EP0643399B1 - High frequency transmission cable - Google Patents

Description

The present invention relates to a cable high frequency transmission, of the type comprising individually insulated and assembled electrical conductors in several beams often protected by shielding, and comprising an overall protective outer sheath.

Such cables are used in particular in the IT domain for high frequency transmission of data, which can be of the order of 100 MHz. They are often of flat exterior shape. The bundles of insulated conductors can be pairs, thirds or fourths. They can also be assembled in at least a set. Conductors isolated from bundles of the same together are then advantageously assembled with steps different for the constitution of the different bundles of this set. The shield then surrounds each set of bundles.

In such a cable, the maintenance and shielding of each set can be made by an insulating tape, by example in polyester, the outside of which is metallic. This ribbon is laid lengthwise or helically covering of its edges, around the whole of bundles. Optionally combined with a set of bundles with different assembly steps, there reduces the crosstalk between beams and reach a limit value of around -35 dB at 100 MHz, but not less.

In such a cable, the proximity of the shielding and insulated conductors which it surrounds also leads to linear capacitance and a linear weakening of the cable which are relatively high.

Document Wo-A-86/05311 describes a flat cable computer in which isolated conductors individually are assembled in pairs protected by a individual shielding screen, these insulated conductors being all positioned in the same plane. In this cable, two insulated conductors positioned side by side are assembled in a pair by a first insulating coating extruded around of these two insulated conductors and thus embedded in it. Each pair is protected by a metallic tape of shielding surrounding it. Protected pairs positioned side by side side by side are assembled by a second insulating coating extruded around them, forming the outer sheath of overall cable protection.

Advantageously two opposite grooves are made on the first coating between the two conductors of the pair concerned and on the second coating between the different pairs thus assembled, for ease of stripping necessary for access to conductors and setting up place of a terminal connector on the different pairs or the cable. For these same reasons, the first coating is made of polyvinyl chloride, non-adherent on the insulation of the conductors made of polyethylene or propylene.

The realization of such a cable is relatively long and is very delicate. It has a significant number extrusion operations. In particular, it requires the outcome of the first assembly coating of the two conductors of each pair and after the second coating of assembling pairs, obtaining positions strict relative values, which are defined initially for desired electrical characteristics of the cable, between different conductors.

The stripping operations are themselves long. The choice of the first PVC coating on PE or PP conductor insulation leads to performance dielectrics less than those obtainable in making it out of PE or PP or one of their copolymers, but making it adhere very strongly to insulated conductors then made very difficult to strip.

In addition, the arrangement in the same plan of the conductors limit the possible assemblies of conductors, which are assembled only in pairs, in this cable.

Document US-A-4,755,629 describes an electric cable high frequency transmission. In particular, this cable has two pairs of insulated electrical conductors individually, a dielectric rod for joining the two pairs while separating them from each other, a screen of shielding around the rod and a protective sheath outside. This ring is of cross section in the shape of an eight to define two cavities for the two pairs and one spacer between these pairs and has two opposite slots opening along the cavities. These slots allow insertion of the pairs in the cavities and facilitate access to each pair for mounting a connector cable terminal. However, they can lead to deformations of the cavities and then displacements of the pair conductors in place, despite the presence of shield covering the periphery of the rod.

The object of the present invention is to produce a cable high frequency avoiding the drawbacks of realizations known above and allowing to reach levels of crosstalk on the order of -40 to -50 dB at 100 MHz.

Its purpose is a high transmission cable frequency, with insulated electrical conductors individually and assembled into several bundles themselves assembled in at least one set, a rod dielectric for assembling the bundles of each set and an overall protective outer sheath, said rod dielectric having contiguous tubular portions defining on the one hand longitudinal cavities independent, assigned to the bundles of the same assembly, each section adapted to that of one of the bundles of this set and each provided with a slot on the periphery of the rod for the placement of the beam in the cavity, and on the other hand at least one zone common to the tubular portions and said spacer between the bundles in place in the cavities, characterized in that it comprises a closed holding element of each of said slots of different cavities containing the beams, for a continuity of dielectric material around the beams place in said cavities and a conservation of the geometry of said beams in place.

