US3639864A

US3639864A - Transportable coaxial cable

Info

Publication number: US3639864A
Application number: US866314A
Authority: US
Inventors: Bernt Klostermark
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-10-22
Filing date: 1969-10-14
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01
Also published as: GB1250430A; SE317424B; DE1934550A1

Abstract

Coaxial cable for connection between an antenna and a receiver in nonpermanent or mobile installations. The cable is joined by short lengths of bendable sections thereby enabling the cable to be folded into an easily transportable unit.

Description

United States Patent [151 3,639,864 Klostermark Feb; 1, 1972 [54] TRANSPORTABLE COAXIAL CABLE [56] References Cited [72] Inventor: Bernt Kloflermark, Smcdsbacksgatan 38, UNITED STATES PATENTS Stockholm, Sweden 2,464,598 3/1949 Meier et al. ..333/95 A X [22] Filed: Oct. 14,1969 '2] I App]. NM 866,314 FOREIGN PATENTS OR APPLICATIONS [55,417 2/1954 Australia ..l74,/68 [30] Foreign Application Priority Data 7 Primary Examiner-Darrell L. Clay Oct. 22, 1968 Sweden ..l4245/68 Anq y ums' D Swecker & Mathis [52] US. Cl. ..333/96, 174/28.68 R, l74/88 C,

I 333/97 R [57] ABSTRACT E f 2 Coaxial cable for connection between an antenna and a 174 lgsA receiver in nonpermanent or mobile installations. The cable is joined by short lengths of bendable sections thereby enabling the cable to be folded into an easily transportable unit.

9 Claims, 4 Drawing Figures PATENTEDFEB nave 3,839,864

5 8 I 13 919121o13n/ TRANSPORTABLE COAXIAL CABLE It is a known desire to keep the cable attenuation as low as possible between an antenna and a radio equipment in order to decrease the power dissipation.

This is of special importance when high frequencies are used, for example in radio relay systems. In permanent installations it is rather easy to install a coaxial cable with a suitable attenuation, also when the cable is rigid because of its construction, and the cable can be bent only once without being damaged.

In known, mobile radio relay stations with a cable which can be wound on a drum, the bendability of the cable, however, limits the choice of a possible cable size. The thicker the cable is, the less the attenuation and also the less the bendability. Cable drums that are too long cannot be transported on the vehicles, and by a too small diameter of the drum in relation to the bendability of the cable, the cable will be damaged already after a few onwindings and offwindings.

Another disadvantage of a cable which is wound on a drum is, that it is affected by extraneous magnetic fields. By nuclear explosions, for example, a very strong, short-lasting magnetic field is generated (the so called EMF-effect), which within a radius of several kilometers from the place of the explosion can damage a cable which is wound on a drum.

An object of the present invention is to provide a coaxial cable, in which the risk for unallowable bending stresses in difficult field conditions is eliminated, and which it is not necessary to keep on a voluminous cable drum, which is susceptible to disturbing magnetic fields.

The invention relates to a transportable coaxial cable, which is mainly characterized by the fact, that it comprises a plurality of equally long pieces or sections of rather rigid coaxial cable and intermediate pieces or sections of rather easily bendable cable, said intermediate pieces being connected to the pieces of rigid cable by electrical connections, which electrically connect partly the inner conductors or cores of the different cables and partly the outer conductors or mantles of said cables, as well as by mechanically strong connections, which take up mechanical loads.

The invention will now be described with reference to the appended drawing.

FIG. 1 shows a short piece of a transportable cable according to the invention,

FIG. 2 shows a longitudinal section of a joint between a rigid piece of cable and a bendable piece of cable according to an embodiment of the invention,

FIG. 3 shows an intersection of a joint between a rigid and a bendable piece of cable according to another embodiment of the invention, and

FIG. 4 shows in a much smaller scale a complete cable, which comprises several rigid pieces and several bendable pieces of cable as well as connection devices at the ends, said cable being folded 180 and tied up in an easily transportable bundle.

The cable which is shown in FIG. 1 comprises a number of practically unbendable, rigid cable pieces or sections 1, as well as a number of rather easily bendable cable pieces or sections 2, which are connected to the rigid cable pieces 1 by permanent joints 3.

Although in FIG. 1 only parts of three rigid cable pieces 1 and two easily bendable cable pieces 2 are shown, the cable may naturally comprise an arbitrary number of each such pieces. The cable pieces 1 should be considerably longer than the cable pieces 2, so that the total attenuation of the cable will be only slightly lower than the attenuation of an equally long cable, which would comprise one single piece, said piece being of the same kind as each of the cable pieces I. The cable pieces 1 and 2 should have the same electrical characteristics, i.e., the same impedance, so that reflections at the joints 3 will be avoided.

It is a condition prevailing for obtaining a cable with a low attenuation, that thejoints are made in a suitable way.

