US2298722A - Impulse transmission system - Google Patents

Description

Oct. 13, 1942. w. T. REA 2,298,722

IMPULSE TRANSMISSION SYSTEM Filed June 30, 1939 2 Sheets-Sheet l Illl'llf a ATTORNEY Oct. 13, 1942. f

w. T. REA

IMPULSE TRANSMISSION SYSTEM 2 Sheets-Sheet 2 I J M- Filed June so, 1959 llll bl IIITL p JNl/ENTOR W 7': REA

ATTORNEY Patented Oct. 13, 1942 UNITED STATES PATENT OFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application June 30, 1939, Serial No. 282,022

9 Claims. This invention relates to communication systems and more particularly to an improved imor messages that may be transmitted over the line. These way stations are frequently located in out-of-way places where it is impossible to secure adequate service for the usual type telegraph systems and more particularly for the repeating apparatus usually required to provide this type of service.

It is an object of this invention to provide improved and simplified telegraph systems for connecting together a plurality of geographically separated telegraph stations.

It is a further object of this invention to pro-- vide a single communication conductor electrically connecting all of the stations together and over which any one of the stations may transmit to all of the other stations.

It is a further object of this invention to provide improved and simplified transmitting and receiving apparatus at each of the stations which does not require the use of the usual type of telegraph repeater and which is simple and reliable in operation and does not require expert maintenance and adjustment.

Briefly, in accordance with this invention, the single metallic conducting path extends to a plurality of geographically separated telegraph stapotential between said path and ground in accordance with the impulses or messages to be transmitted thereby.

Such a system. has been discovered to be quite satisfactory 'when the line connecting the respective stations is relatively short. when the line or system becomes more extensive it has been discovered that certain types ofdistortion may be encountered due to the facts that the cable or capacity is charged quite rapidly by the application of the transmitting potential to the path at any station and that this capacity discharges rather slowly through all of the high impedance receiving devices connected to the line.

It is another object of this invention to provide additional arrangements for greatly reducing this type of distortion.

Briefly, means are provided for connecting a direct ground to the transmission line during the time the transmitting potential is not applied thereto. This arrangement causes the line or cable capacity to charge and discharge at substantially the same rate and thus causes no appreciable distortion of the telegraph or signaling impulses transmitted over the system.

Another object of this invention is to arrange the circuit so that this ground potential which is sometimes called a curbing potential may be applied to the line for a full impulse period or longer if desirable.

It is also within the scope of this invention to connect two or more sections, systems or lines arranged in accordance with this invention together through a suitable repeater.

Another object of this invention, therefore, is to provide a suitable repeater for interconnecting two or more line sections, systems, or lines of the type described so that signals or messages may be transmitted from any station in either section, system, or line to all of the stations of both sections, systems, or lines.

The foregoing objects or other objects and features of this invention, the novel features of which are specifically set forth in the claims appended hereto, may be more fully understood from the following description of a specific embodiment of this invention when read with reference to the attached drawings in which:

Fig. 1 shows in detail the features of such a telegraph system;

Fig. 2 shows the details of a similar system; and

Fig. 3 when placed directly below Figs. 1 and 2 shows the details of a typical repeater which may be employed to connect the systems shown in Fig. 1 and Fig. 2 together.

Fig. 1 shows a telegraph system comprising three telegraph stations 22, 23 and 2 3 all connected together by means of a conductive signaling path. Resistances It and II represent the resistance of this path and condensers l2 and I3 represent the capacity of the line or conductor to ground. Each of the stations is connected to this path as shown in Fig. 1.

It is to be understood that this line may comprise any suitable electrical conductor including open wire and cable conductors as well as telegraph paths or channels of both simplex telegraph systems and telegraph paths or channels of composited telegraph and telephone systems.

A high impedance or high resistance 28 is connected between the path and ground at each of the stations 22, 23 and 24. It is to be understood that the equipment at each of these stations is substantially the same. Consequently, only the equipment at station 22 has been shown in detail. Likewise, this equipment will be described in detail with reference to only station 22. It is to be understood, however, that similar equipment is provided at each of the other stations and that it operates in substantially the same manner as described with reference to the station 22. The grid or input circuit of a suitable electron discharge device 29 is connected to the high impedance 28. In the preferred embodiment of this invention the high impedance 28 will be a high resistance.

