EP1215688A1 - High frequency telecom cable with groups of wire-conductors - Google Patents

Abstract

The cable is of the type comprising groups of insulated conducting wires (1 to 4) distributed in cross section around a central rod (7a) extending longitudinally. In order to maintain the groups of wires, such as pairs, at fixed relative positions and to avoid the need for an extruded internal retaining sheath, the rod comprises cells (81a-84a) each containing a group of insulated wires and opening towards the exterior, and each cell has an opening (91a-94a) with a width less than the diameter of the section of the groups of insulated wires. The opening of each cell allows the passage of an insulated wire while preventing the escape of the group that the cell contains. In addition, the crosstalk couplings between groups of wires are reduced thanks to a transverse distribution of the groups at the vertices of a rhombus, the two groups having the longest twisting pitches being positioned at the ends of the large diagonal of the rhombus. <IMAGE>

Description

The present invention relates to a cable telecommunications for high frequency signals, especially telephone and / or data processing.

More specifically, the invention relates to a cable of telecommunications comprising several groups of insulated conductors, for example four groups G1, G2, G3 and G4, as shown in Figure 1. The groups are usually symmetrical pairs of conductive wires twisted with respective pitches different p1, p2, p3 and p4 and assembled in a helix with another predetermined step. In such a case, the pairs of wires G1 to G4 are held together by an external envelope E, while being free relative to each other in envelope E. Du made of the non-cylindrical geometry of the pairs and in addition under the influence of mechanical stress exerted on the cable, for example during the pairing operation or when subsequent handling of the cable, the pairs overlap each other so that their initial mutual positioning shown in figure 1 is not kept.

Figures 2A, 2B and 2C show three examples modification of the relative positioning of the four pairs of insulated conductors.

Thus, in the "ideal" configuration shown in FIG. 1, the axes of the pairs G1 to G4 are located at the vertices of a square in a section of the cable. The average distance between two adjacent pairs, such as the pairs G1 and G2, is d _adj = 2 d, and the average distance between two opposite pairs, such as the pairs G2 and G4, is d _opp = 2 2 d, d denoting the diameter of an insulated conductor. According to FIGS. 2A, 2B, 2C, the distances _adj and _opp can be locally much smaller and can be close to the diameter d of an insulated conductor.

où
N(d) est le niveau moyen d'affaiblissement paradiaphonique exprimé en dB entre deux paires ayant des pas différents et séparées par une distance moyenne d exprimée en mm,
N(d₀) est le niveau moyen d'affaiblissement paradiaphonique exprimé en dB entre deux paires ayant des pas identiques et séparées par une distance moyenne d₀ exprimée en mm, et
A(d₀) est une constante positive dépendant de d₀.The crosstalk coupling between two pairs is very dependent on the distance of _adj , d _opp between two pairs: the more the pairs are distant the weakest the crosstalk coupling. The following empirical formula translates this dependence of the crosstalk coupling with respect to the distance between two pairs:

or
N (d) is the average level of near-end crosstalk expressed in dB between two pairs having different pitches and separated by an average distance d expressed in mm,
N (d ₀ ) is the average level of near-end crosstalk expressed in dB between two pairs having identical steps and separated by an average distance d ₀ expressed in mm, and
A (d ₀ ) is a positive constant depending on d ₀ .

In order to mitigate the influence of crosstalk and thus increase the performance of high frequency twisted pair cables, we have proposed to maintain the positions of pairs G1 to G4 all along the cable in accordance with Figure 1, while increasing the average distance between pairs. Thus, according to the European patent application EP 0 763 831, a cable with four pairs G1, G2, G3 and G4 includes a central rod JC with cross section in Greek cross, that is to say with four fins of identical length and two to two adjacent perpendicular, as shown in figure 3. The radial fins separate the pairs G1 to G4 the each other. The ring is for example made by extrusion of an insulating coating covering two metallic ribbons in a cross shape to form a shielding between pairs.

For a known arrangement of four pairs G1, G2, G3 and G4 shown in Figure 1 or 4, we always have d _adj <d _opp = d ₁₃ = d ₂₄ .

In the cable shown in Figure 3, the assembly of the four pairs G1 to G4 is surrounded by an EC screen and a GP protective sheath that seals and cable protection. The EC screen is a ribbon metallic, or a plastic tape covered with a metallic layer. The EC screen is ribboned in a helix around the JC rush and the G1 to G4 pairs.

