Multi-pair cable with varying lay length

[0001] The present disclosure relates generally to cables for use in the telecommunications industry, and various methods associated with such cables. More particularly, this disclosure relates to telecommunication cabling having twisted conductor pairs.

[0002] The telecommunications industry utilizes cabling in a wide range of applications. Some cabling arrangements include twisted pairs of insulated conductors, the pairs being twisted about each other to define a twisted pair core. An insulating jacket is typically extruded over the twisted pair core to maintain the configuration of the core, and to function as a protective layer. Such cabling is commonly referred to as a multi-pair cable.

[0003] The telecommunications industry is continuously striving to increase the speed and/or volume of signal transmissions through such multi-pair cables. One problem that concerns the telecommunications industry is the increased occurrence of crosstalk associated with high-speed signal transmissions.

[0004] In general, improvement has been sought with respect to multi-pair cable arrangements, generally to improve transmission performance by reducing the occurrence of crosstalk.

[0005] One aspect of the present disclosure relates to a multi-pair cable having a plurality of twisted pairs that define a cable core. The cable core is twisted at a varying twist rate such the mean core lay length of the cable core is less than about 2.5 inches. Another aspect of the present disclosure relates to a method of making a cable having a varying twist rate with a mean core lay length of less than about 2.5 inches. Still another aspect of the present disclosure relates to the use of a multi-pair cable in a patch cord, the cable being constructed to reduce crosstalk at a connector assembly of the patch cord.

[0006] A variety of examples of desirable product features or methods are set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing various aspects of the disclosure. The aspects of the disclosure may relate to individual features as well as combinations of features. It is to be understood that both the foregoing general description and the following detailed description are explanatory only, and are not restrictive of the claimed invention.

[0024] Reference will now be made in detail to various features of the present disclosure that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0025] FIG. 1 illustrates one embodiment of a cable 10 having features that are examples of how inventive aspects in accordance with the principles of the present disclosure may be practiced. Preferred features are adapted for reducing crosstalk between twisted pairs of the cable, and for reducing crosstalk between adjacent cables.

[0026] Referring to FIG. 1, the cable 10 of the present disclosure includes a plurality of twisted pairs 12. In the illustrated embodiment, the cable 10 includes four twisted pairs 12. Each of the four twisted pairs includes first and second insulated conductors 14 twisted about one another along a longitudinal pair axis (see FIG. 3).

[0027] The conductors of the insulated conductors 14 may be made of copper, aluminum, copper-clad steel and plated copper, for example. It has been found that copper is an optimal conductor material. In one embodiment, the conductors are made of braided copper. One example of a braided copper conductor construction that can be used is described in greater detail in U.S. Pat. No. 6,323,427, which is incorporated herein by reference. In addition, the conductors may be made of glass or plastic fiber such that a fiber optic cable is produced in accordance with the principles disclosed. The insulating layer of the insulated conductors 14 can be made of known materials, such as fluoropolymers or other electrical insulating materials, for example.

[0028] The plurality of twisted pairs 12 of the cable 10 defines a cable core 20. In the illustrated embodiment of FIG. 1, the core 20 includes only the plurality of twisted pairs 12. In alternative embodiments, the core may also include a spacer that separates or divides the twisted pairs 12. FIG. 2 illustrates one example of a star-type spacer 22 (represented in dashed lines) that can be used to divide the four twisted pairs 12a-12d. Other spacers, such as flexible tape strips or fillers defining pockets and having retaining elements that retain each of the twisted pairs within the pockets, can also be used. Additional spacer examples that can be used are described in U.S. patent application Ser. Nos. 10/746,800, 10/746,757, and 11/318,350; which applications are incorporated herein by reference.

[0029] Referring now to FIGS. 1 and 2, in one embodiment, the cable 10 includes a double jacket 18 that surrounds the core 20 of twisted pairs 12. The double jacket 18 includes both a first inner jacket 24 and a second outer jacket 26. The inner jacket 24 surrounds the core 20 of twisted pairs 12. The outer jacket 26 surrounds the inner jacket 24. The inner and outer jackets 24, 26 function not only to maintain the relative positioning of the twisted pairs 12, but also to lessen the occurrence of alien crosstalk without utilizing added shielding.

