US2187158A - Telegraph system - Google Patents

Description

Jan. 16, 1940. F. s. KINKEAD4 2,137,153

v TELEGRAPH SYSTEM i AFiled Aug. 22, 1936 2 Sheets- Sheet 1 Seann i INVENTOR ES. KIN/(EAD "J2/5! 4 ATTORNEY 16, 1940. F. s. Kl-NKEAD TELEGRAPH SYSTEM Filed Aug. 22. 1936 2 sneets-sheet 2 sum.

danku Q0 ,Hwpmma NVENTO? F: 5. K/NKED BYJW/j A Tron/mf relay or switching PatentedJan. 16, 1940 UNlTED STATESA TELEGBAPH SYSTEM Fullerton S.

Kinkeld, Ridgeeld Park, N. J., ll-

lignor to Bell Telephone Laboratories, Incorporated. New York, New York N. Y., a corporation of Application August zz, 193e, serial No. 91,361 '1 claims. (o1. ris-' ro) This invention relates to telegraph systems and more particularly to telegraph systems subjected to interfering ilelds employing gaseous conduction tubes.

Gaseous conduction tubes are usually employed in pairs in telegraph systems for repeating telegraph signal impulses. Each tube of a pair usually restores the other tube to its non-conducting condition when it starts to conduct current, and one or both ofthe `tubes serve to repeat the signal impulses.

ln telegraph systems subjected to interference and lparticularly carrier current telegraph -systems` subject to static interference employing gaseous conduction tubes, the interference irequently vrenders both tubes conducting at the same time. When this occurs it is necessary to restore one .or both tubes to the non-conducting condition by momentarily removing the tube or tubes from the circuit or the potential supplied to the tube before the circuit will again repeat the signal impulses.

It is an object oi this invention to provide additional restoring means which is operative to restore one of the tubes after a predetermined interval ci conduction independently of the condition of the other tube.

inasmuch as one ci the major reasons for using gaseous conduction tubes in telegraphsystems is that they eliminate relay contacts and related trouble and maintenance, a feature of this invention relates tovrestoring means, the circuits ot which are free from relay and other moving contacts, in othery words, these restoring circuits are in a state ot fixed or unvarying continuity.

The terms, "in a xed state otv continuity, "in an unvarying state of continuity, are used in this application to indicate that during the normal operating conditions. of these circuits they are not interrupted by relay or switch contacts and that they-do not depend upon the operation oi relay or switching contacts @on performing their viunctions. These terms do not Exclude contacts used to establish the circuits. Neither do they exclude main battery or power supply switch contacts, the contacts in the tube sockets, or other contacts used to establish the various circuits. However, once the circuits are established they remain inV a fixed state of continuity duringl their operation.

. In accordance with one embodiment of the invention a pair oi'gaseous conduction tubes are employed lto receiveA direct current or low frequency telegraph signal impulses.

-In other embodiments of the invention a pair of gaseous conduction tubes are employed in carrier current telegraph station circuits in combination with high vacuum tubes which act as receiving amplifiers and transmitting oscillators to amplify received carrier current signal impulses and to generate and transmit carrier current signal impulses. L

These and other objects and features of this invention, the scope of which is set forth in the appended claims. may be more readily understood from the following description when read with reference to the accompanying drawing in which:

Fig. 1 shows a direct current telegraph subscribers station circuit employing a pair of gaseous conduction tubes controlled inaccordance with this invention for receiving and repeating direct current signal impulses;

Fig. 2 shows a carrier current telegraph station employing a pairof gaseous conduction tubes controlled in accordance with this invention in combination with high vacuum tubes for receivmg and transmitting carrier current telegraph signal impulses; ln the embodiment shown in Fig. 2 a rectifier is provided for supplying all of the biasing potentials for the various tubes;

Figs. 3 and 3A show a carrier current telegraph subscribers circuit adapted to transmit and receive both carrier current signaling impulses and also carrier current supervisory impulses employing a pairof gaseousconducton tubes controlled in accordance with this invention, in combination with a single high vacuum tube for amplifying received carrier current impulses and also for generating and transmitting carrier current impulses. g

