Abstract:
A cable includes a round core having at least one twisted pair of insulated wires. A jacket surrounds the core, and the jacket includes at least one spline projecting inward from an inner surface of the jacket, wherein at least a portion of the twisted pair is positioned between the spline and a center of the core. The spline extends continuously on the inner surface of the jacket along a longitudinal axis of the core.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates generally to communications cable, cabling, and cordage, and more particularly, to twisted pair cabling with jackets surrounding a cable core.  
         [0002]     Communication cables typically include a number of insulated wires therein. In order to minimize the problem of interference and random noise between the wires, the wires in the cable are generally twisted in pairs. At least one type of high-speed data communications cable includes a core having a filler material, a number of twisted pairs arranged around the filler material, and an insulative jacket surrounding the core. The twisted pairs are arranged in a manner to optimize performance in terms of impedance, attenuation, skew, and cross talk, among other things, for high-speed data and communication networks.  
         [0003]     Certain types of cable have been found to meet frequency response specifications when tested at certain frequencies, according to, for example, the Telecommunications Industry Association and Electronics Industry Association category 5 and category 6 standards. When installed, however, the cables have not proven to consistently perform to their design standards. It is believed that manipulation and handling of the cable during manufacturing, distribution and installation sometimes causes relative movement between the cable jacket and the cable core. Relative movement of the cable jacket and the core can negatively impact cable performance, including, among other things, the “headroom” of the cable, or the differential between the frequency response of the cable at a test frequency and the maximum limit of the cable design. Thus, as the headroom is reduced, the ability of the cable to perform at higher frequencies is compromised. In the midst of increasing frequencies used in modern telecommunications and computer applications, the headroom of the cabling used in such a system is becoming increasingly important.  
         [0004]     Some twisted pair cables are known to include separate compartments for each twisted pair in the cable. The compartments are formed through either the configuration of the jacket or with a separator structure encased by the jacket to prevent movement of the twisted pairs and to prevent crosstalk between the twisted pairs. See for example, U.S. Pat. Nos. 4,777,325 and 6,284,954. The jacket configurations and/or the separation structures, however, add additional cost and complexity to the cable, and can reduce the flexibility of the cable and hence make it more difficult to install. It would be desirable to preserve the headroom of a cable design for maximum performance of the cable in the field at a lower cost and without adversely affecting the flexibility of the cable.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     In an exemplary embodiment, a cable is provided which comprises a round core comprising at least one twisted pair of insulated wires. A jacket surrounds the core, and the jacket comprises at least one spline projecting inward from an inner surface of the jacket, wherein at least a portion of the twisted pair is positioned between the spline and a center of the core.  
         [0006]     Optionally, the core comprises a filler and a plurality of twisted pairs arranged around the filler. The jacket comprises a plurality of splines projecting inward from an inner surface of the jacket and the splines extend continuously on the inner surface of the jacket. The splines extend along a longitudinal axis of the core and the splines are equally spaced from one another.  
         [0007]     In another exemplary embodiment, a cable is provided. The cable comprises a core comprising a central core filler and a plurality of twisted pairs of insulated wires extending about the core filler, and a jacket surrounds the core. The jacket comprises a round inner surface and at least one spline projecting inward from the inner surface, wherein the at least one spline is adapted to prevent relative movement of the jacket and core without separating one of the plurality of twisted pairs from another of the plurality of twisted pairs.  
         [0008]     According to another exemplary embodiment, a cable is provided. The cable comprises a round core comprising a central core filler and a plurality of twisted pairs of insulated wires extending about the core filler. A round jacket surrounds the core, and the jacket comprises an inner surface and a plurality of splines projecting inward from the inner surface. The plurality of splines are adapted to prevent relative movement of the jacket and core without separating the plurality of twisted pairs from one another. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  illustrates an exemplary cable formed in accordance with an exemplary embodiment of the invention with the jacket partially peeled from the cable core.  
         [0010]      FIG. 2  is a perspective view of the cable core shown in  FIGS. 1 and 2  with the jacket unwrapped.  
         [0011]      FIG. 3  is a cross sectional view of the cable shown in  FIG. 1  along line  3 - 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  illustrates a cable  10  formed in accordance with an exemplary embodiment of the invention. For the reasons explained below, the cable  10  is configured to preserve and protect the headroom of the cable  10  (i.e., the differential between the frequency response of the cable at a test frequency and the maximum limit of the cable) during handling of the cable  10  to optimize the performance potential and consistency of the cable  10  in use in for, example, a high-speed communications or data system  
         [0013]     The cable  10  includes a core  12  and a jacket  14  surrounding the core  12 . The core  12  includes a round filler  16  and a number of insulated wires  18  extending around the filler  16  and arranged in twisted pairs. In the illustrated embodiment, eight wires  18  are arranged in four pairs about the filler  16 . It is appreciated, however, that greater or fewer numbers of wires  18  may be employed in greater or fewer numbers of pairs in alternative embodiments. The filler  16  and the wires  18  are fabricated from known materials familiar to those in the art. It is appreciated that filler  16  may be formed in various alternative shapes to the round or cylindrical shaped filler  16  illustrated in  FIG. 1 .  
