EP0373120A1

EP0373120A1 - Coaxial cable and making method therefor

Info

Publication number: EP0373120A1
Application number: EP89830037A
Authority: EP
Inventors: Sergio Mueller
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-09
Filing date: 1989-02-03
Publication date: 1990-06-13
Also published as: IT8822904A0; IT1227546B

Abstract

There is disclosed a coaxial cable for transmitting high frequency signals,comprising an inner conductor thereabout there is extruded a plastics material coating provided with two or more outwardly projecting legs adapted to perfectly center the inner conductor within a tubular plastics material element so as to enclose a comparatively great amount of air as a dielectric material.

On the outside of the insulating tubular element there is arranged a second conductor,substantially parallel to the inner conductor,the assembly being enclosed by an outer coating,or protecting sheath made of PVC or any other suitable electrically insulating material.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an improved coaxial cable and to the method for making this cable.
As is known,in the high frequency signal transmission field,for example for TV,telephonic communications,alarm,control and the like applications,there are presently used coaxial cables consisting substantially of a conductor pair,with one of the conductors being arranged inside the other.
Known coaxial cables,however,are affected by some drawbacks the most important of which are a non perfect electrical insulation,with a consequent signal loss,some ageing of the insulating materials included in the cables and a comparatively high weight.
Other drawbacks can be caused by a non perfect symmetry of the central conductor of the cable,which causes in turn a consequent loss or deformation of the signals being transmitted.

SUMMARY OF THE INVENTION

Thus,the task of the present invention is to obviate the above mentioned drawbacks by providing a coaxial cable,and a method for making it,having a comparatively small weight and cost while providing good electrically insulating and signal transmission characteristics.
Within the scope of the above task,a main object of the invention is to provide such a coaxial cable in which the central conductor is arranged in a very stable and symmetric way.
Another object of the invention is to provide such a coaxial cable having electrical characteristics substantially invariable in the time.
According to one aspect of the present invention,the above mentioned task and objects,as well as yet other objects,which will become more apparent hereinafter,are achieved by an improved coaxial cable for transmitting high frequency signals,characterized in that said coaxial cable comprises an inner conductor,thereabout there is extruded a plastics material coating which is provided with two or more legs outwardly projecting therefrom along the overall length thereof,said legs being adapted to properly center said inner conductor within a plastics material tubular element,so as to enclose a comparatively high air amount as a dielectric material,on the outside of said insulating tubular element there being arranged a second conductor, substantially parallel to said inner conductor,the assembly of said inner conductor,insulating tubular element and second conductor being enclosed in an outer coating or protecting sheath made of PVC or other insulating material.
In this connection it should be pointed out that the insulating coating,provided with longitudinally projecting legs,which encompasses the inner conductor may be twisted so as to assume a helical arrangement.
Moreover the mentioned longitudinal legs the outer edges of which press against the inner face of the insulating tubular element,can be provided in a number of two,as diametrically opposite arranged,or three or,preferably,four so as to assure,in cooperation with the twisted arrangement,a perfect centering of the inner conductor,even if the cable is possibly bent at one or more regions thereof.
With respect to the second conductor,or outer conductor,it can be made according to several embodiments,depending on the provided applications,as it will be disclosed in a more detailed way hereinafter.
More specifically,according to a first embodiment,about the insulating tubular inner element,between this latter and the outer sheath,a shield can be provided as the second or outer conductor,made of a tinned or silvered red copper braid.
A second embodiment provides for the insertion,between the inner insulating tubular element and the outer sheath,of an aluminium sheet,or a copper sheet,coupled to a polyester material and having the conductive side facing the sheath and contacting a conductor,or ground wire,either of the unipolar or stranded type,made of tinned or silvered red copper and extending parallel to the inner conductor.
A third embodiment provides to replace the mentioned aluminium or copper sheet with a polyester coupled aluminium or copper strip helically wound about the insulating tubular inner element with the insulated side of said strip facing said tubular element,the conductive side of said strip facing said sheath and contacting a conductor,or ground wire,either of the unipolar or stranded type,made of tinned or silvered red copper,which extends parallel to the inner conductor.
The insulating element provided with longitudinal legs which encloses the inner conductor (made of tinned or silvered red copper ) and the tubular inner element are made of polyethylene or other suitable electrically insulating material,whereas the coating or enclosing sheath is preferably made of PVC.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other characteristics of the improved coaxial cable and making method therefor according to the present invention will become more apparent hereinafter from the following detailed description of some embodiments thereof,with reference to the accompanying indicative but not limitative drawings,where:

