US1432781A - Means fob - Google Patents

Description

, v H. s. OSBORNE; MEANS FOR AND METHOD OF AVOIDING INTERFERENCE APPLICATION nuzo' IULYBI. 1918; 1 432 7 Patented Oct. 24, 1922.

c $9 I Q I g i I I E Q U -I**-r Q I I M I Q- JL I I' Q I I I I I I l I I I I I I I I [1, Q y v v V V V INVENTOR. H 5. Osborne BY mama/3% ATTORNEY 40 conditions to be met.

Patented Oct. 24, 19 22.

mom) s osiaoann'or NEwfYoRx, N. Y., assionon TO AMERICAN TELEPHONE AND UNITED, STATES 1,432,781 PATENT OFFICE.

TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

Imus on AND METHOD E AVOIDING INTERFERENCE.

"Application filed na 31,

cuits of ocean cables and is here illustrated 1 and described-as applied to such a=circuit,

1 but it is to be understood that its usefulness is not limited thereto; e l 7 As is well known, the signal impulses received over ocean cables are extremely weak and difficult to record as compared with ordina landline signals and it is customary F to re uce the disturbances in the cable circuits by grounding thereturn circuit at a point at sea, often several miles distant instead ofiat the cable 'oflice. Thisavoids dis-' turbainces due to local ground-potentials. It does not, however, entirely eliminate disturbing influences because the conductors running from the cable office to the cable and to the sea ground, respectively, ma be 80 subject todisturbingpotentials induce nei hboring power circuits or the like. t

is t e object of the present invention to provide meansfor overcoming these difiicul- 85 The invention will be more fully understood by a reference to the accompanying drawings in which'Fi re 1 illustrates diammatically one em 'diment thereof and i 12. '2'represents a circuit illustrating the Fig. 1 shows diagrammatically the ordinary terminal connections for duplex operation of a cable circuit, wherein the cable 1 is'connected to the apparatus 2 in the cable as bfiioe by a conductor 3- 1. The recording apparatus 5 is connected between the conductor 3-4 and the artificial line ,6, in parallel with the ratio arms 7 and 8 'which provide the connecting point for one side of the sendin apparatus9,*'the other side being groun ed, all as is customary in duplex cableoperation. Instead of ounding the artificial line ,6 andthe sending apparatus 9 locally, 'it is common as above indicated to 56 connectthern metallically with asea ground 1918. 'Serial No.24 7,608.

to avoid local disturbing potentials. Such a ground connection is indicated on the draw ings at 10, with a conductor 1112 extending between the cable oifice and the sea Y i a r so I The conductors 34l and 11-12 maybe ground.

subject to disturbing potentials, and due to the unbalanced condition of the circuit with; respectto such potentialsthey will beevi-' den'ced. 1n the receiving apparatus5 to" the 1 confusion of transmitted signals. F or instance, in the system illustrated in Fig. 1, it maybe supposed that a disturbing potential is caused in that sectionoi the conductors 3 -4and11-'12 lying betweenthe dotted lines a-b and -0cZ. This potential will ordinarily be of the same sign and magni- 1 pacity to ground throughout its length andmore or less leakage, the induced potentials a" and y if equal would not afiect the receiving apparatus 5 since they would neutralize each other therein. For the purpose of illustrating the effect of the leakage and capacity to ground, we may imagine each of the circuits 34 and 11-12 to be" connected, at the points 3 and 11 respectively, to the common ground 13 through like impedances 14 and 15, as indicated in Fig. 2. The 0pposite end of the conductor Lil-12 is grounded at 10, (the-sea ground) while the opposite end of the conductor 3- 1 reaches ground 17-only after passing through the entire cable 18 which is of high impedance as compared with the ground 10. Considering, then, the admittance to ground of conductors 3- 1 and 1112 the potentials a: and y are applied to parallel circuits which may be'traced, respectively as follows a 4, 3, 141, 13, 17, 18, 1 and 12, 11,15, 13, 10, 12. The potential y is consumed entirely by the impedance of the circuit 11-12 andthe' impedance 15, the point 12 and ground-10 being regarded as electrically the same for the purposes of this illustration. The potential w is consumed in the impedance of the circuit -i-3 and impedance 14, which are equal to the corresponding impedances of the other circuit, plus the impedance of the cable 18. It is, therefore, obvious that the voltage drop across the impedance 15 will be greater than the voltage drop across the impedance 14; and since the two impedances are connected to the common ground 13, which may be regarded as at zero potential it will be obvious that the point 11 will have a higher potential than the point 3 and that a circuit connected between 11 and3, such as the receiving circuit 5 in Fig. 1, will receive a current due to this difference of potential.

