COAXIAL CABLE HAVING A SIDE TAP CONNECTOR ASSEMBLY AND PROCESSES FOR MANUFACTURE

FIELD OF THE INVENTION

This invention relates to coaxial electric signal cables and connectors, and particularly to side tap connectors for tapping into a coaxial electric signal cable at any predetermined point and to processes for assembling the connector and coaxial cable.

BACKGROUND OF THE INVENTION

Coaxial signal cables are routinely used to transmit data from one point to another. Such cables comprise a center conductor surrounded by a dielectric material insulation, and a second conductor surrounding the dielectric material, usually comprised of braided conductor strands. The second conductor serves as an electrical shield, both to keep the transmitted signal from radiating out, and to keep unwanted radiation from entering the signal line. An overall jacket serves to protect the conductors from the environment the cable is used in. Coaxial signal cables are used to connect electronic equipment such as computer networks and work stations for digital and analog data transmission, audio and video data transmission as used in cable TV systems, as well as in acoustical arrays such as sonar arrays. It is frequently needed to splice into a coaxial signal line, for example to make a tee connection to branch out to a signal distribution point. Splicing is usually done by physically tapping into a coaxial cable along its length at a convenient point for branching. This can become tedious, complicated, and time consuming where the tap connectors are complicated and/or require special tools and skills for installation. Such splicing generally results in a large, bulky connection which is not suited for such applications such as underwater towed acoustical arrays which must generally have size

and weight minimized.

Several methods are currently used to tap into a coaxial cable. One method is to cut the coaxial cable, terminate each end with a connector, and to connect each connector to a branching connector, such as a tee connector. This method is labor intensive, requires special tools, and results in a bulky connection. This method also has an interrupted signal path, causing a degradation of electrical performance, particularly when used to transfer data at high rates. In a second method, some form of a saddle clamp device is used, in which the saddle clamp positions the connector in relation to the coaxial cable, and some means is provided to pierce or remove the outer layers of shield and dielectric material, and a pin or post is made to contact the center conductor. Connectors of this type are taught in U.S. Patent 2,805,399 to Leeper, and U.S. Patent 4,691,976 to Cowen. The Leeper invention is complicated, requiring specially designed and fitted parts, and relies on almost perfect positioning of both the center conductor and the connector for reliable operation. The Cowen invention likewise requires many complicated and specially fitted parts for proper operation, and results in a bulky connection.

A third method of making side tap connections is taught by Buck in U.S. Patent No.'s 5,163,852 and 5,203,721. The methods taught by Buck provide for a low profile connection with an unbroken signal conductor in the coaxial line. However, these inventions have drawbacks as well. The invention of U.S. Patent No. 5,163,852 requires labor intensive tinning, soldering, and cutting of the braided outer conductors. The resulting disruption of the braid is compensated for by the placement of cylindrically curved conductive top and bottom caps. This results in a relatively stiff tap section, as well as additional soldering steps for assembly. The invention of U.S. Patent No. 5,203,721 eliminates the need for tinning, cutting and soldering of the braided outer conductors, but is not easily anufacturable when the pin heights are greater than about 0.050 inches, and this method does not lend itself to easily changing the tap dimensions such as pin height, and pin center spacing.

There is a need for a coaxial side tap assemble which does not

sever either the center conductor or the braided outer conductors of the signal line, is not bulky when in place, is easy to use without special tools or skills, and can be easily adapted to differing center-to-center spacings of the tap pins, and to differing pin heights, especially pin heights greater than about 0.050 inches.

SUMMARY OF THE INVENTION

The invention comprises a coaxial cable having a side tap assembly and processes for its manufacture. The coaxial cable comprises a center conductor surrounded by a dielectric material insulation. The dielectric material is surrounded by an electrically conductive outer conductor comprised of a plurality of strands of conductors braided around the dielectric material. A protective polymer jacket is generally applied over the braided outer conductor.

The tap assembly is comprised of a section of the cable where the insulation has been removed to expose the center conductor. A plastic cap in the shape of a hollow tube of generally circular cross-section and having a longitudinal slit opening is fitted over the insulation of the cable and under the braided outer conductor at the tap area. The plastic cap has two generally circular openings approximately opposite the longitudinal slit opening. An insulated center conductor contact pin is attached to the center conductor of the cable at the tap area where the section of cable insulation is removed and extends perpendicularly through one of the generally circular openings of the plastic cap, through the braided outer conductor, and through the protective polymer jacket. A shield contact pin in the shape of an "L" is placed such that the short portion of the "L" is generally parallel to and co-planar with the center conductor pin, and extends through the other generally circular opening in the plastic cap, through the braided outer conductor, and through the protective jacket. The long portion of the "L" is parallel to and contiguous with the insulation of the cable and extends from under the plastic cap to be in contact with the braided outer conductor.

