Sept; 17, 1946. R, TAYLOR HAL 2,407,910 ELECTRICAL SIGNALING SYSTEM Filed June 30, 1943 - ‘ INVENTOR'S REGINALD TAYLOR GEORGE moms BAKER ATTORNEY Piatented Sept. ‘17, 1946 2,407,910 UNITED STATES PATENT OFFICE 2,407,910 ELECTRICAL SIGNALING SYSTEM Reginald Taylor and George Thomas Baker, Liverpool, England, assignors, by mesne assign-l ments, to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 30, 1943, Serial No. 492,832 In Great Britain August 20, 1942 11 Claims. 1 The present invention relates to electrical sig naling systems such as automatic telephone sys tems in which trains of impulses are utilised to effect the setting of automatic switches or the like and is particularly concerned with arrange ments for overcoming the e?ects of distortion in the break-make ratio of impulses comprising in (Cl. 179—16) 2 of distorted impulses are received on a “speed tim ing” impulse responding circuit including an elec tro-mechanical impulse storage and regenerating device, so that received impulse trains are re transmitted in a form corrected as regards ratio and at the nominal speed for the system con cerned. Such an arrangement does more than is really terruptions in a normally closed circuit. Such distortion as is Well known is due to the e?ect necessary for satisfactory selector operation, since of the inductive and capacitative properties of the 10 it is only the impulse ratio which is distorted dur line on the responding relay and may become very ing transmission, the speed of impulsing being serious where long lines or a number of impulse unaffected. The present invention provides an repetitions are involved. impulse responding circuit which, in accordance The chief object of the invention is to provide with the impulsing speed concerned, will produce a simple and reliable arrangement for correct 15 a suitable outgoing impulse ratio which will be ing for the effects of distortion and enabling the acceptable to the receiving apparatus involved. ratio of received impulses to be restored to its According to one feature of the invention, in an original or even a more desirable value. electrical signaling system employing trains of The invention may be of particular value in impulses comprising interruptions in a. control connection with systems employing to some ex 20 circuit, an impulse repeater is provided in which tent at least switches having circuit arrange incoming impulses are repeated without storage ments of the type disclosed in our application at the speed at which they arrive but with a ratio of break to make substantially independent S. No. 434,762 ?led Mar. 14, 1942. It is shown that such switches need no longer be dependent upon of this speed and of the ratio of the incoming impulses. the usual break to make ratio of received im pulses, but rather upon the period which elapses According to-another feature of the invention, between corresponding points in successive im in an electrical signaling system employing trains _ pulses so that the only limit is that the actual of impulses comprising interruptions in a, control speed of impulsing must not be so slow that the circuit, an impulse repeater is provided in which period between similar points in successive im 30 the length of the ?rst repeated interruption is pulses exceeds a predetermined amount. When ?xed and the length of subsequent interruptions such period is exceeded, a switching operation is is adjusted dependent on the speed of the incom arranged to take place characteristic either of ing impulses but regardless of their ratio of break the end of an impulse train or of the release to make. of the connection depending upon the ?nal con 35 A further feature of the invention is that in an dition of the control circuit. Such a method of electrical signaling system employing trains of impulsing is sometimes referred to as “speed tim impulses comprising interruptions in a control ing.” The “speed timing” impulse responding cir-. circuit, an impulse repeater is provided in which cuit thus provides a means of response to incom incoming impulses are repeated without storage ing impulses which operates equally well no mat ter how badly they are degraded due to the re 40 at the speed at which they arrive but with a ratio of’ break to make which progressively ap proaches a predetermined value for successive impulses of a train. The invention will be better understood from In order that advantage can be taken of such 45 the following description of one method of carry active nature of the line and its terminations or to the number of stages of ‘impulse repetition involved. arrangements on existing automatic telephone ing it into e?ect, which should be taken in con junction with the accompanying drawing com plOying “speed timing” selectors into ordinary prising Figs. 1-3. These all show the invention networks of existing types, it is necessary to pro applied to an outgoing impulse repeating relay vide means for remaking received distorted im 50 set at a tandem automatic telephone exchange, networks or for interworking from networks em pulses so that they can be passed on in a form access to the relay set being had over one 01' more acceptable to existing equipment. ' ranks of tandem selector switches operated over One means, particularly applicable to long dis a junction