To correct this condition it is necessary to so vary theimpedance between one side 01" the line and ground that the two terminals are brought to the same potential for all frequencies employed. For this purposeit is necessary that the impedance 3-17 (referring to Fig. 2) be to the impedance 1110 as impedance 14 is to impedance 15. In a case then such as illustrated. in Fig. 2 where 3-17- excee ds ill-10 the impedance at 15 must be made less than. the impedance at l l. A convenient method of accomplishing this result in the ordinary cable circuit is to connect an impedance between the point 11 and ground as indicated in Fig. 1. The character of this connection will depend upon the character of the circuit with which itis used. Where the impedance to be balanced consists of resistance and capacity as it-frequently will in ocean cables this shunt will consist of like elements-as illustrated in Fig. 1, where use is made of a resistance 20 in series with an artificial line 21 the latter comprising resistance and shunt capacity It will be clear. from an inspection of the drawing that such a shunt connected between the point 11 and ground will reduce the impedance between these points and will therefore decrease the potential drop. between them, and if properly proportioned will. reduce the potential of the point 11 to correspond with that of the point 3 with the result that no current will flow in a cir cuit connected between them due to the in: duced potentials 0c and y.

It should be understoodthat the cl P1311031? tion of the invention is not limited to the case where the potentials and y are equal but in any case where they are known the proportion above mentioned between the im pedances can be varied to satisfy. conditions by adding or subtracting impedance at the proper points as will be obvious.

It will be understood, of course, that, in the actual circuit the impedance indicated at 14 and .15 in Fig. 2 are distributed along the entire length of the conductors 34 and 11-12, but the principle by which the shunt affects the correction remains in general the same. Theoretically the shunt should be connected at the midpoint of the impedance represented by the conductors 3-4L and 11-12 but since the point at which the disturbances may arise will vary from time to time, no definite point for the connection of the shunt 19 can be assigned and it has been found that the connection of the shunt close to the point 11 will substantially equalize the potentials at 3 and,11;.itor all induced potentials likely to be metpand throughout a. wide range of frequencies. In general the resistance 20 of the shunt 19 should have a magnitude.

Experiments show that in the average ocean cable system, a long artificial. line at 21 is unnecessary, a. total product of capacity and resistance (K. R), of 0.013 giving practically asgood results as larger values. A shorter cable than. this, however, gives less perfect neutralization. V

The operation ofv the system. will be obvious from the foregoing description. It the points 3 andll arebrought-to the same potential, no currentwill fiow through. the apparatus of the cable ofiiceconnected to these pointssince whatever is includedin. the circuit from thereon will have equal and opposite potentials applied'thereto. Ifthere is capacity toground or substantial leakage in the artificialline 6 or other elementsot' the sending and receiving apparatus, there would be some unbalance in receivinginstrument 5,

but ordinarily any such leakage or capacity to ground is so small that it may be disregarded. Actual tests with a shunt connection to, the circuit, as herein described, show that the disturbances in the receiving instrument 5 are reducedby about ninety per cent.

It is to be understood that. the invention is not, limited to the particular circuits hereinshownand described and it will be obvious to those skilled in the art that modifications in details may be made without departing t'romthe spirit. of the invention.

What is claimedisz- 1.1n a signal transmitting system, a metallic transmission line, a duplex set for sending and receiving signals thereover ineluding an artificial line between which and the main line the receiving instrument of the set is connected, a conductor connecting the duplex set with the ocean cable, a second conductor connecting the transmitting dedisturbing outside sources.

2. In a signal transmitting system, a metallic transmission line, a duplex set for sending and receiving signals thereover including an artificial line between which and the main line the receiving instrument of the set is connected, a conductor connecting the duplexset with the ocean cable, second conductor connecting the transmitting device of the duplex set and the artificial line with ground, a shunt between said second named conductor and ground and comprising a resistance and an artificial line, for equalizing voltages at the terminals of said duplex set due to potentials induced in said conductors by disturbing outside sources.

In testimony whereof I have signed my name to this specification this thirtieth day of July, 1918.

HAROLD S. OSBORNE.

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