The JC central ring only preserves the spacing minimum between pairs of wires. Pairs in place are only maintained by the EC ribbon screen placed around the assembly of the pairs. The structure of this cable does not prevent geometric defects caused by poor positioning of the pairs when assembling the pairs or by mechanical stresses during handling cable, for example when cable installation.

As shown schematically by way of example at Figure 4, the pair G3 is very eccentric by compared to its correct position against the central rod JC, and the pairs G1 and G2 are significantly offset to the top. These geometric defects in the relative positioning of the pairs degrade the properties of cable transmission, causing asymmetries and peaks of weakening of reflection.

In addition, the EC peripheral screen matches substantially the square profile of the assembly of pairs and doesn't create a circular arch like shown schematically in Figure 5. The position of the screen in relation to the different pairs is then poorly controlled, which can similarly degrade transmission of high frequency signals in the cable.

To overcome these positioning faults relative pairs and tend towards the ideal structure with a perfectly cylindrical screen around of the four pairs, the set of pairs G1 to G4 with the JC ring is surrounded by a thin retaining sheath GM which is extruded in the form of a cylindrical tube and which is surrounded by the EC screen which is based on the GM sheath, as shown in Figure 3. Maintaining pairs and the positioning of the screen is then provided by the GM extruded support sheath.

However, the GM retaining sheath requires a additional extrusion operation, which increases the cost of the cable.

The GM sheath also requires preparation specific cable for connecting ends of the cable pairs at the ends of at least another pair of cables by connectors. To access the pairs to be connected by connectors, the end of the GM retaining sheath must be opened and cleared, either by means of a tearing line, either by means of a tool edged. The connector assembly time is thus increased.

The present invention aims to provide a cable for telecommunications comprising four groups of wires insulated conductors, overcoming disadvantages cited above relating to crosstalk couplings between the groups of insulated wires and the retaining sheath internal, while maintaining a relative positioning ideal for groups, such as wire pairs insulated conductors in the cable.

To this end, a telecommunication cable to high frequency with four wire groups insulated conductors distributed in cross section around a central rod extending longitudinally, is characterized in that the cable has a substantially cross section elliptical, and the central rod positions in section transverse four groups of wires substantially at vertices of a rhombus, and the two groups located at ends of the small diagonal of the rhombus have no twist smaller than those of the two groups located at the ends of the long diagonal of the diamond.

In the cable of the invention, the two groups having the longest twist pitches are like this positioned at the ends of the long diagonal of the diamond so as to considerably reduce the crosstalk which is predominant in the cables according to the prior art, which increases cable performance. In practice, the rod central has a substantially I-shaped cross section whose wings separate the groups of wires.

Wire groups such as wire pairs insulated conductors, can be more precisely held at the tops of the rhombus in four cells formed in the rod in cross section and substantially centered at the vertices of the rhombus. These sockets each contain a group of isolated wires and each have an opening leading to outside and having a width less than diameter of the section of the groups of isolated wires.

Thanks to the width of the cell openings less than the diameter of the group section, each group cannot escape naturally from their alveolus, while offering the possibility of passing a part of only one group thread at a time across the opening. The central rod according to the invention makes as a means of separating and spreading wire groups but also means for keep groups together without requiring additional extrusion of a holding sheath.

Alternatively, the width of the cell openings may be even smaller and less than diameter of the insulated wires, which increases the protection and maintenance of groups of wires. The material of the rod is then preferably flexible, allowing some flexibility in terms of openings.

According to a first variant, the opening of less one cell is between wings hoses of two peripheral segments of the rod.

According to a second variant, the opening of minus one cell is between the end of a peripheral flexible lever hinged at the end of a substantially radial branch of the rod forming a side of the socket and the end of another branch of the rod forming another side of the cell.