[0030] In particular, the addition of the outer jacket 26 to the cable 10 reduces the capacitance of the cable 10 by increasing the center-to-center distance between the cable 10 and an adjacent cable. Reducing the capacitance by increasing the center-to-center distance between two adjacent cables reduces the occurrence of alien crosstalk between the cables. Accordingly, the outer jacket 26 has an outer diameter OD1 (FIG. 2) that distances the core 20 of twisted pairs 12 from adjacent cables. Ideally, the cores 20 of twisted pairs 12 of adjacent cables are as far apart as possible to minimize the capacitance between adjacent cables.

[0031] There are, however, limits to how far apart the double jacket 18 can place one cable from an adjacent cable. Practical, as well as economical constraints are imposed on the size of the resulting double jacket cable. A cable cannot be so large that it is impractical to use in an intended environment, and cannot be so large as to preclude use with existing standard connectors. In the illustrated embodiment, the outer diameter OD1 (FIG. 2) of the outer jacket 26 is between about 0.295 inches and 0.310 inches.

[0032] The disclosed double jacket is provided as two separate inner and outer jackets 24, 26, as opposed to a single, extra thick jacket layer. This double jacket feature reduces alien crosstalk by distancing the cores of adjacent cables, while at the same time, accommodating existing design limitations of cable connectors. For example, the double jacket 18 of the present cable 10 accommodates cable connectors that attach to a cable jacket having a specific outer diameter. In particular, the present cable 10 permits a user to strip away a portion of the outer jacket 26 (see FIG. 1) so that a cable connector can be attached to the outer diameter OD2 of the inner jacket 24. In the illustrated embodiment, the inner jacket 24 has an outer diameter OD2 of between about 0.236 and 0.250 inches.

[0033] The inner jacket 24 and the outer jacket 26 of the present cable 10 can be made from similar materials, or can be made of materials different from one another. Common materials that can be used to manufacture the inner and outer jackets include plastic materials, such as fluoropolymers (e.g. ethylenechlorotrifluorothylene (ECTF) and Flurothylenepropylene (FEP)), polyvinyl chloride (PVC), polyethelene, or other electrically insulating materials, for example. In addition, a low-smoke zero-halogen material, such as polyolefin, can also be used. While these materials are used because of their cost effectiveness and/or flame and smoke retardancy, other material may be used in accordance with the principles disclosed.

[0034] In the manufacture of the present cable 10, two insulated conductors 14 are fed into a pair twisting machine, commonly referred to as a twinner. The twinner twists the two insulated conductors 14 about the longitudinal pair axis at a predetermined twist rate to produce the single twisted pair 12. The twisted pair 12 can be twisted in a right-handed twist direction or a left-handed twist direction.

[0035] Referring now to FIG. 3, each of the twisted pairs 12 of the cable 10 is twisted about its longitudinal pair axis at a particular twist rate (only one representative twisted pair shown). The twist rate is the number of twists completed in one unit of length of the twisted pair. The twist rate defines a lay length L1 of the twisted pair. The lay length L1 is the distance in length of one complete twist cycle. For example, a twisted pair having a twist rate of 0.250 twists per inch has a lay length of 4.0 inches (i.e., the two conductors complete one full twist, peak-to-peak, along a length of 4.0 inches of the twisted pair).

[0036] In the illustrated embodiment, each of the twisted pairs 12a-12d of the cable 10 has a lay length L1 or twist rate different from that of the other twisted pairs. This aids in reducing crosstalk between the pairs of the cable core 20. In the illustrated embodiment, the lay length L1 of each of the twisted pairs 12a-12d is generally constant, with the exception of variations due to manufacturing tolerances. In alternative embodiments, the lay length may be purposely varied along the length of the twisted pair.

[0037] Each of the twisted pairs 12a-12d of the present cable 10 is twisted in the same direction (i.e., all in the right-hand direction or all in the left-hand direction). In addition, the individual lay length of each of the twisted pairs 12a-12d is generally between about 0.300 and 0.500 inches. In one embodiment, each of the twisted pairs 12a-12d is manufactured with a different lay length, twisted in the same direction, as shown in Table A below.

[0038]

TABLE A
	Twist Rate
Twisted Pair	(twists per inches)	Lay Length L1 (inches)
12a	3.03 to 2.86	.330 to .350
12b	2.56 to 2.44	.390 to .410
12c	2.82 to 2.67	.355 to .375
12d	2.41 to 2.30	.415 to .435

[0039] In the illustrated embodiment, the first twisted pair 12a (FIG. 2) has a lay length of about 0.339 inches; the second twisted pair 12b has a lay length of about 0.400 inches; the third twisted pair 12c has a lay length of about 0.365 inches; and the fourth twisted pair 12d has a lay length of about 0.425 inches. As will be described in greater detail hereinafter, each of the lay lengths L1 of the twisted pairs described above are initial lay lengths.