line from a calling automatic exchange, tance dialling, is disclosed in our application S. while the relay set itself connects with an out No. 446,900 ?led June 13, 1942, in which trains 55 going junction from the tandem exchange to a 2,407,910 3 4 distant automatic exchange. Fig. 1 shows the complete circuits of the relay set in question, ‘while Figs. 2 and 3 are fragments only showing will be suitably reduced from the 55 m. s. value‘. The second output make period which will be greater than the ?rst output make period owing to the reduction of the break period will then alternative circuit connections involving a so determine the length of the third output break called stabilising condenser QY which functions period and so on. In this manner the output to reduce the oscillatory nature of the output im break and make periods are so adjusted as to give’ pulse ratio control exerted by the circuit of Fig. 1. at. all speeds a break/make ratio which will be Before proceeding with the detailed circuit de acceptable to the selector switches. ' scription the principle of operation will be dealt‘ Referring now to Fig. l, the incoming left-hand with generally and it may be pointed out that the 10 negative, positive and P leads extend from levels circuit arrangement entirely ignores the ratio of of the tandem exchange selectors, while the right incoming impulses, and functions on the basis hand negative and positive leads connect with of their speed alone to give a suitable output ratio an outgoing junction to the distant automatic which will be acceptable to any selector in the exchange. system. , It is assumed that the telephone networks em The‘, various timing functions involved in the operation of the circuit are performed by con ploy selector switches of the decimal step-by-step two-motion type employing the well-known, A, ‘B’ and C impulse responding relay triad and re denser/resistance timing circuits each ‘of which after a predetermined charging period builds up a suiiicient potential across its condenser to strike sponsive to impulses at a nominal speed of ten impulses per second and of a nominal break to a gas discharge tube connected in circuitthere- , with and so to energise a relay to perform the make ratio of 2-1. The switches are readily responsive to impulses required controlling function. The tube NTA, preferably a neon tube, and associated condenser QX perform the timing function in connection with the “ratio replacement” feature of the relay having a speed range of from 8—l2 I. P. S. pro viding there is no serious ratio distortion, the transmitted break and make periods over this range of speeds being as follows, set, while neon tube NTB in association with con denser QW performs the “speed timing” func Speed Break period Make period tion so .as to enable the appropriate circuit 30 changes to be made at the end of each train of impulses. , ‘ . . ' Preferably the neon tubes are arranged to strike at a voltage of the order of .150 volts and this voltage is built up across the condensers which are connected to .the exchange battery of 50 volts by_ connecting in series therewith a high voltage supply HV, at a potential of 150 volts, via a suitable adjustable resistance. The supply HV isgshcwn separately in various parts In an impulse repeating relay set adapted to function in accordance with the presentinven tion, until the ?rst impulse has been received it is impossible to determine the impulse speed con cerned, and hence to avoid storage, the length of the?rst output break impulse is set to a ?xed 40 of the circuit as different batteries (in the same manner as is the ordinary 50 volt exchange bat value regardless of speed. A suitable value for the tery supply), and its negative pole is connected predetermined ?rst break period is 55 m. s. which is satisfactory both to the magnets and also to the B and C relays which, since they are already energised when impulsing starts have a good L' margin on the ?rst impulse'and generally tend to- fail only on the last of a long train of say 9 or‘ 10v impulses. , On the ?rst release of the relay set impulse re sponding A relay, a 55 m. 5. break period is deliv eredin the output circuit regardless of the length of time the A'relay stays down. After the 55 m. s. period the remainder of the ?rst impulse is then measured, that is to say, until the A relay once again releases at the commencement of the break It" to earth so that a charging voltage of 200 volts is available from the two batteries in‘series. When the relay set is taken into use, relay A operates and at contacts at brings up relay B which locks over contacts hi and at contactsbZ prepares a circuit for the outgoing pulsing relay PU, at contacts 174 applies guard earth to them coming P lead, at contacts 125 connects a loop comprising“ the supervisory relays Dand I across the outgoing negative and positive conductors in order to seize the distant automatic equipment, and at contacts b3 completes a charging circuit for condenser QX v'ia thepotentiometer arrange ment comprising adjustable resistances YY and YZ. The values of thes'eresistancesare such‘that condenser QX will be charged to avoltage some what lower than the striking voltage ofgthe neon If this output make period is 28 m. s., thus cor responding to the 55 m. s. break which obtains Gt) tube NTA, say about 100 volts, and the'circuit is now ready to receive trains of impulses. 