Abstract:
A coaxial connector for connecting an end of coaxial cable to a threaded port, comprising a post, a nut, a connector body and fastener members has been revised to improve connector&#39;s electrical and mechanical characteristics. The new features of the invention include a post and insertion engagement tools. The post has a first end, a second end, a circular passageway placed between first end and second end, at least two different diameters in the circular passageway wherein, in a cable-connector assembly, the first end is adapted to be inserted into a cable end and the second end opening is adapted to be a forced fit with the cable core wherein the said forced fit secures uninterrupted current flow at a high frequency through the core&#39;s outer conductor and seals the electromagnetic interference leak through the gap between the second end opening and cable core.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Equations used: Short line reflection coefficient and its use for compensating discontinuity capacitance. Amphenol Corporation, N. Sladek 1960. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the invention
       The present application relates to coaxial cable connectors and its electrical as well as mechanical performance specifically related to a post member. Art of relevance are classified in U.S. Pat. No. Class 439, Subclasses 578, 583, 584 and 585.       
 
         [0004]    2. Description of the related art
       The coaxial connectors of the present application are pertained to most of coaxial connectors, where a connector comprises a nut member, a post member, a connector body member, and fastener members for all types of coaxial connectors which have post members and longitudinally compressive mechanism or radially clamping mechanism, using suitable installation hand tools. There are two common problems in this type of connectors. See prior arts in  FIG. 1C ,  FIG. 2A  and  FIG. 2B .       
 
         [0006]    A. Electrical Characteristic Problems as a Transmission Line
       In the past, coaxial cables were constructed with center conductor, coaxial insulation, coaxial braid, and coaxial outmost jacket. At present time, majority of coaxial cables were constructed with center conductor, coaxial insulation, coaxial laminated shield tape, coaxial braid and coaxial outmost jacket. A coaxial cable connector comprising a post member has a unique problem. At high frequency, by skin effect, laminated shield tape which is the first outer conductor, is a major current path. There is a gap between post inside wall and outside surface of laminated shield tape covered core. There is an uncertainty in current continuity between them. A post having a first end, a second end, a flange proximate the second end; a circular passageway placed between first end and second end, Post inside surface  203 ,  FIG. 2B  is usually plated metallic material and core surface  204 ,  FIG. 1C  is laminated shielding tape. When a cable and connector are fully assembled, since core outside diameter  202 ,  FIG. 1C  is smaller than post inside diameter  201 ,  FIG. 2B , in the longitudinal distance  200 ,  FIG. 2A , core surface  204 ,  FIG. 1C  does not make secure contact to post inside wall surface  203 ,  FIG. 2B . When  206 ,  FIG. 2A  transverse electromagnetic wave supporting current, propagate through the cable toward nut; from the plane  205 , wave propagation mode is no longer guaranteed as a normal transverse electromagnetic mode, because transverse electromagnetic mode supporting conductive current  206  flows only through the post as  FIG. 2A . Inside surface of laminated shielding tape  198  is the first outer conductor of a cable but longitudinal distance of  200  from the plane  205  this long phase length is isolated from the signal propagation. For an example, if a post length is 20 mm, at high frequency as 3 Giga Hertz, phase length is 7.2 degrees, a significantly long phase length is isolated. Even though some points of core surface touch the post inside wall, there is no pressure between touching points and it can not be considered as a solid electrical continuity. The isolated insecure electrical length  200  creates frequency correlated electromagnetic disturbances. This propagation mode could get worse by vibration and metallic surface deterioration in time.   See enlarged section A of  FIG. 2A . As second problem, through the gap between post inside surface  203  and core outside surface  204 , electromagnetic interference  207  leaks in or out.   Briefly, these all causes contribute to
           (1) constant or intermittent high return loss and hazardous electromagnetic noises to digital and analog signal transmission system.   (2) through the gap between post inside wall and core outside surface, electromagnetic noise leaks take place.   
               
 
         [0012]    B. Mechanical Problem
       In connector assembling operation, prepared cable&#39;s core insertion engagement with the first end of connector post is difficult. To assemble a coaxial cable to a connector, a cable end must be prepared as  FIG. 1C . A prepared cable end has exposed center conductor, dielectric core covered by laminated shielding tape and cable jacket with braid wires folded back  187  over jacket. Post member&#39;s cylindrical sharp end is adapted to be inserted into prepared cable end around the core, and coaxially beneath said conductive braid without damage of core is difficult because
           (1) core outside diameter is very close in size to post member inside diameter and cut section core is not accurate circular shape to fit post circular end shape.   (2) this operation is carried out in blind because post member end is located several mm inside of connector opening.   
               