The assembly of the invention is prepared by removing a short section of insulation from the insulated center conductor at the point a tap is desired, prior to the time of applying the braided outer conductor. An insulated electrically conductive center tap pin is connected, such as by soldering, to the exposed center conductor of the cable at the point the insulation is removed. The center tap pin may be comprised of a solid copper conductor, and the insulation on the center tap may be comprised of electrically insulating shrink tubing applied after the soldering step. A shield contact pin is formed by bending an uninsulated electrically conductive member, such as a solid copper conductor, in the shape of an "L", and positioning it in relationship to the center tap pin such that the short leg of the "L" is parallel to and co-planar with the center tap pin, and the long leg of the "L" is parallel to and in contact with the insulation of the cable. A plastic cap of the same or matching cylindrical curvature as the insulation of the cable, preferably being comprised of a thin-wall insulating tube having a longitudinal split opening along its length, and having two generally circular openings approximately opposite the split which are spaced in line a distance apart corresponding to the desired distance between the center tap pin and the shield contact pin, is placed over the tap area such that the insulated center conductor pin and the shield contact pin extend perpendicularly through their respective openings, and the plastic cap encloses substantially all of the opening in the cable insulation which was formed when the section of insulation was removed. A braided outer conductor is now applied around the cable insulation and the plastic cap, the braided conductors tightly contacting the shield contact pin along a portion of the long leg of the "L" and braiding around the base of both the insulated center conductor pin and the shield contact pin where they extend perpendicularly from the cable. To facilitate the application of a protective jacket, the center conductor pin and the shield contact pin are bent down, preferably into the area between them, so as to minimize the diameter change from the area of the tap to the rest of the cable. The cable is then jacketed with a protective polymer in an extrusion process known in the art generally as tube extrusion, and allows the bent tap pins to pass through the extrusion die

unhindered. Once the jacket is in place, the jacket is opened at the tap area by making a small slit in the area of the bent-down tap pins, and the tap pins are then bent back up straight again. With the assembly of the invention center to center spacing of the tap pins may easily be set or changed simply by changing the spacing of the two openings in the plastic cap member. The pin height is simply set or changed by making the pins slightly longer than desired at the time of manufacture, and then trimming to length as a final step. The pin height and spacing may be easily designed for a variety of connector types including through-hole soldering to a printed circuit board and tee connections which are comprised of sockets which plug directly to the pins. A cable of the invention may have multiple taps within a given length, only some of which actually get used, the others remaining un-used under the protective polymer jacket. A cable of this type is useful for applications where it is not known at the time of cable manufacture how many, and at what spacing, certain taps are needed such as in local area networks for computers and workstations.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side view of the tap area of an insulated center conductor 1 with a section of insulation 14 removed 2 showing center conductor pin 4 with insulation 5 connected to center conductor 3.

Figure 2 is a side view of the tap area showing the insulated center conductor pin attached, and the shield contact pin 6 in position.

Figure 3 is a side view of the tap area with the plastic cap 7 in place.

Figure 4 is a side view of the tap area with the braided outer conductor 8 applied.

Figure 5 is a side view of the tap area with the center conductor pin and the shield contact pin bent down.

Figure 6 is a side view of the tap area after the application of a protective polymer jacket 11. Figure 7 is a side view of the complete tap after the center

conductor pin and the shield contact pin are bent up straight again.

Figure 8 is a blown up perspective view of the tap components in spatial relationship to each other.

DETAILED DESCRIPTION OF THE INVENTION

The invention and processes for its manufacture are now described with reference to the drawings to more fully and carefully delineate the components of the invention, and how they are assembled by the processes of the invention. Figures 1 through 7 show the steps of the assembly process in sequential order and serve to describe the invention as well.

