US1992220A - Interpolating receiving system - Google Patents

Description

Feb. Z6, 1935. w. A. KNooP INTEROLATING RECEIVING SYSTEM 2 Sheets-Sheet 1 Filed May 13' 1929 AA VVV mmmmmmmnmmmmmmm Ff ik @y ab' @y dv Il Il n n Jig-H Feb. 26, 1935. w A KNQQP 1,992,220

INTERPOLATING RECEIVING SYSTEM I Filed Mayl, 1929 2 Sheets-Sheet 2 mii F/G. 3

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i s arl l l? l Z5 /M/EN 70H W I4. KNooP A TmR/vfy l Patented Feb. 26, 1935 UNITEDN STATESV PATENT"ortica"; y Y A l1,992,229 Y 'u i 'l i INTERPoLA'rING RECEIVNG SYSTEM A William A. Knoop, HempsteacLN;` Y.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York` Application May 13, 1929, serial No. scarsi y Y 41 Claims. (Cl. 178-7-88) This invention relates to high speed synchron-` This expression is somewhat misdeseriptive ofthe system of this invention (because short impulses are rebuilt without vibration of any relay i and therefore, in this Yspecification the expression interpolating receiving system will be used to deiine a system which restores, or interpolates short signal impulses Which have been attenuated to mitting the impulses into the next line section. As the speed of transmission over a submarine cable or a long transmission line is increased -the single impulses `of dot length, whether positive or negative polarity, often become so attenuated, that is so reduced in v:strength and distorted or altered in wave shape form by the transmitting medium, that With the customary voltages applied, perfect receptionat high speed is difcult. This condition also exists in signals of a length greater than the single or dot impulse in that the beginning of theimpulse is attenuated so that theiirst part of the signal which corresponds to the nrst part of the combination is not correctly received. The eiect of such distortion and loss of energy is considerably minimized'by the use of the Grul-H stad relay which comprises a three winding polarized relay. The usual Gulstad relay is provided With a line Winding, `an opposing winding, and an accelerating winding', the latter two being locally operated. By proper local circuit arrangements, including condensers and resistances, the 40 current flowing through one of the local windings operates the relay armature to its opposite contact, which thereupon closes "a circuit sothat current of reverse polarity iiows through the winding and the armature is moved back toits original position. If the armature vibrates between its contacts in synohronism with the transmission of the signals, the effect on the local apparatus is the same as if impulses of periodically reversed polarity were being received. In this manner at- 50 tenuated impulses, although too Weak to operate the line relay armature, are not lost. By adjusting the resistances and condensers in the local circuits, the relay tongue can be arranged to vibrate between its armature contacts at lany desired frequency. However, considerable d ifliculty l such an extent that they are incapable oi coni trolling a receiving relay or; a relay `for retrans-A -1 is experienced withthis relay systemndue tothe fact that no means-is provided for insuring absolute synchronism between thevvibration of the armature and thereceived signalingimpulses.` K

Considerable diicultyis also experienced dueto the fact that the vibration causes continuousv Wear of thearmaturecontacts. f

Attempts to overcome the-diiculties ,disclosed `of January 6,1925.` In these'two patents, distributors` aredisclosed which rotate at the proper speedfor maintaining Vthe vibration of the armature of the relay operating asa Gulstad relay in synchronism with the received impulses. The resistances,andcondensers of the Gulstad system are replacedv partially by `distributors which control the speedof relay operation'. Here again,

' however, the armature of the relay vibrates continually and there is therefore the same drawbackof` wear on the armature. 3 Y l The present invention `provides arrangements for operatingV velectro-responsive devices of `the Gulstad relay ,type-in such-a manner that there` is normally no Wear on the armature part Vand the operation is automatically maintained Vin synchronism with the signal impulses.

`This invention also provides for operating elec--y Another object of thisinvention isto provide means for repeating attenuated signaling impulses by electromagnetic means arranged in such circuits that their armaturesdo not vibrate While signals are not being received. 1 f

IStill another object of this inventionV isto provide means whereby the printer selecting magnets maybe energized to operate them for a greater percentageof Vthe signal period than could normally be obtained under the Gulstad relay system. A il `I-Ieretoforey as noted above, ithas been a practice to rebuild or restore short impulses at `the receivingstation by means of `relay systems in which a relay vibrates under the control of-,special `distributor segments to automatically restore signal impulses of unit length. Such: vibrating relay systemshave rather definite `speed limitan ac tionsand long loaded telegraph cables are now in existence which have a possible speed of transmission exceeding that at which they are capable of operating satisfactorily.

