B connects negative batteri/3. indicated 2MB, over a path similar to that traced for station A, which passes ultimately through testing resistance 2 l 9B to hub 22 The manner in which one of the telegraph lines is connected into the concentration group will now be explained. The circuit of the line east will be used for this purpose. This telegraph line is a four-wire metallic circuit. Its operation is described in detail in the application of R. B. Hearn, Serial No. 342,431, filed June 26, 1940, now Patent No. 2,259,637, granted Oct. 21, 1941. A s therein described, the circuit may be arranged to function either half duplex or full duplex dependent upon whether it is connected into a full duplex or a half duplex concentration group. In this instance it is connected into a half duplex concentration group and therefore is arranged to function half duplex.

Refer now to Fig. 1 which shows in detail a four-wire metallic telegraph line connecting a distant telegraph central ofllce, located, it is assumed, to the east, into the concentration group at the oce where the concentration group is established and which indicates diagrammatically, by a rectangular box, an identical telegraph line for the telegraph line west which, it is assumed, connects a central oflice located to the west into 75 the concentration group. Although a four-wire metallic circuit is shown for this purpose, carrier line circuits, one-way polar circuits, and other line circuits, when terminated in proper inverse neutral type repeaters, may be used in place of the four-wire metallic line and the associated inverse neutral repeater shown.

The upper two line conductors of Fig, 1 constitute the path over which the distant repeater to the east receives from the concentration group. The lower two line conductors of Fig. 1 constitute the path over which the distant repeater to the east transmits into the concentration group.

Relays |0| and |02 are polar relays in the transmitting circuit at the distant central oice. When the armatures of these relays arein the positions indicated, which is for the marking condition, a path may be traced from ground through battery |03, through resistance |04, the left-hand contact and armature of relay lill, through inductance coil |05, the top winding of polar relay |05, the armature and right-hand contact of relay |02 and' through resistance |07 back to ground. Apparatus corresponding to coils |24, |25 and |26 together with the associated condenser |38 may be inserted, if desired, in this path at the distant central terminal, in the same manner as they are connected in the two top conductors of Fig. l. The function of this apparatus is to suppress noise caused by telegraph thump on the telephone circuit operated over the same pair of cable conductors. The effect of the current in the top winding in the path traced above is to operate the armature of relay |06 into engagement with its right-hand or marking contact. The operation of the circuit through the bottom winding of relay |06, known in the art as a vibratory circuit, is to tend to speed up the action of the relay. It is well known in the art and will not, therefore, be described herein in detail.

When the armature of relay |06 is in engagement with its right-hand or marking Contact, a circuit may be traced from ground through negative battery |08, through resistance |09, through the right-hand or marking contact and armature of relay |06, through resistances ||0 and and through the top winding of polar relay ||2 to ground. The effect of this current is to actuate the armature of relay ||2 into engagement with its right-hand or marking contact. No current ows through the bottom winding of relay ||2 for this condition as the circuit through the bottom winding of relay ||2, connects at one end to the hub 22| of the concentration group and at the other end to negative battery. This circuit may be traced from negative battery H5 through resistances ||6 and ||1, through the bottom windings of polar relays I8 and I9, through the lefthand armature and front contact of relay H3, through the bottom winding of relay |2, through the right-hand front contact and armature of relay I|3, through the right-hand or marking contact and armature of relay H2, through leg conductor |20, through Fig. 2 into Fig. 3 to parallel branches. One branch continues through the top armature and back contact of relay 30|, through test resistance 303 and the back contact and armature of relay 304 to lthe hub 22| of the circuit. The other branch extends in multiple through the tips of the multiple jacks Slt, 3H, 3 |8, etc., one of which is accessible at each position in the telegraph service board of this invention.

A biasing circuit for relays 8 and I I9 may be traced from battery H5, through resistance |29 and the top windings of relays |I8 and H9 to. ground. The eiect of this current tends to actuate the armatures of relays ||8 and ||9 to engage with their right and left-hand contacts' respectively for the marking condition. This eiect is not opposed as there is no current flowing through the bottom windings of these relays for the marking condition of the concentration group, since all of the legs of the concentration group terminate in battery of thesame polarity for the marking condition. v

The loop over which the distant office to the east receives may be traced from ground, through battery l2| to its positive terminal, through rei25, through the bottom line conductor to ther distant terminal, through the winding of the receiving relay |21, through the top line conductor, through the top windings of the repeating coil |26, through the top windings of inductance colis |25 and |24, through the armature and righthand or marking contact of relay i I8 and resistance |30 back to ground.

The four-wire line to the west indicated by the rectangular box at the bottom of Fig. 1 is arranged in the identical manner as that described for the four-wire line to the east. It connects negative battery of the same magnitude as battery H5 in the east line through an identical circuit to leg conductor I3 which corresponds to conductor |20 of the east line, through the top outer armature and back contact of relay SW and test resistance 303W, through the back contact and armature of relay 304W to hub 22|.

Thus each line and each loop leg connects negative battery of the same magnitude to the hub of the concentration group for the marking condition.

If a spacing signal is transmitted from any station loop circuit or from any telegraph line forming part of the concentration group, the leg of the circuit transmitting the spacing signal will be connected to ground which grounds the hub and operates a relay in each of the other legs to transmit the spacing signal into each of the other connected circuits. performed will now be explained.

It will be assumed that the operator at station A opens the contacts of the transmitting key 2&2V

to send a spacing signal. This breaks the loop circuit for station A, heretofore traced. The top winding of relay 2li! is deenergized. The armature of relay 2|0 is actuated, under the iniiuence of current through its bottom winding, to engage with its left-hand or spacing contact which is grounded. This disconnects negative battery 2|6 from the leg which extends through resistance 2 9 into the hub 22| and connects ground through resistance 2|9 to hub 22|.

When ground is connected to the hub, a circuit may be traced from hub 22| through the upper armature and back contact of relay 22GB, through test resistance 2 IEB, through the armature and right-hand or marking contact of relay 2|0B, through the bottom winding of relay 2|2B and resistance 2|8B, to battery 2 ISB. The effect of this current flowing through the bottom winding of relay 2 |2B preponderates over the eiect of current iiowing through the top winding of relay 2|2B which has been holding the armature of relay 2|2B in engagement with its left-hand or The manner in which `this is marking oontactand theA armatureof relay 2|2B is actuated to engage with its. right-hand or spacing Contact.

Loop B is arranged in the identical manner described for loop A. When loop A was traced it was shown that the two ends of the loop terminated in vbattery of opposite polarity for the marking condition. Similarly, the two ends of loop B terminatein battery of the opposite polarity for the marking condition. When, however, the armature ofrelay 2|2Bvis actuated 'to engage with its right-hand armature, negative battery is disconnected from one end of the loop and both ends are terminated in positive battery of the same magnitude so thatfno currentA flows in the loop. The sounder 209B Aat station B is deenergi'zed'and a spacing signal is received at station B.