Electron discharge device 29 is provided with electron emitting element 39 which may be heated in any suitable manner, as for example, by means of the heater 3| which is supplied with power from source 32 through transformer 33. It is to be understood, however, that any other suitable electron emitting element may be provided and that the electron heating element may be directly or indirectly heated as is well known in the prior art. The electron discharge device is also provided with a control element or grid 34 and an anode plate 35.

Only a simple three-element electron discharge device is shown in the drawings. It is to be understood, however, that other suitable electron discharge devices may be employed, such as the well-known tetrode, pentode and beam tubes. Tube 35 may also be a gaseous discharge tube if it is so desired. In this case some suitable extinguishing means may be employed in the output circuit of the device to interrupt a discharge through it after a short interval of time after the discharge has been initiated by the application of a signaling condition to the line as will be described hereinafter. The details of the method of operation of these various types of electron discharge devices and their associated local or auxiliary circuits have not been set forth or described herein because they are well known in the prior art and function in a normal and usual manner. It is to be understood, however, that they may be employed in place of the three element device 29 shown in Fig. 1 as well as the electron discharge devices 36, 81 and B8 of Figs. 2 and 3, and that they will operate in their normal and usual manner.

In the electron discharge device 29 it is assumed that the control element 34 maintains continuous control of the discharge current passing through the device and that this control element or grid 34 is capable of interrupting the discharge through the device as well as creating a discharge current through it. Normally a positive potential is applied to the cathode or electron-emitting element by means of a potentiometer comprising resistances 31. The grid 34 is normally at ground potential as will be described hereinafter. Consequently, the grid 34 is maintained negative with respect to the cathode and thus tends to greatly reduce, if not to altogether prevent, a discharge flowing through the output circuit of device 29.

The anode or plate 35 is connected to a source of positive potential through the upper winding of relay 39. There is also an obvious biasing circuit through the lower winding of relay 39. Current flowing through the lower winding of relay 39 tends to maintain the armature of relay 39 in the position shown which tends to maintain the circuit through the printing magnet 49 closed. Current flowing through the upper winding of relay 39 tends to overpower the current flowing through the lower winding of this relay and thus to operate its armature to its righthand position where it interrupts the circuit flowing through the winding of the printing magnet 49. The transmission path is normally connected to ground through a corresponding high resistance 28 at each of the other stations of the system. Consequently, the grid or control element 34 will be maintained at substantially ground potential during this time. Consequently, due to the negative bias applied between the grid and cathode of tube 29, substantially no current flows through the upper winding of relay 39 so relay 39 maintains the circuit through the printing magnet 49 closed and thus holds the telegraph receiving equipment, which is a teletypewriter in the preferred embodiment of this invention, in its normal position.

When positive potential is applied to the conductor extending to the other stations at any of the stations connected thereto, a positive potential will likewise be applied to the grid or control element 34 of the electron discharge device 29. This will cause or permit sufiicient current to flow through the upper winding of relay 39 to overpower the current flowing through the lower winding of this relay and operate the relay to its right-hand position where it interrupts the circuit to the printing magnet 49. Relay 39 is designed to respond very rapidly to the pulses transmitted over the system and to repeat them to the receiving magnet 49.

As pointed out above, it is understood that similar receiving magnets, relays and electron discharge devices are provided at the other stations connected to the systems so that the signaling impulses may be received at each of the stations.

The transmitting channel is normally connected to the armature of relay 4| and through the contacts of relay 4| to the armature of relay 42. Relays 4| and 42 are controlled by the transmitting contacts 43. Relays 4| and 42 are provided with an obvious circuit through the upper windings, the current through which tends to operate these relays to their left-hand position. However, so long as the transmitting contacts 43 remain closed the circuit is completed from positive battery through their lower windings and network 44 to ground through the transmitting contacts 43. Current flowing in the lower windings of these relays is sufliciently powerful to overcome the effects of the current flowing through the upper windings of these relays and causes the relays to be operated and maintained in the positions shown in the drawings.

It should be noted that during the time contacts 43 are closed and thus relays 4| and 42 maintained in position shown in Fig. 1, the circuit through the armature and right-hand contact of relay 4| and armature 42 is opened. Consequently, the line is connected only through the high resistance 28 to ground at station 22. The line is similarly connected to ground at each of the other stations 23 and 24.

