Abstract:
The cable connection method is a method of connecting to conductors within a triaxial electrical cable, without completely severing the cable, allowing compact, low cost connections to be made while having the added benefit of strain relief of the cable around the connection point and even within the cable itself.

Description:
PRIORITY 
     This application claims priority through U.S. Provisional Application No. 61/135,974 filed by Henry B. Wallace on Jul. 25, 2008 for “Low Capacitance Audio Cable.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The cable connection method is a method of connecting to conductors within a triaxial electrical cable, without completely severing the cable, allowing compact, low cost connections to be made while having the added benefit of strain relief of the cable around the connection point and even within the cable itself. 
     2. Description of the Prior Art 
     Coaxial cables have been in use for many years. A common problem is connecting to a coaxial cable to access the signal on the inner conductor of the cable without completely severing the cable. Many inventions have been created to aid the goal of connecting to coaxial cables, typically by puncturing or removing part of the outer shield and insulation to access the inner conductor. These will be reviewed, and their applicability in connecting to triaxial cables evaluated. 
     For the purposes of reference, a triaxial cable is considered to have a first center conductor, an inner tubular shield conductor situated around the first center conductor and separated from it by a dielectric material (with optional semi-conductive outer layer for handling-noise suppression), an outer tubular shield conductor situated around the inner shield conductor and separated from it by an additional dielectric material, and an overall insulating layer. 
     Edlen, et al. (U.S. Pat. No. 2,694,182, Nov. 9, 1954) discloses a coaxial cable tap that pierces the outer insulator, shield and inner insulator to contact the center conductor using a hinged clamp assembly. Peripheral probes contact the shield to connect it electrically to other coaxial cables. While this performs suitably with coaxial cables, triaxial cables have and additional conducting layer that would require impractical piercing parts to connect to each conductor, such piercing parts being specially insulated and demanding critical positioning. 
     A functionally similar method is disclosed in Rheinfelder (U.S. Pat. No. 3,543,222, Nov. 24, 1970), and consists of a coaxial cable tap that pierces the outer insulator, shield and inner insulator to contact the center conductor and route its signal to one or more other coaxial cables. For triaxial cable connection, this is impractical, as cited for Edlen, above. 
     Rheinfelder (U.S. Pat. No. 3,625,623, Dec. 7, 1971) describes a method of accessing the conductors in a coaxial cable using a boring tool situated radially with respect to the central axis of the cable. Such a boring method adequately exposes the center conductor in a coaxial cable, but would not adequately also expose the inner shield conductor in a triaxial cable such that it could be easily connected to. 
     Down, et al. (U.S. Pat. No. 4,738,009, Apr. 19, 1988) discloses a coaxial cable tap that removes a semicircular section of the cable, then connects to the shield and center conductor using a clamping shell assembly. This method and assembly results in a coaxial cable tap construct that appears from the drawings to be approximately 10 to 15 times the cable diameter in length, which is unacceptably large. However, removal of a semicircular section of a triaxial cable would allow access to all three conductors and connection thereto. 
     The prior art is concerned with making connections to coaxial cables as are typically used in cable television distribution and radio frequency systems, where the connections must be made without interrupting service to customers, and where the impedance of the completed connection must not disturb the signals or system. In the case of a connection being made during factory assembly of a product, interruption of service is not an issue, and simpler methods may be used. With audio cables and systems, the characteristic impedance of the cable and connections is not important. While the prior art regarding coaxial cable taps provides some direction, it does not provide a solution that affords compact, low cost, strain relieved connections to audio triaxial cable. 
     After an electrical connection is made to a cable, it is also important to stabilize the connection against physical damage and encroaching moisture and contaminants. This is typically done with a sealing gasket or potting (encapsulating) operations. Of interest here are strain reliefs formed using epoxy or other potting compounds, as opposed to discrete molded plastic strain reliefs or seals. 
     For example, Jenets (U.S. Pat. No. 6,439,929, Aug. 27, 2002) discloses a standard strain relief application: “Often times, these terminating backshells are intended to be filled with a potting compound, such as at non-conductive epoxy or the like, which will protect soldered wire joints from the environment and to prevent corrosion, while at the same time providing some degree of strain relief to soldered wire joints.” Similar disclosure is found in Burger, et al. (U.S. Pat. No. 6,146,196, Nov. 14, 2000): “After termination, the back end of the coaxial contact system would be potted with epoxy to further lock in place and to provide strain relief.” 
     Takahashi, et al. (U.S. Pat. No. 5,679,008, Oct. 21, 1997) describes a similar strain relief: “It is preferable that the vinyl jackets  54  of the coaxial cables  5  are fixed to the circuit boards  41  with epoxy resin in order to reinforce the attachment of the coaxial cables  5 , providing strain relief.” 
     The prior art is replete with examples of the use of epoxy resins as stabilizing, sealing, and strain relief agents when used in the construction of cable connections. However, not disclosed is the possibility and express intention that the epoxy used in the potting process wicks into the cable along the interfaces between the various members of the cable&#39;s structure, cures there, and provides strain relief actually within the structure of the cable itself. 
