Patent Publication Number: US-5830009-A

Title: Device for connecting a coaxial plug to a coaxial cable

Description:
The invention concerns a device for connecting a coaxial plug to a coaxial cable as defined in the preamble of claim 1. 
     Such coaxial cables with a corrugated outer conductor and where called for also a corrugated inside conductor including the correspondingly connected plug are used in various sizes and power ratings to transmit high-frequency power, for instance in mobile radio networks, radio and TV facilities, directional radio systems, radar and satellite ground stations etc. worldwide in large numbers. 
     Exceedingly high quality of assembly is required for the connection between the conductor parts of the coaxial plug and the corrugated outer conductor or inner conductor of the coaxial cable in order to meet the high electrical and mechanical requirements especially of good contacts and highest possible loss-free transmission. 
     As regards the heretofore known connection devices of this species, the connection for instance of the outer conductor of the corrugated sheath cable in to the corresponding outer conductor of the coaxial plug is implemented by screwing a contacting bush, in the form of a retaining bush, onto the outer cable conductor until said bush hits the plastic insulator of the cable. Then the projecting outer conductor tube of the corrugated sheath cable is bent outward by 90° C. manually or using complex assembly mechanisms to make it rest against the end surface of the screwed-on contact bush. 
     The corrugated inner cable conducting tube is connected in the same manner to the inner plug conductor. For that purpose an inner-conductor contact piece is screwed into the inner cable conductor and thereupon a correspondingly projecting end of the inner cable conductor is flanged inward by about 45° on a conical part of this inner-conductor contact piece. 
     In both cases the flanging of the corrugated cable conductor tubes entails on one hand mechanically affixing the contact bush or inner-conductor contact piece to the particular cable conductor and on the other hand implementing the flanging simultaneously forming the electrical contact surface. Consequently the electrical connection quality between the coaxial cable and the coaxial plug critically depends on the quality of flanging. 
     Depending on size, installing such cable fittings will require labor time from 20 to 120 minutes. Thus the cited connection can be made only at high demand in time and hence at high cost. 
     Lastly phase matching frequently requires that the assembled connection between the coaxial plug and the coaxial cable be disassembled again in order to shorten the cable by a length for instance of 2-5 mm. This procedure also is highly time-consuming because the flanging must be bent back into its initial position to allow screwing off the contact bush or the inner conductor contact-piece and re-cutting the particular cable conductor. After that the particular cable conductor must be flanged again. As a result substantial time will have been expended. 
     Based on this state of the art, the object of the invention is to so design the connecting device of the said species that it may be assembled or disassembled rapidly without resort to specialized tools and that while offering simple component design it will very well meet both electrical and mechanical requirements. 
     The features used in solving this problem are stated in claim 1. Advantageous embodiments are described in the further claims. 
     The connecting device of the invention comprises a contact bush such that at its plug side it forms clamping tongs with resilient clamping segments; these clamping tongs evince a conical compressive surface and can be radially pressed, by means of a cooperating compressive cone present at the plug side, against the corrugated cable conducting tube. 
     In this manner the contact bush is affixed most effectively to the particular corrugated cable conducting tube; at the same time, the radially resilient clamping segments ensure defined contact at the first corrugation turn, i.e. thread of the corrugated cable conductor tube is assured. This contact at the mentioned site is critical, and it is achieved in the invention in that the thread of the contact bush illustratively in the form of a contoured thread matched to the corrugated cable conductor tube is rotated free by 360° after the first thread. As a result the clamping segments of the clamping tongs are able to act as springs and, on account of their being clamped together radially by the plug-side compressive cone are compressed over a circumferential angle of 360° and thereby achieves defined contact. 
     Preferably the contact bush of the invention is made of a silvered brass material offering good high-frequency conductivity. 
     The threaded part, ie the contoured thread of the contact bush preferably runs over its entire length including the clamping tongs. In this respect and as already mentioned, the clamping segments are designed in such manner that in their radially compressed position implemented by the plug-side compressive cone they make contact with the first threaded turn of the corrugated cable conductor tube. 
     In order to make possible and/or to enhance this radial clamping of the clamping segments, the invention provides that the clamping tongs be offset by an annular channel from the remaining part of the contact bush, said channel being of a depth larger than the threaded troughs of the contoured thread. However in lieu of an annular channel it is also possible to secure the resiliency of the individual clamping segments in another suitable manner, for instance by means of an appropriately lesser wall thickness of the clamping tongs. 
     When the connecting device of the invention used to connect the outer conductor of the coaxial plug to the corrugated outer conductor cable tube is put in service, the configuration is such that contoured thread of the contact bush forms an inside thread and that the conical compressive surface of the tongs is located at the outside of these tongs. 
     In this case an advantageous design of the invention provides that the plug-side compressive cone be present at the inner circumferential surface of the plug housing forming the outer conductor. 
     On the other hand if the connecting device of the invention is meant to connect the inner conductor of the coaxial plug to the corrugated cable inner conductor tube, then the contoured thread of the contact bush shall be a male thread and the conical compressive surface of the tongs will be present at the inner periphery of these tongs. 
     In the latter case the invention provides that the plug-side compressive cone be present at the outside of a contact bolt of which one end can be screwed by a male thread into the contact bush for the purpose of compressing the clamping segments against the cable inner conductor tube and of which the other end evinces a cylindrical segment to be resiliently coupled to the inner conductor of the coaxial plug. 
     Lastly the invention relates to the inner-conductor contact bush comprising at its plug-side end a stop in the form of an annular collar projecting outward from the free end of the clamping tongs. Thereby a defined position of the inner-conductor contact bush is secured relative to the cable inner conductor without requiring special work on said inner conductor. 
     Accordingly the invention on the whole allows cutting the previously known assembly time and cost by up to and more than 50%. Another substantial advantage is that special tools are not required to implement the connection. Hence assembly can be carried out in problem-free manner on the site also. Any phase matching entailing shortening of the cable also can be carried out easily in a short time. 
     The invention offers exceedingly advantageous simplification of the designs of plug elements. As a result substantial savings are achieved compared to the known connecting devices. 
    
