Optimized twisted pair using low modulus pair separator

Abstract

A jacketed cable includes a first twisted pair formed by a first insulated conductor twisted with a second insulated conductor with a first dielectric tape residing therebetween. The first dielectric tape may foamed and / or include a plurality of through holes with sizes and spacings to tune impedance and / or balance a delay skew amongst multiple twisted pairs and / or reduce crushing of the first and second insulation layers of the first and second conductors. A method of manufacturing may optionally include heating or chilling the first dielectric tape and / or chilling the first and second insulated conductors prior to forming the first twisted pair to a temperature different from the ambient temperature, thereby tuning the impedance of the first twisted pair and / or adjust the delay skew of the first twisted pair relative to other twisted pairs and / or reduce crushing of the first and second insulation layers of the first and second conductors.

Description

OPTIMIZED TWISTED PAIR USING LOW MODULUS PAIR SEPARATORBACKGROUND OF THE INVENTION1. Field of the Invention

[0001] The present invention relates to a twisted pair cable for communication of high-speed signals, such as a local area network (LAN) cable. More particularly, the present invention relates to a twisted pair cable having a perforated and / or highly compressible dielectric tape between first and second insulated conductors of a twisted pair.2. Description of the Related Art

[0002] As depicted in Figures 1 and 2, U.S. Patent No. 7,999,184 shows a LAN cable 1 having a jacket J surrounding first through fourth twisted pairs A, B, C, D which are spaced from each other by a separator 3. Each of the twisted pairs A, B, C, D includes a first insulated conductor 5, a dielectric tape 7, and a second insulated conductor 9, wherein the first insulated conductor 5 is twisted with the second insulated conductor 9 with the dielectric tape 7 residing between the first insulated conductor 5 and the second insulated conductor 9.

[0003] As best seen in the close-up cross sectional view in Figure 2 of the twisted pair A, the width of the dielectric tape 7, which extends between opposing edges 11 and 13, is set to extend beyond the first and second insulated conductors 5 and 9. By this arrangement, the opposing edges 11 and 13 of the dielectric tape 7 circumscribe an area 15, around the twisted pairs A, B, C, D. The area 15 creates a spacing between the twisted pairs A, B, C, D and the separator 3 and between the twisted pairs A, B, C, D and the jacket J. This spacing around the twisted pairs A, B, C, D can improve the electrical performance of the cable 1, such as by reducing crosstalk.

[0004] In typical cables of the background art, the first insulated conductor 5 would be formed by a first conductor 17 of about twenty -three gauge size, surrounded by a layer of a first dielectric insulating material 19 having a radial thickness of about tens mils or about eleven mils for a typical CAT 6 cable. Likewise, the second insulated conductor 9 would be formed by a second conductor 21 of about twenty -three gauge size,surrounded by a layer of a second dielectric insulating material 23 having a same or similar radial thickness.

[0005] An improvement over the cable of Figures 1 and 2 is shown in the Applicant’s US Patents 11,424,052; 10,573,430; 9,978,480; 9,418,775 and 7,999,184, which are herein incorporated by reference. The improved cable enhanced one or more performance characteristics of a LAN cable, such as reducing insertion loss, matching impedance, reducing propagation delay and / or balancing delay skew between twisted pairs, and / or to enhance one or more mechanical characteristics of a LAN cable, such as improving flexibility, reducing weight, reducing cable diameter and reducing smoke emitted in the event of a fire.

[0006] A primary feature of the improved cable in the Applicant’s Patents involved a first dielectric tape being different in shape, size or material content as compared to a second dielectric tape. More particularly, Figure 3 is a perspective view of a twisted pair cable 31, in accordance with the prior art. Figure 4 is a cross sectional view of the cable 31 taken along line IV— IV in Figure 3. The cable 31 includes a jacket32 formed around and surrounding first, second, third and fourth twisted pairs 33, 34, 35 and 36, respectively. The jacket 32 may be formed of polyvinylchloride (PVC), a low smoke zero halogen thermoplastic compound, polyethylene (PE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE), or other foamed or solid materials common to the cabling art.

[0007] A separator 37 within the jacket 32 resides between and separates the first and fourth twisted pairs 33 and 36 from the second and third twisted pairs 34 and 35. In Figures 3 and 4, the separator 37 is formed by a thin strip of dielectric material, having a thickness of about twenty mils or less, more preferably eighteen mils or less, such as about fifteen mils. However, other sizes and shapes of separators 37 may be employed, such as plus-shaped or star-shaped separators, sometimes referred to as a flute, isolator, or cross-web. The separator 37 may be formed of any solid or foamed material common to the cabling art, such as a polyolefin or fluoropolymer, like fluorinated ethylene propylene (FEP) or polyvinylchloride (PVC).

[0008] As best seen in the cross sectional view of Figure 4, the first twisted pair33 includes a first insulated conductor 38, a first dielectric tape 39, and a second insulatedconductor 40. The first insulated conductor 38 is twisted with the second insulated conductor 40, in a helical fashion, with the first dielectric tape 39 residing between the first insulated conductor 38 and the second insulated conductor 40.

[0009] The second twisted pair 34 includes a third insulated conductor 41, a second dielectric tape 42, and a fourth insulated conductor 43. The third insulated conductor 41 is twisted with the fourth insulated conductor 43, in a helical fashion, with the second dielectric tape 42 residing between the third insulated conductor 41 and the fourth insulated conductor 43.

[0010] The third twisted pair 35 includes a fifth insulated conductor 44, a third dielectric tape 45, and a sixth insulated conductor 46. The fifth insulated conductor 44 is twisted with the sixth insulated conductor 46, in a helical fashion, with the third dielectric tape 45 residing between the fifth insulated conductor 44 and the sixth insulated conductor 46.

[0011] The fourth twisted pair 36 includes a seventh insulated conductor 47, a fourth dielectric tape 48, and an eighth insulated conductor 49. The seventh insulated conductor 47 is twisted with the eighth insulated conductor 49, in a helical fashion, with the fourth dielectric tape 48 residing between the seventh insulated conductor 47 and the eighth insulated conductor 49.

[0012] Figure 5 is a close-up view of the first twisted pair 33, which is similarly constructed although not identically constructed (as will be detailed later in the specification) to the second, third and fourth twisted pairs 34, 35 and 36. Each of the first through eighth insulated conductors 38, 40, 41, 43, 44, 46, 47, 49 is formed by a conductor K surrounded by a layer of dielectric insulating material R, such as a polymer or foamed polymer, common to the cabling art like fluorinated ethylene propylene (FEP), polyethylene (PE) or polypropylene (PP). Further, the insulating material R may be formed by an enamel coating, or another nonconductive coating from a diverse art like motor armature windings. The conductor K may be solid or stranded, and may be formed of a conductive metal or alloy, such as copper. In one embodiment, the conductor K is a solid, copper wire of about twenty three gauge size.

[0013] In one embodiment, the insulating material R may have a radial thickness of about seven mils or less, more preferably about five mils or less. This radial thicknessof the insulating layer R is at least 20% less than the standard insulation layer thickness of a conductor in a typical equivalent twisted pair wire, more preferably at least 25% to 30% less. Typically, such a thin insulation layer R would not be possible due to the incorrect impedance obtained when the conductors K of the first and second insulated conductors 38 and 40 become so closely spaced during the twisting operation due to the thinner insulating layers R. The interposed first dielectric tape 39 eases the mechanical stresses during twisting so that the thinner insulating layer R is undamaged and also spaces the conductors K apart so that a proper impedance may be obtained, e.g., one hundred ohms.

[0014] As best seen in Figure 5, the first dielectric tape 39 has a first width which extends approximately perpendicular to an extension length of the first dielectric tape 39 from a first edge 51 of the first dielectric tape 39 to an opposing second edge 53 of the first dielectric tape 39. The first width is less than a diameter of the first insulated conductor 38 plus a diameter of the second insulated conductor 40 plus a thickness of the first dielectric tape 39, wherein the thickness is measured by the spacing created between the first and second insulated conductors 38 and 40. A typical spacing might be between four to twelve mils, such as about eight mils or about ten mils. By this arrangement, the twists of the first twisted pair 33 occupy a space within the dashed line 55, which is circumscribed by the helical twisting of the first and second insulated conductors 38 and 40. In this arrangement, the first through eighth insulated conductors 38, 40, 41, 43, 44, 46, 47 and 49 may contact each other if adjacent and also may contact the inner wall of the jacket 32.

