US3433890A - Signal transmission cable - Google Patents

Description

United States Patent 3,433,890 SIGNAL TRANSMISSION CABLE Ralph P. Gabriel, Chobham, Surrey, and Rupert I. Kinross, Shepperton, England, assignors to Communications Patents Limited Filed Feb. 7, 1967, Ser. No. 614,450 Claims priority, application Great Britain, Feb. 10, 1966,

5,858/66 US. or. 174-116 Int. Cl. H01b 7/00, 11/02 12 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with electric wave communication cables of the multi-pair type and particularly but not exclusively with such cables which are suitable for establishing a signal-distributing network of a wired broadcasting system which pertains to the distribution of a plurality of different sound and television programmes.

An object of this invention is to provide an improved cable of the type concerned which whilst being reasonably easy to manufacture enables a high degree of immunity from cross-talk or cross-view to be obtained.

Accordingly, the invention provides an electric wave communication cable comprising a group of pairs of twisted together insulated conductors characterised in that at least one of the interstitial spaces present within the circumscribing cylinder of at least one such pair is occupied solely by an electrically non-conducting nonmetallic member with the object of preventing displacement of said one pair with respect to an adjacent pair.

The said member, that is to say the displacementpreventing member, is preferably in filamentary form and extends alongside the twisted together pair of conductors with which it is associated for the entire length of this pair. For example, this displacement-preventing member can be constituted by a string or thread of polyethelene or other suitable electrically insulating material.

In preferred embodiments of the invention a plurality of pairs of twisted together insulated conductors are arranged in a compact symmertical group about a centre core element and both of the interstitial spaces present within the circumscribing cylinder of each such pair is occupied by a displacement-preventing member.

For some applications it is satisfactory if only alternate pairs of a group of pairs of twisted together conductors are provided with such displacement-preventing member.

Whilst in general it will be found convenient for the displacement-preventing member to have a circular crosssectional shape, it is realised that occasions might arise where the member should have a cross-sectional shape other than circular, for example to ensure that a greater part of its surface coincides with the circumscribing cylinder of the pair with which it is associated.

In order that the invention can be understood more readily it will now be described, by way of example only, with reference to the accompanying drawing the single 3,433,890- Patented Mar. 18, 1969 figure of which is a cross-sectional view of an electric wave communication cable in accordance with one preferred embodiment of the invention.

In the cable shown in the drawing six pairs, 2, 3, 4, 5, 6, 7, of twisted together insulated conductors, each pair being twisted according to a different pitch, are arranged as a compact symmetrical group around a centre core element. The latter in this case comprises three pairs, 8, 9, and 10 of twisted together insulated conductors, each pair being twisted according to a different pitch and the three pairs arranged as a twisted together (spiralled) group. Each of the three pairs 8, 9, and 10 have electrical characteristics which render them suitable for the transmission of audio frequency signals and each of the pairs 2, 3, 4, 5, 6 and 7 are suitable for the transmission of high frequency signals (say up to 15 mc./s.) The circumscribing cylinder of each of the high frequency pairs 2, 3, 4, 5, 6 and 7 has the same diameter as that of the circumscribing cylinder of the group of audio pairs 8, 9 and 10 in order to obtain the desired compact symmetrical arrangement in which the circumscribing cylinder of each of the pairs 2, 3, 4, 5, 6, and 7 is in contact with the circumscribing cylinder of an adjacent pair. In one example of such a cable the audio pairs 8, 9 and 10 comprise conductors of 0.020" diameter plain copper (6 /2 lb./rnile wire) each sheathed with an 0.0065 radial thickness of polyethelene and the conductors of the high frequency pairs are 20 S.W.G. plain copper each sheathed with a radial thickness of polyethelene such that the twisted pair has a characteristic impedance of approximately ohms.

In accordance with the invention each of the interstices of each of the six high frequency pairs is provided with a displacement-preventing member which is in the form of a string or thread of solid dielectric material such as polyethelene. These strings are indicated in the drawing at 11. Preferably these strings 11 have a circular crosssection their diameter being not greater than /a of the diameter of the insulated conductors forming the high frequency pairs so that the strings do not extend beyond the confines of the circumscribing cylinders of these high frequency pairs.

