United States Patent (19)
`Nutt et al.
`
`11
`(45)
`
`4,262,164
`Apr. 14, 1981
`
`(54) TELECOMMUNICATIONS MULTIPAIR
`CABLE
`75) Inventors: Wendell G. Nutt, Dunwoody; Joseph
`P. Savage, Jr., Tucker, both of Ga.
`73) Assignee:
`Bell Telephone Laboratories,
`Incorporated, Murray Hill, N.J.
`(21) Appl. No.: 97,810
`22 Filed:
`Nov. 27, 1979
`51) Int. Cl. ..................... H01B 11/04; H01B 11/06;
`H01B 7/02
`52 U.S. Cl. ........................................ 174/34; 174/36;
`174/110 F
`58 Field of Search .................... 174/23 R, 23 C, 27,
`174/32, 34, 36, 110 PM, 110 F, 113 R, 113 AS
`References Cited
`U.S. PATENT DOCUMENTS
`4,058,669. 1 1/1977 Nutt et al. .............................. 174/34
`4,174,236 11/1979 Dougherty et al. ......... 74/110 FX
`OTHER PUBLICATIONS
`Metcalf, E. D., "Cellular Insulation as an Answer to
`Material Conservation', Proceedings of the 13th Interna
`tional Wire and Cable Symposium, Atlantic City, N.J.,
`pp. 53-58, Dec. 3-5, 1974.
`Mitchell, D. M., "Dual Insulation Conserves Cable
`Materials', Bell Laboratories Record, vol. 54, No. 8, pp.
`
`(56)
`
`225-228, Sep. 1976, Published by Bell Laboratories,
`Murray Hill, NJ.
`Durham et al., "LOCAP: A Low-Capacitance Cable
`for a Hih-Capacity System', Bell Laboratories Record,
`vol. 52, No. 7, pp. 217-221, Jul.-Aug. 1974, Published
`by Bell Laboratories, Murray Hill, NJ.
`Hoth, D. F., "The T1 Carrier System', Bell Laborato
`ries Record, vol. 40, No. 10, pp. 358-363, Nov. 1962,
`Published by Bell Laboratories, Murray Hill, NJ.
`Nutt, W. G., et al., "Multipair Cables for Digital Trans
`mission', National Telecommunications Conference Pro
`ceedings, pp. 21.1.1-21.1.5, Dec. 1978.
`Primary Examiner-Laramie E. Askin
`Attorney, Agent, or Firm-Sylvia J. Chin
`57
`ABSTRACT
`A multipair telephone cable (50) has been specifically
`developed for voice frequency and T1 carrier fre
`quency transmission between cities. The copper wire
`gauge, dielectric diameter, and insulation expansion are
`uniquely designed so that this single cable design can be
`used for either air core or waterproof versions of the
`cable. Advantageously, both cable versions are compat
`ible with existing carrier and voice frequency electron
`ics. Also, the load coil spacing for voice frequency
`transmission and the regenerative repeater spacing for
`carrier transmission coincide in both versions.
`
`2 Claims, 4 Drawing Figures
`
`MUTUAL CAPACITANCE
`(nF/MILE)
`IN WATERPROOF CABLE
`
`83
`
`73
`
`63
`
`53
`
`43
`
`40/. 22 s
`
`T CARRIER LOSS (dB/kft)
`25
`
`20
`
`
`
`24
`22
`COPPER WIRE GAUGE
`
`26
`
`

`

`U.S. Patent
`
`Apr. 14, 1981
`
`4,262,164
`
`A/G 4
`
`
`
`83
`
`73
`
`MUTUAL CAPACITANCE $3
`(nF/MILE)
`'
`IN WATERPROOF CABLE
`
`53
`
`20
`
`24
`22
`COPPER WIRE GAUCE
`
`26
`
`U.S. Patent
`
`Apr. 14, 1981
`
`4,262,164
`
`
`
`Tt CARRIER LOSS
`
`(dB/kft)
`
`wo/2
`
`FIG. 4
`
`83
`
`B
`
`MUTUAL CAPACITANCE |
`(nF/MILE)
`IN WATERPROOF CABLE
`
`33
`
`
`
` 2022S
`COPPER WIRE GAUGE
`
`Page 2
`
`
`
`CommScope Exhibit 1024
`
`

`

`1
`
`10
`
`15
`
`25
`
`TELECOMMUNECATIONS MULTIPAR CABLE
`FIELD OF THE INVENTION
`This invention relates to telephonic transmission sys
`tems, and more particularly to telephone cables in
`stalled between cities.
