US1586895A - Submarine-cable signaling - Google Patents

Description

June 1 1926.

- 1,586,895 J. J. GILBERT SUBMARINE CABLE SIGNALING Fil M y 1922 2 Sheets-Sheet 1 //71//1/0n- John J. GI/b/f June 1 1926. v 1,586,895

J. J. GILBERT SUBMARINE'CABLE SIGNALING Filed May 15, 1922 2 SheetS -Sheet 2 W My tr l

Patented Tune l, was.

PATENT,

JOY-IN J'GILBERT, O1? PORT WASHINGTON, NEVT YORK, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, 033 NEW YORK, N. Y., A GOBPORAIIGN OF NEW YORK.

SUBMARINE-CABLE srenanrne.

Application fiiana 15,

This invention relates to two-way operation oi high speed signaling conductors such as inductively loaded submarine cables.

An object of the invention is to provide a method and means for two-way operation over high speed signaling conductors, when it is diliicult to maintain a balance between the conductor and an artificial line sutlicient to permit of duplex operation.

Another object is to provide a method and means for two-way operation oi a signaling conductor by which the receivers are maintained out of operative relation with the conductor during transmitting intervals.

Ordinary submarine cables are not adapted to high speed signaling because of the excessive distortion produced by the large distributed capacity. It has not been the practies to load long telegraph cables with inductance toovercome the etlect of the capacity, although many suggestions for such loading have been made. Until recently iron was considered the only suitable material for inductive loading and it appears that it would be quite as effective to increase the Sif QG ol' the copper conductor as to load with iron. lt was doubtful, however, it the improvemen effected by either expedient would justify the additional expense. There has recently been discovered, however, a nickeldron alloy, which has been appropriately termec permalloy, which has a remarkably high permeability for the low magnetizing forces utilized in signaling systems. This alloy, when properly prepared and made into a ribbon of proper proportions and laid spirally upon a cable conductor in the proper way, very greatly increases the permissible speed of signaling. For a more complete disclosure of this material and its method of preparation, see U. S. application of G. W. lillmcn, S rial No. 473,877, liled lv'lay 31, 1921. An obstacle to the use of such loading has arisen, however, in the form of a failure of the artificial line, ordinarily employed in duplex operation, to maintain a sulhciently exact balance at the high available signaling speeds.

its is well ltnown the ordinary cable terminal circuit arrangement comprises a socall duplex bridge, two of the ratio arms conting of equal impedance such as con densers and the other two comprising the cable and an artificial line respectively. The

1922. Serial No. 561,138.

transmitter is ordinarily connected between the apex of this bridge and ground and the receiver is connected in conjugate relation to the transmitter. The artificial line is made up of sections of lumped impedance elements to simulate the impedance of the cable. The cable impedance, however, varies from time to time due to temperature changes, earth currents, etc, so that an 0c casional readjustment of the artificial line is necessary. The higher. the signaling frequencies employed, the more diflicult it becomes to maintain an exact balance and at the signalingspeeds now available such a balance cannot be maintained with terminal apparatus ordinarily used.

This invention provides a method of duplex operation which does not depend upon the conjugate relationship oi transmitter and receiver. Signals are transmitted over a submarine cable at relatively low velocity as compared with transmission over ordinary land lines so that an appreciable period elapses between the time when the transmitting key is closed and the arrival of the transmitted pulse at the receiver. In its preferred form this invention consists. in si multaneously transmitting signals at both ends of the line during a period equal to the time required for a signalto traverse the line and then connecting both ends of the line to the receiving apparatus for an equal period during which the signals that were impressed upon the line during the transmission period are received.

The invention will be understood from the following description and the accompanying drawings, in which Fig. l is an arrival curve for a high speed permalloy loaded cable; Fig. 2, a curve representing current lll'1 ressed upon the cable at the transmitter; llig. 3, a signaling current impulse; Figs. 4 and 5, diagrammatic showings of two cmbodiments of the invention; and Fig. 6 a lengthening network shown diagrannnatically at L of Figs. 4 and 5.

Referring to Fig. l, a curve is plotted to show the relation between received current I and elapsed time T while an electromotive force is applied to the cable at the transmitting station, as by the closure of a key. The received current is Zero during the definite interval 5:0 to t T and at the latter instant suddenly assumes the value i and increases gradually to its final steady value. The quantities T and ,2 can be determined by the formulae:

T.=s. ot

in which S is the length of the cable, 6 is the base of the Naperian system of logarithms and R, LandG are the cable parameters, resistance, inductance, and capacitance per unit length of the cable. For the derivation of these formulae, see The theory of the submarine telegraph and telephone cable by H. V. Malcolm, 1917, page 51 The head of the arrival curve is not quite vertical owing to distortion produced by variable resistance and dielectric losses.

The current I impressed upon the cable by a steady voltage applied continuously is represented in Fig. 2. If this voltage s applied for a short period of time only, as in the form of a dot signal the impressed current takes the form shown in Fig.

