Electrical connectors – Including or for use with coaxial cable – Having screw-threaded or screw-thread operated cable grip
Patent
1995-03-13
1996-09-24
Bradley, P. Austin
Electrical connectors
Including or for use with coaxial cable
Having screw-threaded or screw-thread operated cable grip
439932, 29828, H01R 905
Patent
active
055585388
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the termination of screened cables, including coaxial cables and screened wires.
The need to match the characteristic impedance of a signal transmission cable with the nominal impedance of the cable's termination is well known. Impedance mismatch typically produces reflections of the transmitted signal, resulting in undesirable signal attenuation and the production of echos which transmit false information.
In an effort to produce impedance-matched terminations of signal transmission cables, a variety of termination methods have been used, the most common of which involve crimping, clamping and/or soldering. For example, U.S. Pat. No. 3,541,495 discloses a connector for terminating a coaxial cable, having an outer contact body for terminating the cable braid. The outer contact body is provided with a window which is covered by a heat-recoverable sleeve, and located between the sleeve and the window is a ring of solder. In order to terminate the braid of a coaxial cable inserted into the device, the heat-recoverable sleeve is heated, causing the solder to melt and form a connection between the braid and the outer contact body. Whilst this type of connector may be used to form reliable terminations of coaxial cables, it is prone to impedance mismatch, because the internal diameter of the outer contact body of the connector inevitably has to be greater than the external diameter of the cable braid, in order to enable ease of insertion of the cable. The characteristic impedance of a coaxial cable is dependant upon the ratio between the diameter of the outer conductor and the diameter of the inner conductor, and so any change in the position of the outer conductor (e.g. the change from cable screen to outer contact body) will alter the characteristic impedance.
A coaxial cable termination device which generally provides a much greater degree of impedance matching is manufactured and sold by Raychem Corporation of Menlo Park, Calif., USA and Raychem S. A of Cergy Pontoise, Paris, France, under the trade mark "PLUGPAK". This device utilises a tinned copper braid and a ring of solder located inside a heat recoverable sleeve in order to terminate the braid of a coaxial cable. In use, the sleeve is heated, causing it to shrink about the exposed braid of a coaxial cable inserted into the device, and causing solder ring to melt. Because its strands are relatively loosely braided, the tinned copper braid of the device is also able to shrink in diameter, and this normally eliminates the possibility of impedance mismatch at the termination, which may have arisen due to a change in the distance between the inner and outer conductors. However, the degree to which this shrinkage is possible is limited by the braid itself and the construction of the device, and it has been found that when relatively small diameter cables are terminated using this device, impedance mismatch may sometimes occur. There is therefore a need for a termination device which provides impedance matching whilst being able to terminate a greater range of cable sizes. More generally, there is also a continual need to improve upon the methods of terminating all types of screened wires and cables, and in particular to increase the reliability of their terminations in terms of screening effectiveness and grounding of the cable screen.
According to one aspect of the present invention, there is provided a device for terminating a cable having a screen and at least one inner: conductor, which comprises: of the cable, which has two open ends and which is provided with an internal screw thread that tapers from one of its open ends; screw thread of the outer body and tapers towards a constriction at least when screwed into the tapering screw thread; and is located within the constriction of the metallic coil; by inserting an exposed portion of it into the tube of metallic foil and screwing the metallic coil further into the outer body by means of the tapering screw thread, thereby constricting the coil further and causing the metallic fo
REFERENCES:
patent: 4454376 (1984-06-01), Holder et al.
Bradley P. Austin
Burkard Herbert G.
Kim Yong
Novack Sheri M.
Raychem S.A.
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