Abstract:
An adaptor or termination assembly for a mini-coax cable is made up of an extension tip which receives the inner conductor pin on the cable, a first sleeve which fits over an exposed end of the dielectric layer, and a second sleeve which surrounds an exposed end of the outer conductor, all as a preliminary to inserting the assembly into a standard sized connector body and assuring a positive connection between the cable and connector body in such a way as to avoid creating impedance which will downgrade the signal passing through the cable into the connector.

Description:
BACKGROUND AND FIELD OF INVENTION 
     This invention relates to coaxial cable connecting devices; and more particularly relates to a novel and improved adapter for connecting mini-coax cables to a connector. 
     Mini-coax cables are increasingly being used in installations having space limitations and where only a short run of cable is needed. Typically, the mini-coax cables are on the order of 2.5 mm. to 4 mm. in diameter. Typical applications for such cables are for security cameras as well as telecommunications. A difficulty in using the smaller cables however is in manually preparing the cable to connect to a post or terminal in the field. For example, there is the problem of separating the conductive and non-conductive layers when preparing the end of the cable for connection and in such a way as to prevent shorting between layers. A typical example is in connecting to a BNC connector having a preassembled crimping ring, such as, that set forth and described in my U.S. Letters Pat. No. 6,352,448. It is extremely difficult to force  2  sleeve on the BNC connector between the dielectric and braided layers and often leads to shorting between the conductive braid layer and center conductor wire or pin. Furthermore, it is important to be able to maintain proper alignment and centering of the interconnecting conductor wire or pin at the lead end of the cable when advancing into position within the BNC connector as well as to promote ease of positive connection to avoid creating an impedance tending to downgrade the signal through the cable and connector. 
     From the foregoing, there is a definite need for an adapter for coaxial cables and particularly the smaller diameter cables which will overcome the aforementioned problems and result in a positive, secure connection between the cable and connector in a minimum number of steps. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide for a novel and improved adapter for coaxial cables. 
     It is another, object of the present invention to provide for a novel and improved adapter for small diameter coaxial cables which can be installed in the field in a minimum number of steps with minimal tooling required. 
     It is a further object of the present invention to provide for a novel and improved adapter for coaxial cable installations which assures accurate alignment between the cable and connector preliminary to crimping of the connector onto the cable and prevents shorting between the cable layers with one another as well as with conductive portions of the connector. 
     It is a still further object of the present invention to provide for a novel and improved adapter for preparing the end of a coaxial cable for installation into an end connector having a preassembled crimping ring. 
     In accordance with the present invention, an adapter is provided for connecting the end of a coaxial cable to a hollow connector body wherein the cable is of the type having inner and outer concentric electrical conductors, an annular dielectric separating the conductors and an outer jacket of electrically non-conductive material, the inner and outer conductors being exposed and the inner conductor projecting beyond the dielectric at one end of the cable; and the adapter comprises an extension member including a tip of electrically conductive material provided with a recess into which the inner conductor can be inserted, a first sleeve of electrically non-conductive material surrounding the dielectric layer, and a second sleeve of electrically conductive material surrounding the exposed end of the outer conductor. In a preferred form thereof, the first sleeve is dimensioned such that it can be advanced over the extension tip and will cause a trailing end of the extension tip to be compressed snugly into firm engagement with the central conductor pin. Further, the second sleeve is dimensioned to advance over both the tip and plastic sleeve, and a reduced or thicker portion of the second sleeve will bear against an enlarged portion of the first sleeve and at the same time stiffen or rigidify the entire adapter assembly. The sleeves are dimensioned such that a standard size crimping ring, for example, on a BNC connector will cause the second sleeve to be compressed into sealed engagement with the end of the cable, and the first sleeve will insulate the outer conductive braided layer from to prevent shorting. In addition, a trailing end of the second sleeve is slotted to divide the trailing end into prong-like segments having internal and external teeth so that the trailing end of the second sleeve can be compressed into engagement with the cable without crushing the dielectric layer. 