• la figure 1 déjà commentée est une section d'un câble de télécommunication à quatre paires de fils conducteurs isolés selon une configuration idéale de la technique antérieure traditionnelle ;
• les figures 2A, 2B et 2C déjà commentées montrent respectivement en section transversale des modifications du positionnement relatif des quatre paires du câble de la figure 1 ;
• la figure 3 déjà commentée montre schématiquement une section d'un câble à quatre paires positionnées aux sommets d'un carré grâce à un jonc en croix à quatre ailettes identiques selon la demande de brevet EP 0 763 831 ;
• les figures 4 et 5 montrent un défaut de positionnement de paires dans des sections de câble avec jonc en croix, respectivement sans et avec un écran métallique ; et
• les figures 6 à 9 sont des sections transversales de câbles avec quatre groupes disposés aux sommets d'un losange selon plusieurs réalisations de l'invention.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which:

• FIG. 1, already commented on, is a section of a telecommunication cable with four pairs of insulated conductor wires according to an ideal configuration of the traditional prior art;
• FIGS. 2A, 2B and 2C already commented on respectively show in cross section modifications of the relative positioning of the four pairs of the cable of FIG. 1;
• FIG. 3 already commented on schematically shows a section of a cable with four pairs positioned at the vertices of a square by means of a cross rod with four identical fins according to patent application EP 0 763 831;
• Figures 4 and 5 show a faulty positioning of pairs in sections of cable with cross rod, respectively without and with a metal screen; and
• Figures 6 to 9 are cross sections of cables with four groups arranged at the vertices of a rhombus according to several embodiments of the invention.

Referring to Figure 6, a cable high frequency telecommunications Ca according to the invention has a structure with axial symmetry and includes four groups of wires electric insulated individually 1, 2, 3 and 4. Each insulated electrical conductor consists conventionally by a solid conductor or a strand of fine metal wires 5 and an insulating sheath individual 6 surrounding conductor 5, and has a diameter d.

In figure 6 as in the figures following 7, 8 and 9, each group includes only two insulated conductors and thus constitutes a symmetrical pair of electrical conductors isolated which are twisted together with a pitch of respective twist. However, each group can include more than two insulated conductors, for example three or four wires to make up a third or fourth.

The Ca cable has a central rod 7a in which are arranged in cross section four circular cells 81a, 82a, 83a and 84a in the form of C, constituting longitudinal grooves for contain groups of wires 1, 2, 3 respectively and 4 and almost wrap them. The diameter of alveoli is substantially equal to the diameter 2d of the group section. The alveoli are arranged in the rod so as to center the four groups of wires 1, 2, 3 and 4 substantially at the vertices S1a, S2a, S3a and S4a of a rhombus.

The cable has an axial symmetry passing through the center of the diamond. So groups 1 and 3 are arranged at the ends of the small diagonal of the rhombus and therefore symmetrical with respect to the center of the diamond, and groups 2 and 4 are substantially arranged at the ends of the long diagonal of the rhombus and therefore symmetrical with respect to the center of the diamond. The Ca cable then has a cross section substantially elliptical.

To further limit the crosstalk between the groups of wires arranged symmetrically, groups 1 and 3 contained in the cells 81a and 83a located at the ends S1a and S3a of the small diagonal of the rhombus and thus the closest have short twisting steps p1 and p3 different from each other and smaller than the long twisting steps p2 and p4 different from each other of the two groups 2 and 4 contained in the cells 92a and 94a situated at the ends S2a and S4a of the long diagonal of the rhombus and thus the most distant. One of the following sets of inequalities relating to the torsion steps pi to p4 of groups 1 to 4 is satisfied:
p1 <p3 <p2 <p4, or
p1 <p3 <p4 <p2, or
p3 <p1 <p2 <p4, or
p3 <p1 <p4 <p2.

The rhombus preferably guarantees the inequalities D _C <D ₁₃ <D ₂₄ of the distance between two adjacent groups with respect to the length D _C of one side of the rhombus, that is to say the distance D ₁₃ between the two close opposite groups 1 and 3 on the small diagonal is shorter than the distance D ₂₄ of the two distant opposite groups 2 and 4 on the large diagonal. This ensures a much weaker crosstalk coupling between the groups of wires 2 and 4 having the longest twisting steps, while maintaining a relatively large distance D _C between adjacent groups.

According to the invention, each cell 81a to 84a has a radial opening 91a to 94a located at the periphery of the rod 7a and opening outwards. The width ℓ of the opening is less than diameter 2d of the section of a group of wires for that the group contained in the cell cannot escape from the socket. Furthermore, according to this first embodiment, the opening width ℓ is greater than the diameter d of an insulated wire 5-6 in order to ability to easily pull end or part a group thread contained in the cell, by example when preparing a connection for this wire with a wire from another cable.