Referring now to Fig. 1 line I0 is from a distant telegraph station and is connected to the primary windings of transformers II and I2 and transmitting resistance il.A The sending contacts 40 34 are connected in parallel with xed resistance s through the tipsof jacks 28 and 29 and plugs @Il and 3l, it being assumed that these plugs are inserted in the respective jacks to connect the teletypewriter 32 with thestation circuit shown in Fig. 1. Resistance 9 is provided to improve the wave shape of transmitted signals. The use of this lixed resistance 9 is possible with sensitive gas-lled tubes I3 and I4 for receiving sig- 50 nal impulses and tends to make the impedance of the line more constant during the transmission of signal impulses. The secondary windings of transformers I I and I2 are connected to the grids of tubes I3 and I4 through current-limiting re- 55 la heated cathode, a

sistances I 3 and I6, Irespectively. The center point of the secondary I I and I2 is -connected through battery or biasing potential to ground. Battery 35 provides a suitable grldbias for tubes I3 and I4. As shown in Fig. 1 this biasing battery applies a negative potential to the grids of tubes I3 and I4 but may equally well apply a positive potential i1' tubes I3 and I4 are of a type which requires positive bias on the respective grids. The heaters1 of tubes I3 and I4 are energized from the source of alternating current I8 through a transformer I`I. Rectifier I9 is also connected to the source of alternating current I8 and supplies the plate potential for tubes I3 and I4. Rectier I8 may include any filter network such as is commonly used to smooth out the rectied current.

Tubes I3 and I4 as shown in Fig. 1 comprise heater for heating the cathode, a grid or control member and an anode. These' elements are enclosed in an envelope which contains a suitable gas such as mercury vapor or argon at a low pressure. In tubes of this type the grid or control member is usually eiiective to control the starting of a'discharge current be.- tween the anode and cathode but is ineffective to stop the current once it is started. Tubes of this type have been called by various names. such as trigger tubes. grid controlled arc discharge grid controlled rectiners, thyratrons, etc.4

It is to be understood that while three-element gaseous conduction tubes I3 and I4 have been shown in Fig. 1, other types of tubes may be used equally well. For example. directly heated cathod may be employed or multi-element or screengrid gas-illled tubes may be employed.

The anodes or plates of tubes I3 and I4 are inductively connected together through windings 2i and 22 of transformer 23 and condensers 24 and 2i. The output of tube I3 is connected to the receiving magnet 33 of the teletypewrit'er 32. The output circuit of tube I4 is provided with resistance 23 which cooperates with condenser 2l in auch a way that tube u is extinguished s short is rendered conducting. resistance 26 and condenser 25 to restore tube I4 to the non-conducting condition isindependent oi' the operation of time I3.

The operation oi' the\ sending contacts 34 of teletypewrlteru in accordance with the signal need not be repeated here. A more complete description of suitable teletypewriter apparatus may be found in U. S. Patents 1,595,472 granted August 10, 1926to H. L. Krum and 1,904,164 granted April 18, 1933, to Si. Morton et al. It is to be understood, however, that other teletypewriter apparatus may be used equally well with the circuits shown in the various gures of the drawings.

It is to be noted that the transmitted impulses will an'ect transformers, II and I2 in substantially the same manner as the impulses received from line Il and 'will actuate the teletypewriter and will cause it to print a home copy.l of the transmitted message.

When power is connected to the tubes I3 and I4 of Fig. 1 either or `both oi' the tubes may be- 'come conducting or neither of them may become conducting until tube I3 becomes signalimpulses are received.l -If conducting it remains cimcluetwindings of transformers r.typewriter 32', sleeve of plug required ing until a spacing impulse is received. If tube I4, however, is turned on it will be extinguished a short time afterwards because resistance 26 is of such a .value that the potential drop across itrises to such a value that the potential between the anode and cathode of tube I4 falls below the value required to maintain a discharge through tube I4 whereupon tube I4 is extinguished. If neither tube becomes .conducting when the power is turned on, the ilrst impulse received will cause the corresponding tube to become conducting and the next impulse of the opposite character will cause the other tube to become conducting, and so on. In order to more fully explain the operation of these tubes in repeating signal impulses assume that tube I3 is conducting, that tube I 3 is rendered conducting by marking impulses and that tube I4 is momentarily rendered conducting by spacing impulses. Assume further that the contacts of transmitting device 34 of teletypewriter 32 remain closed during the reception of signaling impulses. This is the normal manner of operation of teletypew'riter apparatus. Y