0 at a speed of 12 I. P. S., the second output break When relay A releases in response tothe break period can also be 55 m. s. with a resultant make period of the ?rst impulse received, relay PU rap period of 28 m. s. and these Values can remain idly operates, locks over contacts pul and at con unchanged throughout the train. If the ?rst out _ tacts 1M6 opens the outgoing seizing loop so as'to put make period exceeds 28 m. s. thereby indicat repeat the break period of the impulse to the dis ing-that the speed is of a. value less than 12 I. P. S., tant automatic exchange. At contacts pus it a suitable increase in the second output .break completes a charging circuit for condenser QX period- will be made. The second output make period of the second impulse, this period con stituting the make period of the ?rst output im pulse. Via the variable resistance YXjand at contacts complete second impulse time and the second 70 pueit operates relay C to prepare forth‘e charg ing of the “speed timing” condenser QW Via var break period will thereupon determine the length for the third break period and so on. Similarly, iable resistance YW and contacts 02, the charg in the unlikely event of the make period being ing of this condenser being prevented at present less than 28 m. s., thereby indicating a speed ex by the connection of the low resistance shunt ceeding 12 I. P. S., the second output break period 75 thereon via contacts pu4 and resistance YA. period comprising the difference between the 5 2,467,916 Contacts zmZ connect neon tube NTA and relay E. across condenser QX, while the remaining con volts will therefore be greater so that the break. period of the nextiimpulse will be lengthened. In the unlikely event of, the released period of tacts pal are only required in the modi?cations ‘ shown in Figs. 2 and 3. Relay C in Operating, at relay PU being too short to correspond to a 55 . contacts cl disconnects the original potentiom m. s., breakperiod, thereby indicating an impulse eter circuit, looks at contacts 03 and at contacts 04 short-circuits the supervisory relays D and I to provide an impedance-free impulse repeating loop to the distant exchange. On the operation of relay PU condenser QX 10 speed of greater than 12 I. P. S., condenser. QX Will have insuflicient time to discharge back to its original 100-volt value and the period required to charge up to the tube striking value will be shortened, thus giving a corresponding reduction will start charging up and it is arranged that it will reach the striking voltage of neon tube NTA in the break period of the second impulse. in 55 m. s. Tube NTA then strikes and brings . In the above described manner the break and make periods of the output impulse for each re ceived impulse is adjusted so as to give a suitable up relay E which at contacts el releases relay PU regardless of whether the impulse responding 15 ratio on all speeds so as to produce the most relay A is still normal or not, and completes a satisfactory operation of the selector switches.‘ locking circuit for itself if relay A is ‘still normal. It should be mentioned that in some circum-.v Relay PU in releasing, at contacts pu3 completes stances it may not be essential to maintain in the a discharge path for condenser QX via resistance output the nominal 2-1 break to make ratio at all YZ, at contacts Ipu? closes the loop to the distant 20 impulsing speeds as in order to secure the most‘ exchange so as to terminate the break portion of satisfactory operation of the selector switches it ' the outgoing impulse and at contacts p114 re may be desirable to effect slight alterations in moves the shunt from across condenser QW so as to initiate the charging of this condenser. Re lay C, it will be seen, remains looked over con tacts er2 and 03 independently of relay PU and further consideration of the operation of the “speed timing” circuit for controlling relay C and involving tube NTB and condenser QW will be deferred until the operation of the “ratio replace ment” circuit has been completed. As previously mentioned, relay PU in restoring the outgoing ratio over the speed range. _ Considering now the operation of the speed timing circuit involving condenser QW and tube‘ NTB, this functions by determining whether the actual length'of each impulse is greater or less 1 than a ?xed predetermined period which is ap proximately equal to the length of the longest impulse which can be tolerated, namely, a 143 m. s. impulse which corresponds to the minimum dial speed of 7 I. P. S. ' at contacts pu3 completes a discharge circuit for If the predetermined value is exceeded without condenser QX,'while at contacts 1W2 it opens the a further impulse arriving, it is an indication operating circuit for relay E. The latter relay is either that the impulse train has ?nished or that maintained operated for so long as relay A re the calling party has hung up prematurely. In mains normal over contacts cl, b2 and al and the former case the timing circuit on coming this arrangement ensures that relay PU shall not into operation and bringing up relay ER releases re-operate until the next release of relay A. relay C at contacts e72 and re-introduces