US1917882A - Signaling system - Google Patents

Description

J. J. GILBERT Il IVY ALIA VVV 5E Il l AM vnr HVV AAA

SIGNALING SYSTEM Filed Jan. 27, 1932 July l1, 1933.

/A/l/EA/TOR J J G/L BERT ATTORNEY Patented July 11, 1933 UNITED STATES PATENT oFF-icE JOHN J. GILBERT, or noUGLes'roN, NEW Your; essierNonl To BELL TELEEHONE LABO- RATORIES, INooRPo-Rernn, or* NEW YORK, N; Y., A CORPORATION oF NEWYORK Application med aanname?, i932.' serial No. 589,195.

This invention relates to the transmission of electric currents, and provides improvements in the tivo-Way transmission ofsuch currents, for instance, in the two-Way repeating of telephone or carrier telegraph currents.

It has been discovered that Where useis made of high speed switching means, or other quick-operating meansresponsive to transmission, for controlling a repeating circuit, in order that When the repeatingcircuit isin use it may operate effectively in only one direction at a time, the operation of thev control means may be deleteriously adected by transient. energyrwhich may discharge from the line connected to the output of the repeater` after the input to that line has ceased. In general, when the input transmission to the line ceases, some energy will return from it and Will enter the output ofthe repeater. lThere are various factors Vwhich may cause energy sent out by a repeater to reenter it. For example, the energy may be reliected from terminal apparatus or it may be stored in the line and sent back to therepeater, or stored in terminal apparatus and fed back to the line and repeater upon cessation of input from-the repeater to the line.

In addition to the kick-back energy which manifests itself in the form of an alternating current, a residual charge remains upon the line after the transmitter has been disconnected from the line. This residual charge produces a slowly decaying current in any direct current path which is present at the terminal. In the case of a long submarine cable the initial value of this current is about 30 to 40 decibels down from the level of the previously impressed signals; it may take several times the transmission time of the cable for this current to decay to a value 100 db. further down; rIhis decaying or relaxation current is due chiefly to the low frequency components of the transmitted signals which are much slowerin dying out than`V is that when the receiving amplifier is connected to the line when such a current is Howing, there is a sudden change in terminal impedance which generates high frequency voltages; currents produced by these Voltages are transmitted through the receiving amplifier' as a disturbing click.

A general` object of this invention is to avoid the effect upon receiving apparatus connected to a line conductor of the residual charge Which remains stored in the conductor after the transmitter has been disconnected.

In order to attain the above and other objects of this invention, the receiving or output circuit ofthe cable or transmission line is bridged betweenV conjugate points of the transmission line and an artificial line, and the transmitter is connected to the apex of the bridge circuit. The side branch of the bridge circuit Which is connected to the artificial line includes means such as a lter or choke coil whereby the amplitudes of high frequency currents transmittedinto the artificial line are small compared With those Vcurrents transmitted into thecable, so that the low frequency components of the transmitted currents are transmitted in equal proportions into the cable and the artificial line. After the transmitter has been disconnected,there are residual'V charges (relaxation currents, chiefly of low frequency components) in both the transmission line and the artificial line. These charges from the two lines balance each other and consequently produce no resultantefect upon the receiving circuit.

In general, high frequency components of telephone signals die out rapidly, and inthe normal operation of a system such as is contemplated by this invention, these high frequency currents are practically completely dissipated before the receiving circuit is connected to the line. It is usually important that high frequencies be impressed upon the transmission line in full volume. Therefore, a feature of this invention is a filter or choke coil arrangement for preventing the artificial line from exerting a drain on the high frequency components from the transmitter. By virtue of this feature, although the loW" frequency components sent to thel transmission Vline and the artificial line are y approximately equal, the high frequency components Which enter the artificial line are very small.

The invention may be better understood from the following detailed description of its features and of its principles of operation, in connection With vthe accompanying drawing in Which identical reference characters designate similar parts, and in which:

Fig. I shows aj diagrammatic representation of a submarine telephone system constituting one embodiment of the invention; and

Fig. 2 shows a diagrammatic representation of a submarine telephone system consti'- tuting another embodiment of the invention; In F ig. l the outputs of a transmitter TV capacity type as shown. The bridge circuit also contains the armature contacts of two voice operated relays l0 and l1, one in eachy branch. These lrelays are controlled by the transmitter T and the amplifying detector AD to automatically close their contacts on transmission of signals and to open them ou reception ofsignals. The receiving or output circuit R of the system is bridged',

shown, between conjugate points ofthe cable C and' the artificial line AL. The receiving circuit includes the armature Contact of a. voice operated relay l2. Relay l2 Works` in a manner opposite to that of voice operated relays 10 and l1, that is, it is open on transmission and closed on reception of sig'- nals.. The relays l0, 11 and l2 are of the fast-operating and slow-releasing type. The resistances R and R are adjusted so that the low frequencies transmitted into the cable and the artificial line are equal in The filter L is chosen so as to have negligible i impedance compared with that of resistance R at low frequencies, but highimpedance compared With that of R at highx frequencies, so that thev am-plitudes of the high frequency currents transmitted into the artificial line AL Will. be small compared With those of the current transmitted into the cable. This arrangement possesses the further advantage that the load on the transmitter is reduced..

