Web for separating conductors in a communication cable

Abstract

A telecommunications cable and separator spline. In one example the cable includes a cable jacket defining an elongate cable core, a conductor assembly including four twisted pairs of conductors disposed along the core and a plurality of parallel elongate localized and like distensions in an inner surface of the cable jacket. The distensions are substantially evenly spaced about an inner surface of the cable jacket. In one example, the distensions are the result of a series of filler elements placed between the cable jacket and the cable core and which wind helicoidally along and about the cable core. The separator spline includes first and second elongate dividing strips having a substantially H shaped cross section and arranged side by side, and twists helicoidally along its length. In one example the separator spline and the insulation surrounding the twisted pairs of conductors is manufactured form a material having the same dielectric constant.

Description

FIELD OF THE INVENTION

The present invention relates to a web for separating conductors in a communications cable. In particular, the present invention relates to a cross talk reducing separator web, or spline, which ensures predetermined positioning of twisted pairs of conductors relative to one another.

BACKGROUND TO THE INVENTION

One problem which must be surmounted when implementing high speed data communications such as the 10 Gigabit Ethernet is the reduction in cross talk between adjacent cables, typically referred to as Power Sum Alien Near End Cross (PSANEXT) and Power Sum Alien Equal Level Far End Cross Talk (PSAELFEXT). One technique which has been proposed and been shown effective in lower speed networks is the use of separator web or spline running along the length of the cable and positioned between the four (4) twisted pairs of conductors which are used for transferring data along the cable. One drawback of these prior art designs is that when such prior art cables are placed adjacent to one another (as is typically the case in cable runs and conduit and the like), the twisted pairs having the longest twist in a given cable are the same distance from the geometric centre of the cable as the other twisted pairs. As an increase in proximity of twisted pairs of conductors located in adjacent cables and having longer twist lays increases PSANEXT and PSAELFEXT (due to an increased coupling between twisted pairs having longer lays relative to those having shorter lays). In addition, each individual pair exhibits relatively high levels of unbalance known to cause common mode signal noise. This can lead to a degradation in the performance of (and therefore the signals being transmitted by) each of the cables which cannot be compensated for due to the large number of noise signals originating from like pairs of a typically a large number of adjacent cables (up to 6 adjacent cables and 48 disturbing twisted pairs of conductors in a worst case).

SUMMARY OF THE INVENTION

The present invention addresses the above and other drawbacks by providing a telecommunications cable comprising a cable jacket defining an elongate cable core, four twisted pairs of conductors disposed along the core, each of the conductors comprising a conductive core surrounded by an insulation, and a spline separating the four twisted pairs of conductors from one another. The spline and the insulation are fabricated from a material having a matching dielectric constant.

There is also disclosed a telecommunications cable comprising a cable jacket defining an elongate cable core, four twisted pairs of conductors disposed along the core and a plurality of parallel displacing ridges in an outer surface of the cable jacket, the ridges substantially evenly spaced about an outer circumference of the cable jacket and winding helicoidally along the cable about the core.

Furthermore, there is described a telecommunications cable comprising a cable jacket defining an elongate cable core, a conductor assembly comprising four twisted pairs of conductors disposed along the core, and a plurality of parallel elongate localised and like distensions in an inner surface of the cable jacket, the distensions substantially evenly spaced about an inner surface of the cable jacket. The distensions prevent the conductor assembly from coming into contact with the inner surface.