The small axis of the rod 7a is thus greater than 4d.

Wire groups 1 to 4 are perfectly held at the bottom of the cells 81a to 84a. The elliptical periphery of the rod 7a allows a screen (See figure 7) metallic, or plastic coated with a metallic layer, to rest on the without altering the relative positioning of the groups of sons who are not in contact with the screen thanks to the small width of the openings 91a at 94a.

The groups of wires are thus stabilized at fixed positions in the cable only by the very slightly open cells, and so by the section transverse of the central rod 7a substantially crosswise recirculated, which improves the performance of cable transmission, especially when mechanical handling of the cable.

According to a second embodiment shown in Figure 7, the cable Cb has a rod 7b which has a cross section with four straight branches substantially identical radial 71b to 74b, forming cell sides and terminated by segments elliptical devices 75b to 78b forming double gallows. The rod 7b thus has substantially a cross-section in potent cross. The alveoli 81b to 84b of the rod 7b are equally distributed to the vertices of a central rhombus but have a section appreciably lozenge whose side is substantially greater than the diameter 2d of the group section. At the top of the section of each cell 81b to 84b, located at the end of the diagonal substantially radial of it, an opening 91b is made to 94b between the ends of two segments elliptical neighbors of the rod 7b. The two branches and the wings of two segments framing a cell are substantially tangent to the elliptical section enveloping group of sons contained in the cell.

The width ℓ of the openings 91b to 94b is still less than 2d, and may be less than diameter d of insulated wires 5-6. Indeed, the wings peripheral segments 75b to 78b are flexible and have their connections with the respective branches 71b to 74b substantially thinned to form flexible hinges. The wings of two segments neighbors limiting an alveolus bend toward the exterior thanks to the flexible hinges to release one end or part of a group wire contained in the socket.

In the cable Cb shown in Figure 7 are represented a metallic screen or in part metallic ECb which surrounds the rod 7b and rests on the elliptical peripheral segments 75b to 78b of the rod 7b, as well as a cylindrical protective sheath extruded GPb. The screen and protective sheath assembly can also be provided for others cable embodiments of the invention illustrated in Figures 6 to 9.

According to the third embodiment of cable Cc shown in figure 8, instead of saving cell openings 91b to 94b centered between two branches of the rod 7b, the opening 91c to 94c of a cell 81c to 84c in the rod 7c of the cable Cc is provided between the free end of a flexible lever device in respective elliptical segment 75c to 78c articulated by flexible hinge at the end of a respective branch 71c to 74c of the rod 7c forming a side of the socket, and the hinged end of the respective next adjacent branch 72c, 73c, 74c, 71c forming the other side of the cell. The first one respective abovementioned branch 71c to 74c, the second respective branch 72c, 73c, 74c, 71c and the lever 75c to 78c substantially tangent to the section wraparound elliptical of the respective thread group 1 to 4 substantially form the sides and the arc elliptical of a 90 ° sector constituting the section transverse of a respective cell 81c to 84c of rod 7c.

The levers 75c to 78c being longer than the wings of segments 75b to 78b, the travel of levers around the flexible hinged ends of the branches 71c to 74c is larger and therefore the width of the openings 91c to 94c can be much smaller than that of openings 91b to 94b, and significantly smaller than the diameter d of the wires isolated 5-6. This further improves protection and maintenance of groups of wires in the rod.

In the Cd cable according to a fourth realization, shown in figure 9, the rod 7d has still a substantially I-shaped cross section able to position the four groups of wires 1, 2, 3 and 4 at vertices S1d, S2d, S3d and S4d of diamond. The branches 71d to 74d of the rod 7d to ends of the I separate the groups of wires. The branches 72d-73d, 74d-71d of the I-section of the rod 5d form ves to support respectively the two groups of wires 2 and 4 with long pitch positioned at the ends S2d and S4d of the long diagonal of the diamond. The other two groups of wires 1 and 3 with steps short positioned at the ends S1d and S3d of the small diagonal of the rhombus are located between the branches, against the core of the I-shaped section of the rod 7d. The pairs of branches 72d-73d and 74d-71d of the 5d rod substantially constitute symmetrical ves and open to the outside with respect to the cable axis Cd, the sides of the vee being able to be appreciably circular or elliptical. The soul of the 5d rod enters the vee can be rectangular hollow or full.