The present invention'is exemplified by an embodiment in lwhich a three-position line relay or mixing relay -controls the impulses which two halving relays, each controlling the other, transmit to each other, in accordance withline impulses whereby line impulses acting through the line or mixing relay cause` the two relays to transmit to the printer magnets orretransmitting relays impulses coming in from the line. When the line relay is uncontrolled by incoming impulses and stands in its mid-position the two halving relays each assumesY opposite positions and relay to the printer. magnets or retransmitting relays properly timed and phased unit impulses. 4 y, Fig. 1 is acircuit diagram, with developed distributors, of a circuit inV accordance with the invention; f

Fig'. 2A is a series of graphs explanatory of the operative actionof the parts of Fig. 1;

f' Fig. 3 is a circuit diagram of a modiiied form using. asingleprinter magnet; and.

Fig. 4 is a circuit diagram of'a further modied circuit.` f

DescriptionY f circuit. of Fig. 1

A cable .10 is'connected to a transmitter transmitting impulses at such high speeds that. the unit length impulses do notsarrive at Vthe receiver in operative amplitude. Amplifier 11 typies any suitable amplier. of `thereceived''impulses and has its output-circuit connected to relay LR Vwhich isa line or mixing relay.. Shaping networks of the'type ordinarily employed will be used, in practice but are not shown. f

Relay LR isa three-position line relay whose armature remains in a central position on of both of its contacts whenv no signal impulses of effective amplitude are being received. its right hand? contact is connected to-positive battery and its. lefthand contact'to negative battery. Its armature isconnected by a resistance r' to point 14 on a potentiometer resistance 1' which isV dividedV intoV fourl parts by points 12, 13.ar1dV 14, Whiclrmay be adjustable. Point 141s adjustably connected along' the middle section of potentiometer r. -When the armature of relay LR isl in its middle position point 13is negative with respect to point 14 and point 12'is positivewith respect to point 14. When-the'armatureis to the left, point I4 isnegative with respect to point 13; when the armature is to the right, point 14' is positive with respect to Apoint. 12.

RelaysV R1- and PR1 in parallel are controlled bytwovcircuits extending' from either of points 12 or '1231 through the right or. left hand contacts of relay R2, Segments la, conductive brush 1'5, ring 16 and conductor 17, to point 14.

,RelaysRz and PRz in parallel are controlled by two circuits extending from either points 12 or 133 through the right or left hand contacts'oi' relay R1, conductive brush 15',V segments 2d, ring 16', and conductor 17 to point 14.V Y

Alternate printer magnets of a channel suchl as magnets 1, y 2, 3,14, 5 are connected' to separate sets of distributor-'segments 18 and-19, each set of segments being connected by a brush to a corresponding'ring of long segments, ring 20 being thelong segments for short segments 18, and .ring 21 being the long segments-for short segments 19.V Dead segments are located between the live segments 18V and 19. The dead segments may be considerably shorter than a unit impulse and the live segments considerably longer thereby permitting the transmission, to the relatively slowacting printer magnets, of a Vrelatively long impulse, without the use of pulse lengthening Vtubes or other devices. In other words, the segments 18 and i9Y are longer than the distance from the center of a segment 1a to the center of a next adjacent segmentV 2a. The impulses transmitted to the printer magnets may be made anx/'length from shorter to longer than al unit impulse by making the live segments ci suitable length. To indicate a ve channelrsystem the printer magnets of channel #l are designated 1, 2, 3, 4, 5, of channel #2, 1I, 21, 31, 4I, 5I, etc., up to 51V.

Fig. 2 discloses in curve 30 a train of transmitted impulses, in curve 40 a corresponding train Y Y of received impulses,V in curve 5G the correspondingly proper movements of relay R1, in curve 60 the correspondingly proper movements of relayV When noisignals or" controlling amplitude are The time of transmission Y Varriving relayLR stands in its central position.` and relays R1 and R2 standstill on opposite con'-V tacts and arernaintained cri-opposite contacts each 1 by the otherq-Relays PR1 and PE2 follow the corl responding relays R1 and R2 and likewise stand still on opposite contacts. The circuit `for controlling relays R1 andPRl isl from point 12, of

vpositivepolarity, through right Contact of relay R2, windings of. R1 and PE1 in parallel from right to left, segments 1a., brush 15, ring 16 and conductor 17 to point 14. The circuit for controlling i relays R2 and PR2 is from point 13, of negative polarity, through left contact of relay R1, Windings of relaysRz and PRz in parallel from left to right, segments 2a, ring 16, and conductorV 17 to point 14.

