US2878459A - Telephone plug - Google Patents

Description

Mardi 17, 1959 R. G. BARKER 2,878,459

TELEPHONE PLUG Filed May 5, 1958 /5 'E f Ilwllllllllrlllge'll fifi INVENTOR.

RAN DOLFH G. BARKER MVA-@MW ATTORN EYS 2,878,459 Patented Mar. 17, 1959 TELEPHUNE PLUG Randolph G. Barker, West Bridgewater, Mass. v Application May 5, 1958, Serial No. 732,965

1 Claim. (Cl. 339-183) This invention relates to an improvedl telephone plug for use with a standard switchboard. A telephone plug must be capable of engaging in a standard jack inv a switchboard. Plugs `for such use have two terminals consisting respectively of a ball tipand a tube about an inch long, both terminals having a diameter of one quarter inch. These terminals are connected respectively to the wires of a coaxial cable, the ball. tip being connected to the inner wire, the tube being connected to the outer wire which is insulated from the inner wire butv is arranged to surround it so Ias to act as a shield for it'. The two terminals are insulated from each other, and the several parts and insulating elements of the ordinary plugs must be carefully assembled in producing the phone plugs now on the market.

Coaxial cables are used with telephone plugs to avoid serious disturbances in the telephone circuits from induetion currents caused by stray lields. The inner wire or core is surrounded by insulation and the other wire surrounds this insulation like a sleeve to serve as an electrostatic shield for the inner wire. This sleeve is conveniently formed by helically wrapping about the inner insulation a number of fine wires `applied in side-by-side contact to form a band the side edges of which touch in successive convolutions so that a continuous metal shield is thus formed about the inner wire and its insulating coat. The end of this band of wires is connected directly or indirectly to the tubular terminal of the plug. As customarily done, this often leaves a gap in the shield at the junction of the band and the tubular terminal. To close this gap, a metal sleeve of considerably larger diameter than the tubular terminal is usually provided to cover the gap Iand to serve also as a handle for manipulating the plug.

According to the present invention, the terminals of the plug are manipulated in such a way as they are being assembled and soldered to the cable that the formation of a gap in the shield is provided, and the insulation between the terminals is introduced by injection so that the parts of the plug are more easily and compactly assembled, the heavy metal handle is eliminated, and the number of parts of the plug is materially reduced.

For a more complete understanding of the invention, reference may be had to the following description thereof, and to the drawing, of which- Figure l is a perspective view of a telephone plug embodying the invention;

Figure 2 is an elevational view, on a larger scale, of the two-wire coaxial cable to be attached to the plug, parts being broken away to show the various elements of the cable in sections;

Figure 3 is an elevational view of the cable shown in Figure 2, with a tubular plug terminal in position to be attached to the outer wire, the terminal being partly broken away;

Figure 4 is an elevation of the cable with both terminal members of the plug attached thereto, the tubular terminal being shown in sections;

Figure 5 is an elevation of the cable with a sectional view of the completed plug thereon; and

Figure 6 is a section on the line 6 6 of Figure 5.y A conventional telephone plug consists pri-marily of two terminals connected respectively to the wires of a 2-wire I cable.y The two terminals are, respectively, a ball tip and' i' a cylindrical tubular sheath, the outer diameter of both sulated' therefrom. For convenience of manufacture andhandling, the tubular outer conductor may be in the form of a band or ribbon of smalll wires arranged in side-byside contact. These wires are wound helically around the insulation which surrounds the central or inner conductor. Since the successive convolutions of the helix are in edge to edge contact, the result is a continuous sleeve which acts effectively as a shield for the inner conductor against induction from stray fields.