During the time tube I3 is conducting, a path may be traced from the positive terminal oi.' the rectifier I3 through resistance 21, sleeve of Jack 23 and plug 3i, the receiving magnet 33 of teleimpulse -is received over line I l a potential will be induced inthe secondary winding of transformer .I2 in such a direction as to cause tube I4 to become conducting.` Tube I4 in becoming conducting causes condenser 2l, which had previously become charged through resistance 23,' to discharge through winding 22 of transformer 23 and the anode-cathode circuit of tube I4. The discharge of this condenser 25 through winding 22 of transformer 23 induces a voltage in the wind- 2| 1of transformer 23 which is applied to the anode of tube I3 through condenser 24 in such a direction as to momentarily reduce the potential of the anode of tube I3 below the value required to maintain tube I3 ionized or conducting. Tube I3 will thereupon be rendered. non-conducting. later when condenser 2l discharged tube I4 will also cease to be conducting because the value of re-A sistance .23 is so high that the-potential drop across it causes othe potential applied to the anode of tube I4 to become less-positive than that required to maintain the tube conducting. If the next marking impulse arrives before tube I4 is extinguished as pointed out above it will render tube I3 conducting through transformer II. Tube I3 in becoming conducting will cause con; denser y24, which has become charged during the interval when tube I3 was non-conducting, tc discharge through winding 2'I-'of transformer 23 and the anode-cathode circuit of tube I3. @The becomes conducting when the power discharge of condenser 24 through winding l2| of transformer 23 will induce a voltage in the winding 22 of transformer 23 which is applied to the 'anode or plate of tube I4 in such a direction that tube I4 will be extinguished because the anodecathode potential willsbe reduced below the value to maintain tube I4 conducting. In the ,preferred embodiment of this` invention, however, tube I4 becomes extinguished due to the action of resistance 23 and condenser 2l before the arrival of the next marking impulse, when this impulse arrives it will renderV tube I3 conducting again.

'awaits but will produce no further effect upon the operation of tube I4, because the potential induced in winding 22 is in such a direction as to reduce` rent does not ilow in this path. If, as assumed,-

tube I3 is conducting during'the time marking impulses are received over line III current will flow through magnet 33 in response to marking lli impulses received over line III and willv be interrupted in response to spacing impulses received over line I0 because tube I3 is extinguished duri'rg the reception of spacing impulses over line It is evident that if both tubes I3 and I`4 are simultaneously rendered conductive by disturbing voltages induced in line I0, tube I4 will become non-conducting a short interval of time later and that tube I3 will become non-conducting upon the reception of the iirst spacing impulse so that the system will again become operative and will require no attention either to extinguish one or vboth of the tubes or to insure that the proper tube is operating at `any given time.

The signal impulses arriving over line Ill may either be of current and no-current or they may be positive and negative signal impulses. As shown in Fig. 1, the transmitting contacts 34 of teletypewriter 32 are arranged to transmit signal impulses of current and no-current to line I0. Under these conditions it is the usual practice to receive the same kind of impulses over line III.

It is to benoted, however, that the receiving circuit shown in Fig. l. will operate equally well with neutral impulses, i. e., current and no-current impulses or polar signal impulses, that is, positive signal impulses and negative signal impulses'.

The circuit in Fig, 2 is adapted to receive and ltransmit carrier current telegraph signal impulses.

The transmitting contacts 34 of the teletypewriter 32 are connected to an oscillator tube 54. During the time these contacts are closed the feedback or plate coil of transformer 52 is shortcircuited so that the tube 54 will not oscillate.

When these contacts are open, however, tube 54 will oscillate at a carrier current frequency largely determined by the constants of transformer 52 and the eondensers connected to its windings. This carrier current is then transmitted through windings 49 of the hybrid coil 41 to line I0 and balancing network '48. In case it is desired to receive a "home copy of the message currents transmitted overline -I'I balancing network 48 is slightly unbalanced so that sufficient energy flows through transformer to actuate amplifier tube 34 which in turn will cause the home printer to be actuated in accordance with the signal impulses transmitted. The operation of the transmitting circuit is well known and need not be repeated in greater detail.

As shown in Fig. pentode tube. It is to be understood, however, that a three-element, four-element or other type of tube may be employed to transmit the signal impulses when it is so desired.A As shown in Fig. 2 the vplate potential for tube 54 issupplied by rectler I3 which,I in' turn,- is connected to a source of alternating current I8. Rectifier I9 may be of anysuitable type and may include the 2 the oscillator tube 54 is a.

usual filters and networks commonly employed in rectifiers for supplying plate battery for vacuum tubes. The filament or heater circuit of tube 54 has not been shown. It is to be understood that this heater circuit as well as the heater circuit for 5 the other tubes 43. I3 and I4 shown in Fig. 2 may -be of any suitable or convenient type. These filaments or heaters may bev energized from the source IB of alternating current through a suitable transformer or they may be energized from 10 any other suitable source of electric power.