 
       BRIEF SUMMARY OF INVENTION 
       [0016]    From the background of invention, 2 major problems were identified. 
         [0017]    A. Electrical Characteristic Problems as a Transmission Line
       (1) Intermittent hazardous electromagnetic noises to digital and analog signal transmission system.   (2) Through the gap between post inside wall and core outside surface, electromagnetic leaks take place.       
 
         [0020]    B. Mechanical Problem; in Connector Assembling Operation,
       (1) Prepared cable core&#39;s engagement into connector post end is difficult.   (2) Frequently, core end is damaged by sharp end of post member.       
 
         [0023]    To resolve the above identified problems, post and insertion engagement tools are invented. 
         [0024]    See  FIG. 1A ,  FIG. 1B ,  FIG. 1C ,  FIG. 1D  and  FIG. 1E . 
         [0025]    Post 
         [0026]    Post members&#39; first end diameter  201  receives prepared cable&#39;s core diameter  202  in clearance fit and post&#39;s second opening  209  inner surface  197  has forced fit with prepared cable  204 ; after cable and connector are assembled current  206  flows laminated shielding tape  198  and post  203  in parallel. Since, said forced fit between post second opening  197  and cable core  204  secures electrical continuity, there is no isolation of cable core inside of post from signal propagation as prior art, transverse electromagnetic mode is well reserved. 
         [0027]    Post&#39;s second opening  209  has edgy  210  having shape and surface finish adapted to be used for cleaning, resizing outside surface of  204  and normalizing shape of prepared cable&#39;s core  204  before performing next connector cable assembly operation. In next operation surface  197  and  204  rubbed each other second time and enhance electrical continuity. 
         [0028]    Insertion Engagement Tools 
         [0029]    For easier engagement of cable core into post and reduce core damage, an insertion engagement tools  183  and  193  are invented. See  FIG. 1D  and  FIG. 1E . Illustrations in  FIG. 3B  and  FIG. 3C  show how they work. 
         [0030]    Engineering Review of Transmission Line of Connector 
         [0031]    See  FIG. 1A ,  FIG. 1B ,  FIG. 1C ,  FIG. 1D ,  1 E,  FIG. 4A  and  FIG. 4B . 
         [0032]    Once a connector is fully assembled, in  FIG. 1A , cable&#39;s core end  196  and post&#39;s second end flange face  195  are flush and post&#39;s inside surface  197  and core&#39;s outside  204  make a forced fit for a secure electrical continuity. A return loss by forced fit region,  208  reviewed. See  FIG. 4A  and  FIG. 4B . 
         [0033]    Characteristic Impedance Calculation 
         [0034]    As an example, a RG6 connector is selected. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 core dia 
                 dielectric 
                 conductor 
                   
                   
                 impedance 
               
               
                 mm 
                 mm 
                 mm 
                 Er 
                 root of Er 
                 ohm 
               
               
                   
               
             
             
               
                 4.73 
                 4.52 
                 1.02 
                 1.44 
                 1.20 
                 74.5 
               
               
                   
               
             
          
         
       
     
         [0035]    Equation 
         [0000]      Za=138 *log(4.52/1.02)/(root of Er)=74.5 ohm 
         [0036]    In this calculation characteristic impedance at force fit area is 74.5 ohms 
         [0037]    Return loss Calculation 
         [0038]    See  FIG. 4A  and  FIG. 4B . 
         [0039]    Legends 
         [0040]    Zs: system impedance 75 Ohm 
         [0041]    Za: impedance at interested area Ohm 
         [0042]    B: phase constant at Za region: radian/meter 
         [0043]    S: longitudinal distance of interested area meter 
         [0044]    Ksa: reflection coefficient looking toward Za at point s-a. 
         [0045]    Kas: reflection coefficient looking toward Zs at point a-s. 
         [0046]    Kt: total reflection coefficient 
         [0047]    RL: return loss -dB 
         [0048]    Equations 
         [0000]        Kt =( Ksa+Kas * EXP(− j 2BS))/(1+ Ksa*Kas *EXP(− j 2BS))
 