When it is desired to transmit impulses or message currents from station 22, contacts 43 are operated in accordance with the signaling impulses to be transmitted. These contacts may be operated in any suitable manner but in the preferred embodiment of this invention they are operated from a teletypewriter keyboard, as is well understood in the telegraph ant When contacts, 43 open they interrupt the circuit through the lowerwindings of relays; 4| and 42. When the circuit through the lower; winding of relay 4! is interrupted the current flowing through the upper winding of this relay tends to operate, the relay to, its left-hand position and the armature of this relay is immediately so operated; In its, left-hand position it connects positive battery to the line or conductor extending to the other stations. potential to the grid 34 of the electron discharge device 29,at station 22 and also to similar apparatus at the other stations. This causes the impulse to be repeated to the receiving devices at the, respective stations; At station 22513118 impulse is repeated to the receiving, device and produces a home copy of themessage transmitted.

When contacts 43' reclose they again complete 4| and cause the armature of this relay to be operated to its right-hand position and thus dise connect the positive battery from the transmission circuit extending to the other stations. This would cause distributed capacity l2 and [3 to. discharge to ground to the high resistance input circuits similar to high resistance 23 at each of the other stations. Inasmuch as this may take appreciable time due to the fact that the resistance is quite high, the signaling impulses may be considerably distorted. Of course, this distortion could be reduced by adding suitable resistance in series with the positive battery connected; to the line during the transmission of spacing impulses so that the build-up of potential on the distributed capacity 12 and l3 of the line may be retarded and may be substantially equal to the rate of discharge of this capacity. Such an arrangement, however, is not very satisfactory since it would cause both a slow charge and discharge of the line capacity, and thus would limit thespeed at which impulses could betransmitted over the system. This method is also unsatisfactory because the distortion of the impulse arriving at the different stations along the line would be different due to the fact that charging and discharging rates of all of the distributed capacity of the line could not be made the same. If the rates were made equal at one station orat one position along the line, they would not be equal at other stations or positions along the line. Hence, this method, in addition to limitingthe transmission speed over the line, would also provide satisfactory transmission to onlyone, or at the most, a very few of the telegraph stations along the line.

To overcome this difficulty the second relay 42 is added. When contacts t3 are opened, as described above, and relay ii operated to its lefthand position where it applies positive battery to the line, the upper terminal of condenser 4! is rapidly charged to the positive potential from battery 51' through resistance 46 andthe parallel combination of copper-oxide rectifier 48 and resistance G5. The cpper-oXide rectifier is so connected that this charging current flows through the rectifier in the direction in which the rectifier has a low resistance. Resistance 45 will usually be considerably higher than this low resistance and thus not materially-afiect the charging rate of the upp r terminal of condenser 41. The upper terminal of this condenser is also charged in a circuit from battery from the lower winding of relay 42. However, due to the addi- 10. This applies a positive and resistance 58 to the transmission line.

tional charging path through the copper-oxide rectifier, the upper terminal of condenser 41 is rapidly charged to full battery potential so that the current flowing through the lower winding of relay 42 rapidly falls to zero, thus permitting the current flowing through the upper winding of relay 42 to operate its armature to its left-hand position.

Then when contacts 43 again reclose and the armature of relay 4| is operated to its right-hand position, a circuit is completed for connecting ground through the low resistance 58 to the transmission line in a circuit from ground through the left-hand contact and armature of relay 42, right-hand contact and armature of relay 4! At this time relay 42. does not immediately follow relay 4| and operate to its right-hand position because the discharging current from condenser 41 is forced to flow through the high resistance 45 in parallel with the copper-oxide rectifier 48. The copper-oxide rectifier 48 now has a high resistance to this discharging current condenser 4T because-it must flow through the copper-oxide rectifier in the reverse direction. Consequently very little, if any, current flows through the lower winding of relay 42 until a considerable portion of the charge upon the upper terminal of condenser 41 flows to ground through the high resistance 45 in parallel with the inverse or high impedance of the copper-oxide rectifier 48. It should also be'n-oted that full battery potential is not applied to the lower winding of relay 42 since the left-hand terminal of the parallel combination of copper-oxide rectifier 48 and resist ance 45 is connected to the common point between resistances 46 and 5t. Resistances 46 and 59 provide a potentiometer for applying reduced potential to the lower winding of relay 42. Hence it requires considerable time for sufficient current to flow through the lower winding of relay 42 to operate this relay to its right-hand position and remove the ground connected to the transmission line.

