Manual / Guide · 1955
AE Training Bulletin 810: Pulse Repeaters
Pulse repeater operation.
Manual / Guide · 1955
Pulse repeater operation.
! al A U T O M A T I C ELECTRIC TRAINING SERIES Bulletin al PULSE 1 I REPEATERS "8 O R I G I N A T O R S O F T H E D I A L T E L E P H O N E 810 This is one of the helpful booklets in the AUTOMATIC ELECTRIC TRAINING SERIES on STROWGER AUTOMATIC TELEPHONE SYSTEMS E l e c t r i c a l P r i n c i p l e s of Telephony Mechanical P r i n c i p l e s of Telephony Fundamentals of Apparatus and Trunking T h e Plunger Lineswitch and Associated M a s t e r -Switch R o t a r y Lineswitch The Connector The Selector Pulse Repeaters Trunking Power and Supervisory Eq uipment P a r t y - L i n e Connector E: and ~ r u n k - ~ u n t i n g Connectors Reverting-Call Methods The T e s t and Verification Switch T r a i n Toll Switch T r a i n Switching Selector -Repeater P r i v a t e Automatic Exchanges with PABX Appendix Community Automatic Exchanges Manual Switchboards Linef inder Switches May we send you others pertaining to equipment in your exchange? CONTENTS Page . . . . . . . . . . . . . . . . . . . . 1 D-c pulse-repeating methods . . . . . . . . . . . . . . 1 Loop pulsing . . . . . . . . . . . . . . . . . . . 1 Battery pulsing . . . . . . . . . . . . . . . . . . 2 Simplex dialing . . . . . . . . . . . . . . . . . . 2 Composite dialing . . . . . . . . . . . . . . . . . 2 1 . INTRODUCTION . FUNCTIONS O F PULSE REPEATERS . . . . . . . . . . . . 2 3 . ONE-WAY PULSE REPEATERS (Loop-pulsing type) . . . . . . 3 4 . REPEATERS FOR TWO-WAY TRUNKS . . . . . . . . . . . 5 Loop-pulsing type . . . . . . . . . . . . . . . . . . . 6 Battery-pulsing type . . . . . . . . . . . . . . . . . . 7 5 . TWO-WAY PULSE REPEATER (SX dialing) . . . . . . . . . . 8 Outgoing call . . . . . . . . . . . . . . . . . . . . 8 Incoming call . . . . . . . . . . . . . . . . . . . . 10 Recording-completing ("C .L. R.") holding . . . . . . . . . 11 6 . PULSE-CORRECTING REPEATERS . . . . . . . . . . . . . 12 One-way incoming pulse-correcting repeater . . . . . . . . 12 7 . OTHER REPEATERS AND PULSING METHODS . . . . . . . . 1 4 Repeaters f o r two-way automatic-to-manual trunks . . . . . . 14 Switching selector-repeater . . . . . . . . . . . . . . . 14 Selector.repeater . . . . . . . . . . . . . . . . . . . 14 High-low supervision . . . . . . . . . . . . . . . . . 14 Duplex signaling . . . . . . . . . . . . . . . . . . . 14 A-c dialing . . . . . . . . . . . . . . . . . . . . . 14 Voice-frequency dialing . . . . . . . . . . . . . . . . 14 Carrier-frequency dialing . . . . . . . . . . . . . . . 1 4 2 Typical One-Way Impulse Repeater PULSE REPEATERS 1.0 INTRODUCTION Impulse repeaters a r e devices consisting principally of relays, which relay (or repeat) dial pulses originating in one office to the switching equipment in another office. They a r e used in conjunction with Strowger automatic telephone systems and are employed a s fixed components of inter-office trunks. While the repeater derives its name from its repeating function, there a r e three principal reasons for employing repeaters on inter-office trunks. These are: {A) ECONOMY - T h e need f o r a third (control) wire in the inter-office trunk is eliminated thereby reducing wire expense. T h e r e p e a t e r accomplishes this (when engaged in a call) by placing a "holding" ground on the control circuit to all preceding switches in the train. - (B) TFUINWESON EFF'ICLENCY Since the performance of a telephone transmitter is dependent upon the amount of direct-current flow, it is desirable to restrict the distances over which transmission current is supplied. This i s accomplished on inter-office trunk calls by having the repeater in the originating office (instead of the connector in the distant office) supply current to the calling telephone. The transmission efficiency of the calling station is therefore the same on inter-office calls a s on local calls. jC) REPEATING OF IMPULSES - The need to repeat impulses which arise8primarily from the preceding two functions, provides still another important advantage. This advantage is an inherent characteristic of the relaying process in that a new source of impulsing c u r r e n t is introduced a t each relaying (repeating) point. The impulsing current on the respective portions of the circuit is consequently maintained at a level, higher than if cwrent were supplied from one source through the entire telephone circuit. This higher impulsing current assures better impulsing performance. Impulse repeaters which can relay calls in an outgoing to originate from both ends of a trunk (two-way trunk) then an impulse repeater is required in each office. Where calls originate from only one end of a trunk (one-way trunk) the other (terminating) end may be connected directly to an incoming selector, connector or "incoming repeater" in the terminatingoffice. ("Incoming repeaters" relay only the calls received at