As FIGS. 2 and 3 show, the rigid cable pieces 1 can comprise an inner conductor or core 4, which consists of a rather unbendable or rigid copper bar or copper tube, as well as in outer conductor or mantle 5, which can be a rather unbendable or rigid copper pipe. In such coaxial cables, both the inner conductor 4 and the outer conductor 5 customarily have cylindrical shapes. Between the core 4 and the mantle 5 insulation is arranged, which may fill the intermediate space or alternatively may consist of insulating washers 6, two of said washers being shown in each of the FIGS. 2 and 3. On the outside of the mantle 5 an outer insulation 7 of polyvinyl chloride or the like is arranged. At the joint said insulation 7 is stripped off as illustrated, so that it ends at 8. The easily bendable cable 2 may comprise an inner conductor or core 9 of a multicore copper wire, said wire being surrounded by a mantle with the shape of a sleeve of metal braid 10 or the like. On the outside of the mantle an insulation is arranged, which is indicated by 11. This'insulation is stripped off at the joint and ends at 12. As in the cable 1 the core 9 may be centrally held in the mantle 10 by either a solid insulation or by insulating washers 13, which are spaced from each other. At the joint 3 a hole is drilled in the core 4 of the rigid cable 1, and the core 9 of the bendable cable 2 is inserted in said hole as is shown at 14. The core 4 of the rigid cable 1 may squeeze the core 9 of the bendable cable 2, or said cores may be soldered together at the joint 14.

In theiembodiment according to FIG. 2 the mantle or sleeve 10 of the bendable cable 2 is furthermore stretched out and slipped over the end part of the mantle 5 of the rigid cable I, said part projecting outside the insulation 7, as is shown at 15. At this joint the sleeve of metal braid 10 may be soldered to the mantle 5 or be squeezed by tie wire or the like. On the outside of the joint, which is thus formed between the

points

8 and 12, the joint may be surrounded by an insulation, which is indicated by 15, and which may comprise a tape, which is wound on it, or a shrinkable or slotted insulating tube, said tube being possibly at first thread over for example the cable piece 2' and thereafter being moved back onto the joint. On the outside of the joint 3 and also on the outside of the whole cable an outer insulation 17 of for example PVC-plastic is arranged, which hermetically seals the different joints of the cable. Said PVC-plastic will be arranged when the joints of the cable arecompleted and will extend from the one end of the completed cable to the other.

In the embodiment according to FIG. 3 the mantle of the bendable cable 2 is cut off at 18. It does not have to be a sleeve of metal braid but may comprise for example a wrapping, consisting of a tape which is wound with overlapping. A special sleeve of-metal braid 19 is in said embodiment thread over the whole bendable cable piece 2 and arranged so as to extend over and past the two joints 3, by which joints the bendable cable 2 is connected to the adjacent, rigid cable pieces 1. The sleeve ofmetal braid 19 is electrically and mechanically connected (for example by soldering) to the free mantle ends 20 of the rigid cable pieces 1 as well as to the stripped off ends 21 of the mantle of the bendable cable 2. The rest of the sleeve of metal braid 19 is located on the insulation 11 of the bendable cable 2, which is shown to the right in FIG. 3. The outer insulation 17; which covers the whole complete cable and its joints, however, is arranged on the outside of the sleeve of metal braid 19.

In the device according to FIG. 3 the sleeve of metal braid 19 forms an electrical connection between the mantles of the different cable pieces. At the same time said sleeve forms such a mechanical connection, which absorbs mechanical loads in the longitudinal direction of the cable, which loads may occur between the rigid cable pieces. In the embodiment according to FIG. 2 it is mantle 10 of the bendable cable which has the shape of a sleeve, will be loaded with some of the longitudinal, mechanical loads.

In the device according to FIG. 3 the sleeve of metal braid 19 can be a so called pulling sleeve of a kind known per se, i.e., a braided sleeve of a springy wire, which is compressive in its longitudinal direction and whose diameter increases by compression. Such a sleeve, however, is often made of a ferromagnetic or some other material, which is not suitable for transmission of high-frequency electrical energy. Therefore in such cases a sleeve of copper braid (not shown) should be arranged on the inside of the pulling sleeve.

Instead of using a ready insulated coaxial cable as initial material, a cable can be used which has no insulation on the outside of the outer conductors (the mantle). When the different parts of the cable have been connected in one of the ways, which have been described above, the cable will be provided with a continuous outer insulation 17 of plastic or rubber which may provide a hermetical cover.

In order to make sure that the joint 14 of the cores of the cable will not come into touch with the surrounding sleeve of metal braid or 19, an insulation block 24 can be arranged around the joint 14, if desired. This insulation can comprise an insulating body, which may be divided into two halves and arranged around the joint, or moulded around the joint by a special tool. The insulating body may either be solid or provided with grooves or recesses (radial or axial), for decreasing the dielectric constant of the insulating body to a suitable value.

The joint 14 does not have to be the kind, which has been described in connection with the shown embodiments. The joint may alternatively comprise a jointing tube, in whose two ends the ends of the

cores

4 and 9 have been inserted and soldered or squeezed.

FIG. 4 shows how a cable according to the invention has been folded 180 to an easily transportable bundle, which is kept together by straps 22. In this embodiment several sections of the rigid coaxial cable 1, all having substantially equal lengths, are shown connected together by sections of flexible or bendable cable 2. The bendable sections allow for 180 bending, as illustrated.

