US1888558A - Method of and means for reducing crosstalk in cable systems - Google Patents

Method of and means for reducing crosstalk in cable systems Download PDF

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Publication number
US1888558A
US1888558A US586263A US58626332A US1888558A US 1888558 A US1888558 A US 1888558A US 586263 A US586263 A US 586263A US 58626332 A US58626332 A US 58626332A US 1888558 A US1888558 A US 1888558A
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Prior art keywords
crosstalk
circuits
cable
balancing
phantom
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Expired - Lifetime
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US586263A
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English (en)
Inventor
Kenneth E Latimer
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AT&T Corp
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Western Electric Co Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/32—Reducing cross-talk, e.g. by compensating
    • H04B3/34—Reducing cross-talk, e.g. by compensating by systematic interconnection of lengths of cable during laying; by addition of balancing components to cable during laying

Definitions

  • This invention relates to telephone transmission systems and more particularly-long distance telephone cablesusing voice frequency circuits worked on a four-wire basis or carrier frequency circuits, but is also applicable to open wire lines.
  • the invention has for its primary Object the reduction of crosstalk, but there are also other objects which will become apparent in the course of v the explanation which follows.
  • mission times (and cut-oil frequencies in the case of Pupin loading) substantially equal on all circuits in a groupwhether they be side circuitsor phantom circuits,and whetli-' or or not a diflerence of attenuation will be.
  • a communication-cable comprising con I invention
  • Figs. 1 and -2 arefdiagrams employed to aid in a'mathematical explanation of the pecific circuit, arrangements for practicingthe invention. 1 J
  • FIG. 3 and 4 illustrate diagran'nnatically.
  • each unbalance such as a can therefore evidently be balanced or represented by two condensers such "as 01 and C provided that the phase conditions are suitable and that the difierence between the attenuations of the circuits does not vary With frequency, so that by suitably choosing the values of the balancing condensers a simultaneous balance of each element of crosstalk is practicable apart from velocity differences. I We can therefore of a repeater section beconsidered as replaced by' two'crosstalks a and a inFig.
  • phase of the crosstalk current due to a small capacity unbalance between the two circuits is, at the point at which it occurs, exactly 90 out of phasewith the voltage at that point, while themagnitude of the current, on circuits of constant impedance, will be proportional to the frequency.
  • the voltage induced in the disturbed circuit by a mutual inductance from the disturbing circuit will be exactly 90 out of phase with the current in the disturbing circuit, the magnitude again being proportional to the frequency on circuits of constant impedance.
  • 1, 2 and 3 are three cable circuits
  • &6 are three-phase splitting devices
  • 7-9 are terminal equipments
  • 10-13 are balancing condensers
  • phase split ter i rotates the phase of the currents passing in condensers 11 and 13 by the required amount.
  • Resistance unbalance crosstalk leads to crosstalk voltages which are in phase with the inducing current. This type of crosstalk only occurs in the case of phantom to side crosstalk and in this case if the resistance unbalance crosstalk-is sufliciently high'it may be necessary or desirable to correct it by inserting a small resistance in series With one wire of the side circuit" in question.
  • the degree to which the impedance of the terminatingequipment should match that of the line depends on the magnitude of the reduction in far end crosstalk required. .Thus if it is required to reduce crosstalk to onetenth of its original'value, thenthe impedance of the terminal equipment must in general match that of the line within a singing-point of 206%, while'if it is required to reduce it to one-thirtieth a singing point of 30d?) is re-' quired, andso on. This is'a considerably higher standard than has hitherto been considered necessary on four-wire voice fre -I matching between the line and equipment I may however be utilized as'a phase splitting device. If it is desired to obtain this effect,
  • the circuit of Fig. 4 could be used, the devices l 4, 5 and 6 being in this case attenuating pads having the same impedance. as the cable.
  • the equalization of velocities necessary for practicing the invention can be obtained by several different methods
  • the equalization of velocities of circuits of .a given type, e. g. side circuits maybe carried outby crosssplicing the cable at one or more points within the repeater section in accordance with total capacity and total inductance measurements, or alternatively, velocity .measurements which may conveniently be made by N the -open circuit, short-circuit impedance method.
  • the splices would be. carriedout in such a way that upon all circuits of a given type the product of total capacity and total inductance would be as nearly as possible the same.
  • One method is to vary the average inductance of the phantom coils to give the same average velocity on the phantom circuits as is expected'tobe obtained on the side circuits.