offices to the incoming equipment in those offices. These a r e discussed in section 6. The sections preceding section 6 a r e concerned mainly with repeaters of the "outgoing" variety.) Impulse repeaters can be classified generally into three categories. These a r e one-way repeaters, repeaters for two-way trunks and two-way repeaters. The one-way repeater relays calls in one direction only (outgoing) and is employed on one-way trunks. A repeater for two-way trunks is essentially a one-way repeater which has been properly adapted to allow two-way operation of inter-office trunks. When such repeaters a r e part of a trunk circuit, the repeater at one end is automatically "busied out" to prevent its seizure, if the repeater at the other end has been seized for a call. The two-way impulse repeater relays impulses in two directions and is seized from either end of the trunk. However, the conditions involving the use of two-way repeaters, plus the general requirement of reducing 3-wire facilities to two-wire inter-office trunks, require that a two-way repeater be employed at each end of the trunk.. Both repeaters a r e active on calls originating from either end of the trunk. Two-way impulse repeaters a r e employed where it is desirable to insert repeating coils in the transmission circuit (for the elimination of noise, matching of impedances) or where the requirement of using composite o r simplex dialing makes the introduction of repeating coils compulsory. 1.1 D-C Purse Repeating Methods Impulse repeaters may employ one of several (d-c) methods for repeating dial impulses a s follows: loop pulsing, battery pulsing, simplex (SX) dialing and composite (CX) dialing. The schematics accompanying the explanation of these methods below, a r e greatly simplified. - (A) Loop Pulsing Figure 1 illustrates the looppulsing method. When the impulse repeater i s seized at the local (originating) office the loop circuit i s closed direction, are located in the offices which originate calls t o the line relay (A-1) of an incoming switch in the over inter-office trunks. Thus, if it is possible for calls distant office. When line relay A of the local repeater STROWGER AUTOMATIC (D) Composite Dialing - Figure 4 shows the composite method of impulsing which is similar to the simplex method. The trunk is composited as shown and the line relay of the originating repeater responding to dial impulses, alternately connects and disconnects resistancebattery to a dial leg. At the distant (terminating) end, a relay (A-1) opens and closes the loop to the incoming switch. The dial leg return is made through ground. (For additional information regarding simplex and composite s y s t e m s r e f e r to A.E.Co. Bulletin 331 entitled, "Repeating Coils and Their Uses.") (B) Battery Pulsing - The battery-pulsing method is illustrated in figure 2. Line relay A of the impulse repeater in the local (originating) office, follows the dial pulses and alternately connects and disconnects resistance-battery and resistance-ground to each side of the trunk, respectively. At the distant end, the inter-office trunk is connected through each winding of line relay A-1, to ground and negative-battery respectively. Thus, the batteries at both the originating and terminating offices, are employed for impulsing, return for each side of the trunk being made through ground. The use of two batteries in this fashion perm its dialing over longer trunks or trunks of higher resistance. 2.0 FUNCTIONS OF IMPULSE REPEATERS (C) Simplex Dialing - With this method, (illustrated in figure 3) repeating coils are employed at the ends of the inter-office trunk. The dial leg is derived from the mid-points of each repeating coil as shown; the operation of the line relay in the originating repeater, alternately connects and disconnects resistance-battery to the dial leg. At the terminating end, a relay (A-1) associated with the dial leg alternately opens and closes the loop to the incoming switch causing it t o step. Return, a s in all simplex systems, is made through ground o r a REPEATER The repeater performs a variety of functions in order to accomplish the purposes enumerated in section 1. In general, these functions, listed in the order in which they occur, are: (a) To ground the control lead at the originating exchange in order to hold all of the preceding switches in the train operated. (b) To m a k e itself busy against s e i z u r e by other c a l l s . I INTER - OFFICE I INCOMING SWITCH I A LINE RELAY TRUNK 1 Fig. 1 LOCAL REPEATER R1 "'+'"-'-7*1-----LlNE RELAY A SYSTEMS ground lead. It should be noted that this dialing arrangement r e q u i r e s the use of a repeater a t each end of the trunk. responds to the dial pulses, the loop to the distant office is alternately opened and closed. This causes line relay A-1 of the incoming switch to correspondingly restore and operate and step the switch towards the desired line. LOCAL TELEPHONE I I Fig. 2 I 1 (DISTANT OFFICE) Al LINE RELAY Loop Pulsing I INCOMING SWITCH (DISTANT OFFICE) I 7 1 LINELELAY Battery P u k i n g PULSE LOCAL REPEATER (ORIGINATING) , REPT. COIL II INTER- OFFICE .RUN% I Y z 4. m -I 4 U I I I I ------- I I I +LINE m REPEATERS I 1I I I I I I I ------- I . I I "H"v - DIALLEG I I I I Fig. 3: DISTANT REPEATER (TERMINATING) . REPT. COIL ' ; rz 0 9 L -SW. 5U E 0 I- , A1 DIAL LEG c Simpler Dialing Fig. 4. Composite Dialing (c) To close the loop to an incoming switch in the called office and to repeat impulses to the switches in that office. (d) To reverse the current supply polarity to the calling telephone Tor answer supervision when the connector in the called office reverses battery polarity at the distant end. (e) To supply transmission current to the calling telephone. (f) To allow all the switches involved in establishing the connection, to release when the calling party's handset is replaced. While the method of performing these functions may vary with repeaters of different design, the types described in the next three sections will afford an understanding of the techniques involved. 3.0 ONE-WAY TMPULSE REPEATER (LoopPulsing Type) The circuit of a typical one-way impulse repeater for use in conjunction with battery-searching selectors, is seen in figure 5. When the repeater is seized by a preceding switch (usually a local selector) a circuit i s established between both windings of relay A over the calling loop. This circuit may be seen by tracing from ground on relay A , tfirough the associated 200-ohm winding, a break contact on relay D, out over the + LlN3, through the calling telephone, back over the - CINE, through another break contact on relay D, and the other 200-ohm winding of relay A to negative-battery. Relay A operates, connects the + TRK lead with the + LINE and places ground on relay B. Relay B operates; (1) places ground on the top (polarizing) winding of shunt field relay E , (2) places ground on the C lead which holds the preceding switches operate$ and guards the repeater against seizure by other switches, (3) STROWGER AUTOMATIC TELEPHONE SYSTEMS prepares a circuit to relay C, (4) disconnects the - TRK lead from relay D and associates it with the - LINE thereby completing the transmission circuit. The latter action also closes the trunk loop to an incoming switch in the distant office, through the bottom winding of relay E. Relay E, a shunt field relay, does not operate at this time because of the opposing field polarities of i t s top and bottom windings. 3.2 Talking Circuit .< When the called party answers the current polarity over the trunk is reversed. This reverses the current through the bottom winding of relay E. The magnetic fields of the bottom and top windings now aid, and relay E operates. Relay E operating, places ground on relay D. Relay D operates, places a second ground on the C lead and reverses the calling line connections to relay A. Relay A now supplies transmission current in reverse polarity to the calling telephone for supervisory purposes. The circuit is ready for transmission. 3.1 Impulse Repeating The impulses delivered by the dial of the calling telephone alternately restore and operate relay A of the repeater which opens and c l o s e s the trunk loop. Each time relay A restores, ground is extended to relay C (slow D Figure 6 shows, in simplified form, the transmission circuit of the inter-office call through the repeatered 1 E C B A SHUNT-FIELD RELAY -t *CHI* C UI TEST 4 500 STOPPING BATTERY * 1 . 1800 1 +TRK. H-61873 Fig. 5. One-Way (Outgoing) Tmnrrlse Repeater r e l e a s e ) through a make contact on relay B (slowrelease). Relay C operates and remains operated during each s e r i e s of impulses (dialed digit of call number); relay B remains operated during the entire impulsing seauence. MODIFIED - Loop Pulsing trunk. It will be seen that transmission battery to the calling telephone is supplied through the windings of the repeater's line relay. The called telephone receives transmission current from the back-bridge relay of the connector in the distant office. The bottom winding of the shunt-field relay, bridging the trunk completes the trunk loop to the line relay of the connector. This holds the switch train in the terminating office and makes its r e l e a s e dependent upon the action of the repeater. Relay C operating, (1) places a low resistance (100 ohms) shunt across the bottom winding of relay E to reduce loop resistance during impulsing, (2) removes 500-ohm battery from the C lead. During the pause between successive digits, relay A remains operated and keeps ground from relay C while replacing it on relay B. Relay C restores and removes the 100-ohm shunt from the bottom winding of r e l a y E. T h i s p r e p a r e s the circuit for transmission through condensers P and N. Each timethe 100-ohm shunt is removed bythe restoration of relay C, the bottom winding of relay E remains bridged a c r o s s the trunk and thus, maintains a closed loop for holding the switches in the distant office. (This "holding bridge" is of a sufficiently high impedance, s o as to limit or prevent the by-passing of voice currents during Relay A restoring; (1)opens the trunk loop which releases the switch train in the distant office - this action also de-energizes the bottom winding of relay E, (2) opens the circuit to relay B. Relay B is slow to release so transmission,) that the circuit to relay C is momentarily maintained, 3.3 Releasing the Repeater (A) Calling Party Disconnects F i r s t - Referring to figure 5 again, when the handset at the calling telephone is replaced, the circuit to line relay A i s opened which allows relay A to restore. 