Method And Apparatus For Securing A Connector To A Coaxial Cable

Abstract

A method and apparatus for securing a connector to a coaxial cable, and in particular to a multilayer core coaxial cable, without causing any damage or disturbance to the core. A split ferrule is fitted together over an exposed portion of the core at the end of the cable and is then pushed back with a sleeve formed on the rear of the ferrule being forced between the cable core and outer conductor. When the ferrule is in place, it is secured to the cable by suitable means, such as crimping, and the forward portion of the ferrule is utilized to secure the ferrule, and thus the cable, to a connector body.

Description

This invention relates to a method and apparatus for securing a connector to a coaxial cable, and more particularly to a split ferrule which may be utilized to effect such a connection to a multilayer core coaxial cable without causing fraying or other damage to the dielectric cable core.

In most applications where a connector is secured to a coaxial cable, a cylindrical ferrule having an elongated shoulder is placed over the end of the cable and the shoulder is forced back between the cable core and the outer conductor of the cable. The cable is then secured to the ferrule by crimping or other means and the forward end of the ferrule is utilized to secure the cable to a connector body.

With standard coaxial cables using extended polyethylene and Teflon dielectrics, this procedure causes no problems. However, standard cables are only moderately flexible and, in applications where a highly flexible cable is required, a multilayer core is employed. When a tight-fitting ferrule is forced over the end of such a cable core, it generally picks up the end of the core, causing portion of the core to be pushed back. With large cables and connectors, this is not a serious problem. However, with small, precision coaxial connectors, where VSWR is critical, such disturbance to the cable core cannot be tolerated.

It is, therefore, a primary object of this invention to provide a method and apparatus for securing a connector to a multilayer core coaxial cable without causing any damage or disturbance to the core.

A more specific object of this invention is to provide a ferrule which may be used in conjunction with cables having a multilayer core without causing damage or disturbance to the cable which would adversely effect VSWR.

In accordance with these objects, this invention provides a ferrule which is formed by fitting together at least two ferrule segments. These segments may be fitted together over an exposed cable core at the end of the cable to form a ferrule having an enlarged cylindrical portion and an elongated cylindrical sleeve of smaller diameter concentric therewith. The sleeve ends in a tapered surface which is adapted to fit under the outer conductor of the cable. Since the ferrule is already in a position over the cable core before any sliding occurs, it does not cause dielectric bunching and other distortion to the dielectric which occurs when attempting to thread the dielectric through the bore of a one-piece ferrule. Means for aligning the segments are provided so that they may be properly fitted together. The end of the ferrule adjacent the enlarged portion forms a flat surface perpendicular to the axis of the ferrule which surface may be utilized as a trimming jig for the cable core when the ferrule is properly positioned.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a cutaway diagram of an assembled connector and cable utilizing the teachings of this invention.

FIG. 2 is a cutaway side view of a pair of ferrule segments suitable for use in a preferred embodiment of the invention.

FIG. 3 is a front view of the ferrule segments shown in FIG. 2.

Referring now to FIG. 1 it is seen that coaxial cable 10 is formed of an inner conductor 12, a multilayer insulating core 14, a braided outer conductor 16, and an insulating outer cover 18. In securing cable 10 to a connector body 19, outer conductor 16 is first cut back a short distance from the end of the cable, the distance being about an inch but not being critical, and outer cover 18 is then cut back by an additional distance of about an inch from outer conductor 16. A bushing 20 of a metallic conducting material, a crimp ferrule 22 of a similar material, and a coupling ring or collar 24, which is also of a metallic material, are then slipped in succession over the end of cable 10. Collar 24 has an internally threaded ring 26 projecting therefrom.

A ferrule 28 of a metallic conducting material, such as brass, is then fitted over the exposed portion of cable core 14. FIGs. 2 and 3 show ferrule 28 in more detail. From these FIGS. it is seen that ferrule 28 is formed of two like segments 28A and 28B. Each of these segments includes an enlarged semicylindrical portion 30, and an elongated sleeve 32. The end of portion 30 has a short 45.degree. angle chamfer 34 and a flat surface 36 the function of which will be described shortly. The rear corners of portion 30 are also chamferred. Each sleeve 32 has a ridged surface 38 and ends in a surface which tapers at a slight angle such as, for example, 15.degree.. The mating surface of the segments of ferrule 28 have semicircular indentations which combine, when the segments are fitted together, to form an internal bore 42 having a diameter approximately equal to the diameter of multilayer core 14. A pair of aligning pins 44 are fitted and secured in a mating pair of openings in one of the segments and, when the segments are properly aligned, fit into a pair of openings 46 in the other of said segments. The pins 44 and openings 46 may thus be used to align the two segments when they are being fitted together. Portions 30 also have a slot 48 formed around their outer surface. The function of slot 48 will be described shortly.

