GB2252458A

GB2252458A - Internal conductor connecting device for coaxial cables

Info

Publication number: GB2252458A
Application number: GB9127332A
Authority: GB
Inventors: Georg Spinner
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-01-11
Filing date: 1991-12-24
Publication date: 1992-08-05
Anticipated expiration: 2011-12-24
Also published as: DE4100696C1; GB9127332D0; FR2671675A1; ITMI913439A0; IT1252574B; ITMI913439A1; GB2252458B; FR2671675B1

Description

2252458 k.

Internal Conductor Connectinq Device for Coaxial Cables The invention relates to a device for connecting a tubular internal conductor of a coaxial cable to the internal conductor of a coaxial fitting extending the cable.

In known connecting devices of this kind a sleeve is formed on or secured to the end of the internal conductor to be connected. The sleeve engages over the tubular internal conductor and radially resiliently contacts it. A necessary requirement for making the connection is therefore that firstly the external conductor and the dielectric of the coaxial cable are set back relative to the end edge of the tubular internal conductor a distance which precisely corresponds to the assembly dimension, that is to say they are cut off in such a way that the tubular internal conductor projects by the desired dimension. If the coxial cable is a cable with an external conductor of annular corrugation configuration, an additional complication arises by virtue of the fact that external conductor connections which are simple and reliable to form require the external conductor to be cut off accurately in the region of its largest diameter (that is to say at the top of a "crest" of the corrugation configuration). In such a situation the severing cut is set back further than the required dimension by which the tubular internal conductor projects and then in a further severing cut the tubular internal conductor is once again shortened to the length required as the assembly dimension. That known mode of assmebly is extremely impractical in particular when the connection is required only for the purposes of series measurements on corresponding coaxial cables because that mode of assembly takes up a great deal of time and necessarily results in the cable becoming shorter. A further disadvantage lies in the change of diameter in the internal conductor, which occurs in the region of the connecting location and which requires suitable structural compensatory measures in the region of the external conductor if the reflection factor is also to be maintained at the location of the connection.

According to the invention, there is provided a device for connecting a hollow internal conductor of a coaxial cable to the internal conductor of a coaxial extension fitting wherein the internal conductor of the coaxial fitting includes a central axial blind hole whose inside diameter is approximately equal to the outside diameter of the internal conductor, the peripheral wall of the blind hole being divided into radially resilient bar portions by axially extending slits extending from the end edge of the blind hole, one end of an intermediate internal conductor being slidably accommodated in the blind hole and loaded by a compression spring in the direction of the internal conductor, the intermediate internal conductor being of the same diameter as the internal conductor, the other end of the intermediate internal conductor being (1) of a reduced diamter, and (11) axially displaceably accommodated in the internal conductor, said other end carrying a sleeve with radially resilient bar portions which contact the inside wall of the internal conductor and the axial displacement travel of the intermediate internal conductor in the direction of the internal conductor being limited by a stop member.

The invention is therefore based on the problem of providing a device of the kind set forth in the introductory part of this specification, which permits the connection to be made without preliminary specific preparation of the end of the coaxial cable and which results in contact being made in a fashion which is satisfactory from the high frequency operation paint of view.

The present proposal affords the advantage that the coaxial fitting which extends the cable, generally being a plug connector, only needs to be pushed onto the end of the coaxial cable as the internal conductor connection is basically made automatically so that it is then only necessary to ensure contacting and at the same time clamping of the external conductor of the cable and the coaxial fitting. Suitable structures are known for that purpose, which only require a cap nut to be tightened. The proposed connector is therefore particularly suitable for carrying out high-speed and/or series measurements on coaxial cables.

The compression spring which loads the intermediate internal conductor in the direction towards the tubular internal conductor and which obviously must be of such a size that it is certain to overcome all frictional resistances which occur ensures that the intermediate internal conductor bears with its peripheral shoulder, without any gap, against the end edge of the tubular internal conductor. It is only a gap-free transition of that kind that guarantees a low reflection factor.

Preferably, the end region of the other end of the intermediate internal conductor including the part of the sleeve which is connected thereto is in the form of a centering member.

This improvement provides for accurately colinear positioning of the intermediate conductor with respect to the tubular internal conductor, even if the latter is in turn not precisely centrally disposed in the external conductor of the cable.