Let it be supposed that a long positive impulse is sent from the transmitter beginning at time c.

lay LR is released and returns its armature to its central position. vPoint 13 then again becomes negative with respect to point 14 and since point i3 is connected to theleft hand contact of relay R2, upon which its armature is now resting, a circuit Vis closed from point 13, left contact of R2, and windings of relays R1 andPRi in parallel, a segment 2a, ring i6, and conductor 17 to point 14. The negative current through windings of relays R; and PR1 causes them to move their armatures to the right, whereupon R1 and Rz-again stand in opposite positions and regenerate alternate positive and negative limpulses until the line relay LR is again operated, which will happen, in the case illustrated by Fig. 2 at about time h. From curves 3G, 40, 50, 60 and 70 the operation of the system for other combinations-oi long and short transmitted impulsescan readily be traced; VV'I'he `printer magnets aredivided Ainto `two VIt will be noted that after any long impulse` such .as occurs at time `c to e or g to the relays R1, R2 are so positioned that the subsequent impulse or impulses of unit length to be regenerated are always incorrect order. 1

It will be noted that the relays R1 and R2, to-` gether with the relays PR1 and PRa comprise electromagnetic means'provided with armatures for relaying impulses received from the' transmission line 10 to the receiving printer magnets 1, 2, 3, etc. The relays'R1 and R2 each is connected to control the `other by means of circuit arrangements which maintain the armatures of said relays in` engagement with a predetermined contact when no impulses are being received over the line in effective amplitude." The predetermined contact uponv which these relays R1 and R2 stand is determined by the sign of thelong impulse, of Atwo or more unitsV duration4 last received. When the relays R1 and Raremain in xed position the impulses relayed to the printer magnets are of alternate polarity.A The distributor rings 16, together with segments 1a, 2a, etc., constitute one distributor; the rings 18, constitute another distributor; and the rings 19, 21 another distributor. The last twofnamedmay be arranged ina single rowas shown in Fig. 4 orin two rows as-shown in Fig. 1. The two-row `arrangenfient `has the advantage that the live segments to the printer magnets may be over 100% or" the time duration of a unitsignaling impulse as transmitted, thereby y'insuring that the printer magnets will be energized by an impulse of proper polarity for the full time during which the relays PR1 and PR2 maintain their armatures upon `any given contact. There is no physical limitation upon therelationship of the distributors controlling the relays R1, R2, and those controlling the printer magnets except that they be synchronized and adjusted toi suitable phase relation.

Description Vand operation of circuit of Fig. 3

This circuit is a modified form of that of Fig.

1 and uses a singleprinting relay. The corre- Y spending` parts of Fig. 1 are in light lines and identiiedV by corresponding characters. The modified velements are designated by heavy lines and comprise a printer relay PR1,2 which isconnested between the armature of relay LR. and the ringld.` Conductor 17 of Fig. 1 is omitted from Fig. 3. Relay PR1,2 follows the movements of each signal impulse whether locally regener` ated or incoming to the three-elementline relay LR. Relay PR1,2 controls the printer magnets 1, 2, 3 .1 51V, etc., to select or not in accordance with the impulse transmitted over the line.`

Description of circuit of Fig. 4 Fig. 4 is a further modified circuit. The re' lays LR, R1, R2, PR1and PR?. of Fig. 4 are generor" relays R1 and R2 are veach connected to batteryv through 500 ohm resistances. The general relation between the values of the 500 ohm and the 250 ohm resistances is essential for operation although these exact values are unnecessary.

groups, alternate magnets belonging to a group.