         [0049]    When S is short distance; 
         [0050]    Approximation can be made. 
         [0051]    Kt=(jBS(2Ksa/(1-(Ksa*Ksa)))) 
         [0052]    RL=−20*log(Kt) 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 S 
                 frequency 
                 Zs 
                 Za 
                 B 
                   
                   
                 RL 
               
               
                 meter 
                 giga Herts 
                 ohm 
                 ohm 
                 rad/meter 
                 Ksa 
                 Kt 
                 dB 
               
               
                   
               
             
             
               
                 0.003 
                 3 
                 75 
                 74.5 
                 62.800 
                 −0.003 
                 0.001 
                 57.99 
               
               
                   
               
             
          
         
       
     
         [0053]    Return loss by the forced fit region is 57.99 db. 
         [0054]    Brief description of cable connector assembly 
         [0055]    See  FIG. 1B ,  1 C,  FIG. 3A ,  FIG. 3B  and  FIG. 3C . 
         [0056]    Step 1 
         [0057]    Prepare cable as  192 ; center conductor  190 , core and braid wires back over jacket  187 . 
         [0058]    Resize, reshape, and surface cleaning  204  by inserting prepared cable into opening  209  about 6 mm and remove. 
         [0059]    Step 2 
         [0060]    Insert cable  192  into opening  201  and press in all the way until core&#39;s surface  196  flush to flange surface  195 . 
         [0061]    Use insertion engagement tool  183  or  193  for an engagement. 
         [0062]    Conclusion 
         [0063]    In this cable-connector assembly operation, the prepared cable end is pushed through the post first end opening until the core end flushes to post second end flange and the forced fit between core outside diameter and post secures electrical continuity; it achieves transverse electromagnetic mode and prevents electromagnetic interference leak  207  of  FIG. 2A . 
         [0064]    According to the above return loss calculation, return loss by the forced fit region is 57.99 db and is acceptable. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0065]      FIG. 1A  is a longitudinal cross-sectional view of a preferred embodiment of a connector according to the present invention, illustrating transverse electromagnetic mode supporting conductive current flows through laminated shielding tape in high frequency. A forced fit between core surface and post inside wall near the post flange secures the electrical continuity and prevents electromagnetic noise generation and its leaks. 
           [0066]      FIG. 1B  is a longitudinal cross-sectional view of the post member of the connector of the  FIG. 1A . Post has a reduced inside diameter near the post flange. 
           [0067]      FIG. 1C  is a longitudinal cross-sectional view of prepared cable, comprising exposed center conductor, laminated shielding tape covered core, and cable jacket with braid combed back. 
           [0068]      FIG. 1D  is a present invention showing an insertion engagement tool, that the length is longer than uncompressed connector. 
           [0069]      FIG. 1E  is a present invention showing an insertion engagement tool, that the length is longer than exposed center conductor of a prepared cable. 
           [0070]      FIG. 2A  is a prior art of longitudinal cross-sectional view of the connector. Through the longitudinal length of the post, there are gaps between post inside wall and laminated shielding tape of a core and the transverse electromagnetic mode is not warranted in the loose fit region at a high frequency. 
           [0071]      FIG. 2B  is a prior art of longitudinal cross-sectional view of a post. 
           [0072]      FIG. 3A  shows a surface cleaning, sizing and reshaping operation of prepared cable&#39;s core, using connector second opening&#39;s smooth edge and reduced diameter of the post, before inserting a cable to a connector first opening. 
           [0073]      FIG. 3B  shows insertion of a prepared cable into a connector with a tool  183  in cable and connector assembling operation. 
           [0074]      FIG. 3C  shows insertion of a prepared cable into a connector with a tool  193  in cable and connector assembling operation. 
           [0075]      FIG. 4A  is a longitudinal cross-sectional view of a preferred embodiment of a connector according to the present invention. 
           [0076]      FIG. 4B  is cross-sectional view of the forced fit area S that secures electrical continuity and prevents electromagnetic leak. 
           [0077]      FIG. 5  is exploded view of components of a connector. 
           [0078]      FIG. 6  is an enlarged, longitudinal sectional view of the preferred post with more details 
