US2366837A - Pulse repeating system - Google Patents

Description

Jap. 9, 1945. R. B. SHANCK 2,366,837

PULSE REPEATING SYSTEM Filed July vl0, .1943 3 Sheets-Sheet l E/G. I

EkoM CALL/NG END l FROM CALLED END` FROM CALLED E/vo /N VEN TOR A. B. .SHANCK Jan.9,1945. R, B SHANCK 2,366,837

PULSE REPEATING SYSTEM Filed July l0, 1943 5 Sheets-Sheet 2 yI'N VE N TOR R. a. SHA/vak ATTORNEY o `lvatented Jan. 9, 1945 l UNITED STAT ES PATENT OFFICE o PULsEJRfErEAfrING SYSTEM r r Roy B. Shanclr,` Douglas `Manor, NQY., assignor i I to Bell Telephone Laboratories, Incorporated New York N. Y., a corporation olf` New York Application July 1ro, 1943, sentano. 494,209V :1u claims. l (Crue-84)" r The invention relates `to pulse repeating systems and more particularly to systems 'ot this type operating on a duplex basis.

It is an object of the invention to provide a pulse repeating system with, a simplied duplex` balanceand capable of eicientoperation under `conditions oi` line` variations and interference Itis a more specific object of the invention to l provide a system of this type which with standardizedequipment is adapted for repeating ser lecting and supervising pulses for telephone switching systems over lines oi greatly differing found in the fact that the trafc requirements in-` clude the transmission 1in both directions over` the line circuit of supervisory signals or pulses` The operations are complicated by the requirement thatgin the series of operations involved in the setting up of acconnection, the line circuit is placed under two different conditions, whichmay be termed theidle andthe busy conditions.

The pulse repeating system is adapted to receive dialing pulses from a vcalling station, `which `over the line circuit, this relay being unaected `by outgoing `signals when the impedance bali ance is perfect. For this purpose the polar relay may be connected in any well-knownmanner as byhaving its windings. directly included .in the two balancing branches or connected in a bridge between the balancedcircuits in accordance with r T well-known practice in telegraph repeatingsystems. .The system is also equippedfor the transmission of busy signals `comprising a series of 3` pulses of a` predetermined `frequency, -usually i about 80 cycles'per minute,"which are impressed l uponthe duplex circuit `by operation of the pole changer.

Asis well knownit has hitherto been necessary to establisha fair balance between the line cirl pressed on an unbalanced system unbalance currents arise which may operate `the receiving recuitand the baiancingnetwcfk in dunes systems of either type referred to above, in order to prevent the receiving relay from responding to theoutgoing pulses. `Whensignals:are imlay.` Thus, in the differential duplexcircuit the `currents in the two operating windings will be unequal orfunbalanced `andthe stronger current may operate the relay' In the bridge duplex circuit the potentials appliedjto the relay winding are unequal and anequalizing or unbalance `the windings and` may current will iiow through operate the i relay.

In accordance witha feature of theinvention,`

the balancing network issimplied and is standmaybe a remote telephone subscriber's station or a local operators dialing circuit, and to `repeat the pulses over an outgoing line circuit to a r distant telephone exchange, equipped for automaticswitching in `responseto the dialing pulses for the selectionsof another exchange or another n The repeating circuit includes a pole changardized to supply a fair balance for a large variety of line circuits so that it may be manufactured at comparatively low cost; In accordance with T T the invention the system is furthermore arranged` sorthat it will be unnecessary to adjust the balancing networl; to compensate for sporadic vari- 4 ations in the line circuitsduring ordinary operating conditions including temperature and leakage conditions. This simplification of the balancing network is further effective in reducing the largeamount of designing work involved in the provisionotf'` a large variety of differently ing relayior applying twodifferent transmitting 3 x n i i T present day `severe demands for accuracy.

potentials to the line circuitcorrespondirig to the two 'conditions of the pulses, namely,` marking and spacing or currentandno current. "The pulses from the pole `changing relay are pressed upon a duplex circuit including the line 1 circuit in one branch and a `balancing circuit inthe other tranen' relayisincluded in the A polar .receivin'gl o duplex'circuit for reception of signals incoming dimensioned balancing networksforthe corresponding varieties of -line circuits to satisfythe For the purposes"just outlined the invention operations, which would `loe due to improper responses bythe receiving' relay during the transtain average or `predomiriant line conditions among the large variety of conditions met with in the plant. Such a network may thus provide an accurate balance for -a large number of lines, but will necessarily be less accurate in the balancing of line circuits having diverging char-, acteristics without, however, establishing a circuit condition which would result in false operations due to unbalance conditions caused by line variations or interference.