The carrier current signal impulses received over line I0 pass through windings 50 of hybrid coil 41 and divides part of each impulse passing through coils 5I tov balancing network 48. The 15 remaining portion of each of the impulses pass through the primary winding of transformer 45 and induce voltages in the secondary winding -thereof which may be tuned to the frequency of the carrier current in any suitable manner as for example by condenser 46. The secondary winding of transformer 45 is connected to the imput circuit of amplifier tube 43. Amplifier tube 43 as shown in Fig. 2 is a high vacuum three-element heater type amplifier tube.- It is to be under- 25 stood, however, that other types of tubes may be employed such as directly heated cathode tubes or a multi-element vacuum tube in case higher amplification is desired. As shc Nn in Fig. 2 the grid bias for tube 43 is provided by network 44. 30 The anode-cathode current iiowing through this network produces a Voltage drop which tends to make the cathode more positive with respect tol ground and therefore more positive with respect to the grid. In other words, the grid is more negative than the filament by the amount -of voltage drop across network 4d. The anode potential is supplied from rectifier I3 in the same manner as it is supplied'for the oscillator tube 54.

The received signal impulses are amplified by tube 43 and transmitted through the output transformer 42 to demodulator bridge 4I. Here the signal impulses are demodulated and applied to the primary winding 3l of the input trans- 45 former of gaseous conduction tubes I3 and Id. Thus when impulses of carrier current are receiv'ed over line Ill the amplified impulses are applied to the demodulator bridge 4I which demodulates the signal impulses and supplies the low frequency impulses to the primary winding of transformer 3l causing direct current to flow through this winding 3l when carrier current is received from line I0.

As shown vin Fig. 2, a single input transformer having windings 3l, 38, 39 is provided for applying the signal impulses to the gaseous discharge tubes I3 and I4. It is to be understood, however, that two separate impulse transformers may be employed as shown in Fig. l or that a single imen pulse transformer as shown in Fig. 2 may be employed in Fig. l when it is so desired.

The demodulated carrier current owing in Winding 3l of the input transformer induces a voltage in the winding 39 in such a direction as 05 to cause tube I4 to become conducting. If tube I3 is non-conducting at this time no further ac' tion takes place until condenser 25 is discharged sufilciently so that the potential drop across it is insuiiicient to maintain a discharge through tube I4. At this time tube I4 will become extinguished. Resistance 26 is provided to charge condenser 25 during the timetube I4 is non-conducting but is of so high a value thatit will not supply sufficient 'current to rmaintain the poten- 15 tial drop across the tube I4 above the critical value required to maintain current owing between the anode and cathode circuit of the tube. When the carrier current impulse ceases in line I0 the amplined and de modulated current will also cease owing through winding 31 of the input transformer. This will induce a voltage in winding 38 of the input transformer in such a direction that tube I3 will become conducting. This will cause the current to flow through the anode-cathode circuit of tube I3A and through the printer magnet 33 of the teletypewriter 32 which is, in series with the anode-cathode circuit of tube I3. Upon the reception of another carrier current impulse the amplified and demodulated current will again flow through transformer winding 31. This will'again cause tube Il to become conducting. Tube I4 in becoming conductive supplies an extinguishing voltage to the anode of tube I3 through condenser 33 in a well-known manner which causes tube I3 to become nonconducting. A short interval of time later, as previously described, when the potential of `condenser 25 falls below a certain value tube I3 will also become non-conducting providing tube I3 has not again become conducting in response to the cessation of the received carrier current signal impulse. Iftube I3 becomes conductive before tube I4 becomes non-conductive tube I3 causes tube I 4 to be extinguished by applying an A extinguishing potential through condenser 33 -in a well-known manner.

If, due to some interfering or static potential received from line Ill, both tubes I3 and I4 are simultaneously rendered conducting, tube i3 will be extinguished by potential across condenser 25 falling to below the critical value independently of the condition of tube I3. Whenl then an impulse of carrier current is again received from line I3 tube I4 will be rendered conducting and extinguish tube I3 as previously described and the circuits operate thereafter in a normal manner. Thus under these conditions the circuit will automatically resume an operative condition without any attention or maintenance as soon as signal impulses are again received.

