Abstract:
A hybrid cable includes a cable jacket, elements stranded within the cable jacket, and armor between the elements and the cable jacket. The armor is configured to provide electro-magnetic interference shielding and grounding as well as crush and impact resistance for the hybrid cable. The elements include electrical-conductor elements and one or more fiber-optic elements. The electrical-conductor elements include a metallic conductor jacketed in a polymer, where the electrical-conductor elements are each within the range of 10 American wire gauge (AWG) to 1\0 AWG. The one or more fiber-optic elements include optical fibers within a polymeric tube. At least six of the elements are stranded side-by-side with one another around a central element, which is one of the electrical-conductor elements or one of the one or more fiber-optic elements.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/680,011 filed on Aug. 6, 2012, the content of which is relied upon and incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Aspects of the present disclosure relate generally to hybrid cables that include both fiber-optic and conductor elements, which may be stranded together for use in fiber-to-the-antenna (FTTA) type applications. 
         [0003]    Cellular service providers may deploy Remote Radio Head (RRH) solutions throughout their antenna networks, a process that involves locating power radio frequency (RF) amplifiers at the top of the antenna (e.g., cell tower; radio tower; cell site). Remote Radio Head (RRH) solutions accordingly require cabling arrangements that deliver both power for the amplifiers and the high bandwidth capabilities of a fiber cable. Handling and routing of multiple cables, such as separate power cables and fiber optic cables, may be cumbersome, and may result in redundant armoring and jacketing as well as wasted space in ducts or other routing guides between the base and top of an antenna tower. A need exists for a hybrid cable arrangement that combines electrical conductors with fiber optic cables under a single cable jacket in a space-efficient manner, while still providing low attenuation of the optical fibers carried by the optical elements of the cable. 
       SUMMARY 
       [0004]    One embodiment relates to a hybrid cable, which includes a cable jacket, elements stranded within the cable jacket, and armor between the elements and the cable jacket. The armor is configured to provide electro-magnetic interference shielding and grounding as well as crush and impact resistance for the hybrid cable. The elements include electrical-conductor elements and one or more fiber-optic elements. The electrical-conductor elements include a metallic conductor jacketed in a polymer, where the electrical-conductor elements are each within the range of 10 American wire gauge (AWG) to 1\0 AWG. The one or more fiber-optic elements include optical fibers within a polymeric tube. At least six of the elements are stranded side-by-side with one another around a central element, which is one of the electrical-conductor elements or one of the one or more fiber-optic elements. 
         [0005]    Another embodiment relates to a hybrid cable, which includes a cable jacket and elements stranded within the cable jacket. The elements include electrical-conductor elements and one or more fiber-optic elements. The electrical-conductor elements include a metallic conductor jacketed in a polymer, and the one or more fiber-optic elements include optical fibers within a polymeric tube. At least six of the elements are stranded around a central element that is one of the electrical-conductor elements. The at least six of the elements and the central element are round in cross-section and have a diameter that is within 15% of the diameter of the largest one of the diameters of the at least six of the elements and the central element. 
         [0006]    Yet another embodiment relates to a hybrid cable, which includes a cable jacket, elements stranded within the cable jacket, and armor between the elements and the cable jacket. The armor is configured to provide electro-magnetic interference shielding and grounding as well as crush and impact resistance for the hybrid cable. The elements include electrical-conductor elements and one or more fiber-optic elements. The electrical-conductor elements include a metallic conductor jacketed in a polymer, where the electrical-conductor elements are each within the range of 10 American wire gauge (AWG) to 1\0 AWG. The one or more fiber-optic elements include optical fibers within a polymeric tube. At least six of the elements are stranded around a central element that is one of the electrical-conductor elements, and the at least six of the elements and the central element are round in cross-section, having a diameter that is within 15% of the diameter of the largest one of the diameters of the at least six of the elements and the central element. 
         [0007]    Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The accompanying Figures are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the Detailed Description serve to explain principles and operations of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which: 
           [0009]      FIG. 1  is a sectional view of a hybrid cable according to an exemplary embodiment. 
           [0010]      FIG. 2  is a sectional view of a hybrid cable according to another exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Before turning to the Figures, which illustrate exemplary embodiments in detail, it should be understood that the present inventive technology is not limited to the details or methodology set forth in the Detailed Description or illustrated in the Figures. For example, as will be understood by those of ordinary skill in the art, features and attributes associated with embodiments shown in one of the Figures may be applied to embodiments shown in others of the Figures. 