`BACKGROUND OF THE INVENTION
`The communication links between two central offices
`are known as trunks. When the central offices are in
`different cities, they are called intercity trunks; when
`one central office is in a large city and the other central
`office is in a relatively small remote community, they
`are called outstate trunks. Multipair cables are often the
`transmission medium used for intercity and outstate
`trunks to connect central offices located in different
`cities. Intercity and outstate cables are typically buried
`but may also be installed aerially or in ducts.
`20
`Today most intercity and outstate trunks utilize car
`rier systems although some still transmit at voice fre
`quency. The T1 carrier system, which is described in
`the Bell Laboratories Record, Vol. 40, No. 10, November
`1962, pp. 358-363, is the dominant carrier system used
`to connect cities 10 to 50 miles apart. Voice frequency
`transmission is still important on these cables because
`some pairs are needed for: (1) voice frequency trunks
`(2) fault locate and order wire circuits for T1 carrier
`and (3) subscriber services in certain situations.
`The T1 carrier system was designed to utilize a 22
`30.
`gauge wood pulp insulated conductor exchange cable.
`This cable, which was originally developed for voice
`frequency transmission, has conductor pairs with a mu
`tual capacitance of 83 nanofarads/mile (nE/mile). Each
`T1 system provides 24 channels on two pairs by displac
`35
`ing two voice channels. The repeater or regenerator
`equipment for carrier or high frequency transmission
`for the pulp cable was designed to use a repeater spac
`ing which coincided with a standard load coil spacing
`of 6000 feet for voice frequency transmission. This al
`lowed for easy transition from voice to carrier transmis
`sion. The repeater equipment was, and still is, designed
`to accommodate at 5.1 dB/kft loss, the loss of the 22
`gauge pulp cable at T1 carrier transmission.
`For several years after the introduction of the T1
`45
`carrier system, trunk expansion was accomplished by
`converting from voice to carrier transmission on up to
`about half the pairs in pulp cable. But system needs
`increased so that, beginning about 1972, cables fre
`quently came to be needed in which all pairs could be
`used for carrier while still having voice transmitting
`capability.
`Meanwhile, voice frequency cables had evolved to
`new designs which utilized new materials and manufac
`turing processes. For instance, pulp cable, which is
`55
`Susceptible to lightning damage in aerial installations,
`had been largely replaced for such applications by air
`core plastic insulated conductor (PIC) cable. As an
`other example, pulp cable's susceptibility to failure by
`water entry in buried installations caused it to be sup
`60
`planted by waterproof cable. Waterproof cable was
`originally made with solid plastic insulated conductors
`and the spaces between pairs filled with petroleum jelly.
`Now, waterproof cable is also made with dual expanded
`plastic insulated conductor (DEPIC) cable filled with
`petroleum jelly.
`These replacement cables are all designed primarily
`for voice frequency transmission and accordingly, re
`
`4,262,164
`2
`tain the 83 nF/mile standard mutual capacitance. Each
`replacement cable is also available in 19-, 22-, 24-, or
`26-gauge conductor sizes, the same gauges as are stan
`dard for pulp cable. So long as the conductor material
`and gauge are duplicated and the mutual capacitance is
`83 nF/mile, the voice frequency transmission of the
`pulp cable is duplicated. Hence the load coil spacings
`for the replacement cables are still normally 6000 feet
`and utilize the standard voice frequency electronics,
`But to achieve the same voice frequency characteris
`tics, the dielectric layers of the conductors in the re
`placement cables differ in dimension so that the three
`replacement cables have different transmission perfor
`mances, i.e. different transmission loss at the T1 carrier
`frequency. For instance, for the 22-gauge air core PIC
`cable, the resultant T1 carrier repeater spacing is ap
`proximately 7.0 kft; for the filled (waterproof) PIC
`cable, it is 8.0 kft; and, for the filled DEPIC cable, it is
`7.3 kft. From this it can be seen that the coincident load
`coil and repeater spacings conceived for the original
`22-gauge pulp cable has been lost. The result often has
`been that the telephone companies space T1 carrier
`repeaters, even on these improved cables, at 6000 feet to
`be coincident with the load coils.