The group of six high frequency pairs with their displacement-preventing members is spiralled about the centre core element and the whole symmetrical assembly is wrapped with a layer 12 of suitable insulating material, such for example as one or more strips of Melinex. This wrapped assembly is enclosed within a polyethelene sheath The strings 11 function to reduce the possibility of deformation or relative displacement of the high frequency pairs during manufacture of the cable and during subsequent use of the cable with the result that the precise symmetrical arrangement of the high frequency pairs is not only more readily attained during manufacture but is better maintained during subsequent handling of the cable, thus ensuring the attainment and maintenance of a high degree of immunity from cross-talk or crossview.

Such a cable may be provided with a conductive screen around the wrapped assembly. Such a screen may be formed in known manner by a helical or longitudinal tape of conductive material, such for example as an aluminium or copper tape, or by a conductive metallic braid, or by a coating of conductive, non-metallic material, such for example as carbon. This screen is located between a layer of polyethelene which surrounds the wrapped assembly and an outer sheath of polyethelene.

If desired, the centre core element about which the group of high frequency pairs is arranged may comprise a single pair of twisted together insulated conductors, the

circumscribing cylinder of this pair having the same diameter as the circumscribing cylinder pertaining to each of the six high frequency pairs.

What we claim is:

1. An electric wave communication cable comprising a plurality of pairs of insulated conductors each twisted together at a pitch different from that of the others, the conductors of each pair forming a pair of interstices therebetween;

an electrically non-conducting non-metallic member extending with one of said pairs of insulated conductors and positioned in one of the pair of interstices of said conductors for preventing displacement of said one of said pairs of conductors relative to adjacent others thereof.

2. An electric wave communication cable as claimed in claim 1, wherein said non-metallic member comprises a filament of polyethylene extending for the length of said pair of conductors.

3. An electric Wave communication cable as claimed in claim 1, further comprising a central core element having a circumscribing cylinder, and wherein six pairs of insulated conductors each have a circumscribing cylinder having a diameter equal to that of said central core element.

4. An electric wave communication cable as claimed in claim 1, wherein each of a pair of electrically nonconducting non-metallic members extending with one of said pairs of insulated conductors is positioned in -a corresponding one of the pair of interstices of said conductors for preventing displacement of said one of said pairs of conductors relative to adjacent others thereof.

5. An electric wave communication cable as claimed in claim 2, wherein said non-metallic member has a circular cross-section having a diameter of not more than two-thirds the diameter of each insulated conductor of said pair of conductors.

6. An electric wave communication cable as claimed in claim 4, wherein each of said non-metallic members comprises a filament of polyethylene extending for the length of said pair of conductors.

7. An electric wave communication cable as claimed in claim 4, further comprising a central core element having a circumscribing cylinder, and wherein six pairs of insulated conductors each having a circumscribing cylinder having a diameter equal to that of said central core element.

8. An electric wave communication cable as claimed in claim 6, wherein said non-metallic member has a circular cross-section having a diameter of not more than two-thirds the diameter of each insulated conductor of said pairs of conductors.

9. An electric wave communication cable as claimed in claim 7, wherein each of a pair of electrically non-conducting non-metallic members extending with each of three alternate pairs of insulated conductors is positioned in a corresponding one of the pairs of interstices of each of said three alternate pairs of conductors for preventing displacement of each of said three pairs of conductors relative to adjacent others thereof.

10. An electric wave communication cable as claimed in claim 7, wherein each of a pair of electrically nonconducting non-metallic members extending with each of the pairs of insulated conductors is positioned in a corresponding one of the pairs of interstices of each of said pairs of conductors for preventing displacement of each of said pairs of conductors relative to adjacent others thereof.

11. An electric wave communication cable as claimed in claim 7, wherein said central core element comprises three pairs of insulated conductors each twisted together.

12. An electric wave communication cable as claimed in claim 10, wherein each of said non-metallic members comprises a filament of polyethylene extending for the length of each of said pairs of conductors.

References Cited UNITED STATES PATENTS 469,522 2/1892 Hayes 174-116 X 796,100 8/1905 Wilson 1741l6 X 2,109,334 2/1938 Kaden 174-116 X 3,102,160 8/1963 Cook 174113 X 3,023,267 2/1962 Rubinstein 174113 X 3,209,064 9/1965 Cutler 174-113 X LEWIS H. MYERS, Primary Examiner.

ELLIOT GOLDBERG, Assistant Examiner.

US. Cl. X.R.

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