[0040] The cable core 20 of the cable 10 is made by twisting together the plurality of twisted pairs 12a-12d at a cable twist rate. The machine producing the twisted cable core 20 is commonly referred to as a cabler. Similar to the twisted pairs, the cable twist rate of the cable core 20 is the number of twists completed in one unit of length of the cable or cable core. The cable twist rate defines a core or cable lay length of the cable 10. The cable lay length is the distance in length of one complete twist cycle.

[0041] In manufacturing the present cable 10, the cabler twists the cable core 20 about a central core axis in the same direction as the direction in which the twisted pairs 12a-12d are twisted. Twisting the cable core 20 in the same direction as the direction in which the twisted pairs 12a-12d are twisted causes the twist rate of the twisted pairs 12a-12d to increase or tighten as the cabler twists the pairs about the central core axis. Accordingly, twisting the cable core 20 in the same direction as the direction in which the twisted pairs are twisted causes the lay lengths of the twisted pairs to decrease or shorten.

[0042] In the illustrated embodiment, the cable 10 is manufactured such that the cable lay length varies between about 1.5 inches and about 2.5 inches. The varying cable lay length of the cable core 20 can vary either incrementally or continuously. In one embodiment, the cable lay length varies randomly along the length of the cable 10. The randomly varying cable lay length is produced by an algorithm program of the cabler machine.

[0043] Because the cable lay length of the cable 10 is varied, the once generally constant lay lengths of the twisted pairs 12a-12b are now also varied; that is, the initial lay lengths of the twisted pairs 12 now take on the varying characteristics of the cable core 20. In the illustrated embodiment, with the cable core 20 and each of the twisted pairs 12a-12d twisted in the same direction at the cable lay length of between 1.5 and 2.5 inches, the now varying lay lengths of each of the twisted pairs fall between the values shown in columns 3 and 4 of Table B below.

[0044]

TABLE B
	Initial Lay	Approx. Lay	Approx. Lay	Resulting Mean
	Length prior	Length w/Cable	Length w/Cable	Lay Length after
	to Core Twist	Lay Length of 1.5	Lay Length of 2.5	Core Twist
Twisted Pair	(inches)	(inches)	(inches)	(inches)
12a	.339	.2765	.2985	.288
12b	.400	.3158	.3448	.330
12c	.365	.2936	.3185	.306
12d	.425	.3312	.3632	.347

[0045] As previously described, the cable lay length of the cable core 20 varies between about 1.5 and about 2.5 inches. The mean or average cable lay length is therefore less than about 2.5 inches. In the illustrated embodiment, the mean cable lay length is about 2.0 inches.

[0046] Referring to Table B above, the first twisted pair 12a of the cable 10 has a lay length of about 0.2765 inches at a point along the cable where the point specific lay length of the core is 1.5 inches. The first twisted pair 12a has a lay length of about 0.2985 inches at a point along the cable where the point specific lay length of the core is 2.5 inches. Because the lay length of the cable core 20 is varied between 1.5 and 2.5 inches along the length of the cable 10, the first twisted pair 12a accordingly has a lay length that varies between about 0.2765 and 0.2985 inches. The mean lay length of the first twisted pair 12a resulting from the twisting of the cable core 20 is 0.288 inches. Each of the other twisted pairs 12b-12d similarly has a mean lay length resulting from the twisting of the cable core 20. The resulting mean lay length of each of the twisted pairs 12a-12d is shown in column 5 of Table B. It is to be understood that the mean lay lengths are approximate mean or average lay length values, and that such mean lay lengths may differ slightly from the values shown due to manufacturing tolerances.

[0047] Twisted pairs having similar lay lengths (i.e., parallel twisted pairs) are more susceptible to crosstalk than are non-parallel twisted pairs. The increased susceptibility to crosstalk exists because interference fields produced by a first twisted pair are oriented in directions that readily influence other twisted pairs that are parallel to the first twisted pair. Intra-cable crosstalk is reduced by varying the lay lengths of the individual twisted pairs over their lengths and thereby providing non-parallel twisted pairs.

