US1978419A - Transmission system - Google Patents

Transmission system Download PDF

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Publication number
US1978419A
US1978419A US606135A US60613532A US1978419A US 1978419 A US1978419 A US 1978419A US 606135 A US606135 A US 606135A US 60613532 A US60613532 A US 60613532A US 1978419 A US1978419 A US 1978419A
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United States
Prior art keywords
cable
conductor
pairs
conductors
talk
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Expired - Lifetime
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US606135A
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English (en)
Inventor
Homer W Dudley
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AT&T Corp
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Bell Telephone Laboratories Inc
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Publication date
Priority to FR754288D priority Critical patent/FR754288A/fr
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US606135A priority patent/US1978419A/en
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Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B11/00—Communication cables or conductors
    • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
    • H01B11/20—Cables having a multiplicity of coaxial lines

Definitions

  • the present invention follows from the discovery by applicant that in a signaling cable comprising a number of pairs'of coaxial conductors, as disclosed, for example, in the application for patent referred to above, induced voltages tending to produce near-end cross-talk are inherently neutralized to a large degree.
  • the neutralizing effect is so great in" fact that near-end crosstalk is less serious than far-end cross-talk, and the levels of both are low enough that conductor pairs within the same cable may be used indiscriminately for transmitting signals in the same frequency ranges in either the same or opposite directions.
  • the invention herein claimed lies, therefore, not so much in the cable itself as in its combination with suitable signaling apparatus. Its nature will appear more fully in the discussion and detailed description of preferred embodiments that follow.
  • Figs. 1A, 18, 4A, 4B, 5 and 6 showthe structure of cables adapted for use in applicant's transmission system
  • Fig. 2 represents diagrammatically the cable of Fig. 1 and the circuit with which it may be used in accordance with the present invention
  • Figs. 3A to 3D illustrate the effect of cross-talk in applicants system and in systems known heretofore;
  • Fig. '7 represents one preferred form which the central conductor may take.
  • FIG. 8 shows a carrier wave transmission system embodying the present invention.
  • a cable in accordance with the present invention which comprises four pairs of coaxial conductors enclosed within a tubular lead sheath 5.
  • Each coaxial pair may comprise a thin tubular outer conductor 1 preferably of copper, and a central return conductor 2 also of copper.
  • the latter may be'a solid wire asshown, .or alter-- natively, a stranded wire, a small tube or, other suitable structure.
  • the outer .conductor may be a drawn copper tube as shown, or formed of sheet copper or stranded wire, or of any other form that will provide a substantially tubular conducting path anda fair degree of mechanical flexibility.
  • the diameter of the outer conductor may be of the order of a quarter or half inch.
  • Fig. 3B plotted against distance.
  • the dielectric is gaseous or chiefly so.
  • Beads or washers 3 of insulating material are strung along the central conductor at intervals of the order of an inch, or as required for mechanical support, to prevent contact between inner and outer conductors.
  • Thedielectric constant and conductivity of this material should be as low as possible to minimize losses.
  • a continuous serving of metal or fiber tape 4 is preferably applied to the four conductors to bind them to gether.
  • a mechanically improved structure. is
  • the signal power in line W "logarithmically expressed, and that in line- W/calso, decreases approximately uniformly with the distance from the repeater A1; that in in adjacent lines. varies. as” the signal levelat the corresponding point of the disturbing line.
  • the effector an inducedvoltage depends, however, not aloneon its magnitude but also on what part of thecircuit .it arises in..
  • a voltage inducedfrom line W to line W near repeater A1 will have less effect at repeater Az than an equalvoltage induced near the latter repeater, .sincein the former case the induced The,
  • the coupling between ciruits is the same at all points and the total effective induced voltage increases as the first power of the r length of the repeater section.
  • Over-all crosstalk in both cases should be at least decibels below the level of signals.-;lnasmuch as coaxial conductorilines are adapted for long distance transmission, the cross-talk arising ineach rev peater section must be kept at a very low level.
  • cross-talk can be reduced by electrically insulating the coaxial conductor pairs from each other.
  • the advantage maybe material, but only where short lengths of cable are involved, as ten to three hundred feet.
  • the conductors thus insulated cross-talk varies approximately as the square of the length of the cable, and for lengths greater than roughly W two miles greater cross-talk may result than with uninsulated conductors.
  • the several coaxial conductor pairs of the cable are preferably bound together in good electrical contact as hereinbefore described in connection with Fig. 1.
  • Figs. 4A and 4B a typical multi-layer cable in accordance with the present invention.
  • the central layer comprises four pairs 10 arranged as at the corners of a square,
  • each pair may be, for example, 0.3
  • the lead sheath may be placed over the lead sheath.
  • the of conductors will depend on the environment in" which the cable is to be used, as the cable maybe laid for example, in a conduit, embedded in soil, or hung on line of poles. In some cases i an extra waterproof cover may be extruded over the assemblage or over the individual outer conductors to keep moisture and dirt out of thespace between the central and return conductors. This feature maybenecessary where the outer conductors are braided or constructed in any other manner that would permit moisture and dirt to penetrate.
  • Additional layers of conductor pairs may be provided.
  • successive layers are given opposite directions of lay both to improve the me- 5' eral rule that the length of lay should be large strands to avoid skin and proximity effects within than No.40 B. & S. gauge.
