Coaxial Cable Connector

Abstract

A connector for coaxial cables suitable for use on a group of cables having the same impedance characteristics and similar nominal size but different structural details. A backshell of the connector which is sufficiently large to receive each cable of the group fastens to a body which contains a mass of dielectric material in which a central conductor contact is fitted. A seat and collar with complementary frustoconical surfaces adapted to receive an outwardly and forwardly flared end of the outer conductor of the cable are positioned generally within the transition between the backshell and the body. Complementary fastening means on a body and the backshell force the collar and seat together against the flared end of the outer conductor.

Description

BACKGROUND OF THE INVENTION

The invention described herein was made in the course of, or under contract AT(29-2)-20 with the U.S. Atomic Energy Commission.

This invention relates to connectors for coaxial cables of the RF (radio frequency) type.

The use of coaxial cables in the transmission of intelligence by way of the propagation of electromagnetic energy is well known. It is also well known that the maintenance of uniform impedance characteristics throughout the transmission path is essential in order to minimize distortion of the intelligence during transmission. Accordingly, coaxial cables are designed and manufactured to certain standardized increments of impedance characteristics such as 50 ohms, 75 ohms, 100 ohms, etc., to which other components of an intelligence link, i.e., transmitter, receiver, amplifier, etc., also conform.

In some applications in which coaxial cables are used, the environments to which various portions of the transmission link are exposed are drastically different. One such application is in the telemetry networks utilized in connection with testing nuclear explosives. A portion of the link may be required to withstand high temperature. Another (or same) portion may be required to have high mechanical strength in order to support its own weight over many feet, such as when the test is of an explosive emplaced for detonation thousands of feet below the surface of the earth. High mechanical strength may also be required in portions of the links placed on the surface of the ground in places where surface vehicles may on occasion run over them. Some portions of the links may need to be gas tight, moisture proof, or satisfy any number of other criteria. On the other hand, there may be significant portions of particular transmission links where very minimal physical characteristics are adequate.

The particular service environment to which a cable is designed will, of course, affect its cost. When it is realized that one nuclear test may entail the use of a thousand or more individual telemetry links, each traversing thousands of feet, it can be appreciated that considerable savings can be realized by the selection of a number of cables of differing physical characteristics to satisfy particular requirements of the various portions of each telemetry link. However, a large number of individual criterion for cable applications as well as individual manufacturing preferences and/or techniques of cable manufacturers has resulted in a proliferation of cable configurations.

For instance, a single manufacturer provides five different cables of 50 ohm impedance and seven-eights inch nominal diameter. Each of these five cables has its own advantages with respect to each of the others. The inner diameter (I.D.) of the outer conductor varies from 0.795 to 0.965 inch and the outer diameter (O.D.) from 0.948 to 1.005 inches for these five cables. Four of the five have heliax outer conductors. The outer diameter of the inner conductor, which in the case of this manufacturer are all tubular, varies from 0.312 to 0.358 inch. There is only one duplication in this group of five with respect to all conductor dimensions. Another manufacturer provides three cables in this same nominal size and impedance characteristic. Each has non heliax outer conductors having an O.D. of 0.875 inch and an I.D. varying from 0.758 to 0.801 inches. Each of these three has a solid core inner conductor, the O.D. of which varies from 0.288 to 0.300 inch. When the total number of manufacturers, nominal cable sizes, and impedance ratings are considered, it can be seen that the number of individual cables available is truly legion.

The problem of supplying connectors for this multitude of cables is not insignificant. It can be appreciated that the costs involved in procuring, maintaining inventory, and other handling for a multitude of difference cable connectors can be very significant, and particularly so for large users of cables. It has been only in relatively recent years that a number of standard interfaces for coaxial cable connectors have been developed in order to insure that, for example, all 50 ohm cables (within certain size limitations) can be connected together, provided the connectors used with them incorporate a particular standard interface. However, generally speaking, each particular cable has utilized a different connector with a backshell designed for attachment onto that particular cable configuration and essentially none other. Accordingly, a user of all eight of the cables alluded to above has in the past had to procure, warehouse, handle, etc., seven different cable connectors.

SUMMARY OF INVENTION

Accordingly, it is an object of this invention to provide a cable connector which permits one connector to be suitable for use on a group of coaxial cables having the same impedance characteristics and the same or similar nominal size, but having different structural details. Briefly summarized, this and additional objects of the invention are accomplished by a connector with a backshell having an inner cylindrical surface of larger diameter than the outer conductor of the largest of the group of cables, and a body with an inner cylindrical surface with a diameter larger than that fastened to the forward end of the backshell. The body contains a mass of dielectric material within which is fitted a central conductor contact which receives the inner conductor of the cable. Complementary frustoconical surfaces on a seat and a collar, positioned longitudinally between the two inner cylindrical surfaces, generally traverse the radial distance between the two inner cylindrical surfaces. An outwardly and forwardly flared end portion of the outer conductor of the cable is received between these frustoconical surfaces of the seat and collar. Complementary fastening means on the body and the backshell fasten the body and backshell together and force the frustoconical surfaces against the flared end portion of the outer conductor of the cable.

