EP3246925A1

EP3246925A1 - Balanced pair data transmission line

Info

Publication number: EP3246925A1
Application number: EP17382314.7A
Authority: EP
Inventors: Josep Sanabra Jansa
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-05-31
Filing date: 2017-05-31
Publication date: 2017-11-22

Abstract

The present invention relates to a balanced pair data transmission line (2) which comprises two electric conductors (200, 200') each having a longitudinal extension body; an insulating covering (20) which surrounds both of said electric conductors (200, 200') along the length of their respective bodies, said insulating covering (20) comprising surface depressions in each of the faces of the outer surface of said covering (20) close to the perpendicular line at the centre of the straight line between the two centres of said conductors (200, 200'); at least one longitudinal aperture (4) arranged along the central longitudinal axis of the insulating covering (20) between said conductors (200, 200'), keeping the two conductors (200, 200') covered with said covering (20); and at least one pre-cut (30, 30') arranged on at least one of said surface depressions of the outer surface of said insulating covering (20).

Description

TECHNICAL SECTOR

The present invention relates to the technical sector of data transmission lines, in particular to the technical sector of data transmission cables of the type which comprises at least one pair of conductors through which the electric signals are transmitted, the signals in both conductors being generally out of phase with each other by 180º.
This type of cables, comprising at least one pair of conductors of which the electric signals may be out of phase with each other by 180º, is referred to and/or known in the prior art as balanced cables or alternatively as 'balanced pair cables'.

BACKGROUND OF THE INVENTION

A conventional balanced pair is usually made up of two electric conductors of circular cross section, each of said conductors being covered by a covering or sheath made of a dielectric material which is also of circular cross section, said dielectric covering being arranged concentrically with each of the electric conductors. Dielectric is the name given to a material that has low electrical conductivity and consequently is a material that is insulating or a poor conductor of heat or electricity. Next, the electric conductors each covered respectively with a dielectric material are usually arranged adjacently to one another as shown in Fig. 1, that is, with a portion of the outer longitudinal surface of one conductor in contact with a portion of the outer longitudinal surface of the other conductor.
Said balanced pair may be symmetrical, although in the majority of applications, particularly in telecommunications, the two conductors of said pair are twisted together helicoidally, thus reducing the electromagnetic disturbance or crosstalk which a balanced pair of conductors, through coupling, usually produces on other balanced pairs of conductors which may be comprised in the same data communications cable. Because the two electric conductors of the balanced pair are twisted together, said conductors are kept close to each other, thus helping the pair maintain a constant impedance.
The crosstalk between different balanced pairs, whether twisted together or not, in the same communications cable can also be reduced by using a protection system, also known in the prior art as shielding or a shielded system which consists of a conductive mesh which may cover either each balanced pair of the cable or the set of balanced pairs in the same cable, acting as a shield against interference and electrical noise. Alternatively, some communications cables combine the individual shielding of each of the pairs of conductors of the cable with the overall shielding of the set of pairs in the same cable.
As is well known in the prior art, some of the parameters which characterise the behaviour of data communications cables of the type which comprise at least one balanced pair as described above are the following:

Insertion loss: this is the power loss in the signal which runs along a transmission line (in this case through the pair of electric conductors) owing to the insertion of a device in the path of said transmission line; this is normally expressed in decibels (dB). Insertion loss is a measure of the signal attenuation along the pair.
Impedance: this is a measure of the opposition of a transmission line (in this case through the pair of electric conductors) to the flow of a current when a voltage is applied thereto. The impedance variable is usually represented by the letter Z and its value is measured in ohms (symbol Ω). In the case of a balanced pair, the impedance (Z) will be a function of the material characteristics and geometric characteristics used for said balanced pair. The design of the cable which will comprise at least one balanced pair which must be capable of providing an established standard value, which is usually 100 ohms. Said impedance value (Z) is applicable to all the components of the transmission line (or balanced pair) in order to adapt all the elements thereof correctly in order to minimise losses. The object will be to maintain a constant nominal value of 100 ohms along the balanced pair.
Return loss: this is the loss power lost at a point of the transmission line (in this case through the pair of electric conductors) owing to the reflection of a portion of the original power. It is a measure which reflects how well-matched the impedances of the transmitter, transmission line and receiver are, as well as the existence of discontinuities in the transmission line, represented here by the cable and the pairs of which it is made up. It is normally expressed in decibels (dB). A lack of matching and the existence of discontinuities cause power reflection towards the transmitter, resulting in greater insertion loss.
Crosstalk: this is the electromagnetic disturbance which a balanced pair of conductors, through coupling, usually produces on other balanced pairs of conductors which may be comprised in said data communications cable.