• l'écarteur est sensiblement plan sur les parties périphériques correspondantes du jonc.
• ledit jonc est de section droite sensiblement elliptique et comporte deux cavités opposées l'une à l'autre et centrées sur le grand axe de la section elliptique, dont les fentes respectives sont terminales sur ledit grand axe,
• chaque écarteur présente une épaisseur minimale d'au moins 0,2 mm et de préférence de 0,3 à 0,5 mm.
• lesdites fentes sont étroites et ont une largeur inférieure à quelques dixièmes de millimètres et de préférence de l'ordre de quelques centièmes de millimètres.
• le câble comporte plusieurs joncs d'assemblage des faisceaux en autant d'ensembles, disposés et maintenus côte à côte dans ladite gaine extérieure.

This cable can advantageously also have at least one of the following additional characteristics:

• the spacer is substantially flat on the corresponding peripheral parts of the rod.
• said rod is of substantially elliptical cross section and comprises two cavities opposite one another and centered on the major axis of the elliptical section, the respective slots of which are terminal on said major axis,
• each spacer has a minimum thickness of at least 0.2 mm and preferably from 0.3 to 0.5 mm.
• said slots are narrow and have a width less than a few tenths of a millimeter and preferably of the order of a few hundredths of a millimeter.
• the cable comprises several rods for assembling the bundles into as many sets, arranged and held side by side in said outer sheath.

The features and advantages of this invention will emerge from the detailed description of a exemplary embodiment illustrated in the attached drawings.

In this drawing, the single figure is a sectional view a high frequency transmission cable, according to the invention.

This cable is flat and has two quads 1. Each quart is made up of a twist of four solid conductors 2, in particular copper, each coated with insulation 3 in PE or PP preferably.

These two quartes are housed in a dielectric rod 5, ensuring the assembly of the two quarters, their maintenance and their separation. The dielectric rod 5 has for this purpose two cavities 6 in length receiving these two quarters.

Each of these cavities is of circular section, adapted to that of quartets 1. It is opened by a narrow slot 7 on the periphery of the rod, initially or at the installation of the fourth. This slot is wide very weak, a few tenths of a millimeter or more advantageously of the order of a few hundredths of millimeter only, for later closing.

This dielectric rod 5 is an extruded profile, produced preferably polyethylene or polypropylene. He's from substantially elliptical section, for a flat shape desired cable, with its two cavities and their slots centered on the major axis of its section. He plays the role spacer for maintaining and separating the two quarters. Her central area between the two cavities is thick minimum of at least 0.2mm and is preferably of the order of 0.3mm for 1.3mm diameter insulated conductors about.

The cable further comprises a shielding screen 8, in the form of a ribbon laid lengthwise and overlapping its edges around the dielectric rod and the two fourths as well assembled, and a screen continuity wire 9, interposed between the screen and the dielectric rod. This screen can be metallic or be dielectric and then metallized and in particularly aluminized. It ensures the closed maintenance of slots in the various cavities of the rod it surrounds.

The overlap one on the other of the edges of the screen away from the opening slots of the cavities. In this example, it is made on one of the large faces of the rod dielectric. The same applies to the laying of the screen continuity which in this example is substantially centered on the other large face of the profile.

This set of two quarters thus protected is covered with an outer sheath 10 of overall protection. This sheath ensures a tight hold of the screen around the rod whose cavities are thus closed. It is extruded directly on the screen as soon as it is installed. She can be made of PE, PP or preferably PVC or other material cladding classic.

The realization of this cable is quick and simple. She is done on a manufacturing line not shown, comprising means for scrolling the rod, two sets spacers fitting into the slots in the rod cavities for their opening by elastic deformation, means of guidance and insertion of the two quartes into the cavities open rod, means for guiding the continuity wire screen against the rod, guiding and setting means place shielding tape around the rod and a die extrusion end of the outer protective sheath.