The manner in which thev same spacing signal is received at the east central telegraph terminal will now be explained.

`When the spacing signal is received in the hub from station` A, ground, as has been shown, is connected through resistance` 2|9 to hub 22| and a circuit may be traced through the armature and back contact of relay 30d through testing resistance SH3, through the top outer back contact and armature of relay 30|, through leg conductor |20, through Fig. 2 into Fig, 1, through the armature and right-handcontact of relay ||2, through the right-hand armature and front contact of relay H3, through the bottom winding of relay H2, through the left-hand front contact and armature of relay I3, through the bottom windings of relays i lsand H8, through resistances l l and l It and battery l5 to ground. The effect of current flowing in the bottom windings of relays H9 and I|8`for thiscondition is such that it tends to actuate the armature ofrelay H9 to engage with its right-hand contact and the armature of relay I8 to engage with its left-hand contact and this elect preponderates over the ei'ect of the current iiowing through the top windings, so the armature of relay |19 is actuated to engage its righthand contact and the armature offrelay ||8 is actuated to engage tslleft-hancl contact.

When lthe armatures lof relays H9 and H8 are actuated as described in the foregoing paragraph, the polarity of battery |2| in relation to the two ends of the east send line through the receiving relay at the distant ofce will be reversed. That this is so may be understood by observing that there are, two conductors extending from each of resistances |22and |3 respectively. One conductor. extends from each resistance to contacts which are in engagement with the armatures of relays H9 andl I8 when their armatures are in the positions shown in Fig. 1 and one conductor extends from each of said resistances to a contact on the other of therelays with which each armature makes engagement when in the spacing condition. .Thus as the two relays |19 and H8 respond to a spacing signal, the polarity of battery |2| connected to the ends of the line i'or the marking condition is reversed, resulting in a spacing signal being transmitted to the distant receiving relay |21.

The spacing signal originating at station A is transmitted to the'distant receiving relay connected to the west line in the same manner as described above for the east line.

Thus as the armature of the relay 2|0, which receives from station A and transmits toward the hub, is actuated so as to connect ground and negative battery alternately to the hub 22|, the

armature of the receiving relay in the inverse neutral repeater of each of the other legsrconnected to the hub, whether it be a loop leg or a line leg, is operated simultaneously to transmit spacing and marking signals into its loop or line.

When signals are transmitted from a distant oiiice over a telegraph line, it will be assumed over the east line, relays and |02 in the distant oirlce are operated from a connected circuit not shown. This reverses the connections between the two conductors of the bottom two-wire line and battery |03. Relay |06 is'in turn actuated. As the armature of relay |06 is actuated between positive and negative battery, relay I I 2 responds. As the armature of relay ||2 is actuated, negative battery and ground are alternately connected to hub 22| and marking and spacing signals are impressed upon all other legs forming part of the concentration group.

In the same manner signals may be transmitted from the distant western oilice rover the west line into its respective inverse neutral re.

peater and thence to the hub to actuate the send'- ing relay in each individual inverse neutral re-v Breaking operation in a duplex concentration group It is possible to transmit a break signal from any circuit connected into a half duplex concentration group, to prevent any circuit which is transmitting to the other circuits of a concentration group from continuing to transmit. The manner in which this is performed will rst be described for the condition in which signals are being transmitted from the distant oillce over the east line and the attendant at loop station A breaks. f

When signals are being transmitted from the distant oce over the east line, it has been shown that relays |06 and ||2 :follow the signals to connect ground and negative battery alternately to hub 22 I. If the attendant at station A wishes to stop the transmitting from the east line, so that station A may transmit, key 202 is opened and is maintained in the open condition. The opening of key 202, as has been described, results in ground being connected to the hubwhen relay 2 I 2 next closes its marking or right-hand contact. Since the key 202 is maintained open, a permanent ground is connected to the hub resulting in a permanent spacing signal being transmitted from the hub out over each connecting leg. In the case of the line which is receiving signals from the distant oice, if the yarmature of relay I I2 is in engagement with its left-hand or spacing contact, in response to a spacing signal transmitted from the east line toward the hub, nothing will happen momentarily in its send side, as ground from the hub will be connected to one end of conductor |20 and it will meet ground on the left-hand or spacing contact of relay I|2. As soon as the armature of relay II2 is actuated to engage with its right-hand Contact, however, the ground from the. hub will be connected to one end of the path through the bottom windingsrof sending relays |I9 and II8 and battery II5 will be connected to the other end over the circuit heretofore traced. Under this condition the armature of relay I2 is maintained in engagement with its right-hand contact, as the effect of the current flowing through the bottom winding of relay I I2, tending to actuate the armature of relay I I2 toward the right, preponderates over the effect of spacing signal current from relay |06 tending to actuate the armature of relay I|2 toward the left. Relays IIS and ||9 will be operated when the armature of relay II2 is on its right-hand contact, from ground connected to the hub. With the armatures of relays II8 and IIS actuated to their spacing contacts, a permanent spacing signal is transmitted toward the distant cnice to the east as a breaking signal.

If either loop stat'ion is transmitting, any line or the other loop may break. l't will be assumed that station A is transmitting and that the east telegraph line breaks. This is performed in the following manner. A permanent spacing signal is transmitted from the east telegraph terminal into the hub, operating relay |05 to its left-hand or spacing contact. This will operate relay II2 to spacing when relay 2I0 next closes its right or marking contact to remove ground from hub 22 i. This results in the connection of permanent ground to hub 22| from the left-hand contact and armature of relay ||2. A circuit may be traced from the grounded hub 22|, through the armature and back contact of relay 220, through resistance 2li), to the armature of relay 2I0. If the armature of relay 2I0 is again in engagement with its left-hand or spacing Contact, nothing happens momentarily. When the armature o1 relay 250 next engages its right-hand contact, the circuit will be extended through the bottom winding of relay 2 I2 and resistance 2 I8 to battery 2I6. This operates the armature of relay 2I2 so that its armature engages its right-hand or spacing contact. This disconnects negative battery 2N2 from one end of the loop through station A and connects both ends of the loop to positive battery 203. This results in a permanent spacing signal being transmitted over the loop which is received by sounder 209 at station A as a breaking signal.

As a general proposition, it may be stated that, when inverse neutral repeaters are interconnected, a spacing signal transmitted toward the hub, by any repeater connected to the hub, will result in the connection of ground to the hub and' a spacing signal will be transmitted simultaneously from the hub through all of the other repeaters connected into the hub, and further, a permanent spacing signal transmitted from any repeater while another repeater in the concen tration group is transmitting toward the hub, will result in the loss of control, by the station which is transmitting, of the relay in the repeater which transmits toward the hub, when the station which is transmitting next sends a marking signal toward the hub. The relay which transmits toward the hub will then be held to marking and simultaneously the permanent spacing breaking signal will be transmitted to the station which was transmitting.