Generally, a balanced pair as described above usually has few design options to optimise the behaviour thereof. In addition, the manufacturing process is characterised by the initial production of separate electric conductors for subsequent configuration of the pair, which may be by twisting together the two conductors. The inferior hardness of the insulators and possible variability of mechanical stresses in the manufacturing process contribute to variability in the deformation of the two conductors. Moreover, significant differences in the physical length of the conductors may also cause a reduction in the balancing of the pair.
An additional problem presented by a balanced pair as discussed above, that is, a pair of electric conductors individually covered with their respective dielectric material and arranged adjacently to one another, is the possibility that one of the two conductors may separate from the other at some point along the length thereof. Said separation at some point along the length thereof may cause an isolated variation in the impedance and therefore an increase in the return loss. In addition, the variation in the impedance due to the isolated separation of the two electric conductors will also depend on the type of cross section of the electric conductors of the pair.
For example, small changes of position in the case of non-circular electric conductors are usually more likely to happen and involve more significant variations in the transmission behaviour of the cable. To illustrate this, the applicant has carried out various electromagnetic simulations, which are set out in the conclusions. A pair of circular conductors and insulators with an impedance of 100 ohms and a pair of elliptical conductors and insulators with the same impedance and attenuation were simulated.
In a first example, Fig. 2 first shows, on one hand, a first pair of electric conductors (-100-, -100'-) of circular cross section individually covered with their respective dielectric material (-10-, -10'-) and positioned adjacently to one another in accordance with the prior art, but with their respective longitudinal axes displaced linearly in the direction perpendicular to the straight line between the two centres of said electric conductors (-100-, -100'-); and on another hand shows a second pair of electric conductors (-800-, -800'-) of elliptical cross section individually covered with their respective dielectric material (-80-, -80'-) and positioned adjacently to one another in accordance with the prior art, but with their respective longitudinal axes linearly displaced in the direction perpendicular to the straight line between the two centres of said conductors. Fig. 3 shows a table of the variation in impedance (ordinate axis) as a function of frequency (abscissa) due to the linear displacement of axes for each type of pair as shown in Fig. 2. As can be seen in the graph of Fig. 3, for this type of displacement of the axes of electric conductors (-100-, -100'-) of circular cross section and of electric conductors (-800-, -800'-) of elliptical cross section, which would normally be superimposed, a variation in the impedance is produced which is greater for electric conductors (-800-, -800'-) of elliptical cross section.
In a second example, Fig. 4 first shows, on one hand, a first pair of electric conductors (-100-, -100'-) of circular cross section individually covered with their respective dielectric material (-10-, -10'-), said conductors (-100-, -100'-) being separate from one another in the direction of the straight line between the two centres of said conductors (-100-, -100'-); and on another hand also shows a second pair of electric conductors (-800-, -800'-) of elliptical cross section individually covered with their respective dielectric material (-80-, -80'-), said conductors (-800-, -800'-) being separate from one another in the direction of the straight line between the two centres of said conductors (-800-, -800'-). Fig. 5 shows a table of the variation in impedance (ordinate axis) as a function of frequency (abscissa) due to the separation of the conductors (-100-, -100'-, -800-, -800'-) of each type of pair as illustrated in Fig. 4. As can be seen in the table of Fig. 5, for this type of separation of the two electric conductors (-100-, -100'-, -800-, -800'-), the variation in impedance is also greater for electric conductors (-800-, -800'-) of elliptical cross section.