           [0079]      FIG. 7  is an enlarged, longitudinal cross-sectional view of the connector nut with more details. 
           [0080]      FIG. 8  is an enlarged, longitudinal sectional view of the connector body with more details. 
           [0081]      FIG. 9A  is an enlarged, frontal view of the connector grommet 
           [0082]      FIG. 9B  is an enlarged cross-sectional view of  FIG. 9A  at section A-A with more details. 
           [0083]      FIG. 10  is an enlarged, longitudinal cross-sectional view of the connector rear cap with more details. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0084]    This invention is applicable to all types of coaxial connector which comprises a post member. In this detailed description of the invention, a Perfect 10 connector, PV6UE-05 is selected for an example. 
         [0085]    After a prepared end of coaxial cable is properly inserted through the open end  100  of an open connector, the connector is placed within a suitable compression hand tool for compression, substantially assuming the closed configuration of  FIG. 1A . With additional reference directed to  FIG. 1A  and  FIG. 5 , the preferred rigid, tubular metallic nut  30  has a conventional faceted, preferably hexagonal drive head  32  integral with a protruding, coaxial stem  33 . 
         [0086]    Conventional internal threads  35  are defined in the nut or head interior for rotatable, threadable mating attachment to as a suitably threaded socket. The front opening  28  of the connector appears at the front of stem  33  surrounded by annular from face  34 . A circular passageway  37  is concentrically defined in the faceted drive head  32  at the rear of nut  30 . Passageway  37  is externally, coaxially bounded by the outer, round peripheral wall  38  forming a flat, circular end of the connector nut  30 . An inner, annular shoulder  39  on the inside of head  32  is spaced apart from and parallel with outer wall  38 . A leading chamfer  40  and a spaced part rear chamfer  41  defined on hex head  32  are preferred for easy handling. 
         [0087]    An elongated, tubular body  44  preferably molded from plastic is rotatably coupled to the nut  30 . Body  44  preferably comprises a tubular stop ring  46  that is integral with reduced diameter shank  48  sized fit as illustrated in  FIG. 8 . The elongated, outer periphery  52  of shank  48  is smooth and cylindrical. The larger diameter stop ring  46  has an annular, rear wall  54  that is coaxial with shank  48 . An end cap  56  is pressed unto body  44 , coaxially engaging shank  48 . The end cap  56  discussed hereinafter will smoothly, frictionally grip body  44  along and upon any point upon body shank  48 , with maximum travel or displacement limited by stop ring  46 . In other words, when the end cap  56  is compressed unto the body of connector and the connector assumes a closed position; annular wall  54  on the body stop ring  46  will limit maximum deflection or travel of the end cap  56 . The resilient, preferably molded plastic body  44  is hollow stop ring  46  has an internal, coaxial passageway  58  extending from the annular front face  59  defined at the body front a major portion of the ring length. Passageway  58  extends to an inner, annual wall  60  that coaxially border another passageway  62 , which has a larger diameter that passageway  58 . The elongated passageway  62  is coaxially defined inside shank  48  and extends to rear, annular surface  64  coaxially located at the rear end of the shank  48 . For moisture sealing, it is preferred that generally annular sealing grommet  67  be employed. The enhanced sealing grommet  67  is coaxially disposed within end cap  56  as explained in detail hereinafter. 
         [0088]    With primary reference directed now to the post  70  rotatably, mechanically couples the hex headed nut  30  to the plastic body  44 . The metallic post  70  also establishes electrical contact between the braid of the coax cable and the nut  30 . The tubular post  70  defines an elongated shank  71  with a coaxial, internal passageway  72  extending its front  73  and rear  74 . A front annular flange  76  is spaced apart from an integral, reduced diameter flange  78 , across a ring groove  80 . A conventional 0-ring  82  is preferably seated within ring groove  80  when the connector is assembled. Post external barbs  86  is press fitted into the body  44 , frictionally scatting within passageway  58 . In assembly it is also noted that post flange  76  axially contacts inner head wall  39 . Inner post flange  78  axially abuts front face  59  of body  44  with post  70  penetrating passageway  58 . The sealing 0-ring  82  is circumferentially frictionally constrained within nut  30  coaxially inside passageway  37 . The post member has been revised to improve coaxial cable connector&#39;s electrical and mechanical characteristics. The post including a first end  74 , a second end  73 , and a flange  76  proximate the second end  73 ; circular passageways  