[0015] In Figure 5, the dielectric tape 39 is formed as a single unitary structure (e g., the dielectric tape does not include multiple pieces attached together or layered). Figure 5A illustrates that the solid dielectric tape 39 of Figure 5 may be replaced with a dielectric tape 39A having a hollow core filled with a gas, like air (with a dielectric constant of 1.0) or a foamed insulation material (with a dielectric constant approaching 1.0). By filling the hollow core with a gas or material with a lower dielectric constant than a material used to form the first dielectric tape 39 or 39A, the overall dielectric constant of the first dielectric tape 39A may be reduced. The hollow core may extend the entire length of the dielectric tape 39A, resulting in a “strawdike” structure.Alternatively, support structures may be formed at intervals along the length of the dielectric tape 39A to form closed-cell air pockets, each having a short length, such as 1 / 2 inch, one inch, two inches, etc. Alternatively, one or more support structures may be formed within the hollow core, which extend along the length of the dielectric tape 39A and connect between the lateral walls of the hollow core to resist crushing of the hollow core during the twisting of the first twisted pair 33A. The first twisted pair 33A depicted in Figure 5A may be substituted into the place of the first twisted pair 33 depicted in Figure 4.

[0016] The first through fourth twisted pairs 33, 34, 35 and 36 may be stranded together in the direction 57 (see the arrow in Figure 3) to form a stranded core. In one embodiment, the core strand direction 57 is opposite to the pair twist directions of the first through fourth twisted pairs 33, 34, 35 and 36. However, this is not a necessary feature, as in a preferred embodiment, the strand direction 57 is the same as the pair twist directions.

[0017] In preferred embodiments, the strand length of the core strand is about five inches or less, more preferably about three inches or less. In a more preferred embodiment, the core strand length is purposefully varied, or modulates, from an average strand length along a length of the cable 31. Core strand modulation can assist in the reduction of alien crosstalk. For example, the core strand length could modulate between two inches and four inches along the length of the cable 31, with an average value of three inches.

[0018] The first twist length W (See Figure 3) of the first twisted pair 33 is preferably set to a short length, such as between approximately 0.22 inches and approximately 0.38 inches. The second twist length X of the second twisted pair 34 is different from the first twist length W and is between approximately 0.22 inches and approximately 0.38 inches. For example, the first twist length W may be set to approximately 0.26 inches and the second twist length X may be set to approximately 0.33 inches.

[0019] In one embodiment, the first twist length W purposefully modulates from a first average value, such as 0.26 inches. For example, the first twist length could purposefully vary between 0.24 and 0.28 inches along the length of the cable. Likewise,the second twist length X could purposefully modulate from a second average value, such as 0.33 inches. For example, the second twist length X could purposefully vary between 0.31 and 0.35 inches along the length of the cable.

[0020] The third twisted pair 35 would have a third twist length Y and the fourth twisted pair 36 would have a fourth twist length of Z. In one embodiment, the third twist length Y is different from the first, second and fourth twist lengths W, X and Z, while the fourth twist length Z is different from the first, second and third twist lengthsW, X and Y. Of course, the third and fourth twisted pairs 35 and 36 could employ a similar twist length modulation, as described in conjunction with the first and second twisted pairs 33 and 34.

[0021] Figure 6 is a close-up cross sectional view of a twisted pair 60, having a dielectric tape 61 with an alternative shape, in accordance with the prior art. The dielectric tape 61 has a width which extends approximately perpendicular to an extension length of the twisted pair 60 from a first edge 62 of the dielectric tape 61 to an opposing second edge 63 of the dielectric tape 61. The width, in the embodiment of Figure 6, is equal to or less than the diameter of the first insulated conductor 38. Less material is used to form the dielectric tape 61 in the embodiment of Figure 6. This presents advantages in reducing the amount of consumable material in the case of a fire, and in reducing the amount of smoke emitted from the cable 31 in the case of a fire. This structure may also reduce the weight and outer diameter of the cable and improve the flexibility of the cable.

[0022] As seen in Figure 6, the dielectric tape 61 has a cross sectional shape in a direction perpendicular to an extension length of the twisted pair 60, which presents a first recessed portion 64 for seating the first insulated conductor 38 and a second recessed portion 65 for seating the second insulated conductor 40.

[0023] The cross sectional shapes of the dielectric tapes 39 and 61 in Figures 5 and 6 are mirror symmetrical. However, it is not necessary that the shape be mirror symmetrical in order to achieve many of the advantages. Further, the first and second recessed portions 64 and 65 of the dielectric tape 61 in Figure 6 are semi-circular in shape. However, it is not necessary that the first and second recessed portions 64 and 65 be semi-circular. In fact, the recesses in the dielectric tape 39 of Figure 5 for receivingthe first and second insulated conductors 38 and 40 are not semi-circular in shape. Also, the first and second recessed portions 64 and 65 may include serrations to create pockets of air adjacent to the seated portions of the first and second insulated conductors 38 and 40.

[0024] Figure 7 is a cross sectional view of a twisted pair cable 66 employing the first twisted pair 60 of Figure 6. The twisted pair cable 66 also includes similarly configured second, third and fourth twisted pairs 67, 68 and 69. The twists of the first, second, third and fourth twisted pairs 60, 67, 68 and 69 occupy respective spaces within the dashed lines 55 (See Figure 6) due to their twisting down the length of the cable 66. In this arrangement, the first through eighth insulated conductors 38, 40, 41, 43, 44, 46, 47 and 49 may contact each other and also may contact the inner wall of the jacket 32.

[0025] Figure 8 is a close-up cross sectional view of a twisted pair 70, having a dielectric tape 71 with an alternative shape, in accordance with the prior art. The dielectric tape 71 has a width which extends approximately perpendicular to an extension length of the twisted pair 70 from a first edge 72 of the dielectric tape 71 to an opposing second edge 73 of the dielectric tape 71. The width, in the embodiment of Figure 8, is equal to or less than the diameter of the first insulated conductor 38.

[0026] The embodiment of Figure 8 illustrates that the dielectric tape 71 need not have recessed portions 64 and 65 (as shown in Figures 5 and 6) to seat the insulated conductors 38 and 40. Rather, the dielectric tape 71 may be formed as a generally flat member. The dielectric tape 71 will remain between the first and second insulated conductors 38 and 40 due to the frictional forces created during the twisting operation, when the twisted pair 70 is formed.

[0027] Figure 8A is a close-up cross sectional view of a twisted pair 70A, having a dielectric tape 71 A with an alternative shape, in accordance with the prior art. The dielectric tape 71 A has a width which extends approximately perpendicular to an extension length of the twisted pair 70A from a first edge 72A of the dielectric tape 71A to an opposing second edge 73A of the dielectric tape 71A. The width, in the embodiment of Figure 8A, is equal to or slightly less than (e.g., two to four mils less than) the diameter of the first insulated conductor 38 plus the diameter of the second insulated conductor 40 plus a thickness of the dielectric tape 71 A.

[0028] The embodiment of Figure 8A illustrates that the dielectric tape 71 A may be a generally flat member having a width which is approximately equal to the diameter of the first insulated conductor 38 plus the diameter of the second insulated conductor 40 plus a thickness of the dielectric tape 71 A, such as about seventy -two mils plus or minus about three mils.

[0029] Figure 8B is a cross sectional view of a twisted pair cable 76 employing the first twisted pair 70A of Figure 8 A, in accordance with the prior art. The twisted pair cable 76 also includes similarly configured second, third and fourth twisted pairs 77, 78 and 79. The twists of the first, second, third and fourth twisted pairs 70A, 77, 78 and 79 occupy respective spaces within the dashed lines 55 (See Figure 8A). In this arrangement, the first through eighth insulated conductors 38, 40, 41, 43, 44, 46, 47 and 49 may contact a plus-shaped separator 37A (sometimes referred to as an isolator, a flute or a crossweb) and also may contact inner ends of projections or fins 32A on the inner wall of the jacket 32. Figure 8B shows twelve projections 32A, however more or fewer projections may be included, with the goal being to hold the core of twisted pairs 70A, 77, 78 and 79 in the center of the cable 76 while creating air pockets around the perimeter of the core of twisted pairs.

[0030] With all of the cable designs of the prior art, the cable designer must account for required fundamental performance criteria of a twisted pair cable. The configurations, relative placements, dimensions and materials of the cable elements must be selected to meet the required fundamental performance criteria. Parameters which are normally considered in the design of a cable are impedance, material type and material mass reduction to pass bum and smoke testing, attenuation / insertion loss and delay skew.

