Corrugated Coaxial Cable

Abstract

A connector is disclosed for use with coaxial cable of a type having a rigid armoring sheath which is corrugated and which surrounds a coaxial outer conductor and an inner conductor supported along the center of the cable with dielectric material. The connector includes a one-piece outer conductive shell which is crimped down directly onto the armoring sheath of the cable at its ends and an inner contact structure comprised of a sleeve crimped onto the center conductors of the ends of cables and supported within the outer shell by dielectric inserts. The outer shell has an undeformed inner diameter sufficient to pass over the outside of the armoring sheath for installation of the inner contact structure prior to a final positioning of the outer shell and crimping thereof onto the cable. The outer shell is not much larger in maximum diameter than that of the cable and is relatively smooth to facilitate multiple usage in coaxial tubes carrying twenty or more coaxial cables.

Description

Frequency space limitation is forcing the telephone industry to change from microwave space transmission to coaxial cable transmission with most cables being placed underground. One cable developed for such use includes a center conductor of solid copper held by discs or spirals of dielectric material within an outer copper conductor, all surrounded by a rigid, corrugated sheath. Cables of this construction are combined in ten or more pairs within a heavy metal tube laid underground. Cable systems made of such tubes are extended for hundreds of miles underground with amplifiers located every several miles to maintain an adequate signal level. The development of coaxial cable which is mechanically strong to maintain concentricity and efficient signal transfer in underground usage coupled with the fact that many thousands of miles of individual cable must be laid having tens of thousands of joints has, in turn, created a need for a connector which is mechanically and electrically compatible with the cable but which is inexpensive and can be applied quickly and reliably in the field. Additionally, the connector for such use must be compact so as to be employed in multiple within a protective joint of limited size.

The present invention relates to a coaxial connector for coaxial cable having a rigid corrugated protective sheath and particularly to a coaxial splice capable of carrying communication signals of appreciable frequency with minimum loss and signal reflection.

It is the object of the present invention to provide a coaxial device for splicing coaxial cables quickly and reliably in the field. It is another object to provide coaxial cable splice techniques which can be accomplished in the field with a minimum requirement of skill. It is still another object to provide a coaxial splice for use with corrugated coaxial cable of a type used by the telephone industry.

The foregoing objects are obtained by the present invention through the use of a connector which had only two parts which must be handled to interconnect the ends of corrugated coaxial cable. One part forms a center contact structure and is comprised of a malleable metal sleeve with dielectric inserts affixed to each end. The other part is a one-piece malleable metal shell internally dimensioned to slide over a cable end so as to permit the center contact structure to be crimped onto the center conductors of the cable with the shell then being positioned over the outer sheath of the cable ends and crimped directly onto the corrugated sheath of the cable. The crimp employed deforms portions of the outer shell in a corrugated fashion to match up with the corrugation of the sheaths and provide a mechanical and an electrical joining of the cable ends.

In the drawings:

FIG. 1 is a perspective view of a tube containing a plurality of coaxial cables interconnected by coaxial connector splices in accordance with the invention;

FIG. 2 is a view of an individual splice as shown in FIG. 1 but considerably enlarged;

FIG. 3 is a perspective and exploded view of the coaxial splice of FIGS. 1 and 2 separated from dressed coaxial cable ends;

FIG. 4 is a longitudinal view in partial section of a splice in accordance with the invention as terminated to corrugated coaxial cable ends and further showing to the left dies in the process of deforming the outer shell against the corrugated sheath of the cable; and

FIG. 5 is a perspective view of a tool carrying the dies shown in FIG. 4.

Referring now to FIG. 1, T represents a tube of a type laid underground to form part of a coaxial cable system. Tube T is typically comprised of a lead shell L lined and covered with a protective plastic S. Tube T typically contains ten pairs of coaxial cables 10 and in addition a number of individual electrical leads. Cables 10 are joined by splices 16 within a protective joint J interconnecting the ends of tubes T. Tubes T containing lengths of cables and leads are installed in a trench with the cable ends being terminated when necessary according to the length thereof. This is typically done in the field and in the trench. Alternatively, splices are made adjacent to the trench with completed joints being then lowered into the trench.

The individual cables 10 are shown in FIGS. 2 and 3 comprised of a solid center conductor 12 concentrically mounted within an outer conductor 14 which is secured within a corrugated protective sheath 15. The center conductor 12 is supported concentrically of the outer conductor by dielectric discs fitted within the outer conductor or in certain constructions by dielectric material extending spirally along the length of the cable and wrapped around the center conductor. A typical cable has a solid copper center conductor 12 approximately 0.100 of an inch in diameter with dielectric discs approximately 0.085 of an inch thick formed of polyethylene material spaced every inch along the cable. The outer conductor 14 is 0.004 of an inch copper sheet material formed into a tubular configuration and bonded to the outer sheath 15 which is a tin-plated steel 0.010 of an inch having a soldered butt-lap seam. The resulting cable structure is quite rigid.

FIGS. 1, 2 and 4 show a splice version 16 of the invention terminating the ends of cables 10. This termination is designed to mechanically join the cable ends and to electrically join the inner and outer conductive portions of the cable so as to provide a transmission path for signals carried by the cables. As shown in FIGS. 3 and 4, the invention splice 16 is comprised of essentially two parts, an outer conductive shell 18 and an inner contact structure 24. The inner contact structure 24 includes a hollow sleeve 26 of a reduced diameter at each end 28 which is fitted within a dielectric support element 32. Support elements 32 each include an inner bore 34 which receives 28 and a pair of ports 36 are included to provide passage for gas in the event the cables are pressurized. The support elements 32 are locked to sleeve 34 by flairing end portions 28 after the elements have been mounted on the sleeve.