Internal contacting of the tubular external conductor by the intermediate internal conductor should preferably occur in the region of the former, which is adjacent the edge. That is ensured by following optional features of the invention:

W that the sleeve which is carried on said other end of the intermediate conductor is connected thereto only in the region of the end edge thereof and the radially resilient bar portions of the sleeve being formed by axial slits extending from the free end of the sleeve and so prestressed that their envelope surface in the unloaded condition is a conical surface or a cambered conical surface; 00 that the radially resilient bar portions of the sleeve (when present) are individually set askew by twisting about their respective longitudinal axes; (M) that the intermediate internal conductor has a recess at its said other end in the region of the radially resilient bar portions of the sleeve; and/or Ov) that at the transition of the recess of the intermediate internal conductor (when present) to the central portion of the same diameter as the tubular conductor thereof, there is provided an annular shoulder for supporting the free ends of the radially resilient bar portions of the sleeve.

Preferably the stop member comprises a screw which engages through a central longitudinal bore in the intermediate internal conductor and which is screwed into a central screwthreaded bore in the bottom of the blind hole in the internal conductor of the coaxial fitting.

This embodiment provides that the intermediate internal conductor is nonlosably, i.e. securely, fixed to the internal conductor of the coaxial fitting, irrespective of the axial displaceability of the former with respect to the latter. In addition, in that construction, the stop member takes over a substantial part of the function of centering of the intermediate internal conductor with respect to the internal conductor of the coaxial fitting.

Conveniently the slits in the peripheral wall of the blind hole extend only to approximately half the depth of the blind hole, the blind hole being of a reduced inside diameter from the end of said slits to its bottom and the end of the intermediate internal conductor, which is accommodated in the blind hole, having an end portion of correspondingly reduced diameter.

This embodiment provides for a kind of telescopic guidance for the intermediate internal conductor in the internal conductor of the coaxial fitting and thus precludes the possibility of tilting movements in particular at the beginning of the operation of introducing the intermediate internal conductor into the tubular internal conductor.

A structural alternative form of that embodiment, which has the same effect, is one in which the slits in the peripheral wall of the blind 1 1 hole extend only to approximately half the depth, and fitted into the blind hole is a bush which at its free edge has an external shoulder which bears against the inside wall of a cylindrical recess in the intermediate internal conductor.

There now follows a description of a preferred embodiment of the invention, by way of example, with reference being made to the accompanying drawings in which:

Figure 1 is a view in longitudinal section of the connecting device of the invention; Figure 2 Figure 3 is a view on an enlarged scale of the contacting region between the intermediate internal conductor and the internal conductor of the coaxial fitting; shows another embodiment of the contacting region shown in Figure 2; and Figure 4 is a view on an enlarged scale of the contacting region between the tubular internal conductor and the intermediate internal conductor.

Referring to Figure 1, shown therein on the left is a coaxial cable 1 comprising a tubular (i.e. hollow) internal conductor 2, a dielectric 3, an external conductor 4 and an insulating sheathing 5.

A coaxial fitting in the form of a coaxial plug 6 is connected to the coaxial cable 1. The plug 6 includes an external conductor 7 which is held by a disc 8 of insulating material in an external conductor 9. A cap nut 10 serves for connection for example to a coupling (not shown). An external conductor housing 11 on the cable side is screwed to the external conductor 9.

A ring 12 serves for contacting of the external conductor 4 of the cable with the external conductor housing 11. The ring'12 has at least one longitudinal slit and two taper surfaces 12a and 12b which are oriented in opposite directions, at its external periphery. Co-operating with the taper surfaces 12a and 12b are taper surfaces which face in the same direction on the one hand at the internal periphery of a clamping ring 13 and on the other hand at the internal periphery of the external conductor housing 11. When a screw cap sleeve 14 is tightened or screwed onto the external conductor housing 11 the clamping ring 13 is increasingly pushed over the ring 12 so that the ring 12 is radially compressed and produces the desired clamping force.

An intermediate internal conductor 15 serves to connect the internal conductor 7 of the plug 6 to the internal conductor 2 of the cable 1. The intermediate internal conductor 15 comprises a central portion 15a of the same diameter as the internal conductor 2 of the cable. A part of the portion 15a is accommodated in a blind hole 16 in the internal conductor 7 of the plug. In the embodiment shown, the blind hole is disposed centrally. The details of the structure can be seen more closely from Figure 2. The blind hole 16 has a first portion whose inside diameter is approximately equal to the diameter of the central portion 15a of the intermediate internal conductor 15. In that portion the wall of the blind hole 16 is divided by longitudinal slits into radially resilient bar portions 17, the ends of which bear against the external periphery of the intermediate internal conductor 15 and thus contact it. The adjoining portion of the blind hole 16 is of a reduced inside diameter, to which there corresponds a reduced outside diameter of the end part 15b of the intermediate internal conductor 15, thus providing a telescopic guide arrangement. Disposed in the blind hole 16 is a compression spring 18 which loads the intermediate internal conductor 15 in a direction towards the tubular internal conductor 2.

