US1616162A - Electric-current transmission - Google Patents

Description

Feb. 1,1927. 1,616,115?

W. J. ADAMS, JR

ELECTRIC CURRENT TRANSMISSION Filed Sept. l0. 1924 Cil potential for the through a resistance 10 which mav be of the Patented Feb. 1, 1927y UNITED STATES PATENT OFFICE.

WILLIAM J'. ADAMS, JR., OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, 'OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

ELECTRIC-CURRENT TRANSMISSION.

.application led September 10, 1924. Serial No. 736,835.

This invention relates to transmission of etectricv currents and aims to provide a ilexible line ot' propagation for them without unduly shunting current across the line of propagation and without permittingl undue interference fromf extraneous electrical fields. An especial object is to lavoid such undue shunting effect and interference where the flexible line of propagation comprises aV con ection between` impcdances which are higi for alternating currents to be transmitted, as for instance a connection between a condensertransmitter and an electron discharge a'mplier.`

In accordance with the invention. for connecting the impedances between which current is to be transmitted there is provided a. iexiible 'electrical cord comprising tivo electrical conductors, one of which is arranged to shield the other from extraneous electrical fields, and insulating means maintaining thecapacity and leakage resistance of the cord at such values as to substantially avoid deleteriously sbunting the currents to be transmitted.

'lhe single figure of the drawing shows one embodiment of the invention, with parts of the cord shown broken away to exhibit its internal structure.

lu thc drawing the cord 2 is shown connecting a condenser transmitter '8 to an electron tube amplifier 4. The space current battery 9 for the first stage of the amplifier is shown as supplying polarizing condenser transmitter order of 15 megohms. A resistance 1l, which may be of the order of two megohms, and capacities'12 and 153, which may be of the order of two microfarads form a filter to prevent fluctuations of the voltage of battery 9 from affecting the transmitter 3.

The condenser transmitter 3 may be a telephone transmit-ter having a capacity, for example of the order of 400 micromicrofarads. Its impedance at speech frequencies will then he very high` and therefore it is shown connected directly to the grid of the input stage of the amplifier through a suitable blocking condenser l5 wit-hout tbe interposition of a transformer. resistance 16 which may be of the order ot 15 megohms, isconnected across the grid and filament of the first stage of the amplifier. to maintain the grid at a constant negative average potential.,

Any capacity between the conductors of the cord Connecting the transmitter to the amplifier is in shunt with the transmitter, with`| respect to the amplifier, and therefore occasions transmission loss. On account of the relatively low capacity of the transmitter itself, this loss, when ordinary flexible cords of any considerable length are used, is quite large. The fiexible cord 2 is therefore constructed, as described hereinafter, to have low capacity between its conductors'. Moreover. unless proper shielding` is employed, the deleterious effect of any inductive interference to which the conductors of the cord connecting the Ytransmitter to the amplifier are subjected, due to extraneous electrical fields, may be pronounced because of the loW magnitude of the voltages delivered to the input of the amplifier by the transmitter. Therefore, the fiexihle cord 2 is constructed, as described, hereinafter, with two concentric conductors,- one of which shields the other. Further. as also described hereinafter, rubber or other insulating material impervious to moisture and having high insulation resistance, is preferably interposed between the inner conductor and the outer conductor, to afford high insulation,resistance and to prevent moisture from setting up irregular leakage paths which would result in excessive noise currents. However, the thickness of the interposed rubber should he as small as is consistent with the attainment of the requisite insulation resistance, so that ,the rubber, wbich has high specific inductive capacity, will not unduly increase the capacity between tlie conductors` The center of the cord 2 is a fiexible conductor 20, preferably consisting of a plurality of conducting strands of tinsel thread.

These strands are not individually shown,

since they are of general type of construction referred to 'in U. S. patents to Sawyer 269,328, DecemberlQ, 1882 and Reed 286,968` October 16. 1883, cach strand or tinsel thread being a thread of fibrous material Wound 'helically with metallic tape. These strands are twisted together to form conductor 20, which is then served with two layers of fioss or a similar insulating material 21., these layers being laid with the direction of winding reversed. Over these servings is placed an insulating coating 22 of soft rubber, which', as indicated above, should be as thin as is consistent with the attainment ot the insulatiilm resistance which it must proq vide. Over the rubber is provided a flexible fibrous insulating covering 23, preferably of sill; braiding, the rubber 22 and the braiding Q3 extending substantially to the ends ot conductor Q0.

Over the braiding are applied three flexible fibrous insulating` coverings, 2l, 25 and 2G, preferably of sill; braidings, each extending between the points at which the.

irce conductors of the cord 2 are to emerge from the finished cord, and being discontinued at those points. l

Overthe braiding QG is applied a liexible conducting and shielding braiding` QT, preferably of gold tinsel thread, this braiding 2T terli'iinating in a i'ree, closelv braided conductor at each end.

Over the tinse'l braiding 2T is applied a flexible fibrous insulating covering 28, preferably of silk braiding, extending out over the bare tinsel braided free conductors formed by the ends of the braiding 27.

Over die braidinfr 28 is applied a flexible insulating braiding 29, preferably of silk, terminated in a whipping 30 ofl silk, shellaced, at the amplifier end of the cord, and, at the other end, extended out over the braiding 28 as indicated in the drawing, or, if desired, at the latter end, closely braided and brought ott' from the cord as a stay cord or tie cord, from the point where the f'ree conductors emerge from the cord, for instance, in the fashion shown in U. S. patent to Kaisling 738,545,September S, 1903.

The capacity between the conductors of' the cord preferably should not exceed about a0 micromicrofarads per linear foot. Moreover, the cord should be as short as is consistent with convenience. A length of about ten feet has been found suitable in a cir-- cuit of the type shown in the drawing.

lVhat is claimed is:

1. In combination, a condenser subject to variations of its capacity, corresponding to sound waves, and an electrically conductive cord, said cord comprising electrically conductive means connected to one electrode of said condenser, an electrically conductive casing connected to lanother electrode of said condenser and encasing said means, and insulating means spacin said conductive means from said conductlve casing suiiciently lo render the electrostatic capacity between said conductive means and said easing small relative to the variations to which the capacity of said condenser is subject.

2. In combination, a condenser type telephone instrument and a cord for connecting said instrument in a circuit, said cord comprising a flexible center conductor, a flexible conductive shield serving as a return conductor, and flexible insulating material separating said center conductor from said shield suiiciently to render the capacity of said cord low compared to that of said transmitter.

In combination, a condenser transmitter and a cord for connecting said instrument in a circuit, said cord comprising a flexible center conductor and a braided tinsel shield sufficiently separated by flexible insulating material to' render the capacity 'between said conductor and said shield small, compared to that of said transmitter.

it. In combination, a condenser transmitter and a cord for connecting said i11- strument in a circuit, said cord comprising a rubber covered, tinsel, center conductor and a braided tinsel shield sufficiently separated by a plurality of layers ot' insulating braid to render the capacity of said cord small compared to that of said transmitter.

5. In combination, a condenser transmitter, an electron discharge device having electrodes, and a cord connecting said transmitter to said electrodes, said cord comprising a flexible center conduct-.or and a flexible conductive shield separated by a plurality of' layers of flexible insulation maintainingthe capacity and leakage resistance ot the cord at .such values as to substantially avoid lil)

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