US 1987442 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Jan. 8, 1935.
H. J. HARRIS SIGNALING CABLE Filed June 5, 1952 FIG-l INVENTOR H. J. HARRIS A TTORNE Y Patented Jan. 8, 1935 UNITED STATES PATENT OFFICE SIGNALING CABLE Application June 3, 1932, Serial No. 615,173
This invention relates to electrical transmission systems and more particularly to multi-pair telephone cables.
An object of the invention is to improve the mechanical and electrical characteristics of the structure which separates and insulates the conductors of a multi-pair cable.
The insulating material between the conductors of a telephone cable generally serves two purposes. The first of these'is to prevent the conductors from coming into direct contact with each other and thus short-circuiting the system; The second is to hold the conductors in a more or less definite position relative to each other and thus to fix the electrical constants of the circuit. The insulation is therefore a factor of major importance in any circuit where the two sides are close together and where the constants of the circuit are of great significance. Since the efliciency of a circuit used for the transmission of telephone or carrier wave currents is determined largely by the constants of that cir- =cuit, it is important that the insulation hold the conductors in such relative positions that the most satisfactory values for such geometrical constants as capacitance and inductance are obtained. It is likewise highly desirable that the inherent properties of the insulation be of such nature as to produce the lowest possible dielectric losses.
Heretofore it has been common practice to use in connection with telephone cables individual insulation for the conductors, comprising such ma- 'terials as rubber, asphalts, textile braids, and paper ribbon. In some cases a combination of a helical strand of insulating material and an external wrapping of paper ribbon is applied to each conductor.
In accordance with the present invention a cable is provided in which the conductors are bound together in groups and insulated from each other by means of strands of cotton, paper or other suitable dielectric material braided about the conductors. Preferably, the conductors are thus bound together in pairs or in groups of four, and the groups are twisted together or otherwise assembled to form the cable. The individual groups need not be wrapped with a ribbon of paper to insulate them from each other, since the braiding material binding the conductors of each group can be arranged to separate the groups sufilclently for this purpose. The resulting structure is highly flexible. A relatively small amount of solid insulation is used and the dielectric losses on accordingly small, yet the conductors are effectively insulated from each other. At the same time the conductors are bound firmly into position relative to each other so that the capacitances of the several pairs are substantially equal. The specific method of braiding shown has ad- 5 vantages which will be disclosed hereinafter.
Other objects and features of the present invention will appear in the following description, reference being made to the drawing, in which Figs. 1, 2 and 3 illustrate methods of insulating groups of 2, 3 and 4 conductors, respectively;
Fig. 4 shows the preferred group structure; and
Fig. 5 shows a telephone cable in accordance with applicant's invention.
Referring now to Fig. 1 there is illustrated a method of insulating a single pair of conductors. Around the two parallel conductors 1, is applied helically a string or cord 2 of insulating 'material. A second insulating string 3 is placed between the conductors; it is looped in and out of the convolutions of the first insulating string in such manner that when it is drawn taut the convolutions of the first insulating string are restricted from longitudinal displacement. The insulating material employed may be ordinary or impregnated cotton, acetylated cotton or other suitable fibrous material. Preferably the strands should be firm enoughto hold their shapes when the cable is flexed. 30
The invention is also well adapted for the use of extruded filaments of metastyrol, cellulose acetate and other compositions'of sufllciently great flexibility and insulation resistance.
In Fig. 2 is illustrated, chiefly for purposes of explanation, the manner of binding and insulating three conductors. A strand I of insulating material is applied helically about the group of parallel conductors 4, 5 and 6. A second insulating strand 8, which occupies generally a central position with respect to the conductors, is looped over the successive turns of the helix. Thus, it emerges at a and loops over strand '7 which, there, is on that side of the triangular prismatical structure including conductors 5 and 6. It next emerges at b and loops over strand 7 where it passes across that side of the structure including conductors 4 and 5. At cit again emerges and binds strand 7 to the third side of the triangular structure. 50
The extension of the method to the insulation of four conductors is shown in Fig. 3. The group of parallel conductors 10 to 13 is enclosed within the helical insulating strand 14. A second strand 16 which occupies a generally central position emerges at successively different sides of the structure and loops over successive portions of the helical winding.
In the preferred embodiment of the invention shown in Fig. 4, the four conductors are enclosed within a double helix of insulating material. The strands comprising these helices are represented as 16 and 17. With each helix is associated a central string 18, 19. Preferably the points of emergence of these latter strings progress about the structure in the same helical sense, but opposite to that of the external helical windings. As one of a number of possible alternatives, the cen tral strings may beapplied as shown in Fig. 3. The separation of the conductors from each other can be controlled accurately by properly choosing the size of the central string. Ordinarily the distance between conductors should be somewhat greater than the diameters of the conductors.
The separation from surrounding and supporting bodies such as adjacent groups of conductors can be likewise controlled quite definitely by altering the size 01' the strand applied helically about the conductors. This flexibility of control is often of considerable value where it is desired to regulate the relative magnitude of the direct capacitance of a conductor to its mate and that of one conductor to other conductors or ground. The ratio of the first capacitance to the second may be decreased by using between the conductors of a group a string larger than that surrounding the group. The reverse effect may be produced by spiralling around the group a string larger than that used between the conductors of a group or by addingover the outer string a ribbon wrapping. Any material surrounding the quad, it will be noted, however, is traversed by the field existing between the several conductors and ground and accordingly introduces a dielectric loss.
In Fig. 5 is shown a complete cable comprising a-number of groups of conductors insulated and separated with string binding. Preferably the groups are each twisted before they are laid up into the cable. The assemblage may be wrapped with paper tape 20 and covered with a lead sheath 21.
The insulating method in accordance with the present invention has advantages from a manufacturing standpoint. Insulation, in accordance with this invention, may be applied mechanically to two or more conductors initially straight and parallel to each other. Consequently, if the binding string is held tightly while it is being applied helically, the two or more conductors will be firmly bound together as in machines used specially for binding purposes. All of the insulated conductors will therefore tend to be equal in length, and as a result the circuits will possess the usual desirable qualities of better balance resulting from equality of length. The fact that this scheme involves insulating a number of conductors in one operation will tend to ofiset the lower linear speed at which it may be necessary to apply this type of insulation. Furthermore, since a take-up mechanism will be necessarily provided to pull the conductors along through the insulating machinery, this mechanism may at the same time be rotated so as to twist the insulated group.
Various modifications of the cable structures disclosed herein as specific embodiments of the invention will readily occur to those skilled in the art. The invention is therefore to be limited only within the scope and spirit of the appended claims.
What is claimed is:
l. A high frequencysignaling cable comprising a plurality of groups of at least three bare conductors each, the dielectric between all of said conductors being largely gaseous, a strand of insulating material wound helicall'y about each of said groups, and a second, central strand of insulating material emerging on successively different sides of each of said groups to loop over axially successive convolutions of said helical strand.
2. A signaling cable adapted for carrier telephone transmission comprising a plurality of me tallic conductors separated by a dielectric that is largely gaseous, said conductors being grouped in quads with a first filament of insulating material wound helically around each of said quads and a second filament of insulating material looping over the convolutions of said first filament to bind said first filament to the sides of said quad, the distance between said conductors being determined substantially only by said insulating filaments.
3. A multi-circuit cable adapted for transmission at high frequencies comprising a multiplicity of conductors arranged in groups of at least four each, and two or more filaments of non-conducting material disposed about the conductors of each of said groups to bind said conductors to-