Additionally, there is disclosed a separator spline for use in a telecommunications cable. The spline comprises first and second elongate dividing strips having a substantially H shaped cross section and arranged side by side. The spline twists helicoidally along its length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a raised side view of a telecommunications cable in accordance with an illustrative embodiment of the present invention;

FIG. 2A is a transverse cross section of a telecommunications cable in accordance with an illustrative embodiment of the present invention;

FIG. 2B is a transverse cross section of a telecommunications cable in accordance with an alternative illustrative embodiment of the present invention;

FIG. 2C is a transverse cross section of a telecommunications cable in accordance with a second alternative illustrative embodiment of the present invention;

FIG. 2D is a transverse cross section of a telecommunications cable in accordance with a third alternative illustrative embodiment of the present invention;

FIG. 2E is a detailed view of a transverse cross section of the telecommunications cable of FIG. 2C; and

FIG. 2F is a detailed view of a transverse cross section of a telecommunications cable in accordance with a fourth alternative illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Referring now to FIG. 1, a telecommunications cable, generally referred to using the reference numeral 10, will now be described. The cable 10, is comprised of four (4) twisted pairs of conductors 12 separated by a separator web 14 and encased in a cable jacket 16. In a particular embodiment one or more filler elements as in 18 can be included positioned between the cable jacket 16 and the conductors 12. Additionally, a shielding foil or the like (not shown) may also be included between positioned between cable jacket 16 and the filler elements 18.

Still referring to FIG. 1, as known in the art, the twisted pairs of conductors 12 are typically twisted with different twist lays (i.e. number of twists per unit length). These twist lays can be regular and predetermined or can vary along the length of the cable 10, for example between a maximum and a minimum value. In the latter case, the twist lays can vary either randomly or in accordance with a predetermined pattern (for example steadily increasing or decreasing over a predetermined distance). Of note is that the direction of lay is often reversed at points along a given twisted pair of conductors as in 12 in order to simplify manufacturing.

Still referring to FIG. 1, the separator web 14 separating the twisted pairs of conductors 12 from one another also typically twists helically along a length of the cable 10 such that the individual twisted pairs of conductors as in 12 follow substantially parallel helical paths along the length of the cable. Similar to the twist lay of the individual twisted pairs of conductors as in 12, the lay of the individual twisted pairs of conductors as in 12 (typically referred to as the strand lay) as the travel along the length of the cable 12 can be either constant or can vary between a minimum and maximum stand lay. In the latter case, the rate of variance can be either or random or predetermined (again, for example, a steady increase or decrease between a minimum and maximum stand lay along a length of the cable 10).

Referring now to FIG. 2A, in an illustrative embodiment of the present invention, a separator web 14 comprising two (2) separating parts 20, 22 having an L shaped transverse cross section and touching along a heel 24 thereof is provided. The separating parts having the L shaped transverse cross-section 20, 22 separate the core of the cable 10, as defined by the cable jacket 16 into four quadrants. One of each of the twisted pairs as in 12 rests in each of the quadrants. A second pair of substantially flat, parallel and opposed spacing elements as in 26, 28 are attached along an outer edge as in 30 of each of the separating parts having the L shaped transverse cross-section 20, 22.

In a particular embodiment each of the separating parts having the L shaped transverse cross-section 20, 22 is fabricated together with its spacing element as in 26, 28 thereby forming an “h” shaped web portion. During cable manufacture the two (2) “h” shaped web portions (each comprised of a separating part having an L shaped transverse cross-section 20, 22 and a spacing element as in 26, 28) in parallel and subsequently stranded together with the four (4) twisted pairs of conductors as in 12 to form the core of the cable 20 and in particular the finished separator web 14. In this regard the separating parts having the L shaped transverse cross-section 20, 22 of each “h” shaped web portion touch along a heel thereof (which incidentally coincides with the geometric centre A of the cable 10).

The position of the two (2) “h” shaped web portions can be offset or staggered relative to one another which in turn staggers the positioning of the four (4) twisted pairs of conductors as in 12 relative to one another. In particular, the twisted pairs of conductors as in 12 having the longest twist lays (illustratively twisted pairs 12₁ and 12₃) can be positioned closer to one another and the twisted pairs having the shorter twist lays (illustratively twisted pairs 12₂ and 12₄) can be positioned farther from one another. In this regard, a radius r₁ of a double helix formed by the twisted pairs 12₁ and 12₃ having the longer twist lays is less than a radius r₂ of a double helix formed by the twisted pairs 12₂ and 12₄ having the shorter twist lays. As a result, the twisted pairs 12₁ and 12₃ having the longer twist lays are located closer to the geometric centre (designated by the point A) of the cable 10 than the twisted pairs 12₂ and 12₄ having the shorter twist lays.