Figure 3 shows another construction for that connecting region. Here, a bush 21 is pressed into the blind hole 16 in the smaller-d!a meter portion thereof. At its free edge the bush 21 has an external shoulder 21a with which the inside wall of a cylindrical recess 15h in the end face of the intermediate internal conductor 15 is in contact. The intermediate 1 internal conductor 15 is thus guided between the bush 21 and the radially resilient bar portions 17 of the internal conductor 7 of the coaxial fitting.

The intermediate internal conductor 15 has a further portion 15c of reduced diameter (see Figure 1), which extends into the tubular internal conductor 2. The details of the structure can be seen more closely in Figure 4. Formed at the transition of the central portion 15a to the portion 15c is an annular surface 15d which bears snugly against the annular end face of the tubular internal conductor 2, under the force of the spring 18. The portion 15c is enclosed by a sleeve 19 which is fixed to the end of the intermediate internal conductor 15, which is in the form of a centering head 15e, and extends as far as the annular surface 15d. The sleeve 19 is divided by numerous longitudinal slits into individual contact bar portions 19a which are set askew by being twisted about their respective longitudinal axis and which are biased radially outwardly in such a way that the additional contacting effect between the intermediate internal conductor 15 and the tubular internal conductor 2 occurs predominantly in the region thereof which is near the front end. Over the length of the contact bar portions 19a the portion 15c of the intermediate internal conductor 15 has a recess 15f which permits the spring bar portions 19a to be moved resiliently towards each other. Provided at the transition of the recess 15f to the annular surface 15d however is an annular shoulder 15g which supports the free ends of the spring bar portions 19a.

The axial displacement travel of the intermediate internal conductor 15 relative to the internal conductor 7 of the plug is limited by a screw 20 which passes through a suitable bore in the intermediate internal conductor 15 and which is screwed into a screwthreaded bore 7a in the internal conductor 7 of the plug.

Claims

1. A device for connecting a hollow internal conductor of a coaxial cable to the internal conductor of a coaxial extension fitting wherein the internal conductor of the coaxial fitting includes a central axial blind hole whose inside diameter is approximately equal to the outside diameter of the internal conductor, the peripheral wall of the blind hole being divided into radially resilient bar portions by axially extending slits extending from the end edge of the blind hole, one end of an intermediate internal conductor being slidably accommodated in the blind hole and loaded by a compression spring in the direction of the internal conductor, the intermediate internal conductor being of the same diameter as the internal conductor, the other end of the intermediate internal conductor being W of a reduced diameter, and (H) axially displaceably accommodated in the internal conductor said other end carrying a sleeve with radially resilient bar portions which contact the inside wall of the internal conductor, and the axial displacement travel of the intermediate internal conductor in the direction of the internal conductor being limited by a stop member.

2. A device according to Claim 1 wherein the end region of the other end of the intermediate internal conductor including the part of the sleeve which is connected thereto is in the form of a centering member.

3. A device according to Claim 1 or Claim 2 wherein the sleeve which is carried on said other end of the intermediate internal conductor is connected thereto only in the region of the edge thereof, and the radially resilient bar portions of the sleeve being formed by axial slits extending from the free end of the sleeve and so prestressed that their envelope surface in the unloaded condition is a conical surface or a cambered conical surface.

4. A device according to Claim 3 wherein the radially resilient bar portions of the sleeve are individually set askew by twisting about their respective longitudinal axis.

5. A device according to any of Claims 1 to 4 wherein the intermediate internal conductor has a recess at its said other end in the region of radially resilient bar portions of the sleeve.

6. A device according to Claim 5 wherein at the transition of the recess of the intermediate internal conductor to the central portion of the same diameter as the tubular internal conductor thereof, there is provided an annular shoulder for supporting the free ends of the raidally resilient bar portions of the sleeve.

7. A device according to any of Claims 1 to 6 wherein the stop member comprises a screw which engages through a central longitudinal bore in the intermediate internal conductor and which is screwed into a central screwthreaded bore in the bottom of the blind hole in the internal conductor of the coaxial fitting.

8. A device according to any of Claims 1 to 7 wherein the slits in the peripheral wall of the blind hole extend only to approximately half the depth of the blind hole, the blind hole being of a reduced inside diameter from the end of said slits to its bottom and the end of the intermediate internal conductor, which is accommodated in the blind hole, having an end portion of correspondingly reduced diameter.

9. A device according to any of Claims 1 to 7 wherein the slits in the peripheral wall of the blind hole extend only to approximately half the depth of the blind hole, and fitted into the blind hole is a bush which at its free edge has an external shoulder which bears against the inside wall of a cylindrical recess in the intermediate internal conductor.

10. A device generally as herein described, with reference to or as illustrated in the accompanying drawings.

11. Any novel combination or sub-combination disclosed and/or illustrated herein.