It should be noted that the contacts 3l of teletypewriter 32 are shown normally closed in Fig. 2 just as they are shown in Fig. 1. However. when the contacts 34 are closed in Fig. 2 no carrier current is transmitted over the line I Il whereas in Fig. 1 when the contacts are closed direct current is transmitted over linev Il. It is to be further noted that as in Fig. 1 tube I3 is normally conducting responds to current in line I3 and causes current to iiow through the printer magnet 33 whereas in Fis. 2 tube I3 while normally conducting and causes current to now through printer magnet 33 it responds to no-current impulse in line III. However, since the teletypewriter responds in both cases exactly the same a similar type of instrument may be used. the inversion of the impulses in line I3 being ac. complished within the circuit of Fig. 2 by. as for example, reversing the circuit connections tothe input transformer comprising windings 31, 33 and 33 or demodulator bridge II and by the connection to oscillator 33.

A feature of Fig. 2 is that the circuits of all of the tubes are arranged to have all their biasing potentials supplied from a single rectifier source I3. As previously pointed out network 33 provides grid bias for tube 43. In a similar manner network 33 provides the required grid bias for a printing magnet in response to oscillator tube 34. Network 33 provides, in a similar manner, a bias for the gaseous conduction tubes I3 and I I. However, since neither of these tubes may be conducting for intervals of time, it is necessary to provide a potentiometer 'arrangement which will insure that there will always be suilicient bias on the grids of the tuh to maintain them in a non-conducting condition.

By suitable choice of the potentiometer resistance, the desired bias under the various conditions of the operation of these tubes may readily -be obtained. While similar arrangements forsupplying the biasing potentials to the tubes of the other figures have not been shown in the other gures, it is to be understood that the biasing potentials for the tubes shown in the circuits of the other figures may be readily obtained in the same manner by the use of networks such as shown in Fig. 2. Figs. 3 and3Ashowacarriercurrentteletype-- writer subscribers stationcircuit which may be connected to a distant teletypewriter switching exchange through intermediate telephone switching exchanges and over telephone wires and equipment similar to the circuit shown in applicants application Serial No. 11,194 filed March 15, 1935, Patent No. 2,106,352 issued Jan. 25,

1938. but employing gaseous conduction tubes.

Gaseous conduction tubes controlled in accordance with this invention have the following advantages: they are sensitive and readily'operate attenuated impulses received over such an extended line. However, such an extended line is susceptible to inter? feringiields, such as static, so care must be taken to prevent improper operation of the tub due to this static. Means are provided for transmitting carrier current supervisory signals as well as carrier current intelligence signals over the and having the 'same carrier current or channels. In addition, the telemotor control, as well as the control frequencies typewriter is as shown in 111g. 3 with all the nected from sources of power.

In ordertoinitiateacall, thesubscribermomentarily depresses the-start key 13 which closes its contactsand causes relay 33 tooperat'e in a circuit through the contacts of key 13, the winding of relay 34 to the source of alternating current I3. Relay 3l in operating locks operated in a path from source I3 through its own winding and upper made contacts, the lower contacts of relays. 33 and 33 in parallel, contacts of the emergency stop key 1I to the opposite side of the source of power I3. Relay 3,3-in operating also connects source I3 to the printer motor 33,

'to rectifier I3 and to transformer I1. This ating condition and it is supplying voltage to its output leads,itwillcauserelay33tooperatein a circuit'from positive terminalzof the rectifier through the-1vinding of relay 33 to grmmd and thence backtothegroundedterminalofrectier I3.- The operation of relay 33 transfers he T .andRleadsoflinefromringex-U andselay theheatersaromas l 65 to a bridge network 11 which provides a path .for direct current between T and R. leads of 34 of teletypewriter 32 will be actuated in accordance with the signal impulses to be transmitted. The operation of contacts 34 open-circuit certain coils ofthe bridge network 11 which causes this bridge to become unbalanced. When this bridge becomes unbalanced it provides a feedback path from the plate circuit of tube 56 to its input or grid circuit which causes tube 56 to oscillate at a frequency determined by the constant of its circuits including condenser 46. The

oscillation of tube 56 transmits a carrier current impulse over, line Ill. A portion of the oscillating current of tube 56 is also transmitted through transformer 42 and demodulating network 4| to tubes I3 and I4 to actuate receiving printer mgnet 33 of teletypewriter 32 to print a home copy" in a manner similar to the manner which will be described hereinafter when the teletypewriter responds to carrier current impulses received over line I0 from a distant point. Tube 56 may be of any suitable type of high vacuum tube capable of both amplifying and oscillating.

As shown in Fig. 3 a heater type cathode threeelement vacuum tube is employed. It is to be,

understood, however, that other types of vvacuum tubes may be employed equally well as, for example, if a greater output power or amplification is required, a power output pentode tube may be employed as will be readily understood by anyone skilled in the art.

