US2301189A

US2301189A - Telephone set cord

Info

Publication number: US2301189A
Application number: US420635A
Authority: US
Inventors: Langford J Bowne
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1941-11-27
Filing date: 1941-11-27
Publication date: 1942-11-10
Anticipated expiration: 1959-11-10

Description

Filed Nov. 27, 1941 FIG 0 m m r A mvmvron By 1.. J. BOWNE r2 2 c m G r F u r! Patented Nov. 10, 1942 TELEPHONE SET CORD Langford J. Bowne, Howard Beach, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 27, 1941, Serial No. 420,635

4 Claims.

This invention relates to telephone transmission systems and, more particularly, to flexible cables or cords for so-called operators telephone sets comprising a transmitter and a pairof receiver units attached to a headband. Such cords usually consist of four conductors, two for means of the transmitter and one of the receiver units and at the same time monitor, 1. e., listen,

on another line.

When this additional pair of conductors for the monitoring receiver, is included in the telephone set cord; thereby increasing the number of conductors to six, it has been found that under certain degrees of atmospheric humidity undesirable cross-tall: between the two pairs of re ceiver conductors and between the transmitter pair and the pair connected to the monitoring receiver is experienced due to an unavoidable capacity unbalance between the conductors within the cord.

An object? of the present invention is to reduce cross-talk in flexible cords of the character described.

While the above object might be attained by carrying the monitoring pair of conductors in a separate cord or cable, a single cord is considered more desirable and to obtain the desired reduction in cross-talk by electrostatically shielding the receiver pairs from each other and reducing the capacity unbalance between the transmitter conductors and the monitoring conductors.

A feature of the invention, whereby the desired result is obtained, resides in the addition of an additional or seventh conductor within the cord winch is connected at both ends to one of the transmitter conductors and in so arranging the several conductors within the cord that the three transmitter conductors lie in a plane between the two receiver pairs to act as an electrostatic shield therebetween, and that a substantially uniform capacity exists between each receiver conductor and the transmitter conductors.

The invention will be understood from the following description and the accompanying drawing, Fig. 1 of which shows, schematically, an operators telephone set, and its. associated cord arranged in accordance with the present invention whereby crosstalk between the two receiver pairs of the cord is substantially eliminated when the operator is talking on oneline and monitoring on another line at the same time; and Fig. 2 shows a cross section of the telephone set cord.

Referring to the drawing, Fig. 1, an operators telephone set OT comprising a transmitter T and receiver R is shown connectedby, conductors ti, t2 and TI, 1'2, contained in a flexible cable or cord C, to an operators telephone circuit 00 rminating a line Ll whereby two-way -conversation between the operators transmitter-T and the receiver R and the line Ll may be carried A second line, L2, is also shown connected to another receiver unit MB of the operators set OT by means of a third pair of conductors mrl and m1'2 contained in the cord or cable C whereby the operator, by means of receiver unit MR, may monitor, i. e., listen on the line L2 whilg talking on line Ll.

In addition to the conductors tl, t2 and TI, 1'2 and mrl and 11112, an extra conductor t3 is also included in the cord C which conductor is shown as terminating at the two ends of the cord and connected at each end to the transmitter conductor t2.

By referring to Fig. 2 it will be noted that the above conductors are closely and uniformly arranged within the cord so that they lie in three parallel planes, one consisting of conductors H and r2, another consisting of conductors mrl and mr2 and the third or intermediate plane including the conductors tl, t2 and 153.

From the foregoing it will be noted from the drawing that the three closely positioned conductors tl, t2 and t3 lying in a plane between conductors Tl, r2 and mrl and mr2 from an effective non-magnetic shield between the two receiver circuits thereby substantially eliminating the possibility of crosstalk interference between them.

Further, if the transmitter conductors tl, t2 and t3 and the monitoring receiver conductors mrl and mri! are all uniformly spaced with respect to each other, the capacity unbalance between either side of the transmitter circuit and the monitoring receiver circuit will be zero due to the fact that transmitter-conductor tl is connected in parallel with conductor 153 which parallel conductors neutralize and balance out the capacity unbalance efiect of i2 on either of the conductors mrl or mrZ. For example, if we assume at any instant a positive potential on conductor t2 an equal negative potential will be present on both conductors ti and t3 which obviously will neutralize the effect on either conductor mrl or mrl of the positive potential of t2.

In normal practice, the positive side of the operators telephone circuit battery B, Fig. l is grounded and therefore conductor IE2 is grounded at one end and a more effective and stable shield between the two receiver circuits is therefore provided if the same conductor, t2, is also grounded at the other end of the cord, as shown in the drawing.

What is claimed is:

1. In a telephone transmission system comprising a cable including two sets of two conductors each for separate transmission in the same direction and a third set for transmission in the opposite direction, means for reducing crosstalk between said first two sets and between said third set and either of the other two sets characterized in this that said individual sets of conductors lie in parallel equidistant planes with the third set intermediate the other two, said third set having three conductors the outer two of which are connected together, and all of said seven conductors being so spaced with respect to each other that a substantially uniform capacity exists between each conductor of the first two sets and its two adjacent conductors of the third set.

2. In a telephone transmission system comprising a cable including two sets of conductors each for separate transmission in the same direction and a third set for transmission in the opposite direction, means for reducing crosstalk between said first two sets and between said third set and either of the other two sets characterized in this that the conductors of said in dividual sets lie closely adjacent each other in different parallel planes closely adjacent and equidistant from each other, with the third set intermediate the other two and having three conductors the outer two of which are connected together at each end of the cable.

3. In a telephone transmission system comprising a cable including seven conductors arranged in three separate groups for providing three independent transmission circuits, means for reducing crosstalk between said independent circuits characterized in this that the conductors of each circuit group lie closely adjacent to each other in closely adjacent parallel planes, two of said circuits comprising two conductors each and the third circuit comprising three conductors whose plane is intermediate the other two, and having its outer two conductors connected togather to form one conductor of a circuit pair.

4. In a telephone transmission system comprising a cable including seven conductors arranged in three separate groups for providing three independent transmission circuits, means for reducing crosstalk between said independent circuits characterized in this that the conductors of each circuit group lie closely adjacent to each other in closely adjacent, parallel planes, two of said circuits comprising two conductors each and the third circuit comprising three conductors whose plane is intermediate the other two, the outer two of said three conductors being connected together at each end of the cable, the third conductor of said three-conductor group being equidistant from the other six conductors and each conductor of the two outer groups being equidistant two of the conductors of the third group.

LANGFORD J. BOWNE.