[0031] The impedance of a pair is a function of the spacing between the conductors, the twist length of the pair and the effective dielectric constant as seen by the electric field surrounding the twisted pair. Standards dictate the desired impedance of a twisted pair, which is usually 100 Ohms. Thus, the combination of twist length, conductor spacing, effective dielectric constant, etc. must be selected to attain the desired impedance. For a given twist length, if the effective dielectric constant is reduced, the conductors can be spaced closer together, thus reducing the size of the twisted pair andreducing the volume and / or mass of polymer material used in the construction of the twisted pair. It is therefore desirable to reduce the material content as much as possible, while maintaining the mechanical rigidness of the twisted pair to, for instance, minimize crush during the twisting and stranding process.

[0032] The dielectric constant of a vacuum is the lowest achievable and set as 1.00 as a reference. Air and most gasses have approximately the same dielectric constant. Solid polymers with good electric properties suitable for insulation and / or tapes, on the other hand, have a dielectric constant (i.e. a ratio relative to air) in the range of about 2.0 to 3.0. Foamed polymers are, in effect, a mixture of solid polymers and air resulting in an effective dielectric constant that is a weighted average of the volume occupied by the polymer and the volume occupied by air. Thus, if a solid tape made of a material with a dielectric constant of 2.3 is foamed at a 25% rate, the dielectric constant is reduced to 1.975 (i.e. 2.3*75% + 1.0*25%). The effective dielectric constant experienced by a twisted pair is a function of its nearby surroundings including its insulation, any tapes deployed, nearby j ackets, adjacent twisted pairs, etc. Since smaller conductors lead to smaller cables, it is thus desirable to decrease the effective dielectric constant as much as possible, while ensuring the mechanical rigidness of the twisted pair is adequate to maintain the crushing force induced during the twisting operation.

[0033] As noted above, twist length is also an important consideration. If perfectly round insulated conductors are twisted into a twisted pair at an infinitely long twist length, the cross-section of the twisted pair results in perfectly round conductors. If, on the other hand, the twist length is very short, the cross-section of the twisted pair results in a non-round cross-section due to the angle of the cross-sectional cut of each insulated conductor of the twisted pair. This geometric effect lowers the impedance of the twisted pair. In addition, there is more material inside space occupied by the twisted pair, i.e., the area circumscribed by the dashed line 55 in Figures 5-8. This added material increases the effective dielectric constant of the fields surrounding the twisted pair and further decreases the impedance of the twisted pair. The combined effect can be compensated for by reducing the effective dielectric constant (such as by foaming), or by separating the conductors of the twisted pair further to increase the impedance back up to the target impedance, such as 100 Ohms.

[0034] Another factor that must be considered is the attenuation of the twisted pair. The insertion loss of the worst twisted pair in the cable is generally specified. The shorter the twist length, the longer the helical length of the conductors that make up the twisted pair. Thus, for the same conductor sizes, shorter twist lengths result in higher signal attenuation, even if impedance has been compensated for. As a result, cable designers often compensate for this effect by deploying larger conductors for the shorter twist lengths in a cable. Ideally, the conductors of each twisted pair can be compensated for but, in practice, for operational efficiency and component standardization, the conductors of the longest two twisted pairs may be specified to one level, while the conductors of the shortest two twisted pairs may be specified to a second level which is larger.

[0035] Yet another factor that must be considered is delay skew which is the difference in delay between the twisted pairs. The tighter the twist, the higher the dielectric constant experienced by the twisted pair, and thus the higher the delay. Also, the tighter the twist, the further that a signal needs to travel to pass from a first end of the cable to a remote, second end of the cable. Compensating for reduced impedance and higher insertion loss by deployment of larger conductors and increased spacing between conductors further increases delay and thus the delay skew between twisted pairs. Thus, basically, all these effects are compounded causing substantial increase in delay skew.

[0036] Delay skew can actually be a controlling item for compliance with established industry standards. Thus, designs that reduce delay skew are highly desirable. To date, one of the more important tools available to the cable designer to deal with delay skew has been foaming the insulation layers of twisted pairs at different percentages. This topic is more fully addressed in the Assignee’s prior US Patent 5,814,768, which is herein incorporated by reference.SUMMARY OF THE INVENTION

[0037] Although the cables of the background art perform well and meet the current design requirements, the Applicant has appreciated some drawbacks.

[0038] In practice, the Applicant has appreciated that portions of the thin insulating layers R pressing against the dielectric tape 39, 39A, 61, 71, 71A between thefirst and second insulated conductors 38 and 40 tend to slightly crush. The crushed areas are indicated by arrows 2 and 4 in Figure 9. For example, the insulation layers R may suffer a five to fifteen percent reduction in thickness relative to the original thickness of the extruded insulation layer R. The crushing is primarily due to the stresses applied to the insulation layers R during a twisting operation within a twinner machine. The crushing is generally greater on the more tightly twisted pairs. Also, the crushing seems to be related to the speed of the twisting operation, e.g., a faster speed of operation of the twinner causes more crushing of the insulation layers R.

[0039] Also, if a “straw-like” hollow core of the dielectric tape 39A of Figure 5 A is employed, the hollow core tends to collapse and close, as the first and second insulated conductors 38 and 40 are twisted together within the twinner. Also, it proves to be expensive and unfeasible to provide intermediately spaced support structures within the hollow core to resist a collapse of the hollow core of the dielectric tape 39A in Figure 5A.

[0040] It is an object of the present invention to provide an improved cable design that addresses one or more of these appreciated drawbacks.

[0041] The Applicant has appreciated that a change in a cable design to improve one performance aspect of the cable often reduces another performance aspect of the cable. A balancing and tradeoff in performance parameters is required to construct a cable, which meets the various specification requirements. It is a great benefit to the cable designer to add one or more tools to the toolbox to assist in balancing the tradeoffs in performance parameters of the cable.

[0042] For example, in order to reduce delay skew, it may desirable to deploy a different tape structure to purposely attain a higher effective dielectric constant to slow a signal speed on a twisted pair with a longer twist length and thus reduce delay skew. In practice, cables with four twisted pairs generally deploy two twist lengths that are short and fairly similar in length, and two longer twist lengths that are longer and also fairly similar in length. The short twist lengths are placed diagonally in the core (e.g. 177, 179 in Figure 15) and the longer two twist lengths are also placed diagonally in the core (e.g. 178, 180 in Figure 15). Since the diagonal pairs are physically further apart than the adjacent pairs, they exhibit excellent crosstalk isolation even through their twist lengths are fairly close together in value. To address all the constraints simultaneously, a designcan be optimized by, for instance, deploying tapes with closely spaced perforations on the tightest two twists and tapes with longer spaced perforations or no perforations at all for the longest two twists. In certain circumstances, it is also possible to deploy the same thickness tapes for all four pairs and rely strictly on the perforation arrangement to achieve the desired performance, therefore, simplifying the production process.

[0043] These and other objects can be accomplished by a cable wherein the first dielectric tape is formed of a solid or foamed material which includes a plurality of through holes, penetrating therethrough. The plurality of through holes may be formed as plural columns of spaced through holes along the length of the first dielectric tape. The size and spacing of the through holes in the first dielectric tape may be used as a tool to balance the delay skew within the cable.

[0044] These and other objects are accomplished by a cable including a jacket surrounding a first twisted pair formed by a first insulated conductor twisted with a second insulated conductor with a first dielectric tape residing between the first and second insulated conductors. The first insulated conductor includes a first conductor surrounded by an insulation layer of first dielectric material having a first compression modulus. The second insulated conductor includes a second conductor surrounded by an insulation layer of second dielectric material having a second compression modulus. The first dielectric tape is formed of a third dielectric material having a third compression modulus, wherein the third compression modulus may be different than the first compression modulus, at a same temperature, as part of a cable design optimization. For example, the third compression modulus may be less than 265% of the first compression modulus or less than 150% of the first compression modulus, or more preferrable less than the first compression modulus.

[0045] These and other objects are accomplished by a method of manufacturing the cable which includes heating or chilling the first dielectric tape and / or chilling the first and second insulated conductors prior to forming the first twisted pair to improve a relative compression modulus between the first dielectric tape and the insulation layers, so that crushing of the insulation layers is reduced. The “chilling-before-twisting” operation on the first and second insulated conductors may increase the compression modulus to resist crushing of the insulation layers on the first and second insulatedconductors. The heating (or chilling of the first dielectric tape, e.g., to a temperature greater than the chilling temperature of the insulated conductors) may assist in controlling a level of the compression of the first dielectric tape during the twisting operation, so as to balance a delay skew in a multi-pair cable, while minimizing the crushing of the insulation layers of the insulated conductors.