After the operator at the central station has received the necessary information she will respond by transmitting signal impulses to the subscriber. These impulses arrive over line I0 and are applied to the bridge network 11 and thence to the grid circuit of tube 56 where they are amplified and applied to the output transformer 42. Under these conditions the sending contacts 34 of the teletypewriter 32 are clos-d so bridge 11 will be substantially balanced. Consequently there will be no feedback path between the anode or output circuit of this tube and its input or grid circuit.

If it is desired, the balance of the bridge or bridge arrangement 11 may be purposely made imperfect so that a small amount of feedback or regeneration between the input and output circuits of tubes 56 is obtained thereby increas-l ing the amplification and output of this tube'. However, it is essential that under these conditions the feedback remains below the value necessa-ry to maintain oscillations between the circuits of this tube. V

The amplified carrier current signal impulses are applied to demodulating network 4I vthrough transformer 42 where they are demodulated.

The resulting low frequency direct current impulses ow through the winding 31 of the input transformer to tubes`|3 and I4. Under these conditions tubes I3 and I4 operate in the manner described with reference to Fig. 2 to repeat the signal impulses to the receiving magnet 33 of the teletypewriter 32, each tube serving to extingui'sh the otherwhen it starts conducting. Tube I4 is provided with additional. extinguishing networks comprising resistance 26 in combination with condenser 25 which will extinguish tube I4 a predetermined time interval after it has become conducting independently of the condition or operation of tube I3 should both tubes become conducting at the same time due to any accidental or stray elds being simultaneously applied to the input circuits of both tubes as a starting condition.

After the connection has been established between. two telegraph stations similar to Fig. 3 or between Fig. 3 and any other teletypewriter station which is capable of transmitting and receiving telegraph signal impulses through suitable circuits to Fig. 3, the subscribers at the two stations may communicate with each other. During this time the operation of the circuit shown in Fig. 3 will be as described above, sending contacts 34 causing the bridge 11 to be unbalanced whereby tube 56 will act as an oscillator and transmit corresponding carrier current signaling impulses over line I0. Likewise, during thel time impulses are being received, amplifier 56 will amplify the carrier current impulses and transmit them to tubes I3 and I4 through transformer 42 and demodulator network 4I to actuate the receiving magnet 33 of theteletypewriter 32.

If at any time either before, during, or after the transmission of signaling impulses between the subscribers stations, subscribers station shown in Fig. 3 desires to recall the telegraph switching operator, he will momentarily depress recall key 59. The operation of recall key 59 causes the operation of relay 51 in a circuit traced from ground at the bottom contacts of recall key 53. windingof relay 51, current fregulating resistance 13 to the positive terminal of rectier I3. This causes relay 51 to operate. in operating disconnects the grid circuit of tube I4 from the winding 39 and connects it to resistance 14 and condenser 16. The upper contacts of the recall key 59 charge condenser 16 toa negative potential considerably greater than that required to prevent discharges through tube I4. When recall key 59 is released, condenser 56 will start to discharge through resistance 14.