the The voltage to which condenser QX discharges 40 supervisory relays .D and I across the outgoing is dependent on the time relay PU is normal, i. e. leads at contacts 6T3, while in the latter case until the beginning of the break period of the since the A relay will be normal, relay B will second received impulse at which time relay PU also be released at contacts erl and will restore is re-operated, and at contacts p143 reconnects the relay set to normal. ‘ condenser QX up to the charging circuit via re 45 If impulses follow one another within the pre sistance YX. If this released period of relay PU, determined time period, the next impulse will which determines the make period of the ?rst reset the timing device by discharging condenser outgoing impulse, is just the correct length to QW'and the timing operation will recommence. correspond to a 55 m. s. break, i. e. if it is no This re-setting operation is repeated for each longer than the 28 m. 5. make period which‘ ob impulse of a train until the last impulse of the tains at 12 LP. S., it is arranged that condenser train has been received when the tube NTB is QX will have discharged to the same value, able to strike and operate relay ER as described namely 100 volts, as at the commencement of the above. ‘ ?rst break. Hence the second output break will In the arrangement described in the previously ‘ also be 55 m. s. with a resultant make of 28 m. s. 55 mentioned speci?cation No. 434,762 the timing as determined by the di?erence between the complete impulse length of 83 m. s. and the out put break period of 55 m. s. and these values will remain unchanged throughout the train. If, therefore, impulses are received at a speed of 12 I. P. S., thenregardless of their ratio they are repeated with a replaced break to make ratio circuit is adapted to effect a switching operation after 143 m. s. measured from the beginning of the break period of the ?rst impulse of a train period. In the present instance, instead of using of 2-1 (55 m. s. break, 28 m. s. make) corre one 143 m. s. timing circuit to compare the period (neglecting the magnet operating time), the ar rangements being that it will be reset if a suc ceeding break is received within this 143 m. s. sponding to the nominal 2-1 ratio at which they extending between, say, the beginning of one were transmitted at the distant sending end, and 65 break period to the same point in the‘ next, it . which is most suitable for the satisfactory oper is more convenient to make use of the two avail ation of the distant automatic exchange selectors. able timing circuits acting in conjunction. If the length of time relay PU is released ex Relay PU in operating to initiate the break ceeds 28 m. 5., thereby indicating that the length period of the ?rst outgoing impulse brings up of the complete impulse is greater than 83 m. s. 70 relay C to prepare for the charging up of the and hence that the impulsing speed is less than speed timing condenser QW. After the lapse of 12 I. P. S., condenser QX when discharged via re the 55m. s. ?rst output break period which sistance YZ will drop below its original voltage remains ?xed regardless of the speed in ques of 100 volts and the time required for charging tion, relay PU releases and initiates the charging it up again to the tube striking voltage of 150 7.5 up of ‘condenser QW. In the worst case, i. e. at 2402916 . the minimum speed of impulsing of 7 I. P. S. . 8 period will be 45' m. sand condenser'QX will relay PU will not again operate till 143—55=88 dischargeto a value lower than 100 volts. 7 If the m. 5. later andv condenser QW is therefore ar 2-1 break/make output ratio is also to be mail“ ranged to reach the striking voltage of neon tube tained'at this speed, the next charging time re- 7 ' quired by condenser QX to reach the tube NTA striking value must then be 66% m. s. to pro NTB in a time not less than 88 m. s. so as to pro- . vide an overall timing period of 143 m._ s. In the case of an impulse train at any impulsing speed duce the appropriate second output break period for 10 I. P. S. Under this condition condenser above the minimum of '7 I. P. S.,- relay PU will QX will subsequently only have 331/3 m. s. dis- ' operate to initiate the break period of the next impulse before the lapse of 143 m. s. from its 10 charge time during the second output make peri od. It will then reach a voltage somewhere ?rst operation and hence condenser QW will between the 100 volt Value and the value to which be discharged without the tube striking. At the it discharged in the 45 m. s. first make, and end of the second output break period as deter mined by the impulsing speed concerned, relay clearly the third charging periodwill not there ‘ PU in releasing will initiate the timing of a 15 fore be as great as 662/3 m. -s. so that the third second 88 m. s. period and so on until the end output break period will lie somewhere between of the impulse train. At the end of the train relay PU will fail to re-operate and condenser QW will therefore reach 55 and 662/3 m. s. and so on. - The correction afforded by- the scheme as shown in Fig. 1 is thus oscillatory in nature and ' the striking voltage of tube NTB 88 m. s. after 20 is particularly marked if the maximum correction is placed on the second output impulse