1 t , PULSE , REPEATERS Therefore, upon the restoration of relay A, relay C momentarily operates. The utility of this particular feature i s made apparent in section 3.3B following. Relay B restores; (1) completely opens the transmission circuit by disconnecting the - TRK lead from condenser N, (2) removes ground from, and thereby de-energizes the top winding of relay E, (3) removes multiple ground from the C lead, (4) opens the circuit to relay C. Relay C r e s t o r e s and re-establishes the circuit t o 500-ohm stopping battery. Relay E restores, removing ground from relay D. Relay D restores; (1) removes ground from the C lead (which releases the local switch train) and r e p l a c e s i t with 500-ohm stopping battery, (2) r e v e r s e s the line connections to relay A t o normal. The trunk circuit is now available for additional calls. (B) Called Party Disconnects First - When the called party r e p l a c e s the handset, battery polarity t o the repeater over the trunk leads, is again reversed. This r e v e r s e s the field polarity of the bottom winding of which now the of the (polarizing) winding' therefore restores and ground f r o m relay D. Relay D restores; (1)reverses the calling line connections to relay A to normal, (2) replaces multiple ground on the C lead with 500-ohm battery. The circuit remains in this condition and the switch trains in both offices a r e held, however, until the repeater i s released by the calling. party. . When the calling party finally disconnects, the circuit to relay A i s opened. Relay A restores; (1) opens the trunk loop which de-energizes the bottom winding of relay E and r e l e a s e s the switch train in the distant (called) office, (2) removes ground from relay B and places it on a make contact of relay B. As relay B is slow to release, ground is extended through this make contact, to relay C which operates momentarily. Relay C disconnects 500-ohm battery from the C lead and thus provides a short interval (immediately after the release of relay B) during which the preceding switch train in this (originating) office, is given time to release and the repeater is guarded against seizure. Relay R restoring; (1) de-energizes the top winding of relay E, (2) removes ground from the C lead, (3) opens the circuit to relay C . Relay C restores and replaces 500-ohm battery on the C lead. The circuit is again at normal. 3.4 Busying Repeater From Distant End If the circuit is in normal condition, the repeater can be busied from the distant end by grounding the - TRK lead. Ground on this lead operates relay D of the repeater. Relay D busies the switch by replacing 500-ohm battery on the C lead with ground. Relay D will remain operated until the trunk lead is ungrounded at the distant end. 4.0 REPEATERS FOR TWO-WAY TRUNKS Two-way operation of inter-office trunks may be accomplished through the use of what are essentially one-way repeaters, properly adapted for the purpose. While t h e s e r e ~ e a t e r srelav imuulses in onlv one direction (outgoing) they allow two -way operation of trunks by incorporating an arrangement wherein the trunk leads a r e normally associated directly with an incoming selector (or connector). On an incoming call, the repeater is inactive insofar a s the repeating of impulses or transmission of voice currents is concerned. When the same repeater is seized for an outgoing call, the trunk leads a r e automatically transferred from the incoming switches to the repeater. A "repeater for two-way trunks" is to be distinguished from a "two-way" repeater which relays impulses in both directions incoming and outgoing. Where two-way trunking i s employed with either type, however, a repeater is required at each end of the inter-office trunk. Several typical examples of repeaters for two-way trunks are given below. - CALLING LINE Fig. 6. Transnission Circuit of the Inter-Off ice C a l l STROWGER AUTOMATIC 4.1 Repeater For Two-Way Trunk (Loop-Pulsing Type) . with ground. The repeater at this (terminating) end is therefore, busied and safeguarded against seizure by the local selectors during an incoming call. Figure 7 illustrates the circuit of a typical repeater (loop-pulsing type) for two-way trunks. This circuit is