         [0012]    Hybrid cables (e.g., cables of  FIGS. 1-2  disclosed herein) include electric-conductor and fiber-optic elements stranded (e.g., helically wound) for enhanced performance of associated optical fibers as well as overall cable flexibility, where the electric-conductor elements are relatively-high capacity conductors ranging from 10 AWG to 1/0 AWG (i.e., about 5.26-53.5 mm 2  area, about 2.588-8.252 mm diameter, about 3.86-1.21 turns of wire per cm, and about 3.277-0.3224 Ω/km for stranded wires, or the equivalent). Typically such heavy conductors may not be stranded due to the associated forces required to bend and constrain the conductors, and/or because stranding adds length, increasing cable manufacturing expenses due to material costs (e.g., copper conductors). However, Applicants have found that stranding the fiber optic subunits with the conductors provides a robust hybrid cable, with improved data transmission via less attenuation of the optical fibers. 
         [0013]    Aspects of the present disclosure relate to the placement and size of the individual stranded elements of the hybrid cables in order to improve the cost, size, and data-transmission performance of the cable. Stable hybrid cable cores, due to stranding as well as the placement and size of the stranded elements as disclosed herein, also contribute to improved long-term performance, weather-ability, and stability of the cable due to enhanced mechanical coupling between the stranded elements. 
         [0014]    Referring to  FIG. 1 , a hybrid cable  110  includes elements  112 ,  114  stranded around a central element  116 . The elements  112 ,  114  include stranded copper conductors  118  (e.g., 8 AWG) insulated in polyvinyl chloride (PVC) jackets  120  (or another polymeric material, such as fire-retardant (FR) polyethylene (PE)). In some embodiments, the diameter of the cable  110  (i.e., outer diameter of the radial cross-section, as shown in  FIG. 1 ) is less than 20 mm due to the efficient arrangement of internal cable components, but may also be greater than 10 mm. The central element  116  (e.g., central member) of the cable  110  provides a surface for stranding the elements  112 ,  114 , and also includes optical fibers  122  in buffer tubes  124  stranded about a rod  126  within a polymeric tube  128  (e.g., outdoor-rated PVC jacket). 
         [0015]    According to an exemplary embodiment, aramid yarn or other strength members may be included within the tube  128 . Alarm wires  130  may be positioned in the interstitial spaces between stranded elements  112 ,  114 , and armor  132  surrounds the stranded elements  112 ,  114 . According to an exemplary embodiment, the alarm wires  130  include two 18 AWG alarm conductors, which may carry an alarm signal; such as if connected antenna hardware requires maintenance. The alarm wires  130  may carry other signals instead or in addition thereto. According to an exemplary embodiment, the armor  132  may be a corrugated steel, copper, or aluminum armor, which also serves as a ground conductor and/or an electro-magnetic interference (EMI) shield. In other embodiments, the armor  132  may be dielectric. 
         [0016]    Exterior to the armor  132 , the cable  110  of  FIG. 1  includes a polymeric jacket  134  (e.g., polyethylene, flare-retardant polyvinyl chloride, medium density polyethylene, zero-halogen polymer, outdoor polyvinyl chloride). In various alternate embodiments, the conductors  114 ,  116  are relatively high-capacity conductors, in the range of 10 AWG to 1\0 AWG (e.g., 8 gauge, 6 gauge), providing a large electrical capacity for powerful electrical equipment (e.g., cell site, radar, FTTA applications), as well as providing axial strength to the cable. 
         [0017]    Aspects of the present disclosure relate to the particular efficient placements and uses of the stranded elements  112 ,  114  and structure of the cable  110 , as opposed to the general concept of a hybrid cable containing both optical fibers and conductors. For example, stranding of the elements  112 ,  114  of about the same size as one another and in close proximity to one another, as disclosed herein, may provide for improved cable  110  flexibility, as well as improved performance of the optical fibers  122  (e.g., less attenuation than un-stranded cables). 