`All magnets of both groups are connected toa common ring 24 by brush 25' which sweeps over lSegments 25 connected tothe several. printer magnets 1, 2, 3, 4, 5, 1I etc., up to 5W, in a five channelsystem, although any reasonable number of channels either even or odd may be employed. For reversing the impulses to opposite channels, the ring 24 may be split at the `end of each` channel and the-alternate channell length segmentsconnected to positive and negative battery respectively. Battery on the armatures of relays PR1 and PRZ may then be replaced by ground. 1 Y

Operation ofcircuit of Fig. 4 When the line relay stands in neutral position,

as when no linesignals of controlling amplitudel are arriving, relays R1 and Rz'eachholds the other in opposite positions and also hold relays PRi andrPRz in opposite positions. The printer magnets will receive impulses of positivefand zero polarity alternately thereby correctly reproducing the regenerated impulses. When long impulses control the line relay LR the one of relays R1 and R2 corresponding to the unit time vduring which the relay LR'becomes operated is operated. This transmits correspondingly long impulses to the printer magnets. The cycle of operations indicatedin Fig. 2 is equally applicable to Fig. 4.

Two features of operation require mention. When the relay LR operates, a pulse is delivered to the controlled magnet R1 or Rz stronger than that delivered when they merely hold each other in opposite position. Likewise when relay LR fallsback to neutral position and relays R1 `and R2 are on the same contact the next pulse delivered to move one of them is extra strong. The occurrence of these extra strong impulses at the proper times to move the relays With'the occurrence of 'weaker impulses when they merely are to be held in position is a desirablefeature of the system.

What is claimed is: 1. Ina receiver of a synchronous distributor impulse transmission system of the type in which unit length impulses are regenerated and plural unit length impulses are transmitted,` electro- Y magnetic means directly controlled by the receivedimpulses in combination with al plurality of relays functioning to regenerate and relay to a set of distributor segments unit length impulses when standing still uncontrolled by said electromagnetic means and to relay to said set of distributor segmentsplural unit impulses when controlled by said'electromagnetic means.

2. In a system in accordance with claim 1, a

pulse lengthening arrangement comprised in that the set of distributor segments are'divided into' a plurality of serieswhereby a live segment of said set may be not less Vthen 100% of the length corresponding to a unit` impulse. 1

normally stand still to regenerate unit impulses during the time said regenerative relays are uncontrolled by said'line relay means.

4. A system in accordance with` claim 3 in which the line electromagnetic means is a threepositionrelay..

5. A system in accordance with claim 3 in which said regenerating relaysV each controls the other .through a circuit extending through a distributor and connectedv to contacts of said line relay means' to be under the control of said line relaymeans.

6. In a synchronous telegraph system, an interpolating receiving circuit characterized in this that is comprises a plurality ofrelays individually yconnected ,with a corresponding plurality of printer rings'on Vthe receiving distributor whereby the. regeneration of unit impulses of alternately opposite polarity may be effected without movement of the relay armatures.

'7. In a synchronous telegraph system comprising-.a rotary distributor, an interpolating circuit characterized in this, that a plurality oi relays are individually connected with a corresponding plurality .of printer rings on the distributor, and

aplurality of. groups of segments for relaying alternate positive and negative impulses whenever said relays remain quiescent as the result of the reception of insumicent line current to actuate 8. .In a synchronous telegraph system compris- Y ing a rotary distributonan interpolating circuit characterized this, that a plurality of relays are individually connected with a corresponding plurality oiprinterrings on the distributor, a plurality of groups ofrsegrnents for relaying alternate positive and negative impulses whe-never said relays remain quiescent as the result of reception of insucient line current toV actuate them, and

`connections whereby two successive segments (one each vfrom two of said groups) transmit on impulses of the same polarity whenever one of said relays is actuated from one position to another by an incoming impulse of line current.

9. In a' synchronous telegraph receiving system, a plurality of repeating devices adapted to supply positive and negative impulses, synchronlous vswitching means for distributing received signal impulses to said repeating devices inV rotation and for concurrently applying to each repeatingY device an impulse from the preceding device or" such polarity as to tend to operate said device to a position ropposite that oi the'preceding device, signal recording means, and synchronous switching means for distributing lm- ,pulsesY repeated by said repeating devices to said signal recording means.

