EP1215688B1 - High frequency telecom cable with groups of wire-conductors - Google Patents

Description

The present invention relates to a telecommunication cable for high frequency signals, including telephone and / or teleinformatic.

More specifically, the invention relates to a telecommunication cable comprising several groups of insulated conducting wires, for example four groups G1, G2, G3 and G4, as shown in FIG. figure 1 . The groups are generally symmetrical pairs of twisted wires with respective different pitches p1, p2, p3 and p4 and helically assembled with another predetermined pitch. In such a case, the pairs of wires G1 to G4 are held together by an outer envelope E, while being free with respect to each other in the envelope E. Because of the non-cylindrical geometry of the pairs and furthermore under the influence of mechanical stresses exerted on the cable, for example during the assembly operation of the pairs or during subsequent manipulations of the cable, the pairs interlock with one another so that their initial mutual positioning shown in FIG. the figure 1 is not preserved.

The FIGS. 2A, 2B and 2C show three examples of modification of the relative positioning of the four pairs of insulated conducting wires.

d, d dénotant le diamètre d'un conducteur isolé. Selon les figures 2A, 2B, 2C, les distances d_adj et d_opp peuvent être localement beaucoup plus petites et peuvent avoisiner le diamètre d d'un conducteur isolé.Thus, in the "ideal" configuration represented in figure 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 _dd = 2d, and the average distance between two opposite pairs, such as the pairs G2 and G4, is d _opp = 2 $\sqrt{2}$

d, d denoting the diameter of a conductor isolated. According to FIGS. 2A, 2B, 2C the distances of _adj and d _opp may be much smaller locally and may be around the diameter of an isolated 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 smaller the crosstalk coupling. The following empirical formula expresses this dependence of the crosstalk coupling with respect to the distance between two pairs: $$\mathrm{NOT}\left(\mathrm{d}\right)\mathrm{=}\mathrm{NOT}\left({\mathrm{d}}_{\mathrm{0}}\right)\mathrm{+}\mathrm{AT}\left({\mathrm{d}}_{\mathrm{0}}\right)\log \left(\frac{\mathrm{d}}{{\mathrm{d}}_{\mathrm{0}}}\right)$$

or
N (d) is the mean level of paradoxical loss expressed in dB between two pairs having different pitch and separated by a mean distance d expressed in mm,
N (d ₀ ) is the average level of paradoxical loss expressed in dB between two pairs having identical pitch and separated by an average distance d ₀ expressed in mm, and
A (d ₀ ) is a positive constant dependent on d ₀ .

In order to mitigate the influence of crosstalk and thereby increase the performance of twisted pair high frequency cables, it has been proposed to maintain the positions of pairs G1 to G4 all along the cable in accordance with the figure 1 , while increasing the average distance between pairs. So, according to the request of European patent EP 0 763 831 a four-pair cable G1, G2, G3 and G4 comprises a central junction JC of cross-section 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 from each other. The ring is for example made by extrusion of an insulating coating covering two metal strips crosswise so as to form a shield between the pairs.

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

In the cable shown in the figure 3 , all four pairs G1 to G4 is surrounded by an EC screen and a GP protective sheath that provides sealing and protection of the cable. The EC screen is a metal ribbon, or a plastic ribbon covered with a metal layer. The EC screen is helically wrapped around the JC ring and pairs G1 to G4.

The central ring JC preserves only the minimum spacing between the pairs of wires. The pairs in place are only maintained by the EC banded screen placed around the pair assembly. The structure of this cable does not prevent geometrical defects caused by poor positioning of the pairs during the assembly of pairs or by mechanical stress during subsequent handling of the cable, for example during the installation of the cable.

As shown schematically as an example in the figure 4 , the pair G3 is very eccentric with respect to its correct position against the central ring JC, and the pairs G1 and G2 are substantially shifted upwards. These geometric defects in the relative positioning of the pairs degrade the transmission properties of the cable, causing dissymmetries and peaks of weakening of reflection.

In addition, the EC peripheral screen substantially matches the square profile of the pair assembly and does not create a circular arch, as schematically shown in FIG. figure 5 . The position of the screen relative to the different pairs is then poorly controlled, which can similarly degrade the transmission of high frequency signals in the cable.

