US2623093A - Electrical communication cable - Google Patents

Description

Dec. 23, 1952 E. w. SMITH 2,623,093

ELECTRICAL COMMUNICATION CABLE I Filed May 5, 1949 souo POLYETHYLENE. LAYER-6 CONDUCTOR INSULATION\7 (/y cououcfoflsg IOBSTEEL AMOURING TAP:

POLYETHYLENE TAPE; {g on,

jl UXILIARY TWIN CORE 615m :zsquencv can con:

' comuc-nye TAPE IENTRAL cououc-roa INVEN OR Patented Dec. 23 1952 England,- assignor to Canada -Wire and Cable Company Limited, Leaside; Ontario; Canada, a

s..c.umqr tion 1- ;.rnliae ion Maxfii wie aeri 9 .55

tr 1n Great-BritaingMay: 2311948 -ill -zlgflfi) .1 =1lThisinvention:relatesato communication$85215 and is concerned more sparticularly with multixxcore-cablesl capable *of, :car-rying a:- large flnu bv 1:01"::telephone; :circuits :or; .a smaller number 10f broadcast or television circuitsandincorporating- 318,150 auxiliary pairs; or "quads? for-supervisin attended-.repeaters.

.Thexinventionghas for its object to provide a multiecore-gcablezof: th s til-1 .8 whichawillab ihigh ;:efficient ,electrically-b utwhich. will be relatively cheapto manufacture and install, lightin weight -.:and";1mafiected; by mo,isture; sowthat it? can "be plaid in waterlo edeor damp;- locations.

- In the past, cablesof-this type have-been made up :of .two :or more ;-tubu;lar gcoaxial cores' of, airsnacedeconstruction withanQuter:conductorlw .sisting; of a :plurality ;of long-lay copper tapes,

q-preterably interlocking or a single longitudinal.

tape bent to form a cylinder with a; longitudinal butt-joint, ,and'these coaxialcores have been laid up with a number (e. g. twelve) of ordinary paper insulated telephone nuadsz-fonservicing the repeater'. stations th r omnosite ,cable. ins finally. lead sheathed overall to provide-"security against ingress of moisture. It will be apparent that such constructions are "extremely heavy and that ingressofymoisture, due ionexample to mechanical damage ,ofytheleadsheath-wouldquicklylead; to the waterlogging of the entire -system and; interi ruption of;.transmission.

",flhe-inventionbroadly stated r-resides iii-employing injtheicable, insulating; terials which-ere :both, extremely goodwdielectrics; and also substantially impervious to, water, thushenabling the use of a lead sheath to be'eliminate'd'and economizing in bothweight and cost.

' According to the presentiinvention thes-cores in the communication cable comprise a central con- 1 ductor, anintermediate layer-of: solidinsulation -*material,*-an outer conductor consisting-"of-aconductive tape applied-longitudinally over the solid insulation with its edges overlapping and secured in position by a conductive tape applied helically over thelongitudinal tape and an outer thermoplastic sheath applied over said outer tape, said solid insulation layer consisting of polyethylene or a material having substantially similar dielectric characteristics and resistance to water penetration.

In accordance with one feature of the present invention a coaxial core for use in a communication cable of the type referred to consists of a central conductor separated by a solid thermoplastic water-resistant dielectric from an outer v conductor composed of a single. conductive tape .--:anplie.d lensitudinallyhwiths a bs an i re nandbou dzin;position b a sho tv ay co u eritapew applied w t ve pp n e rwth .whol bein cov red y a app 0f w r-r ,rsistant nQ -.meta1 :tap

In accordance with another feature of the irryentiona multi-core communication cable of the type referred :to comprises a number (preferably t:w0 ;or our) of eoaxial cores aslset out above laid upwith aplurality of-twisted twin or quad cables r-providiyngwrepeater supervisory and control cir- .cuits,;the conductors of such twins or quads beineinsulated-wltha solid thermoplastic and -water,resistant dielectric, and the whole being ziilledlcircular and served with jute or other contventionalmaterial, lightly armoured with steel tape ;and-;finally covered with compounded fabric tapes or jute yarn.

:E eier bl c t 11 35 q a t of sin le .s and conductorsinsulated with dielectric ma- .,-terial ,;col oured as required -for identification, ,"twistedtogether and filled circular with a simislar. dielectric. and. advanta ou .z e e I s y --:th e tsu h. pairs. rgqua s. a e- 11p t th -r.-s .iaszto 011m. azcpn enic t a s m i lay timthe-i rstices. b twee 1 he c0 x lw fIfh iadectriema er li m o d th oue out s n preferably/polyethyleneor a mixture thereof. with yothenmaterials such,as-polyisobutylene, but the {301;8S50f'517h6 signal pairs may in some cases be insulatedwwith, va lower grade of water-resistant dielectric, :such as polyvinyl chloride or similar compounds.