[0046] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limits of the present invention, and wherein:

[0048] Figure 1 is a cross sectional view of a twisted pair cable, in accordance with a first embodiment of the prior art;

[0049] Figure 2 is a close-up cross sectional view of a twisted pair in the cable of Figure 1;

[0050] Figure 3 is a perspective view of a twisted pair cable, in accordance with a second embodiment of the prior art;

[0051] Figure 4 is a cross sectional view of the twisted pair cable of Figure 3 taken along line IV— IV;

[0052] Figure 5 is a close-up cross sectional view of a twisted pair from Figure 4;

[0053] Figure 5A is a close up cross sectional view of a twisted pair similar to Figure 5, but illustrating that the dielectric tape may include a hollow air pocket;

[0054] Figure 6 is a close-up cross sectional view of a twisted pair, having a dielectric tape with an alternative shape, in accordance with a third embodiment of the prior art;

[0055] Figure 7 is a cross sectional view of a twisted pair cable employing twisted pairs in accordance with Figure 6;

[0056] Figure 8 is a close-up cross sectional view of a twisted pair, having a dielectric tape with an alternative shape, in accordance with a fourth embodiment of the prior art;

[0057] Figure 8A is a close-up cross sectional view of a twisted pair, having a dielectric tape with an alternative shape, in accordance with a fifth embodiment of the prior art;

[0058] Figure 8B is a cross sectional view of a twisted pair cable employing twisted pairs in accordance with Figure 8 A;

[0059] Figure 9 is a close-up cross sectional view of the twisted pair of Figure 8, but illustrating insulation crush on the insulated conductors adjacent to the dielectric tape, in accordance with the prior art;

[0060] Figure 10 a close-up cross sectional view of a twisted pair showing little or no crush on the insulated conductors adjacent to the dielectric tape and crush on the opposing surfaces of a dielectric tape, in accordance with a first embodiment of the present invention;

[0061] Figure 11 is a perspective view of the dielectric tape of Figure 10 prior to a twisting operation;

[0062] Figure 12 is a top view of a dielectric tape, in accordance with a second embodiment of the present invention;

[0063] Figure 13 is a top view of a dielectric tape, in accordance with a third embodiment of the present invention;

[0064] Figure 14 is a top view of a dielectric tape, in accordance with a fourth embodiment of the present invention; and

[0065] Figure 15 is a cross sectional view of a cable having four twisted pairs in accordance with the present invention.DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0066] The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention areshown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0067] Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise.

[0068] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0069] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as "between X and Y" and "between about X and Y" should be interpreted to include X and Y. As used herein, phrases such as "between about X and Y" mean "between about X and about Y." As used herein, phrases such as "from about X to Y" mean "from about X to about Y."

[0070] It will be understood that when an element is referred to as being "on", "attached" to, "connected" to, "coupled" with, "contacting", etc., another element, it canbe directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, "directly on", "directly attached" to, "directly connected" to, "directly coupled" with or "directly contacting" another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed "adjacent" another feature may have portions that overlap or underlie the adjacent feature.

[0071] Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly.

[0072] Figure 15 is a cross sectional view of a twisted pair cable 176, in accordance with the present invention. Figure 10 is a close-up cross sectional view of a twisted pair from Figure 15. The cable 176 includes a jacket 32 formed around and surrounding first, second, third and fourth twisted pairs 177, 178, 179 and 180, respectively. The jacket 32 may be formed of polyvinylchloride (PVC), a low smoke zero halogen thermoplastic compound, polyethylene (PE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE), or other foamed or solid materials common to the cabling art.

[0073] The twists of the first, second, third and fourth twisted pairs 177, 178, 179 and 180 occupy respective spaces within the circular dashed lines due to the twisting of each pair down the length of the cable. In this arrangement, first through eighth insulated conductors 138, 140, 141, 143, 144, 146, 147 and 149 may contact a plus-shaped separator 37A (sometimes referred to as an isolator, a flute or a crossweb) and also may contact inner ends of projections or fins 32A on the inner wall of the jacket 32. Althoughthe plus-shaped separator 37 A is shown, the flat tape separator 37 of Figure 4 may be used instead to separate two twisted pairs from the other two twisted pairs, or no separator may be used in the cable core to separate a twisted pair from the other twisted pairs. Alternatively, a small solid or hollow tube separator may be inserted in the center of the core of the cable to keep it mechanically stable. In all embodiments, the core is preferably stranded. Figure 15 shows twelve projections 32A, however more or fewer projections may be included, with the goal being to hold the core of twisted pairs 177, 178, 179 and 180 in the center of the cable 176, while creating air pockets around the perimeter of the core of twisted pairs.

[0074] As best seen in the cross sectional view of Figure 10, the first twisted pair 177 includes the first insulated conductor 138, a first dielectric tape 137, and the second insulated conductor 140. The first insulated conductor 138 is twisted with the second insulated conductor 140, in a helical fashion, with the first dielectric tape 137 residing between the first insulated conductor 138 and the second insulated conductor 140. The second twisted pair 178, third twisted pair 179 and fourth twisted pair 180 may be similarly formed.

[0075] Each of the first through eighth insulated conductors 138, 140, 141, 143, 144, 146, 147 and 149 is formed by a conductor K surrounded by a layer of dielectric insulating material R, such as a polymer or foamed polymer, common to the cabling art like fluorinated ethylene propylene (FEP), polyethylene (PE) or polypropylene (PP). Further, the insulating material R may be formed by an enamel coating, or another nonconductive coating from a diverse art like motor armature windings. The conductor K may be solid or stranded, and may be formed of a conductive metal or alloy, such as copper. In one embodiment, the conductor K is a solid, copper wire of about twenty- three gauge size. Alternatively, the conductor K may be twenty-four gauge, twenty-two gauge or twenty-one gauge in size.

[0076] In prior art Figure 9, the insulating material R had a first radial thickness 150 of about seven mils or less. Due to the crush at arrows 2 and 4 the insulation material R had its thickness reduced by about five to fifteen percent to a second radial thickness 152 of about six mils or less. Very little crushing occurred in the surfaces of the first dielectric tape 71 because a compression modulus of the first dielectric tapewhen formed of PP was more than 250% of the compression modulus of the insulation layers R of the first and second insulated conductors 38 and 40 when formed of FEP, e.g., about 265% of the compression modulus of the insulation layers R of the first and second insulated conductors 38 and 40. Therefore, a thickness of the insulation layers R of the first and second insulated conductor 38 and 40 was increased by the cable designer to compensate for the crushing that was expected to occur during the twisting operation.

[0077] The first dielectric tape 71 had a thickness 154 of about eight to ten mils, e.g., nine mils, which created a spacing 156 between the conductors K of the first and second insulated conductors 38 and 40 of about twenty to twenty-two mils, e.g., twenty- one mils. The twenty-one mil spacing 156 allowed the first twisted pair 70 to present about a one hundred ohm impedance and to have a suitable delay skew in relation to the other twisted pairs within the cable, after the crushing of the insulation layers R.

[0078] As shown in Figure 10, the Applicants appreciated that a volume / mass of the materials contained within the twisted pair 177 could be reduced by preventing or greatly reducing crushing of the insulation layers R1 and R2 of the first and second insulated conductors 138 and 140, and instead allowing crushing on a midsection of the first dielectric tape 137. The increased thickness of the first dielectric tape 137 adds less material to the twisted pair in comparison to the material removed by making the insulating layers R1 and R2 thinner at a reduced thickness of 150A. By making the first radial thickness 150A of the insulation layers R1 and R2 thinner, such as five to six mils, and allowing the first dielectric tape to crush instead of the insulation layers R1 and R2, the overall material within the twisted pair can be reduced.

[0079] Furthermore, with the space occupied by the twisted pair 177 being reduced (see dashed line 55 in Figure 8), the entire core is smaller and thus less jacket material can be used. Reducing the material in the cable also reduces the weight of the cable 176 and fuel load of the cable 176, which can help to lower the smoke produced by the cable 176 in the event of a fire, reduce shipping costs and save on material costs. The Applicant also appreciated that the insulation layers R1 and R2 of the first and second insulated conductors 138 and 140 is typically formed by a FEP material for cables with a plenum fire rating, which is comparatively more expensive than the alternative materials used to form the first dielectric tape 137, thus resulting in additional cost savings.