[0048] The presently described method of providing individual twisted pairs with the particular disclosed varying lay lengths produces advantageous results with respect to reducing crosstalk and improving cable performance. In one application, the features of the present cable 10 can be used to provide an improved patch cord.

[0049] Referring now to FIG. 4, one embodiment of a patch cord 50 manufactured in accordance with the principles disclosed is illustrated. The patch cord 50 includes the cable 10 previously described. Connector assemblies or jacks 30 are attached at each end of the cable 10. In the illustrated embodiment, each of the jacks 30 includes a connector housing 32, a plug housing 34, and a channeled insert 36. Each of the connector housing 32, the plug housing 34, and the channeled insert 36 includes structure that provides a snap-fit connection between one another. Other types of jacks can be used in accordance with the principles disclosed. One other type of jack that can be used is described in U.S. patent application Ser. No. 11/402,250; which application is incorporated herein by reference.

[0050] Referring now to FIGS. 5-7, the connector housing 32 of the disclosed jack 30 has a strain relief boot 38 sized to fit around the outer diameter OD2 of the inner jacket 24 (FIG. 1). During assembly, the connector housing 32 is positioned such that the end of the inner jacket 24 is flush with a surface 40 (FIGS. 5 and 6) of the connector housing 32. Referring to FIG. 1, the outer jacket 26 is stripped away from the inner jacket 24 a distance to accommodate the length of the strain relief boot 38 and permit the flush positioning of the inner jacket 24 relative to the connector housing 32. The plurality of twisted pairs 12 extends through the connector housing 32 (FIG. 5) when the connector housing 32 is placed on the end of the cable 10.

[0051] When the connector housing 32 is in place, as shown in FIG. 5, the channeled insert 36 (FIG. 8) is snap fit to the connector housing 32. The connector housing 32 has a somewhat loose fit about the outer diameter OD2 of the inner jacket 24. Snap-fitting the channeled insert 36 to the connector housing 32 secures the connection of the jack 30 (i.e., of the channeled insert 36 and the connected connector housing 32) to the cable 10. In particular, referring to FIGS. 8-10, the channeled insert 36 includes a number of flexible prongs 56. The connector housing 32 includes a ramped interior surface 58 (FIG. 6). When the prongs 56 of the channeled insert 36 are inserted within the connector housing 32, the ramped interior surface 58 of the connector housing 32 contacts and radially biases the prongs 56 inward. This causes the prongs 56 to clamp around the outer diameter OD2 of the inner jacket 24, and thereby secure the jack 30 to the end of the cable 10.

[0052] Referring to FIGS. 8 and 9, the channeled insert 36 further defines four pair-receiving apertures 42a-42d (FIG. 9) and eight channels 44 (FIG. 8). Each of the pair-receiving apertures 42a-42d receives one of the twisted pairs 12. Each of the channels 44 receives one of the insulated conductors 14 of the twisted pairs 12. The apertures 42a-42d of the channeled insert 36 separate and position each of the twisted pairs 12 for placement within the channels 44, as shown in FIG. 11.

[0053] In the illustrate embodiment of FIG. 11, the conductors 14 of the second twisted pair 12b are positioned within the channels 44 at positions 1-2; the conductors 14 of the third twisted pair 12c are positioned within the channels 44 at positions 4-5; and the conductors 14 of the fourth twisted pair 12d are positioned within the channels 44 at positions 7-8. The first twisted pair 12a is known as the split pair; the conductors 14 of the split pair 12a are positioned within the channels 44 at position 3-6. Other wire placement configurations can be utilized in accordance with the principles disclosed, depending upon the requirements of the particular application. When the conductors 14 of each of the twisted pairs 12a-12d are properly positioned with the channeled insert 36, the conductors 14 are trimmed, as shown in FIG. 12.

[0054] Referring back to FIG. 4, with the conductors 14 trimmed, the plug housing 34 of the jack 30 is snap-fit onto the connector housing 32 and the channeled insert 36. The plug housing 34 includes eight contacts (not shown) located to correspondingly interconnect with the eight insulated conductors 14 of the twisted pairs 12. The eight contacts of the plug housing 34 include insulation displacement contacts that make electrical contact with the conductors 14. In the illustrated embodiment, the conductors 14 of the second twisted pair 12b terminate at contact positions 1-2; the conductors of the first twisted pair 12a (the split pair) terminate at contact positions 3-6; the conductors of the third twisted pair 12c terminate at contact positions 4-5; and the conductors of the fourth twisted pair 12d terminate at contact positions 7-8.