When the pulse repeating system is idle, the pole changing or sending relay will apply an idle condition to thetoll line, which may be assumed to be a spacing or no current condition, the other end of the' line circuit being assumed to apply a similar condition to the line. In response to the seizure of the repeater station by a calling station or an operator, the po-le changer applies a busy or marking condition to the toll line. After the transmission of dialing pulses, the distant station also applies a marking or answering condition to the line circuit which consequently will operate the polar receiving relay at the repeating station.

After this'condition has been reached, further pulses may be transmitted in either direction over the line circuit. For example, a rering pulse may be transmitted by the sending station in the form of a pulse which will cause the distant exchange to rering the called line; busy flashes may be transmitted back to the calling line; and switchhook flashes may be transmitted in either direction.

The polar receiving relay at the repeater station will respond to .incoming pulses fromthe line circuit and will respond to the answering.

condition' imposed upon the line circuit from the distant end by operating to marking position. Thus, the receiving relay is arranged to control circuit equipment which, in well-known manner, may be arranged to respond in proper sequence to the traf-c signals, such as fanswering and busy, from the called line. It may furthermore be arranged to function in response to dial pulses from the distant station, when the call is in the opposite direction, for control of the selecting operation of telephone switches at the exchange with which the repeater is immediately associated.

It will, therefore, be seen that in a sense the repeater operates under full-duplex conditions, inasmuch as it will operate with either of two polarities applied to either vor both ends of the line circuit. However, though the repeater is required to operate in both directions, it will operate only in one direction at a time so that for any particular line condition the repeater will heroperating on a half-duplex basis.

This particular condition permits the introduction of a feature of the invention which basically resides in rendering the receiving relay ineffective during the transmission of outgoing signals and restoring the receiving relay circuit to effectiveness upon termination of the retransmission of outgoing signals.

In accordance with amore speciiic feature of the invention, holding pulses are caused to flow through the receiving relay during the transmission of outgoing pulses to prevent kick-oifk of the relay, and for this purpose a holding circuit is connected directly or indiricetly to one or more windings of the receiving relay only during the sending conditions. By` this provision any unbalance current from the line and balancing circuits due to the outgoing pulses will be opposed or its effect overcome.

In accordance with another specicfeature of the invention, the holding impulse circuit includes capacitance means which may be alternately charged and discharged for producing the desired holding effect once for each outgoing transition.

fIn accordance with still another specific feature of the'invention, the direction of the holding impulses is controlled by the position of the receiving` relay at any time, as determined by the line potential applied at the distant end.

The invention will now be described more in detail as to its organization and operation and as applied to specic embodiments. In the dev scription reference will be made to the attached representing a specic application of the invention and including the features of the invention; and Y Figs. 5, 6 and 7 are similar circuit diagrams of a repeater circuit representing other specific applications of the invention and including different modications of the arrangement shown in Fig. 4.

Referring to the drawings, it will be assumed that a subscribers -station is connected to a telephone exchange and desires to make a call to a distant subscribers station at another telephone exchange. The two exchanges are connected together over toll lines.`

In accordance with established trafic conditions in the telephone plant, the subscriber first removes his receiverl from the hook, thereby establishing a calling condition. Thereafter the subscriber operates his calling dial which transmits the usual groups of dialing pulses. The distant exchange then applies an answering condition to the line circuit and rings the` called subscriber, who answers by lifting his receiver off the hook, thereby establishinga busy condition. If the called subscriber should be busy, a continuous series of busy pulses will be transmitted back to the calling station at the rate of pulses per minute. n Other busy conditions, `as for local trunks or distant trunks, are indicated by similar pulses of different frequencies. Upon the distant subscriber disconnecting prematurely, a rring impulse may be'transmitted from the calling end of the line circuit. Subscribers `switchhook flashes may be transmitted at any time in either direction.