In order to overcome these relative positioning defects of the pairs and to tend towards the ideal structure comprising a perfectly cylindrical screen around the four pairs, the set of pairs G1 to G4 with the JC ring is surrounded by a thin GM support sheath which is extruded as a cylindrical tube and which is surrounded by the EC shield which leans on the GM sheath, as shown in FIG. figure 3 . The maintenance of the pairs and the positioning of the screen is then ensured by the extruded maintenance sheath GM.

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

The GM sheath also requires a specific preparation of the cable for connecting the ends of the pairs of the cable to the ends of pairs of at least one other cable by connectors. To access the pairs to be connected via the connectors, the end of the GM retaining sheath must be opened and disengaged, either by means of a tear-off wire or by means of a cutting tool. The assembly time of the connectors is thus increased.

The present invention aims at providing a telecommunication cable comprising four groups of insulated conductor wires, overcoming the aforementioned drawbacks relating to the crosstalk couplings between the groups of insulated wires and to the internal holding sheath, while maintaining an ideal relative positioning of the groups, such as pairs of insulated conductor wires, in the cable.

To this end, a high-frequency telecommunication cable comprising four groups of insulated conducting wires distributed in cross section around a central rod extending longitudinally, is characterized in that the cable has a substantially elliptical cross section, and the rod central position in cross-section four groups of son substantially at the vertices of a rhombus, and the two groups located at the ends of the small diagonal of the rhombus have smaller twist steps than those of the two groups located at the ends of the large diagonal of the diamond.

In the cable of the invention, the two groups having the longest twist steps are thus positioned at the ends of the large diagonal of the rhombus so as to considerably reduce the crosstalk coupling which is preponderant in the cables according to the prior art. which increases the performance of the cable. In practice, the central rod has a substantially I-shaped cross section, the wings of which separate the groups of wires.

Groups of yarns such as pairs of insulated conductive yarns can be more accurately held at the apices of the diamond in four cells formed in the rod in cross-section and substantially centered at the vertices of the rhombus. These cells each contain a group of insulated wires and each have an opening opening outwardly and having a width smaller than the diameter of the section of groups of insulated son.

Thanks to the width of the openings of the cells smaller than the diameter of the section of the groups, each group can not escape naturally from its cell, while offering the possibility of passing a part of a single thread of the group at a time through the opening. The central rod according to the invention thus serves as a means for separating and separating the groups of wire, but also means for holding the groups together without requiring additional extrusion of a holding sheath.

Alternatively, the width of the cell apertures can be even smaller and be smaller than the diameter of the insulated wires, which increases the protection and retention of the wire groups. The material of the ring is then preferably flexible, allowing some flexibility at the openings.

According to a first variant, the opening of at least one cell is between flexible wings of two peripheral segments of the rod.

According to a second variant, the opening of at least one cell is between the end of a flexible peripheral lever articulated at the end of a substantially radial branch of the rod forming one side of the cell and the end another branch of the ring 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 features 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 accompanying drawings in which:

• the figure 1 already commented is a section of a telecommunication cable with four pairs of insulated conductor wires in an ideal configuration of the traditional prior art;
• the FIGS. 2A, 2B and 2C already commented respectively show in cross section changes in the relative positioning of the four pairs of the cable of the figure 1 ;
• the figure 3 already commented schematically shows a section of a cable with four pairs positioned at the vertices of a square thanks to a cross rod with four identical fins according to the request of EP 0 763 831 ;
• the Figures 4 and 5 show a pair positioning defect in sections of cable with cross rod, respectively without and with a metal screen; and
• the 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.

With reference to the figure 6 a high-frequency telecommunication cable Ca according to the invention has an axially symmetrical structure and comprises four groups of individually insulated electrical conductor wires 1, 2, 3 and 4. Each insulated electrical conductor wire is conventionally constituted by a solid conductor or a thin wire strand 5 and an individual insulating sheath 6 surrounding the conductor 5, and has a diameter d.