In a third example, Fig. 6 shows a first pair of electric conductors (-100-, -100'-) of circular cross section individually covered with their respective dielectric material (-10-, -10'-) and positioned adjacently to one another as in the prior art, but with their longitudinal axes displaced axially relative to one another, and a second pair of electric conductors (-800-, -800'-) of elliptical cross section individually covered with their respective dielectric material (-80-, -80'-) and positioned adjacently to one another as in the prior art, but with their longitudinal axes displaced axially relative to one another. Fig. 7 shows a table of the variation in impedance (ordinate axis) as a function of frequency (abscissa) due to the axial displacement of the longitudinal axes of the electric conductors (-100-, -100'-, -800-, -800'-) of each pair type as illustrated in Fig. 6. As can be seen in the table of Fig. 7, for this type of axial displacement with rotation of the two electric conductors (-100-, -100'-, -800-, -800'-) on the touching surfaces thereof, the pair of electric conductors (-100-, -100'-) of circular cross section maintains the same impedance whereas the pair of electric conductors (-800-, -800'-) of elliptical cross section shows a significant variation in impedance.
Each of the phenomena described above can be produced repeatedly at different points along the same pair, causing significant increases in return loss and, in addition, increases in attenuation, lowering the performance of the pair and of the cable comprising said pair.
Solutions which attempt to mitigate some of the above-mentioned problems are known in the prior art.
For example, US patent 5,606,151 discloses, in a first embodiment, the use of an adhesive along the contact surfaces between the insulators of the two conductors which are twisted together in order to avoid said separation. Given that the outer surfaces of the insulators are normally cylindrical, the contact surfaces between said insulators are usually practically linear. Consequently, the use of an adhesive for bonding said cylindrical contact surfaces of the insulators would be difficult to achieve and it would be very difficult to ensure a constant connection between the pair of insulated and twisted conductors. An alternative method described in the same US patent 5,606,151 involves the respective insulators being held together by means of an integral join rigidly connected to each of them along the entire cable. Said rigidly connected join, however, has very little mechanical stability between the conductors and in addition causes difficulties in separating said connection when the insulated connectors are to be separated in order to connect each to the corresponding lugs of a contact or connection terminal.
US patent 9,418,775 discloses the use of a tape with a low dielectric constant for positioning between the cylindrical contact surfaces of the insulators of each of the twisted conductors. The tape is arranged such that the independently insulated conductors are twisted together against said tape so that said tape is arranged between the twisted conductors. Said embodiment does not ensure constant stability of the connection between the twisted conductors, causing variations in the impedance (Z) along the length of the pairs, which may cause insertion loss.
US patent 7,737,358 discloses a conventional pair of conductors covered with an insulating layer shared by both conductors. The cross sections of said conductors are semi-circular or D-shaped, the planar surfaces of said conductors being opposite each other with the object of achieving a more concentrated distribution of the electric field lines which are propagated from one conductor to the other, and thus to reduce the crosstalk of the pair of conductors towards other neighbouring pairs of conductors. Given that the semi-circular cross sections of the conductors do not allow or hamper the twisting together of said conductors, to achieve the effect of a pair of twisted conductors, as described in US patent 7,737,358 , after the process of coextruding the insulator on the pair of conductors, the pair set with the common insulator is rotated longitudinally on itself. However, rotating the pair set with the insulator does not allow twisting that is the same or has the same effect as conventional twisting between two pairs of independently insulated conductors. Nor does the embodiment in said US patent 7,737,358 allow a constant distance to be maintained between the pairs of conductors directly affecting the impedance (Z) of the pair of conductors. In addition to the above, said embodiment creates many difficulties in identifying each of the conductors of the pair, separating said conductors, or connecting them to the corresponding lugs of a contact or connection terminal.
As can be observed, the earlier embodiments have a series of limitations in terms of performance, cost, use of material, dimensions or applicability, which can all be improved according to the present invention.