Circuit for permitting station connected into a half duplex concentration group to call switchboard The arrangement of Figs. 1,2, 3 and 4 per Fig. A is equipped with a calling-in signal by means of which any loop station connected into the concentration group may signal the attendant who is administering the concentration group at the service board.

The three jacks associated individually with each station loop and each telegraph line in any particular concentration group are all located in the same attendants position at the service board. The service board is a multiposition board. Various concentration groups are administered at various positions. The attendant in charge of a particular position controls a certain number of concentration groups such as the concentration group per Fig. A, comprising Figs. l, 2, 3 and 4.

The manner in which an attendant at a station, such as station A, may summon an attendant at the position in the service board where the concentration group is being administered is as follows.

The attendant at station A grounds one side of the station loop circuit. This may be done by momentarily actuating the call signal key 221 in Fig. 2, which rst grounds the lower loop conductor through the set and opens the upper loop conductor.

When the station loop circuit is closed, the effects of the currents in the top and bottom windings of differentially connected relay 206 neutralize each other, so that the armature of relay 206 remains in the condition shown. During the transmission of a spacing or a break signal from station A, when the loop is opened, no current flows through either winding of relay 206. No current flows when a spacing signal is transmitted toward station A as both ends of the loop are connected to battery of the same polarity and magnitude for this condition. When the lower loop conductor is grounded and the upper loop conductor is opened, however, a circuit may be traced from ground through sounder 209, make contact and armature of key 202, through the tip and break contact of jack 208, the break contact and ring of jack 201, the top winding of relay 206, the top winding of relay 2I0, inductance coil 2| I, the armature and left-hand Contact of relay 2I2, resistance 2|3 and battery 2 I4 to ground, operating relay 206. With relay 206 operated, a circuit may be traced from ground through the armature and front contact of relay 206, the bottom armature and back contact of relay 220, conductor 222, which may be considered electrically as the hub of the calling-in circuit into Fig. 3, conductor 305, the back contact and armature of relay 306, through the winding of relay 301 to battery, operating relay 301 which locks from its bottom contacts under control of relay 306. The operation of relay 301 connects battery through the top armature and front contact of relay 301 through the iilament of lamps 308 and 309 in parallel to ground, lighting both of these lamps as a signal that some station associated in the concentration group is calling in. One of these lamps, such as the primary appearance lamp 308, is located at the same position as the one in which the loop and line concentration jacks of the concentration group are located. The secondary appearance lamp 309 is located at an adjacent position to provide the advantage of teamwork since with this arrangement any of four service board attendants may answer the call through the associated jacks.

Any other station, such as station B, connected through a station loop into the concentration group may light the same lamps 308 and 300 by an operation similar to that described for station A. This should be apparent from reference to the station loop and loop repeater for station B. Ground from thearmature of relay 206B is connected through the bottom armature and back contact of relay 220B to conductor 222 in parallel with the ground from relay 206.

In response to the lighting of the lamps 308 or 300, the service board attendant administering the concentration group may connect an attendants telegraph transmitting and receiving set circuit operating on the inverse neutral principle to jack 3I0 or jack 3| I. This connecting circuit will `not be described in detail hereunder as it does not form part of the present invention. At this point attention is called to the fact that battery connected to the sleeve of the attendants circuit operates relay 306 over an obvious path. .The operation of relay 306 breaks the operating path heretofore traced for the operation of relay 301 and relay 301 releases, extin guishing the lamps. The hub of the concentration group, conductor 22|, is connected in multiple to the tip of jacks 3I0 and 3II to provide a connection for the transmitting lead in the attendants circuit. By means of inverse neutral repeater connected to the tip of jacks 3| I, it is. possible for the attendant to transmit and receive signals to andY from the various stations and lines comprising the concentration group or to monitor on all signals transmitted through hub 22|.

The rings of jacks 3I0 and 3II are connected in multiple to the common calling-in or signal hub conductor 222. This is to provide a recall featurein the attendants connecting cord. A recalling operation is performed at a station in the same manner as a calling-in operation. If an attendants cord circuit is already connected to either jack 3I0 or 3|I andany one of the stations connected into the concentration group through a station loop repeater wishes to again summon the attendants attention, the lower station loop conductor is grounded. This connects ground, in the manner already described, to conductor 222 and to the ring of both jacks 3I0 and 3|I. This ground operates a relay in the attendants cord circuit connected to either jack V.to light a supervisory lamp as an indication that a station is recalling.

Connecting supervisor circuit and other circuits to concentration group Jacks 3I0 and 3II also provide means for establishing a connection -to a supervisor. By means of a patching cord circuit it is possible to connect a test signal supply circuit to the concentration group through jacks 3I0 and 3| I. Also, jacks 3I0 and 3l I may be used with suitable connecting circuits for the measurement of bias or distortion.Y

Releasing a line from a. half duplex concentran tion group Because each telegraph line to a distant city and each telegraph loop to a local station appearing in the telegraph service board is terminated in'its own individual inverse neutral repeater, it is possible in the system disclosed herein to make changes in a concentration group such as removing lines or loops, adding lines or loops or substituting lines or loops, without the need for making compensatory adjustments in the leg side of any repeater to accommodate the change. The invention herein permits these changes to be made flexibly at the switchboard position where the concentration group is administered. with a minimum of eiort on the part of a service board attendant.

It is necessary on occasion to make temporary changes in a concentration group, such as to replace a line or loop which may be defective or to provide additional acilitites in a concentration group such as additional lines or loops, or to remove a line or loop at the termination of its daily service period. The manner in which a telegraph line is disconnected from a concentration group will now be explained. The east line will be used for the purpose.

To perform this operation a control plug, such as plug 3|2, having its ring and sleeve conductors interconnected, is inserted into a cooperating jack, such as release control jack 3|3. This connects the ring and sleeve of jack 3|3. A circuit may then be traced from ground, through the middle winding of relay 35, to the sleeve ol' jack 313, through the sleeve of plug .3|2 to the ring oi plug 32, through the ring of jack 313 and the top winding of relay 3|5, vthrough battery 3M back to ground, operating relay. 3|5. The operation of relay 3|5 connects ground through its upper armature and front contact and the winding of relay 30| to battery, .operating relay 30|. The operation of relay 30| breaks the connection between the leg conductor 20 and the hub 22| as previously traced, thus disconnectingthe east line from the concentration group. The operation of vrelay 30| also breaks the connection which extends from battery through the winding of relay |13 in Fig. l, and conductor IM, into Fig. 3, through the bottom middle armature and back contact of relay 30| and the top back contact and armature of. relay 302 to ground, thus disconnecting ground formerly furnished through the top armature and back contact of relay 302. Relay H3 releases. rThis places the inverse neutral repeater in the east line in its normal condition which is the full duplex condition.