[0080] Figure 10 shows the first twisted pair 177 which includes the first insulated conductor 138, the first dielectric tape 137, and the second insulated conductor 140. The first insulated conductor 138 is twisted with the second insulated conductor 140 with the first dielectric tape 137 residing between the first insulated conductor 138 and the second insulated conductor 140 to form the first twisted pair 177. The first insulated conductor 138 includes a first conductor K surrounded by a layer of first dielectric material R1 having a first compression modulus. The second insulated conductor 140 includes a second conductor K surrounded by a layer of second dielectric material R2 having a second compression modulus. The first dielectric tape 137 is formed of a third dielectric material 139 having a third compression modulus. The first dielectric tape 137 is formed as a single unitary structure (e.g., the first dielectric tape 137 and the other dielectric tapes within the twisted pairs of the cable 176 do not include multiple pieces attached together or layered).

[0081] In a best case scenario, to minimize or greatly reduce the crushing of the first and second dielectric materials forming the insulation layers R1 and R2, the first compression modulus and the second compression modulus are both set to a greater value than the third compression modulus of the third dielectric material 139. In other words, the third compression modulus is less than the first compression modulus, and less than the second compression modulus, at a same temperature. However, in the prior art twisted pair 70 of Figure 9, the first dielectric tape 71 had a compression modulus which greatly exceeded the compression modulus of the insulation layers R of the first and second insulated conductors 38 and 40. For example, with a first dielectric tape 71 formed of PP, its compression modulus is about 265% of the compression modulus of the insulation layers R formed of FEP, and about 154% of the compression modulus of insulation layers R formed of PE. Therefore, any reduction of the compression modulus of the first dielectric tape 71 relative to the compression modulus of the insulation layers R of the first and second insulated conductors 38 and 40 would reduce the crushing of the insulation layers R.

[0082] For example, reducing the compression modulus of the first PP dielectric tape 71 to be less than 250% of the compression modulus of FEP insulation layers R would in theory allow for a thinning of the thickness of the FEP insulation layers R,while maintaining the desired impedance of one hundred ohms. In one example, reducing the compression modulus of the PP dielectric tape 71 to less than 180% of the compression modulus of FEP would show significantly more cushioning, i.e., reduced crushing, of the FEP insulation layers R. Also, reducing the compression modulus of the PP dielectric tape 71 to be less than 150% of the compression modulus of PE insulation layers R would in theory allow for a thinning of the thickness of the PE insulation layers R, while maintaining the desired impedance of one hundred ohms. Again, reducing the compression modulus of the PP dielectric tape 71 to less than 120% of the compression modulus of PE would show significantly more cushioning, i.e., less crushing, of the PE insulation layers R.

[0083] Compression modulus is also known as compressive modulus, modulus of compression and compressive Young’s modulus. The higher the compression modulus, the stiffer the material. The ability to be crushed under a force could also be expressed in terms of compliance. Compliance can be considered the inverse of stiffness, where stiffness is the extent to which an object resists deformation in response to an applied force. Hence, compliance can be considered the extent to which an object deforms, e.g., crushes, in response to an applied force.

[0084] In a preferred embodiment, the first and second dielectric materials of the insulation layers R1 and R2 are formed of a same type of material, such as FEP, and the first compression modulus and the second compression modulus are the same, at a same temperature. Dependent upon the material of the insulation layers R1 and R2, the third compression modulus is less than 250% of the first compression modulus, such as less than 150% of the first compression modulus, such as less than the first compression modulus, such as less than 90% of the first compression modulus, or less than 75% of the first compression modulus, at a same temperature. For example, the third compression modulus could be less than 60% of the first compression modulus, at a same temperature.

[0085] Figure 10 illustrates how the first dielectric tape 137 has an initial thickness 158. During the twisting operation, the first insulated conductor 138, the first dielectric tape 137, and the second insulated conductor 140 are fed into a twinner. The twinner performs the twisting of the first insulated conductor 138 with the second insulated conductor 140 with the first dielectric tape 137 residing between the firstinsulated conductor 138 and the second insulated conductor 140 to form the first twisted pair 177. During this operation, the first dielectric tape 137 is compressed to form a necked-down portion between the points of contact with the first insulated conductor 138 and the second insulated conductor 140. A thickness 160 of the necked-down portion is less than the initial thickness 158, e.g., one to four mils less, such as two to three mils less.

[0086] Figure 11 is a perspective view of the dielectric tape 137 of Figure 10 prior to the twisting operation within the twinner. The dielectric tape 137 may be formed of a solid material with a lower compression modulus as compared to the PP material typically used for the dielectric tape 71 of Figure 9, or a material which has its compression modulus lowered by other methods. A first method to lower a compression modulus of the first dielectric tape 137 is to foam or highly foam the material 139 forming the first dielectric tape 137. The material 139 used to form the first dielectric tape 137 passes through an extruder wherein a foaming agent and / or gas bubbles are injected into the first dielectric tape 137. It is believed that the level of foaming exponentially decreases the compression modulus of the material 139, e g., a 10% increase in the foaming percentage leads to a 19% decrease in the compression modulus, and / or a 50% increase in the foaming percentage leads to a 75% decrease in the compression modulus. After the extruder, the first dielectric tape 137 is cooled, such as passing it through a chilled water bath, and then the first dielectric tape 137 is taken up on a spool or reel to be supplied to the twinner for the twisting operation.

[0087] Figure 12 is a top view of a dielectric tape 137A prior to the twisting operation within the twinner, in accordance with a second embodiment of the present invention. A second method to lower a compression modulus is to form the dielectric tape 137A as a flat tape having a substantially flat first surface 160 extending between first and second side edges 161 and 163, and a substantially flat second surface, opposite to the first surface 160, extending between the first and second side edges 161 and 163. A distance between the first surface 160 and second surface defines a thickness of the dielectric tape 137A. A plurality of through holes penetrate through the first and second flat surfaces 160. In a preferred embodiment, the plurality of through holes includes afirst column of spaced through holes 165 located midway between the first and second side edges 161 and 163.

[0088] Figure 13 is a top view of a dielectric tape 137B prior to the twisting operation within the twinner, in accordance with a third embodiment of the present invention. The plurality of through holes may further include a second column of spaced through holes 167 located between the first column of spaced through holes 165 and the first side edge 161. Also, a third column of spaced through holes 169 may be located between the first column of spaced through holes 165 and the second side edge 163.

[0089] The first column of spaced through holes 165 is formed by through holes, each having a first dimensional area. The second and third columns of spaced through holes 167 and 169 are formed by through holes, each having a second dimensional area. In Figure 13, the first and second dimensional areas are approximately equal to each other.

[0090] Figure 14 is a top view of a dielectric tape 137C prior to the twisting operation within the twinner, in accordance with a fourth embodiment of the present invention. The embodiment of Figure 14 is very similar to the embodiment of Figure 13 except that the first dimensional area is larger than the second dimensional area. In other words, the second and third columns of spaced through holes 167A and 169A are formed by smaller through holes.

[0091] Figures 13 and 14 illustrate an offset nature of the first column of spaced through holes 165 relative to both the second and third columns of spaced through holes 167(A) and 169(A), and an aligned nature of the second column of spaced through holes 167(A) relative to the third column of spaced through holes 169(A). In other words, a line 171 passing through a center of a through hole within the second column of spaced through holes 167(A) and passing through a center of a through hole within said third column of spaced through holes 169(A), is perpendicular to both the first side edge 161 and the second side edge 163. This line 171 does not pass through a center of a through hole within the first column of spaced through holes 165. In fact, the line 171 does not pass through any portion of a through hole within the first column of spaced through holes 165.

[0092] The alignments, allow for more holes to be added to the dielectric tapes 137B or 137C while still maintaining a structural integrity, which allows the tapes 137B and / or 137C to be fed at a fast speed through the twinner for the twisting operation. The spacing and sizes of the through holes 165, 167(A) and 169(A) are selected so that the first and second insulated conductors 138 and 140 cannot bend into the through holes 165, 167(A) and 169(A), but rather pass flatly over the tops of the through holes 165, 167(A) and 169(A).

[0093] A perimeter shape of each through hole 165, 167(A) and 169A) need not be circular. Figures 13 and 14 show a perimeter shape of the second and third columns of spaced through holes 167(A) and 169(A) as being circular. Figures 12-14 show a perimeter shape of each through hole within the first column of spaced through holes 165 as being rectangular or square with rounded corners.

[0094] It should also be noted that the crush strength of the tape is primarily driven by the size and spacing between the first column of holes 165 shown in Fig 12. The linear rip strength of the tape, on the other hand, is driven primarily by the length of the jagged lines tearing the tapes as shown on the right edges in Figures 12, 13 and 14, noting that it is easier to rip a tape from side edge 161 to side edge 163 when the rip line passes through one or more of the through holes in the first, second and third columns. For the solid dielectric tape 71 implemented in current designs, the rip strength is greater than needed, thus through holes 165, 167(a) and / or 169(A) can be added to make it easier to rip off the dielectric tape 137A, 137B or 137C during installation, while retaining adequate strength to remain intact during the twisting process and adequate to help define the space 55 (See Figure 8A) occupied by the twisted pair 177. The through holes 167(a) and 169(A) in the second and third columns in Figure 14 are smaller than those in Figure 13 in case stronger tape rip strength is desired. In order to reduce combustible material, larger through holes 165, 167(a) and / or 169(A) that are optimized in their shape and location are preferred.