The diagram in Fig. 1 shows the signaling current in the line circuit at the time of a call; Thus, when the line circuit is seized, the line current increases from a no current or spacing condition to a steady marking current condition. Thereafter the marking current is interrupted by the dialing pulses, whereupon the line current remains steady. In the case of a subsequent rering the line current is momentarily interrupted. Fig. 2 refers to the conditions at the called end 'of the toll line, which normally is applying a Fig. 3 shows conditions at the called exchange when a busy condition exists in which case the steady marking condition is interrupted by spacing conditions.

Fig. 4V is a circuit diagram of a repeater circuit n erate shortly after. Relay 400 applies battery to the duplex circuit and over the line to the distant exchange E for operationlof the switch control circuit 49 I.

Relay 44u` completes the capacitance circuit through condenser C and a charging'impulse will ow as follows: from plus battery 463 through rectifier 46| over break contact of relay 460, make contact of relay 440, break contact of relay 43|), through the resistance Ra, condenser and inductance, through the lower operatingwinding of relay 45'0 to minusy battery on relay 400. l This current will be in a direction to aid the biasing winding of relay 450 in holding the relay against the spacing contact. Shortlyl thereafter the condenser circuit will be opened by the delayed operation of relay 43B, and condenser C discharges through resistance Rb.`

The subscriber now operates the dial, the contacts of which produce spacing impulses, as shown in Fig. l, by short interruptions of the ground connection to the line SL. On the arrival of the first impulse relays 400 and 43S release and relay 440, being slow in releasing, remains attracted for a short interval during each short interruption by the dial. The capacitance circuit is now closed over the make contact of relay 440 and the break contact of relay 430, thereby again sending a holding pulse through relay 450; under this condition, however, the circuit is terminated at ground on relay 400, thereby somewhat reducing the intensity of the holding impulse which, however, will ber of rsuicient strength to hold relay 450 in spacing position over any unbalance` circuit. When relay 440 releases the capacitance circuit is opened and condenser C discharges.

yAt the end of the rst dial pulse relay 400 operates to again apply battery to the duplex circuit; relay 43 remains temporarily retracted; and relay 440 is quickly attracted The impulse circuit through condenser C thus is again completed and a charging impulse applied to relay 450; when relay 430 is attracted, the impulse circuit is again opened and condenser C discharges through resistance Rb in preparation for thev next transition. During each pulse series relayfll will repeat each marking and spacing transition, and relays 430 and 440 will cooperate to send ashort holding impulse through relay 450 every time relay 400 reaches either one of its contacts; Thus,

with proper delay action of relays 430 and 440, the holding impulse through relay 450 may be of suilicient duration to lock relay 45u in its position while a pulse transition passes through the windings of relay 45E), 'thereby preventing kick-ofi of relay 450 in response to unbalanced currents in the toll lineand the network BN` through the operating windings of relay 450. Thestrength of theholding impulse may, of course, be deter.- mined` by the battery potentials and by adjustment of resistance Ra. The shaping of the 'ho-ldving impulse relative to the line transitions may lequipmentY 41) forthe proper receptiongof lthe the battery connectionto the line.

answering signal. Relay 450 .alsooperatesrelay 460 to reverse the battery #connections for vthe capacitance circuit. L i The'y desired connection may now-be assumed to have been `established land the called` subscriber will be rung by the ringing equipment at the exchange E. When the calledsubscriber answers, the conversation may; be carried` on over a talking circuit, not shown in the drawings,- but which Awould be closely associated with the toll line TL, as by being included in the same cable quad or by some composite arrangement. i Y