It has been explained that the circuit per Fig. l may function either full duplex or halfk duplex dependent upon whether it is connected into a full duplex or half duplex concentration group. When it was connected into the half duplex concentration group as explained above, it was conditioned to function half duplex through the operation of relay H3. Now that it has been released, the repeater is restored to its normal iull duplex condition. Even though it is no longer serving in the concentration group described above, it may be appropriated for use with another concentration group which may operate full duplex or half duplex. If the new concentration group is to operate full duplex, relay H3 will remain unoperated.` If the new concentration group operates half duplex, relay H3 will be again operated.

To return to the operation of relay 30|, its operation sends a permanent spacing signal to the distant eastern terminal. This .is performed as follows. A circuit may be traced from ground through the armature and back contact of relay 302, through the top inner front contact and armature of relay 30|, through conductor |32, through the left-hand back contact and armature of relay H3, which is now released, through the bottom windings of relays H9 and H8, through resistances, Ill and IIB and negative battery ||5 back to ground. This operates relays ||9 and ||8, reversing the polarity .of battery |2| as connected to the sending line and tant eastern terminal.

The operation of relay 30|, also, by the transfer of its bottom innermost armature from its back to its front contact, disconnects ground from the sleeves of the multiple jacks 3|6, 3|? and 358 and connects the sleeves of these jacks to battery through the windings of relays 302 and 3110. The object of the connection of ground to the sleeve while the line is connected into a concentration group was to permit monitoring on the circuit through a multiple jack. The plug of a monitoring circuit may be inserted into a multiple jack at any position in the board and ground on the sleeve of the multiple jack operates a relay in the monitoring circuit which conditions the monitoring circuit for monitoring. The purpose of the change from ground on the sleeve to battery through the relays will be un derstood from the description below.

The operation of relay 30| performs one other switching operation. l't extends a circuit, which may be traced from ground, through the filament of lamps 32|, 32,2 and 323 in parallel, through the bottom outermost front contact and armature of relay 30|, through the bottom back contact and armature of relay 302 and through conductor 320 to a front contact of relay 40| in Fig. 4 which forms part of the idle indicator control circuit which will now be explained.

Idle indicator control circuit for indicating Zine available for connection to concentration group It has been explained that each telegraph line connecting the service board to a distant city, Whether connected into concentration jacks at a particular attendants position or not, is extended through a group of multiple jacks throughout the switchboard line-up. Some means must be provided for distinguishing between the lines which are serving as part of an operating concentration group and those which are available to be connected into a concentration group on a temporary basis by means of a patching operation. A line may be connected into a concentration group or it may be released from, or not connected to, a concentration group for relatively long intervals. If a lamp were lighted throughout either interval as an indication of the condition, it would mean that many lampsk would be burning in the switchboard at all times. This has a number of disadvantages including battery drain, reduced life of lamps and reduced contrast between lighted and unlighted lamps, such as station calling-in signal lamps 308 and 309 described above.

In order to provide the advantages of a normally unlighted switchboard, and the other advantages enumerated above, the idle indicator control circuit is furnished. Its function is to light the lamps associated with all idle telegraph lines to distant cities momentarily, in response to the actuation of a key by an attendant who requires such a line, so that a selection of a line to a particular city may be made if such a line is available.

If an attendant at a particular position in the telegraph service board line-up requires a telegraph line to a distant city and wishes to know which lines are available so that he may make a selection, the attendant operates a key such as 402, Fig. 4, at the particular attendants position. There is one such key at each position in the line-up. Keys at other positions are indicated by keys 403 and 404. When key 402 is operated, relay 005 is operated over an obvious circuit. The voperation of relay 405 closes a circuit Vfrom ground through the bottom front contact and armature of relay 405, through the Vwinding of relay Llli and resistance @lil through battery to ground. Relay 465 will operate and lock up through its top middle front `contact and armature to ground. The operation of relay it will connect ground through its Abottom inner front contact and armature and the winding of relay lill to battery, operating relay till. The operation of `relay MI will connect battery through its various contacts in parallel to a number of conductors extending to various leg multiple circuits. Each of said conductors is arranged so that it may be `multipled to a number of leg multiple circuits. A circuit may be traced from battery through the top armature and front Contact of relay dill, through conductor Stil, through the bottom armature and back contact of relay 362, through the bottom. outermost ar mature and front contact of relay 3M and through the filaments of lamps 32l, and 323 in parallel to ground, lighting each of the lamps, as an indication that the telegraph line circuit to a distant city associated with these lamps is available for use. Only such. circuits as are available for use will have their associated idle indicating lamps lighted as the path to the lamps inthe case of circuits which are not idle will 4not be closed.

The lamps indicating that a circuit is available for use remain lighted for a short interval only, while a selection of one of them-is being made and then the lamps are extinguished through the operation of the idle indicator control circuit. The manner in which this is performed will now be explained.

When relay M6 is operated a circuit may be traced from plate battery SL38 through resistance 409 and conductor dill, through resistances All and M2 in parallel, through the bottom armature and front contact .of relay Mid, through the filament of vacuum tube M3 and resistance 4M to ground, lighting the ilament. After a momentary interval key M2 is released, in lturn releasing relay ill. This removes ground which has been connected through the front contact and top armature of relay 95 to the upper terminal of condenser M5 and condenser lid is charged .over a path from battery Mil through resistance 399, through resistance M5 the top innermost armature and front Contact of relay 406 to the upper terminal of condenser M5, the bottom terminal of which is grounded. When the top plate of condenser @l5 and the grid of tube M3. connected in parallel with the top plate of the condenser, have assumed a proper positive potential with respect to the cathode of tube M3, current will iow through the plate circuit of the tube from positive battery limi, through resistance 4.99,. through the winding of relay lll to the plate of tube fila, from the `plate to the filament of tube H3 and through resistance lid to ground, operating relay fili, The magnitude of resistance M5 and the capacity of condenser H5 establish the interval necessary to charge condenser H5 to the proper positive potential and the interval been established for use with the idle indicating lamps of the inverse neutral circuits at approximately six seconds.

When relay lil is operated, ground is connected to the leit-hand terminal of resistance fili?. This shortcircuits the through the winding of relay E-ili to ground, releasing relay The release of relay ME breaks the path heretofore traced through the filament of tube ll-li. The

release of relay 656 also disconnects battery 353 'from the top terminal of condenser ll i il. The battery connection of the condenser will be replaced by direct ground through the top outermost armature and back contact of relay 46S which will discharge condenser M5. When the filament of tube M3 is extinguished current will no longer flow through the tube and relay lill will be released. The idle indicator control circuit i is thus returned to normal.