BRIEF DESCRIPTION OF DRAWING

The single FIGURE of drawing is a longitudinal section of a coaxial cable connector in accordance with the invention, with an end of a cable to be connected and a standard interface inner contact assembly shown in exploded, broken away relationship.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the single FIGURE of drawing, the connector 10 in accordance with the invention is shown in conjunction with interface inner contact assembly 12 and coaxial cable 14, each of the latter two shown in exploded away relationship from their connection positions. The major components of connector 10 are backshell 16 and body 18 which are joined together by suitable means such as complementary screw threads 20, body 18 being the male member. Snugly fitted within body 18 is a mass of dielectric material 22 into which connector inner conductor 24 is snugly fitted. Contact sleeve portions 26 and 28 at either end of conductor 24 are adapted to receive and make electrical connection with inner conductors 30 and 32 of interface assembly 12 and coaxial cable 14, respectively. Inner cylindrical surface 33 of backshell 16 and contact sleeve 28 are each large enough to receive the largest individual member of that group of cables for which a particular connector 10 is intended. Seat 46 and collar 52, each made from a conducting material, are positioned, generally speaking, in the transition between the backshell and the body. These will be explained in more detail hereinafter.

A slotted, tubular insert 34 of a conductor material may be utilized to facilitate the electrical connection with inner conductor 32 in those configurations of cable 14 within the group of cables for which connector 10 will be utilized for which conductor 32 is too small to snugly fit within contact sleeve 28. The front end of connector 10, together with inner contact connector assembly 12, make up a standard interface for connectors of a particular impedance rating. Accordingly, conductor 30 and sleeve 26 are designed to fit snugly together, and the use of an insert such as 34 is not necessary.

Of course the front end of connector 10 may be joined to the front end of any other connector of same impedance rating which utilizes the same standard interface. One nut 29, retained on body 18 by snap ring 31, is utilized to tighten the two connectors together. The nut on the other connector is run rearwardly off of threads 35 out of the way of the first nut and is merely retained on the body as a nonfunctioning part. The two connectors may be identical in the event the cables to be joined are both within the same group of cables for which a particular connector 10 is designed. In the event the cable falls outside of that group, the second connector may be identical in concept to connector 10 but have a configuration rearwardly of the standard interface which differs in dimensional detail. On the other hand, as long as the second connector is of the same impedance and embodies the standard interface, connection can be made, and the remaining structural details of the second connector are of no real significance.

Now that major components of connector 10, cable 14 and the interface including assembly 12 have been described, the remaining structure of the connector and cable will be described in conjunction with a description of the procedure by which the cable is prepared and joined to connector 10. In preparing cable 14 for connection to connector 10, outer protective cover 36, outer conductor, or shield, 38, dielectric 40 and inner conductor 32 are trimmed to the relative lengths shown. These relative lengths can be readily determined by a suitable trimming guide. An outer, substantially annular portion of dielectric 40 is removed to form shoulder 41 and outer cylindrical surface 42 for a purpose to be explained later.

Backshell 16, unfastened from body 18, is then dropped over the end of cable 14 and moved along the cable until forward end 43 of the outer conductor is exposed beyond the forward end 44 of the backshell. Seat 46, if not integral with backshell 16, is also placed over the end of the cable and positioned against shoulder 48. Slits are then cut in forward end 43 of the outer conductor by any suitable tool, such as a diagonal cutting shears. End 43 is then flared radially outwardly into the configuration shown. The flaring may be done directly against surface 56 of seat 46, or against a suitable backing block, either by hand or with the assistance of a suitable flaring tool. The slits are expanded during the flaring into notches 50.

A collar 52 having rearwardly facing surface 54 generally frustoconical in nature and complementary to surface 56 of seat 46 and forwardly facing frustoconical surface 57 which fits snugly against the complementary surface 59 of dielectric 22 is placed on the forward side of end 43 of outer conductor 38 of cable 14. Body 18 with mass of dielectric 22 and connector inner conductor 24 contained therein is then screwed into backshell 16. This brings the end of cable inner conductor 32 into position within contact sleeve 28 (or sleeve insert 34 if such is utilized), and complementary frustoconical surfaces of shoulder 48 and collar 52 into forceable engagement with flared forward end 43 of the cable. Complementary protuberance 58 and indentation 60 firmly grip flared end 43. The dimensions of collar 52 relative to dielectric 22 and backshell 16 permit relative rotation of the collar with respect to the backshell and dielectric thereby facilitating the connection of the backshell and body and the forceable engagement of the flared end of the cable.