[0095] In most prior art dielectric tapes, the compression modulus and the dielectric constant of the dielectric tape, whether solid or foamed, is uniform down the length of the dielectric tape. This is not the case when perforations, e.g., through holes 165, 167(a) and / or 169(A), are added. The width of the dielectric tape may be about 72mils, as shown in Figures 8 A and 8B, or more narrow as shown in Figures 8 and 9. In the case of the wider dielectric tapes, the rectangular through holes with rounded corners 165 may have a length that is around l / 4th the width of the dielectric tape, e.g., about 18 mils, when the thickness of the dielectric tape is around 7 mils. Thus, the dielectric tape length between through holes 165 is more than 2.5 times the dielectric tape thickness.

[0096] The length between the rounded rectangular through holes 165 and the length of the rounded through holes 167(A) and 169(A) could also be increased relative to the thickness of the dielectric tape (excluding crush) to, for instance, be at least 3x, or at least 4x, or at least 5x the tape thickness. The larger the ratio of tape length between through holes to dielectric tape thickness, the closer to linear scaling the average compression modulus and effective dielectric constant of the dielectric tape becomes relative to the presence of material. In other words, if the ratio of the length between through holes in the tape to the thickness of the dielectric tape is large and 10% of the length down the center of the dielectric tape is perforated with through holes 165, 167(A), 169(A), the average compression modulus of the dielectric tape will be decrease by about 10% as opposed to 19% with a foamed tape. Similarly, if 50% of the length down the center of the dielectric tape is perforated with through holes, the average compression modulus of the dielectric tape will decrease by just 50% as opposed to 75% as with a foamed dielectric tape. Thus, perforating the dielectric tape retains far superior average mechanical crush resistance for the same level of material reduction as compared to foaming, as long as the ratio of the dielectric tape length between through holes is large compared to the dielectric tape thickness. The effective dielectric constant reduction, based upon the added air introduced between the first and second insulated conductors, is about an equal reduction. Hence, showing that perforations, e.g., through holes, are a superior way for reducing the effective dielectric constant when it is not desired to lose crush resistance.

[0097] In sum, it is believed that the added area of the through holes 165, 167(A) and 169(A) linearly decreases the effective average compression modulus of the material 139, e.g., a 10% increase in the area of through holes leads to a 10% decrease in the effective average compression modulus, and / or a 50% increase in the area of through holes leads to a 50% decrease in the effective average compression modulus. Thethrough holes 165, 167(A) and 169(A) also reduce the material costs, reduce the fuel load and weight of the cable and reduce the dielectric constant of the dielectric tape. It should also be noted that the extruded material used to produce the dielectric tapes of Figures 12-14 may also include a level of foaming to further reduce the effective average compression modulus, to further reduce the dielectric constant and to further reduce the material used to form the dielectric tapes of Figures 12-14.

[0098] The through holes 165, 167(A) and 169(A) may be formed within the dielectric tapes 137A, 137B and / or 137C by a variety of methods. In simplest form, punches may puncture through the extruded dielectric tapes 137A, 137B and / or 137C after they pass through the chilled water bath and prior to being taken up on the spool or reel. The punches may produce free or hanging chads, which could be vacuumed up or blown off of the dielectric tapes 137A, 137B and / or 137C, so that the reeling of the dielectric tapes 137A, 137B and / or 137C will operate smoothly and cleanly. Alternately, heated probes could melt the through holes 165, 167(A) and 169(B) and deposit the removed materials as molten drips into a collection bin for recycling. Alternatively, lasers could create laser ablation to cause material to vaporize or volatilize to form the through holes 165, 167(A) and 169(A).

[0099] In general, dielectric tapes are made in wide sheets and then cut to the desired width at high line speed. Punching holes into the tape may generally require lower line speeds. As a result, it may generally be more cost effective to punch the holes as a lead-in to the twisting operation where the tape advances at a much slower rate. There may be other reasons to perform the hole punching in tandem with the twisting operation. One example is that the same tape can be used for twisted pairs with different twist lengths where, for shorter twist lengths perforations are added at a relatively close spacing while for longer twist lengths perforations are added at a relatively long spacing or no perforations are added at all.

[0100] The second, third and fourth twisted pairs 178, 179 and 180 may be similarly formed to the first twisted pair 177 depicted in Figure 10. In other words, the dielectric tape separating the two insulated conductors is formed of a material having a lower compression modulus as compared to the dielectric material used in the insulation layers R1 and R2 surrounding the conductors K. Because the twist lengths between thefirst, second, third and / or fourth twisted pairs are typically selected to be different from each other to substantially reduce internal crosstalk, it is important to balance any delay skew between the twisted pairs.

[0101] It may be beneficial to select different dielectric tape structures to use within the different twisted pairs 177, 178, 179 and 180. For example, dielectric tapes 137, 137A, 137B and / or 137C may have different thicknesses, different materials, different hole sizes, different spacings between holes down the length of the tape and / or different foaming percentages for use in the different twisted pairs 177, 178, 179 and 180.

[0102] For example, all four of the dielectric tapes could be formed as shown in Figure 11 of a same type of material, and all having the same effective average compression modulus at the same temperature. However, a thickness of the dielectric tape used in the first twisted pair 177 is different, such as by at least one mil, as compared to a thickness of at least one of the other dielectric tapes used in the second, third and fourth twisted pairs 178, 179 and 180. Also, the dielectric tape used in the second twisted pair 178 is different, such as by at least one mil, as compared to a thickness of the other dielectric tapes used in the third and fourth twisted pairs 179 and 180. Also, the dielectric tape used in the third twisted pair 179 is different, such as by at least one mil, as compared to a thickness of at least one of the other dielectric tapes. For example, the first and second twisted pairs 177 and 178 use a dielectric tape of a first thickness and the third and fourth twisted pairs 179 and 180 use a dielectric tape of a second, different thickness. Alternatively, different through hole patterns / counts and / or foaming percentages could be used in the four dielectric tapes of the four twisted pairs 177, 178, 179 and 180. Using different dielectric tapes can be useful to balance the various delay skews in the twisted pairs 177, 178, 179 and 180.

[0103] Yet another option is to make all of the dielectric tapes identical and to use a different temperature for one or more of the dielectric tapes to affect the compression modulus of the one or more dielectric tapes. For example, if the dielectric tape for the fourth twisted pair 180 is found to have too low of a compression modulus at ambient temperature, it may be chilled prior to the twisting operation. In other words, the dielectric tape may be brought to a first temperature below the ambient temperature, such as less than fifteen degrees Celsius, or less than ten degrees Celsius, or less than fivedegrees Celsius. Having the dielectric tape of the fourth twisted pair 180 chilled just before the twisting operation within the twinner will increase the compression modulus of the dielectric tape of the fourth twisted pair 180, which will increase the distance 160 for the fourth twisted pair 180. Hence, the more chilled the dielectric tape, the greater the distance 160, which is effectively like increasing the thickness of the dielectric tape.

[0104] If the dielectric tape for the first twisted pair 177 is found to have too high of a compression modulus at ambient temperature, it may be heated just prior to, or during, the twisting operation, such as to more than five degrees Celsius above ambient temperature, or more than ten degrees Celsius above ambient temperature, to decrease its compression modulus. Therefore, by chilling or heating identical dielectric tapes to different temperatures for different twisted pairs 177, 178, 179 or 180, it is effectively the same as using different thicknesses of dielectric tapes within the twisted pairs 177, 178, 179 and 180, which can be another way to tune the impedance to the desired level such as 100 Ohms and / or balance delay skew. Of course, the different chilled or heated dielectric tapes may be used in various combinations with the changed thicknesses, materials, levels of foaming and through hole counts / patterns in order to tune the impedance and / or balance delay skew.