almost identical to that shown in figure 5 (one-way) but another relay, designated "H", is provided. The trunk D A TELEPHONE SYSTEMS 4.11 Release - Release of this repeater is accomplished in virtually the same manner a s that of the one-way 8 C E 500 (SHUNT-FIELD) T"\/\r.lwH~. t IT" 4 4 .STOPPING BATTERY -TRK. D J A C K '1- TEST +TRK. H-61412 BUSY KEY A.T.B. MODIFIED T O INCOMING SELECTOR OR CONNECTOR Fzg. 7. Repeater for Two-Way Trunk - Loop Pulszng leads a r e normally connected to an incoming selector or connector through a pair of break contacts on relay H. When the repeater is seized from the local selector banks with subsequent operation of relay B, ground is extended to relay H which disconnects the trunk from the incoming switch and connects it to the repeater. On an incoming call when the repeater at the distant end has been seized, the loop to the incoming switch at this end .is closed through the break contacts of relay H. The incoming switch (selector o r connector) upon being seized, places ground on the CSW lead. Relay D receives this ground through a break contact on relay H, and operates. Relay D operating, removes 5 0 0 - o h stopping battery from the local selector C lead and replaces it ORIGINATING OFFICE REPEATER Fig. 8. type described in section 3, the relays restoring in the same sequence. The additional relay H i s de-energized upon the restoration of relay B. Relay H i s slow to release so that on outgoing calls, the switch train in the called office has time to release before the incoming switch in this (originating) office i s reconnected to the trunk. This prevents the incoming switch in this office from "locking up" to the switch train in the called office should the called party disconnect last. If the restoration of relay H were not delayed, in this instance, reverse battery polarity irom the connector in the terminating office, would remain on the trunk a t the time when the incoming switch in the originating office was reconnected to the trunk (Figure 8). TERMlNATlNG OFFICE REPEATER Demonstrating Manner in which Incoming Switch at Originating End might "Lock Up" to Switches at Terminating End if Re lay H were Fast Re leasing --% 1 PULSE REPEATERS 4.12 All Trunks Busy (A.T.B.) Feature - The "All Trunks Busy" (A.T.B.) feature seen in the circuit of $ figure 7 (omitted from figure 5 for simplicity) provides an indication of, and supervision over an all-trunks-busy condition. This feature or a similar feature is widely employed in impulse repeaters. It will be seen from figure 7, that upon seizure and the subsequent operation of relay B, ground is removed from the A.T.B. lead. If this trunk circuit were the last available, all grounds would then have been removed from the A.T.B. lead. Absence of ground on this lead can be made to operate an A.T.B. meter o r other supervisory. equipment by releasing a normally operated relay. The ground is restored to the A.T.B. lead when the repeater is released and the trunk is again available for use. - When the trunk i s seized from the distant end, the incoming switch at this end, places ground on the CSW lead. example, on an outgoing call, when relay A restores on the f i r s t pulse, relay C (slow release) i s energized. Relay C operates make-before-break contacts which; (1)prepare resistance-ground and resistance-battery to the - TRJS and + TRK leads respectively, through pairs of make contacts on relay A, and (2) remove the original seizing bridge (number 1 winding of relay E) from the trunk. (Relay C operating, also shunts the number-1 winding of relay E momentarily with a resistance 1000 o h m s - in o r d e r to absorb inductive kicks.) Therefore, whenever relay A operates during the succeeding pulses of the series, it connects resistanceground and resistance-battery to the + and - trunk leads. This aids the rapid reoperation of the distant pulsing relay between pulses (open periods) and assures reliable pulse repetition (See Sec. 1.1B). At the end of each f TEST JACK -1. D -LINE TEST JACK N - 150 4 P +LINE If I\ \ ? - , t SELECTOR OR CONNECTOR H.61866 Fig. 9. Repeater for Two-Way Trunk - This operates relay D to busy the repeater (See Sec. 4.1). Relay D operating, removes ground from the A.T.B. lead. until the trunk i s released at the distant end. series, relay C restores, removes resistance-ground and resistance-battery and replaces the original seizing bridge. 