`Disclosed in U.S. Pat. No. 4,058,669, issued to Nutt et
`al and assigned to the assignee of the present applica
`tion, is an optimized T1 carrier and voice frequency
`cable. This cable has a coincident repeater and load coil
`spacing of 6000 ft (6300 ft maximum) and utilizes the
`newly available materials and processes. This cable is
`intended for metropolitan area trunks ranging in length
`from 2 to 20 miles with the cable usually installed in
`ducts and frequently on routes in which T1 repeater
`manholes are already built at spacings of 6000 ft. The
`design of this cable called for new voice frequency
`electronics, as well as new T1 carrier electronics. The
`new T1 carrier electronics has the same gain as the T1
`repeater equipment designed for the 22-gauge pulp
`cable at the T1 design frequency.
`More background information is given in applicants'
`article, "Multipair Cables for Digital Transmission,”
`National Telecommunications Conference Proceedings,
`Dec. 3-6, 1978. This article, to the extent relevant to
`this application, is hereby incorporated by reference.
`One object of the present invention is to design for
`transmission between cities a more efficient family of air
`core and waterproof cables with conductors having
`improved performance characteristics for both voice
`frequency and carrier frequency transmission. Another
`object is that such cables are compatible with the exist
`ing voice frequency electronics for 83 nP/mile cables
`and the existing carrier frequency electronics used for
`the cable disclosed in U.S. Pat. No. 4,058,669. Still an
`other object is that such cables are cost efficient from
`both the carrier and voice frequency standpoints. Also,
`a still further object is that such cables use less copper as
`well as expanded insulation which is economical and
`efficient.
`SUMMARY OF THE INVENTION
`A cable design which uses insulated conductors of a
`specific nominal wire size and expanded insulation of a
`specific range of thicknesses and expansion, has been
`developed which forms the basic building unit of either
`a waterproof or an air core cable. Both the air core and
`waterproof cable versions using this design are not only
`compatible with existing voice frequency and T1 car
`
`50
`
`65
`
`

`

`15
`
`4,262,164
`3
`rier electronics, the repeater spacing for T1 carrier
`transmission and the load coil spacing for voice fre
`quency coincides for both cable versions though the
`coincident spacing is different for the two versions.
`Making the voice and T1 carrier spacings coincident
`advantageously allows for smooth conversion from
`voice to carrier service on any cable pair.
`To achieve all the above, the inventive cable com
`prises insulated conductors having the following char
`10
`acteristics. In one embodiment, the insulated conduc
`tors are each designed with a nominal 24-gauge copper
`wire having an insulative dielectric layer which is ex
`panded in the range from 30 percent to 50 percent and
`has an outside diameter from 46 to 52 mils.
`In a second embodiment, the insulated conductors are
`each designed also with a nominal 24-gauge copper
`wire but has an insulative dielectric layer comprising an
`expanded inner coat and a solid outer coat of polyolefin
`(DEPIC). In this second embodiment, the insulated
`20
`conductors each have a diameter over dielectric (DOD)
`from approximately 46 to 52 mils, and an expansion of
`the expanded inner coat from approximately 35 to 55
`percent. The second embodiment is desirable because
`the DEPIC insulation has very desirable manufacturing
`25
`and field performance characteristics.
`Performance efficiencies are achieved. Now the sam
`sites can be used for housing both load coils and T1
`carrier repeaters as done with 22-gauge wood pulp
`30
`cable. Also, the cables are compatible with existing.
`electronics. Even better though, the cables can be either
`waterproof or air core. Hence, a single manufacturing
`setup for insulating conductors, twisting pairs, and as
`sembling the cable core can be efficiently used to manu
`35
`facture both waterproof and air core cables.
