US2600111A - Coaxial cable with spiral spacer - Google Patents

Description

June 10, 1952 H. D. ISENBERG 2,600,111

COAXIAL CABLE WITH SPIRAL. SPACER Original Filed Feb. 8, 1946 JNVENTOR. HANS. D. ISENBERG WWW Patented June 10, 1952 CQAXIAL CABLE WITH SPIRAL SPACER D. Isenberg, Wilmette, 111..

Original application February 8, 1946, Serial No. 646,464. Divided and this application Novem= her 12, 1947, Serial No. 785,271

(Cle 174 253) 4 Claims.

The present invention relates to air or gas insulated or coaxial cable. This application is a division of applicants copending application Ser. No. 646,464, filed February 8, 1946,, now Patent 2,434,073.

Coaxial cable of the air or gas insulated type used commercially in wide band high frequency circuits is conventionally comprised of two coaxially arranged conductors which are held apart by insulating discs provided at spaced points along the two conductors to support the inner conductor centrally within the outer conductor and thus provide a dielectric air or gas space therebetween.

This construction is not only costly, but requires 1 that the cable be formed in relatively short lengths or sections which must be joined in order to obtain a cable of any considerable length.

It is an object of the present invention, therefore, to provide an improved air insulated or coaxial cable that may be continuously formed to e any desired length.

It is another object of the invention to provide an improved coaxial cable structure which may be economically constructed on a continuous and fully automatic basis and yet is of rugged construction, such that it may be roughly handled and distorted in use without loss of its electrical properties.

It is still another object of the invention to provide an insulating filament of improved construction uniquely adapted for use in continuously forming the improved coaxial cable herein disclosed.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which:

Fig. 1 is a side view partially in section, illustrating a segment of the finished cable characterized by the features of the present invention; and

Fig. 2 is a sectional view taken along the lines 2-4 in Fig. 1.

Referring now to the drawings, the present improved air insulated or coaxial cable is there illustrated as comprising a continuous filamentary element II of plastic insulating material wound into helical convolutions I3 disposed along the length of the inner conductor I2 of th cable, and so constructed that certain thereof, 1. e., the convolutions 13a are radially spaced from the conductor to support an outer sheath 21, and others thereof, 1. e., the convolutions I312 engage the conductor I2 at spaced points along the length thereof to support the radially spaced convolutions 1311 from the conductor.

More specifically considered, the filament l I is made of a heat settable or heat annealable plastic which has the property of being settable in a fixed configuration, either when heated to a predetermined temperature, or when heated to a semi-plastic state and then cooled. Specifically this filament may be formed of a phenolic resin, a methyl methacrylate resin, 2. vinyl chloride acetate resin, a polystyrene resin, a polyvinyl chloride resin or any material having similar properties. This filament is of novel construction. As best shown in Fig. 1, the filament is of generally Z-shaped cross-section and is provided with rabbets on opposite sides and at the opposite margins thereof so that it may be formed into helical convolutlons with each convolution interlocking with the adjacent convolution to form a rabbeted joint. The surface Ila of the filament, which is adapted to contact the conductor 12, isshown as being arcuate, but may be any non-planar surface that will provide minimum contact, i. e.

l a line contact between the conductor I2 and the filament II. This minimum contact is an important feature of the improved filament, because tests have established that at ultra-high frequencies dielectric losses decrease with a decrease in the amount of contact between a conductor and a dielectric. Preferably, the outer surface Nb of the filament is planar in order that the interlocking convolutions of the filament may form a member having a substantially continuous outer surface. This is especially desirable if the outer sheath 2! is a non-conductor. If, however, the sheath 21 is a conductor such that the structure forms a coaxial cable, and if dielectric losses are to be reduced to a minimum, the surface lib may also be a non-planar surface. As will be understood, the plastic filament ll possesses elasticity so that the cable may be bent through a fairly short radius, if necessary.