Relay 51 in operating also. open-circuits the lower left-hand coil of the bridge network 11 which will cause tube 56 to become an oscillatol and transmit carrier current to line I 0 similar to the operation of contacts 34 which open-circuit the same coils or circuits of bridge 11 as described above. The innermost top contacts of relay 51 causes relay 51 to lock up independently of the position of recall key 59 over a path traced from ground through its own contacts, upper break contacts of relay 58, winding of relay 51 through current limiting resistance 13 to the positive terminal of rectifier I9. The lower contacts of relay 51 transfer the plate or anode of tube I4 from the extinguishing circuit of tube I3 to the positive terminal of rectifier I9 through Relay 51 charge on condenser 18 will have been discharged through resistance 14 so that the potential on this condenser will fallito a value to permit or tive terminal of rectifier I9. Resistance 12 is also connected in parallel with the anode-cathode circuit oi' tube I4 and is of such a value as to reduce the potential drop between the anode and cathode of this tube below the critical value required to maintain a discharge through the tube so that the tube is extinguished. The upper contacts of relay 58 `in further operating break the locking circuit of relay 51j traced above from ground on its innermost top contacts, through the top break contacts of relay 58 to the winding of relay 51. Relay 51 in releasing closes the circuit of the lower left-hand coil of bridge 11 and thus interrupts the carrier current transmitted to line I0. Relay 51 in releasing -also releases relay 58 and restores the signaling circuit to its signaling condition whereupon the operator after having recognized the recall signal will transmit signaling impulses to the subscriber to determine what additional service is required. The subscriber then may communicate with the operator and other subscribers stations to which he may be connected as hereinbefore described. At the termination of a call, the normal way of restoring the teletypewriter and circuit to normal is to transmit some particular character or group of characters, such as "upper case H. Upon the transmission oi' upper case H all the teletypewriters equipped with the motor stop feature, a code bar or lever 19 will be momentarily actuated. This momentarily closes contact 92 which completes the circuit of relay SI from ground through contacts l2, winding of relay CI to the positive terminal of rectier I9. The operation of relay II will through its bottom contact cause the operation of relay 60 in a circuit from ground through the bottom contacts of relay 9|, winding of relay 90, the positive terminal of rectiner I9. Relay 90 then locks operated in a circuit from ground through its innermost top contacts and windings to the positive terminal oi" rectifier I9. Relay l0 in operating connects ground to the winding of relay 51 in the same manner that the' recall key connected ground through the winding of this relay and, in addition, connects an additional condenser-15in parallel with condenser 16. The upper contacts of relay II charge both condensers 1I and 1i to a negative'potential considerably higher' than the potential required to prevent a discharge -through tube Il. 'IEhe ground connected to the winding of relay l1 by relay 99 .operates relay 51 and causes the transmission of carrier 'current signal impulsesover line I0 in a manner similar to 'that abovedescribed when recall key 59 was operated. In this case, however, condenser 1I being in parallel with condenser 19 -further increases the time required for the potential of these condensers to fall to the value which will permit or cause a discharge through tube Il to operate relay IL This longenperiod of time during which carrier current is continuously transmitted over line I l is interpreted bysapparatus at the teletypewriter switchboard as a"disconnect signal so that the operator will disconnect the subscribers. The

operation of relays B1 and 58 are with this exception substantially the same as described when a recall key is operated. However, when relay Il operates it opens the locking circuit of relay I4 because, under this condition, relay 60 is also operated. Relay M in releasing due to the opening of its locking circuit disconnects the source of power I8 from the teletypewriter motor 63, rectifier I9, and the cathode heaters oi tubes 56, Il and Il. When the potential is removed from the rectier, the potential of the positive terminal falls to zero and relay $0 will release thus restoring the entire circuit to normal.

In case there is trouble which renders the upper case H motor start mechanism inoperative, the subscriber may stop the teletypewriter motor and return the circuit oi' Fig. 3.to normal by momentarilyfoperating the emergency stop key 1|. 4The operation of this stop key opens the locking circuit of relay 94 which causes this relay to release and restores the circuit to normal and stops motor 6I as previously described.

It should be noted that under signaling conditions, that is, the transmission oi' message current impulses, tubes I 3 and I l are extinguished by circuit arrangements which do not employ relay contacts. 'I'he operation of the supervisory relays is much less frequent than the receiving magnet and tubes so that these relays will not require much attention or maintenance.

In order to call the subscriber at station 3, the operator at the central station or switchboard will cause ringing Acurrent or alternating! current to be applied to one of the conductors of the line,` for example the ring R, which will cause ringer $1 to ring in a circuit from the ring R conductor through the winding oi ringer 61 to ground through condenser Il. In case the subscriber does not answer and the operator or the station desiring to communicate with the subscriber wishes to leave a message, .the operator will applyrlnging current to the tip conductor of the line I0 which will apply ringing or alternating current to the tip conductor which will cause relay I! to operate ina circuit through condenser 66 to ground. The operation of relay l! will cause relay 94 to operate in a manner similar to the operation of the start key hereinbefore described and the operator or other subscribers ofthe system may then transmit message currents to the teletypewriter which will be recorded by it after which the teletypewriter station oi.' Fig. 3 may be restored to normal by the reception of a motor stop snal as, for example, upper case H.

Fig. 3A shows a modiiled calling arrangement which may be substituted for the arrangement shown in Fig. 3 to the left of the dot-dash line A-A. In the modification shown in Fig. 3A all the calling signals are transmitted over one conductor of line Il, for example the ring conductor R. In case it is desired to merely call the subscriber, alternating current superimposed upon negative direct current is transmitted over this conductor. 'I'he alternating current iiows through the windings of vringer 91, relay Il and condenser l0 to ground. Relay l! operates on the alternating current and connects the winding oi polarized relay 1l` in parallel with condenser ll. This proviides a path of direct current in addition to the alternating current path permitting negative current to also iiow over the line and through ringer I1 and relay Il. Ringer lispolariaedsothatitwillringwhenmpplied l vention have been described,

v discharge is initiated through tional means in a extinguishing with negative current and alternating current Relay 'I9 is polarized, however, so that it will not respond to negative current. In case the subscriber does not answer, the operator can then apply a positive current in addition to the ringing current to the ring conductor-in which case relay again operates and connects the polarized relay winding 66. In this case, however, ringer 61 will not respond to positive current plus alternating current flowing through its ever, will respond and will close an operating circuit for relay 64 which will lock up and condition the apparatus at the subscribers station for receiving messages as hereinbefore described.