`Finally, the cables developed in accordance with this
`invention are cost efficient. They use 38 percent less
`copper than the state of the art cables. They are cost
`efficient in diameter, i.e., designed for more pairs per
`cable for any given cross section. This reduces installa
`tion costs, increases reel lengths, and decreases trans
`portation costs affected by the size of the cable. Also,
`less electronics is needed over a span for both voice and
`carrier transmission since the repeater and load coil
`45
`spacings are improved overall. In one embodiment, the
`cable has an 8 kft spacing for the waterproof cable
`version and 8.7 kft spacing for the air core cable ver
`sion.
`50
`The invention, its objectives, features, and advan
`tages will be readily apparent from a reading of the
`description to follow of illustrative embodiments.
`BRIEF DESCRIPTION OF THE DRAWING
`55
`FIG. 1 is a transverse cross-sectional view of an insu
`lated conductor having an expanded insulative dielec
`tric layer;
`FIG. 2 is a transverse cross-sectional view of an alter
`nate insulated conductor having an insulative dielectric
`layer comprising an expanded inner coat and a solid
`outer coat or skin;
`FIG. 3 illustrates a transverse schematic diagram of a
`multipair cable made with the conductors in FIG. 1 or
`2; and
`65
`FIG. 4 is a graph illustrating the characteristics of the
`FIG. 2 conductors used for a waterproof multipair
`cable made in accordance with this invention.
`
`4.
`DETAILED DESCRIPTION
`FIGS. 1 and 2 depict in cross section the structural
`configuration of insulated conductors 10 and 11 respec
`tively, which can be used in applicants' inventive cable
`design. In FIG. 1, insulated conductor 10 comprises a
`copper wire 12 and a single insulative dielectric layer 14
`of polyolefin expanded with an inert gas. In FIG. 2,
`insulated conductor 11 comprises a copper wire 13
`having an insulative dielectric layer 15. The dielectric
`layer 15 includes an inner coat 17 of polyolefin ex
`panded with an inert gas, and an outer coat or skin 19 of
`solid polyolefin. A solid skin 19 is advantageous because
`it makes possible improved control of the inner coat 17
`during manufacture. The solid skin 19 is also useful as a
`good mechanical layer for resisting crushing of the
`inner coat 17 and it can easily be color coded.
`FIG. 3 depicts how a typical telecommunication
`multipair cable 50 can be constructed by grouping a
`plurality of the conductors 10 or 11. First, the insulated
`conductors 10 or 11 are twisted into pairs. Next, the
`twisted pairs of insulated conductors 10 or 11 arranged
`in units 40 of 12 pairs, 13 pairs, 25 pairs, 50 pairs, 75
`pairs, or 100 pairs according to some known twisting
`scheme, say for example, the twist frequency scheme
`disclosed in U.S. Pat. No. 4,058,669.
`Then the cable units 40 are assembled in a cable core
`52 which includes a transverse screen 54 separating the
`units 40 into two groups 56 and 58, so that two way
`transmission can occur in the cable 50. The interstices in
`the core 52 can be left empty if an air core version of the
`cable is desired or else filled with a waterproofing mate
`rial such as petroleum jelly if a waterproof version of
`the cable is desired. In FIG. 3, the illustrative cable 50
`has a cable sheath 60 comprising an aluminum inner
`jacket 62, a steel jacket 64, and an outer jacket 66 of
`polyethylene.
`The FIG. 4 graph shows with region 20 a most pre
`ferred range of insulated conductor characteristics
`which the conductors 10 and 11 can have to construct a
`waterproof telecommunications multipair cable, such as
`cable 50, to realize the invention's advantages. In this
`graph, the region 20 is bounded by an upper line 30, a
`vertical line 26, lower line 31, and vertical line 32. The
`two lines 30 and 31 represent diameters outside the
`dielectric layer (DOD) of the conductors, which are 46
`mils and 52 mils respectively. The vertical lines 26 and
`32 define substantially a range for copper wire diame
`ters which are nominally 24-gauge and are approxi
`mately 21 and 19.5 mils respectively.
`The information in the FIG. 4 graph is shown specifi
`cally for waterproof cables filled with petroleum jelly,
`and on the assumption that the FIG. 2 conductors 11 are
`used. The conductors 11 are assumed to have a dielec
`tric layer 15 consisting of an inner coat 17 of 50 percent
`expanded plastic or polyolefin and a 2 mill outer skin 19.