[0105] In addition to the softening, i.e., lowering of the compression modulus, of the dielectric tape relative to the insulation layers R1 and R2 to prevent crushing of the insulation layers R1 and R2 during the twisting operation, the insulation layers R1 and R2 may be pre-chilled before the twisting operation in the twinner to fortify, i.e., increase the compression modulus, of the insulation layers R1 and R2 to resist crush. Also, once the four twisted pairs 177, 178, 179 and 180 are formed in a configuration to tune the impedance and / or balance delay skew, the four twisted pairs 177, 178, 179 and 180 may to chilled to a temperature well below ambient, such as less than ten degrees Celsius, more preferably less than five degrees Celsius, so as to “lock in” the configurations prior to a bunch stranding operation. In the bunch stranders, the first, second, third and fourth twisted pairs 177, 178, 179 and 180 are twisted to form the core strand. The pre-chilling before stranding of the core will minimize any additional crushing which might bring the delay skews out of balance.

[0106] Some examples of cable designs to tune impedance and balance delay skew between the twisted pairs 177, 178, 179 and 180 would be to have the first temperature of the dielectric tape of the first twisted pair 177 less than a temperature of the first insulated conductor 138, which may be at ambient temperature. Another example is having the first temperature of the dielectric tape of the first twisted pair 177 greater than a temperature of the first insulated conductor 138, which may be at ambient temperature. The former example would stiffen the dielectric tape to create more distance between the first and second conductors K of the first and second insulated conductors 138 and 140, while the latter example would lessen the distance between the first and second conductors K of the first and second insulated conductors 138 and 140. Of course, the compression modulus of the dielectric tape in either example should be kept sufficiently low as compared to the compression modulus of the insulation layers R1 and R2 to prevent or substantially minimize crushing of the insulation layers R1 and R2.

[0107] In the formation of the second twisted pair 178, a third insulated conductor 141, a second dielectric tape 190, and a fourth insulated conductor 143 are fed into a twinner for a twisting operation. Prior to the twisting operation, the second dielectric tape 190 is chilled or heated to a second temperature different from the ambient temperature. Then, the twisting operation causes the third insulated conductor 141 to be twisted with the fourth insulated conductor 143 with the second dielectric tape 190 residing between the third insulated conductor 141 and the fourth insulated conductor 143 to form the second twisted pair 178.

[0108] In some embodiments, the second temperature is different from the first temperature so as to influence the spacing between the conductors K within the second twisted pair 178. Alternatively, or in addition, the first dielectric tape 137 has a different thickness as compared to the second dielectric tape 190.

[0109] During the twisting operation, the first dielectric tape 137 is compressed by a first degree between the contact areas of the first and second insulated conductors 138 and 140 to form a first reduced thickness 160. Likewise, the second dielectric tape 190 is compress by a second degree between the contact areas of the third and fourth insulated conductors 141 and 143 to form a second reduced thickness. In some embodiments, the first reduced thickness 160 is different from the second reducedthickness by at least 1 mil. To cause the difference in the reduced thicknesses, first dielectric tape 137 may be heated or chilled to a temperature different from the second dielectric tape 190 just prior to the twisting operation.

[0110] Moreover, the first and second insulated conductors 138 and 140 may be chilled to a third temperature below an ambient temperature prior to the twisting operation to form the first twisted pair 177. Further, the third and fourth insulated conductors 141 and 143 may be chilled to a fourth temperature below an ambient temperature prior to the twisting operation to form the second twisted pair 178. The third and fourth temperatures may be different from each other, such as at least three degree Celsius in difference. Further, the third and fourth temperatures may be less than fifteen degrees Celsius, more preferably less than ten degrees Celsius, such as less than five degrees Celsius. Most preferably, the third and fourth temperatures are less than the first and second temperatures of the dielectric tapes, such as cooler by at least ten degrees Celsius, more preferably cooler by at least twenty degrees Celsius, such as cooler by at least thirty degrees Celsius

[0111] Although the cables illustrated in the drawing figures have included four twisted pairs, it should be appreciated that the present invention is not limited to cables having only four twisted pairs. Cables having other numbers of twisted pairs, such as one twisted pair, two twisted pairs or even twenty-five twisted pairs, could benefit from the structures disclosed in the present invention. The twisted pair twist directions, lengths and modulations, as well as the strand twist directions, lengths and modulations shown in the prior art cables described herein may be employed in the cables in accordance with the present invention.

[0112] Further, although the drawing figures have illustrated that each of the twisted pairs within the cable have a dielectric tape, it would be possible for less than all of the twisted pairs to have the dielectric tape. For example, the first through third twisted pairs could include a dielectric tape, while the fourth twisted pair could be formed without a dielectric tape. Further, although the drawing figures have illustrated an unshielded cable, it is within the scope of the appended claims that the cable could include a shielding layer and / or a core wrap between the core of twisted pairs and the inner wall of the outermost j acket.

[0113] Further, although some drawing figures have illustrated a jacket including fins or projections for creating air pockets around the perimeter of the core of twisted pairs, a jacket having a smooth inner wall is also possible in combination with the embodiments of the invention. Also, the materials employed for the various components of the cable described in conjunction with the prior art cables described herein may be used in the present invention.

[0114] One preferred advantage of the present invention is keeping the thicknesses of the expensive insulation layers R1 and R2 as thin as possible and treating the dielectric tapes between the insulated conductors of the twisted pairs 177, 178, 179 and / or 180 as cheaper, sacrificial compression elements, so that the insulation layers R1 and R2 are not significantly compressed or crushed during a twisting operation. In all of the embodiments herein, the dielectric tapes can be formed by a solid material, a foamed material, a solid material with through holes, or a foamed material with through holes.

[0115] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

We Claim:

1. A cable comprising: a first insulated conductor, a first dielectric tape, and a second insulated conductor, wherein said first insulated conductor is twisted with said second insulated conductor with said first dielectric tape residing between said first insulated conductor and said second insulated conductor to form a first twisted pair; and a jacket formed around said first twisted pair, wherein said first dielectric tape has a first surface extending between first and second side edges of said first dielectric tape, and a second surface, opposite said first surface, and extending between said first and second side edges, wherein a distance between said first and second surfaces defines a thickness of said first dielectric tape; and wherein said first dielectric tape further includes means to reduce an average compression modulus of a material forming said first dielectric tape.

2. The cable according to claim 1, wherein said means to reduce an average compression modulus of a material forming said first dielectric tape include a plurality of through holes, penetrating through said first and said second surfaces.

3. The cable according to claim 2, wherein said plurality of through holes includes a first column of spaced through holes located midway between said first and second side edges.

4. The cable according to claim 2, wherein said plurality of through holes includes a first column of spaced through holes located in a position on said first surface of said first dielectric tape which abuts said first insulated conductor, and a position on said second surface of said first dielectric tape which abuts said second insulated conductor, so as to lower an average effective dielectric constant of materials existing between said first and second insulated conductors.

5. The cable according to claim 2, wherein said plurality of through holes includes a first column of spaced through holes located in a position on said first surface of said firstdielectric tape which abuts said first insulated conductor, and a position on said second surface of said first dielectric tape which abuts said second insulated conductor, so as to lower an average compression modulus of materials existing between said first and second insulated conductors.

6. The cable according to claim 3, wherein a spacing between said through holes in said first column is at least 1.5 times the thickness of said first dielectric tape.

7. The cable according to claim 3, wherein a spacing between said through holes in said first column is at least twice the thickness of said first dielectric tape.

8. The cable according to claim 3, wherein a spacing between said through holes in said first column is at least three times the thickness of said first dielectric tape.

9. The cable according to claim 3, wherein said plurality of through holes further includes a second column of spaced through holes located between said first column of spaced through holes and said first side edge.

10. The cable according to claim 9, wherein said plurality of through holes further includes a third column of spaced through holes located between said first column of spaced through holes and said second side edge, and wherein said first, second and third columns of spaced through holes reduce a tear strength of said first dielectric tape to allow to easier termination to a connector and also reduce materials within said cable.

11. The cable according to claim 10, wherein said first column of spaced through holes is formed by through holes, each having a first dimensional area, and said second and third columns of spaced through holes are formed by through holes, each having a second dimensional area.

12. The cable according to claim 11, wherein the first and second dimensional areas are approximately equal to each other.

13. The cable according to claim 11, wherein the first dimensional area is larger than the second dimensional area.

14. The cable according to claim 10, wherein a line passing through a center of a through hole within said second column of spaced through holes and passing through a center of a through hole within said third column of spaced through holes is perpendicular to both said first side edge and said second side edge.

15. The cable according to claim 14, wherein the line does not pass through a center of a through hole within said first column of spaced through holes.

16. The cable according to claim 15, wherein the line does not pass through any portion of a through hole within said first column of spaced through holes.

17. The cable according to claim 10, wherein a perimeter shape of each through hole within said second and third columns of spaced through holes is circular.

