US2509341A - Coaxial cable termination - Google Patents

Description

May 30, 1950 .1. GoLDsMlTH COAXIAL CABLE TERMINATION Filed Nov. l2, 1946 atentecl May 30, 1,950l

UNITED STATES ICE COAXAL CABLE 'TERMINATIONi fnorationiof Illinois ApplicatonNovemher 12,-"1946, Serial N0"709344 1. A4: Claims.

'l This inventicnrelates 4to coaxialetransmission lines and is specificallyfdirected tothe-provision of lan improved coaxial -oable termination.

CoaxialV lines 'fare required konnmanyv types of l electronic apparatus vand iieXible coaxial Icableiofll i--tion izo-provide anarticle ofA manufacture corn- "lprising a-tting adapted tobesecured to the end 'lof a coaxial cablel as a' terminal element. `As here disclosed,VV the fit-ting not only `serves -toeestabli-sh 'electricalconnection-With the-'conductors of the fc'able, `but also seals the/cable ends and-mechani-vr -callyanchors'the'cable in position--1n thisconv:meot-ion i-t may be pointed out from alrnechanical standpoint itis not only necessary tol-'securey the `#metalliciconductors-fof the cable but itisalso defies-irablefto securefthe-outer insulating layerlofinthe cable and the woven Wirearmor surroundinglit. Electrically-,most satisfactory results areobtained by a direct-*soldered connection with they conductors, and-in the case off-the--outer conductor it ':isflpreferable-fto have a vsoldered connection of l? annular form extending completely around.` the Aconductor. A perfect-hermetic seal betweenithe centralV and outside conductors-Voi the.A cable is i also' important,-`Y since Vit Yis s Well kn'ovvnl thatiin l'electrical apparatusof the type.utilizing these,

r. .cables :the entry-oi any moisture intoy the coaxial aline is detrimental tothe operation of the .equipar ment and that` for most efficient operation it is essentialA that! the. space between.r .thevconductors -1-ftight manner.. It is also desirablethatthe general :appearance of the: iitting .be neatandcompact and that it be sufficiently rugged to .withstand i 'rough use.

'It isltherefore the principalobjectof the inf,

"abe: completely-sealed in a moisture proofrand air@ Another object of 'the invention-resides in the provision of a terminal 'ttingfso'"constructed ffthat it may bequicklyfandeasily.applied. to a length offcoaxial A.calolerby any Workman Vofordi- .#-Inarv fslrill,M Without `the use .'ofiispeeial` tools tand f- Without training in.v special# techniques.

A1' still furtherobject of the :invention resides sf'in'fthe. provision a' `fittingfhavingkthef. features indicated faboveg-yet r'simple 'in1 design;Y neat and 4compact inV appearance, rugged.' inf construction,

and adapted 'to :economical -rnethods "of imanufacture; onrconventionalztypes of. automatic pro- .l-fduction machinery.

The foregoingfobjects areaccomplished by'the invention here disclosed, "sincef the 'ttings illusltached Willfsecurely anchor? the. cable and a lphysicalfsensa-seal "the endff of. 'the .c`able, 1 and .L establish i electrical connection i with the conduc- 1=1torsof-the:cahlef Further, itlisvso designed that -v it mayfbe.attachedwtosthe cable by'anylordinary "workman Without rspecialftraining:orfspecial tools,

l and in a veryffew moments time.

"i In generalir the. ttingA consists'. fof. agitubular `@sleeve with a threaded. bore'fto gripthe Youterlin- -`Vsu'lationlofI thea cable and al'iiange :andiclamping `nutfto :anchorlthe end :of the Woven'exterior armor of the cable, together With meansxtossecurefthe outer conductortothe sleeve andan insulator through Wh-ich a lead from: thescenterconductor v rinayextend.v The outer insulationrand. armor may f be secured to'theittinglbeforerthe electrical connectionsbetweenr*v 'eitherJ the outer conductor of the cable, or thevcentralfconduotor 1 areA soldered, Juso that-the armor'and.insuiation'serveutc secure 'fi-the cable to the .terminal tting. :Thus aanyposr1: sibilityo undue =strai1ron the electricali connections that are later soldered is eliminated.

"In the difatvingthesingle figure is acentra'l sectional f View through? the. cablectermination', the

y'cable and fitting. b'eingishownin Iassembled position.

