Electrical connectors – Including or for use with coaxial cable
Patent
1994-07-19
1996-08-20
Bradley, P. Austin
Electrical connectors
Including or for use with coaxial cable
439161, 439730, 439874, 439932, H01R 1704
Patent
active
055473954
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the formation of electrical connections to coaxial cables and especially to the termination of the screens of such cables.
In modern communication systems it is important that connections to coaxial cables, for example connections between cables employing a coaxial connection, connections to printed circuit boards and the like, are impedance matched in order to minimize the amplitude of signal reflections. Clearly also the connections should be made with a low installed cost. At present coaxial cables are usually terminated at coaxial connectors in one of three ways: by crimping, by clamping or by means of solder. The solder arrangements generally exhibit the best electrical performance but are normally employed only for prototype assembly in view of their cost, whereas the crimp type of termination exhibits relatively poor electrical characteristics but is susceptible to relatively high volume production. In addition, it is often not possible to make crimp replacement terminations in the field. Cable clamp arrangements, on the other hand, can be employed in the field but are only susceptible to low volume production.
According to the present invention, there is provided a termination arrangement for a coaxial cable, which comprises a dimensionally heat-recoverable sleeve that encloses a connecting element for the screen of the cable and a quantity of solder for forming a permanent electrical connection between the connecting element and the cable screen, the connecting element comprising a ferrule having a generally cylindrical portion which has one or more axial slits that allow its diameter to change and which is held in a state of larger diameter by the solder and/or the sleeve, the element changing to a smaller diameter state when the sleeve is recovered.
In order to terminate the screen of a coaxial cable, the cable jacket, screen and dielectric layer are each cut back in order to expose an appropriate length of the central conductor, dielectric and screen, the arrangement is positioned over the cable so that the exposed length of the cable screen is located within the generally cylindrical portion of the connecting element, and the assembly is briefly heated, for example by means of an infrared lamp or a hot-air gun, in order to cause the sleeve to recover, the solder to fuse and the connecting element to contract around the cable screen. The arrangement according to the invention has the advantage that it is relatively simple in construction, thereby allowing high volume production, but can form a termination with a high degree of impedance matching with the cable. In addition, it is possible to repair a cable screen termination with one according to the invention in the field. As is well known, the degree to which different parts of a coaxial line are impedance matched will depend on the ratio of diameters of the screen and the central conductor as well as the relative permittivity of the dielectric. According to the present invention, the connecting element may be configured so that, when the termination arrangement is installed about a coaxial cable, the connecting element will contract to a predetermined value but no more. Thus, the connecting element may be arranged so that it will contract enough to form a snug fit with the outer surface of the exposed screen without deforming the screen significantly and thereby affecting the characteristic impedance of that part of the cable. Although the connecting element does not compress the cable screen enough to deform it significantly, i.e. enough to alter the impedance characteristics, a good electrical connection will be formed between the connecting element and the cable screen due to the solder.
The arrangement may be employed in any of a number of configurations. For example the connecting element may be biassed to a state of smaller diameter and be held in its state of larger diameter by the solder and/or by the sleeve so that when the arrangement is heated and the solder fuses or the heat-recoverable sleeve material b
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Bradley P. Austin
Burkard Herbert G.
Demello Jill
Novack Sheri M.
Raychem S.A.
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