Cylindrical surface 42, formed by trimming cable dielectric 40 as previously related, fits snugly within the rearwardly extending tubular portion 62 of dielectric mass 22, the function of these interfitting portions of dielectric being to increase the air gap spark path between the inner and outer conducting members of the cable and connector. It will be noted that a similar arrangement is provided at the front end of body 18 and interface 12.

It can be seen from the foregoing, then, that frustoconical surface 57 in its position longitudinally between inner cylindrical surfaces 33 of the backshell and 64 of the body serves as a transition for the outer conductor of the coaxial link including cable 14 and connector 10. The inner surface of the outer conductor of the cable-connector assembly expands from outer conductor 38 through that transition to inner surface 64 of body 18. It will be noted that the various expansions and contractions in the size of the outer surface of the inner conductor finds correlative changes in the size of the inner surface of the outer conductor throughout connector 10. Those skilled in the connector art will appreciate that such correlation is necessary in order to minimize distortion of the intelligence in its transmission through the connector, i.e., impedance mismatch.

In the event it is desired that the connector be sealed from the atmosphere, or be liquid or gas tight, suitable means such as jam nut 66, bushing 68, tubular seal 70, made of a deformable material such as rubber, and set screw 72 may be provided at the rearward end of backshell 16. As is apparent from the drawing, screwing jam nut 66 into the rearward end of backshell 16 by means of complementary threads 74 forces bushing 68 against seal 70 thereby deforming it in a longitudinal and radially inward direction until it comes into sealing engagement against the outer surface of cable 14. Suitable means, not shown, may be provided on the backshell for introducing gas under pressure, if desired.

It is to be understood that although the phrase "the same or similar nominal size" has been used herein to describe a group of cables with which a single connector configuration according to the invention may be used, it is not intended by such usage that any particular connector according to the invention is necessarily limited to application to any one particular "nominal size" that may have attained, or may hereafter attain recognition in the connector art. For instance, it will be readily apparent to those skilled in this art that one connector in accordance with the invention would be satisfactory for a group including cables of one-quarter, three-eights, one-half inch and other similar nominal sizes with, of course, the same electrical characteristics.

While the foregoing describes the fundamental novel features of the invention as applied to a preferred embodiment, 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 is claimed 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, said combination comprising:

1. a backshell having an inner cylindrical surface of larger diameter than the outer conductor of the largest of said group of cables,

2. a body adapted for connection to the forward end of said backshell having an inner cylindrical surface of larger diameter than said surface of said backshell and containing:

a. a mass of dielectric material snugly fitting within said cylindrical surface of said body and essentially filling said body and having a frustoconical surface extending rearwardly and radially inwardly from said cylindrical surface of said body to at least traverse the radial distance to said inner cylindrical surface of said backshell and

b. a central conductor contact snugly fitting within said dielectric material, said contact having a rearwardly facing tubular portion of sufficient inner diameter to receive therewithin the largest inner conductor of said group of cables, and a forwardly facing portion adapted for connection with the inner conductor of a second connector,

and said body having a forward portion adapted for connection with a second connector,

3. a collar of a conducting material having a forwardly facing frustoconical surface complementary to said frustoconical surface of said mass of dielectric material and extending from said inner cylindrical surface of said body to at least traverse the radial distance to said inner cylindrical surface of said backshell and having a rearwardly facing and rearwardly and radially inwardly extending generally frustoconical surface,

4. a seat having a forwardly facing frustoconical surface complementary to said rearwardly facing surface of said collar, said complementary frustoconical surfaces on said seat and collar adapted for receiving an outwardly and forwardly flared end of the outer conductor of said cable therebetween, the longitudinal position of said seat and said collar being generally between that of said inner cylindrical surfaces of said backshell and said body and said complementary frustoconical surfaces of said seat and said collar generally traversing the radial distance between said inner cylindrical surfaces,

5. complementary fastening means of said body and said backshell, the operation of which fastens said body to said backshell and forces said collar and seat together against said flared end of said outer conductor.

2. The connector of claim 1 wherein said seat and collar have complementary protuberances and indentations in said complementary frustoconical surfaces for gripping the flared end of the outer conductor of the cable.

3. The connector of claim 1 wherein said complementary fastening means are male and female screw threads.

4. The connector of claim 3 wherein said body is the male member.

5. The connector of claim 1 including means on the rearward end of the backshell for sealing the connector from the atmosphere.