The operation of the system shown in Fig. l is as follows: Ve assume the armatures of relays l0, ll and l2 in the position shown which is that correspondingF to the transmission of speech from the transmitter T. As stated above, theseV relays release their'respective armatures with a delayed action. When amplitude.A

the near end subscriber stops talking, the contacts of relays l0 vand ll remain closed for a short time interval to allow the Weak endings of the signal currents to pass, even though they fail to maintain the output of the amplifying-detector AD" operative. After that time has elapsed thev contacts of relays 10 and l1 are released (opened) whereby the transmitter is disconnected from the line. At'this moment there are residual charges of equal potentials, com posed chiefly of low frequency currents, i. e., the relaxation currents, in the transmission liney C and the artificial line AL. The armature contact of relay l2 is now closed and thusl the charges in the twolines being of equal" potentials, balance eachother, andcon-4' turbance) in the receiving circuit.

vIn the 'mod`ficationof the invention Which is. shown in Fig. 2, the submarine telephone system illustrated' comprises a main cable Cl and transmitting and receiving earth cables TEC and REC, respectively. The receiving earth' cable REC is connected"n tothe primary Winding of the receiving transformer RT and the main cable CI is connec-ted;V toV the primary Pfof receiving transformer RT.Q' The conta-ct ofvoice operated relay l0l is closed on transmission and open on reception` of signals. The secondary Winding S- of the transmitting transformer TT is connected as shown over theA armature of relay 10; to the main cable Cl and to the transmitting earth` cable TEC'. A filter Ll isconnected in series: with the artificialv line ALl simulating thefcable. In a manner similar to filter L of Fig. l, the filter Ll is' constructed so a-sto offer a low impedance tov loW frequencies and a high impedance to high frequencies, in order to prevent unnecessary drain onfthe'transmitting amplifier. In order to prevent unbalancing' the vnetwork on reception-v of signals, and' to cause, statics or interfering voltages in the receiving earth cable REC to balancey Statics or interfering voltages in the main cable C1, a similar lilter L2 and artificial AL2 line are Vconnected as shown inV the circuit of the' receiving earth cab-le REC. The-terminal sections' of thel sending and receiving earth connections TEG and REC respectively and of the main cable C1 may be enclosed Yin the same armor (as shown) to formv a Ycomposite cable C. At a; short distance (le. g about 5 miles) from shore, the conductor ofthe sending earth cable TEC is connected to the armorv of casequently"` produce noappreciable effect (disble: C,fan.dat a distance ofthe order of about` 200r miles from shore the. conductor of the receiving earthl cable REG is connected as shown through an impedanceY element Z to the4 grounded concentric return conductor; CR of the mainy the distantendt. The provision: of the cable- Cl which extends.: to;V

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pedance element Z is for the purpose of terminating the receiving earth REC in such a manner that its impedance, as Vseen from the near terminal, closely approximates that of the main cable C1. f

The operation of the embodiment of the invention shown in Fig. 2 is as follows: We assume the armatures of relays 10 and 12 in the position shown which is that corresponding to the transmission of speech by the transmitter T. Relays 10 and 12 release their armatures slowly. During speech transmission the primary windingP of the receiving transformer R-T is short-circuited so as to prevent any of the transmitted energy from Aaffecting the receiver R and to permit the transmitted energy to divide between the transmission line (conductor C1) and the artificial line AL1 in the proper manner. When the near end subscriber stops speaking, the armature of relay 12 is released first, and the releasel of the armature of relay 12 removes the short-circuit across primary winding I). Relay 10,'in Vreleasing its armature, disconnects the transmitter T from the line. The residual charges stored in the cable and in the artificial line, which are of approximately equal values, balance each other and have no serious disturbing ef-v fect upon the receiver R.

Vhat is claimed is:

V1. A submarine signaling system comprising a cable, a receiving circuit, means for `connecting and disconnecting said cable to `and from the circuit at frequent intervals, andv means including an articial line for overcoming the effects of residual cable voltages in said circuit at the instant when said cable is connected thereto. Y

2. In a signaling system, a transmission line, a sending mechanism and a receiving mechanism, means for alternately connectingand disconnecting said mechanism to and from said'line, and means for preventing excessive currents at the time of connecting the receivingV mechanism to the transmission line, said means comprising a device connectable to the receiving mechanism and adapted to counteract the residual line voltage. Y

3. In a signaling system, a transmission line, an artificial line', a receiving circuit con-V nectable toboth lines, meansfor .transmitting i low frequency currentsin equal, andv high frequency currents in unequaly proportions,'

into said transmission line and artificial line respectively, whereby residualcharges in the transmission line due to previously transmitted low frequency currents do not in- `juriously affect the receiving circuit whenV the latter is connected to said line. n

4. System as defined in claim 3 in which said frequency transmitting means includes a filter and a resistance element, said ilter having a low impedance at low frequencies and a hi 'h impedance at high frequency, as compare with the impedance of said resistance element. 7

5. A'signaling system comprising a transmitting circuit and a receiving circuit', a line f conductor and a balancing conductor therefor, means for alternately connecting and disconnecting said line conductor to and from said receiving circuit, the receiving circuit being bridged to conjugate points of saidv conductors, whereby, the effect upon the receiving circuit of any residual charge which remains stored in said conductors after disconnection therefroiii of the transmitting circuit is reduced. f Y

6. A deep sea telephone system comprising a main cable, a sending earth cable and a receiving earth cable, a transmitting circuit adapted to be connected to points across said main cable and saidvsending earth cable, a

receiving circuit adapted to be coupled to points between said main cable and said receiving earth cable, means for switching said main cable to and from thereceiving circuit,

'and an artificial or balancing cable for said main cable, whereby low frequencycurrents in said main cable are prevented from detrimentally affecting said receiving circuit.

7 System as defined in claim 6, further y' characterized by a balancing cable across points of thel sending earth cable and the receiving earth cable respectively whereby the effects of interfering currents in the receiving sea earth cable are causedto balance the iio effects of interfering currents in the main cable.

In witness whereof, I hereuntoV subscribe my name this 21st day of January, 1932. JOHN J. GILBERT.

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