Still referring to FIG. 2A, locating the twisted pairs having longer twist lays closer to the centre A of the cable 10 has a number of effects. For example, and now as will be apparent to a person of skill in the art, the twisted pairs having the longer twist lays of adjacent cables will now be farther apart. As discussed above, the coupling between twisted pairs having longer lays is greater than those having shorter lays and therefore an increase in distance between those twisted pairs having longer twist lays in this manners leads to a reduction in PSANEXT and PSAELFEXT. Additionally, the increased distance is filled primarily with dry air which is a better dielectric than plastics, which also leads to a reduction in coupling and a resultant twisted pairs having the longer twist lays. Furthermore, the twisted pairs having shorter lays generally incorporate more conductive material per unit length than twisted pairs having longer twist lays, and therefore a shielding effect arises.

Still referring to FIG. 2A, the “h” shaped web portions of the separator web 14 also serve to prevent the twisted pairs of conductors 12 from touching the inside surface 32 of the cable jacket 16. As known in the art, such cable jackets are typically manufactured from PVC or the like which has relatively high dielectric constant with a resultant increased loss factor. By separating the twisted pairs of conductors 12 from the inside surface 24 of the cable jacket 16 using air space and the separator web 14, the composite dielectric constant and loss factor can be lowered. As a result, less copper conductor and insulation must be used to meet, for example, the attenuation requirements of the Category 6 augmented standard.

Of note is that the individual “h” shaped web portions of the separator web 14, although illustrated as being reverse mirrored images of one another, do not have to be of the same dimension. Indeed, in a particular embodiment the dimensions of each of the “h” shaped web portions can be different in order to achieve a desired positioning of the twisted pairs of conductors 12 relative to one another, relative to the centre A of the cable 10 and relative to the inside surface 24 of the cable jacket 16.

Referring to FIG. 2B, in an alternative illustrative embodiment, the two (2) “h” shaped web portions are co-joined, either during manufacture of the separator web 14 or subsequently using a bonding technique such as a suitable adhesive, welding, etc.

Referring now to FIG. 2C, in a second alternative illustrative embodiment of the cable 10 of the present invention, the separator web 14 is comprised of two (2) “H” shaped web portions 34, 36. Each of said “H” shaped web portions 34, 36 is comprised of a central strip 38, an inner strip 40 attached towards a centre 42 thereof at right angles to an inner edge 44 of said central strip 38 and an outer strip 46 attached towards a centre 48 thereof at right angles to an outer edge 50 of said central strip 38. Similar to the “h” shaped web portions as discussed hereinabove the position of the two (2) “H” shaped web portions 34, 36 can be offset or staggered relative to one another which in turn staggers the positioning of the four (4) twisted pairs of conductors as in 12 relative to one another. In particular, the twisted pairs of conductors as in 12 having the longest twist lays (illustratively twisted pairs 12₂ and 12₄) can be positioned closer to one another and the twisted pairs having the shorter twist lays (illustratively twisted pairs 12₁ and 12₃) can be positioned farther from one another. As a result, the twisted pairs 12₂ and 12₄ having the longer twist lays are located closer to the geometric centre (again designated by the point A) of the cable 10 than the twisted pairs 12₁ and 12₃ having the shorter twist lays.

The H shaped web portions 34, 36 also illustratively include a pair of filler elements as in 52. The filler elements as in 52 are positioned between the inner surface 32 of the cable jacket 16 and the H shaped web portions 34, 36. The filler elements illustratively serve to introduce more air space as in 54 between the inner surface 32 of the jacket 16 and the twisted pairs of conductors as in 12. Additionally, the filler elements as in 52 ensure that the inner surface 32 of the jacket 16 is smooth in those regions where the jacket 16 is proximate to the H shaped web portions 34, 36.