According to the presentl invention, as illustrated on the drawing, the plugcomprisesa ball tip 10 ofA standard size and shape and a sheath 12, which is of standard diameter and is preferably ll/s long. These parts are of metal, preferably nickel-plated brass. The improved plug can best be described by the methods by which it is attached to the two-wire cable 16. This cable consists of a central conductor 18, which is preferably a stranded wire and is surrounded by a covering of suitable exible insulation material 2t). Helically wound on the insulation 20 is a band of wires arranged Side by side so that they constitute an outer conductor 22 which is virtually tubular and thus shields the inner or central conductor 18. The outer conductor 22 is covered by a protective and insulating coating 24.

The ball tip 10 consists of a knob-like extremity with a diameter of 1A" and a neck 26 of reduced diameter which widens out to a base 28 having the' same diameter as the ball. From the center of this base a hollow stem 30 projects, having a length of 5/16, an outside diameter of about j7/10", and a small axial bore. The sheath 12 is a metal tube having an outer diameter of 1A and a length of 1% In preparing the cable 16 for connection to the terminal members 10 and 12, the outer layer of insulation 24 is stripped from the end portion of the cable to expose a length Vof the outer conductor 22 which is at least half the length of the sheath 12 and preferably is slightly longer than the sheath, e. g., 11./4. The next step is to unwind part or all of the exposed outer conductor, but for a distance from the end of the cable less than the length of the sheath 12. If, for example, 1% of the conductor 22 has been exposed, about is unwound, the remaining 1/2 being seized by suitable means such as a bit of adhesive tape 34. The inner insulation is then stripped to expose about 3716 of the central conductor. The unwound portion of the wire 22 is twisted into a single strand as indicated in Figures l, 2, 3 of the drawing and this strand is bent back from the end of the cable. The sheath 12 is then slipped over the end of the cable until the exposed portion of the central conductor 18 emerges from the trailing end 36 of the sheath 12. The hollow stem 30 of the ball tip is sweated to the stripped portion of the central conductor 18 so as to make a soldered joint therewith. The sheath 12 is then retracted until its trailing end 36 is spaced about 1/16 from the base 28 of the ball tip. As is evident from the drawing, the tubular shield formed by the outer conductor 22 of the cable extends unbroken into the leading end of the sheath 12 and the clearance between the outer conductor and the sheath is small, so thatthere is no gap in the shielding of the inner conductor 18. No additional shielding member therefore is required. Y

The twisted strand of wires of the conductor 22 is then bent around the leading end of the sheath 12 and is soldered as at 38 to the sheath, as indicated in Figure 4. The parts thus assembled are then placed in a suitable jig (not shown) by which the sheath 12 and ball tip 10 are held in spaced aligned position. The jig is preferably part of a mold into which liqueed plastic material is injected by a suitable means (not shown). This plastic fills the space between the interior of the sheath 12 and the cable parts and stem 30 therein and also lls the narrow gap betweenthe trailing end 36 of the sheath 12 and the base 28 of the ball tip 10. The mold in which the plastic is injected may be, and preferably is, made to form in addition a cylindrical block 44 which envelops the soldered joint 38, the leading end portion of the sheath 12, and the adjacent portion of the cable 16. This block 40 gives the plug a nished appearance, it is light in weight, and it also serves as a convenient handle by which the plug can be manipulated.

I claim:

A telephone plug having as terminals a tubular metal sheath and a ball tip having a diameter greater than the interior diameter of said sheath, in combination with a coaxial cable comprising a central conductor, insulation surrounding said conductor, and an outer conductor surrounding said insulation; said cable extending into one end of said sheath, said central conductor being electrically connected to said ball tip at the other end of said sheath, said outer conductor extending unbroken into said sheath and having a direct soldered connection with said sheath, the clearance between said outer conductor and said sheath being small, whereby said central conductor is completely shielded by said sheath and the outer conductor, and a unitary body of molded plastic insulation filling the remaining space in said sheath, insulating said ball tip from said sheath and covering the soldered joint between said outer conductor and sheath, the end portion of the sheath remote from the ball tip, and a portion of said cable outside of and adjacent to said sheath.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES `Electrical Manufacturing, December 12S-130.

1952, pages

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