69 ,  68  and  72  is placed between first end and second end; the new feature of invention is that the circular passageway has at least two different diameters; in  FIG. 1C , the first end receives cable core,  204  and penetrates between braid,  187  and core of a cable and second end opening, inside surface  197  makes a forced fit with cable core surface,  204  in assembly operation; said forced fit between post second opening and cable core secures electrical continuity. This prevents isolation of the first outer conductor of cable region,  200 , laminated shielding tape  198  from signal propagation and secures transmission line to preserve transverse electromagnetic mode. To facilitate insertion engagement of cable core into post and reduce core damage, an insertion pilot tool  183  and  193  are invented. 
         [0089]    A prepared cable insertion engagement tool  183  having rod shape, first end and second end with length  181 ,  FIG. 1D , longer than an uncompressed connector length  179 ,  FIG. 3A , wherein outside diameter  194  is clearance fit with inside diameter  209  of the said connector post; first end has round finish  188 ,  FIG. 1D  around rod and center hole chamfer  186 , wherein center hole diameter  191  is clearance fit with the cable&#39;s center conductor  190 ; center hole depth  182  is deeper than exposed center conductor length  182 . 
         [0090]    A prepared cable insertion engagement tool  193  having rod shape, symmetrical first end and second end with longitudinal length  180  longer than cable&#39;s exposed center conductor length  182 , wherein outside diameter  194  has clearance fit with inside diameter  209  of the said connector post, has round finish  188  around rod and center hole chamfer  186 ; longitudinal center hole, diameter  191  is clearance fit with said cable center conductor  190 . 
         [0091]    The preferred end cap  56  is best illustrated in  FIGS. 10 and 5 . The rigid preferably metallic end cap  56  comprises a tubular body  92  that is integral and concentric with rear neck  94  of reduced diameter. The neck  94  terminates in an outer, annular flange  95  forming the end cap rear and defining a coaxial cable input hole  100  with beveled peripheral edge  98 . In all annular ring groove  96  concentrically defined about neck  94 . The ring groove  96  is axially located between body  92  and flange  95  is defined by concentric, annular face  93 . The external ring groove  96  is readily perceptible by touch. However, it is preferred that resilient ring  57  be seated within groove  96  in embodiments. Internal ring groove  99  seats the sealing grommet  67 . Hole  97  at the rear of end cap  56  communicates with cylindrical passageway  100  concentrically located within neck  94 . Passageway  100  leads to a larger diameter passageway  102  defined within end cap body  92 . Ring groove  99  is disposed between passageways  100  and  102 . Passageway  102  is sized to frictionally, coaxially fit over shank  48  of connector body  44  in assembly. There is an inner, annular wall  105  concentrically defined about neck  94  and facing large passageway  102  within body  92  that is a boundary between end cap body  92  and cap neck  94 . Grommet  67  bears against wall  105  in operation. Once a prepared end of coaxial cable is pushed through passageway  100  and  102  it will be expanded in diameter as it is axially penetrated by post  70 , and subsequent withdrawal from the connector will be resisted by contact with the deformed grommet  67  whose axial travel is resisted internal wall  105 . The smooth, concentric outer surface of the connector body&#39;s shank  48  fits snugly within end cap passageway  102  when the end cap  56  telescopingly, slidably fitted to the connector body  44 . Cap  56  may be firmly pushed unto the connector body  44  and then axially forced a minimal, selectable distance to semi-permanently retain the end cap  56  in place of the body coaxially frictionally attached to shank  48 . There is no critical detented position that must be assumed by the end cap. The inner smooth cylindrical surface  104  of the end cap  56  is defined concentrically within body  92 . Surface  104  coaxially, slidably mate with the smooth, external cylindrical surface  52  of the body shank  48 . Thus the end cap  56  may be partially, telescopingly attached to the body  44 , and once coax is inserted as explained below, end cap  56  may be compressed unto the body, over shank  48 , until the coax end is firmly grasped and the parts are locked together. It is preferred however that the open mouth  106  at the end cap front have a plurality of concentric, spaced apart beveled rings  108  providing the end cap interior surface  104  with peripheral edges or “teeth”  110  that firmly grasp the body shank  48 . Preferably there are three such “teeth”  110 . When the end cap  56  is compressively mated to the body  44 , teeth  110  can firmly grasp the plastic