`The graph has an abscissa for a range of copper wire
`gauges and an ordinate for the mutual capacitance of
`conductor pairs in waterproof cable.
`While the optimization has been performed for the
`waterproof cable design used in buried installation,
`simply omitting the filling compound provides an air
`core cable also essentially optimized.
`Also, while the graph is based on the FIG. 2 conduc
`tor 11, in the range of conductor characteristics being
`analyzed, a conductor 10 having a 45 percent expanded
`dielectric layer 14 is equivalent to the conductor 11
`
`

`

`mill outer skin. 19.
`
`-
`
`-
`
`-
`
`-
`
`-
`
`5
`
`10
`
`5
`
`Gauge
`22
`23
`24
`25
`26
`
`Capacitance
`83
`74
`66
`58
`50
`
`4,262,164
`5
`6
`having the 50 percent expanded inner coat 17 and the 2
`originally used 22-gauge 83 nF/mile pulp cable had a
`T1 carrier design loss of 5.1 dB/kft. Point 25, in close
`An explanation of the other information on the FIG.
`proximity to a 5.0 dB/kft T1 carrier loss line 24, desig
`4 graph will help in understanding the significance of
`nates the 83 nP/mile conductor 11 that can be used to
`the optimum region 20. On this graph, point 22 repre
`build a waterproof cable which affords a 6 kft T1 re
`sents the 83 nP/mile 22-gauge conductor 11 used to
`peater spacing. The point 25 represents a conductor 11
`construct the waterproof DEPIC cable that has a T1
`of approximately 23.6 gauge.
`carrier loss of 4.4 dB/kft and a 7.3 kft spacing between
`From the above, it is apparent that reducing the mu
`repeaters. Line 27 represents a locus of waterproof
`tual capacitance can increase the spacing needed for the
`DEPIC cables all having T1 carrier loss of 4.4 dB/kft.
`voice frequency equipment. However, it is also desired
`Line 21 represents a locus of conductors 11 having the
`that the spacing can increase at the same rate for T1
`minimum diameter outside the dielectric layer (DOD)
`carrier repeaters. Line 26 has been found to represent a
`for any given T1 carrier loss. Line 23 represents a locus
`locus of conductor designs that will have coincident
`of cable designs, which when using the conductor char
`repeaters and load coils. It advantageously is a substan
`acteristics shown, have a minimum cost for any given
`tially straight vertical line which falls approximately on
`T1 carrier loss.
`the 23.6 wire gauge. On this line 26, T1 carrier loss has
`For instance, the combinations of copper wire gauge
`been found to decrease in proportion to the decrease in
`and mutual capacitance giving the 4.4 dB/kft loss of
`capacitance so that the T1 repeater spacing can increase
`22-gauge 83 nP/mile cable are:
`at the same rate as the load coil spacing.
`Line 28 represents a locus of conductor characteris
`tics having 4.0 dB/kft T1 loss, the lowest loss of the
`prior art cables it is desired to replace, i.e. the water
`proof 22-gauge PIC cable. The intersection of lines 26
`and 28 is within the desired optimum region 33 for a
`conductor 11 but an even wire gauge is preferred. To
`obtain an even wire gauge and to move nearer to the
`center of the optimum diameter and cable cost region
`33, locus 28 was followed to the nominal design point
`29, i.e. 24-gauge 60 nP/conductor, which is substan
`tially in the center of the optimum region 20.
`An actual waterproof version of a multipair cable
`similar to cable 50 has been made pursuant to the con
`ductor characteristics in the region 20 as given in FIG.
`4. Also, an air core version utilizing the same insulated
`conductors has been made. Both the air core and water
`proof cables use a plurality of twisted pairs of dual
`expanded plastic-insulated conductors 11, where each
`conductor has a copper wire 13 with a nominal 24
`gauge, an inner expanded coat 17 of polyolefin ex
`panded from 35 to 55 percent, and an outer solid skin 19
`of solid polyolefin of approximately 1.5 to 2.5 mils. The
`diameter over the dielectric layer 15 is nominally 49
`mils.