         [0014]     The jacket  14  surrounds the core  12  and is fabricated from a known insulative, i.e., nonconductive, material. The jacket  14  includes a smooth inner surface  20 , and a number of ribs or splines  22  extending inward from the inner surface  22  toward the core  12 . When the jacket  14  is in place over the core  12 , the splines  22  maintain the core  12  is position relative to the jacket  14 . That is, as the cable  10  is handled and manipulated, whether in manufacturing, distribution, or installation of the cable  10 , the splines  22  secure the core  12  in a stationary position relative to the jacket  14 . As such, the headroom of the cable  10  will not be influenced or affected by handling and installation of the cable  10 .  
         [0015]      FIG. 2  is a perspective view of the cable  10  with the jacket  14  unwrapped from the core  12 . The core  12  extends generally along a longitudinal axis  30  of the cable  10 , and the wires  18  in the core  12  are arranged with the filler  16  according to, for example, a left hand lay as those in the art will appreciate. It is appreciated that the filler  16  and the wires  18  may be alternatively arranged and configured in different embodiments. The lay length or technique of the wires  18  may be varied to achieve particular objectives or specifications of the cable  10  for a particular use.  
         [0016]     The lay of the wires  18  in the twisted pairs forms a wavy outer profile wherein portions  32  of the outer surfaces of the wires  18  are located a greater radial distance from the longitudinal axis  30  than other portions  34  of the wires  18 . The inner surface  20  of the jacket  14  contacts the portions  32  of the wires  18 , and the splines  22  of the jacket  14  extend adjacent the portions  32  of some of the wires  18 . Therefore, by positioning some of the portions  32  adjacent to or against the splines  22 , the portions  32  of the wires  18  contact the splines  22  and prohibit the core  12  from moving or shifting relative to the jacket  14  as the cable  10  is handled. Alternatively, the splines  22  contact the jacket  14  and prevent the jacket  14  from moving or shifting relative to the core  12  as the cable  10  is handled. Rather, as one of the core  12  and the jacket  14  rotates about the longitudinal axis  30  in the direction of arrow A, the other of the core  12  and the jacket  14  rotates an equal amount about the longitudinal axis  30  and the relative position of the core  12  and the jacket  14  is preserved or maintained.  
         [0017]     The splines  22  extend continuously along the length of the cable  10  and also extend substantially parallel to the longitudinal axis  30  and to one another. While longitudinally extending splines  22  have been found effective to prevent the core  12  from moving relative to the jacket  14 , and vice-versa, it is understood that the splines  22  may be otherwise oriented in alternative embodiments. It is also contemplated that the splines  22  need not be continuous to substantially achieve the benefits of the instant invention. That is, the splines  22  may extend for less than an entire length of the cable  10  (i.e., in a direction of arrow B), and the splines  22  may include gaps along the length of the splines in various alternative embodiments.  
         [0018]      FIG. 3  is a cross sectional view of the cable  10  illustrating the wires  18  arranged in four pairs  40  about the filler  16  which is centrally located in the cable  10 . Each of the wires  18  includes a conductor  42  and insulation  44  surrounding the conductor  42 . The conductor  42  and the insulation  44  of the wires  18  are fabricated from known materials and are dimensioned appropriately to carry electrical signals suitable to meet the needs of the communication or data system associated with the cable  10 .  
         [0019]     The splines  22  extend radially inward from the round or cylindrical inner surface  20  of the jacket  14  for a small distance sufficient to prevent relative movement of the core  12  and jacket  14 , but insufficient to significantly affect the overall flexibility of the cable  10 . Additionally, and as illustrated in  FIG. 3 , the wires  18  are located between the ends of the splines  22  and the filler  16  of the core  12 . Thus, while the splines  22  prevent relative movement of the core  12  and the jacket  14 , the splines  22  do not separate the wires  18  from one another.  
         [0020]     An outer surface  50  of the jacket  14  is cylindrical or round, therefore minimizing material costs for the jacket  14 . The jacket  14  may be extruded over the core  12  during the manufacture of the cable  10 , although it is appreciated that the jacket  14  may be formed and/or extended over the core  12  according to other processes and techniques known in the art. The jacket  14  may further be formed into another shape in an alternative embodiment in lieu of a round jacket as illustrated in  FIG. 3 .  
         [0021]     In the illustrated embodiment, four splines  22  are provided that are equally spaced from one another. Greater or fewer numbers of splines  22 , however, may be employed in various alternative embodiments of the invention. While substantially rectangular splines  22  are illustrated in  FIG. 3 , other shapes of splines, including but not limited to triangular shaped splines, may be employed in different embodiments. Also, while radially extending splines  22  are illustrated, the invention is not considered so limited. Other arrangement of splines  22  may be provided which also achieve a stationary arrangement of the core  12  and the jacket  14 .  
         [0022]     The splines  22  are provided at relatively low cost to the cable  10  and prevent the core  12  and the jacket  14  from moving relative to one another. Associated degraded performance of the cable  10  is therefore avoided and the headroom of the cable is preserved for optimal signal transmission through the cable  10 . The flexibility of the cable  10  is substantially unaffected while consistent performance and reliability for high frequency networking applications is achieved.  
         [0023]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.