It will now be assumed that `some special cir,- cumstance arises, as for example, that'the distant subscriber hangs up prematurely, necessitating the sending of further pulses fromthe calling end, for example, a rering pulse, as indicated in Fig. 1. The relay 400 lwould interrupt Relays 430 and 440 would again cooperate to senda charging impulse through relay 45D. Due to the changed line condition and the .operation o i relay'450 'to marking, relay 46|) now'completes the charging circuit from the high negative battery 464,' rectifier 462, make contact of relay 460', make contact of relay 440, break contact of relay 430, through the condenser and relay klliill'to ground at relay 400. Thus, the chargingimpulse. will pass through the lower winding of relay450 in a direction to aid the operating windings and of suiilcient strength to overcome effect of unbalanced currents, thereby holding relay l45t!` in marking position during the` mark-to-space transition. .At the `end of the rering pulse relay 40|] returns to apply battery to the line `circuit; relay 433 quickly releases, and relay 440 remains temporarily attracted, thereby'again` completing the holding circuit through relay u -in the same direction to the lock relay in marking.

Inthe case of a busy lcon-dition existing at the distant end after all dial pulses were transmit-'- ted, a series of pulses, shown in Fig. 3, would be transmitted by the contacts 49|] over the line TL, through the windings of relay 450 andv network BN to ground, causing relay 450Hto operate in unison with the busy pulses and apply corresponding busy pulses to the circuit 410 for:

suitable response. The consequent operation of relay 460 will have no `eiiect upon the condenser circuit.

In the case of a call incoming to repeater station R, relay 450 wouldbe operated to marking in response to the application of battery at the distant exchange E to the line.' Subsequent interruptions, as 'by dial pulses, would cause relay 450 to oscillate and. apply corresponding pulses to the Vcircuit 410 for selective operation of switches. In response to this selective operation a switch will ultimately connect'the subscribers Astation S to the repeater station R.` This switch is diagrammatically represented by contacts LF; contacts LF may also represent a linei'lnder switch for connecting the subscriber station to the repeater in response to a call by the subscriber. With the subscriber connected in this manner, switchhook flashes ymay be vtransmitted back to the station Ejin the ymanner'already described. A I

In case the subscriber S is busy, the connection at switch LF will remainopen and the circuit 410 may 'be arranged to automatically operate the key -4Il for application of busy signal from interrupter 4I. Relay V400 will operate in unison with the busy pulses-Wand relays @tand l, `over .contacts l are beyond control.

Vailing` position. f l l Referring now, more particularly to the em- Il .will produce vcorresponding holding impulses for relay 450, as already described.

On observing the busy signalpthe distant `call-` ing station at E `will hang up and thus will send a1 disconnect ,signal by applying steady-ground 490 through the windings otrelay 4511, thereby Operating the relay tospacing.. The` circuit 410 responding to this 'operation` may be arranged to automatically disconnect ,the inter-` rupter 410 by meanslof contacts 4H., whereupon l wholeV systeinjwill be restored to idle `condi-l` .the

tion.. i e e i The inductance I is .inserted between the vconpose ofshapingthe outgoing pulses in any desiredmanner. l l

The purpose ofthe condenser circuit connected .to the local branch of thefduplex circuit is atv. .tained during thetransrnission .of outgoingpulses.` Thus, inV accordance with the invention and as .already explained above, thekbalancing network the charging impulses through the condensers Cif is` of l simple` construction and is 4designed so that i `networks of .this kind may be used universally `with toll lines of different lengths and different l vcharacteristics. It is, ofcourse, within the scope of theinvention that a `few .standardize-d types of network may be provided, each type to fbef used with lines havingcharacteristics within comi parativlelywnarrow limits and the differenttypes of network supplementing one another to .sat-

.isfy the .requirements of. all types of lines. Thus,

any one network will be connected to `a particular line circuit and may -establish only an approximate balance, and the unbalance may be so pronounced that the .receivingrelayordinarily would l.