The improved method and apparatus used in continuously making the present improved cable are fully disclosed and claimed in applicant's copending application Ser. No. 646,464, now Patent 2,434,073. Briefly, the method embraces the steps of continuously moving the inner conductor l2 longitudinally, winding the continuous filamentary element H of insulating material about the conductor 12 to form th helical convolutions which surround the conductor ll, actuating a winding mandrel to so change the diameter of winding that the convolutions [3a are radially 3 spaced from the conductor 12 and convolutions I3b engage the conductor 12 at spaced points therealong, and then forcing the adjacent convolutions toward each other to increase the overlap between the complementary rabhets of the filament l i and thus form a continuous unbroken sheath around the conductor 12. During the last-described step, heat is applied to the convolutions [3 to eirect setting thereof wit-h full overlap therebetween.

From a further consideration of the drawing, it will be noted that the resulting insulating supporting structure comprises spaced groups of convolutions [3a of equal diameter which are radially spaced from the inner conductor 12 and are alternated with convolutions l3?) which embrace the conductor l2 and serve to support the radially spaced convolutions I30. from this conductor. It will also be understood that since the thermo-plastic or thermo-setting filamentary element H is heated to its setting or annealing temperature incident to the formation of the convolutions, a permanent set is imparted to the convolutions 13 which enhances the tendency of these convolutions to reassume the formed positions thereof when distortion pressures imposed thereon are relieved.

Concurrently with formations of the helical convolutions l3 in the manner just described, the outer sheath 2! of the insulating or conducting material is progressively wound around the convolutions l3 to complete the cable structure. This material is in strip form and may be self-adhering so that the overlapped thereof are bonded to prevent separation after the serves to enhance the rigidity of the completed cable structure.

While there has been described what is at present considered to be a preferred embodiment of the invention, it will be understood that various modifications may be made therein which a are within the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. An insulated cable comprising an inner conductor and a continuous filament of either thermosetting or thermoplastic material helically wound around said conductor to itself form a continuous flexible sheath, the convclutions of said sheath being interlocked with rabbet joints,

said sheath having certain convolutions found so as to provide substantially a one turn spiral of reduced diameter directly contacting said conductor and radially spacing it from the remainder of said convolutions.

2. An insulated cable comprising an inner conductor, and a continuous filament of either thermosetting or thermoplastic material wound in helical convolutions around conductor, certain of said convolutions being radially spaced from said conductor and others of said ccnvolutions of reduced diameter being wound to provide substantially one turn spirals directly contacting and supporting said conductor, the spaced convoluticns having interlocking edges, whereby they form acontinuous flexible sheath around said conductor.

3. An insulated cable comprising a continuous electrical conductor, a tubular outer covering, and insulating means supporting said conductor centrally within said covering and spacing the same therefrom, said insulating means compris ing a filament having a non-plane surface on at least one side thereof and complementary rabbets at opposite margins and on opposite sides of said filament, said filament being formed into successive groups of helical convolutions joined by interlocking of said rabbets and arranged in contact with said outer covering and having a single complete convolution intermediate each of said groups directly supporting said conductor and helically disposed thereon with the nonplane surface of said filament contacting said conductor and with the opposite ends of the intermediate convolutions each merging in gradual curvature with the end of an adjacent corresponding helical convolution of a group.

4. A coaxial cable, comprising a continuous electricalinner conductor, an outer conductor surrounding the same and insulating means sup porting said conductors in coaxial relationship. said insulating means comprising a continuous plastic filament having complementary ra sets at opposite margins and on opposite sides thereof, and said filament being wound in helical convolutions around said inner conductor thereby forming an unbroken flexible sheath which contacts said outer conductor, with substantial portions of certain convolutions surrounding and directly contacting said inner conductor spacing it from the remaining convclutions.

HANS D. ISENBERG.

REFERENCES CITED The rcllowing references are of record in the- .de of this patent:

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