It is seen that the current in the latter case consists of the signal a, '6 followed by a tail 5, c, which continues for a length of time depending upon the constants of the cable and of the elements of the networks employed at the sending end for shaping the signal. It is possible by proper design ot these networks to eliminate the tall or at least reduce it so that, in an interval of time comparable with the length of the signal a, 5, its value becomes small compared with the magnitude of a signal received from the distant end of the cable.

Referring to Fig. 4, which shows one embodiment of the invention, the cable C terminates at each end in two branch circuits containing the transmitter and the receiver respectively. These branches are alternately associated with the cable by means of switches S, S, which are maintained in synchronism by any well known means-for example, by means of the type commonly employed in printing telegraph systems. These switches are shown as circular in form each comprising an insulating segment and a conducting segment, the brushes maintaining contact with the periphery of these segments. The speed of rotation is such that the transmitters are operatively connected with the cable for a certain definite period which is substantially the same as, or less than, the time required for a transmitted signal pulse to arrive at the receiver. The transmitters are then disconnected from the cable by the switches S, S which then operatively associate the receivers with the cable for a like period. The transmitter employed is preferably automatic and may be of any well known form, such as a tape transmitter, and means are provided for arresting the motion of the tape and associated apparatus during the receiving periods. This mechanism may be associated with the shaft of the switch S by mechanical coupling G.

Reception may be by ear or by any suitable .1

mittal of a signal at the distant end of the cable at the time $20, there will be an interval T during which nothing will be received at the near end of the cable. It is possible, therefore, without interfering with the reception of the signals from the distant end of the cable, to employ this interval for the transmission of signals at the near end of the cable, and the apparatus of Fig. 4 is designed to accomplish this purpose. At the end of the period T,, however, the first of the signals which has been transmitted from the distant end will arrive, and therefore at this time, or a little previous, it will be necessary to disconnect the transmitter, replacing it by apparatus for receiving the signals which are about to arrive. Assuming that this procedure has been adopted at both ends, it can be seen that the trains of received signals will last for a period of time T immediately after which there will be a gap of length T in the sending, due to the fact that the distant terminal has been changed over from transmitting to receiving. The interval of time required at each end of the cable between the last transmitted signal and the first received signal depends upon the time that is taken by the tail of the former to fall to a value that will not interfere with the received signals. The magnitude of the tail may be reduced, for example, by means of a transmitting condenser K of the kind ordinarily used in sending end shaping, or the transmitting apparatus may be inserted in a terminal bridge arrangement such as used in ordinary duplex telegraphy, but with a degree of balance much inferior to that required in the usual method of operation.

If a terminal bridge such as that mentioned in the last paragraph is to be employed, the system may take the form shown in Fig. 5. The terminal bridge circuits are of the form ordinarily employed in duplex operation, but the artificial lines A L do not simulate the impedance of the cable with sufficient accuracy to permit signals to be received at either terminal during transmis sion at that terminal. Signaling is accom plished by the method described above in connection with Fig. 4. The switches S,

.iitl

S alternately connect the transmitters and the receivers to the line for a period equal to or less than the propagation period T as in Fig. 4. In place-of the mechanical coupling G, G of Fig. i starting and stopping of transmitting and recording mechanism may be controlled by auxiliary electric contacts as here shown. The artificial lines A L very closely simulate the impedance ofthe cable for that portion of the transmitted current whichtorms the tail of the signal, as shown in Fig. 3. This is the portion of the transmitted signal current which is mosteasily balanced and the eilect of which upon the local receiver may therefore be eliminated.

It large irregularities of impedance occur along the cable, it may be necessary to balance the disturbances reflected from these This will entail corresponding changes in the switch arrangements at the cable terminals, which it might be inconvenient to malt It is therefore proposed to place at each terminal in series with the cable a lengthening network L, shown diagrammatically in Fig. 6, the purpose of which is to increase the time required for propagaticn of a signal without unduly increasing the overall attenuation. This may comprise one or more sections of network, each having an inductance Z and capacity l2. Additional need for the lengthening network may arise from the fact that the time T of the cable alone may not be suitable for the signaling speed, for instance, T, might be equivalent to 2 ,4; cycles of the signal speed in which case it would be desirable to increase T by a network until the total time of cable and network was 3 cycles.

Although this invention has been described with particular reference to a sub marine cable system it may obviously be used in other types of signaling systems.

lVhat is claimed is 1. The method of two-way signaling be tween two stations wiich comprises alternately simultaneously transmitting from both stations and receiving at both stations "for equal periods.

2. a method of two-way signaling over a submarine cable which comprises transmitting simultaneously from both terminals for a period not greater than the time required for an initial pulse to reach'the receiver, ceasing to transmit at the end of said period at both terminals, receiving at both terminals for a like period and repeating in regular succession said steps of transmitting and receiving.

3. A method of two-way signaling over a submarine cable which comprises transmitting simultaneously from both terminals for a period substantially equal to the time required for an initial pulse to reach the re ceiver, ceasing to transmit at the end of said period at both terminals, receiving at both terminals for a like period and repeating in regular succession said steps of transmitting and receiving.

4. The method of two-way signaling over a conductor which has an appreciable propagation period and is provided with means for operatively associating it with both terminal transmitters simultaneously and associating it from them and for operat-ively associating said conductor with both terminal receivers during the time that the transmitters are disassociated which method comprises operating said means at a rate which will cause said associating and disassociating to occur at intervals dependent upon said propagation period.