figures 1 and 2 are respectively a perspective and cross-sectional view illustrating two possible embodiments of the coaxial cable according to the present invention;
figure 3 is a longitudinal cross-section view illustrating a portion of the subject coaxial cable comprising only the inner conductor,its insulating legged element and the insulating tubular element enclosing them;
figure 4 is another longitudinal cross-section view illustrating a portion of a complete coaxial cable according to the present invention,that is including the second conductor or outer conductor and the outer protecting sheath;
and
figure 5 is a cross-sectional view relating to figure 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the figures of the accompanying drawings,the coaxial cable 1 according to the invention comprises two conductors,that is a first inner conductor 2 and a second outer conductor 3 which are electrically insulated from one another and enclosed within an outer coating or envelope,or protecting sheath.
More specifically,the inner conductor 2 is embedded,for example by means of an extruding operation,within an insulating coating 4,of a plastics material,provided with longitudinal outer legs 4′ and 4˝ adapted to center the conductor 2 within an insulating tubular element 5,also made of a plastics material,by pressing against the inner face thereof.
As mentioned,the longitudinal legs may also be three and,preferably,four as evenly arranged about the conductor.
According to one aspect of the method for making the subject coaxial cable,the assembly consisting of the conductor 2 and its insulating element 4,having the mentioned longitudinal legs,can be subjected to a suitable helical twisting step,so as to provide a perfect centering of the conductor 2 even if the cable would be subjected to bending.
As shown,about the tubular element 5 there is arranged a second or outer conductor 3,in turn covered by the outer protecting sheath 6.
In a simpler embodiment,not shown,the second or outer conductor 3 can consist of a copper braid shield.
According to a second embodiment (as shown in figure 1),between the insulating inner tubular element 5 and the protecting sheath 6 there is arranged an aluminium or copper sheet 7,coupled to a polyester film 8,with the conductive side of said sheet being arranged toward the sheath 6 and contacting a conductor 3 extending parallel to the inner conductor 2.
According to a third embodiment,(as shown in figure 2) the mentioned sheet 7 is replaced by a strip helically wound about the tubular element,the conductive side 7 of said strip facing the sheath 6 and contacting a conductor 3 which is parallel to the inner conductor,2.
From the above disclosure it should be apparent that the invention fully achieves the intended task and objects.
While the invention has been disclosed and illustrated with reference to preferred embodiments thereof,it should be apparent that the disclosed embodiments are susceptible to several modifications and variations,all of which will come within the scope and spirit of the accompanying claims.

Claims

1- An improved coaxial cable for transmitting high frequency signals,characterized in that said coaxial cable comprises an inner conductor,thereabout there is extruded a plastics material coating which is provided with two or more legs outwardly projecting therefrom along the overall length thereof,said legs being adapted to properly center said inner conductor within a plastics material tubular element,so as to enclose a comparatively high air amount as a dielectric material,on the outside of said insulating tubular element there being arranged a second conductor,which is substantially parallel to said inner conductor,the assembly of said inner conductor,insulating tubular element and second conductor being enclosed in an outer protecting sheath made of PVC or other electrically insulating material.

2- A coaxial cable according to claim 1,characterized in that the insulating coating which encompasses said central conductor is provided with three longitudinal legs evenly arranged about said central or inner conductor.

3- A coaxial cable,according to claim 1,characterized in that said insulating coating encompassing said central conductor is provided with four longitudinal legs evenly arranged about said central or inner conductor.

4- A coaxial cable,according to claim 1,characterized in that said insulating coating encompassing said central conductor is helically twisted.

5- A coaxial cable,according to one or more of the preceding claims,characterized in that the second conductor,arranged between said insulating tubular element and protecting sheath consists of a tinned or silvered red copper shielding braid.

6- A coaxial cable,according to one or more of the preceding claims,characterized in that said second conductor consists of an aluminium or copper sheet coupled to a polyester film,wound about said insulating tubular element and with its conductive side facing said protecting sheath and contacting a conductor,or ground wire,either of the unipolar or stranded type,made of tinned or silvered red copper and extending parallel to said center or inner conductor.

7- A coaxial cable,according to one or more of the preceding claims,characterized in that said second conductor consists of an aluminium or copper strip,coupled to a polyester film and helically wound about said insulating tubular element with the conductive side facing said protecting sheath and contacting a conductor or ground wire,either of the unipolar or stranded type,made of tinned or silvered red copper and extending parallel to said center or inner conductor.

8- A coaxial cable,according to one or more of the preceding claims,characterized in that said insulating element provided with longitudinal legs and said insulating inner tubular element are made of polyethylene or other electrically insulating plastics material,said protecting sheath being made preferably of PVC.

9- A coaxial cable according to one or more of the preceding claims,characterized in that said first conductor is centered within an insulating tubular element thereabout there is arranged a second conductor,in turn enclosed within an outer coating forming said protecting sheath.

10- A coaxial cable for transmitting high frequency signals and making method therefor,according to one or more of the preceding claims,and substantially as broadly disclosed and illustrated for the intended task and objects.