Referring again to FIG. 1, the segments of ferrule 28 are fitted together with sleeve portions 32 over core 14. Damage to the core which would occur when attempting to thread the core through the bore of a one-piece ferrule is thus avoided. The mated segments are then slid back along the core with sleeve 32 being wedged between the core and braided outer conductor 16. The tapered surface 40 of the sleeve assists in this wedging action. When the ferrule is positioned as shown in FIG. 1, with the cutback end of outer conductor 16 abutting the shoulder between portion 30 and sleeve 32, a snapring 50 is fitted into slot 48 to hold the segments of ferrule 28 together. The flat surface 36 of the ferrule may then be utilized as a trimming jig for cutting cable core 14. This exposes a short portion of inner conductor 12.

Collar 24 may then be slid back over outer conductor 16 into the position shown in FIG. 1 in abutment with the shoulder between portions 30 and 32 of ferrule 28. Ferrule 22, with bushing 20 wedged in it, is then slid up over conductor 16 into position adjacent to collar 24, clamping the braided outer conductor 16 between bushing 20 and ferrule 28. The connection of cable 10 to ferrule 28 is completed by crimping ferrule 22 with a crimp tool in a standard fashion. The ridges 38 on shoulder 32 coact with outer conductor 16 to provide a more secure connection.

The elements of connector 19 which are now to be described, and their manner of connection, do not form part of the present invention, but are presented for illustrative purposes only. Other elements adapted to perform the desired function could be utilized in their place.

A dielectric washer 51 is then placed over the center conductor 12 abutting the surface 36, and a contact 52 is secured to the exposed end of conductor 12. This may be effected by, for example, sliding conductor 12 into an internal bore in contact 52 and securing the contact to the conductor by a drop of solder in solder port 54. A connector body 56 having an externally threaded ring projection 58 may then be fitted over contact 52 and secured to cable 10 and ferrule 28 by screwing together the threads on rings 26 and 58. Body 56 has an internal bore 60 with an insulating sleeve 62 seated in a counterbore thereof. A coupling nut 64 secured to body 56 by slipring 66 may be utilized to connect the contact assembly shown to a mating contact assembly.

A split ferrule design has thus been disclosed which enables a ferrule utilized to secure a coaxial cable to a connector to be fitted on the cable, without damaging a multilayer cable core. The shape of the ferrule, and its relative dimensions would, of course, vary with the specific connector application, and other equivalent elements may be utilized in place of pins 44 for aligning the ferrule segments. Further, while for most applications there is no need to divide ferrule 28 into more than two segments, a ferrule formed of three or more mating segments is within the contemplation of the invention.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be apparent to those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A method of securing a connector to a multilayer core coaxial cable having an inner and an outer conductor comprising the steps of:

sliding a cylindrical crimp ferrule and a cylindrical connector member onto said cable, said connector member having a cylindrical bore of diameter slightly larger than that of said cable and an enlarged counterbore;

trimming a predetermined amount of said outer conductor from the end of said cable;

fitting the segments of a split ferrule together over the exposed end of said cable core, said ferrule, when fitted together, having an enlarged cylindrical portion, an elongated cylindrical sleeve of smaller diameter concentric with said enlarged portion, and a flat surface formed perpendicular to the axis of said ferrule on the enlarged portion end thereof;

sliding said fitted-together ferrule up said core with said sleeve being forced between said core and said outer conductor;

moving said connection member into engagement with said fitted-together ferrule with at least a portion of said enlarged portion fitted in said counterbore, and securing said member, and thus also said ferrule, to a mating connector body;

crimping said crimp ferrule over the portion of said outer conductor which is over said ferrule sleeve; and

utilizing the flat, enlarged portion end of said split ferrule, when its sleeve is properly positioned between said outer conductor and said core, as a trimming jig for trimming said core.