  • Fig. 1 may be used in the cable of Figs. 4A and 4B.
  • oppositely directed circuits are preferably alternated with each other.
  • the conductor pairs may be rearranged or transposed so that no pair is subjected to more cross-talk than another.
  • FIG. 5 Another type of cable is shown inFig. 5.
  • the central portion of the space within the sheath is occupied by coaxial conductor pairs 13.
  • One or more pairs of coaxial conductor circuits may be thus placed.
  • the remainder of the space is filled with twisted pair circuits 12, which may be arranged as quads or in any other suitable manner.
  • the coaxial pairs 17 are arranged in a circle just within the lead sheath 15, and the central region is filled with quads, or twisted pairs 16.
  • any of the cables herein described may be used for the transmission of television signals, carrier wave or otherwise.
  • Television channels are less affected by noise and cross-talk than are telephone channels. Accordingly the frequency range above the useful telephone'channel range may economically be used for television transmission. Induction from one television circuit to another results in distortion of the television images. In a sense any such disturbance may be termed cross-talk.
  • the construction of the central conductor merits special attention. Aside from the absolute diameters of the conductors comprising a pair, the elfective resistance of the central conductor is the chief factor determining the attenuation of the 1 system. Where a solid conductor is used, the alternating current resistance may be much greater than the resistance to drect current be-- cause of skin effect. As noted hereinbefore the central conductor may advantageously in many cases comprise a number of small strands of fine insulated copper wire so braided or twisted together as to provide a uniform distribution of current throughout the cross-section of the con 130 ductor.
  • the size of strandto be used depends on the frequency which the cable is to transmit. The higher the frequency, the smaller must be the the individual strands. With small strands, however, asmaller proportion of the cross-section of the conductor is occupied by conducting ma terial and more by air and insulating material; Another limitation is in thediificulty of manufacturing and handling strands much smaller In any particular case a compromise between the several factors involved must be reached.
  • a simple method of stranding would be to divide all the strands into three or four bunches, twist each bunch separately and then twist the several bunches together. This would not be very effective, however, because many strands near the center of thebunches would tend to remain 15;
  • stranding such as indicated in FigJ'l
  • the total number of strands is'divided in groups of from two to six, and each group is twisted; for purposes of illustration, assume there are three strands per group.
  • the twisted groups in turn are divided into other groups e f-from two to six; or in the case assumed, three, and twisted to form nine ropes.
  • ropes in turn,-may be twisted togetherrin groups
  • -Another possibility is to ,arrange the strands so that they travel more nearly longitudinally at the outside of the conductor, and more nearly circumferentially or radially toward the center.
  • the interior of a conductor may be hollow, the strands being Q. woven in re-entrant manner .to-form a tubular structure. A core of string, cord, or other suitable material may be inserted.
  • Another method of obtaining a varying current density is to use poor insulation between strands to encourage the leaking off of current when the strands are near the center of the conductor. Alternatively, the.
  • leakage of current may be induced by using very long stranding pitches so that a strand stays near the center of the conductor for a considerable distance.
  • Fig. 8 shows a typical signaling system embodying the present invention.
  • At New York or some other city A terminating an extensive communication system are located the carrier wave signaling circuits there indicated on the drawings.
  • Similar circuits at various suburban points Band C and at a nearby city D, such as Morristown, 'N. J., are tied intd the system by 'means of coaxial conductor cables 10f the type shown, for example, in Fig. 4A and 43. From D cables might be extended to distant cities represented at E. Sucha line-orseveral of them might be laid between New York and Chicago,
  • r l I Within the terminal city A mayabe located several stations S1, S2, S3, etc., where signals in a, multiplicity of voice frequency circuits, as those associated with a local telephone exchange system, are applied to respective carrier waves."
  • the transmitting circuits at each station are represented, though incompletely, by the several. telephone or other law frequency circuits 21, modulators 23 and band passing filters 25.
  • Output signals are amplified and applied to one coaxial conductor pair of a multi-circuit cable 29, 30, 31, etc.
  • Carrier wave signals received over another coaxial pair. in the same cable are separated. by band passing filters 26, and then reduced to audio frequencies in demodulators 24.
  • the number of conductor pairs in each of the cables 29, 30, 31, etc. is of course not limitedto two, and a greater number may be used if more than approximately one hundred channels are required at any of the stations S1, S2, etc.
  • several cables, 29, 30, 31, etc. which, for example, may be laid in conduits under the city streets, may branch into a single cable 35 at various points .to form the complete cable 36.
  • Another cable 37 from various suburban points may join cable 36 to form.
  • cable 38 which leads to -the nearby city D.
  • the circuits at the suburban stations which are associated with cablev 37 may be of the'same type as those represented at S1.
  • Some of the conductor pairs in cable 37 may branch into cable 36, others into cable 38, while still others may make a T connection with through circuits between points A and D.
  • the latter conductor pairs may then be used for connection with either A or D as changes in thedistribution of trafiic may require.
  • one group of conductors 39 is separated for connection into another type of transmission system, to be referred to hereinafter.
  • the remainder. continues through cable to a distant city such as Philadelphia.
  • the latter circuits are separated within the station at D into groups 40 and 41, the former carrying signals in the E-W direction and the latter in the opposite direction.
  • Each group is associated with a suitable repeater 42, 43, which comprises individual amplifiers for the several conductor pairs.