[0055] As previously described, the jack 30 is secured to the end of the cable 10 by the clamping force of the prongs 56 on the outer diameter OD2 of the inner jacket 24. To further ensure the relative securing of the jack 30 and the cable 10, additional steps are taken. In particular, as shown in FIG. 6, a through hole 46 is provided in the connector housing 32 of the jack 30. The through hole 46 extends from a first side 48 of the connector housing 32 to a second opposite side 52. In the illustrated embodiment, the through hole 46 is approximately 0.063 inches in diameter. As shown in FIG. 13, adhesive 54 is deposited within the hole 46 to form a bond between the inner jacket 24 and the connector housing 32 of the jack 30. The adhesive ensures that the jack 30 remains in place relative to the end of the cable 10.

[0056] In general, to promote circuit density, the contacts of the jacks 30 are required to be positioned in fairly close proximity to one another. Thus, the contact regions of the jacks are particularly susceptible to crosstalk. Furthermore, contacts of certain twisted pairs 12 are more susceptible to crosstalk than others. In particular, crosstalk problems arise most commonly at contact positions 3-6, the contact positions at which the split pair (e.g., 12a) is terminated.

[0057] The disclosed lay lengths of the twisted pairs 12a-12b and of the cable core 20 of the disclosed patch cord 50 reduce problematic crosstalk at the split pair 12a. Test results that illustrate such advantageous cable or patch cord performance are shown in FIGS. 14-17.

[0058] Referring to FIG. 14, test results of the performance of a first patch cord having four twisted pairs are illustrated. Each of the twisted pairs of the first patch cord has a particular initial twist rate different from that of the others. The cable core defined by the four twisted pairs of this first patch cord is twisted at a constant rate that defines a constant lay length of 2.0 inches. The test results show that the twisted pair (the split pair) corresponding to contact positions 3-6 (Pair 36) experiences an unacceptable level of signal coupling (e.g., noise transmission or cross talk). In particular, the split Pair 36 exceeds a maximum limit shown in FIG. 14 by as much as 2.96 decibels at a frequency of 486.9 MHz. This amount of signal coupling falls outside the acceptable performance standards established by the telecommunications industry.

[0059] FIG. 15 illustrates the performance of a second patch cord having four twisted pairs, each twisted pair having the same particular initial twist rate as that of the first patch cord represented in FIG. 14. In accord with the principles disclosed, however, the cable core defined by the four twisted pairs of this second patch cord is randomly twisted such that the patch cord has a randomly varying lay length of between 1.5 inches and 2.5 inches. The test results show that none of the twisted pairs, including the split pair corresponding to contact position 3-6 (Pair 36), experiences an unacceptable level of signal coupling. Rather, the split Pair 36, for example, has its greatest signal coupling at a frequency of 447.61. At this frequency, the split Pair 36 still has not reached the maximum limit, and is in fact 4.38 decibels from the maximum limit. This amount of signal coupling falls within the acceptable performance standards established by the telecommunications industry.

[0060] FIGS. 16 and 17 illustrate similar cable performance test results. FIG. 16 illustrates the overall signal transmission/signal coupling performance of the first patch cord having the constant lay length of 2.0 inches. The first patch cord exceeds the maximum limit shown in FIG. 16 by as much as 0.57 decibels at a frequency of 484.41 MHz. This amount of signal coupling falls outside the acceptable performance standards established by the telecommunications industry. In contrast, FIG. 17 illustrates the second patch cord manufactured with the randomly varying lay length of between 1.5 and 2.5 inches. The second patch cord experiences its greatest signal coupling at a frequency of 446.98 MHz. At this frequency, the second patch cord still has not reached the maximum limit, and is in fact 3.09 decibels from the maximum limit. This amount of signal coupling falls within the acceptable performance standards established by the telecommunications industry.

[0061] The patch cord 50 of the present disclosure reduces the occurrence of crosstalk at the contact regions of the jacks, while still accommodating the need for increased circuit density. In particular, the cable 10 of the patch cord 50, reduces the problematic crosstalk that commonly arise at the split pair contact positions 3-6 of the patch cord jack. The reduction in crosstalk at the split pair (e.g., 12a) and at the contacts of the jack 30 enhances and improves the overall performance of the patch cord.

[0062] The above specification provides a complete description of the present invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, certain aspects of the invention reside in the claims hereinafter appended.