Additionally, and in a particular variant of the second alternative illustrative embodiment, the two (2) “H” shaped web portions 34, 36 are co-joined, either during manufacture of the separator web 14 or subsequently using a bonding technique such as a suitable adhesive, welding, etc.

Referring now to FIG. 2D, in a third alternative illustrative embodiment of the present invention, the separator web 14 comprises a first strip 56 onto a first side of which is attached a second strip 58 and onto a second side of which is attached a third strip 60. The second strip 58 and third strip 60 are attached to the first strip 54 such that the second strip 58 is nearer one end of the first strip 54 than the third strip 60, thereby giving the separator web 14 a staggered X transverse cross section. Additionally, one or more filler elements as in 62 is provided. The filler elements as in 62 can be either individually wound about the twisted pairs of conductors as in 12 and the separator web 14 during manufacture or alternatively can form part of or otherwise be attached to a sheath as in 64 which surrounds the twisted pairs of conductors as in 12 and the separator web 14. The filler elements as in 62 introduce air spaces as in 66 between the twisted pairs of conductors as in 12 and the inner surface 32 of the cable jacket 16.

Referring now to FIG. 2E, in practice when the (typically PVC) cable jacket 16 is extruded over the twisted pair 12/separator web 14 the filler elements 48 introduce a series of elongate depressions in the inner surface of the cable jacket 16 which results in corresponding series of four (4) ridges as in 68 being formed in the outside of the cable jacket 16 in the region of the filler elements 38. As the separator web is twisted helicoidally along the length L of the cable 10, the ridges as in 68 also twist along the length L of the cable 10. One advantage of such a construction is that the provision of a plurality of ridges as in 68, in this case four (4), ensures that adjacent cables as in 10 are unable to nest, which increases the distance between adjacent cables, thereby reducing PSANEXT and PSAELFEXT with a corresponding improvement in high frequency performance. Additionally, the cable jacket 16 may also slightly deform the ends as in 70 of the two (2) “H” shaped web portions 34, 36 where the filler elements 52 are located, thereby ensuring the twisted pairs as in 12 remain displaced from the inner surface 32 of the cable jacket 16.

Additionally, the balance of the pairs may be further improved by ensuring that the materials used to manufacture the separator web 14, the filler elements 52 and the insulation surrounding the twisted pairs of conductors 12 all have the same or similar dielectric properties.

Referring now to FIG. 2F, in a fourth illustrative embodiment of the present invention the inner surface 32 of the cable jacket 16 may be fluted during the extruded process to include a series of small raised undulations or distensions as in 72, illustratively of partially-spherical cross section. The distensions as in 72 typically run straight along the length of the cable 10, or alternatively twist helicoidally opposite to the direction of helicoidal twist of the twisted pair 12/separator web 14 assembly, and therefore do not nest between the filler elements as in 52 of the separator web 14. As a result, a smaller number (illustratively four or five distensions as in 72) of smaller diameter can be used, thereby reducing the amount of material which must be added in order to form the distensions as in 72, while still achieving an improved separation between the twisted pairs of conductors as in 12 and inside of the cable jacket 32. In an illustrative embodiment the height of the distensions as in 72 is at least about 25% of the thickness of the jacket.

Although the present invention has been described hereinabove by way of an illustrative embodiment thereof, this embodiment can be modified at will without departing from the spirit and nature of the subject invention.

Claims

1. A telecommunications cable comprising: four twisted pairs of insulated conductors;a separator configured to provide four quadrants in the cable within which the four twisted pairs of insulated conductors are individually disposed; anda cable jacket surrounding the four twisted pairs of insulated conductors and the separator along the length of the telecommunications cable;wherein the separator comprises a central portion, first and second side portions positioned parallel to the central portion on either side of the central portion, and first and second cross portions positioned on opposite sides of the central portion and substantially perpendicular to the central portion;wherein the first cross portion joins the first side portion to the central portion, and the second cross portion joins the second side portion to the central portion; andwherein the first and second cross portions are offset relative to one another along a height of the central portion.