     Further in accordance with the present invention, one method of installing a cable of the type described in a hollow connector body comprises the steps of inserting the inner conductor into a recessed end of an extension member, inserting the extension member into a first sleeve composed of electrically non-conductive material until the first sleeve bears against an end of the material, and inserting the extension member and first sleeve into a second sleeve and advancing the second sleeve over the first sleeve until a trailing end of the second sleeve overlies a portion of the outer conductor, and the second sleeve can be contracted into engagement with the outer conductor. 
     The above and other objects, advantages and features of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of a preferred form of the present invention when taken together with the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded, longitudinal section view of one form of mini-coax cable and a tip; 
     FIG. 2 is another exploded, longitudinal section view of the cable and assembled tip shown in FIG. 1 and a first sleeve to be assembled onto the cable; 
     FIG. 3 is another exploded, longitudinal section view of the cable assembly shown in FIG. 2 with the sleeve of FIG. 2 assembled and a second sleeve preliminary to assembly onto the cable; 
     FIG. 4 is another exploded, longitudinal section view of the preferred form of cable assembly with the first and second sleeves assembled preliminary to insertion into a connector; 
     FIG. 5 is a sectional view illustrating the preferred form of cable assembly in a fully inserted position within the connector preliminary to crimping the connector into engagement with the cable assembly; 
     FIG. 6 is an end view of the assembly shown in FIG. 5; 
     FIG. 7 is a sectional view similar to FIG. 5 after the crimping operation is completed; and 
     FIG. 8 is an end view of the assembly shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings, the present invention may be best typified by describing a novel form of termination assembly in combination with a standard RGB mini-coax cable C and a BNC connector  12  modified in a manner to be described. As a setting for the present invention, the cable C is made up of an inner or central conductor pin or wire  20  which is surrounded by a dielectric insulator  22  of electrically non-conductive material, such as, a rubber or rubber-like material, a braided conductor layer  24 , and an outer jacket  26  of an electrically non-conductive material, such as, a rubber or rubber-like material. The end of the cable C is further prepared for assembly by removing a limited length of the outer jacket  26  and braided conductor  24 , and another limited length of the insulator layer  22  is removed to expose an end of the pin  20  along with the foil layer, not shown, surrounding the pin  20 . The braided conductor layer  24  is peeled back and away from the insulator  22  and doubled over as at  24 ′ to cover the leading end of the jacket  26 . 
     In accordance with the present invention, the leading end of the cable C is further prepared by a termination assembly or adapter which is defined by an extension member including a tip  30 , first sleeve  32  and second sleeve  34  combined into assembled relation onto the end of the cable C, as illustrated in succession in FIGS. 2 to  4 . The tip  30  is composed of an electrically conductive material, such as, metal and is in the form of an elongated slender body  36  terminating in a rounded nose  38  at one end and in a slightly enlarged portion  40  which is recessed at the opposite trailing end. The end portion  40  defines an elongated opening or bore  40 ′ and is separated into split end portions  42  by diametrically opposed slots  44 . The end portion  40  is dimensioned to receive the full length of the center conductor pin  20  so that the end portion  40  of the tip  30  bears against the leading end of the dielectric  22 . 
     The first sleeve  32 , as shown in FIG. 2, is of an electrically non-conductive material and is of generally tubular configuration having a relatively thin-walled leading tubular portion  44  and relatively thick-walled and enlarged trailing tubular portion  46  and shoulder  45  therebetween. The sleeve is dimensioned to fit snugly over the tip  30  to a position such that the leading tubular portion  44  is in surrounding relation to the slotted end  40  of the tip, and the trailing tubular portion  46  is in surrounding relation to the inner dielectric layer  22  and bears against the end of the doubled-over braided portion  24 ′. 