If at any time a key such as w3 is operated momentarily, in turn operating relay 405 before the timing circuit has been permitted to complete its cycle, condenser M5 will be discharged from ground connected to the top front contact and armature of relay lli and the entire timing cycle will be repeated.

Replacing a Zine forming port of a half duplex concentration group with a Zine which has been released from a dilierent concentration group The concentration group is arranged so that a line forming part of a concentration group may be replaced by a second line. This second line may be a line which has been released from another concentration group or it may be a spare line. A spare line is one which is not normally connected into a concentration group, a spare line terminates in multiple jacks and a leg multiple circuit, but it is not provided with a group of three concentration jacks and connected into a hub as is a line which is arranged to normally form part of a concentration group. I

In this section the operation of replacing a line in a concentration group by a line which has been released from another concentration group will be described.

In order to replace a line forming part of a concentration group with a new line which has been released from a concentration group and is temporarily idle, rst the idle indicating circuit described in the foregoing is operated, so that an idle line to the proper distant city may be indicated, if one is available, in order that the idle line may be selected for use. If such a line is available, the attendant, by means of a patching operation, through the leg patching cord circuit, shown at the right of Fig. 3, will connect the new line to the concentration group and, as a result of the patching operation, the old line will be automatically released from the concentration group and the new line will function in its stead.

For the purposes of this explanation, it will be assumed that the line West has been previously .released from another concentration group in another position of the board and it will be assumed that it connects at the distant end to the desired distant termination. The line West will be used to replace the line east.

Plug 324 will therefore be inserted into jack lW when lamp SZIW lights, indicating that the line is idle. Plug 325 will be inserted into jack 3 I3. A circuit may then be traced from battery through the windings of relays 383W and SQZW in series, through the bottom innnermost front contact and armature of relay 3lilV7, relay SllW being operated while a line is released, through the sleeve of jack MSW, through the sleeve of plug 32d, sleeve of plug 325, sleeve of jack EL3 and the low resistance middle winding of relay 355 to ground. Relays 399W and 302W operate in series with the low resistance middle winding of relay SI5. Relay 355 operates. The operation of relay M5 in turn operates relay Sill. The

operation of relay breaks the leg path from the east line repeater into the hub 22| of the concentration group, disconnecting the east line from the concentration group and performs all of the other operations heretofore described attending the operation of this relay.

The leg of the new line repeater is connected through the tip of jack 3I6V, tip of plug 324, tip and break contact of jack 326, tip of plug 325, tip of jack 3|3, test resistance 3D3, break contact and armature of relay 3M into hub 22! to incorporate the line West into the concentration group.

It was pointed out that relays SISW and 302W operated in the west line which has replaced the east line in the concentration group. The operation o'f relay 3|9W connects ground to conductor IMW which extends into the winding of a relay in the West inverse neutral repeater corresponding to relay H3, which conditions the west repeater to function half duplex in the same manner as described for the east repeater. Relay 302W in operating in the new leg multiple circuit for the new line opens the idle indica-ting circuit for the West line as the West line has now been appropriated and disconnects ground from the leg of the repeater removing the permanent spacing signal which was transmitted to the distant Western terminal while the line was idle. The operation of relay 302W also locks relay 3|5W from ground through its top armature and front contact to hold relay 315W operated. The reason for this is that the west line was made available for use by a releasing operation, such as just described above, or by means of inserting a control plug into a control jack, as previously described. This operation is performed at another position in a jack corresponding to jack 3| 3W, namely at the particular position where the concentration group With which the West line is assumed to be normally associated is administered, The removal of the releasing plug would release relay 3l5W and reconnect the west line into the concentraion group With which it is normally associated. This is prevented by the locking of relay 3|5W when relay 382W operates.

The foregoing explains how a line released from the concentration group with which it is normally associated may be appropriated by an attendant to replace a line normally forming part of another concentration group.

The manner in which a line which is normally spare, as distinguished from a line which is released from a concentration group with which it is normally associated, is connected into a half duplex concentration group as a substitute for a line forming part of a half duplex concentration group will now be explained.

Replacing a Zine forming part of a half duplex concentration group with a, spare Zine As stated above, spare lines are distinguished from lines ordinarily forming parts of concentration groups, in that spare lines appear only in multiple jacks at each attendants position and are not extended through their leg multiple circuits into three individual concentration jacks at a particular position, through which they are extended to a hub so that they normally form part of a particular concentration group. A spare line may be appropriated, by means of a patching operation from one of its multiple jacks, at any position, to a particular jack in a line normally forming part of a concentration group, to replace a line normally forming part of a concentration group.

In order to replace a line normally vforming part of a concentration group With a spare line, a patch is made from a multiple jack of the spare line to the control jack of the line which is to be replaced.

For purposes of this explanation it will be assumed that the West line is now a spare line. In order that the west line may simulate a spare line, it will be assumed that its relay 30|W is permanently operated. Each spare line through,- out the board is arranged so that electrically it is the equivalent of a line which normally forms part of a concentration group, except that each of the circuits extending through the various armatures of its relay correspondingv to relay 30IW is closed through its respective front contact instead of through its back contact as shown for the normal unoperated condition of relay 3DIW in Fig. 3. Further, a spare line is not provided with a concentration jack circuit.

It will be assumed that the spare West line is to be used to replace the east line which normally forms part of a half duplex concentration group. First the idle indicator circuit is operated and a lamp such as 32|W is lighted indicating that the line is available. The plug 324 is inserted into jack 3|6W and plug 325 is inserted into jack 3I3.

As a result of this operation the tip of the spare line is extended into the hub of the concentration group in the same manner as described above. The sleeve of the spare line is extended over a circuit, exactly the same as described before, for a released line, starting from battery connected to relay 3l 9W in the spare line and ending in ground connected to relay 3I5 in the replaced east line. Relays 3|9W, 302W and SI5 are operated in series. Relay 3|9W in operating conditions the repeater in the West line to function half duplex as described heretofore. Relay 302W in operating disconnects the idle indicating circuit at its bottom armature and front contact. The operation of relay 302W also operates relay 3|5W as described above, but this performs no useful function in the case of a spare circuit, as it did in the case of a. released circuit described above. The operation of relay 3| 5 releases the replaced line from the concentration group.

Adding a released Zine to a half duplex concentration group It will now be assumed that the west line has been released from a concentration group at another attendants position and that it is to be added to the concentration group comprising the east line instead of replacing the east line.