2. The telecommunications cable as claimed in claim 1, wherein a combination of the central portion, the first cross portion and the first side portion is approximately H shaped in cross-section; and wherein a combination of the central portion, the second cross portion and the second side portion is approximately H shaped in cross-section.

3. The telecommunications cable as claimed in claim 1, wherein the first cross portion is attached approximately mid-way along a height of the first side portion.

4. The telecommunications cable as claimed in claim 1, wherein the separator and the four twisted pairs of insulated conductors are helically stranded together along the length of the telecommunications cable.

5. The telecommunications cable as claimed in claim 1, wherein the separator is a unitary structure.

6. The telecommunications cable as claimed in claim 1, wherein the first and second side portions are positioned to prevent the four twisted pairs from contacting the cable jacket.

7. The telecommunications cable as claimed in claim 1, wherein each twisted pair comprises two conductors each surrounded by an insulation and helicoidally twisted together; and wherein the separator comprises a material having a dielectric constant that is substantially the same as a dielectric constant of the insulation of the twisted pairs.

8. The telecommunications cable as claimed in claim 1, wherein the four twisted pairs of conductors include a first twisted pair having a first twist lay length, a second twisted pair having a second twist lay length, a third twisted pair having a third twist lay length, and a fourth twisted pair having a fourth twist lay length; wherein the first and second twist lay lengths are shorter than the third and fourth twist lay lengths; andwherein an arrangement of the four twisted pairs of conductors within the telecommunications cable and the offset positioning of the first and second cross portions are such that the third and fourth twisted pairs are located closer to a geometric center of the cable than are the first and second twisted pairs of conductors.

9. The telecommunications cable as claimed in claim 1, further comprising four filler elements, each filler element being attached to a respective end of the first and second side portions and positioned between the respective side portion and the cable jacket.

10. The telecommunications cable as claimed in claim 1, wherein the cable jacket is fluted to include a plurality of raised distensions on an inner surface of the cable jacket.

11. A telecommunications cable comprising: four twisted pairs of insulated conductors;a separator comprising a first h-shaped portion and a second h-shaped portion, the separator configured to provide four quadrants in the cable within which the four twisted pairs of insulated conductors are individually disposed; anda cable jacket surrounding the four twisted pairs of insulated conductors and the separator along the length of the telecommunications cable;wherein the first and second h-shaped portions touch along a heel thereof.

12. The telecommunications cable as claimed in claim 11, wherein the first and second h-shaped portions are co-joined at the heel.

13. The telecommunications cable as claimed in claim 12, wherein the first and second h-shaped portions have substantially the same dimensions.

14. The telecommunications cable as claimed in claim 12, wherein the separator and the four twisted pairs of insulated conductors are helically stranded together along the length of the telecommunications cable.

15. The telecommunications cable as claimed in claim 12, wherein the first and second h-shaped portions are positioned to prevent the four twisted pairs from contacting the cable jacket.

16. The telecommunications cable as claimed in claim 12, wherein each twisted pair comprises two conductors each surrounded by an insulation and helicoidally twisted together; and wherein the separator comprises a material having a dielectric constant that is substantially the same as a dielectric constant of the insulation of the twisted pairs.

17. The telecommunications cable as claimed in claim 12, wherein the four twisted pairs of conductors include a first twisted pair having a first twist lay length, a second twisted pair having a second twist lay length, a third twisted pair having a third twist lay length, and a fourth twisted pair having a fourth twist lay length; wherein the first and second twist lay lengths are shorter than the third and fourth twist lay lengths; andwherein an arrangement of the four twisted pairs of conductors within the telecommunications cable and an offset positioning of the first and second h-shaped portions are such that the third and fourth twisted pairs are located closer to a geometric center of the cable than are the first and second twisted pairs of conductors.

18. The telecommunications cable as claimed in claim 12, wherein the first and second h-shaped portions are positioned within the cable as reverse minor images of one another.