1Q. In a synchronous telegraph receivingr sysf tem, a plurality oi relays each having an operating winding means and an armature operable between contacts connected to opposite poles of source of potential, synchronous distributing means for distributing received signal impulses to the winding means of each relay in rotation andl reversed polarity to said magnets, a distributor, means including said distributor for operating',

Vthe armatures of said electromagneticA means,

each electromagnetic means beingv under the control of the other, and means independent of said rdistributor for operating said.armatures of said electromagnetic means in responsey to impulses received over a cable or signaling line.

l2. In a telegraph system.,` a cable or signaling line over which signalingiimpulsesare attenuated, a plurality of receiving magnets, electromagnetic means, adistributor, means including said electromagnetic means and said distributor for operating said printer magnets in accordance with the operation of said electromagnetic means,

tures,` printing magnets, meansV including theY armatures of said electromagnetic means for operating said Vprinting magnets in accordance with the signals transmitted oversaid signaling line,

said meansincluding a distributor, and means together with said distributor whereby the armatures of the electromagnetic means move only in response tothe received impulses.V

14. In a telegraph system,V a, signaling line, means transmitting code combinations'of impulses over sai-d signaling line, means whereby onlyV certain of said impulses are received, a distributor, and electromagnetic means including armatures therefor for relayingall of the impulses transmittedover said signaling line to said distributor, said electromagnetic means operative to move its armatures only in response to impulses actually received.

15. In a signaling system, Va transmission line, means for transmitting impulses overrsaid transmission line, printer receiving magnets, av distributor, second means together with said distributor for transmitting impulses of reverse polarity tovsaid printer receiving magnets, while maintaining said second mean-sin iixed position, and means independent of said distributor for operating said second mentioned means in response to received impulses.

16. In a signaling system, a signaling line over which the impulses sent are so attenuated that the rst portion of each4 impulse is not received at the receiving end, printer receiving magnets, a distributor, means together with said distributor for operating said printer magnets in accordance with said received impulses, said means being maintained normally non-operative duringl the transmission of dash signals while repeating said dash impulses to said printer receiving magnets.

17. In a telegraph system, l printer receivingy magnets, electromagnetic means for transmitting impulses of reversed polarity to said printer magnets periodically,4 a distributor, means to-l gether with said distributor whereby said electromagnetic means controls the operation oi if are so attenuated` that the dot impulses are not received, a plurality `of printerlnagnets, a first and a second electromagnetic means, eachV of toV tributor, means for operating said electromagnetic means in response to impulses receivedover said signaling line,` said means being independent of said distributor, and means for operating said Yprinter magnets, under control of said elecf tromagnetic means, said means including said distributors.

19. Ina-signaling system, a signaling line over` which` impulses transmitted are` so attenuated that the impulses of dot character are notfully received, a plurality of printer magnets, a nrst and a second electromagnetic means, a distributor, means .including said distributor for operating each of said electromagnetic means under control of the other, means including said distributor for operating said receiving magnets under the control of said electromagnetic means,

said printer magnet, beingoperat'edV inaccord'-` ance with `the impulses transmitted over said signaling line, and means for operating said,A

electromagnetic means only in accordance' with the impulses received over said signaling line.

20.` In a telegraph system, the combination atV` a terminal station or` a repeating station, of an incoming signaling line, electro-responsive devices, a distributor, second means together ,with` said distributor for transmitting impulses res verse polarity to said electro-responsive devices,

while maintaining said `second means .inapre-` determined position, and means independent of l said distributor for operating said second nientioned means in response to received signal impulses. 21. In a signaling system, over which the signaling impulses transmitted are so attenuated that the dot impulses are not received, printerj receiving magnets and'electromagnetic means in cluding armatures therefor arranged to-cperate said printer magnets in accordance with said signaling impulses transmitted over said signaling line, said electromagnetic means being arranged to hold their armatures in engagement with a predetermined fixed contact While operating said printer magnetsin response to the dot 7 pulses of periodic reversed polarity to said printer'` magnets, said means being maintained ina predetermined iixed position while transmitting said` impulses of reversed polarity, and means for .operating said rst mentioned means in response to signaling impulses transmitted over said signaling system. f

said transmission line, printer receiving magnets, means for transmitting :impulses of reversed polarity to saidA printerV receiving magnets while maintaining said means in `lixed position and means for loperating said first mentioned means in response to received impulses.

ceiving magnets, electromagnetic means including armatures therefor for` transmittinglim- `pulses of reversed polarity to said receiving magnets, said armatures being maintained in engagement with their -xed contacts while transmitting said impulses andV means responsive to received impulses for operating said armatures to their reversed position.

' 26. In a telegraph system, a signaling lineover A,25. `In a telegraph system,` a pluralityl of re-` which signaling impulses transmitted are so .attenuated` that the dot impulses are lost,receiving electromagnetic means includingv armatures, printer magnets, means including the armatures of said electromagnetic means, for operating said printer magnets in accordance with the signals transmitted over said signaling line, and means includingcircuit arrangements whereby the armatures of said electromagnetic meansare moved` Y `ing all of the impulses transmitted over said sig-` naling line, said electromagnetic means being operative to move its armatures onlyin response to actually received impulses.