" "Thecoaxial `cable itselfconsi-'sts of. a centerf con- -V rounded :by a tubular. outerfrconductonhwhich ordinarily loonsistsof afwoven wire sleeve-il 2. i IlThe =-outer-conductorf2 isfcover'edrby alayer of in- -sulation li31andfwo-ven Wire armor iid; surrounds f the insulationl 'topiotect 'I thef-cable againstv mechanicalldamage. 55

The fitting With which this invention is-particularly concerned is generally tubular in form and includes a cylindrical sleeve I having internal threads I6 to grip the surface of the insulating layer I3 and an external flange I1 threaded to receive a clamping nut I8. The clamping nut is adapted to force a washer I9 against the flange Il to clamp the extreme end portions 2l of the individual wires of the armor I4 against the flange Il. This serves to mechanically anchor the armor to the fitting, and since the washer I9 need not rotate when the nut I8 is tightened there is no tendency to twist the armor.

It may be mentioned at this point that while the ange Il, washer I9 and nut I8 provide a means for terminating the cable armor and mechanically securing the termination fitting to the armor, yet the fitting is equally well adjusted to application to unarmored cables; and when applied to a cable without the outer layer of woven wire armor is applied in exactly the same manner except that the nut I8 is idle.

The tting includes a central section 22 which is also of cylindrical form and unitary with the sleeve I5 and flange Il, but of somewhat less' diameter than the internal diameter of the threads I6. This section is adapted to closely surround the outer conductor I2 of the cable, and isv provided with a number of radial ports .23 extending through the Walls of the bore so that solder 20 may be applied through these ports to unite the conductor l2 with the inside surface of the cylindrical section 22. The fitting also includes a cylindrical bore 25 adapted to mount an insulator 26. The insulator is preferably of polystyrene, which has important advantages over glass or ceramic materials in high frequency work, since either glass or ceramic insulators present a marked impedance discontinuity and consequent power loss because of the high dielectric constant and poor power factor of these materials. As the present design uses a low loss bushing, the mismatch and power loss are avoided and proper dimensional proportions are attained. Insulator 26 is further designed with annular serrations to increase the electrical ance between conductors in the presence of moisture; thus raising the break-down voltage across the termination.

The insulator 26 is fitted in the bore to bear against the shoulder 2l and is hermetically sealed to the fitting by spinning the extreme edge 28 of the fitting inwardly. Since the insulator 29 is formed of polystyrene, when the edge 28 is spun the heat generated by the spinning operation and the pressure exerted by the spinning tool will combine to 4cause a perfect hermetic seal to be established between the insulator and the metal.

The insulator 26 carries a central ferrule 3| having an orifice 32 at its outer end. These parts are assembled by heating the ferrule and forcing it into a drilled opening in the insulator while hot, so that the simultaneous application of heat and pressure causes a perfect hermetic seal between the metal surface of the ferrule and the plastic surface of the insulator.

The fitting is also provided with a unitary annular flange 33 and a threaded portion 34 so that the cable can be mechanically fastened to other apparatus by inserting the end of the fitting through a mounting bracket and tightening a nut 35 to .clamp the bracket between the nut and the flange 33.

To assemble the fitting and install it on a piece of flexible coaxial cable, the cable is first stripped to expose a length of the central conductor I0. The outer conductor I2 and dielectric layer II are then both stripped back slightly further, so that each have a surface exposed. If desired, solder may be applied to the surfaces of the conductor I2 so that the woven ends of the wire will not fray, and so that later soldering will be facilitated. The clamping nut I8 and washer I9 are slipped over the end of the cable, and the end of the braided armor I4 is loosened. The cable is then ready for insertion into the fitting.

Before inserting the cable, it is preferable to place a sealing compound 30 inside the bore of the fitting to aid in the establishment of a perfect hermetic seal. Numerous compounds are available for this purpose, but the one known on the market as Dow-Corning Sealing Compound No. 4 achieves excellent results.

The cable may then be inserted into the tting by passing the `Central conductor I into the ferrule 3l and out through the orifice 32 -until the outer insulating layer I3 of the cable is received in the open threaded end of the tubular sleeve l5. The fitting is then threaded to the insulating layer. The individual screw threads I6 will form grooves in the outer surface of the insulation and when the insulation is threaded to the full depth indicated will provide a very effective mechanical grip between the tting and the insulating layer of the cable. The loose ends of the woven wire armor I4 may now be drawn upwardly around the outside of the tubular sleeve I5 and the washer I9, which has previously been placed in position on the cable, is drawn up to the position shown so that the free ends 2| of the individual wires of the cable armor lie between the washer I9 and the flange Il and extend outwardly in a generally radial direction. 'Ihe outwardly extended ends of the wire may now be trimmed to proper length so that the clamping nut I8 can be drawn upwardly and threaded on the iiange Il. As the clamping nut I8 is tightened it will force the washer I9 in firm clamping engagement with the ends of the individual wires comprising the cable armor and will thus mechanically anchor the armor as well as the outer insulation of the cable to the fitting.