If in the meantime contacts 43 have again reopened, relay 4| will be again operated to its left-hand position where it will again apply positive battery to the transmission line for the transmission of another impulse over the line. At this time the upper terminal condenser 41 will again be rapidly recharged to battery potential so that when contacts 43 again reclose the discharging cycle of condenser 41 will be restarted from the beginning.

With this arrangement the charging and discharging time of the capacity of the telegraph path is substantially the same since it is charged and discharged through substantially the same paths. Furthermore, the charging and discharging paths are of low resistance; consequently, the charging and discharging time is quite small so the system is capable of operating a relatively higher speed. It should be noted that the operation of relay 42 to its right-hand position may be delayed for a greater time than the time of a single impulse period without interfering with the transmission over the system in any way X- cept in the case of a break signal. In case it is desired to transmit a break signal to the station transmitting, it is necessary that the break signal exceed this operating time of relay 42, otherwise it would not be received because it would not be applied to the grid or control element of tube 29 since the line is already connected to ground through a very low resistance.

This efiectively short-circuits the receiving device at this time and renders it unable to respond to such a break signal. However, when the break signal exceeds this period and relay 42 operates to its right-hand position, it removes the short circuit, thus permitting tube 29 to respond to and repeat the break signal to the receiving device 40.

Fig. 2 shows a system quite similar to the system shown in Fig. 1. In this case, however, four stations, 25, 25, 21 and 9, are shown connected to the system instead of three stations as in Fig. 1. In addition, stations 26 and 2'! are shown connected to the system through a branch line, represented by resistances l8 and and distributed capacities l9 and 2|. Transmission to and from these stations connected to the branch line is as described with reference to Fig. 1 for each of the stations connected to the main line. It is to be understood that any suitable or desirable network may be employed to connect the respective stations together, the only essential requirement being that the network provide a metallic conducting path between all of the stations.

Each station of the system shown in Fig. 2 is equipped with apparatus as described in detail with reference to station 22 of Fig. 1. The apparatus is shown in detail in station 9 of Fig. 2. However, since this equipment is the same as shown and described in detail with reference to station 22 of Fig. 1, this detailed description will not be repeated, it being understood that the equipment at station 9 and also at stations 25, 25 and 21 operates in the same manner as described with reference to the stations connected to the system shown in Fig. 1.

It is also within the scope of this invention to interconnect the two systems or lines in accordance with this invention. In each of the systems or lines is relatively short they may be connected directly together as, for example, by connecting conductors 55 and 55 of Figs. 1 and 2 together. When these conductors are thus connected together the systems shown in Figs. 1 and 2 operate as a single system in the same manner as described with reference to the system shown in Fig. 1 except that seven stations instead of three stations are connected to the system.

In case either or both of the individual systems shown in Figs. 1 and 2 is a relatively large system or extends over a relatively large territory so rectly below Figs. 1 and 2 and leads 55 of Fig. 1

and 56 of Fig. 2 connected to leads 55 and 56, respectively, of Fig. 3, the two systems will be connected together through the repeater shown in Fig. 3.

When the systems are so connected through the repeater they again form in effect a single large telegraph system. It is to be understood that in the case of very large systems repeaters may be employed at various points where they may be desirable or necessary or the repeater may be employed to connect two separate and independent systems together as pointed out above. In both cases the system or systems operate in substantially the same manner and provide facilities whereby any station of a single large system or of either of the two systems connected together may transmit messages to all of the other stations and may receive messages from any of the other stations.

Assume now that the system shown in Fig. 1 is connected to the system shown in Fig. 2 through the repeater shown in Fig. 3, as pointed out above, and that signaling impulses are transmitted from the transmitting contacts 43 at stations 22 of Fig. 1. As pointed out above, when the transmitting contacts 43 open, relay 4| operates to its left-hand position where it connects positive battery to the transmission circuit and thus to lead extending to the repeater shown in Fig. 3. Lead 55 is connected through the armatures and left-hand contacts of relays 12 and 13 to the high impedance or resistance 10. When positive potential is applied to lead 55 as described above, a positive potential will also be applied to the high resistance 10. High resistance H1 is connected to the grid or input element of tube 88 and applies a positive potential thereto.