    
     The invention is elucidated below in relation to the drawings. 
     FIG. 1 is schematic section of the connecting device of the invention when assembled, 
     FIG. 2 shows a section of the contact bush for the outer cable conductor, 
     FIG. 3 is a front view 
     FIG. 4 is a section of the contact bush for the inner cable conductor, and 
     FIG. 5 is a front view corresponding to said contact bush. 
    
    
     As shown in the drawings and in particular in FIG. 1, the shown connecting device is used to connect a coaxial plug 1 to a coaxial cable 2. In the embodiment shown, this coaxial cable 2 is in the form of a flexible corrugated copper sheath cable and in this design comprises an outer cable conductor 4 in the form of a corrugated copper tube enclosed by a plastic cover 3 and of an inner cable conductor 5 centrally held by an insulator relative to said outer conductor, said inner conductor 5 also being in the form of a corrugated tube. 
     A contact bush 7 is provided to connect the corrugated outer cable conducting tube 4 to the corresponding outer conductor part of the coaxial plug 1, that is to the plug housing 6, said bush 7 evincing the configuration shown in FIGS. 1, 2 and 3. This contact bush 7 comprises a an inner thread 8 designed as a contour thread matching the thread of the outer cable conductor 4. Thereby said thread 8 is easily screwed onto the outer cable conductor 4 in such a way that the free end of the outer cable conductor 4 is flush with the plug-side of the contact bush 7. 
     The drawing further shows that at its plug-side end the contact bush 7 comprises clamping tongs 10 with resilient clamping segments 11, said segments in the shown embodiment being formed by the clamping tongs 10 evincing four equally spaced axial slits 12. Obviously an arbitrary number of slits 12 also may be provided. 
     The drawing shows that the thread 8 of the contact bush 7 runs over the entire length of this bush including the clamping tongs 10. To assure the spring and resiliency and clamping functions of the clamping tongs 10, the tongs design is such that they are offset by an annular channel 13 relative to the remaining part of the contact bush 7, said channel evincing a greater depth than the thread troughs 14 of the contoured thread 8 (FIG. 2). 
     The clamping tongs 10, i.e. their resilient clamping segments 11 evince an outer conical compressive surface 15. Said compressive surface 15 cooperates with a matching compressive cone 16 present at the inner circumference of the plug housing 6 forming the outer conductor part in such manner that the resilient clamping segments 11 of the clamping tongs 10 when in the radially compressed position implemented by the plug-side compressive cone 16 will contact the full first thread turn of the outer cable conductor 4, that is over an circumferential angle of 360°. 
     The radially clamped position of the clamping segments 11 also is implemented when the coaxial plug 1 is affixed to the coaxial cable 2. This mode is obtained conventionally in the shown embodiment using screw connections, the screws 17 passing through matching boreholes 18 in an annular flange 19 of the outer-conductor contact bush 7 and being screwed into threaded boreholes of an annular flange 20 present on the coaxial plug 1. 
     The described connecting device furthermore implements connection--construed in the same sense--of the corrugated cable conductor inner tube 5 to the pertinent inner conductor part of the coaxial plug 1. This plug inner conductor part is a resilient sleeve 21 in the embodiment shown and is kept centered in the coaxial plug 1 by an insulating spacer 22 affixed to the plug housing 6. 
     The inner-conductor contact-bush 107 corresponding to the outer-conductor contact bush 7 therefore comprises a thread 108 in the form of a contoured male thread. Also the conical compressive surface 115 of the clamping tongs 110 located at the inside circumference of the tongs, ie at their clamping segments 111, is offset by an outer annular channel 113 from the remaining part of the inner-conductor contact-bush 107. In this case too the outer radial annular channel 113 evinces a greater depth than the thread depths 114 of the contoured thread 108 in order to ensure resiliency of the clamping segments 111. 
     The compressive cone 116 cooperating with the inner conical compressive surface 115 of the inner-conductor contact-bush 107 is present at the outside of a contact bolt 23 as shown in FIG. 1. This contact bolt can be screwed by means of an outer thread part 110 into the inner-conductor contact bush 107 to radially compress the resilient clamping segments 111 of the clamping tongs 110 against the corrugated cable inner-conductor 5. Also this contact bolt 23 comprises a cylindrical section 25 which is insertable for the purpose of coupling to the inner-conductor part of the coaxial plug into the matching resilient bush 21 wherein it can be fastened in place by an inner-conductor central screw 26. 
     The contact bush 107 comprises a stop 27 at its plug-side end for the purpose of screwing the inner-conductor contact-bush 107 a specified length into the corrugated cable inner conductor 5. Said stop assumes the shape of an outwardly projecting annular collar and is present at the free end of the tongs 110. 
     Explicit reference is made thereby to the claims and the drawings regarding features of the invention not individually described above.