     Bryant, et al. (U.S. Pat. No. 7,430,881, Oct. 7, 2008) discloses an optical fiber termination means where epoxy wicks into a tube around a fiber: “ . . . the pigtail  102  may be heated to wick epoxy up through the maria  205 . The protective sleeve  203  may then be reinserted and the epoxy allowed to cure (e.g., via UV curing), thus providing strain relief and securing the protective sleeve  203  without interfering in the optical path.” However, there is no disclosure of the epoxy wicking into the structure of the fiber to provide a strain relief, and all strain relief is external to the fiber. 
     McNeel (U.S. Registration No. H113, published Aug. 5, 1986) discloses an electrical cable termination and sealing method: “A select epoxy resin  84 , such as type CN-874 manufactured by Mereco Company infills housing  82 , surrounding the ends of the pins and sockets such as  52  and  60  within flanges  72 , the laced wire conductors  66  and  68 , brace stem  76 , and a predetermined length of cable  14 . The epoxy resin  84  forms a watertight seal within housing  82  and reacts chemically with cable  14  firmly anchoring it within the housing.” Here there is still no disclosure of epoxy encapsulant wicking into the structure of the cable and forming a strain relief. 
     Objects and Advantages of the Cable Connection Method 
     Several objects and advantages of the cable connection method are:
         1. Connections to the triaxial cable can be made in a small space, typically two to four diameters of the cable in length.   2. No elaborate clamping or shell arrangement is needed, and the frame for encapsulation of the connection may be inexpensive plastic.   3. Connections to the cable may be easily wired by soldering wires to the exposed conductors of the cable.   4. The entire connection area is potted in epoxy, which then wicks into the cable, creating a strain relief.   5. The assembly method requires no high tolerance machined parts or expert assembly skills, and can be accomplished with inexpensive materials.   6. The completed connection is impervious to moisture and contaminants.       

     SUMMARY OF THE INVENTION 
     The cable connection method is a method of connecting to conductors within a triaxial electrical cable, without completely severing the cable, resulting in compact, low cost connections with strain relief and contaminant resistance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing of a typical method of connection of two triaxial cables to a printed circuit board (PCB). 
         FIG. 2  is a drawing of a typical stripping profile of a triaxial cable. 
         FIG. 3  is a drawing illustrating an alternative, compact method of accessing the conductors within a triaxial cable. 
         FIG. 4  is a drawing illustrating another view of the conductors within a triaxial cable after removal of a section of the cable. 
         FIG. 5  is a drawing illustrating connection of a triaxial cable to a PCB using the compact method of conductor access. 
         FIG. 6  is a drawing illustrating the potting of the exposed area of a triaxial cable and connected PCB, and the wicking action that provides strain relief to the cable. 
     
    
    
     DETAILED DESCRIPTION 
     This application involves connecting to the three conductors of a triaxial cable, typically connecting those conductors to a PCB for some signal processing operation, for example a driven shield capacitance reduction scheme. In the past, such a connection was made as in  FIG. 1 , which shows a first triaxial cable  100 , a second triaxial cable  101 , each having a first center conductor  103 , an inner shield conductor  105  situated around the first center conductor  103  and separated from it by a dielectric material  104 , and an outer shield conductor  107  situated around the inner shield conductor  105  and separated from it by a yet additional dielectric material  106 , with an overall insulating layer  108 . Identically stripped lengths of each cable are shown, though various lengths and arrangements may be used depending upon the application. A PCB  102  receives soldered connections  109  to the cable conductors, either the conductors themselves or using additional lead wires, as shown in Scholz, et al. (U.S. Pat. No. 5,151,050, Sep. 29, 1992),  FIG. 3 , and in the specification: “The ground braid  34  is electrically connected to a corresponding terminal  28  by means of a wire  35  surrounding the ground braid  34  and soldered thereto.” 
     Such an assembly is labor intensive to construct in that the cables  100  and  101  must be precisely stripped (all stray braid conductors accounted for and restrained), and each of six conductors must be soldered to the PCB  102 . 
     Another disadvantage of the method if  FIG. 1  is that the size of the assembly is large.  FIG. 2  illustrates the stripping profile of a typical audio triaxial cable, where length “L”  110  is typically 1.5 cm to 2 cm. Thus for an inline connection the length would be at least 3 cm. The cables may be overlapped to some extent to reduce that dimension, but such overlap increases the width required on the PCB. 
     It would be better to tap the cable in some way that saves labor and space. 
     While many methods exist for tapping or connecting to coaxial cable, such methods do not directly apply to triaxial cables due to the additional shield conductor. Tapping elements that pierce the triaxial cable would have to be constructed with fine dimensions in order to contact a single conductor of the three, especially regarding the two inner conductors. Such tapping elements would also have to be positioned with great precision to avoid shorting to other conductors, and to make contact as intended. 
     Coaxial cable tapping methods are also generally designed to not disturb the impedance of the coaxial cable because they carry radio frequency (RF) energy. Any impedance perturbations on an RF coaxial cable, for example, in a cable television system, can produce line reflections that foul signal delivery to the customer. Thus coaxial RF tapping methods must be precise and as noninvasive as possible. 