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

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

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

To further limit the crosstalk between groups of son arranged symmetrically, the groups 1 and 3 contained in the cells 81a and 83a located at the ends S1a and S3a of the small diagonal of the diamond and thus the closest have steps of short twists p1 and p3 different from each other and smaller than the long twists p2 and p4 different between them of the two groups 2 and 4 contained in the cells 92a and 94a located at the ends S2a and S4a of the large diagonal of the rhombus and the most distant. One of the following sets of inequalities relative to the pi to pi p4 pitch steps 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 opposite groups close 1 and 3 on the small diagonal is shorter than the distance D ₂₄ of the two opposite groups distant 2 and 4 on the large diagonal. This provides much lower cross-talk coupling between wire groups 2 and 4 with the longest twist 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 smaller than the diameter 2d of the section of a group of son so that the group contained in the cell can not escape from the cell. In addition, according to this first embodiment, the opening width ℓ is greater than the diameter d of an insulated wire 5-6 in order to easily pull the end or a part a thread of the group contained in the cell, for example during the preparation of a connection of this wire with a wire of another cable.

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

Groups of son 1 to 4 are perfectly maintained at the bottom of the cells 81a to 84a. The elliptical periphery of the ring 7a allows a screen (Cf. figure 7 ) metal, or plastic coated with a metal layer, to rest on the ring, without altering the relative positioning of groups of son that are not in contact with the screen due to the small width of the openings 91a to 94a.

The son groups are thus stabilized at fixed positions in the cable only by the very little open cells, and thus by the cross section of the central rod 7a substantially cross recercled, which improves the transmission performance of the cable, especially when mechanical manipulation 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 identical substantially identical rectilinear branches 71b to 74b, forming cell sides and terminated by elliptical peripheral segments 75b to 78b forming double stems. The ring 7b thus has substantially a crossed cross section potencée. The cells 81b to 84b of the ring 7b are equally distributed at the vertices of a central rhombus, but have a substantially lozenge section whose side is substantially greater than the diameter 2d of the section of the groups. At the top of the section of each cell 81b to 84b, located at the end of the substantially radial diagonal thereof, is made an opening 91b to 94b between the ends of two adjacent elliptical segments of the rod 7b. The two branches and the wings of two segments surrounding a cell are substantially tangent to the enveloping elliptical section of the group of wires contained in the cell.

The width ℓ of the openings 91b to 94b is still less than 2d, and may be smaller than the diameter d of the insulated wires 5-6. Indeed, the wings of the 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 neighboring segments limiting a cell bend outwardly through flexible hinges to clear an end or part of a wire group contained in the cell.

In the cable Cb shown in the figure 7 are represented a metal screen or metal part ECb which surrounds the ring 7b and is based on the elliptical peripheral segments 75b to 78b of the ring 7b, and an extruded cylindrical protective sheath GPb. The screen assembly and protective sheath may also be provided for the other cable embodiments of the invention illustrated in FIGS. Figures 6 to 9 .

According to the third embodiment of cable Cc shown in FIG. figure 8 , instead of providing 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 peripheral flexible lever in respective elliptical segment 75c to 78c hingedly hinged at the end of a respective leg 71c to 74c of the rod 7c forming a side of the cell, and the hinged end of the respective next adjacent branch 72c, 73c, 74c, 71c forming the other side of the cell. The aforesaid respective first branch 71c to 74c, the aforesaid respective second branch 72c, 73c, 74c, 71c and the lever 75c to 78c substantially tangent to the surrounding elliptical section of the respective wire group 1 to 4 substantially form the sides and the arc. elliptical of a sector at 90 ° constituting the cross section of a respective cell 81c to 84c of the ring 7c.

The levers 75c to 78c being longer than the wings of the segments 75b to 78b, the movement of the levers around the flexible hinge 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 the openings 91b to 94b, and much smaller than the diameter of the insulated wires 5-6. This further improves the protection and maintenance of the groups of threads in the rush.

In the cable Cd according to a fourth embodiment, shown in FIG. figure 9 , the rod 7d still has a substantially I-shaped cross section for positioning the four groups of son 1, 2, 3 and 4 at the vertices S1d, S2d, S3d and S4d of the diamond. The branches 71d to 74d of the rod 7d at the ends of the I separate the groups of son. The branches 72d-73d, 74d-71d of the I-section of the ring 5d form ves to respectively support the two sets of threads 2 and 4 with long steps positioned at the ends S2d and S4d of the large diagonal diamond. The other two groups of threads 1 and 3 at no short positions at the ends S1d and S3d of the small diagonal of the rhombus are located between the branches, against the soul of the I-section of the ring 7d. The pairs of branches 72d-73d and 74d-71d of the ring 5d substantially constitute vés symmetrical and open outwardly with respect to the cable axis Cd, the sides of the vés can be substantially circular or elliptical. The core of the ring 5d between the vés can be rectangular hollow or full.