When the fitting is thus secured to the cable, the exposed portion of the outer conductor I2 will be positioned inside of the central portion 22 of the bore and closely adjacent the interior wall surfaces. As heretofore stated, this surface of the conductor I2 has been tinned by the application of solder so that it may be easily united with the fitting by applying hot solder 29 through the ports 23. Any desired number of ports may be used, but it has been found that four are quite satisfactory and that solder applied through the ports will flow completely around the outside of the conductor I2 to make a firm electrical and mechanical joint all the way around the tube.

The electrical lead from the central conductor I0, which extends through the insulator 2B and through the orifice 32 at the end of the ferrule 3l is also sealed at the orifice by a drop of s older l29 which will unite the several strand-S of the conductor to the ferrule. The solder will also flow between the individual strands of the conductor to completely seal the orifice against moisture or air. If desired, a conventional type of connecting lug 36 may then be soldered to the free end of the lead.

The foregoing description should make yit apparent to those familiar with the problems encountered in coaxial cable installations that the teachings of this invention provide a feasible method of perfecting an efiicient cable termination on any of the conventional manufactured forms of flexible coaxial cable. It is also to be noted that the disclosure of this invention shows a cable fitting that is at once simple in construction and well adapted to mass production manufactured on conventional types of production machinery, yet is capable of being installed on conventional cable without special tools and by any ordinary technician. Moreover, the cable termination here disclosed constitutes a distinct advance over previously known installations in that it provides a connection that is not only perfect electrically, but is mechanically strong so that it may be subjected to considerable abuse Without damage and will provide a secure physical anchor for the ends of the cable. Moreover, attention is again directed to the fact that this type of termination not only establishes a perfect electrical connection between the conductors of the cable and their associated equipment, but also establishes a moisture-proof and air-tight seal for the space between the conductors of the cable so that the eiiiciency of operation of the installation cannot be affected by the entrance of Vapor, moisture, etc.

The exact structure of the tting illustrated Having thus described the invention, what I claim as new and desire to protect by Letters Patent is:

1. As an article of manufacture, a terminal fitting for coaxial cable comprising a single sleeve having an internal bore with threaded surfaces adapted to grip the exterior insulation of a section of coaxial cable and a reduced diameter portion of the bore to closely surround the outer conductor of the cable and adapted to be soldered thereto; said reduced diameter portion of the bore having open ports in its walls so that solder may be introduced from the exterior of the sleeve; an insulator mounted in a position coaxial with the sleeve and hermetically sealed to the sleeve, together with a center ferrule extending through and hermetically sealed in the insulator, said ferrule including a opening adapted to surround an electrical lead extending outwardly from the cable, and having an exposed orifice so that said tion of coaxial cable; a reduced diameter portion of the bore to closely surround the outer conductor of the cable and adapted to be soldered thereto; an insulator mounted in a position coaxial with the sleeve and hermetically sealed to the sleeve, together with a ferrule extending through and hermetically sealed in the insulator, said ferrule including an opening adapted to receive an electrical lead extending outwardly from the cable and adapted to closely surround said lead, so that the lead may be sealed to the ferrule by soldering.

3. In a termination for a coaxial cable having a central conductor, a dielectric layer and an outer tubular conductor surrounded by insulation and armor, the combination of a fitting having a sleeve portion surrounding and directly engaging the insulation, means for securing the armor outside of said sleeve portion, means for securing the outer tubular conductor inside of said fitting, and an insulator carried by said fitting and surrounding a portion of the central conductor of the cable extending out of the fitting.

4. As an article of manufacture, a terminal fitting for coaxial cable comprising a single sleeve having an external ange and external screw threads adjacent the iiange for securing the fitting to a mounting bracket; a second flange spaced apart from the mounting flange with external threads thereon and a cooperating nut to clamp the armor layer of a cable in position on the fitting; an internal bore through the fitting with threaded surfaces at one end adapted to grip the exterior insulation of a section of coaxial cable, and a cylindrical mounting bore at the opposite end; an insulator mounted in said bore and hermetically sealed therein, said insulator extending substantially beyond the end of the fitting and having a center ferrule hermetically sealed within the insulator throughout its entire length, with an opening through the ferrule adapted to surround an electrical lead extending outwardly from the cable, and an exposed orifice so that the lead may be sealed to the ferrule by soldering from the exterior of the fitting.

JOSEPH GOLDSMITH.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,152,504 Scott Mar. 28, 1939 2,296,766 Bruno Sept. 22, 1942 FOREIGN PATENTS Number Country Date 286,344 Great Britain Feb. 29, 1928 OTHER REFERENCES Bulletin 4 of the International Resistance Co., 401 North Broad St., Philadelphia 8, Pa., entitled U. S. Army-Navy Coaxial Connectors. Copy receiv-ed Feb. 17, 1945, in Div. 65.

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