  • the cables employed throughout the system may be of the type described hereinbefore. Between any two points a single cable only need be used, since in accordance with the present invention, conductor pairs carry-- ing signals in opposite directions may be included in the same cable. Where the outside diameter of such a cable wouldbe. excessive, however, theconductors may of course be separated to form two or more cables.
  • the conductors 39 which are separated from.
  • This system includes modulating apparatus 49 for transferringthe several 50-500-kilocycle carrier signaling bands transmitted over conductor 39 to respective positions in a frequency band that may extend from five hundred to five thousand kilocycles per second.
  • the resultant signals are then applied to a single pair of coaxialconductors 51 for transmission to a distant city F.
  • a similar pair of conductors 52 carries signals in the Opposite direction. Signals from the latter are applied to apparatus 58 where they are first separated by filters into bands of .approximately four hundred and fifty kilocycles in width and then demodulated to reduce them to 50-500-kilocycle bands.
  • the latter are applied to individual conductor pairs in cable 39.
  • the local telephone exchange system of city D may be con self.
  • the coaxial conductor line of large diameter may be used practically to transmit frequencies of five thousand kilocycles per second and higher, the repeaters being spaced every 25 or 50 miles or otherwise as economy dictates.
  • a thousand or more carrier telephone channels may be carved out of the frequency range thus made available.
  • a single amplifier at a repeater station may serve for these one thousand channels. offsetting these economic advantages to a certain extent is the cost of the copper required for the conductors; but the system is nevertheless from both physical and economic standpoints well adapted for the transmission of signals overa distance of several hundred, or even several thousand miles.
  • difficulty and expense is involved in establishing and separating the many closely-spaced, radio frequency signaling bands.
  • Simple band pass filtering circuits cannot be used for a number of reasons, chief among which is their lack of selectivity. Instead, multiple modulation and demodulation and successive filtering is resorted to. To separate a small number of bands, or even a single one, complex and expensive circuits of this nature are required. The system is therefore not well suited where channels are to be added to or removed from the system at frequent intervals along the line, as is contemplated in the system disclosed by applicant.
  • a coaxial conductor pair of small size that is, of one quarter to one half inch outside diameter, has a useful signaling frequency range of the order of 50-500 kilocycles per second or greater.
  • a hundred or more carrier telephone channels may be superimposed on each pair.
  • Band pass ing filters using piezo-electric crystals are surficiently selective to separate signaling bands in this frequency range, as disclosed in applicants copending application for patent bearing
  • Serial Carrier channels may therefore be readily added to or removed from a pair of conductors as required. If as many as one hundred signaling channels are needed at a particular city along the route of a cable, one or more pairs of conductors may be branched from the cable to serve this point.
  • filters, modulators, demodulators, etc. are used to serve this point.
  • 3'7 and 38 are indicated as transmitting signals in one direction only. In some cases, however, it may be found desirable to transmit signals in both directions over a single pair of conductors,
  • each conductor pair transmits signals in one direction exclusively, since in the case just described, transmission in the oppositedi- ,i
  • a cable comprising a plurality of pairs of coaxial conductors, and means for transmitting carrier telephone signals in the same frequency ranges in opposite directions over different pairs of said conductors, said pairs being shielded from each other only by their respective outer conductors.
  • acable comprising a multiplicity of pairs of conductors, means for keeping the level of near-end cross-talk occurring in said system less than that of far-end cross-talk and both insufficient to cause objectionable interference, said means consisting of one conductor of each of said pairs, said conductor being hollow and arranged with the other conductor of the respective pair within it, and means for transmitting signals in the same carrier frequency ranges in opposite directions over pairs of said cable the outer conductors of which are in conductive contact.
  • a transmission medium comprising a unitary assemblage of coaxial conductor pairs, repeaters at intervals in said respective conductor pairs, and means to transmit in respectively opposite directions over different ones of said pairs signals of the same frequency, said frequency being at least several hundred thousand cycles per second and the energy level of near end cross-talk occurring in any of said pairs being at least sixty decibels less than the energy level of received signals.
  • a cable comprising a multiplicity of coaxial conductor pairs, the outer conductors of said pairs being laid in substansignals in different conductor pairs overlapping at least in part and their lower extremities being determined by the energy level of far-end crosstalk, said system being characterized in that near-end cross-talk is less than far-end crosstalk.
  • a multiplex carrier wave system a plurality of transmitters each producing a different 5 frequency wave for transmission, a coaxial conductor connected in common to all of said transmitters, a plurality of receivers located adjacent V tern, a first station, a second station, a multiplicity of low frequency circuits at each of said stations to be connected into said system, a cable extending between said stations, said cable comprising a plurality of pairs of coaxial conductors each a fraction of an inch in diameter and adapted to transmit with moderate attenuation waves extending in frequency to as high as several hun dred thousand cycles per second, the outer conductors of said pairs being laid in substantially "continuous conductive; contact, a plurality of transmitters and a plurality of receivers at both of said stations, each of said transmitters and receivers including frequency translating means interconnecting a plurality of groups of said low frequency'circuits with conductor pairs in said cable individual to said groups, the frequency range transmitted over one pair of said conductors overlapping the frequency range received over