  • the phantom to side capacity ratio may vary from 1.58 to 1.7 according to the methods of manufactureof the cable, 'gaugeof conductor and even the cable fac' tory,'it will be necessary in certain cases to adopt'slightly different inductances for the phantom circuit, according to circumstances. Care 1s ofcourse normally exercised to msure that the phantom to side capacity ratio remains constant in successive loading sections.
  • the main cable is of quadded. (i. e. multiple twin) type
  • a small quantity of spiral-4; cable maybe included at regular intervals, for instance in every loading section,'either in such a way as to convey the speech currents or connected to the main cable means of a T splice so as to increase the capacityof the section.
  • the phantom to side capacity ratio of spiral-4 cable ismuch higher than that of multiple twin cable, it is evident that the loading section phantom to side capacity ratiocan be conveniently controlledby this procedure.
  • Another version of this arrangement is to use a much larger amount of spiral-4' cableso that the resulting loading section phantom to side ratio is exactly 2 1 as by this procedure the phantom circuits can be made to have exactly the same velocity and attenuationas the side circuits, so I simplifying the balancing of phantom to pair and pair to phantom crosstalk.”
  • As almost equal quantities of multiple twin and spiral-4 cable are required for this arrangement it would be possible to use a cable in which half'the quads were of multiple twin construction and half of spiral 4 construction, it being arranged that' in any loading section a given circuit would consist of wires laid up according to each construction for exactly half the section. 1
  • each condenser may be considered to be replaced by a network of condensers designed to neutralize the unbalance in question without affecting other unbalances.
  • two-wire circuits of a cable are conductors situated in the outer layers surrounding the conductors of the four-wire circuits, the babble or crosstalk in the latter being balanced by the above described methods. At least three effects are obtained by this rearrangement.
  • the fourwire circuits of high quality which unfortunately happen to be the circuits most sensitive to noise, are situated in a region of less noise and interference from outside sources.
  • the singing point of thetwowire circuits is improved.
  • screening between conductors of the fourwire circuits transmitting in opposite directions is to be provided, this may be furnished 7 more economically, as the screen need only conditions and means or methods for reducing them. It may, however, be possible that other types of disturbance may be reduced by similar or analogous expedients, for example, provided that the velocity of transmission of noise voltages to earth is made the same as that of metallic noise voltages, reductions of noise may be effected by similar means.
  • a communication cable comprising conductors forming two-wire and four-wire circuits, said fourwire circuits being nearer the center of the cable than the two-wire circuits, and means for reducing far end crosstalk between said circuits comprising balancing impedance elements connected between certain of said circuits at the near end of said cable.
  • the method of reducing far end crosstalk between the signaling circuits of acommunication cable employing repeaters at the ends thereof which consists in first equalizing the transmission times of the signaling circuits of a given type by cross-splicing the cable at one or more points with in a repeater section to make the total inductance and capacity of said given type circuits substantially the same, and then balancing the far end crosstalk with reactive elements connectedbetween certain'of said signaling circuits at the near end of said cable.
  • a quadded communication cable in which substantially half the quads are of multiple twin construction and half of spiral-4; construction so that each signaling circuit comprises alternate lengths of the two constructions, and

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
US586263A 1931-01-05 1932-01-13 Method of and means for reducing crosstalk in cable systems Expired - Lifetime US1888558A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB355/31A GB376245A (en) 1931-01-05 1931-01-05 Telephone transmission system

Publications (1)

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US1888558A true US1888558A (en) 1932-11-22

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US586263A Expired - Lifetime US1888558A (en) 1931-01-05 1932-01-13 Method of and means for reducing crosstalk in cable systems

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US (1) US1888558A (fr)
FR (1) FR728614A (fr)
GB (1) GB376245A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2675428A (en) * 1940-09-24 1954-04-13 Int Standard Electric Corp Cable balance

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE976650C (de) * 1940-04-17 1964-01-23 Int Standard Electric Corp Kabel fuer Hochfrequenz-Signaluebertragung

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2675428A (en) * 1940-09-24 1954-04-13 Int Standard Electric Corp Cable balance

Also Published As

Publication number Publication date
FR728614A (fr) 1932-07-08
GB376245A (en) 1932-07-05

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