It should be remembered that a plug such as 3|2 is inserted into a jack such as 3I3W in the attendants position, where it is assumed that the west line is normally associated into another concentration group. This operates relay 315W in turn operating relay 30|W in the manner heretofore described.

The attendant who desires to add a line operates the idle indicating key at the position Where the concentration group to which the line is to be added is administered. Once again the idle indicating lamps of all available lines are lighted.

`In order to add the West line to the concentration of which the east line forms a part, the attendant inserts plug 324 into line multiple jack vwith a released line or afspare line.

. line is a spare line.

315W Whenlamp 321W lights. Plug 325 is inserted into jack 321.

VAs a result of this operation the tip of the west ner heretofore described, through the sleeve oi i jack 3I6W, sleeve Vof plugs 324 and 325 and sleeve of jack 321 to direct ground. This operates relays 3I9W and 3(32W which conditions the West line for vhalf duplex operation, disconnects the idle indicator lamp circuit and provides `ground -to hold `relay 3l5W operated in the same manner as heretofore described.

It should be observed `that in the operation o1 adding a line, a different jack in the line concentration jack circuit normally forming part oi `a concentration group is used than the jack which is used for releasing a line or -for replacing a line forming part of a concentration group All of these latter operations involve a releasing operation, which must be performed by connection to -a jack such as 313 vwhich controls the operation of the releasing `relay such as 3&5. When aline is to be simply added to a concentration group, connection is vmade to :jack such as 321 and --the releasing relay remains unaffected.

Adding a `spa-re .line 4to .a half duplex concentration group A spare line may be added to a concentration group. It will be again assumed that the west That is, it is not provided with a group of individual concentration jacks and its relay SiilW is blocked operated,

The attendant, at the position Where the concentration group to which the spare line lis to be added is administered, operates the idle indicator control circuit and, when all of the lamps associated with idle lines light, selects the spare west line tration group of which the east line viorrns a part.

Plug 324 is inserted into jack 313W 'and plug 325 is inserted into jack 321 of the east line. The tip of the west line is connected. into the hub over a circuit heretofore traced. Relays :3! 9W and 3il2W operate vin the same manner and perform the same functions as described above. The west line thus becomes a part of the concentration group with which the east line is normallyassociated.

Supervision in half dupler patching operations assumed that the east line Ais `a spare :line in the idle condition and that a permanent spacing condition is imposed on vit at the distant ter minal.

In such cases, when -an idle indicating lamp lights in response to the operation of a key such for addition to the particular concen- .as lm2 by .an attendant who is y.seeking an available line to a particular distant city, a patch is `not made immediately to ia concentration group. Instead the attendant inserts the plug 50| of a `telegraph cord circuit, indicated `as Fig. 5A, into jack `5&2 of the splitting circuit of Fig. 5. The telegraph cord circuit per Fig. 5A is not shown in detail in this application as it is not a part ,of this particular invention. The attendant also inserts plug 324 rinto a multiple jack, such as 315 and plug 325 into jack 5o3 of Fig. 5. With these circuits interconnected `in this manner, the Vconductor over which communication signals are received over the line circuit incoming from the distant office is extendedthrough the tip of multiple jack 3|6, tip of plug 32d, tip and break contacts of jack 32S, tip of plug 325, tip of jack Itii'ii, 'tip yoi jack A582, tip of plug 55! and into the telegraph cord circuit, Where it passes ultimately through the winding of a telegraph receiving relay such as 5&1, to negative battery. At `the saine time ground is connected through vthe sleeve of jack A5il3, sleeve of plug 325, sleeve of plug sleeve of jack '316, through the'bottom innermost contact of relay V30| which is operated, and the `vvindings .of relays 392 and 3l!) to loattery. Relays 3l@ and 332 operate from the direct ground on the sleeve of jack 503. This operation of relay 382 removes ground from the path heretofore traced through the windings of relays H9 yand 153 to negative battery H5. This results in the removal of the Apermanent spacing signal which was being transmitted to the distant terinitial over Vthe east rline Aand a change of relays iii) ,and :llt `to marking. The operation of relay '3&9 operates relay H3 which changes the line repeater from the full duplex to the vhalf duplex condition.

When the marking signal is received at the distant terminal, the attendant thereat may respond .in such manner that the permanent spacing :condition Yimposed rat the kdistant oilice on relays iii! and H32 is rernoved and changed to marking. As a result of this, relays Hi8 and H2 mi. are .in turn 4changed to the marking condition.

When ground is removed from the armature of relay iii, the permanent spacing signal is re- ;nioved 4from conductor |20 and the tip circuit heretofore traced into fthe telegraph cord circuit. When. :the receiving relay i591 connected Ato the :tip circuit responds to the marking signal, the yattend ant `knows that the east line may be connect-ed 4into `the concentration group, or he may communicate with the distant attendant and cooperate in making any tests necessary to assure proper transmission of the line and associated repeaters. The attendant thereupon disconnects lplug '325 from `jack 553 and connects it instead into ajack vin a line circuit of the concentration group such as jack 313W or v321W depending upon Whether the line is to replace an existing line in a concentration group or be added to a concentration group.

Releasing u station Vcircuit from a. half duplex concentration group Static-n loops normally connected to a concentration group :may be released from the concentration group for test purposes, or for transfer to other `concentration groups or because their daily working period is ended. To perform this operation, a plug such as SI2 having its ring and sleeve conductors interconnected is inserted in a .lack such as 22d.

A circuit path is established as a result .of the above operation extending from ground, through the sleeve of jack 224, sleeve of plug 3I2, ring of plug 312, ring of jack 224 and bottom winding of relay 220 to battery, operating relay 220. The operation of relay 220 disconnects the station vfrom the concentration group, by disconnecting the loop repeater transmission lead from the hub 22| at the top armature and back contact of relay 220 and disconnecting the loop calling-in lead at the bottom armature and back contact of relay 220.

Adding a station circuit to a half. duplex concentration After a loop has been disconnected from a concentration group it may be added to a different concentration group by inserting the plug v324 into a jack such as 225 and the plug 325 into a line jack such as 321. This extends the tip or transmission conductor of the loop repeater through the tip of jack 225, tip of plug A324, tip and break contact of jack 326, tip of plug 325, tip of jack 321, into the hub 22| of the concentration group. It also extends the loop .repeater calling-in conductor through the ring ofiack 225, ring of plug 324, make contact of key 333, which is operated for this pulpGSe, ring f plu-g 325, ring'of jack 321 into the common calling-in conductor or signal hub 222.

While a station loop repeater is released, connection may be made to jacks such as 225 for testing purposes. This provides access to both the transmission conductor and the calling-in conductor of the loop repeater. Ground on the sleeve of the jack 225 is provided for controlling relays in the sleeves of cooperating testing cord 'or jack circuits.