`during transmissionofloutgoing pulses. l

It is furthermore well known that long line circuits, as usedin toll service,` are subject to sporadic variations in their characteristics which l Where a` very :close balance is necessary; it has beenthe practice to .continuouslyobserve the line conditions and lcorrespondingly vary the balance by the network. y l

`.By the provision ofrthe holding circuit for. the

receiving relay appreciable. 'leeway is alforded in the. balancing of` this circuit,` thereby permit-ting the use of universal networks `for balancing over wide rangesane'l` also in special cases obviating the needyfor continual readjustment of the network. W'Ihus, .during sending of `pulses the effect ofany unbalanced currents that would flow in transition,`

`5, thecondenser Cl is connected in thecircuit from plus battery 553 at the relay 560 to ground i l; at relay '.illll.` Condenser `C2 is discharged through` f `resistance R2. l l. l l. .When relay 5.00 olperatesto place battery on theduplex circuit,r`elay 54| will operate to dis- `connect :condenserl and replacefit. by conl denser `C2' so that alcharging impulse will pass l .through the lower operating Winding of `relay 550 1during .the transition'tirne. `Whenrelay 500 opcrates `back touspacing, relay l 5,4 ljisreleased, thereby connecting condenser `Cl into the circuit `and causing asimilar charging impulse `torpass through relay 55B. e e

.the positions shown.. the hold impulses win` in `both cases be in the direction .to hold relay 55.0 i

.inspacing` VWith battery supplied to the line circuit at :the .distant end of the line TL, relay 550 will be operatedtomarking and relay 56!)` will .be energized,`` therebyreyersing the direction of l andCZior holding the relay 550in marking position during the sendingeof cnitgoing` pulses.

. IThe circuit arrangement shown :in` Fig. 6is

imilar .tofthose shown in Eigse and and .is

f particularly ysimilar .to that `in Fig. 5 in having .twolconfdensers CI and C2. includedinthe holdl ing circuit `for relay 650. The arrangement differs fromthat in Fig. .il mainly in the factjthat .the capacitance circuit is inductively coupled `to .the local branch oi the duplex circuit.`

Thus, a transformer .T having` tworprimary .l rwindingsconnected in series with the condensers CI and 02, respectively, has a secondary windcondenser C2, through one transformer .winding `to intermediate potential or out of the line circuit or thenetwork due to imbalance. conditions would be overpowered `by the condenser current `and.:tlieyrelay would not beloperated y l l l Byreversing thefbattery potential for the condenser circuit in yaccordance with the' position ofthe receiving relay it isinsured that the holding impulses will always lock the relayin its prebodiment illustrated. in Fig.. 5 ofthe drawings, the` system'is somewhatsimilar to that shown in Fig. 4.and corresponding elements are`corre spondingly numbered in two iigures.` l

In the circuit of Fig. 5 the, capacitance circuit includes two condensers` `CI andi C2, either of which may. be connected into the `holding cir- `1 cuit. by correspol'idingy operations of relay 51H.`

` 1 Relay `54 I` is included in the dial pulse circuit from the subscribersstation so. that it willgfollow the operations of .sending relay 500 during. dialing as wellas duringthesending of lrering and busy signals.

. Under the. normal conditions `as `shown t at" potentiometer Vcircuit 615.

e e .The resulting `charging .current will `produce an .impulse in `the l secondary windingin the transformer which will pass in the pro-per direction through relay to hold therelay in spacing position. l l During" an `outgoing `mark--to-space transition relay '64| will complete the charging circuit through rectier 66|, condenser CI and the other primary Winding of. the transformer, which Will )produce aA holding impulse through relay B50 in l the same direction as before.`

` `to marking With .battery supplied to the toll .line .TL from the distant exchange E, relay G50 will operate and relay 66.0`Wi1l be operated to apply .l negative charging impulses through thetransform'er and, in turn,`reversing` l the` holding :impulse in the secondary winding of thetransformer and simplification is possible in that. only a single batteryor other direct current source is necessary for the production of lholdingirnpulses unl cipal modiiication Ithat "the receiving relay der. all conditions. This source may furthermore similar to those described above .withthefprin e 150 is connected through two separate windings of the relay..