In the embodiment illustrated in figure 9 , the cells 91d and 93d containing groups of threads 1 and 3 with short pitch are substantially hexagonal and have openings 91d and 93d parallel to the core of the ring 5d and located at the ends of the minor axis of the elliptical section of the rod. The two other cells 82d and 84d containing the son groups 2 and 4 with long steps are substantially pentagonal and have openings 92d and 94d located in front of the ends of the core of the ring 5d and at the ends of the major axis of the elliptical section of the ring. The openings 91d to 94d are thus each comprised between ends of substantially angular or elliptical segments 75d to 78d with flexible wings, similarly to the cable Cb ( figure 7 ).

To improve the maintenance of all four groups of son 1 to 4, the rod 7a, 7b, 7c, 7d is helical around its longitudinal axis. The cells are thus transverse sections of grooves extending parallel and helically around the axis of the ring.

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

According to another embodiment, the helical shape of the grooves results from a twisting of the ring around its axis during a helical assembly operation groups. The material of the ring is then preferably sufficiently flexible to withstand a torsion during assembly with the son groups and sufficiently deformable to flex if necessary the segment wings 75b to 78b, 75d to 78d or levers 75c to 78c peripherals of the rod for inserting or removing insulated wires 5-6.

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

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

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

Claims (11)

1. A high frequency telecommunications cable comprising four groups of insulated conductor wires (1 to 4) distributed in cross-section around a central core (7a) extending longitudinally, the cable being characterized in that it presents a cross-section that is substantially elliptical, and the central core (7a) positions the four groups of wires in cross-section substantially at the vertices (S1a-S4a) of a lozenge, and the two groups (1, 3) situated at the ends (S1 a-S3a) of the short diagonal of the lozenge are twisted at pitches smaller than the pitches of the two groups (2, 4) situated at the ends (S2aS4a) of the long diagonal of the lozenge.
2. A cable according to claim 1, in which the central core (7a) has four setbacks (81a-84a) in cross-section, the setbacks being centered substantially at the vertices (S1a-S4a) of the lozenge, each containing one group of insulated wires and each having an opening (91a-94a) leading to the outside and of width that is smaller than the diameter of the section of the groups of insulated wires.
3. A cable according to claim 2, in which the width of the setback openings (91 c-94c) is less than the diameter of the insulated wires (5-6).
4. A cable according to claim 2 or claim 3, in which the opening of at least one setback (91b-94b; 91d-94d) lies between flexible fins of two peripheral segments (75b-78b; 75d-78d) of the core (7b; 7d).
5. A cable according to claim 2 or claim 3, in which the opening (91c-94c) of at least one setback (81c-84c) lies between the end of a peripheral flexible lever (75c-78c) hinged to the end of a substantially radial branch (71c-74c) of the core (7c) forming one side of the setback, and the end of the other branch of the core forming another side of the setback.
6. A cable according to any one of claims 2 to 5, in which the setbacks (81a-84a) are the cross-sections of grooves that extend helically.
7. A cable according to claim 6, in which the helical shape of the grooves results from the core (7a) being twisted during an operation of helically assembling the groups of wires (1-4).
8. A cable according to any one of claims 1 to 7, in which the core (7d) presents a substantially I-shaped cross-section in which the pairs of branches (72d-73d, 74d-71d) form V-shapes for supporting respective ones of the two groups of wires (2, 4) having long twisting pitch that are positioned at the ends of the long diagonal of the lozenge.
9. A cable according to any one of claims 1 to 8, in which the core is made of a flexible dielectric material.
10. A cable according to any one of claims 1 to 8, in which the core is made of a flexible semiconductive material.
11. A cable according to any one of claims 1 to 8, in which the core is made of flexible dielectric material covered in an electrically-conductive layer.

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