as above the end of the last output break period and tube described by way of example. The introduction NTB will ?ash andv will bring up relay ER. Re of condenser QY into the “ratio replacement” lay ER in operating opens the locking circuit of circuit in the manner shown in Fig. 2 is found to relay 0, and at contacts er3 connects resistance YBacross the outgoing speaking conductors. On 25 produce a marked stabilisation eilect with the result that the outgoing impulse ratio settles release of relay C the supervisory relays D and I down to the calculated suitable value almost ‘im in parallel with resistance YB are introduced mediately. across the outgoing speaking conductors, resist Referring now to Fig. 2, it will be. seen that ance YB serving to obviate any danger of release of the distant battery feeding relay due to the 30 condenser QY is initially charged up to the same 100-volt value as condenser QX. When relay PU initial high impedance of the supervisory re lays. When the voltage on condenser QW falls . operates to connect condenser QX to the charg ing circuit at contacts pu3, the circuit for con denser QY is disconnected at contacts 10141. When condenser QX is to be discharged after having ?ashed the tube NTA and having brought up relay resistance YB is disconnected from the outgoing E, with the resultant release of ‘relay PU, it speaking conductors. initially rapidly shares out its 150 volt striking Further received impulse trains are dealt with voltage/with the 100 volt charge on condenser as before described and after the last train has been received the relay set functions in known 40 QY and both condensers then proceed to dis» charge via resistance YZ. On the next operation manner, relay D which is polarised by recti?ers below the “holding” voltage of tube NTB, this tube will de-ionise and relay ER will commence to release slowly. On the release of relay ER, ' MBA and MR3 serving to extend the called of relay PU in response to the next release of re lay A,‘the discharge of both condensers is termi party’s supervision signals back to the calling side nated and condenser QX commences to re-charge' of the circuit by reversing the connections of 45 When condenser QX is to be discharged, it will relay A tothe speaking conductors. initially share out its 150 volt charge with what If the subscriber should hang up during dial ling, a break simulating an impulse will be re ceived so that when relay E operates after the ever charge has remained on condenser QY after the last discharge and both condensers will then ' condenser QX charging period relay PU will be released and relay E will remain locked to the proceed to discharge through resistanceYZ'as before. Similar remarks apply to each succeed earthed back contacts al so that relay PU cannot be re-operated. 88 m. s. after the release of relay PU tube NTB will ?ash to bring up relay ER ing impulse of the train. which as before opens the locking circuit of relayC. In this instance however since the A relay is not now operated, and since the alterna tive holding circuit for relay B is opened by con tacts erl, relay B will now release and will release relay E and initiate release of the connection. - The best relative values of condenser QY and QX can be determined by calculation of the con denser charge and discharge times and voltages under simple conditions and such calculation shows the marked improvement which can be effected by the'introduction of the stabilising ‘con denser. 7 An alternative method of stabilising is shown Returning again to the “ratio replacement” 60 in Fig. 3 where it will be seen that before con~ denser QX proceeds to discharge via resistance timing circuit, since the 55 m. s. ?xed first output YZ it'shares out its striking voltage of 150 volts break period corresponds to the break period of with whatever voltage condenser QY has accumu a 12 I. P. S. break impulse at the nominal 2-1 lated via variable resistance YV during the break/make ratio, and since it is desirable that , at a speed of 12 I. P. S. the output impulses shall 65 chargingtime of condenser QX. It' should be pointed out that the ‘.'‘ratio' re have this ratio to secure the most satisfactory placement” circuit is completely independent of operation of the selectors, it follows that if the incoming junction resistance values so that it is resultant ?rst output make period is 28 m. s. unnecessary for the circuit to be associated with corresponding to an i'mpulsing speed of 12 I. P. S. it is necessary to make condenser QX discharge 70 any particular junction line. Moreover, since it entirely ignores the ratio of the incoming im~ from 150 volts to say 100 volts in 28 m. s. thus pulses it will function to give the desired output providing a 55 m. s. second break 'period and so on as described; ‘ If however, the received impulses are at a as long as any impulses are received, no matter how badly they are degraded, provided relay .A speed of say :10 I. P; 6., the ?rst output make 75 closes its back contact sufficiently long'to operate 2,407,910 10 relay PU and opens it sufficiently long to release relay E. charge tube for preventing further operations in ' case the time between received break impulses What we claim as new and desire to secure exceeds a predetermined time. 7. In a signaling system, an impulse repeater having an input circuit over which impulsesof varying speed and break to make ratio are re by Letters Patent is: 1. In a signaling system, a repeater responsive to received make and break impulses over an incoming circuit for repeating the same over an outgoing circuit, a relay in the repeater operated by the ?rst interruption of the incoming circuit, a second relay responsive to the operation of the 10 ?rst relay to open the outgoing circuit, a con denser, a gas discharge tube, means for charging the condenser to the striking voltage of the tube, and means responsive to the striking of the tube to terminate the operation of the second relay 15 and thereby close the outgoing circuit. 