EXPLANATION OF THE INVENTION

An object of the present invention is to disclose a high-performance, improved, more efficient balanced pair data transmission line which overcomes the above-mentioned drawbacks of the prior art. In addition, another object of the present invention is to disclose a high-performance data transmission cable which comprises at least one balanced pair data transmission line in which the pairs thereof have a high degree of structural consistency along the length thereof, maintaining the dimensions of the two conductors of the pair, those of the insulators thereof, and also of the relative positioning thereof, maintaining a uniform relative distance therebetween.
In particular, the present invention discloses a balanced pair data transmission line which comprises at least two electric conductors each having a longitudinal extension body and an insulating covering which surrounds both of said electric conductors along the length of the respective bodies thereof. In addition, said insulating covering comprises surface depressions in each of the faces of the outer surface of said covering close to the perpendicular line at the centre of the straight line between the two centres of said conductors. Said configuration of the balanced pair data transmission line according to the present invention in which the two conductors are covered by the same integral insulator is similar to the configuration that would result from combining the two independently insulated conductors and joining them together, the join zone between the independently insulated conductors having depressions, grooves or a reduction of the total outer dimension of the set of independently insulated conductors relative to the outer dimension of the insulating covering in the zones close to the respective axes which are perpendicular to the common axis between the respective centres of the conductors. Thus, on the one hand a paired conductor set covered with a common insulator is achieved, having improved and reinforced mechanical strength of the central portion of the insulating covering compared with the prior art, and, on the other hand, the position of the two conductors can be clearly identified to be able to subsequently separate the insulated conductors in order to connect each to the corresponding lugs of a contact or connection terminal.
Furthermore, said balanced pair data transmission line according to the present invention is configured to comprise at least one longitudinal aperture arranged along the central longitudinal axis of said common insulating covering between the two electric conductors, which in turn keeps the two conductors covered in their entirety with said insulating covering. Thus, the cross section of the insulating covering which separates the two electric conductors is significantly reduced, simplifying the subsequent separation of the conductors in order to connect each to the corresponding lugs of a contact or connection terminal. In addition, said longitudinal aperture, through which air - which has a dielectric constant of about 1 - is propagated, allows the dielectric constant of the intermediate zone of the insulating covering between the conductors to be reduced, which in turn allows the two conductors to come closer together while maintaining the impedance. This smaller distance between conductors entails a greater concentration of the electric field lines. As a consequence of the above, crosstalk is reduced and consequently insertion loss or attenuation will in turn also be lower, providing better performance of the balanced pair data transmission line according to the present invention for the purpose of signal transmission.
Moreover, said surface depressions, also known as grooves, are thicker and stronger than other types of join of the prior art, such as that illustrated in US patent 5,606,151 for example, and represent a substantial and considerable increase in the total height of the join zone, which benefits the mechanical stability of the balanced pair data transmission line according to the present invention. Thus, on the one hand, a set of paired electric conductors covered with a common insulator is achieved, having improved and reinforced mechanical strength of the central portion of the insulating covering compared with the prior art, and, on the other hand, the position of the two conductors can be clearly identified to be able to subsequently separate the insulated conductors in order to connect each to the corresponding lugs of a contact or connection terminal.
Furthermore, said balanced pair data transmission line according to the present invention also comprises at least one pre-cut arranged on at least one of said surface depressions in the outer surface of the insulating covering. At least said pre-cut close to said longitudinal aperture facilitates the process of separating the conductors at the ends of the balanced pair data transmission line according to the present invention, for subsequent connection of each of said conductors to the corresponding lugs of a contact or connection terminal.
Preferably, the balanced pair data transmission line according to the present invention also comprises an additional pre-cut arranged on at least one other of said surface depressions. In this way, as the balanced pair data transmission line according to the present invention has two pre-cuts arranged on each surface depression, this further simplifies the process of separating the conductors at the ends of the balanced pair data transmission line according to the present invention, for subsequent connection of each of said conductors to the corresponding lugs of a contact or connection terminal.
Preferably, said conductors are arranged in parallel inside said insulating covering.
Preferably, the conductors are twisted together uniformly along the length of said conductors inside said insulating covering.
According to a preferred embodiment of the invention, said conductors have a cross section shaped such that the respective opposite faces thereof are circular arcs. Even more preferably, said conductors have a circular cross section. Conductors with a circular cross section have numerous advantages, such as ease of manufacture, ease of application to a terminal by displacement or perforation of the insulating covering, and stability of the single paired set of two individual conductors with a circular conductor and an insulator.
According to another preferred embodiment, said conductors have a cross section shaped such that the respective opposite faces thereof are non-circular. Even more preferably, said conductors have a cross section shaped such that the respective opposite faces thereof are an elliptical arc or an oval arc. The mechanical stability of the design of the balanced pair data transmission line according to the present invention described above allows the use of conductors having a cross section that is other than circular, allowing the electric field which is propagated from one electric conductor to another to be more convergent, which in turn reduces possible outward divergences of electric field lines, thus reducing the crosstalk towards neighbouring pairs of conductors.
Preferably, the balanced pair data transmission line according to the present invention additionally comprises an outer shielding means which covers the set of electric conductors surrounded by said common insulating covering. According to a preferred embodiment, the balanced pair data transmission line according to the present invention also comprises at least two longitudinal apertures for propagating air, each of said apertures being arranged respectively on either side of the balanced pair data transmission line in the direction of the common axis between the centres of the electric conductors and between the outer surface of the insulating covering and a portion of the shielding means. According to another preferred embodiment, the balanced pair data transmission line according to the present invention also comprises at least four longitudinal apertures for propagating air, said apertures being arranged in pairs respectively on either side of the balanced pair data transmission line in the direction of the common axis between the centres of the electric conductors and between the outer surface of the insulating covering and a portion of the shielding means.
An additional object of the present invention is to disclose a data transmission cable which comprises at least one balanced pair data transmission line according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, the accompanying drawings are given as explanatory but non-limiting examples of various embodiments of the balanced pair data transmission line according to the present invention.