4.2 Repeater For Two-Way Trunk (Battery-Pulsing-Type) 4.21 Answer (Reverse Battery) Supervision - Reverse battery supervision in this repeater occurs in a manner s i m i l a r to that stated for the one-way repeater in section 3.2; in this case, however, the operation of relay D also breaks the circuit to relay C and disconnects the C lead from relay H. Relay H, however, i s held by a multiple ground on relay B. A simplified schematic of a battery-pulsing type of r e p e a t e r for two-way trunks, is shown in figure 9. This circuit i s broadly similar to the loop-pulsing type shown infigure 7 except that each side of the trunk i s pulsed with resistance-ground and resistance-battery, respectively. A three-pole relay performs approximately the same functions in this repeater that the shunt field relay p e r f o r m s in the previously described types. Relay H in series with negative-battery provides stopping battery for the local (battery-searching type) selectors. The operation of this repeater otherwise closely parallels - MODIFIED - B a t t e r y Pulsing ; that given in section 4.1 for the loop-pulsing type. There are, however, a few notable points of variance: For The circuit to relay C is broken so that jiggling of the hookswitch or inadvertant movement of the dial at the calling end, will not result in the loss of the switch train at the called end. .This could occur (assuming a continuous circuit t o relay C) when relay A restores upon the first (accidental) pulse. Ground would then be extended to relay C through a make contact on relay B. Relay C operating, would remove the holding bridge and ST ROWGER A U TOMATlC close resistance-ground and resistance-battery to the trunk. Since this ground and battery would appear on the trunk in the same polarity a s the reverse battery being sent back by the distant office connector, no current would flow over the trunk and the switches in the distant office would consequently release. This condition i s not encountered in the loop-pulsing repeater described previously, as the holding bridge is replaced immediately after each impulse (break interval). 4.22 Release - Release for the repeater is similar to that given for the loop-pulsing types in sections 4.11 and 3.3 with minor variances. F o r example, when the calling party restores first; (1) relay A upon restoring, disconnects both sides of the trunk from condensers N and P, (2) r e l a y C is prevented from momentarily operating upon the r e l e a s e of A because of a break contact on relay D in i t s circuit. 5.0 TWO-WAY IMPULSE REPEATER (SX Dialing) The two-way impulse repeater relays impulses in two directions and performs essentially the same functions as the repeaters previously described except that these functions a r e performed whether the circuit is seized f o r a n outgoing o r a n incoming call. As a two-way r e p e a t e r is r e q u i r e d a t each end of the trunk, the repeating of dial pulses during a given call takes place at both the originating and terminating ends. Simplex o r composite dialing is often employed with two-way repeaters. The circuit shown in figure 10 illustrates a typical two-way repeater for SX whose operation is explained below. I 1 , I The pull-out drawing (Fig. 13) at rear of bulletin shows a two-way trunk circuit equipped with these repeaters. Portions of the originating and terminating repeaters, respectively, have been eliminated t o show only the active components for a call in the direction indicated. T h e following circuit conditions should be noted in examining this SX repeater: (a) The dial leg is connected to ground at both ends when the circutt is idle. (b) When the circuit is seized, battery is connected to the dial l e g a t t h e originating end; dial pulses a r e transmitted in the form of battery pulses. (c) Answer supervision i s given at the terminating end by transferring the dial leg from ground to battery. (d) Battery i s connected to both ends of the dial leg during conversation. (e) Release supervision is given when one end of the dial leg is transferred from battery to ground. T h e s e conditions f o r pulsing and supervision a r e referred to as "battery-ground" or "positive-negative" pulsing and supervision. (The same conditions would apply if t h i s r e p e a t e r w e r e used. on a composited, CX, circuit.) TELEPHONE SYSTEMS 5.1 Outgoing Call (Refer to "originating" repeater of figure 13) 5.11 Seizure - The repeater is marked "idle" to the local (battery searching) selectors by the presence of resistance-battery on the C lead. (Resistance-battery is provided by the number -2 winding (500 ohms) of relay G in s e r i e s with negative-battery.) When the control wiper of a local selector encounters stopping battery on the C lead of the r e p e a t e r , a circuit i s established to ground causing relay G to operate. (The operation of relay G at thispoint is inconsequential.) At the s a m e time the loop from the calling party to relay A, is established and relay A operates. This circuit may be seen by tracing the leads from relay A to break contacts on H, through the - TALK and + TALK leads and the windings of the repeating coil, over the LINE and + LINE leads, to the calling party. Relay A operates and places ground on relay B. Relay B operates and; (1) c l o s e s ground to the number-1 winding of relay K, (2) connects together the CH IN and CH OUT leads to close this repeater's portion of the all-trunksbusy (A.T.B.) chain circuit, (3) disconnects the dial leg from relay A-1 and connects it to relay E through a make contact on A. - Relay Koperates, grounds the C lead to hold the preceding switches and, a t the same time, opens the circuit to relay G which now restores. At the terminating end of the trunk the dial leg i s connected to ground (in a similar repeater) through the windings of relay A-1 of that repeater. The resistance-ground on the distant end of the dial leg causes relay E of the originating repeater to operate. (Relay A-1 of the distant repeater also. operates to inaugurate the seizure of that repeater See Sec. 5.21). Relay E operating, keeps ground from relay D. The circuit is now ready to repeat the dial pulses t o the terminating office. 