     The metal sleeve  34 , as shown in FIG. 3, includes a hollow end portion  48  of reduced diameter with respect to the rest of the sleeve and which is adapted to move into snug-fitting relation to the reduced portion  44  of the first sleeve and to bear against shoulder  45  on the first sleeve. A longer portion  50  of the sleeve is of increased diameter with respect to the shorter reduced diameter portion  48  and is sized to fit snugly over the enlarged surface  46  of the first sleeve. The longer portion  50  terminates in a relatively thick-walled end portion  52  having two pair of diametrically opposed, open longitudinal slots  54  which divide the end portion  52  into quadrants or arcuate segments  53 , and the segments  53  are provided with internal and external teeth  55  and  55 ′, respectively. The segments  53  are prong-like and overlie the doubled-over portion  24 ′ of the braided layer  24  as well as a limited portion of the jacket  26  when the sleeve  34  is assembled onto the cable C. 
     Referring to FIGS. 4 to  6 , the connector  12  may be broadly characterized as being of the BNC type including a ferrule  60  with a bayonet slot, not shown, in a leading cylindrical end portion  62  of the ferrule for the purpose of attachment to a suitable post or terminal, not shown, but in accordance with well-known practice. The ferrule  60  is in outer spaced concentric relation to a cylindrical casing  64  which extends beyond the length of the ferrule and includes a rearward extension  66  with axially spaced, external shoulders  68  and  69 . A pair of spacers  71  serve to interconnect and space the ferrule in surrounding relation to the casing  64  as well as to serve as limit stops for a spring element  72 . Inner and outer spaced concentric sleeves  74  and  76  project from the end portions or shoulders  68  of the ferrule  60 . The inner sleeve  74  is of gradually increasing thickness to terminate in an enlarged end  78  which is inserted in pressfit relation to an inner reduced surface portion  68 ′ of the end portion  68 . An inner surface  80  of the sleeve  74  is dimensioned to receive the tip  30  and assembled sleeve  32  with the outermost sleeve  34  slidable axially through the sleeve  74  until the tapered wall of the portion  50  moves into engagement with a complementary inner surface portion  75  at the trailing end of the sleeve  74 . 
     The outer sleeve  76  is composed of a metal or other electrically conductive material including an enlarged annular end portion  82  which bears against the external surface of the inner sleeve  74  as well as the shoulder  68  with a thin-walled cylindrical extension  84  extending rearwardly from the enlarged end  82  and terminating in a thickened end  86  having inner endless ribs or sealing rings  88 . The inner diameter of the end portion  86  is of a normal dimension greater than that of the end portion  52  of the sleeve  34  but is compressible under radial contraction into positive engagement with the end portion  52  as well as a limited surface portion of the jacket  26  in a manner to be described. 
     The connector  12  is completed by a crimping ring  90  which is of a type that can be preassembled on the connector  12  and axially advanced over the outer sleeve  76  to force it into crimping engagement with the slotted end  54  of the sleeve  34  as well as the outer jacket  26 . For this purpose, the crimping ring  90  is made up of an annular body  92  composed of a low-friction material having limited compressibility, such as, DELRIN® or other hardened plastic material. One end  94  of the body  92  is relatively thin-walled having an internal diameter equal to or slightly less than the external diameter of the sleeve  76  so that the crimping ring can be pressfit onto the end of the connector  12 . The body  92  thickens rearwardly away from the end portion  94  in defining a tapered internal surface  95  leading into a cylindrical end portion  98 . An exterior surface of the body  92  is undercut to receive a reinforcing band  96  which is preferably composed of brass and which fits snugly over the ring body  92  and has an external diameter substantially equal to that of the end portion  94 . Accordingly, axial advancement of the crimping ring  90  over the sleeve  52  will cause the end portion  86  to be radially compressed until the ribs  88  move into tight-fitting, sealed engagement with the end  52  of the sleeve  32  and, in turn, cause radial compression of the segments  53  into tight-fitting engagement with the doubled-over portion  24 ′ of the braided layer  24  and the jacket  26 . An important feature of the invention is to dimension the slotted end  52  and specifically the width of the slots  54  to limit the amount of compression of the segments  53  so that the teeth  55  will compress the jacket  26  enough to prevent pull-out but not enough to crush the dielectric layer  22 . Thus, the segments  53  can be compressed from the open position shown in FIGS. 5 and 6 to a position shown in FIGS. 7 and 8 in which the segments  53  are compressed only until the slots  54  between the segments  53  are closed. Accordingly, the width of the slot  54  will control the degree or amount of radial inward contraction of the segments  53  to prevent crushing of the dielectric layer  22 . This is especially important in cables operating at higher bandwidth frequencies in which any bending or crushing of the dielectric can create an impedance that downgrades the signal and prevents good return loss. 