Fig. 1 is a view in cross section of two electric conductors individually covered with their respective dielectric material and arranged adjacently to one another as in the prior art.
Fig. 2 shows a first pair of electric conductors of circular cross section individually covered with their respective dielectric material and arranged adjacently to one another as in the prior art, but with their respective longitudinal axes linearly displaced in the direction perpendicular to the straight line between the two centres of said conductors; and a second pair of electric conductors of elliptical cross section individually covered with their respective dielectric material and arranged adjacently to one another as in the prior art, but with their respective longitudinal axes linearly displaced in the direction perpendicular to the straight line between the two centres of said conductors.
Fig. 3 is a table of the variation of impedance as a function of frequency due to the linear displacement of axes for each pair type as illustrated in Fig. 2.
Fig. 4 shows a first pair of electric conductors of circular cross section individually covered with their respective dielectric material, said conductors being separated from one another in the direction of the straight line between the two centres of said conductors; and a second pair of electric conductors of elliptical cross section individually covered with their respective dielectric material, said conductors being separated from one another in the direction of the straight line between the two centres of said conductors.
Fig. 5 is a table of the variation of impedance as a function of frequency due to the separation of the conductors of each pair type as illustrated in Fig. 4.
Fig. 6 shows a first pair of electric conductors of circular cross section individually covered with their respective dielectric material and arranged adjacently to one another as in the prior art, but with their longitudinal axes axially displaced relative to one another, and a second pair of electric conductors of the prior art of elliptical cross section individually covered with their respective dielectric material and arranged adjacently to one another as in the prior art, but with their longitudinal axes axially displaced relative to one another.
Fig. 7 is a table of the variation of impedance as a function of frequency due to the axial displacement of the longitudinal axes of the conductors of each pair type as illustrated in Fig. 6.
Fig. 8 is a view in cross section of the balanced pair data transmission line according to a first embodiment of the present invention in which the pair of electric conductors is covered with a single insulating covering.
Fig. 9 is a view in cross section of a second embodiment of the balanced pair data transmission line according to the present invention additionally comprising two pre-cuts and a first embodiment of a longitudinal aperture.
Fig. 10 is a view in cross section of a third embodiment of the balanced pair data transmission line similar to that of Fig. 9 but with a different longitudinal aperture.
Fig. 11 is a view in cross section of a fourth embodiment of the balanced pair data transmission line similar to that of Fig. 9, additionally comprising a shielding means covering the balanced pair data transmission line shown in Fig. 9.
Fig. 12 is a view in cross section of a fifth embodiment of the balanced pair data transmission line similar to that of Fig. 10 but with a different cross section of the electric conductors.
Fig. 13 is a view in cross section of a sixth embodiment of a balanced pair data transmission line according to the present invention with a different cross section of the electric conductors and additionally comprising a shielding means which covers the set of the pairs of conductors covered with a common insulator.
Fig. 14 is a view in cross section of a seventh embodiment of the balanced pair data transmission line according to the present invention with a cross section of the electric conductors similar to that of Fig. 12, but with the longitudinal axes of each conductor linearly displaced in the direction perpendicular to the straight line between the two centres of said conductors.
Fig. 15 is a view in cross section of an eighth embodiment of a balanced pair data transmission line according to the present invention with a cross section of the electric conductors similar to that of Figs. 12 and 14, but with the conductors axially displaced relative to one another.
Fig. 16 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 10 in which the thickness of the insulating covering is reduced in the direction perpendicular to the common axis between the centres of the electric conductors.
Fig. 17 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 10 in which the thickness of the insulating covering is reduced in the direction of the common axis between the centres of the electric conductors.