The combination with a submarine cable, of a transmitter at each terminal thereof, means for causing said transmitters simultaneously to impress current signal impulses upon said cable for a period not greater than the time required for a signal pulse to reach the receiver, automatic ID ans for rendering said transmitters inoperative to transmit signal impulses ove' said cable during a period succeeding said transmitting period and of approximately the same length, and receiving means at each termi nal for receivingsaid signal impulses.

6. The combination with a submarine cable, of a transmitter at each terminal thereof, a receiver at each terminal thereoi, and automatic means synchronously driven for alternately operatively associating said transmitters and receivers with said cable at a period not greater than the time required for a transmitted signal pulse to reach the receiver.

7. The combination with a submarine sicnaling cable, of a lengthening networu therein, transmitting and receiving means at each terminal of said cable, and automatic means synchronously driven tor alternately operatively connecting said transmitting and receiving means with. said cable at a period not greater than the time required for a transmitted signal impulse to reach the receiver.

8, The combination with a submarine cable, or a transmitter at each terminal thereof, means for causing said transn'iitters simultaneously to impress current signal impulses upon said cable for a period substantially equal to the time required for a signal pulse to reach the receiver. automatic means for rendering said transmitters inoperative to transmit signal impulses over said cable during a period succeeding said transmitting period and approximately the same length, and receiving means at each terminal for receiving said signal impulses.

9. The combination with a submarine cable, of a transmitter at each terminal thereof, a receiver at each terminal thereof, and automatic means synchronously driven for operatively associating said transmitters and receivers with said cable at a period substantially equal. to the time required for a transmitted signal pulse to reach the re ceiver.

10. The combination with a submarine signaling cable, of a lengthening network therein, transmitting and receiving means at each terminal of said cable, and automatic means synchronously driven for alternately operatively connecting said transmitting and receiving means with said cable at a period substantially equal to the time required for a transmitted signal impulse to reach the receiver.

11,. The combination with a submarine signaling cable, of a lengthening network therein comprising series inductance and shunt capacity, transn'iitting and receiving means at automatic means for alternately operatively connecting said transn'litting and receiving means with said cable at a period not gremer than the time required for a transn'iitted signal. impulse to reach the receiver.

12. The combination wit-l1 a submarine signaling cable, of alengthening network comprising a plurality of sections each of which contains series inductance and shunt capacity, transmitting and receiving means at each terminal of said cable, and automatic means for alternately operatively connecting said transmitting and receiving means with said cable at a period not greater than the time required for a trans-.

mitted signal impulse to reach the receiver.

13. The combination with a. long signaling conductor having a signal propagation period of appreciable length, of a duplex bridge arrangement at each terminal thereof comprising a receiver and a transmitter in conjugate arrangement with each other, an artifical line at each terminal roughly simulating the impedance of said cable and automatic means for alternately operatively associating said transmitters simultaneously with said conductor and dissociating'them therefrom and for dissociating said receivers from said conductors during transmission periods, the periods of transmission being not greater than the signal propagation period of said conductor.

14. The combination with along signaling conductor having a signal propagation period of appreciable length, of a duplex bridge arrangement at each terminal thereeach terminal of said cable, and

of comprising a receiver and a transmitter in conjugate arrangement With each other, an artificial line at each terminal roughly simulating the impedance of said cable but not producing a suiiiciently accurate balance to provide for simultaneous transmission and reception at the same terminal, and automatic means for alternately operatively associating said transmitters simultaneously with said conductor and dissociating them therefrom and for dissociating said receivers from said conductors during transmission periods, the periods of transmission being not greater than the signal propagation period of said conductor.

15. The combination with a-signaling conductor having a signal propagation period of appreciable length, of transmitting and receiving means at each terminal thereof, auton'iatic means for operatively associating said transmitting means simultaneously at each terminal with said conductor and dissociating them from said conductor at a period not greater than the signal propagation period of the conductor, and means for reducing the magnitude of the tails of the transi'nitted signals.

16. In a submarine cable system, means for rendering the transmitter at a terminal station ineii'ective and for sin'iultaneously and automatically rendering the receiver at that station operative to receive signals, and means eii'ective only for frequencies not greater than the signaling frequency for preventing the discharge of the cable after cessation of transmission from interfering materially with the reception of signals.

17. In a submarine cable system, switching means for rendering the transmitter at a terminal station ineffective to transmit signals, means at that station for receiving 'incou'nng signals, and a balancing network which roughly simulates the impedance of said cable for frequencies not substantially greater than the signaling frequency for reducing the interference with received signals of the discharge of the cable after cessation of transmission.

18. In a. telegraph system, a cable and a pair of terminal stations connected to the ends thereof, each of said terminal stations comprising a transmitting mechanism, a receiving mechanism and switching means at one terminal station for connecting the receiving mechanism to the cable simul taneously with the receipt of a current impulse transmitted from the other terminal station.

In witness whereof, I hereunto subscribe my name this 12th day of May A. D. 1922.

JOHN J. GILBERT.

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