2. In a signaling system, an impulse repeater controlled over an incoming circuit by break and make impulses to repeat similar impulses in an outgoing circuit, a relay in said repeater re 20 sponsive to a break in the incoming circuit, a ceived, relay means in said ‘repeater responsive to said received impulses for repeating corre sponding impulses over an output circuit with out storage and at the same speed as received, and timing means comprising an aperiodic cir cuit and a gaseous discharge tube associated with said relay means for causing the break to make ratio of the repeated impulses to have a desired value which is substantially independent of the speed or ratio of the received impulses. 8. In a signaling system, an impulse repeater having an input circuit over which impulses of varying speed and break to make ratio are re ceived, relay means in said repeater responsive to said received impulses for repeating corre sponding impulses over an output circuit with out storage and at the same speed as received, and timing means associated with said relay means for causing the ?rst repeated break im pulse to have a ?xed length and for varying the second relay operated by the ?rst relay to control the outgoing circuit, a condenser, a gas discharge tube, said condenser connected in a charging cir cuit by the operation of said second relay and 25 continuing to charge until it reaches the striking voltage of said tube, and means operated when length of subsequently repeated break impulses the tube strikes for causing restoration of the in accordance with the speed of the received im second relay. 3. A system as claimed in claim 2 in which said second relay closes a discharge circuit for said condenser for a time dependent on the next interruption of said incoming circuit, the amount of discharge controlling the time of operation of said second relay upon its next energization. 4. In an impulse repeater, a line relay respon sive to received impulses consisting of breaks and makes of an incoming circuit, an outgoing cir cuit, a relay controlled by the line relay for open ing the outgoing circuit when the line relay is de energized, a condenser having a preliminary charge and connected for an additional charge by said second relay to time the break of the outgoing circuit, means for discharging said con denser to different points responsive to subse pulses. 30 9. In a signaling system, an impulse repeater, a circuit over which impulses of varying speed and break to make ratio are at times received, relay means in said repeater responsive to said received impulses for repeating corresponding 35 impulses over a further circuit without storage and at the same speed as received, a ?rst timing means associated with said relay means for caus ing the break to make ratio of the repeated im pulses to have a desired value which is substan 40 tially independent of the speed or ratio of the re ceived impulses, and a second timing means as sociated with said relay means for terminating impulsing conditions a predetermined time in terval after the last impulse of a series. 45 10. A signaling system as claimed in claim 9 in quent received impulses to thereby determine the which each of said timing means comprises an time of break of the outgoing circuit upon the aperiodic circuit and a gaseous discharge tube. next operation of said second relay. 11. In a signaling system, a ?rst circuit over 5. A system as claimed in claim 2 including a which impulses are at times transmitted, a gas second condenser and a gas discharge tube for 50 discharge tube, means associated with said ?rst timing the released time of said second relay, and circuit for initiating an impulse over a further means for terminating impulsing conditions if circuit and for initiating the ?ow of an aperiodic said second relay is released for more than a pre current in a circuit connected to said tube in re sponse to the receipt of an impulse over said determined time. 6. In an impulse repeater, a line relay respon 55 sive to received break and make impulses, a sec ond relay controlled by each deenergization of the line relay to repeat a break impulse,-a con denser and a gas discharge tube for timing the break of each repeated impulse in accordance 60 with the time between received break impulses, and a second condenser and a second gas dis ?rst circuit, said aperiodic current causing the tube to ?re a predetermined time interval there after, and said means being operated when said tube ?res to terminate the impulse over said further circuit. REGINALD TAYLOR. GEORGE THOMAS BAKER.