US 3872237 A
A joint between coaxial cable ends includes an outer tubular shell in two symmetrical halves having a wider diameter midsection and narrower diameter ends. Outer sleeves are placed around each shell end over the outer coaxial conductors and reinforcing sleeves are disposed over dielectric spacers within the outer conductors. An inner sleeve is crimped over the two inner conductor ends and a section of dielectric spacer is positioned around the inner sleeve. The outer tubular shell portions are placed around the inner sleeve and spacer with the narrow portions over the reinforcing sleeves and outer conductors. The outer sleeves are crimped over the narrow shell ends to lock them in place. Characteristic impedance across the joint is maintained by a proper sizing ratio between the outer diameter of the inner sleeve and inner diameter of the midsection of the shell.
Description (OCR text may contain errors)
United States Patent to] Eyre et a1.
 JOINT FOR COAXIAL CABLE END  Inventors: John Richard Eyre; Kenneth Richard Way, both of Kent; David Neil Kielty, London, all of England  Assignee: International Standard Electric Corporation, New York, NY.
 Filed: Apr. 3, 1974  Appl. No.: 457,518
 Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS Sweden 174/88 C Mar. 18, 1975 Primary Examiner-Darrell L. Clay Attorney, Agent, or Firm-John T. OHalloran; Menotti J. Lombardi, Jr.; Edward Goldberg [5 7] ABSTRACT A joint between coaxial cable ends includes an outer tubular shell in two symmetrical halves having a wider diameter midsection and narrower diameter ends. Outer sleeves are placed around each shell end over the outer coaxial conductors and reinforcing sleeves are disposed over dielectric spacers within the outer conductors. An inner sleeve is crimped over the two inner conductor ends and a section of dielectric spacer is positioned around the inner sleeve. The outer tubular shell portions are placed around the inner sleeve and spacer with the narrow portions over the reinforcing sleeves and outer conductors. The outer sleeves are crimped over the narrow shell ends to lock them in place. Characteristic impedance across the joint is maintained by a proper sizing ratio between the outer diameter of the inner sleeve and inner diameter of the midsection of the shell.
4 Claims, 5 Drawing Figures JOINT FOR COAXIAL CABLE END BACKGROUND OF THE INVENTION -l. Field of the Invention This invention relates to jointing arrangements for coaxial cores or cables and particularly to an improved joint having diameter ratios of the components selected to maintain a characteristic impedance.
2. Description of the Prior Art Several ways of joining two coaxial cores are already known. In one, for example, the inner conductors of the two cores are brazed together. This, of course, requires equipment with which to braze and also some means of aligning the cores and holding them in juxtaposition so that the brazed joint is both smooth and sound.
Another way, and one which is extensively used, dispenses with the need for brazing equipment and automatically ensures alignment because the two inner conductors are inserted into a sleeve which is then crimped onto the conductors. However, the sleeve must be slightly bigger in outside diameter than is the diameter of the inner conductors. The outer conductors of the bore has, up to now, been joined by a simple tube having an inner diameter substantially the same as the outer diameter of the outer conductors. Thus over the length of the joint there are differences in the ratio of the diameter of the inner conductor, including the sleeve, to the inner diameter of the tube and outer conductor, and these differences cause discontinuities in the characteristic impedance of the core which, although negligible at low frequencies, become increasingly important as the frequency used is raised.
SUMMARY OF THE INVENTION It is therefore the primary object of the present invention to provide an improved coaxial cable joint in which a ratio of diameters between components is chosen to maintain the characteristic impedance of the cores along the joint. This is achieved in the present invention by a jointing arrangement for a coaxial cable core of the kind wherein the inner conductors are joined by means of an inner sleeve crimped thereon. In order to join the outer conductors in such a way that the characteristic impedance of the cores is maintained over the length of the joint, a plurality of shells are positioned to form a tubular enclosure about the joined inner conductors and inner sleeve. The enclosure has a midsection of larger diameter than its ends, with the narrower ends encircling the ends of the coaxial cores to be joined at points where reinforcing sleeves lie under the outer conductors. The tubular ends are in turn encircled by outer sleeves which are crimped to lock the enclosure in position relative to the cores, and the ratio of the inner diameter of the enlarged shell enclosure, where it surrounds the inner conductors and sleeve, to the outer diameter of the inner sleeve, is so chosen as to maintain the characteristic impedance of the cores.
An embodiment of the invention is described below with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded view of a joint arrangement, not accurately to scale so that details may be clearer;
FIGS. 20, b, and c are plan, side and end views of an outer conductor jointing shell shown in FIG. 1; and
FIG. 3 is a section, with scale greatly distorted for clarity, through a completed joint.
DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, two inner conductors, la and 1b, are stripped of all covering for a sufficient distance to allow them to be inserted into an inner metallic sleeve 2. The sleeve has an inner indented surface, readily obtained by running a suitable tap through it, which bites into the inner conductors when the sleeve is crimped onto them.
Before the sleeve is positioned on the inner conductor and crimped to them, an outer metallic sleeve, 3a and 3b, is placed on the end of each core to be jointed and slid over the outer conductor 4a and 4b, and a reinforcing metal sleeve 5a and 5b, which just slides on the dielectric spacer, 6a and 6b, is pushed under the outer conductor.
The sleeve 2 is then crimped onto the inner conductors 1a and lb. A dielectric spacer 8, as shown in FIGS. 1 and 3, is put around the sleeve, preferably a piece of that spacer that was removed when the inner conductors were bared, and held in place by any suitable means.
Next, two outer metallic jointing shells 7x and 7y are positioned about the sleeve, these shells having narrow portions which fit onto the outer conductors 4a and 4b where the reinforcing sleeves have been inserted, and wide portions which enclose the jointed inner conductors and sleeve. As shown here (FIG. I and FIGS. 2a, b, c, which are plan, side, and end elevations, respectively, of one shell) the shells are symmetrical about a plane through the axis of a straight length of cable and parallel to it. The two shells are identical and when in position form a tube with a midsection of larger diameter than the ends.
With the shells in position the outer sleeves 3a and 3b are slid over the narrow ends of the shells and crimped, thus locking the shells into position with respect to the inner conductors and sleeve. The joint is then essentially complete, the sleeve 2 on the inner conductors being surrounded by the shells in such a way that the characteristic impedance of the cores is maintained across the joint by suitably proportioning the inner diameter of the enlarged midsection of the shell enclosure to the outer diameter of the inner sleeve. The assembled joint is shown, in section and with the scale much exaggerated for clarity, in FIG. 3. For strength in the joint, and to provide screening where necessary, a short length of steel tube is positioned about the joint and fixed there. Any stripped-back screening is then brought up to the ends of the tubes surrounding the joint. Finally, insulation can be applied over the whole of the core exposed in order to make the joint.
It is possible that two shells, instead of being as shown in the drawings, are each tubular, having two parts of different diameters, so that when the two parts of larger diameter are butted together the shells form a similar enclosureto that formed by the shells illustrated.
However, two such shells would have to be joined together either beforehand, when being manufactured, or in situ', which would require equipment to make brazed, or soldered, or cold-welded joints between the shells. The shells we have described and illustrated are much simpler to manufacture than the tubular shells, being simple pressings in copper tape of roughly the same thickness as the outer conductors of the cores,
and the enclosure is made in situ with easily handled tools. Thus, although the alternative described is feasible, it is not preferred for practical reasons.
Again, the enclosure could be made of more than two shells, say three similar shells, each substantially 120 at the center of the enclosure. This is feasible but not practical as the more shells there are to assemble into an enclosure the more difficult the assembly becomes. Therefore, two is the preferred number of shells.
While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by'way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.
What is claimed is:
1. A jointing arrangement for a coaxial cable core comprising a pair of cable ends including a pair of adjacent inner conductors, dielectric spacers surrounding said inner conductors at a distance from said ends, a pair of outer coaxial conductors around said spacers, an inner metal-sleeve about the ends of said inner conductors, a dielectric sleeve about said inner sleeve, a pair of reinforcing metallic sleeves around respective said dielectric spacers adjacent each end, said outer coaxial conductors surrounding said reinforcing sleeves,
a plurality of like outer metallic tubular shells positioned to form a tubular enclosure about the adjacent inner conductors and inner sleeve, said tubular shell enclosure having a larger diameter midsection spaced from said dielectric sleeve and having narrower diameter outer ends, said outer ends of said enclosure encircling the respective ends of said outer coaxial conductors over said reinforcing sleeves, and a pair of outer metallic sleeves surrounding respective said outer enclosure ends, said outer sleeves being crimped to lock the tubular shell enclosure in position relative to said inner and outer conductors, the ratio of the inner diameter of said midsection of said tubular enclosure surrounding said inner conductors and inner sleeve to the outer diameter of said inner sleeve being selected to maintain the characteristic impedance of said inner and outer coaxial conductors.
2. The arrangement of claim 1 wherein two symmetrical shells each form half of the tubular enclosure.
3. The arrangement of claim 2 wherein said two shells are identical and symmetrical around a plane parallel to and passing through the axis of a straight piece of coaxial core.
4. The arrangement of claim 3 wherein said inner sleeve is crimped over said inner conductors.