28. In a telegraph system over which signaling.-

impulses are so attenuated that they do not operate receiving apparatus, receiver relays, repeating, means for repeating impulses received over said line to said receiver relays, said means being normally non-operative while impulses are attenuated, and means Vincluding circuit arrangements whereby said first mentioned means repeats said attenuated impulses to said receiver relays.

29. .Inv a telegraph system, the combination at a terminal station ora repeating station, ofan.

incoming transmission line, electro-responsive devices, means serving to supply Vimpulses of `reversed polarity to said electro-responsive devices while maintaining said means in a predetermined position. v

30. In a telegraphsystem, the combination at a terminal stationor a repeating station, of an incoming transmission line, a plurality of electro,- responsive devices, means for supplying impulses of periodic reversedV polarity to said electro-responsive devices,` said means being maintained in'a predetermined iixed position while transmitting said impulses Vof reversed polarity, and

` means for operating said iirst mentioned means in response to signaling impulses vtransmitted over said line.

31. In a telegraph system, an incoming trans-.1l mission line, a plurality of receiving magnets, a

pair of relays having armatures ion transmitting impulses `of reversed polarity to said receiving magnets, said armatures being maintained in engagement with their iixed contacts when transmitting said impulses, and means for transmitting signaling yimpulses received over said 1in a plurality of electro-responsive devices, electro- 24. In a signaling system, a transmission line,V means for transmitting signaling impulses over l magnetic means provided with armatures for relaying impulses received from said transmission line to said electro-responsive devices, means including circuit arrangements for maintaining the armatures ofy said` electromagnetic means in engagement with a predetermined contact while no impulses are beingyreceived over said line,vand means including the armatures of said electro- A terpreting devices, distributor means; extending naling `impulse as transmitted.

magnetic means for periodically.reversing'the polarity of impulses to said electro-responsive devices while no'impulses are being received over said line. l Y

'33. (In an interpolating system, including, vin combination, ,a receiving circuit comprising a pair of relaysgrecording means, and `means dependent -upon the operation of Vone of said relays to supply impulses of more than unit length and render eiec'tive two or more of said recording means.

V34. Ina telegraph System, the combination of a signaling .line over which the shortest unit signaling impulses transmitted arrive so attenuated as not to `be received in effective amplitude with ja relay instrumentality connected to said line to be voperated in response to longer receivedjsignaling impulses,.other relays, distributor meansV for extending a circuit of polarity determined by the existing position of said relay instrumentality in succession tov saidirelays, signal impulseincircuits from one or another oi said other relays to said signal impulse interpreting devices, and interconnections betweenv said other relays controlling them in such manner that said interpreting devices correctly interpret the shortest unit signaling impulses as Well as the longer impulses. j

35. A system in accordance with claim E4, in which the circuit extended by said relay instrumentality is operatively-continued by said relay instrumentality for a time short as compared to Y the time duration ci a full unit signal impulse as transmitted. 'Y Y 36. A system in kaccordance with claim in which the circuitsextended to said impulse interpreting devices are operatively controlled by said other relays for a time duratien which is long compared to the time duration of a full unit sig- 37. A system in accordancewith claim 3d, in which the circuits extended to said impulse interpreting devices include active distributor segments of length corresponding to the time durationY of 100% of a full unit signaling impulse as transmitted. v

f 38. A system in accordance with claim 34, in which the circuits extended to said impulse interpreting devices include active distributor segments f of length corresponding toa time duration far unit signal impulse period While permitting the transmission or" impulses tothe printer magnets for any desired percentage of Vthe unit signal impulse period up t0 100 per cent.

40. n a telegraph system, theY combination of a terminal station or a repeating station, of an incoming transmission line, electro-responsive devices, means serving to supply impulses of reversed poiarity to Ysaid electro-responsive devices While maintaining said means in a predetermined position, distributor means for ,limiting Ythe effect of line impulses upon said electro-responsive de- -ces to a time interval oi short duration and ieans for vextending. on from said electro-respensiye devices operating impulses of duration greater than said time intervals of short duration; jai. A system in accordance with claims() in which the means for extending on the `impulses is circuit interrupting means for limiting the duration of the impulses.

, WILLIAM A. KNOOP.

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