5.12 Repeating Impulses (Relays now operated: A, B, E, K) - Relay A alternately restores and operates in response to the d i d impulses from the calling telephone. Each time relay A restores, negative-battery (through the windings of relay E) i s removed from the dial leg. Pulsing the dial leg in this fashion, causes the terminating repeater t o relay the dial impulses to the incoming s e l e c t o r o r connector a t that end (See Sec. 5.22). Whenever relay A restores during the impulsing, ground is removed from relay 33 and extended to relay C through a break contact on D and a make contact on K. Relay C (slow release) operates on the first pulse of each series (digit of the call number) and remains operated during each series. (Relay B remains operated throughout the entire impulsing sequence.) - Relay C operating, places 100-ohms, through a make contact on K, in multiple with relay E to improve impulsing over the dial leg. (When relay E is shunted by this 100-ohms, it may restore and remain so during impulsing.) At the end of each series of impulses, relay A remains operated, removing ground from relay C. The interval before the impulsing of the {sw. 0 01 G A1 E A El H Dl K 0 REPT. COIL / -LINE -TRK I +TALK -Ti< TO A T R (,, IN 1 ,- f Fig. 10. Two-Way Repeater - SX D i a l i n g A P H-61849 M O D I F I E D STROWGER AUTOMATIC TELEPHONE SYSTEMS next series is now sufficient to allow relay C to restore. Relay C restoring, removes the 100-ohm shunt from relay E. Relay E will again operate if it h a s meanwhile restored as explained above. releases relay A-1 in the terminating repeater which results in the complete release of that repeater and the associated incoming switch train (See Sec. 5.24B). T h e circuit is now at normal. At the end of the entire impulsing sequence, the switches in the terminating office have extended the call to the desired party and now automatically ring the called line. 5.2 Incoming Call (Refer to "terminating" repeater of figure 13) 5.13 Called Party Answers (Relays now operated: A, B, E, K) - When the called party answers, the dial leg at the terminating office, i s transferred from ground to battery (See Sec. 5.23). As this battery i s in the same polarity as the battery furnished through relay E a t this end, relay E restores'and completes a circuit from ground (on a relay B contact) to relay D. Relay D operates and r e v e r s e s battery polarity (for supervision) t o the calling party. The circuit is ready for transmission. 5.14 R e l e a s e (Relays now operated: A, B, D, K) - (A) Calling Party Disconnects First When the calling party. disconnects, the loop circuit to relay A is opened. Relay A r e s t o r e s , removes ground from relay^ and removes battery (through E) from the dial leg. Relay B restores; (1) opens relay K, (2) opens relay D, (3) transfers the dial leg to ground through relay A-1 and (4) opens the A.T.B. chain circuit. Relay K r e s t o r e s and removes ground f r o m the C lead which permits the preceding switch train to restore. Relay D restores and reverses the calling line connections to normal. (The terminating repeater releases when ground is placed on the dial leg and the trunk circuit is again at normal - See Sec. 5.24A. T h e dial l e g is in the idle o r normal condition when ground h a s been applied at both ends.) - (B) . Called Party Disconnects F i r s t - When the called party disconnects first, ground appears on the dial leg as the result of the partial restoration of the terminating repeater. (See Sec. 5.243). The originating r e p e a t e r then operates as follows: Operates from ground On the dial leg and opens the circuit to relay D. Relay D restores and reverses battery over the calling loop for supervisory purposes. The r e ~ e a t e rwill be held in this condition until the callingparty disconnects. When the calling party disconnects, relay A restores and opens the Circuits to r e l a y s E and B. Relay B restoring, opens the circuit t o relay K and removes (through from the dial leg, it with ground from relay A-1. In the interval after relay A releases, but before B and K release, ground from a On A, 'perates C. C operating, opens the circuit to relay D t o prevent its re-operation from ground On a contact' When restores, i