     The connector  12  includes a pin-receiving disk  100  which is mounted across the casing  66  just forwardly of the spacers  71 . The disk  100  is of electrically non-conductive material, such as, a plastic and is provided with a generally conical or tapered opening  104  which serves to guide the tip  30  into centered relation to the connector when the cable C is installed in the connector. The disk  100  is of limited resiliency so that the tip  30  can be given a diameter slightly larger than the opening  104  and be forced to expand by the tip  30  as the tip  30  is advanced through the opening until the opening snaps into engagement with an external groove  37  on the tip  30 . 
     From the foregoing, the preferred method of installation of the coaxial cable C in the connector body  12  comprises the steps of first preparing the end of the cable C as described by exposing the center conductor pin  20  and dielectric  22  as shown in FIG.  1 . The center conductor  20  is stripped as well as the dielectric  22  using a standard wire-stripping tool, followed by folding the cable braid  24  back over the jacket  26  and entirely away from the dielectric  22  so that no part of the braid is in contact with the center conductor  20 . The conductor pin  20  is then inserted into the end of the tip  30 . The tip  30  is inserted into the sleeve  32  until the sleeve  32  covers the exposed dielectric  22 , followed by inserting the tip  30  and sleeve  32  into the outer metal sleeve  34  until the sleeve  34  covers the doubled-over portion  24 ′ of the braid. 
     The completed assembly of the tip  30  and sleeves  32  and  34 , referred to as the termination assembly, has sufficient stability to be inserted into the connector  12  until the tip  30  has advanced, as shown in FIG. 5, through the center opening  104  and until the groove  37  on the tip  30  snaps into position with the surrounding edge of that opening. 
     A standard crimping tool may be employed to axially advance the crimping ring  90  over the sleeve  76  thereby causing the end portion  86  of the sleeve  76  to radially contract and force the ribs  88  into positive engagement with serrations or teeth  55  on the slotted end  52  and in turn causing the end  52  to be crimped into positive engagement with the jacket  26  as well as the braided portion  24 ′. One such tool is set forth and described in copending U.S. patent application Ser. No. 09/960,566 for UNIVERSAL CRIMPING TOOL, filed Sep. 20, 2001 and is incorporated by reference herein. The cooperation between the ribs  88  when forced into the teeth  55 ′ and in turn forcing the internal teeth  55  into engagement with the braided layer  24 ′ as well as the jacket  26  increases the pull-out strength of the termination assembly both with respect to the end of the cable C and of the connector  12 . 
     Mini-coaxial cables are particularly useful in cellular telephones, security cameras and other applications where there are decided space limitations or where short runs of cable are used. It will be evident that the size and proportion of extension tip  30 , sleeves  32  and  34  may be varied according to specific wire or cable diameters and proportioned according to the space allowances between the cable C and the connector  12 . Similarly, the width of the slots  54  may be varied in accordance with the amount of contraction required of the segments  53  to firmly engage the jacket  26  without crushing the dielectric layer  22  as previously described. 
     It is therefore to be understood that while a preferred form of method and apparatus is herein set forth and described, various modifications and changes may be made in the construction and arrangement of parts as well as the specific method of installation without departing from the spirit and scope of the present invention as defined by the appended claims and reasonable equivalents thereof.