Tube 88 is provided with a negative bias between the input or control grid and the cathode 69. This bias is obtained from the potentiometer comprising resistances 6| which apply a positive potential to the cathode of the tube. Since the grid 65 is normally connected to ground or zero potential through the high impedance resistance 10, the grid will be negative with respect to the cathode. However, when a positive potential from line or lead 55 is applied to the high resistance 15, a positive potential will be applied to the grid 65 of tube 88. This will cause an increased current to flow in the output circuit of tube 88 through the upper windings of relays 15 and 16. This current will tend to operate these relays to their left-hand positions. Current flowing through the lower winding of these relays in an obvious circuit tends to hold the relays in the positions shown. However, the current flowing through the upper windings of these relays overcomes this current and operates the relays to their left-hand positions. When relay 15 operates to its left-hand position it applies positive potential to the lead or conductor 56 connected to the transmission system shown in Fig. 2 and thus repeats the positive potential transmitted from station 22 to the stations of the system shown in Fig. 2. Relay [5 in operating also disconnects the high impedance H in the input circuit of tube 81 from lead 56, thus preventing this tube from repeating the impulses back to the system shown in Fig. 1 or interfering with the transmission from this system. Condenser 11 is connected between the left-hand upper winding terminal of relay l6 and ground. The purpose of this condenser is to retard the operation of relay 16 in a somewhat similar manner to the manner in which network 44 retards the operation of relay 42, as described above with reference to the operation of the system shown in Fig. 1.

Relay [6 is retarded for the same purpose that relay 42 of Fig. 1 is retarded. When relay '15 operates, it connects ground to the right-hand contact of relay (5. Thus, when positive potential is removed from lead 55 by contacts 43 of station 22 reclosing and relay 4| operat ng to its right-hand position, relay 15 will similarly operate to its right-hand position due to the fact that the positive potential is removed from line 55 and thus from the input circuit of tube 88. Consequently, the potential of the grid 65 will again become negative with respect to the filament and thus interrupt or greatly reduce current flowing in the output circuit of tube 88. The current flowing through the lower winding of relay 15 will then cause this relay to be operated to its right-hand position where it will connect ground to line 56 of the system shown in Fig. 2. The circuit for connecting this ground may be traced from the left-hand contact and armature of relay l5, right-hand contact and armature of relay 75 to lead 56; This ground is maintained connected to lead 56 during the delay in the operation of relay 16 dueto condenser Tl. When the current through the upper winding of relay 15 was interrupted, condenser 16 starts to charge and its charging current flows through the upper winding of relay TI and, maintains this relay in its left-hand position until this charging current falls to such a value that it no longer overcomes the current flowing through the lower winding of this relay whereupon the relay will operate to its righthand position and reconnect the high impedance l! toline 56.

Thus, the repeater shown in Fig. 3 repeats both the positive potential applied to line 55, to line 56 and also the ground potential applied to line 55, thus insuring proper transmission of the signalling impulses to the system shown in Fig. 2. The term impulse is used in this specification and claims to indicate the application to or the transmission over the system of any signaling condition for the duration of a unit interval of the signaling code or longer, 7

Transmission from any station of the system shown in Fig. 2 to the system shown in Fig. 1 is exactly the same as that described above except that positive potential will be first applied to lead 56 which causes the potential of grid 64 of tube 8'5 to become positive. This in turn causes the operation of relays i2 and 13 in a manner similar to that described with reference to relays l and 76, respectively. The operation of these relays repeats the potential condition applied to the system of Fig. 2 to the system shown in Fig. 1.

As pointed out with reference to the system shown in Fig. 1, it is necessary for the transmission of a break signal over the system that the break signal should exceed the delay period of relays 16 and 13.

It is to be understood that this invention is not limited to the specific details of the systems, stations and circuits shown and described herein but includes many alternative arrangements as will be apparent to those skilled in the art. For example, the cathodes of tubes 29, 36, 81 and 88 are shown heated from sources of alternating current 32, 11 and 63, respectively. It is to be understood that any suitable source of heating current may be employed. Similarly, in case it is not desirable or necessary to provide a home copy of the messages transmitted from any of the stations, the high impedance device at each of the stations similar to high impedance device 28 at station 22 may be connected to the righthand contact of relay 42 instead of directly to the transmission conductor. Furthermore, the repeater shown in Fig. 3 may be near or adjacent any of the other stations of the system as, for example, station 24 or 25. Alternatively, the repeater may not be located near any of the stations of the system but at a considerable distance from any of the stations in any path between any of the respective stations.