Transmitting good night or permanent spacing signal When a station loop repeater is released, it may be arranged to transmit a permanent spacing or good night signal toward the station by inserting a control plug such as 328 into a jack such as 225. This connects ground from the sleeve of jack 225, sleeve of plug 328, tip of plug 329, tip of jack 225 to the transmission conductor of the loop repeater which transmits a permanent spacing signal to the station.

If it is desired to transmit a good night or Further, since the tip of jack 321 is common to the hub, a monitoring circuit, not shown, may be connected to jack 321 and signals may be received in the monitoring circuit from the hub over the tip of jack 321 and through the tip of the plug of the monitoring circuit.

Provision for testing and observing hits on a leg in a half duplex concentration group Jacks 223, 223B, 329, 329W and 326 provide means for connecting a testing circuit to a line or loop leg and testing it separately from the concentration group and for observing for hits by 4means of a trouble indicator'cord circuit, not

tor cord circuit to jacks such as 329, 223 or 326 will permit observation for hits occurring on the associated leg. When a line or loop leg is added to a concentration group through the medium of the patching cord terminating in plugs 324 and 325, such observations Will be obtained through jack 326.

Attention is particularly called to the resistances 2l9 and 2|9B in Fig. 2 and 353, 303W and 333 in Fig. 3. One end of each of these resist'- ances is connected to a tip conductor of one of each of the above jacks; The opposite end of each of these resistances connects through the contacts of the test relay to a ring conductor of the corresponding jack. These resistances are connected in series in the leg lead in each in'- stance. When signals are being received from a leg, a potential drop in a particular direction occurs in its associated resistance. When signals are being sent to the'leg through the resistance, the drop is in the reverse direction. Further, when signals received from one leg are sent to a group of legs associated together in a concentration group, a greater' current ows in this leg than when it is sending to a line or loop. The drop for the first of these conditions is therefore greater. This assumes that at least three repeater legs are joined in a concentration group. `If a linear loop is in trouble, so that it is causing random false spacing signals to be'transmitted toward the hub, this condition may be detected by connecting to jacks, such as 223, 223B, 329 and 329W, a device which is responsive to changes of potential across two points and which discriminates between such changes in reverse direction.

Relays 220, 229B, 394, 304W, and 334 each have a Winding connected between ground and the sleeve of an associated jack.` These relays are arranged so that they may be operated or remain released, depending upon the resistance inserted in the connection to battery in the sleeve circuit of the cooperating cord circuit. When a troubler indicator cord circuit is connected toany one of the jacks for the purpose of observing hits on the associated leg, since the trouble indicator cord is arranged to respond to a drop across the test resistance in a particular direction, the resistance must remain in circuit and the test relay remains unoperated.

Jacks 223, 223B, 329, 329W and 326 also provide means for monitoring on or communicating over a concentration group. The ring of each of these jacks' connects directly to the hub of the concentration group. An inverse neutral repeater terminated in a receiving device only for monitoring, or in a sending and receiving device combined for communication, may be connected by means of a plug to the ring conductor of each of these jacks. Under these circumstances, if it is desired to monitor on the Whole concentration group or communicate over the whole concentration group, the resistance of the connected sleeve circuit Will be high to prevent the operation of the relays, such as 22D, 304 and 334.

If it is desired to split the leg of a loop or a.

line oif from a concentration for testing it sep-l arately, connection is made to jacks such as 223, 329 and 32B and the sleeve of the connecting circuit 1s arranged so that it connects to battery through a low resistance to permit test relays such as 220, 304 and 334 to operate. This disconnects the associated leg from the concentration group. The leg is extended through the associated tip conductor and the hub 22| through the associated ring conductor of the cooperating jack into the connected circuit for testing. By connecting the inverse neutral repeater in the cooperating connected circuit through a splitting key, it is possible to communicate with the leg which has been cut oi from the hub over the tip or with the circuits which remain associated in the concentration group over the ring of jacks such as 223, 329 or 32S.

FULL DUPLEX CONCENTRATION GROUP A full duplex concentration group will now be described.

In a full duplex concentration group, separate independent hubs are required for transmission in opposite directions. The sending loops, receiving loops and lines may be connected together in various ways, depending upon the trafc requirements. The arrangement to be described will therefore be a typical arrangement. In this typical arrangement, a telegraph service board will be used to interconnect an east line, a west line and a local patrons station. Full duplex service is provided between the east terminal and the west terminal over the east and west lines in tandem. The patrons station is equipped with two loops for full duplex operation.

For full duplex operation, Figs. l, 6, '7 and 4 are arranged as indicated in the rectangular box Fig. B, bearing the legend Full duplex concentration group. including two lines and a local station comprising two loops. The two lines may be assumed to be an east line, which extends to a distant eastern terminal, and a west line which extends to a distant western terminal.

Although the detailed description will again assume the use of four-wire metallic line circuits, it should be understood that carrier line circuits, two path polar circuits or differential duplex line vcircuits may be used When terminated in the proper inverse neutral type of repeater which provides separate send and receive legs onl the drop side. The legs appear in leg multiple circuits as previously described and each leg is extended from the leg multiple circuit through a line concentration jack circuit to a hub. The sending leg of one line is connected through the hub to the receiving leg of the other line in each instance.

Since two hubs are required in full duplex operation, one for east-to-west transmission and one for west-to-east transmission, in order to provide a subscribers local station with full duplex service through such concentration groups, it is necessary to provide two separatey loop circuits extending from any subscribers premises to the telegraph service board. One such loop connects a local station circuit including a telegraph transmitting and receiving instrument at the subscribers premises with an individual in verse neutral loop repeater at the service board terminal. It is extended via. the leg of the loop repeater into an individual concentration jack circuit. From this loop concentration jack circuit it is connected into one of the two hubs.

In a similar manner a second sending and receiving instrument on the subscribers premises isA connected through a loop circuit to an individual inverse neutral loop repeater. It is extended via the leg of the loop repeater into an This exemplifies a typical arrangement individual concentration jack circuit. From the concentration jack circuit it connects to the other of the two hubs.

Thus, there is an individual hub and concentration group for transmitting in each direction. Both are independent.

In the case of iull duplex operation,V the concentration group for the east-to-.west hub and the concentration group ior the west-to-east hub are located at the same attendants position at the telegraph service board. If it is desired, a multiple appearancey of the concentration jacks may be provided at a second attendants position. The leg multiple jacks of the line circuits and the idle indicator lamps and control circuit are arranged in the saine manner as described above for a half duplex concentration group.

Refer now to Figs. l, 6, '7 and 4 arranged for full duplex operation. In the numbering of the apparatus for a ull duplex concentration group, numbers only, without any letter suixes, will be usedl as both station loops extend to thev station of but one patron and the sending leg of one line repeater is connected to the receiving leg of its cooperating line repeater.