In a variant not illustrated, the rod may have a section other than that substantially elliptical, being without sharp peripheral edge. It can also include more than two longitudinal cavities, each of section adapted to the section of the beam to be mounted, the beams assembled in the rod which can be quads and / or third parties and / or pairs. The slots of the different cavities can be relatively large. They are then closed by a dielectric gasket attached and retained in each of them or by an external dielectric tape surrounding the rod or by the dielectric layer shielding screen of preferably reinforced thickness.

This dielectric rod cable for holding and separation of the bundles from each set can also be without shielding screen.

Alternatively also, the cable may include several rods surrounded or not by their individual screen of shielding and retained side by side in an outer sheath extruded around them.

• le niveau de diaphonie obtenu, qui est de l'ordre de à - 40 à -50 dB à 100 MHz, avec ou sans l'écran de blindage,
• la protection de la géométrie des faisceaux assemblés dans le jonc, en particulier lors de flexions du câble, et l'amélioration résultante de la régularité d'impédance,
• l'éloignement de l'écran par rapport aux conducteurs et son maintien fermé en long,
• la facilité d'accès aux conducteurs à travers les fentes du jonc rainuré, dès l'ouverture de la gaine extérieure de protection sur laquelle peuvent être également prévues des rainures facilitant son ouverture.

Among the advantages of the cable according to the invention, there are in particular:

• the level of crosstalk obtained, which is of the order of at - 40 to -50 dB at 100 MHz, with or without the shielding screen,
• the protection of the geometry of the bundles assembled in the rod, in particular during flexion of the cable, and the resulting improvement in the regularity of impedance,
• the distance of the screen from the conductors and keeping it closed lengthwise,
• the ease of access to the conductors through the slots of the grooved rod, from the opening of the external protective sheath on which grooves can also be provided to facilitate its opening.

Claims (8)

1. A high frequency transmission cable comprising individually insulated electric conductors (2) assembled together in a plurality of bundles (1) that are themselves assembled together in at least one unit, a dielectric rod (5) for assembling together the bundles in each unit, and an overall protective outer sheath (10), said dielectric rod including joined tubular portions defining firstly independent longitudinal cavities (6) assigned to the bundles of the same unit, each of section adapted to the section of the corresponding one of the bundles and each provided with a slot (7) on the periphery of the rod for installing the bundle in the cavity, and secondly at least one "spacer" zone common to the tubular portions between the bundles installed in the cavities, the cable being characterized in that it includes an element (8) for keeping closed said slots of the various cavities containing the bundles, for continuity of dielectric material around the bundles installed in said cavities and to conserve the shape of said installed bundles.
2. A cable according to claim 1, characterized in that each spacer is substantially plane over the corresponding peripheral portions of said rod.
3. A cable according to claim 1 or 2, characterized in that said rod is of substantially elliptical right cross-section and includes two cavities (6) opposite one another and centered on the major axis of the right cross-section of said rod, with the respective slots thereof being located at the ends of said major axis.
4. A cable according to any one of claims 1 to 3, characterized in that between the bundles held in their cavities, each spacer has a minimum thickness of not less than 0.2 mm, and preferably lying in the range 0.3 mm to 0.5 mm.
5. A cable according to any one of claims 1 to 4, characterized in that said slots have a width that is less than a few tenths of a millimeter, and that is preferably of the order of a few hundredths of a millimeter.
6. A cable according to any one of claims 1 to 5, characterized in that said element (8) for keeping each of the slots of the various cavities containing said bundles closed is a screen surrounding each rod and having margins which overlap mutually and which are offset from the slots.
7. A cable according to any one of claims 1 to 6, characterized in that the bundles of each unit are constituted by two to four twisted-together conductors that are thus held directly in the various cavities.
8. A cable according to any one of claims 1 to 7, characterized in that it includes a plurality of rods for assembling together bundles into a corresponding number of units, said rods being disposed and held side by side inside said outer sheath (10).

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