t opens the circuit to relay C and removes ground f r o m the local selector C lead t o release the preceding switch train. Note that the restoration of relay B removes battery from the dial leg and replaces it with ground. This action 5.21 Seizure - The terminating repeater is seized from the originating end when resistance-battery i s placed on the dial leg by the originating repeater (See Sec. 5.11). Resistance-battery on the dial leg operates relay A-1 in the terminating repeater. Relay A-1 completes part of a c i r c u i t f r o m the - LINE to the SW lead of the incoming switch (selector or connector) and closes ground to relay B -1. Relay B -1 grounds the number -1 winding of relay H and the number -2 winding of relay E -1. Relay E-1 i s merely polarized by this action but relay H operates. Relay H operating; (1)connects the SW lead to the - LINE lead, (2) completes the loop to the incoming switch. This loop may be more clearly seen by tracing the + SW lead t o a make contact on relay H, out on the + LINE lead, through a winding of the repeating coil, over the + TALK lead through the number-1 winding of relay E-1 and the number-2 (non-inductive) winding of H, back over the - TALK lead through another winding of the repeating coil over the - LINE lead t o a make contact on r e l a y A-1 to the - SW lead. - - Relay H also grounds the C lead to make the repeater busy to the local selectors and in addition, connects the CH leads together to close this repeater's part of the A.T.B. chain circuit. Relay E-1 does not operate a t this time because of the opposing field polarities of its windings. This repeater is now ready to receive the dial pulses from the originating repeater. - 5.22 Impulsing - (Relays now operated: A-1, B-1, H) Relay A-1 follows the pulses coming over the dial leg from the originating office and alternately opens and closes the line loop to the incoming switch causing it to step. When r e l a y A-1 r e s t o r e s on the f i r s t pulse: from a (1) ground is extended to relay C (slow contact on A-1through a make contact on B -1 and a (2) the same ground is also break contact on extended t o r e l a y G through i t s 1 and 2 windings. Relay C operates and remains operated during each s e r i e s of impulses. Operation of relay C places the 100-ohm, non-inductive winding of relay K across the sW leads thereby shunting out the number -l arinding of relay E-1, the number-2 winding of relay H and the windings of the repeating coil. This improves the impulsing to the incoming switch. Relay H does not restore a s a result of this shunting action. Relay G operates and is now held by ground on the CSW lead, 5.23 Called P a r t y Answers (Relays now operated: -1, G , H) When the called party answers, A-l, reverse battery is returned over the - SW and SW leads. This reverses the current through the loop to the incoming switch (See Sec. 5.21) and consequently through the number-1 winding of relay E-1. As the field of this - + - PULSE REPEATERS now aids the polarizing (#2) winding, relay E-1 --- winding operates and places ground on the number-2 winding of ) relay D-1. Relay D-1 extends 100-ohm battery to relay A-1 to hold it operated and connects relay E to the dial leg. This causes relay E in the distant (originating) repeater, to release and thereby provide "off hook" (answer) supervision (See Sec. 5.13). The circuit is ready for transmission. 5.24 Release (Relays now operated: A-1, B-1, D-1, E-1, G, H) (A) Calling Party Disconnects First - When the calling party disconnects, the originating repeater releases and places ground on the dial leg (See Sec. 5.14A). Ground appearing on the dial leg a s a r e s u l t of the release of the originating repeater, operates relay E in the terminating repeater. Relay E removes 100-ohm battery from A-1. Relay A-1 restores; (1) opens the loop to the incoming switches which now r e s t o r e , (2) removes ground from B-1. Opening the loop a s described above, de-energizes the number-1 winding of E-1. Release of the incoming switches also removes ground from the CSW lead and consequently from the holding circuit to relay G, the 2 winding of E-1 and the 1 winding of H. Relays E-1 and H a r e momentarily held by relay B-1 (slow release) but relay G releases. When B-1 releases, E-1 and H also release. Relay E-1 restoring opens D-1. Relay D-1 restoring, transfers the dial leg from relay E to ground (through A-1). Relay E restores and the circuit is at normal. i (B) Called Party Disconnects First - When the called party r e s t o r e s , polarity over the SW leads i s again reversed which reverses the polarity of #1 winding of relay E-1. Relay E-1 restores and removes ground from relay D-1. Relay D-1 restores and removes battery (through E ) from the dial leg. Relay D-1 restoring, allows ground (through relay A-1) to be applied to the dial leg. Relay A-1 operates over the dial leg in series with relay E in the originating repeater to give rele