GB2374721A

GB2374721A - Coaxial cable

Info

Publication number: GB2374721A
Application number: GB8612064A
Authority: GB
Inventors: Lyndon Reginald Spicer
Original assignee: STC PLC; Northern Telecom Europe Ltd; Nortel Ltd
Current assignee: STC PLC; Nortel Networks Optical Components Ltd; Nortel Ltd
Priority date: 1986-05-17
Filing date: 1986-05-17
Publication date: 2002-10-23
Anticipated expiration: 2006-05-17
Also published as: GB8612064D0; GB2374721B

Abstract

A coaxial cable intended for use where light weight, good strength, and good electrical properties are important has filamentary members (3) of insulating material forming part of the insulation between its inner (1) and its outer (2) conductors. This material is preferably high-strength orientated monofilaments of methyl pentene, since this has good electrical properties, high strength, and light weight.

Description

COAXIAL CABLE The present invention relates to electrical cables in which light weight, good electrical properties and high strength are important although not limited to coaxial cables, it will be described in its application to such cables.

Where dynamic strain cables are used in marine applications a major aim in their design and manufacture is to achieve minimum diameter for minimum hydro-dynamic drag, maximum strength within the diameter constraint, and optimisation of the electrical properties. In some instances, cable buoyancy is significant.

One known approach to the solution of these problems is to use cables in which the strain. members conduct electricity. The strain members used were of copper-clad steel wire applied contra-helically over an interleaving dielectric, so that they acted both as electrical conductors and strain members.

Present buoyant wire aerial cables for deployment from submarines consist of a coaxial cable centre surrounded by Kevlar (Registered Trade Mark) strain members and extruded buoyancy layers. This severely limits the size and performance of the coaxial cable because each part of the cable only performs one function. Again such a cable's attenuation is such as to necessitate the use of an in-line amplifier, and causes an aerial system using such a cable to be unsatisfactory at some of the higher frequencies of intent.

An object of the invention is to provide cable in which the above disadvantages are minimise.

According to the present invention, there is provided an electrical cable in which the insulation for the conductors includes members of a light-weight insulating material which is relatively strong so as to act also as strength members for the cable.

Since the main application currently considered for such cables is coaxial cables, the present invention also provides an electrical coaxial cable in which the insulation between the central conductor and the outer conductor includes filamentary members of an electrically insulating material which is relatively strong so that they also act as strength members for the cable.

An embodiment of the invention will now be described with reference to the accompanying drawing, which is a cross-section of a coaxial cable embodying the invention.

In the drawing, the inner coaxial conductor 1 is a hollow cylinder of a highly conductive material such as copper, and the outer conductor 2 is a larger hollow cylinder of a highly conductive material such as copper.

Between the two conductors we have a combined strength member and dielectric 3, which consists of a number of filaments of a high-strength insulating material. These filaments are overlaid by an inner jacket indicated at 4, which is also of an electrically insulating material.

The cable also has a final jacket 4 of a tough insulating material. As can be seen, the cable shown has an outside diameter of 16. 5mm.

In one example of cable which embodies the invention, the filaments forming the strength member and dielectric 3 are high-strength orientated methyl pentene monofilaments. These monofilaments perform three functions, dielectric members, strength members, and, in view of their light weight, buoyancy members. Note that a conventional cable in which buoyancy members are added

outside the outer conductor may have an outside diameter which is twice that of the cable shown, or even greater.

An analysis of the cable and its performance shows that the attenuation of a cable such as shown in the drawing is an order of magnitude better than the conventional cable referred to above. Thus at 100 MHz, its attenuation is 25 dB per cable length as compared with 100 dB. The cable shown is also stronger than the conventional coaxial cable ; thus assuming a tensile strength of orientated methyl pentene monofilaments of at least 100, 000 p. s. i. , the cable breaking load is of the order of 5 tons, as compared with 3000 pounds for the conventional cable.

Methyl pentene is the currently preferred material for the filaments because of its electrical and other properties. It has a dielectric constant of 2.12 and a very low power factor, equivalent to or better than that of polythene. In addition its specific gravity is low, e. g. 0.83 as compared with 0.925 for polythene.

Although the currently preferred material for the monofilaments is methyl pentene, other plastics monofilaments can be used, such as orientated polythene.

In some instances, e. g. self-supporting overhead transmission lines, tethered aerostats operating at, for instance, 16000ft, in line-towed array coaxial cables, or land-based coaxial cables subject to tensile loads, buoyancy need not be taken into account, so heavier material can be used.

Claims

CLAIMS: 1. An electrical cable in which the insulation for the conductors includes members of a light-weight insulating material which is relatively strong so as to act also as strength members for the cable.
2. An electrical coaxial cable in which the insulation between the central conductor and the outer conductor includes filamentary members of an electrically insulating material which is relatively strong so that they also act as strength members for the cable.
3. A coaxial cable, substantially as described with reference to the accompanying dr0 : ng.

3. A cable as claimed in claim 2, in which there is an inner jacket of an electrical insulating material between the filamentary members and the outer conductor.

4. A cable as claimed in claim 2 or 3, in which the filamentary members are high-strength orientated monofilaments of methyl pentene.

5. A cable as claimed in claim 2 or 3, in which the filamentary members are high-strength orientated monofilaments of polythene.

6. An electrical coaxial cable in which the insulation between the central conductor and the outer conductor consists of, or includes, monofilaments of methyl pentene, which monofilaments also act as strength members for the coaxial cable.

7. A cable as claimed in claim 6, in which there is an inner jacket of an electrically insulating material between the filamentary members and the outer conductor.

8. A coaxial cable, substantially as described with reference to the accompanying drawing.

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Amendments to the claims have been filed as follows 1. An electrical coaxial cable in which the insulation between a central conductor and an outer conductor consists of, or includes, monofilaments of methyl pentene, which monofilaments also act as strength members for the coaxial cable and are relatively light in weight.

2. A cable as claimed in claim 1, in which there is an inner jacket of an electrically insulating material between the monofilaments and the outer conductor.