Fig. 18 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 12 in which the thickness of the insulating covering is reduced in the direction perpendicular to the common axis between the centres of the electric conductors.
Fig. 19 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 12 in which the thickness of the insulating covering is reduced in the direction of the common axis between the centres of the electric conductors.
Fig. 20 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 11, additionally comprising two longitudinal apertures for propagating air arranged on either side of the balanced pair data transmission line.
Fig. 21 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 11, additionally comprising four longitudinal apertures for propagating air arranged in pairs on either side of the balanced pair data transmission line.
Fig. 22 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 13, additionally comprising two longitudinal apertures for propagating air arranged on either side of the balanced pair data transmission line.
Fig. 23 is a view in cross section of the embodiment of the balanced pair data transmission line of Fig. 13, additionally comprising four longitudinal apertures for propagating air arranged in pairs on either side of the balanced pair data transmission line.
Fig. 24 shows an example of the separation of the electric conductors of the balanced pair data transmission line according to the present invention in order to connect each of said electric conductors to the corresponding lugs of a contact terminal.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Fig. 8 illustrates the concept of a balanced pair data transmission line -2- on which the present invention is based according to a first embodiment, which comprises two electric conductors (-200-, -200'-) each having a longitudinal extension body and an insulating covering -20- which surrounds both of said electric conductors (-200-, -200'-) along the length of the respective bodies thereof. The total dimension of the balanced pair data transmission line -2- as illustrated in Fig. 8 is similar to that which would result from joining two independently insulated conductors, while also covering the upper and lower zones close to the join (illustrated as -1000- in Fig. 1) with portions (-2000-, -2000'-) of said insulating covering -20-.
Said portions (-2000-, -2000'-) of insulating covering -20- each form surface depressions (-2001-, -2001'-) in the outer surface of said covering -20- close to the perpendicular line at the centre of the straight line between the two centres of said electric conductors (-200-, -200'-). Said perpendicular line would pass through said join (imaginary in Fig. 8) illustrated as -1000- in Fig. 1. Said surface depressions (-2001-, -2001'-), also known as grooves, represent a reduction in the total outer dimension of the insulating covering -20- compared with the outer dimension of said insulating covering -20- in the zones close to the respective axes that are perpendicular to the common axis between the respective centres of the conductors (-200-, -200'-).
This configuration according to the present invention allows clear identification of the position of the two electric conductors (-200-, -200'-) at the ends of the balanced pair data transmission line -2-. Furthermore, said configuration according to Fig. 8 assists the separation of the pair of conductors (-200-, -200'-) at the end of the data transmission line -2-. Said separation is necessary in order to house each conductor (-200-, -200'-) independently in the cavity where the respective contacts of an IDC (insulation-displacement connector) for a female RJ45 connector are found, or an IPC (insulation piercing connector), for a male RJ45 connector. Fig. 24 shows an example of a female RJ45 connector -7- which comprises cavities (-71-, -72-) of an IDC where, after separating the electric conductors (-200-, -200'-) of the data transmission line -2-, each electric conductor (-200-, -200'-) can be housed in each respective cavity (-71-, -72-).
Furthermore, said surface depressions (-2001-, -2001'-), also known as grooves, as in Fig. 8, are thicker and stronger than other types of join in the prior art, such as that illustrated in US patent 5,606,151 for example, and represent a substantial and considerable increase in the total height of the join zone, which benefits the mechanical stability of the data transmission line -2-. In this way, on the one hand, a set of paired electric conductors (-200-, -200'-) covered with a common insulating covering -20- is achieved, having improved and reinforced mechanical strength of the central portion of the insulating covering -20-compared with the prior art, and, on the other hand, the position of the two conductors can be clearly identified to be able to subsequently separate the insulated conductors in order to connect each to the corresponding lugs of a contact or connection terminal.