* The invention is illustrated in the-accompany- 35. =ing drawing which is aperspective. sectional view --wot-.wacommunication cable having four -co-axial scores: laid up; with-twin cables.

--..Referring tothe drawing; the cable comprises .v four co-axial type cable coreseach indicated generally rat C-laid up with. twin cables indicated at -T,c-of-whichl=there are-fiver one being (central and the remainder spaced in the recesses between adjacent cores C.

Each core C comprises a central conductor l enclosed in a solid layer 2 of insulation consisting of a thermoplastic water-resistant dielectric. Applied to the insulation layer 2 is a single conductive tape 3, which is wrapped longitudinally about the core so formed, with its edges overlapping and held in position by a metal tape 4, the latter being wound over the conductor 3 with a short lay and applied with overlapping edges. The whole is then finally covered with insulation tape 5. The dielectric used in the composition or the insulation layer 2 and of the tape preferably consists of polyethylene. In the embodiment shown each twin cable T consists of two cores 6, 6, of plain copper wire covered with a laper of insulation 1 also preferably of polyethylene and united in an outer covering of insulation 8 also of polyethylene. The fOlll cores C and five twin cables T are laid up in the positions shown and enclosed in a jute bedding 9 over which are wound steel armouring tapes Ill, the whole being finally enclosed in an outer jute serving l I.

An example of a two core cable in accordance with the invention comprises two'coaxial cores each of which consists of a single conductor, e. g. 0.096" plain copper wire, insulated with polyethylene to a diameter of 0.350". The coaxial return conductor is a single copper tape, ap

proximately 1.3" x 0010". applied longitudinally with an overlap of approximately 50%, and may be crimped. transversely at intervals to enhance its flexibility. This return conductor is bound down by means of a single copper tape applied with a short lay and a overlap followed by a polyethylene tape likewise applied with a short lay and a 20% overlap, the overall size of each co-axial core being approximately 0.407".

The signal pairs for supervising and controlling the repeaters in a two core cable are made up of two cores each comprising a small plain copper wire, 0.028 in diameter, covered with a solid insulation of polyethylene (coloured as required) to 0.068". Two such cores are twisted together and then filled circular and belted with polyethylene to a diameter of 0.152. Three such pairs are then laid up together with a lay opposite to that of the individual pairs to give a six-core assembly having an overall diameter of approximately 0.32.

Laid up with the two coaxial cores, with their outer surfaces in contact, are two groups of three signal pairs and jute wormings to produce a circular form. This assembly is then served with cutched jute yarn and armoured with two steel tapes applied helically with a 50% gap and breaking joint so as to provide a closed armour layer. The cable is finished off by applying two compounded Hessian tapes to give some degree of protection to the steel tapes. The overall diameterof the finished cable is of the order 1.33".

Each of the two coaxial cores constructed as described has a high frequency impedance of approximately 52 ohms and an attenuation at 1.05 mc/sec. of approximately 4 db/km. Assuming, therefore, an attenuation limit of 40 db, the repeater spacing will be approximately 10 km. and since the estimated near-end cross talk is better than 85 db at 60 kc./sec. a pair of such coaxials will provide 240 telephone circuits. Each telephone channel occupies a frequency band of 4 kc./sec. and the channels are packed closely together in the frequency spectrum, but each 4 super-group of 60 circuits is separated by a small gap. The 240 circuits are assemblied in four super-groups covering the frequency range 60 to 1052 kc./sec. with the "go channels in one coaxial and the "return channels in the other.

Obviously, by reducing the repeater spacing it is possible to accommodate a greater number of telephone circuits. For example, with a repeater spacing of 6.5 km. ten supergroups can be accommodated, giving 600 circuits per pair of coaxial cores in the frequency range 60 to 2540 kc./sec., at which higher frequency the attenuation is approximately 6 db/km.

It will be understood that the signal pairs are employed only for supervisory and control purposes in connection with the repeaters, which may be at unattended stations and be fed with power via the inner conductors of the coaxials.

I claim:

A multi-core high frequency land communication cable, comprising in combination a plurality of high frequency co-axial cores, each co-axial core comprising a central conductor, a solid layer of polyethylene enclosing the conductor, an outer conductor comprising a first conductive tape applied longitudinally over'the polyethylen layer with an overlap along its edges and a second conductive tape wrapped with a short lay over the first conductivetape, and a layer of electrical insulation comprising a polyethylene tape applied helically over the second conductive tape; a plurality of auxiliary cores laid up in the interstices between the co-axial cores, each of the auxiliary cores comprising a conductor and a solid layer of polyethylene enclosing the conductor; an insulating bedding in which the cores are embedded; a protective armouring tape over the bedding; and an insulating serving enclosing the armouring tape.

ESMOND WASSELL SMITH.

REFERENCES CITED I The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Nov. 13, 1945

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