`The air core cable version has a nominal mutual ca
`pacitance of 52 nF/mile and a T1 loss of 3.6 dB/kft. The
`waterproof cable version has a mutual capacitance
`which is nominally at 60 nP/mile and has a T1 carrier
`loss just under 4 dB/kft. These values for both cables
`afford coincident load coil and repeater spacings. The
`air core version of the cable made has an 8.7kft repeater
`and load coil spacing, while the waterproof version of
`the cable made has an 8 kft repeater and load coil spac
`1ng.
`A telecommunication multipair cable in this inven
`tion can be constructed in other known ways than illus
`trated in FIG. 3. For some other arrangements, see U.S.
`Pat. No. 4,058,669.
`The spirit of the invention is embraced in the scope of
`the claims to follow.
`We claim:
`1. A telecommunications multipair cable (50) com
`prising one or more units (40) each comprising a plural
`ity of insulated conductors (10) arranged in twisted
`pairs, each conductor comprising a copper wire (12)
`having an insulative dielectric layer (14) of polyolefin
`expanded with an inert gas, characterized in that:
`
`Of these, the 24-gauge 66 nP/mile conductor design is
`nearest the minimum diameter locus 21 and therefore
`has the smallest diameter outside the dielectric layer,
`which would permit a maximum number of pairs in a
`given size cable and would have the lowest field instal
`lation costs. The 26-gauge 50 nP/mile design is near the
`minimum cost locus 23 and therefore has the lowest
`manufacturing cost, primarily because it has the least
`copper which currently contributes significantly to
`cable cost. The region 33 falling between the minimum
`diameter locus and the minimum cable cost locus thus
`represents one optimization which is attractive in de
`signing a waterproof cable, as well as an air core cable,
`for T1 carrier.
`Another optimization relates particularly to this in
`vention, i.e., having T1 carrier repeaters coincident
`with load coils in such a way that standard voice fre
`quency electronic equipment can be used. The most
`45
`widely used voice frequency equipment is that designed
`for 88 mHload coils spaced at 6000-foot (H) increments
`on the 83 nF/mile cable. This is commonly referred to
`as, say, 24H88 for 24-gauge loaded cable.
`The cable and voice frequency equipment will be
`50
`compatible, if the impedance and bandwidth are ade
`quately matched. This will essentially be accomplished
`if the inductance and capacitance of a section of the T1
`carrier cable can be made to match those of a section of
`a standard cable. The inductance of a loaded cable sec
`55
`tion is the inductance of the load coil and the mutual
`inductance for a pair of conductors.
`Since the inductance of a pair of conductors in a cable
`is a little less than one mH/mile, the inductance of a
`loaded cable section is nearly independent of length and
`is about 89 mH. Thus, the problem simplifies to just
`keeping the capacitance per section length constant. As
`the capacitance per mile decreases, the spacing between
`load coils is increased proportionately. For example, if
`the mutual capacitance is reduced by a factor of 2, the
`length of a cable section should be doubled.
`An equivalent insulated conductor. 11 on the FIG. 4
`graph must first be found. As mentioned earlier, the
`
`20
`
`25
`
`30
`
`35
`
`65
`
`

`

`4,262,164
`8.
`7
`each copper wire has a diameter in a range from
`thereover, a second coat (19) of solid polyolefin, with
`approximately 19.5 mils to 21 mills;
`the first coat constituting the major fraction of the
`the dielectric layer has an outside diameter in a range
`thickness of the dielectric layer, characterized in that:
`from approximately 46 mils to 52 mils; and
`each copper wire has a diameter in a range from
`wherein the dielectric layer is expanded by an 5
`approximately 19.5 to 21 mils;
`.
`amount in a range from 30 percent to 50 percent.
`the dielectric layer has an outside diameter in a range
`2. A telecommunications multipair cable (50) com-
`from approximately 46 to 52 mils;
`prising one or more units (40) each comprising a plural-
`wherein the first coat is expanded by an amount in a
`ity of insulated conductors (11) arranged in twisted
`range from 35 percent to 55 percent; and
`pairs, each conductor comprising a copper wire (13) 10
`wherein the second coat has a thickness of 1.0 to 2.5
`having an insulative dielectric layer (15) comprising a
`mils.
`first polyolefin coat (17) expanded with an inert gas, and
`k
`k
`k
`k
`k
`
`-
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`