:In this arrangement the dialing` circuit i SLA .With relays 55D andf560 in` e potential `througl'rrectiiier 662 to the two condensers;` alternately, thereby re. l

"versing the direction of the l e through the relay E50'to l holdthe relay in markingposition. l l

It will be noted that with this arrangement a i rbe the common source for. the relayoperations..V

the` holding .circuit for from the subscribers station extends through relays 100, 14| and142 which operate in unison in response to dial lpulses. By means of the contacts of relays 14| and 142 the condensers Cl and C2 are connected in alternation to battery 16| for charging or to vthe holding circuit through the two lower windings of relay 15|! and to ground at the contacts of relay 160 for discharging.

With the circuit in the condition shown in the drawings condenser C| is connected `over the break contact of relay 14 I, through the lowermost holding windingof relay 150 and over the break contact of relay 16D to ground; the condenser is originally discharged in this circuit. Condenser C2 is vconnected over the break contact of relay 1412 to batteryv 16| and is in charged condition.

When the repeater is seized by the subscriber S, relays 18|), 14| and 142 'are energized."4 Condenser CLis disconnected from relay 15|] and connected to battery for charging. Condenser C2 is disconnected from battery and is connected to relay 150 for discharging through the lower winding in a direction to aid the biasing winding in holding the relay to spacing, the discharge impulse coinciding with the charge of the line circuit TL and the balancing network BN when the armature of relay 1|l0`reaches the battery contact.

For the sending of a mark-to-space transition relays 100, 14| and 142 release.l Condenser C2 is now connected for charging and condenser C| is connected for discharging through the lowermcst winding of relay 15|] also in the direction to hold the relay in spacing position.

In answering condition the distant exchange E applies battery to the line circuit, thereby operating relay 150 to marking which, in turn, operates relay 16|). Relay 160 disconnects the lowermost winding of relay 150 from the holding circuit and connects the other holding winding into the circuit. The connection through this second holding winding is such that the discharge im-v pulses from the condensers CI and C2 through the winding `will lock the relay in marking position during transmission of both kinds of transitions.

Theproperv relation between the pulse transitions in the du'plex circuit and the holding impulsesfrom the capacitance circuit may be adjusted by adjustment-of the inductances I and L in the two circuits. It is., of course', also possible to slightly adjust the timing of relay 100 relatively to relays 14| and 142.

The operation of the type of repeater shown in Fig. 7 has been observed under various circumstances. For this purpose an oscillograph e' 182 was connected into the duplex circuit for observation of the unbalanced currents in the duplex circuit. Anotherv oscillograph 183 was connected into the capacitance circuit for study of the holding impulses. A telephone receiver 18| was included in the contact circuit of relay 150 for the detection of kick-01T. The balancing network included a capacitance 1 I 5 normally adjusted to 4.5 microfarads for good balance. For the observations the capacitance was adjusted over the range between 1.5 and 16.5 microfarads without causing relay 15|) to kick-off. Under the same line conditions but with the holding circuitfor relay 15|] opened by the switch 1 6, the range of capacity variation without causing kick-01T was only about one-third of that observed between the values given above.

It should be understood that the invention may readily be adapted for application to a telegraph repeating system with similar advantages, where sending takes place against vtwo different signaling conditions imposed by the remote station.

What is claimed is:

1. A `two-way signaling system comprising an approximately balanced line circuit `normally maintained alternately in marking and spacing steady state conditions, receiving relay means at one end of said line circuit having contacts `for control of a receiving circuit in response to incoming marking and spacing signal pulses superimposed on said steady state conditions, auxiliary circuit means including relay `means connected to be responsive to outgoing marking and spacing signal pulses to prevent said control by said contacts in response to unbalance currents due to said' outgoing pulses, and switching means connected to be responsive to incoming -line currentstfor the conditioning of said auxiliarycircuit means for the proper prevention of said control under both of said steady state conditions,l said auxiliary circuit means comprising an impulse producing circuit `connected to a winding circuit for said receiving relay means for holding' said receiving relay means in alternate positions in accordance with said alternate steady state conditions.

