Abstract:
The invention describes a method of electrically and mechanically connecting the center conductor of a micro-coaxial RF cable to a coaxial cable connector or bulkhead without the use of traditional soldering or precision tools. The device is essentially a solderless, crimpless connector. The invention allows a cable installer to connect a micro-coaxial cable having a central conductor as small #30 AWG (0.25 mm) to a coaxial cable connector under field conditions. The invention employs a two-stage, spring loaded center pin holding device and a method for using the device to facilitate easy field installation while maintaining mechanical and electrical reliability.

Description:
BACKGROUND OF THE INVENTION 
     1.Field of the Invention 
     2. Prior Art 
     In signal transmission applications, the choice of coaxial cable for conducting the signal is usually determined by the distance between connection points, the signal frequency, the maximum bend radius required, and the connector space available in a particular transmitting and/or receiving device. The longer the cable and the higher the frequency used, the larger the outside diameter needs to be to prevent excessive signal loss. Traditional coaxial cable applications such as Cable TV, Broadband data, and microwave signal transmission, employ coaxial cables with O.D.&#39;s of 0.25-1 inches for distances of 50-1000 feet. In indoor equipment, the shorter distance requirements (typically 6-24 inches), the limitations of limited space and tighter bend radius requirements are overcome by using smaller coaxial cables with O.D.&#39;s of 0.1-0.14 inches. These small OD cables typically require the use of precision micro-connectors such as SMA, SMB and MCX, which must be connected to the cable in a more or less controlled setting such as a laboratory with precise equipment to both hold and electrically attach the cable to the connectors. The central conductor for such microcoaxial cables is usually attached to the connector by either soldering directly to a fixed center pin in the connector, or soldering or crimping the central conductor to a separate small center pin which is then inserted into the connector. The soldering method requires both electricity, and a clean, well lighed area for assembly. The use of small separate center pins, with a diameter of about 0.040 inch, need careful handing and holding during assembly. The installer needs to hold the pin, place it over the cable center conductor, and then perform the solder or crimp procedure. 
     With the increased demands on broadband network centers and field located hubs, there exists a need for higher density coaxial cable bundles having as many as 200 coaxial cables connected between equipment locations 100 feet apart. These new high-density cable assemblies now require field-installable connectors that are installed in lab environments. The high-density equipment backplanes also require microcoaxial cable connectors rather than larger connectors used when only a few low density cables are involved. The new cable requirements have been met with the development of lower loss microcoaxial cable bundles containing as many as 12 coaxial cables (each with a 0.1 in. OD) within in a 0.45 inch diameter jacket. There is a need for a reliable method of attaching these microcoaxial cable connectors to the microcoaxial cables in the field without the need for soldering and special handling equipment. A problem encountered during field installation of microcoaxial cable connectors is chemical contamination of conductive parts of the assembly from the installer&#39;s hands. Precision microcoaxial cable connectors are usually plated with gold to limit oxidation and thus require a level of cleanliness to insure proper performance. It is very difficult to insure this level of clean handling when the installer is required to manually grasp the connection center pin in the microcoaxial connector during installation. 
     Coaxial cables with larger center conductors of over 0.031 in. (0.8 mm) usually use the central conductor as the male center pin within the (assembled) male connector. The central conductor is then inserted directly into the female receptacle that comprises a mating seizing pin. Smaller cables require a male pin to first be attached to the (smaller) central conductor in order to confer the rigidity to the male pin needed to overcome the insertion force required for mating engagement with the female receptacle. Even with additional fixed center pins, the insertion force required for secure engagement can still be limited by the weaker section of the small central conductor not supported by the larger fixed pin. 
     Coaxial cable connector construction and installation is well known in the established art. The present inventor, in copending U.S. patent application Ser. No. 09/599,059, filed Jun. 21, 2000, U.S. Pat. No. 6,217,383 discloses a compression-type coaxial cable connector. The connector, and each of the components associated therewith, has an axial conduit coextensive with the length thereof. When the prepared end of a coaxial cable is advanced through the conduit into the body portion, a shank separates the outer protective jacket and conductive braid of the cable from the dielectric core and interposes the barbed portion of the tubular shank therebetween. A compression sleeve, with the assistance of a compression tool, compresses the cable jacket and braid providing secure attachment. 
     Stirling, in U.S. Pat. No. 5,007,861, discloses a crimpless coaxial cable connector which can be secured to a cable simply by pushing the cable into the connector and subsequently pulling it back. The body of the connector has a bushing mounted within it near the cable-receiving end having a conduit dimensioned to receive the cable. The body of the connector also has within it an annular mandrel having a bore to receive the stripped core of the cable, and having a sleeve adapted to engage the cable beneath the jacket by pushing the cable and the mandrel together. 