The choice of the signaling systems shown in. Figs. 3 and 3A will depend largely upon the facilities provided for sending ringing current over the various subscriber line circuits at either Athe telephone exchange or the telegraph exchange through which line l0 passes and is terminated.

While several speciic embodiments of the init is obvious that there are many other m cations which will readily occur to anyone skilled in the art. For example, the signaling arrangement shown in Fig. 2 may be employed in combination with the switching and supervisory circuit shown in Fig. 3. Again the circuit shown in Fig. 3 may be adapted to receive all the necessary biasing and other potentials from rectifier I9 as shown in Fig. 2.

What is claimed isz.

1. An electric impulse repeater comprising Va pair of gaseous conduction tubes, input and output circuits therefor, a source of unidirectional potential connected in said output circuits which has a value greater than zero at all times, means connected to said input circuit to initiate a discharge through either of said tubes, means connected between the output circuits of said tubes to extinguish either one of said tubes when a the other of said tubes, and additional means in the output circuit of one of said tubes to extinguish said tube independently of the condition of the other of said tubes.

2. An impulse repeater of continuity comprising a plurality of multi-element gaseous conduction tubes, input circuits therefor for discharges through said tubes, output circuits for said tubes, a sour of potential connected in said output circuits which circuit -in a xed state has a value greater than aero at all times, indue-- said output circuits forl tive coupling between one of said tubes when a discharge in another o! said tubes, and addirlxed state of continuity for one of said tubes tly of the condition of said other tubes.

3. AnA electric impulse repeater for repeating impulses of different character comprising a pair of gaseous conduction tubes, input circuits thereforarrangedto initiateadischargethroughone e is initiated one of said tubes every 19 in parallel with condenser Relay 19, howducting, and further means continuity for terminating discharges through .pendently of said tinguishing of said tubes when a discharge is initiated 'through the other of said tubes, and additional means operating independently of said instrumentalities for terminating a discharge through time a discharge therethrough is initiated. 1

4. An impulse repeater circuit comprising a pair of gaseous conduction devices, input circuits connected to said devices, output circuits connected to said devices, a source of substantially constant potential having a value greater than zero connected in said output circuits, inductive and capacitive means interconnecting said circuits for extin one of said tubes when a discharge is initiated in the other of said devices, and resistive means connected .in a iixed state of continuity to one of said output circuits for extinguishing said one tube a short interval after a discharge is initiated therethrough.

-' 5. A carrier current telegraph station circuit comprising in combination carrier current generating and transmitting apparatus and carrier current receiving and amplifying apparatus including a repeating circuit employing a plurality of gaseous conduction tubes, means for supplying potential to the operating circuits of said tubes which has a value at all times greater than zero, and means in said circuit in a xed state or continuity operating independently oi all of but one of said tubes for rendering the said one tube non-conducting after it has been rendered conin a fixed state of any of said tubes when a discharge is initiated through any other of said tubes.

6. A carrier current telegraph station circuit comprising a single electric discharge tube for generating and transmitting carrier current impulses and for receiving and amplifying received carrier current impulses, a rectifying device for demodulating said received and amplified carrier current impulses, a repeating circuit comprising a plurality of gaseous conduction tubes, input circuits-therefor connected to said rectifying device, output circuits for said gaseous tubes, a source or substantially constant potential having a value greater than zero connected in said output circuits, circuit elements connected between said output circuits to e a discharge through either of said tubes when a discharge through the other is initiated, and additional circuit means operating independently of said circuit elements for extinguishing a discharge through one of said tubes a predetermined interval of time after said discharge has been initiated.

'1. An electric impulse repeater comprising a pair of gaseous conduction tubes, input and output circuits therefor, a source of potential having at all times a value greater than zero connected in said output circuits, means connected to said input circuit to initiate a discharge through either of said tubes, extinguishing means connected between the output circuits of said tubes to extinguish either one of said tubes when a discharge is initiated through the other of said tubes and additional means connected in the output circuit 'of one of said tubes operating inde- E means for exsaid one tube. l

ruum'ron s.

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