     With audio cables, the impedance of the cable is relatively unimportant, especially for low-level signal cables. This permits other, less stringent methods to be used to tap or access the signals on the cable. This also allows optimization of other parameters, such as the space occupied by the tap arrangement. 
     The present cable connection method is not affected by the existence or lack of the noted optional semi-conductive layer within a triaxial cable, and as such this feature is not considered further except to say that it should be trimmed properly in the preparation of any connection assembly, which is standard procedure in the prior art. 
     PREFERRED EMBODIMENT 
     Referring to  FIG. 3 , to access the conductors in a triaxial cable  111  it is acceptable to remove a section from the side of the cable. This may be done by grinding, milling, or cutting, or by using another prior art method, as in Down, et al., but with the improvement that the center conductor is exposed in the process. (The method disclosed in Down, et al. leaves the center conductor fully enveloped in dielectric.) Cooling the cable before the removal process helps stiffen the cable and attain a cleaner cut. Such methods work as well on triaxial cable as on coaxial cable, and exposes all three conductors in a semicircular exposed area  120  of extent on the order of the diameter of the cable, typically less than 5 mm for an audio cable. A length  121  of center conductor  103  is exposed in this process, but the conductor is not completely severed. 
     Another view of the exposed semicircular area  120  is shown in  FIG. 4 . All three conductors of triaxial cable  111  are available for connection, including first center conductor  103 , inner shield conductor  105 , and outer shield conductor  107 , as designated in  FIG. 1 . 
     Referring to  FIG. 5 , after the semicircular section of cable  111  is removed, creating an exposure  120 , it is a simple matter to solder wires  130  onto the three cable conductors and connect them to a PCB  131 . The wires  130  may also be attached to the three cable conductors using mechanical pressure or conductive adhesive. Since this is an application for an audio signal cable, and the currents flowing are generally much less than 1 milliamp RMS, the wires may be of fine gauge. 
     It is also feasible to use conductors captured in a connector at fixed spacing, instead of discrete wires. Such conductors may be soldered to the three cable conductors, or maintained in contact using physical pressure or conductive adhesive. 
       FIG. 6  shows the assembly after being potted with epoxy, for example MG Chemicals type  832 B. The critical feature here, unexpected and not disclosed in the prior art, is that the epoxy  143  wicks into the internal structure of the cable  111  through exposure  120  to a distance of 1 cm-2 cm, providing a strain relief  140  inside the cable  111  after the epoxy cures. The internal structure of the cable consists of the components of the cable within the outer layer  108  (not shown in  FIG. 6 ). Such wicking generally occurs to a greater extent along the outer shield  107 , which is acceptable because a strain relief there will protect cable structures within. The cable  111  is shown exiting a plastic or metal potting enclosure  142  through apertures  141  in the walls, the apertures fitting the cable  111  snugly. Each aperture  141  does not compress the cable  111  as in a typical mechanical strain relief. Thus the epoxy wicks inside the cable  111  past the wall of the enclosure  142 . 
     Note that the potting enclosure and wall are not strictly required, and the epoxy wicks into the cable in any case, providing some strain relief against flexure of the cable where it enters the main mass of cured epoxy. 
     With this assembly technique, a strain relief  140  is created without the need for discrete rubber or plastic strain relief parts, and the strain relief is contained within the cable  111  and is not visible. The net effect is that the cable  111  is stiffer near the enclosure wall  142 , retarding wire breakage near the wall as the cable  111  is repeatedly flexed. 
     The epoxy  143  wicking action also serves to reinforce the exposed section of the cable  120  where the semicircular wedge has been removed (the dashed oval in  FIG. 6 ). This restores the cable  111  to a useful and sufficient tensile strength in the vicinity of the connection area. Enhanced wicking and strain relief may be had by potting the assembly under vacuum to draw more of the epoxy into the cable structure. It should be understood that this operation might include positive pressure as needed, depending on the specific configuration of the equipment. 
     Note that the references to strain relief with regard to potting cable assemblies in the prior art assume that the entire mechanical advantage of the potting compound occurs entirely on the outer surface of the cable, and the exposed conductors and insulators thereof. No statement of the advantage of the wicking of the epoxy into the cable is made, and this potential benefit is neglected. 
     Marketing by applicant of an audio cable featuring the cable connection method, after the filing of U.S. Provisional Application No. 61/135,974, has been successful. The audio cables have been praised by professional musicians, and the cables have withstood the typical abuse received from working musicians without failure. 
     The specific configuration of the embodiments discussed should not be construed to limit implementation of this cable connection method to those embodiments only. The techniques outlined are applicable to embodiments in other physical formats, using various methods of exposing the conductors in the triaxial cable, using various connection methods to the conductors in the cable, and using various potting compounds. The cable connection method is functional with a broad range of electrical cable, not just coaxial or triaxial cable. These techniques, structures and methods find applicability outside the realm of audio cables. Therefore, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.