Coaxial cable connectors

Abstract

A coaxial cable connector of the type wherein one connector is suitable for a group of cables having the same nominal size and impedance characteristics. Clamping force is applied on the outer conductor of the cable in the radially inward direction upon fastening the backshell to the body of the connector. A subassembly captivated within the backshell forces a deformable material into sealing contact with the outer surface of the cable upon fastening the backshell to the body.

Government Interests

BACKGROUND OF THE INVENTION

The invention described herein was made in the course of or under Contract AT(26-1)-473 with the U.S. Atomic Energy Commission.

Description

This invention relates to connectors for coaxial cables of the RF (radio frequency) type and, more particularly, high-power, low-loss cables having foam dielectric and components of relatively large size.

The use of coaxial cables in the transmission of intelligence via the propagation of electromagnetic energy is well known. It is also well known that the intelligence transmitting link must be free from impedance discontinuities if distortion of the intelligence is to be avoided. Accordingly, the designer of connectors for coaxial cables for this type of service must work within very severe constraints.

U.S. Pat. No. 3,678,446 to Hilbert R. Siebelist, assignor to the U.S. Atomic Energy Commission, assignee of the present application, described in some detail the difficulties the large user of coaxial cables experienced with regard to providing satisfactory connectors for the multitude of coaxial cables available in any particular nominal size and impedance rating. To briefly summarize the situation described more fully in the Siebelist patent, prior to the Siebelist invention, generally speaking, each cable of a group of cables having the same impedance rating and nominal size had its own connector -- usually manufactured and sold by the manufacturer of the cable -- which had a backshell design that made it suitable for use with that particular cable and essentially none other. The Siebelist connector overcame these difficulties by a particular combination of backshell, body and outer conductor clamping arrangement which was applicable to an entire group of cables of nominal size and impedance rating even though a considerable variance was present within that group of cables with respect to the configuration, dimensions, etc. of their individual components.

The present invention is directed to solution of the same problems to which the Siebelist connector was directed. However, I have found a combination of components in a cable connector backshell and cable outer conductor clamping arrangement which provides certain important advantages over the Siebelist connector.

The connector in accordance with the present invention does not require that the outer conductor of a cable be flared in preparation to assembling the connector onto the cable as does the Siebelist connector. Flaring the outer conductor required a number of hand operations by workmen in the field including the compression of the end of the outer conductor in a specially designed hand operated die set in order to obtain the appropriate flare angle. Moreover, my connector involves a lesser number of loose parts with which the workman in the field must contend and requires fewer steps and utilization of fewer specialized tools in connection with its installation. Accordingly, the connector in accordance with the present invention facilitates and simplifies the connection of cables in the field while retaining the advantages of the Siebelist connector.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a cable connector of the type which permits one connector to be suitable for use on a group of coaxial cables which have the same impedance characteristics and the same or similar nominal size but have different structural details. It is a further object of the invention to provide a connector of this general type which is more easily connected to cables in the field than the connectors previously known.

Briefly summarized, this and additional objects and advantages of the invention are accomplished by a connector having a backshell which admits a number of cables of the same nominal size and employs a radially compressible collet, the configuration of the radially inward surface of which grips the outer conductor of the cable. Means are provided which compress the collet, thereby clamping it onto the outer conductor, upon longitudiinal movement of the backshell with respect to the body of the connector. An environmental seal is forced into engagement with the outer surface of the cable in response to the same longitudinal movement of the backshell that actuates the collet.

The means for compressing the collet include a collet clamp and a longitudinally extending spacer positioned within the backshell. The radially outer perimeter of the collet and the radially inward perimeter of the collet clamp have complementary surfaces which expand radially outwardly in the forward direction. The forward end of the spacer engages the collet clamp. A deformable material is positioned between the rear end of the spacer and the rear end of the backshell. Accordingly, relative longitudinal movement between the backshell and the body of the connector upon fastening the two together causes the collet clamp to be forced forward thereby applying a radially inward force to the collet which clamps the collet onto the cable outer conductor. Simultaneously, the deformable material is carried forward by the rear end of the backshell into forceable contact with the rear end of the spacer. The deformable material is thereby forced to expand in the radially inward direction into contact with the outer surface of the cable to provide a seal.

