Abstract:
A coaxial cable has a conducting shield covered by a jacket. The jacket defies spaced apart, axially extending voids adjacent to the shield. The voids separate axially extending contact regions of the jacket which extend axially and in contact with the shield. The voids and the contact regions are linked circumferentially by a continuous closed curve.

Description:
FIELD 
       [0001]    The invention pertains to electrical wire and cable. More particularly, the invention pertains to wire or cable formed with an external, insulating sheath that has an interior cylindrical undulating surface which only contacts an adjacent internal conductor at spaced apart regions. 
       BACKGROUND 
       [0002]    Known types of coaxial cable have an interior conductor, an insulating core, an overlying metallic braid and an overlying jacket or outer cover. The braided core consists of copper strands braided tightly around the core. The purpose of this braid is to provide a shield against electrical noise. The braid shields the cable preventing any electrical noise from being induced onto the conductor. Any electrical noise will have a negative impact on the performance of the cable. 
         [0003]    The jacket is commonly extruded over an exterior surface of the cable core. In one form, the extrusion tooling has a smooth round tip, which maintains a smooth tight inner surface, and a smooth round die, which produces the smooth outer texture of the cable, to process the insulating compounds over the braided core. This causes the jacket to be tight against the braid 360° around the braided core. The jacket can be extruded tight enough around the braided core that the braided core will leave braid pattern impressions on the inside surface of the jacket. This arrangement also impacts the process of attaching connectors to such cables as the braid needs to be accessible to the connector. 
         [0004]    The above types of cables are usually manufactured to meet all Underwriters Laboratory (UL) requirements for wire and cable. UL specifies a minimum, maximum, minimum average and an absolute minimum at any point wall thickness of the external sheath. Two important parameters are the minimum average and the absolute minimum at any point. If the cable meets the minimum average and the absolute minimum at any point it will satisfy any of the other conditions. The maximum thickness parameter, of course, impacts material requirements and usage. In order to try to minimize usage of materials the wall thickness should be as close as possible to the minimum average and the absolute minimum wall thicknesses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an isometric view, partly in section and partly broken away of a portion of a cable which embodies the invention; 
           [0006]      FIG. 2  is a view in section, perpendicular to an axis of the cable of  FIG. 1 ; 
           [0007]      FIG. 2A  illustrates alternate embodiment to that of  FIGS. 1 ,  2 ; 
           [0008]      FIG. 3  is an isometric view illustrating aspects of an alternate to the cable of  FIG. 1 ; and 
           [0009]      FIGS. 4A-D  are a sequence of sectional views illustrating details of attaching a connector to a cable of the type of  FIG. 1  or  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
         [0011]    In one aspect of the invention, serrations can be formed on the inside of the jacket or external insulating sheath of an insulated electrical wire or cable. In embodiments of the invention, the serrations are formed in a pattern that will maintain the minimum wall requirements of UL and which will not reduce the insulating properties of the jacket. 
         [0012]    The average wall thicknesses are measured from a cross sectional cut of the wire. Measurements are taken 180 degrees apart from each other and averaged for the average wall thickness. The thinnest parts due to the serrations are place such that a serration is 180 opposite of a non-serrated section. Therefore the minimum average wall thicknesses are maintained. The serrations are never so deep as to violate an absolute minimum thickness requirement at any point. 
         [0013]    In addition to minimizing material usage to form the external sheath or jacket, wire or cable which embody the invention exhibit enhanced flexibility and the installation of connectors onto the wire or cable is facilitated by less adherence of the sheath to the braid. 
         [0014]      FIGS. 1 ,  2  illustrate aspects of an embodiment of the invention. A coaxial cable  10  is formed with an external extruded insulating outer sheath  12 . Sheath  12  surrounds and protects a metallic braid or shield  14 . 
         [0015]    Braid  14  in turn surrounds a cylindrical insulating element  16  which in turn surrounds an interior conductor, which could be implemented as a solid metal, or stranded, wire,  18 . The cable  10  is formed generally symmetrically, except as discussed below, about a common axis A. 
         [0016]    As further illustrated in  FIGS. 1 ,  2  serrations, or voids  20   a, b, c . . . n  are preferably formed as sheath  12  is extruded over braid  14 . The serrations, such as  20   i  are bounded by adjacent regions, such as contact regions  22   i ,  22   j  which abut and are in contact with an exterior surface  14   a  of braid  14 . Preferably, to provide a minimum average thickness parameter, as discussed above, protruding, contact region  22   a  is 180 degrees out of phase with void  20   f.    
         [0017]    By patterning the voids, such as  20   i  and contact regions such as  22   n  so as to be oppositely located relative to one another the minimum wall requirements of a standards organization such as UL can be met while reducing materials cost for the jacket, increasing cable flexibility and facilitating easier installation of connectors on the respective cable ends. It will be understood that the void/contact region patterns can take on various shapes without departing from the spirit and scope of the invention. 
         [0018]      FIG. 2A  illustrates a variation with voids  20   i - 1  which have a discontinuous cross-section. The voids  20   i - 1  are spaced apart by contact regions  22   j - 1  which also have a discontinuous cross-section. Other cross-sectional shapes are possible. 
         [0019]      FIGS. 3 ,  4  illustrate various aspects of a cable  10 - 1  of the general type of  FIGS. 1 ,  2  with a connector  34  being attached to an end  10   a  thereof. Elements of the cable  10 - 1  that correspond to elements of the cable  10  of  FIG. 1 ,  2  have been given the same identification numerals. Cable  10 - 1  also includes an aluminum foil shield  16 - 1  that is sandwiched between polyethylene core  16  and braid  14 . 
         [0020]    A connector  34  includes a barrel  34   a , a ferrule  34   b , and a locking ring  34   c . The ring  34   c  slides on jacket  12  and engages barrel  34   a . An alternative connector type could use a crimpable or compression type barrel in place of the locking ring. 
         [0021]    The installation of the connector  34  on the end  10   a  is facilitated by the presence of voids, such as  20   i  which reduce adherence of the sheath  12  to braid  14 . As a result, as best seen in  FIG. 4 , the ferrule  34   b  will slide under the braid  14  and under the portion of the sheath  12 , adjacent to the braid  14  and ferrule  34   b , with less installation force and potentially cleaner separation of the sheath from the braid  14  in that region. 
         [0022]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.