It is also within the scope of this invention to apply negative potential to the transmission path instead of positive potential as described in the specific embodiment set forth herein. In this case the bias normally applied to the tubes would be reversed. This arrangement is particularly adapted to the use of the so-called holding magnet typeof telegraph receiving instrument. In this case the holding magnet could be connected'directly in the plate circuit of the tube. The recordin magnet of any type of telegraph instrument could be connected directly in the output circuit of the tube instead of requiring a repeating relay such as relay 39 at station 22. In case it is desirable to employ a repeating relay, it would be necessary to reverse the polarity of the operating and biasing windings of the relay in order to insure the proper reception of the signaling impulses.

It is to be understood that this invention is not limited to the specific embodiment shown and described in detail in this application but includes many modifications and variations which will be readily apparent to those skilled in the art. For example, the invention is not limited to a grounded telegraph system, such as shown and described above, but may be applied equally well to a full metallic system, in which case it will be necessary to provide two electrical conducting paths extending to each of the stations of the system.

What is claimed is:

1. In a telegraph system, a telegraph line, receiving apparatus normally connected between said line and ground, means for applying transmitting potentials to said line in accordance with the impulses to be transmitted over said line, and means for applyin a curbing potential to said line for a period of time at least as long as the duration of a unit interval of the signaling code.

2. In a telegraph system, a signaling conductor, means for alternately applying a signaling potential and ground to said conductor which comprises a retarded relay, means for operating said relay during the application of said potential to said line, and means for applying said ground to said line during the delay period of said relay.

3. A telegraph system comprising at least three telegraph stations, a metallic electrically conducting path extending to all of said stations, a receiving device at each of said stations including an electron discharge device having an input circuit, a circuit path at each of said stations extending from said conducting path to ground and including said input circuit, and means at each of said stations for alternately applying two difierent signaling conditions to said path in accordance with the information to be transmitted.

4. A telegraph system comprising at least three geographically separated telegraph stations, a single electrically conducting path extending to all of said stations, a receiving device at each or said stations including an electron discharge device having input terminals, a high impedance conducting circuit path at each of said stations extending from said conducting path to ground, an operative connection between said input terminals and said high impedance circuit and means at each of said stations for applying in accordance with the information to be transmitted from that station to the other stations a substantially constant signaling potential to said path.

5. A telegraph system comprising at least three receiving devices each includingan electron discharge device havin input terminals, a transmitting device associated with each of said receiving devices, an electrically conducting path extending to all of said receiving devices, a high impedance circuit path extending between said conducting path and a common potential for each of said receiving devices and an operative connection between each of said high impedance paths and the respective input terminals of said electron discharge device, and an operative connection between each of said transmitting devices and said path for alternately applying in accordance With the information to be transmitted thereover substantially constant signaling potentials to said path.

6. A telegraph system comprising at least three geographically separated stations, an electrically conducting path connecting all the stations together, each station comprising a path to ground of high impedance to direct current, a device of negligible power consumption as compared with an electromagnetic relay and operable by potential differences across said path, receiving means controlled by said device, and a sending instrument adapted to apply unidirectional potentials to said conductor in accordance with coded groups of impulses.

'7. A telegraph system comprising several stations each connected to the other by a wire line conductor to direct current, each station comprising sending means for varying the potential of said wire line with respect to a fixed reference potential unidirectionally in accordance with coded groups of impulses, the variation of potential during each impulse, if any, being of noncode character, a space discharge device havi an output path Whose current flow is controlled by the potential difference across an input path,

and translating means for said code group associated with each said output path.

8. A telegraph system comprising several stations each connected to the other by a Wire line conductive to direct current, each station comprising sending means for varying the potential of said wir line with respect to ground potential unidirectionally in accordance with coded groups of impulses, the variation of potential during each impulse, if any, being of non-code character, a space discharge device having an output path whose current flow is controlled by the potential diflerence across an input path, and translating means for said code groups associated with each of said output paths.

9. A telegraph system comprising at least three geographically separated stations, an electrically conducting path connecting all the stations together, each station comprising a path of high I impedance to direct current between said path and a fixed reference potential, an electronic discharge device comprising an anode, cathode, and control element, a connection between said high impedance path and said control element, apparatus for controlling the potential of said cathode relative to said fixed reference potential, translating apparatus connected to said anode and cathode, and a sending instrument adapted to apply unidirectional potentials to said path in accordance with coded groups of impulses.

WILTON T. REA.

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