Captivation of the spacer and environmental seal within the backshell reduces the number of loose parts with which the workman in the field must contend. Since the interface between the collet and collet clamp can be standardized for the entire group of cables for which the connector is applicable, the collet is the only component of the connector that needs to be specialized for particular cables of the group.

Additional objects and advantages and a better understanding of the invention will be apparent after consideration of the following description of preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 of the drawing is a longitudinal view, primarily in cross-section, of a preferred embodiment of the invention,

FIG. 2 is a longitudinal view of another connector according to the invention partially in section to illustrate an alternative to FIG. 1 with respect to the collet and dielectric arrangement, and

FIG. 3 shows the backshell subcombination of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIG. 1 of the drawing, the components of cable connector 10 are shown in the positions they assume when connection with cable 12 has been accomplished. Cable 12 is a typical coaxial cable having a central inner conductor 14, concentric outer conductor 16, dielectric material 18 between the two conductors and an outer protective covering 22.

The forward portion of connector 10 also has an outer conductor, inner conductor and mass of dielectric therebetween. While the invention is not limited to connectors having any particular arrangement or configuration of parts in their forward portions, a typical arrangement is illustrated in FIG. 1. The outer conductor takes the form of body 24 which may or may not be fabricated from two components as shown in the drawing. Rearward portion 26 of connector inner conductor 28 accommodates entry therein of inner conductor 14 of the cable and forward portion 32 the entry of the inner conductor 33 of a standard interface 34. Forward end 35 of connector dielectric 36 is of a configuration to receive the complementary configuration of dielectric of standard interface 34 in any usual manner which provides the necessary voltage withstand. Nut 38 is utilized to fasten connector 10 to another connection device, which may or may not be identical to connector 10, in the usual manner.

The manner in which cable 12 is clamped within connector 10 to provide the required mechanical strength of the union and the transition of the outer conductor from the cable to the outer conductor (body 24) of the connector will now be described. As will be noted in FIG. 1, the preparation of outer conductor 16 and dielectric 18 of the cable requires only that they be cut flush and the annulus 40 be cut out of the dielectric by a hand tool to accommodate tubular extension 42 of the dielectric 36 to provide satisfactory voltage withstand. Further preparation is unnecessary since securing cable 12 to the connector is effected through the application of a radial force on outer conductor 16. This is accomplished through the combined action of slotted collet 44, collet clamp 46 and backshell 52 in the following manner.

The complementary outer surface 54 of slotted collet 44 and inner surface 56 of collet clamp 46 are frustoconical and expand radiallyoutwardly in the forward direction. Accordingly, relative movement of clamp 46 in the forward direction exerts a radially inward force upon slotted collet 44 which causes the collet to be compressed inwardly upon the cable. The forward movement of clamp 46 is brought about in conjunction with the relative forward longitudinal movement of backshell 52 with respect to body 24 which accompanies the fastening of the backshell to the body through suitable means such as complementary screw threads 58. The forward thrust on clamp 46 is initially imparted through spacer 60 successively from seal 62, washer 64 and rear end 66 of the backshell. However, that final forward thrust on clamp 46 which locks collet 44 onto outer conductor 16 is applied to the clamp through radially inwardly extending, forward facing shoulder 68 of backshell 52.

Seal 62, made from a deformable material such as rubber, spacer 60, washer 64 and end 66 cooperate to seal the connection from the environment in those applications where an environmental seal is necessary or desirable. The forceable engagement of the seal between spacer 60 and washer 64 causes it to expand radially inwardly into sealing contact with outer covering 22 of the cable. Washer 64 provides a metal to metal contact with end 66 to facilitate the rotation of backshell 52 in connection with securing the backshell to the body such as through screw threads 58. The dimensions of backshell 52, spacer 60, washer 64 and seal 62 are selected to insure that sealing contact between the seal and outer covering 22 is effected with that cable of the group of cables with which one connector configuration will be used which has the smallest O.D. The inner diameter of spacer 60 is sufficiently large to accommodate the deformation of excess seal material into the annular space between the spacer and outer covering 22 when connector 10 is utilized with cables of larger O.D.