shank  48  and make a firm connection without radially compressing the connector body, which is not deformed in assembly. The end cup maybe compressed to virtually any position along the length of body shank  48  between a position just clearing annular surface  64  and the annular face  54  at rear of the body stop ring  46  forcibly contacts the annular rear wall  54  of the connector body  44 . At this time the surface  64  of body shank  48  will compressively engage and deform the grommet  67 , sealing the coaxial cable coaxially captivated within the compressed connector. It can be seen that when the end cap  56  is first coupled to the shank  48  of body  44 , the shank  64  is axially spaced apart from the grommet  67 . However, when the fitting is compressed during installation, the shank end  64  is forced into and against the grommet  67 ; force is directed towards coaxial cable with an added vector angle of radial and longitudinal forces to seal it. In  FIG. 1C , a prepared end of coaxial cable  192  has an outer most plastic covering  185 , a concentric braided metal sheath  187 , laminated shield tape  204  and an inner conductor  190 . When the prepared end first forced through the connector rear, passing through the connector hole  97  and through passageways  100  and  102 . The coaxial cable prepared end is forced through the annulus  88 ,  FIG. 3B , between the post  70  and the inner cylinder surface of shank  48  with post  70  coaxially penetrating the coax between the conductive braid  187  and laminated shield tape  204 . The outer metallic braid is folded back, and as seen in  FIG. 3D , makes electrical contact with the post  70  and portions of the end cap  56 . The inner most cable conductor is routed through the post, and protrudes from the mouth  28  of the nut  30 . Axial withdrawal of the coax after compression of the end cap  56  is prevented by the deformed grommet  67  and the inner wall  105 , within the end cap near the jam point  120 . Enhanced sealing grommet  67  is generally toroidal. In cross section it is seen that grommet  67  comprises two primary portions that are integral and coaxial. The outermost portion  130  the outer diameter of grommet  67  is of a generally squarish profile, enabling the grommet  67  snugly seat within the end cap ring groove  99  discussed earlier. The grommet length along outer portion  130  designated by the reference numeral  131 , and in the best mode this distance is 3.6 mm an integral, inner bulbous grommet portion  132  has a length  134  preferably 4 mm that is larger than the outer length  131 . Thus at and along its inner diameter region, grummet  67  is greater in length at its diameter region along width  131 . Preferably, bulbous grommet region  132  comprises a convex nose  133  that, in assembly, points into the interior of the connector toward the head  30 . A slightly inclined neck  143  transitions from the curved, outer edge  140  of the bulbous region to the outer diameter, reduce length region  131  of the grommet that preferably seats within ring groove  99 . The accurate leading edge  140  of nose  133  has a radius  144 , substantially establishing a semicircular geometry. Radius  144  is preferably 20% or the length of the grommet length  131  at its outer portion. When the connector is compressed, shank  48  of body  44  and end cap  56  are forced together. The enhanced sealing grommet  67  is squeezed there between. Specifically region  64  of shank  48  forcibly, contacts grommet  67  at neck  143 , and deform and squeezes the grommet  67 . When squeezed during installation compression, the grommet  67  deforms as in  FIG. 1A . Grommet  67  is axially constrained at this time by rear annular wall  105  in the end cap. Thus, the preferred special sealing grommet  67  disposed in the end cap of the fitting is uniquely shaped with a rounded bulbous convex “nose”. This unique tends to grasp the PVC jacket and aids in locking the coax jacket in position if unusual forces applied to the coax. For example, if the coaxial cable is accidentally pulled outwardly, an axial pull, the bulbous nose  133  presses radialy inwardly on the PVC jacket of the coax, causing extra locking pressure to be exerted and further resisting the accidental extraction of the coax. The bulbous nose function as a special locking devise which reacts only when axial pressure is applied to the coax which might render the electrical connection useless if the coax were to be released outwardly any distance whatsoever from the electrical mating connection. From the foregoing, it will be seen that this invention is one well adapted to obtain all the ends and objects set forth, together with other advantages which are inherent to the structure. It will be understood that certain features and subcombination are of utility and maybe employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. As many possible embodiments maybe made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.