v2. A two-way signaling `system comprisingv an approximately balanced line 4circuit normally maintained alternately in marking and spacing steady state conditions, receiving relay means at one end of said lin-e circuit having contacts for control of a receiving circuit in response to incoming marking and spacing signal pulses superimposed on said steady state conditions, auxiliary circuit means including relay means connected to be responsive to outgoing marking and spacing signal pulses to prevent said control by said contacts in response to unbalance currents due to said outgoing pulses, and switching means connected to be responsive to incoming line currents for the conditioning of 'said auxiliary cir-A cuit means for the proper prevention of vsaid control under both of said-steady state conditions, said auxiliary circuit means comprising an impulse producing circuit connected to a winding circuit for said receiving relay meansfor holding said receiving relay means, and said switching means including relay means having contacts connected for reversing the holding action by said impulse producing circuit in aci control under both of said steady state condiditions.

cordance with said alternate steady state con- 3; A two-way signaling system comprising an approximately balanced line circuit normally maintained alternately in marking'and spacing steady vstate conditions, receiving relay means having contacts for control of a receiving circuit in response to incoming marking and spacing signal pulses superimposed on said steady state conditions, auxiliary circuit means connected to be responsive to outgoing marking and spacing signal pulses to prevent said control by said contacts in response to unbalance currents due to said outgoing pulses, and switching means connected to be responsive to incoming line currents for the conditioning of said auxiliary circuit means or the proper prevention of said tions, said auxiliary circuit means comprising a pulse circuit for producing'oppositely poled impulses through winding means on said receiving relay means for locking said receiving vrelay means during the alternating outgoing transitions, and said switching means comprising con'- i state conditions.`

`tactl means for" reversing th'e polarityv ofv the locking impulses through said receiving relaymeans in accordance-withsaid alternate steady state conditions." i Y Q4: A two-way `signaling system comprising an approximately balanced `linecircuit normally having marking-and spacing steady state conditions alternately appliedtoI theY remote end, receiving relay means at the near endotsaid` line circuit having, contacts for control of a receiving circuit` in `response to incoming marking andv spacing signal pulses superimposed onsaidl steady state conditionsyauxiliary circuit means con# nected to be responsiveto outgoing marking and spacing signal pulses tol prevent" said control by said' contacts inresponse to unbalance currents due to` said outgoing pulsesyandswitcliing means cuit `connected to a winding 'circuit forsaid re-,-

ceiving relay, means for locking said receiving;

lrelay meansl lnfalternate positions in` accordance withl saidl alternate steady state conditions, said auxiliary`- circuit means further including .quick responsive relaylmeans for closing saidimpulse producing circuit in4 response to successive trarn` sitions, and `slow-responsive relay means for opening said impulse circuit ati anfinstantcbetween successivetransitions; i f

7; Altwo-way signalingsystemcomprisingan approximately balanced line circuit normally maintainedalternately in marking and spacing steady state conditions from 1 the remote endl,`

receivingrelay` meanshaving contacts for con-f trol ofl a receiving circuit in response to incom-` ingmarking and spacing signal pulses superimconnected tothe responsiveto said steady state 'conditibns'fcr` conditioning said auxiliary circuit means for the'jprop'er prevention oi said control underbothof said steady state conditions', said "auxiliary circuit' meansn comprising Aan impulse f producing circuit connectedlto `a winding onsaid n receiving4 relay means `for` locking said receiving' `relaymeans during outgoing transitions to marking or to spacing, and said switching means comprising contact means and polarizing means for reversing the polarity of said impulse producing circuit in accordance with said alternate steady l5. |A` two-way signaling system comprising an approximately balanced line circuit normally having markingand spacing steady stateconditions alternately applied to the remote end, receiving relay means at the near end of` said line y circuit having contacts for controlof a receiving winding onvsaid receiving relay means for locking said receiving relay means, and including ca- `pacitance means for producing unidirectional impulses for said locking during each outgoing transition, and said auxiliary circuit means further comprising contact means for completingL said impulse producing circuit once for each out-` going transition. i

n 6. A two-way signaling system comprising an approximately balanced line circuit normally maintained alternately in marking andspacing steady state conditions from the remote end,`