In the embodiment illustrated in FIG. 9, the cells 91d and 93d containing the groups of wires 1 and 3 with short steps are substantially hexagonal and have openings 91d and 93d parallel to the core of the 5d rod and located at the ends of the small axis of the elliptical section of the rod. The two others cells 82d and 84d containing the groups of wires 2 and 4 with long steps are substantially pentagonal and have openings 92d and 94d located in front the ends of the core of the 5d rod and at the ends of the major axis of the elliptical section of the rod. The openings 91d to 94d are thus each included between ends of substantially bent segments or ellipticals 75d to 78d with flexible wings, of analogous to cable Cb (Figure 7).

In order to improve the maintenance of all four groups of wires 1 to 4, the rod 7a, 7b, 7c, 7d is helical around its longitudinal axis. The alveoli are thus cross sections of grooves extending parallel and helically around the axis of the rod.

The helical shape of the rod can come directly from its manufacture, for example by extrusion.

According to another embodiment, the shape helical grooves result from a twist of the rod around its axis during an operation helix assembly of groups. The material of the rod is then preferably flexible enough to withstand a twist when assembling with wire groups and deformable enough to flex the segment wings 75b to 78b, 75d to 78d or levers 75c to 78c peripherals of the rod to insert or remove insulated wires 5-6.

The central rod 7a, 7b, 7c, 7d is preferably made of flexible dielectric material, for example manufactured by extrusion, such as polyethylene, polypropylene, polyvinyl chloride, or elastomer. According to one another variant, the rod is made of a material flexible semiconductor polymer.

To further reduce crosstalk couplings between the groups of conducting wires, the rod 7a, 7b, 7c, 7d is made of a flexible dielectric material covered with a conductive surface layer electrically, such as a layer of varnish, graphite or metal.

According to another embodiment, the central rod 7a, 7b, 7c, 7d has a frame of metallic material covered with an electrically insulating layer forming a surface coating of the reinforcement.

Claims (11)

High frequency telecommunication cable comprising four groups of insulated conductor wires (1 to 4) distributed in cross section around a central rod (7a) extending longitudinally, characterized in that the cable has a substantially elliptical cross section, and the central rod (7a) positions in cross section the four groups of wires substantially at the vertices (S1a-S4a) of a rhombus, and the two groups (1, 3) located at the ends (S1a, S3a) of the small diagonal of the diamonds have smaller twisting pitches than those of the two groups (2, 4) located at the ends (S2a, S4a) of the long diagonal of the rhombus. Cable according to claim 1, in which the central rod (7a) comprises in section transverse four cells (81a-84a) centered substantially at the vertices (S1a-S4a) of the rhombus, each contain a group of single wires and have each an opening (91a-94a) opening towards outside and having a width less than diameter of the section of the groups of isolated wires. Cable according to claim 2, in which the width of the cell openings (91c-94c) is less than the diameter of the insulated wires (5-6). Cable according to claim 2 or 3, wherein the opening of at least one cell (91b-94b ; 91d-94d) is between flexible wings two peripheral segments (75b-78b; 75d-78d) of the rod (7b; 7d). Cable according to claim 2 or 3, wherein the opening (91c-94c) of at least one cell (81c-84c) is between the end of a peripheral flexible lever (75c-75c) articulated to the end of a substantially radial branch (71c-74c) rod (7c) forming one side of the cell and the end of another branch of the rod forming a other side of the socket. Cable conforms to any of Claims 2 to 5, in which the cells (81a-84a) are cross sections of grooves extending helically Cable according to claim 6, in which the helical shape of the grooves results torsion of the rod (7a) during an operation helical assembly of groups of wires (1-4). Cable conforms to any of Claims 1 to 7, in which the rod (7d) has a cross section substantially in I whose pairs of branches (72d-73d, 74d-71d) form ves to support the two groups of wires (2, 4) with long twisted pitch positioned at ends of the long diagonal of the rhombus. Cable conforms to any of claims 1 to 8, wherein the rod is in flexible dielectric material. Cable conforms to any of claims 1 to 8, wherein the rod is in flexible semiconductor material. Cable conforms to any of claims 1 to 8, wherein the rod is in flexible dielectric material covered with a layer electrically conductive.

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