         [0018]    According to an exemplary embodiment, spacing between stranded elements  112 ,  114 , positioned adjacent to the central element  116  (e.g., contacting, within 10 microns of), is designed to provide a robust cable structure. According to an exemplary embodiment, a polygon (see dashed hexagon in  FIG. 1 ) may be defined as passing through the centers of adjoining elements  112 ,  114 , stranded about the central element  116 . The exteriors of the elements  214  are spaced apart from one another at the narrowest distance by an average distance of separation of at least 2% of the total periphery of the polygon, but less than 20% of the periphery (i.e., gap or spacing between stranded elements is between 2-20%), preferably less than 15%, such as 12% or less; where ‘average’ distance refers to the net space of all gaps between adjoining stranded elements  112 ,  114  divided by the total number of adjoining stranded elements (such as all six elements  112 ,  114  around the central element  116  as shown in  FIG. 1 ). Such spacing provides for enough room to account for inaccuracies in tolerances of the sizing of the elements (e.g., subtle changes in diameter) so that the stranded elements  112 ,  114  fit easily together, without radially loading one another; as well as provides for stable positioning, reducing the ability of the stranded elements  112 ,  114  to shift or migrate within the jacket, especially when the cable  110  is bending. 
         [0019]    The cable  110  of  FIG. 1  may further include one or more fiber-optic elements  112  and electrical-conductor elements  114  in the insulator jacket  120  (e.g., dielectric, PVC) stranded about the central element  116 , with a water blocking yarn (not shown) therebetween. The optical fibers  122  are contained in the tube  128  (e.g., the tube mostly consisting of medium density polyethylene or polyvinyl chloride). Exterior to the stranded elements  114 , 116 , the cable  110  includes a water-blocking tape  136 , surrounded by the armor  132 , in turn surrounded by a polymeric jacket  134 . 
         [0020]    According to an exemplary embodiment, a hybrid cable  110  includes at least six electrical-conductor elements  112  stranded about a central element, which may be an fiber optic element (see, e.g., fiber optic element  114  as shown in  FIG. 1 ). In other embodiments, the central element  116  is an electrical-conductor element, as shown in  FIG. 1 . 
         [0021]    According to an exemplary embodiment, the elements  112 ,  114 ,  116  of  FIG. 1  share a common diameter (e.g., within reasonable tolerances; e.g., within 10% of one another). According to an exemplary embodiment, the tube  128 , containing optic fibers  122  and stranded about the central element  116 , has a diameter within a range of +10% to −20% of the diameter shared by the adjoining electrical conductor elements  112 . Sizing the elements  112 ,  114 ,  116 , and especially the stranded elements  112 ,  114 , to match one another, improves the robustness of the hybrid cable  110  by reducing the volume of interstitial space within the cable  110 , and correspondingly reducing the volume of space available for migration of the stranded elements  112 ,  114 . 
         [0022]    Referring now to  FIG. 2 , a hybrid fiber optic cable  210  includes first and second layers  212 ,  214  of stranded elements  112 ,  114 . The first layer  212  of stranded elements  112  are stranded about a central member  116  (e.g., electrical-conductive element, fiber-optic element, glass-reinforced plastic rod). Surrounding the first layer  212 , a water-swellable tape and/or a binder  216  at least partially fills the interstitial space. The second layer  214  includes additional stranded elements  112 ,  114 . According to an exemplary embodiment, the second layer  214  includes more stranded elements  112 ,  114  than the first layer  212 . In other contemplated embodiments, a third layer correspondingly includes still more elements  112 ,  114  than the second layer  214 , and so forth. The fiber-optic elements  114  may be positioned in the exterior-most layer (e.g., layer  214 ), providing ease of access thereto when opening the cable  210 . 
         [0023]    According to an exemplary embodiment, the lay length of the stranded elements  112 ,  114  of cable  210 , and/or any of the other cables disclosed herein, is between 350-450 mm, providing a good empirically-derived balance between element length, cable flexibility, and low-attenuation of optical fibers. Further, the second layer  214  is stranded in an opposite direction to the first layer  212  (or mostly so for S-Z stranding of either or both layers), which avoids interstitial conversion of the layers  212 ,  214  that may increase attenuation due to extra bending of optical fibers carried in the fiber-optic elements  114 . The optical fibers may be multi-mode fibers, but single-mode fibers may also or alternatively be included. Furthermore, the optical fibers may be loosely placed in buffer tubes (as shown in  FIGS. 1-2 ), tight-buffered, or even a ribbon or stacked ribbons of optical fibers. 
         [0024]    According to an exemplary embodiment, the cable  210  is greater than 30 mm in diameter, but less than 40 mm in diameter due to the compact configuration of stranded elements  112 ,  114 ; and includes ten 6 AWG conductors, as well as three 12-fiber buffer tubes. Two 18 AWG conductors  130  and/or filler rods may be positioned within the interstitial spaces surrounding the first layer  212 , above or below the tape and/or binder  216 . According to an exemplary embodiment, water-blocking tape  136 , armor  132 , and a polymeric jacket  134  surround the second layer  214 . 
