US2217162A - Conductor cable - Google Patents

Description

Oct. 8, 1940. A c, DUCA-n 2,217,162

CONDUCTOR CABLE Filed sept. 24, 1957 Patented Oct. 8,. 1940 l UNITED STATES- PATENT oFFi/CE by mesne assignments,

to Transducer Corpo,

ration, New York, N. Y., a corporation of New York Application September 24, 1 937, Serial No. 165,432 In Italy October 19, 1936 s claims. (cl. 174-28.)

. This invention relates .to conductor cables and more particularly to cables of the coeaxilil type, that is to say, in which a plurality of conductors insulated from one another are arranged in the 5' cable about a common axis.

f 'Prior to my invention conductor cables of the co-'axial type have come into common use and are accepted as an important7 part of numerous electrical installations. Such cables are in general made with a central conductor and spacers of various varieties and anexternal annular conductor held in substantially co-axial relation with the central conductor by means of`the spacers and finally an outer insulating sheath designed to prevent moisture from entering the cable.

It is an object of the invention to provide a cable which will be flexible, of attractiveA appearance, simple and economical to manufacture and easily used.

Another object of the invention is to provide a 2 cable which win besexibie and easy to hanne but` which will have low capacitance and low surface leakage losses along the surface of the insulators between the conductors of the cable. f

Another object of the invention is to provide a cable which is so light that it can be treated as ascii-supporting unit and its entire weight even carried by the central conductor, if desired. l Another object of the invention is toprovide a cable capable of exposure to ordinary` fvari` 3o ations of atmospheric conditions without serious variations in its conducting and-di-electric char-'- acteristics. f y 1 With these and other objects in view my invention contemplates the combination of a central conductor with beads of insulating material,

strung thereon adapted to support the outer conduc'tor in co-axial relation and to shift ansularly each on the next so that the cable can be flexed at will and an outer conductor consisting of an 40 open mesh wire braid lsupported by theqsides of the bead. s

In the accompanying drawing I have shown 'two preferred embodiments of my invention. 'I'hese -are given with a view to explaining and illustrating the invention 1nd the best manner of embodyingr it in practical use. These are not, however, intended to be exhaustive nor limiting of the invention, but on the contrary the drawing and the following description are designed to instruct others in the invention so that they will be able to embody it' in numerous, forms and modicationsfeach as may be best suited to the requirements of any particular use. l In the drawing:

v Fig.1 is a view partly in elevation, partly in axial section of a two conductor cable embodying my invention; and

Fig. 2 is a similar view of a three conductor cable embodying my invention.

V Referring first to Fig. l, I have shown therein 5 a central conductor i0, e.l g., of stranded wire. On this are strung beads Il. each of which has a domed end with a contact area I2 having spherical surface and a neck I3 projecting beyond the spherical surface in order to lead away from the central conductor an-y moisture which may enter v between the adjacent beads andilow across .the

spherical surface. 'I'his neck and also the `spherical surface itself serve to reduce surface leakagelosses. 15 Through the ends of the beadv li and the neck I3 is a central opening substantially conical in shape and having its smaller end approximately fitted to the icentral conductor Ill. The conical shape lof this opening is designed to permit the 20 angular movement ofthe beads as the cable is flexed-without producing short bends in the central conductor which might with repeated bending fatigue the metal toa point where a failure 25 would occur. As shown specifically in Fig. 1 of -the drawing, the part I3 of the beads which makes contact with the wire is normally in contact therewith along about, 10% of its length only. Conceivably, however,` if the cable were bent to the minimumlradius possible, the beads might 3o I make contact with the wire alongf as much as 25% of its length. This, however, would-be an Y extreme condition, and would rbe avoidable inpractice by'never bending the cable to the mini- 35 mum radius possible. l A

Each of the beads is, as` shown, thimble shape,

Ii. e., hollow, and its end opposite to the dome forms an annular edge which engages thespherlcal surface of the next bead. Thus a continuous o circular contact is made with the spherical surface and is maintained even when the beads are moved angularlylwith respect to one another as i the cable is flexed. i