     Another radial compression type of coaxial cable connector of the type generally used today for forming an electrical connection between a central conductor within the coaxial cable and a mating fixture is described in detail in U.S. Pat. No. 5,632,651 to Szegda. Various other coaxial cable connectors adapted to from a secure, electrically conductive connection between a coaxial cable and a threaded female port have been developed. Such prior art connectors are discussed, for example, in U.S. Pat. No. 5,024,606 to Ming-Hua, U.S. Pat. No. 4,280,749 to Hemmer, U.S. Pat. No. 4,593,964 to Forney, Jr. et al., U.S. Pat. No. 5,073,129 to Szegda and U.S. Pat. No. 5,651,699 to Holliday. U.S. Pat. No. 5,879,191 to Burris, discusses prior art efforts to provide a coaxial connector which is moisture-proof and minimizes radiative loss of signal from the cable. 
     All of the above-referenced connectors require that a stripped length of the coaxial cable&#39; central conductor project from the end of the cable within the axial bore in the connector for engagement with a conductive receptacle in the mating fixture. The prior art connectors work well with standard coaxial cables having a relatively large gauge central conductor because the stripped length is rigid. The rigid conductor can be forced into a spring receptacle in a mating fixture without difficulty. Microcoaxial cables, however, have a small, fragile central conductor. The stripped length of the central conductor in a microcoaxial cable lacks the structural integrity for insertion into a conductive receptacle in a mating fixture. It is current practice to solder or crimp an electrically conductive cap over the stripped length of central conductor in order to provide sufficient rigidity to the central conductor for use with standard connector assemblies. Accordingly, there is a current need for a solderless device and method for adapting the central conductor of a microcoaxial cable for use with standard coaxial cable connectors without the need for soldering or precision crimping. 
     SUMMARY 
     It is a primary object of the invention to provide a facile means for imparting rigidity to a stripped length of central conductor in a microcoaxial cable. 
     It is a further object of the invention to provide a facile means for imparting rigidity to a stripped length of central conductor in a microcoaxial cable without requiring either soldering or precision crimping. 
     It is yet a further object of the invention to provide an electrically conductive pin adapted to fit snugly over a stripped length of a central conductor of a microcoaxial cable, thereafter seizing the central conductor in locking engagement therewith. 
     It is another object of the invention to provide a tool operable for the facile attachment of an electrically conductive pin to the stripped central conductor of a microcoaxial cable. 
     The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a microcoaxial cable-connector assembly in accordance with a first preferred embodiment of the present invention. 
     FIG. 2 is a partially cross-sectional view of first and second pins in accordance with a first preferred embodiment of the present invention prior to attachment of the pins to the central conductor of a microcoaxial cable. 
     FIG. 3 is a partially cross-sectional view of first and second pins in accordance with a first preferred embodiment of the present invention with the first pin attached to the central conductor of the microcoaxial cable in preparation for attachment of the first pin to the second pin. 
     FIG. 4 is an enlarged view of a portion of FIG. 3 showing the seizing and locking engagement between the first pin and the central conductor of a microcoaxial cable. 
     FIG. 5 is a partially cross-sectional view of the first pin partially inserted into an axial recess in the trailing end of the second pin. 
     FIG. 6 is an enlarged view of a portion of FIG. 5 showing the seizing and locking engagement between the first pin and the second pin with the first pin partially inserted into the an axial recess in the trailing end of the second pin. 
     FIG. 7 is a partially cross-sectional view of the first pin fully inserted into the axial recess in the trailing end of the second pin in preparation for inserting the cable-pins assembly into a microcoaxial cable connector (not shown). 
     FIG. 8 is an enlarged view of a portion of FIG. 7 showing the seizing and locking engagement between the central conductor of the microcoaxial cable and the first pin and between the first pin and the second pin with the first pin fully inserted into the axial recess in the trailing end of the second pin. 
     FIG. 9 is a side elevational view of the leading end of a microcoaxial cable with the first pin of the present invention attached to the central conductor. 
     FIG. 10 is a partially cutaway view of a right angle coaxial cable connector adapted to receive a microcoaxial cable having a first pin attached thereto in accordance with a second preferred embodiment of the present invention. 
     FIG. 11 is an enlarged view of a portion of the right angle coaxial cable connector of FIG. 10 showing the locking engagement between an electrically conductive element in the connector and the first pin. 
     FIG. 12 is a perspective view of a hand-holdable tool useful for inserting the first pin over a stripped portion of the central conductor of a microcoaxial cable. 
     FIG. 13 is a perspective view showing the relationship between the hand-holdable tool of FIG. 12, a first pin in accordance with the present invention and a stripped portion of the central conductor of a microcoaxial cable prior to attaching the first pin to the central conductor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a partially exploded view of a microcoaxial cable-connector assembly is shown, illustrating the current state of the art for microcoaxial cable connection. The term “microcoaxial cable”, as used herein, means a coaxial cable, such as RG179 cable, having a central conductor diameter less than 0.8 mm. and greater than about 0.1 mm. A prior art microcoaxial cable  10  has an outer jacket  11 , an underlying layer of a dielectric material  12  and a central conductor  13 . A microcoaxial cable connector  17  in accordance with the prior art includes a second pin  14  dimensioned to fit within an axial conduit  16  in the connector  17 . The second pin  14  has a trailing end with a cylindrical recess  15  therewithin. In accordance with the prior art, the second pin  14  is soldered or crimped to the stripped length of central conductor  13 . 