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US606135A 1932-04-19 1932-04-19 Transmission system Expired - Lifetime US1978419A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2526942A (en) * 1946-04-15 1950-10-24 Telecommunications Sa Process for reducing the far-end crosstalk between concentric pairs due to tertiary circuits
US3350647A (en) * 1962-10-25 1967-10-31 Communications Patents Ltd Wired broadcasting systems and communication cables therefor
US3651243A (en) * 1968-08-30 1972-03-21 Western Electric Co High-frequency cables
US5519173A (en) * 1994-06-30 1996-05-21 Berk-Tek, Inc. High speed telecommunication cable
US5883334A (en) * 1995-06-13 1999-03-16 Alcatel Na Cable Systems, Inc. High speed telecommunication cable

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE747820C (de) * 1934-03-30 1944-10-16 Hans Bodo Willers Elektrische UEbertragungsleitung fuer hochfrequente Stroeme

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2526942A (en) * 1946-04-15 1950-10-24 Telecommunications Sa Process for reducing the far-end crosstalk between concentric pairs due to tertiary circuits
US3350647A (en) * 1962-10-25 1967-10-31 Communications Patents Ltd Wired broadcasting systems and communication cables therefor
US3651243A (en) * 1968-08-30 1972-03-21 Western Electric Co High-frequency cables
US5519173A (en) * 1994-06-30 1996-05-21 Berk-Tek, Inc. High speed telecommunication cable
US5883334A (en) * 1995-06-13 1999-03-16 Alcatel Na Cable Systems, Inc. High speed telecommunication cable

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