A coaxial cable according to the invention may naturally be provided with coaxial connections 23 at its ends, so that it will be easy to connect between for example an antenna and a transmitter or receiver. The cable may at its ends be provided with bendable parts, on which coaxial connections are arranged in order to facilitate the connection of the cable and to make the cable bendable close to the connections.

Different modifications of the invention can be made within the scope of the appended claims.

I claim:

l. A transportable coaxial cable for use as a transmission line for radiofrequency signals comprising a plurality of rigid sections of coaxial cable having a solid central conductor and an outer conductor, with the ends of said rigid sections being joined by a section of flexible coaxial cable having a multiplewire central conductor and a flexible cylindrical outer conductor, and joints electrically and mechanically connecting adjacent ends of said rigid and flexible sections together, each joint comprising: 7

means at the end of the central conductor of the rigid section electrically and mechanically attaching a free end of the central conductor of said flexible section thereto;

a length of braided flexible cable of conductive material extending from the outer conductor of said flexible cable over the surface of and being secured to the outer conductor of the rigid cable section; and

insulation means extending from the outer surfaces of the rigid and flexible cable sections covering the joint.

2. Transportable coaxial cable according to claim I wherein the inner conductors of both cables are connected with coaxial connections, with the inner conductor of the rigid cable having a central hole into which a free end of the inner conductor of the flexible cable is inserted and secured in good electrical and mechanical contact therewith.

3. Transportable coaxial cable according to claim 1 wherein the outer conductor of the rigid cable section is cylindrical and said length of flexible cable is spread over the adjacent end an of said outer conductor on the rigid cable section.

4. ransportable coaxial cable according to claim 1 wherein the length of braided flexible cable is a separate member which extends over and is electrically and mechanically secured to the outer conductors of both the rigid cable section and the flexible cable section, said separate member comprising a braided sleeve of springy wire which when compressed increases in diameter and when placed under tension decreases in diameter.

5. Transportable coaxial cable according to claim 1 wherein the length of braided flexible cable is an extension of the outer conductor of said flexible cable.

6. Transportable coaxial cable according to claim 1 wherein the rigid sections are disposed in parallel side-by-side relationship with the flexible sections having a reverse bend of l, and means securing the rigid sections together for easy transport of the coaxial cable.

7. Transportable coaxial cable according to claim 1 wherein the rigid sections and the flexible sections of said coaxial cable have substantially the same electrical impedance.

8. Transportable coaxial cable according to claim 1 having at least four sections of coaxial cable, conventional terminals at opposite ends of the cable, and a unitary sleeve of insulating material extending the full length of the cable between the connectors to thereby provide a hermetically sealed cable.

9. Transportable coaxial cable comprising a plurality of equally long pieces (1) of rather rigid coaxial cable composed of an inner conductor and an outer conductor and intermediate pieces (2) of rather easily bendable coaxial cable composed of an inner conductor and an outer conductor, said intermediate pieces being connected to the pieces of rigid cable by joints (3) comprising electrical connections which electrically connect together both the inner and outer conductors of the rigid and flexible coaxial cables and mechanical connections, with the said pieces of rigid coaxial cable and said pieces of bendable coaxial cable having substantially the same electrical impedance.

Claims

1. A transportable coaxial cable for use as a transmission line for radiofrequency signals comprising a plurality of rigid sections of coaxial cable having a solid central conductor and an outer conductor, with the ends of said rigid sections being joined by a section of flexible coaxial cable having a multiplewire central conductor and a flexible cylindrical outer conductor, and joints electrically and mechanically connecting adjacent ends of said rigid and flexiBle sections together, each joint comprising: means at the end of the central conductor of the rigid section electrically and mechanically attaching a free end of the central conductor of said flexible section thereto; a length of braided flexible cable of conductive material extending from the outer conductor of said flexible cable over the surface of and being secured to the outer conductor of the rigid cable section; and insulation means extending from the outer surfaces of the rigid and flexible cable sections covering the joint.

2. Transportable coaxial cable according to claim 1 wherein the inner conductors of both cables are connected with coaxial connections, with the inner conductor of the rigid cable having a central hole into which a free end of the inner conductor of the flexible cable is inserted and secured in good electrical and mechanical contact therewith.

3. Transportable coaxial cable according to claim 1 wherein the outer conductor of the rigid cable section is cylindrical and said length of flexible cable is spread over the adjacent end part of said outer conductor on the rigid cable section.

4. Transportable coaxial cable according to claim 1 wherein the length of braided flexible cable is a separate member which extends over and is electrically and mechanically secured to the outer conductors of both the rigid cable section and the flexible cable section, said separate member comprising a braided sleeve of springy wire which when compressed increases in diameter and when placed under tension decreases in diameter.

6. Transportable coaxial cable according to claim 1 wherein the rigid sections are disposed in parallel side-by-side relationship with the flexible sections having a reverse bend of 180*, and means securing the rigid sections together for easy transport of the coaxial cable.