The outer shell 18 is comprised of a one-piece element formed of sheet metal into a tubular configuration having a seam shown as 20 in FIG. 3. Seam 20 is preferably brazed or otherwise jointed to make the piece integral. At each end of 18 is a portion 22 of reduced diameter. The interior diameter of 22, shown as D, is just large enough to fit over the outside of protective sheath 15 of the cable. FIG. 3 shows, to the right-hand side, the end portion 22 of a shell 18 positioned over a cable end preparatory to termination.

In terminating the cable a portion of the outer conductor 14 and the sheath 15 is first removed to expose a portion of the center conductor 12, as shown in FIG. 3. The center contact structure 24 is then placed in position with the center conductors 12 of each cable end inserted therein. Sleeve 26 is then crimped inwardly in the manner shown in FIG. 4 to permanently join the sleeve to the center conductors 12. This may be done by any suitable crimping tool in a standard manner. Next the shell 18 is slid over the center conductor structure to the position shown in FIG. 4 with portions 22 then deformed inwardly as by crimping to mechanically and electrically connect the shell to the cable outer sheath 15. A tool 40 used to effect both outer crimps is shown in perspective in FIG. 5 and in place in FIG. 4. The tool should include a suitable straight action driving mechanism, a variety of which are available in both hand- and bench-mounted versions. The tool includes an indexing blade 42 which in use is centered within the valley of a corrugation of 15 properly spaced from a cable end. With 42 so positioned, the crimping dies shown in 44 and 46 are then properly aligned in accordance with the remaining corrugations on a cable end. The shell 18 is then worked over the cable end toward 42 and the tool is then operated to drive the dies 44 and 46 relatively together to deform portion 22 of shell 18 inwardly and into the corrugations of 15. The tool is then reversed with the other portion 22 crimped inwardly to terminate the other cable end.

As can be discerned from FIG. 4, the die surfaces are bladelike to result in a series of indentations bringing the metal of 22 into an intimate surface deforming engagement with 15 without crushing the sheath or outer conductor 14. The indexing blade 42 is secured to the fixed dies 44 and is extended inward of the die surface to facilitate cable alignment.

The center region of the outer shell 18 is appropriately enlarged by standard design techniques in order to compensate for the increase in diameter of the center contact sleeve 26 which would otherwise adversely affect the characteristic impedance of the connector in this region. The outer surface of 18 is smooth and not much larger than the cable to facilitate packaging in the manner shown in FIG. 1.

In brief summary, it will be observed that the splice in the invention includes only two parts which must be physically handled with both parts being of a configuration to be readily installed by hand in the field. It will be further observed that the terminating procedure is simple and straightforward.

In an actual embodiment of the invention splice sleeve 26 was formed of an annealed copper 0.025 of an inch in wall thickness, the insert supports 32 were of polyethylene and the outer shell 18 was of annealed copper of 0.020 of an inch in wall thickness. Elements 26 and 18 were both tin plated. A termination like that shown in FIG. 4 was tested mechanically and electrically. It was found that the termination of the center conductors was adequate to prevent center conductor displacement and that the overall termination was capable of standing a tensional load of in excess of 600 pounds, in excess of 300 pounds individually for the center contact and for the outer sleeve. The resulting connection was found to pass signal frequencies without appreciable loss or reflection in excess of 2300 MHz.

Having now disclosed the invention in terms intended to enable a preferred practice thereof, claims are appended which are believed to define what is inventive.

Claims

We claim:

1. A coaxial electrical connection comprising: a coaxial cable having an inner conductor and an outer conductor and a protective sheath extended over said outer conductor, said sheath including sheet metal having annular corrugations therein to provide a rigid tubular structure, a connector mechanically and electrically secured to said cable and including an inner contact element terminated to the cable inner conductor and an outer conductive member terminated to the cable outer conductor, said outer conductive member comprising a shell of malleable metal including a tubular end portion extended over and receiving therein the cable protective sheath, said end portion being crimped inwardly against said protective sheath forming a series of indentations of a configuration overlying and corresponding to the configuration of said corrugations around the periphery of said protective sheath, said outer member having an outer diameter not much greater than the outer diameter of said protective sheath.

2. The connection of claim 1 wherein said shell is comprised of one piece of sheet metal formed into tubular configuration.

3. A splice between coaxial cables each of the type having an inner conductor, an outer conductor and an outer protective sheath formed of corrugated sheet metal, comprising: two component parts, one of said parts being comprised of a center contact element including a sleeve of malleable metal receiving and joining together the center conductors of a pair of said coaxial cables and crimped inwardly in electrical and mechanical connection with said center conductors, said one of said parts including further a dielectric element positioned on each end of said sleeve and engaged against an end of a sheath and outer conductor of a corresponding one of the pair of said coaxial cables, the other of said parts being comprised of a shell of malleable metal including at each end a tubular portion received over and crimped inwardly directly against the protective sheath of each of said coaxial cables, said shell being comprised of sheet metal with a series of deformations in said tubular portion, said series overlying said protective sheath of each of said coaxial cables and of a configuration corresponding to that of the corrugations of said protective sheaths.

4. The splice of claim 3 wherein, said one part consists of said sleeve with said dielectric elements being secured to the ends of said sleeve and in radial-spaced relationship with respect to said shell, and said shell consists of a one-piece metal tubular element.