'I'hese beads are made of an insulating. mates rial, advantageously one which is non-hygr/ scopic and has good dielectric properties. I havel found that a material which is most advantageous both from the point of view that it is non-hygroscopic, that it withstands exposure to the atmos- 50 phere and weathering. and that it has very favorabld and constantl di-electric properties, is' .the class of poly styroi plastics, particularly the marei-iai manufactured and sold in Europe under 1'/ thetrade mark Ipertrolitol". 55

The outer sides of these beads II are substantially cylindrical in form, whereby to support the second co-axial conductor, namely, the open mesh wire braid I5. It is important that the form of the beads II supports the wire of the sheath Without sharp turns and that the wires of the Y it can be quickly dried and will not be entrapped under the wires.

Due to the form of the beads I2 and to the open mesh character of the braid and to the absence of any heavy external insulation in the example illustrated, the cable is extremely light and it will be found in practically all cases entirely practicable to treat it as a self-supporting unit, or even to support it entirely upon the central conductor.

Another advantage of the open mesh braid freely sliding over the surface of the insulation is illustrated at the right-hand end of Fig. l,

gnamely, the simplicity with which connector terminals can be applied. In the case illustrated a narrower cylindrical bead of insulation material I6 is slipped over the end of the central conductor I0 and against the first thimble-shaped bead II. This bead I6 may, as shown in the example. be of a diameter to constitute essentially an extension of the neck I3 of the first bead, or it may 'even be omitted and the neck I3 used for this It will be understood that my invention is ap- Aplicable not only in the simple form shown in Fig.

1 but in other and more complex forms. For example, in Fig. 2, I have shown a three conductor co-axial cable. The inner conductor Il and the intermediate conductor Il may be substantially as described in Fig. 1 and may be separated by similar insulating beads,Y or if desired any other interior structure may be used. v'Over this relatively large ce tral member are strung beads Ila similar to the ads I I but oflarger size and having larger openings substantially Vfitted to the outside diameter of the intermediate conductor Il and over these, in a manner similar to that already described in connection with Fig. 1, is tted the open msh braided sheath Ila.

I claim:

1. A flexible coaxial cable for low-loss'transmission of electrical signals, which comprises a flexible center conductor, a flexible tubular outer conductor substantially coaxial with and spaced from the center conductor, and a plurality'of thimble-shaped beads of insulating material strung on the center conductor, each of said beads comprising a hollow cylindrical portion in contact with and providing a supporting surface for the outer conductor and a likewise hollow substantially hemispherical head portion provided with a small hole for .centering the inner conductor, the wall of the bead being of substantially uniform thickness throughout and so comparatively thin that the parts of the beads which center the inner conductor do not contact said conductor for more than 25 per cent of the length thereof, that a narrow zone of bearing contact between successive beads is insured and that a`s large a portion of the space as practicable between the inner and outer conductors is filled with air, while at the same time provision is made for substantially continuous support of the outer conductor in substantially continuously concentric relation to the inner conductor;

2. A exible coaxial cable according to claim l in which the open end of the cylindrical portion of the bead is formed as a right section of the cylinder whereby a sharp bearing edge for engaging the spherical head of the adjacent bead is provided.

3. A flexible ooaxialcable for low-loss transmission of electrical signals, which comprises4 a flexible center conductor, a exible tubular outer conductor substantially coaxial with and spaced fromthe center conductor, and a plurality of thimble-shaped beads of4 insulating material strungon the center conductor, each of said beads icompriaing a hollow cylindrical portion in contactwith and providing a. supporting surface for the outer conductor an'd a substantially hemi' spherical headportion provided with a small hole for centering the inner conductor, the wall of the bead being so comparatively thin that.the parts 'of the beads which center the inner conductor do not contact said conductor for more than 25 percent .of the length thereof, that a narrow zone of bearing contact between successive beads is insured and that as large a portion of the space as practicable between the inner and outer conductors is filled with air, while at the same time provision is made for substantially continuous support of the outer conductor in substantially continuously concentric relation to the inner conductor.

ADRIANO CAVALIERI DUCATI.

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