FIG. 2 illustrates an alternative arrangement for providing a voltage withstand that provides advantages in making connections of certain types of cables. It is normal practice when making a connection between coaxial components to provide a protrusion of the dielectric of one component into the dielectric of the other component. This increases the air gap spark path between inner and outer conductors to provide a satisfactory voltage withstand. Foamed polyolefin is quite often the dielectric used in coaxial cables whereas polytetrafluoroethylene (TFE) is commonly used in connectors. Since the dielectric constant of TFE is significantly higher than that of the foamed polyolefin, there will be instances when the change in impedance caused by the arrangement of FIG. 1 will be unacceptable as, for instance, when the dielectric of a cable is sufficiently thin that the thinnest practicable protrusion from the connector dielectric too greatly affects the actual dielectric value of the combination.

Accordingly, the embodiment of FIG. 2 provides an arrangement by which the adjustment of the dielectric value can be readily accomplished for particular cables. As shown, outer cable conductor 16' and an outer portion of the cable dielectric 18' are trimmed to accommodate tubular extension 42' of connector dielectric 36'. The compensation of the dielectric value is effected by providing an air gap 72 of sufficient thickness by undercutting the inner side of an extended portion of collet 44' at 74. Since air has a lower dielectric value then foamed polyolefin (or other dielectric used in cables), the thickness of the air gap can be selected to compensate for the higher dielectric value of the TFE and provide in combination with the thicknesses of the polyolefin and the TFE an effective dielectric value, which closely approximates that of the thickness of the polyolefin in the cable. The remaining components of the connector of FIG. 2 are similar in structure and function to corresponding components of the connector of FIG. 1.

It has been found that the assembly of connectors onto cables in the field is facilitated by minimizing the number of components with which the workman must contend. This is accommodated by providing a subassembly of spacer 60, seal 62, washer 64 and backshell 52, which is shown in FIG. 3. The interior parts are captivated within backshell 52 by some suitable means such as stakes 76 which may be formed by use of a punch and hammer. The outer diameter of spacer 60 is relieved at 78 to provide clearance for the stakes.

It will be appreciated from the foregoing that the inner radial, dimensions of backshell end 66, washer 64, seal 62, spacer 60 and collet clamp 46 would be made sufficiently large as to admit the largest cable of the group of cables to which the connector is applied and, in the case of the spacer, to provide space within which excess seal material would be accommodated. It will also be appreciated that the only component that would not be interchangeable among particular cables of the group is collet 44. The inner surface of the collet would be specially formed to sufficiently conform to or to provide adequate gripping of the outer surface of the outer conductor of a particular cable, or sub-group of the group of cables, as to obtain the required mechanical strength and electrical continuity in the union.

While the foregoing describes the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions, substitutions and/or changes may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Claims

What I claim is:

1. In a connector for coaxial cables of the RF type, a combination which permits one connector to be suitable for use on a group of cables having the same impedance characteristics and similar nominal size but different structural details while reducing the number of loose components thereof in order to facilitate its connection onto a cable, said combination comprising:

a. a body having an inner conductor and outer conductor and dielectric therebetween arranged at its forward end for connection with another connector and at its rear end for receiving any one of said group of cables, the outer conductor and some of the dielectric of said cable being removed from a forward portion thereof and said dielectric of said body extending rearwardly over said exposed dielectric of said cable to provide a voltage standoff, and screw threads on the rear end of said outer conductor for connection to a backshell,

b. a collet and collet clamp pair positioned at the rear end of said body for applying clamping force upon the outer conductor of said cable in the radially inward direction, only, upon axially forward movement of said collet clamp relative to said collet, a forward portion of said collet extending over said tubular extension of the dielectric of the body being dimensioned to provide an annular space between said portion of the collet and said extension of the dielectric to provide adjustment of the dielectric value of the space between the outer surface of the inner conductor and the inner surface of said portion of said collet, and

c. a subassembly including a backshell having screw threads at its forward end for connection with said body and a radially inwardly extending portion at its rear end, a deformable seal, a longitudinally extending spacer positioned forward of said seal and means for captivating said seal and said spacer within said backshell, the dimensions of the captivated members and backshell being such that upon the connection of said backshell to said body, said spacer is forced against said seal thereby deforming said seal against said cable to make sealing contact with said cable.