Figure 1 shows the assembly of the invention at the first stage of manufacture. The insulated center conductor of the cable 1 has a section of insulation 14 removed 2 to expose the center conductor 3. The insulation 14 is removed by cutting away, as with a laser beam. Attached to the center conductor 3 is the center conductor pin 4 with insulation 5. The center conductor pin 3 is preferably formed into a J-hook as shown in Figure 8 and preferably soldered onto center conductor 3. The formation of the J-hook gives better mechanical strength to the soldered joint. The insulation tube 5 must extend above and below the level of insulation 14 by an amount which will prevent contact of the center conductor pin 4 and the strands of the braided outer conductor 8 shown in Figure 4. The insulation tube 5 is preferably comprised of an electrically insulating heat-shrink insulation tube which is applied after attachment of center conductor pin 4.

Figure 2 shows the positioning of shield contact pin 6. Shield contact pin 6 is in the shape of an "L", and is positioned such that the short portion 6A forms the second of two generally parallel and co-planar pins with the center conductor pin 4, and the long portion 6B of shield contact pin 6 is parallel and contiguous with insulation 14 and extends in length a distance sufficient to be exposed beyond the plastic cap 7 shown in Figure 3. Shield contact pin 6 may be held in place with adhesive tape to hold the correct orientation during manufacture. If desired, the

adhesive tape may be left on, or removed at the time the braided outer conductor 8 is applied.

Figure 3 shows the plastic cap 7 installed over the insulated core 1 and the tap pins 4 and 6A. The openings 7A and 7B are sized slightly larger in diameter than their respective tap pins 4 and 6A. The opening for the insulated center conductor pin 4 must be large enough to include the insulation 5 as well. The plastic cap is comprised of thin-wall plastic tubing which has a longitudinal split opening 7C along its length as shown in Figure 8. It is a simple matter then to spread the plastic cap 7 at the split 7C and place it over the two tap pins 4 and 6A and the cable insulation 14. The plastic cap serves to set the center-to-center spacing of the two tap pins 4 and 6A, as well as to prevent the braided outer conductor 8 shown in Figure 4 from electrically contacting the center conductor 3 or the center conductor pin 4.

Figure 4 shows the tapped area after the braided outer conductor 8 has been applied over the center conductor insulation 14 and around the two tap pins 4 and 6A. This step is accomplished by using a standard braider known in the art such as that made by the Wardwell company. At the point the strands are braided a large die ring is used to allow the tap pins 4 and 6A to pass through unhindered. A high braid angle, such as about 35ø off of the longitudinal axis of the cable, is necessary to minimize the opportunity for the strands of the braided outer conductor 8 to get snagged by the two tap pins 4 and 6A at the time the braided outer conductor 8 is applied.

Figure 5 shows the two tap pins 4 and 6A bent down in preparation for the application of a protective jacket 11 as shown in Figure 6. Care must be taken when bending down the two tap pins 4 and 6A to avoid over stressing them at the location of the bend. Figure 6 shows the area of the tap after the application of the protective polymer jacket 11. The protective polymer jacket 11 is applied using standard extrusion equipment known in the art. A tube extrusion process is used, with the tip and die sized so as to allow the two bent tap pins 4 and 6A to pass through unhindered.

After the application of the protective polymer jacket 11, a slight lump 12 is an indication of the location of the two tap pins 4 and 6A.

Figure 7 shows the area of the tap after completion of all the manufacturing steps. The area of the protective polymer jacket 13 between the two tap pins 4 and 6A has been slit, as with a sharp knife, or melted as with a hot knife, and the two tap pins 4 and 6A have been bent back straight again. The area 13 of the protective polymer jacket 11 between the two tap pins 4 and 6A may be left as is, or sealed by melting and smoothing back together the protective polymer jacket using a hot knife.

The conductive materials used in this invention are any of the conductive materials known to be useful in the art for coaxial signal lines, including solid and stranded copper and aluminum conductors, both unplated and plated as with silver, tin or gold. The insulation 14 over the center conductor 3 may be any of the materials found useful in the art for coaxial signal lines such as polyethylene or PTFE, but expanded PTFE (ePTFE) is preferred for the cable used in this invention. The protective polymer jacket used in this invention may be any material common in wire and cable manufacture, particularly thermoplastic materials, but the preferred material for the assembly of the invention is polyurethane due to its inherent toughness and resistance to abrasion.

The assembly of the invention is easily manufactured by the processes of the invention, is very light in weight, has a minimum cross-section, is inherently easily adaptable to differing center- to-center spacings of the tap pins, as well as differing height requirements of the tap pins. Easy and rapid connection and termination to a branch coaxial cable or other device such as acoustical transducers is provided. The assembly is useful in towed underwater sensors, such as those used in sonar arrays.