         [0025]    According to an exemplary embodiment, cables  110 ,  210  include a number of electrical-conductor elements  112  (e.g., ten or six 6-gauge thermoplastic high heat-resistant nylon-coated (THHN) conductors) having a diameter (e.g., less than 7 mm diameter; about 6.3 mm diameter) that is approximately equal to that diameter of a number of fiber optic elements  114  also included in the cable. According to an exemplary embodiment, the difference in diameters of the stranded elements  112 ,  114  is less than 50% of the diameter of the largest of the diameters (e.g., less than 25%, less than 10%), or less than twice the diameter of the smallest of the diameters (e.g., less than 1.5 times; less than 1.25 times). In some embodiments, the fiber optic elements  114  contain multiple optical fibers, such as 36 or 24 fibers net. Standard THHN 6-gauge copper conductors have diameters nearly matching those of standard-size buffer tubes of 12-fiber MIC® Cables manufactured by Corning Cable Systems, which may serve as the electrical-conductor and fiber-optic elements  112 ,  114  respectively. In other embodiments, machine tool wire (MTW) (more insulated than THHN) conductors may be used. 
         [0026]    Closely sizing the electrical-conductor and fiber-optic elements  112 ,  114  provides for a uniform shape and well-balanced, stranded cable  110 ,  210 , which in turn improves the performance of the associated optical fibers  122 . According to an exemplary embodiment, single-mode optical fibers of the cables  110 ,  210  shown in  FIGS. 1-2  or variations thereof, have an attenuation of 0.4 dB/km (or less) for 1310 nm wavelength and of 0.3 dB/km (or less) for 1550 nm wavelength in the stranded configuration of the respective cables  110 ,  210 . Such low attenuation is believed to be a significant improvement over hybrid cables that are un-stranded, particularly when the cables are in bending. In other embodiments, the hybrid cables  110 ,  210  may include multi-mode fibers and/or multi-core fibers. 
         [0027]    In some embodiments, the stranded elements  112 ,  114  are helically stranded, while in other embodiments the elements are S-Z stranded (or a combination thereof, between different layers  212 ,  214 ). Preferably, the larger diameter elements  112  (e.g., 2 AWG or 1/0 AWG THHN or MTW) for larger cables (e.g., at least 30 mm in diameter) are helically stranded, due at least in part to reduced lateral loading by the elements  112  upon the jacket  134  within the cable  110 ,  210 , which allows for a thinner jacket  134 . Other embodiments may be S-Z stranded, especially those of smaller diameters (e.g., less than 30 mm in diameter) and associated components. 
         [0028]    Applicants have discovered that sizing the diameters of the fiber-optic elements  114  to be close in size to that of the electrical-conductor elements  112  allows for improved stranding of both elements  112 ,  114  about the central element  116 . In a preferred embodiment, the stranded elements  112 ,  114  are stranded in groups of about seven mod six (e.g., 7, 13, 19, 25, . . . with one of the elements in the center) or one mod five, which allows for a generally even distribution of the elements about the central element  116 , with reduced shifting or asymmetry to the position of the elements  112 ,  114  in the cable  110 ,  210 . In some embodiments, multiple layers  212 ,  214  of stranded elements  112 ,  114  are included in the cable  210 , where the outer layers  214  are stranded about the inner layer(s)  212 , and where the innermost layer  212  may be stranded about a central element  116  (e.g., spacer, guide). 
         [0029]    Utilizing the described hybrid cable design features and design rules offers a number of advantages, including: (1) stable cable cores that allow for enhanced mechanical coupling between the cable elements, which should offer an improvement in long term cable stability in its installation environment; (2) the above-described features and techniques generally allow for a minimum-size cable cross-section, while containing the requisite stranded elements, where smaller cables are less expensive to make—particularly when considering the cost of an overall armor/shield; and (3) data transmission via optical performance will be improved relative to cables that do not include stranded elements, particularly around bends in the cable due at least in part to reduced tension of the optical fibers. Further, use of either an optical element  114  or an electrical-conductive element  112  as the central element  116  further condenses the cable  110 ,  210 , improving efficiency of space, where the electrical conductive elements  112  and/or armor  132  (which may not be included in some embodiments) additionally serve as strength members for the cable in tension or compression. 
         [0030]    The construction and arrangements of the hybrid cable, as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes, and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present inventive technology.