receiving relay means having contacts for `control of a receiving circuit in response to incoming 4marking and spacing signal pulses superimposed on said steady state conditions, auxiliary circuit means connect-ed to be responsive to outgoing marking and spacing signal pulses to prevent said control by said contacts in response n to unbalance currentsdue to said outgoing pulses, and switching means `connected to l to said steady state conditions for the condii tioning of said auxiliary circuit means for the i proper prevention of said control" under both of `said steady state conditions, said auxiliarycirf cuit means comprising an impulsevproducing cirbe responsive i posed on said! steady state conditions," auxiliary circuit means connected to beiresponsive to outgoing marking and` spacing signal pulses to preventsaid` control by said contacts in `response tounbalance` `currents due to said `outgoing pulses, and switching meansconnected.` to berrespcnsive to saidfsteady stateconditions for conditioningf `said auxiliary circuit lmeans for `the proper 'preventionofsaid control under both of said steady state conditions, saidauxiliary circuit meansL comprising an `impulse circuit con- .nectedto a, Winding circuit for said receiving re-` lay means for locking said receiving relay means in alternatepositions in accordancewith said al` ternate steady stateconditions, said impulse circuit includingtwo self-discharging capacitance circuits for producing unidirectional impulses for said locking, and said auxiliary circuit means further including relay means for `completing said impulse circuit alternately through said two ca-i pacitance circuits during alternate outgoing trani sitions. n i n n 8. A two-way signaling system comprising an approximately balanced line circuit normally` vmaintained alternately in marking and spacing steady state conditions from the remote end, receiving relay means having contacts for con-` trol of a receiving `circuit in response to incoming marking andspacing signal pulses superimposed on said steady state conditions, auxiliary circuit meansconnected `to be responsive to out` i going marking and spacing signal pulses to prevent said control by said relay means contacts in response to unbalance currents due to said outgoing pulses, and switching means connected to be responsive to said steady state conditions for conditioning said auxiliary circuit means tor the proper prevention of said control under both of said steady state conditions, said auxiliary cir-` cuit means comprising an impulse circuit con-V nected to a windingcircuitfor-said receiving relay means for locking said receiving relay means inalternate positions in `accordance with said al-` ternate steady state conditions, said impulse cirwcuit including inductance means for producing y unidirectional impulsesfor said locking, and said auxiliary circuit means further including `contact means for closing said impulse circuit once n `for each outgoing transition.

`9. A two-way signaling system comprising an approximately `balanced line circuit,` normally` maintained alternately in marking and spacing steady stateconditions from the remote end, re-

i ceiving relay means having contacts forcontrol of a receiving circuit in response tol incoming marking` and spacing signal pulses superimposed `on said steady state conditions, auxiliary cir cuit means connected `to be responsive to outgc vention of said control under both of said steady state conditions, said auxiliaryl circuit means comprising an impulse circuit connected to a winding circuit for said receiving relay means for locking said receiving relay means in alternate positions in accordance with said alternate steady state conditions, said impulse circuit including two capacitance circuits and a charging source therefor for producing impulses for said locking, and said auxiliary circuit means further includingl relay means for alternately charging said condensers and discharging them in said irnpulse circuit for said locking during each outgoing transition to marking and spacing.

10. A two-Way signaling system comprising an approximately balanced line circuit normally maintained alternately in marking and spacing steady state conditions -from the remote'end, receiving relay means having contacts for control of a receiving circuit in response to incoming marking and spacing signal pulses superimposed on said steady state conditions, auxilitry circuit means connected to be responsive to outgoing marking and spacing signal pulses to prevent said control by said relay means contacts in response to unbalance currents due to said outgoing pulses, and switching means connected to be responsive to said steady state conditions for conditioning said auxiliary circuit means for the proper prevention of said control under both of said steady state conditions, said auxiliary circuii-l means comprising an impulse circuit connected to a winding circuit for said receiving relay means for locking said receiving relay means in alternate positions in accordance with said alternate steady state conditions, said impulse cir-4-` cuit including two inductance circuits for prof ducing similarly directed impulses for said locking during each outgoing transition to marking and spacing, and said switching means includin'g relay means connected for reversing said impulses for said locking corresponding to said steady state conditions. o

ROY B. SHANCK.

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