     Turning now to FIGS. 2-8, the present invention provides an electrically conductive first pin  20  having a leading end  21  and a hollow trailing end  22  is shown in side cross-sectional view interposed between the stripped central conductor  13  of the microcoaxial cable  10  and the second pin  14  of the connector  17 . The first pin  20  has a first spring barb  40  (FIG. 4) adjacent the hollow recess  41  within the first pin. When the central conductor  13  is inserted into the hollow recess  41  in the first pin and advanced thereinto, the first spring barb  40  is forced outwardly in the direction of the arrows X, and seizes the central conductor to prevent retraction or removal of the first pin from the central conductor. After the first pin is attached to the central conductor of the microcoaxial cable, as shown in FIGS. 3 and 4, the leading end  21  of the first spring  20  is inserted into the cylindrical recess  15  in the trailing end of the second pin as shown in FIGS. 5 and 6. Advancement of the first pin into the cylindrical recess  15  in the second pin compresses second spring barbs  42  on the outer surface of the first pin in the direction of arrows Y, preventing removal of the first pin from the recess  15  as shown in FIG.  7  and in greated detail in FIG.  8 . The second pin  14 , thus affixed to the central conductor and in electrical communication therewith, is then inserted into the axial conduit  16  in the prior art connector  17  and locked thereto by conventional cable attachment means. The rigidity of the second pin enables the cable connector assembly to be affixed to a mating fixture without damaging the central conductor or compromising the structural integrity of the electrical connection. 
     A right angle coaxial cable connector, such as illustrated at numeral  100  in partially cutaway view in FIG. 10, is commonly used in the art where space considerations dictate. The right angle coaxial cable connector  100  includes a cable receiving port  101  having an axial cylindrical conduit  102  therein dimensioned to receive a coaxial cable, an electrically conductive connector post  103  having a hole  104  therein. The hole  104  is is disposed on the connector post  103  coaxially with the axial conduit  102 . In a second preferred embodiment of the present invention, the first pin  20  is inserted over a stripped length of a microcoaxial cable central conductor as shown in FIG.  9 . The cable-first pin assembly  90  is then inserted into the conduit  102  in the cable receiving port  101  and advanced thereinto until the leading end  21  and the second spring barb  42  on the first pin  20  pass through the hole  104  in the connector post  103 . The spring barb  42  prevents retraction of the microcoaxial cable from the connector  100 , as shown in greater detail in FIG.  11 . 
     As mentioned earlier, handling of the conductive elements comprising the microcoaxial cable-connector assembly can leave an oxidizing residue thereon that con be detrimental to electrical conduction and lead to electrical failure. Accordingly, a first pin installation tool is provided as shown at numeral  120  in FIG.  12 . The tool  120  includes a handle  121  having a cylindrical recess  122  in a leading end thereof. The cylindrical recess  122  is dimensioned to house the leading end  21  of the first pin  20  without compressing the second spring barbs  42  on the outer surface of the first pin. In order to attach the first pin  20  to the central conductor  13  of a cable  10 , shown in FIG. 13, the leading end of the first pin is inserted into the cylindrical recess  122  where it is held snugly but without substantial compression. The stripped length of the central conductor  13  is inserted into the hollow recess in the trailing end  22  of the first spring and advanced thereinto until it cannot be further advanced. The cable  10  is then retracted from the tool  120  with the first pin securely attached to, and in electrical connection with, the central conductor. The resulting assembly can then be used for facile attachment to a microcoaxial cable connector as discussed hereinabove. 
     In summary, the present invention overcomes the need for hand contact with the conductive elements in a microcoaxial cable-connector assembly and provides means for conferring rigidity to a stripped length of a central conductor by the use of the dual holding pin system. The small center conductor is first inserted into a low insertion force seizing pin, preferably contained in a large plastic hand holder. The larger plastic pin holder is then removed leaving the first seizing pin affixed to the central conductor. The first pin is then inserted into a second seizing pin located within the connector, providing additional compressive force between the central conductor and the first pin. In order to insert the first pin into the second without bending the center conductor, the first pin is supported through contact with exposed face of the dialectic layer around the center conductor. This method also eliminates the problem found in connectors with crimp-on center pins. The method of crimp-on center pins is not usually attempted with microcoaxial cable conductors as small as 0.25 mm OD such as are found in the new microcoaxial cables. Until now, the only reliable attachment method for these small cables has been soldering which has inherent craftsmanship limitations when installed in the field. The invention provides a device and method which allows the first pin to be pushed into the second forming a complete system. Upon insertion into the second pin (inside the connector) the first pin is compressed further to provide a reliable holding force and locked to prevent withdrawal. After insertion of the thus prepared microcoaxial cable into the connector, the outer jacket of the cable is crimped to the connector using traditional crimp tools. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.