It was shown in the description above that the east line in Fig. 1 was convertible from a full duplex to a half duplex and vice Versa. It was shownv that when a line was released froma concentration group or serving as a spare: line, the relay such as i i3' in the line repeater was released and the line repeater was conditioned to function as a full duplex repeater. In such` case two separate legs extended fromv the repeater through the leg multiple circuit. On the other hand, when a line was normally connected to a half duplex concentration group, relay l I3 was operated and only one leg from the line repeater was used,k in which case sendingl and receiving was performed over the single leg. In the arrangement now to be described, the line is normally connected into a full duplex concentration group. Under such a condition relay H3v remains released and two legs extend from the line repeater through the leg multiple circuit and into separate line concentration jacks for each leg. To. provide for the four line legs from the two lines, four sets of line concentration jacks are required. When signals are transmitted from the distant terminal to the east, negative battery and ground, are alternately connected to receive leg conductor |20. Conductor i20- connects through conductors 62?] and 120, through thef top outer armature and backV contact. of relay 1.0i, through test resistance 192, and the back contact and armature of relay m3 to hub 16,4 which is the east-to-west hub.

Thek send leg, by meansv of which signals are transmitted to the distant west terminal, is connected to the same hub, so that the east termi,- nal may transmit to the west terminal. The circuit may be traced from hub 'm4, through the ar- 'mature and back contact of relay 133', resistance T06, throughthetop inner back contact-and armature o relay i, through` conductors 136; S36 and |36 into the rectangle exemplifying therwest repeater and line. There theV path will be continuedl through the left-hand breakv contact and armature of a relay such as ll'3 (which remains released), through the bottom windings of relays such as H9 and i i8 in series, through resistances such as H1 and H6 in series to negative battery such as H5. Thus signals impressed on relays lill' and m2 at the east terminal` passi through hub lill! to a receiving relay such as |21 at the west terminal.

In a similar manner, signals impressed on relays vsuch as l iii and |82 at the west terminal connect negative battery and ground for marking and spacing through the contacts of a relay such as I |2 in the west repeater. These signals are impressed through conductors ISI, 63| and 13|, through the top outer armature and back contact of relay 181, through resistance 108 to hub 135, which is the west-to-east hub. From hub 185 a path may be traced through the armature and back contact of relay 'm9, resistance 1li), top inner back contact and armature of relay conductors 132, 632 and I 32, left-hand back contact and armature of relay H3, bottom windings of relays ||9 and H8, resistances ||1 and H6 to negative battery l5. This results, as has been previously shown, in the reception of signals by receiving relay |21 at the east terminal. vOne loop from the local station is connected through an individual loop repeater and an individual group of concentration jacks to hub 104, and the other through corresponding facilities to hub 155.

yIn tliestation circuit shown in Fig. 6 there is a telegraph key and a sounder in each loop. The equipment in the station loops may be varied to suit conditions. For example, where a station circuit is to be restricted to receiving only, the equipment on the loop would comprise only a sounder. The polar relay, by means of which 'the inverse neutral repeater receives signals transmitted from the local station and transmits them toward the hub, would be blocked in the mark position or would be removed from its jack mounting and replaced with a dummy relay base strapped to obtain the same eiect. Such loops would not be equipped for calling in the service board attendant, hence the call signal key, at the station, corresponding to key 221 in Fig. 2 and the differentially connected relay, such as 286 in Fig. 2, would be omitted.

AWith the concentration group described, the east and west line may communicate on a full duplex basis. Signals transmitted from the east tothewest terminal will be recorded by the sounder in-'one loop at the local station. Signals transmitted from the west to the east terminal will be recorded'by the receiving instrument in the other loop at the local station. The telegraph key in one loop at the local station may be used to communicate with the east terminal. .The ltransmitter in the other loop at the local station may be used to communicate with the west terminal.

Attention was called above to the fact that the connections for full duplex service are widely Variable dependent on` the traliric desired. As an illustration, it is possible to connect a group of lines such as described herein, so that they radiate from a service board in many directions and to interconnect all of their sending legs intoacommon hub. A loop from a local station having a transmitting instrument could be connected to the common hub to establish a broadcast arrangement. All of the receiving legs of line repeaters from the various distant terminals could be connected into a common hub and extended through a separate loop to the receiving instrument at the local station. Transmission from the various distant stations to the local station could'be scheduled on a time basis to prevent interference or, if one distant terminal were transmitting to the local station and a second Releasing a Zine from a full duplex concentration group The manner in which a line which normally forms part of a full duplex concentration group is released from a concentration group will now be described.

To exemplify this operation the east line will be released from the concentration group described above. To release the east line, a ring sleeve short circuiting plug, such as plug 3|2, is inserted in jack A1| This establishes a circuit from ground, throu-gh the sleeve of jack 1H, sleeve of plug 3|2, ring of plug 3|2, ring of jack 1|| and top winding of relay 1|2 to battery, operating relay 1|2. The operation of relay 1|2 in turn operates relay 10| over` an obvious circuit, to break the connections of the send and receive legs of the east line from hubs and 1M at the top inner armature and back contact and top outer armature and back contact, respectively, of relay 1|] The west line may be released by a similar operation performed in a corresponding jack in the west line.

Replacing a line forming pant of a full duplex concentration group with a line which has been released from a different concentratiOn group In order to substitute a released line for a line normally forming part of a full duplex concentration group, it is first necessary to nd a released idle line Vto the desired distant terminal which is available to serve as a substitute. In the case of all idle lines, both released and spare, a path is closed from ground connected to the filaments 'of the idle indicating lamps of each circuit in multiple, through its associated leg multiple circuit, to battery in the idle indicator control circuit. The attendant operates the idle indicator control key at the position Where the concentration group is being administered. This lights the multiple lamps of every telegraph line in the service board which is not at the moment serving in a concentration group. The attendyan1;4 selects one connected to the desired distant terminal from reference to a designation strip associated with the lighted lamps. A patch is made from the multiple jack associated with the available line, at the attendants position Where the concentration group is administered to the control jack of the line in the full duplex concentration group which is to be released and replaced bythe newline. vThis automatically releases the old line; and connects the two legs of the new line into the'tWo hubs.

It will be assumed, in order to demonstrate this operation, that the concentration group con- Vsists of the west line and the local station loops. It will be assumed also that the east line is idle. The' eastV line, it will be assumed, normally forms part of another concentration group instead of the concentration group described above, from which other concentration group it has been released by an operation such as described in the preceding section herein.

Under the above circumstances, the two line concentration jack circuits associated with the two 'legs of theveast line would appear at the position where rthe concentration group with vvhichthe east line is normally associated is ad-

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