18. The cable according to claim 10, wherein a perimeter shape of each through hole within said first column of spaced through holes is rectangular or square with rounded comers.

19. A method of manufacturing a cable comprising: providing a first insulated conductor, a first dielectric tape, and a second insulated conductor, wherein the first dielectric tape has a first surface extending between first and second side edges of the first dielectric tape, and a second surface, opposite the first surface, and extending between the first and second side edges, and wherein a distance between the first and second surfaces defines a thickness of the first dielectric tape; feeding the first dielectric tape to machine to form a first plurality of through holes, penetrating through the first and said second surfaces;feeding the first insulated conductor, the first dielectric tape with the first plurality of through holes formed therein, and the second insulated conductor to a twinner for a twisting operation; and twisting the first insulated conductor with the second insulated conductor with the first dielectric tape residing between the first insulated conductor and the second insulated conductor to form a first twisted pair.

20. The method according to claim 19, wherein the machine forming the first plurality of through holes is located upstream of the twinner, such that the first dielectric tape passes through the machine to have the first plurality of through holes formed therein and then feeds into the twinner at a common manufacturing line speed.

21. The method according to claim 19, wherein the machine forming the first plurality of through holes feeds the first dielectric tape to a take-up reel, and the take-up reel is moved to the twinner prior to said feeding the first insulated conductor, the first dielectric tape with the first plurality of through holes formed therein, and the second insulated conductor to the twinner.

22. The method according to claim 19, further comprising: chilling or heating the first dielectric tape prior to the twisting operation to a first temperature different from the ambient temperature.

23. The method according to claim 22, wherein the first dielectric tape is heated prior to the twisting operation so as to decrease a compression modulus of the first dielectric tape.

24. The method according to claim 22, wherein the first temperature is greater than a temperature of the first insulated conductor.

25. The method according to claim 19, further comprising:providing a third insulated conductor, a second dielectric tape, and a fourth insulated conductor, wherein the second dielectric tape has a first surface extending between first and second side edges of the second dielectric tape, and a second surface, opposite the first surface, and extending between the first and second side edges, and wherein a distance between the first and second surfaces defines a thickness of the second dielectric tape; feeding the third insulated conductor, the second dielectric tape, and the fourth insulated conductor to a twinner machine for a twisting operation; twisting the third insulated conductor with the fourth insulated conductor with the second dielectric tape residing between the third insulated conductor and the fourth insulated conductor to form a second twisted pair; stranding the first and second twisted pairs together to form a strand; and extruding a jacket around the strand.

26. The method according to claim 25, wherein the thickness of the first dielectric tape is different from the thickness of the second dielectric tape.

27. The method according to claim 25, further comprising: feeding the second dielectric tape to machine to form a second plurality of through holes, penetrating through the first and second surfaces of the second dielectric tape.

28. The method according to claim 27, wherein a spacing between the through holes in the first plurality of through holes is different from a spacing between the through holes in the second plurality of through holes.

29. The method according to claim 27, wherein a size of the though holes in the first plurality of through holes is different from a size of the through holes in the second plurality of through holes.

30. The method according to claim 25, wherein the second dielectric tape has no through holes penetrating through the first and said second surfaces of the second dielectric tape.

31. The cable according to claim 1, wherein said first insulated conductor includes a first conductor surrounded by a layer of first dielectric material having a first compression modulus, said second insulated conductor includes a second conductor surrounded by a layer of second dielectric material having a second compression modulus, and said first dielectric tape is formed of a third dielectric material having a third compression modulus, wherein said first and second dielectric materials are formed of a same type of FEP material, and wherein the third compression modulus is less than 250% of the first compression modulus, at a same temperature.

32. The cable according to claim 1, wherein said first insulated conductor includes a first conductor surrounded by a layer of first dielectric material having a first compression modulus, said second insulated conductor includes a second conductor surrounded by a layer of second dielectric material having a second compression modulus, and said first dielectric tape is formed of a third dielectric material having a third compression modulus, wherein said first and second dielectric materials are formed of a same type of PE material, and the third compression modulus is less than 150% of the first compression modulus, at a same temperature.

33. The cable according to claim 31, wherein the third compression modulus is less than 180% of the first compression modulus, at a same temperature.

34. The cable according to any one of claims 31 or 32, wherein the third compression modulus is less than the first compression modulus, at a same temperature.

35. The cable according to claim 31, further comprising: a third insulated conductor, a second dielectric tape, and a fourth insulated conductor, wherein said third insulated conductor is twisted with said fourth insulatedconductor with said second dielectric tape residing between said third insulated conductor and said fourth insulated conductor to form a second twisted pair, and wherein said first twisted pair is stranded with said second twisted pair to form a stranded core.

36. The cable according to claim 35, wherein said third insulated conductor includes a third conductor surrounded by a layer of third dielectric material having a fourth compression modulus, said fourth insulated conductor includes a fourth conductor surrounded by a layer of fifth dielectric material having a fifth compression modulus, and said second dielectric tape is formed of a sixth dielectric material having a sixth compression modulus, wherein said fourth and fifth dielectric materials are formed of a same type of PE material, wherein the sixth compression modulus is less than 180% of the fourth compression modulus, at a same temperature.

37. The cable according to claim 35, wherein said third insulated conductor includes a third conductor surrounded by a layer of third dielectric material having a fourth compression modulus, said fourth insulated conductor includes a fourth conductor surrounded by a layer of fifth dielectric material having a fifth compression modulus, and said second dielectric tape is formed of a sixth dielectric material having a sixth compression modulus, wherein said first, second, fourth and fifth dielectric materials are formed of a same type of FEP material, and the first compression modulus is the same as the second compression modulus, which is the same as the fourth compression modulus, which is the same as the fifth compression modulus, all at a same temperature, and wherein a thickness of said first dielectric tape is different by at least one mil as compared to a thickness of said second dielectric tape.

38. A method of manufacturing a cable comprising: providing a first insulated conductor, a first dielectric tape, and a second insulated conductor; feeding the first insulated conductor, the first dielectric tape, and the second insulated conductor to a twinner machine for a twisting operation;chilling the first and second insulated conductors to a first temperature different from the ambient temperature, but not the first dielectric tape, prior to the twisting operation; and twisting the first insulated conductor with the second insulated conductor with the first dielectric tape residing between the first insulated conductor and the second insulated conductor to form a first twisted pair.

39. The method according to claim 38, wherein the first temperature is less than 15 degrees Celsius.

40. The method according to claim 38, wherein the first temperature is at least 10 degrees Celsius above ambient temperatures.

41. A method of manufacturing a cable comprising: providing a first insulated conductor, a first dielectric tape, and a second insulated conductor; feeding the first insulated conductor, the first dielectric tape, and the second insulated conductor to a twinner machine for a twisting operation; heating the first dielectric tape to a first temperature different from the ambient temperature, but not the first and second insulated conductors, prior to the twisting operation; and twisting the first insulated conductor with the second insulated conductor with the first dielectric tape residing between the first insulated conductor and the second insulated conductor to form a first twisted pair.

42. The method according to claim 41, wherein the first temperature is greater than a temperature of the first insulated conductor.

43. The method according to claim 41, further comprising: chilling the first and second insulated conductors prior to said twisting operation.

44. The method according to claim 41 , further comprising: providing a third insulated conductor, a second dielectric tape, and a fourth insulated conductor; feeding the third insulated conductor, the second dielectric tape, and the fourth insulated conductor to a twinner machine for a twisting operation; and twisting the third insulated conductor with the fourth insulated conductor with the second dielectric tape residing between the third insulated conductor and the fourth insulated conductor to form a second twisted pair.

45. The method according to claim 44, further comprising: heating the second dielectric tape prior to the twisting operation to a second temperature different from the ambient temperature, wherein the second temperature is different from the first temperature.

46. The method according to claim 44, wherein the first dielectric tape has a different thickness as compared to the second dielectric tape.

47. The method according to claim 44, wherein the first dielectric tape is compressed by a first degree between the contact areas of the first and second insulated conductors to form a first reduced thickness, and the second dielectric tape is compress by a second degree between the contact areas of the third and fourth insulated conductors to form a second reduced thickness, and wherein the first reduced thickness is different from the second reduced thickness by at least 1 mil.

48. The method according to claim 44, wherein the first and second insulated conductors are chilled below an ambient temperature prior to said twisting to form the first twisted pair.

49. The method according to claim 48, wherein the third and fourth insulated conductors are chilled to a temperature below an ambient temperature prior to said twisting to form the second twisted pair.

50. The method according to claim 49, wherein the first and second insulated conductors are chilled to a lower temperature as compared to the third and fourth insulated conductors.

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