To assist the manual separation of the two electric conductors (-200-, -200'-) at the ends of the data transmission line -2- for subsequent connection of the conductors to a connection terminal, the configuration of Fig. 8 may include at least one intermediate longitudinal aperture -4- or perforation arranged along the central longitudinal axis of the insulating covering -20- between said electric conductors (-200-, -200'-), keeping said conductors covered with said covering -20- at all times, as illustrated in Fig. 9 as a second embodiment. Thus, the cross section of the insulating covering -20-which separates the two electric conductors (-200-, -200'-) is significantly reduced, facilitating the subsequent separation of the conductors (-200-, -200'-) at the ends of the data transmission line according to the present invention in order to connect each to the corresponding lugs of a contact or connection terminal. In addition, said longitudinal aperture -4-, through which air - which has a dielectric constant of about 1 - is propagated, allows the dielectric constant of the intermediate zone of the insulating covering -20- between the electric conductors (-200-, -200'-) to be reduced, which in turn allows the two electric conductors (-200-, -200'-) to be brought closer together while maintaining the impedance. Said smaller distance between electric conductors (-200-, -200'-) entails a greater concentration of the electric field lines. As a consequence of all the above, the crosstalk is reduced and consequently the insertion loss or attenuation will in turn also be lower, providing improved performance of the data transmission line according to the present invention for the purposes of signal transmission. At least said longitudinal perforation -4- may be the result of including core pins in the zone between the two electric conductors (-200-, -200'-) in the extrusion process during the manufacture of the data transmission line according to the present invention.
The aperture -4- may have various forms, such as rectangular (see Fig. 10 in a third embodiment), circular, elliptical or adapted to the contour of the conductor. It is advisable for the configuration thereof to allow the existence of some thickness of the insulating covering -20- on the surface of each conductor in order to keep said conductors insulated from any other nearby conductor element, even after the process of separating the pair of electric conductors into two units.
Furthermore, said data transmission line -2- according to the present invention also comprises at least one pre-stamped pre-cut arranged on at least one of said surface depressions (-2001-, -2001'-) of the outer surface of the insulating covering -20- (not illustrated). At least said pre-cut close to said longitudinal aperture facilitates the process of separating the conductors (-200-, -200'-) at the ends of the balanced pair data transmission line -2- according to the present invention, for subsequent connection of each of said conductors to the corresponding lugs of a contact or connection terminal.
Optionally, said data transmission line -2- according to the present invention may comprise two pre-stamped pre-cuts (-30-, -30'-) each arranged on surface depressions in the outer surface of the insulating covering -20-, as illustrated in Fig. 9. Said pre-cuts (-30-, -30'-) close to said longitudinal aperture -4- will further simplify the process of separating the electric conductors (-200-, -200'-), for subsequent connection of each to the corresponding lugs of a contact or connection terminal.
Each pre-cut (-30-, -30'-) may be of continuous or variable depth. If the data transmission line -2-comprises two pre-stamped pre-cuts (-30-, -30'-) each arranged on surface depressions in the outer surface of the insulating covering -20-, said pre-cuts need not necessarily be symmetrical in terms of the depth or position on both sides of the common axis of the electric conductors (-200-, -200'-). Each pre-cut (-30-, -30'-) may be partial on all the sections of the pair of electric conductors (-200-, -200'-) or total on some of said sections or over the entire length of the pair of electric conductors (-200-, -200'-). Each pre-cut (-30-, -30'-) may or may not be straight. The advantage of pre-cuts which are not straight is greater in the case of a total pre-cut of the join zone because it restricts unwanted relative displacement of the two halves of the pair in a direction perpendicular to the common axis between the centres of the electric conductors (-200-, -200'-).
Each pre-cut (-30-, -30'-) may be produced in the same extrusion zone during the manufacture of the data transmission line -2- according to the present invention or in a subsequent operation. The production of the pre-cut may be with or without deliberate removal of material. A pre-cut without removal has at least two advantages:

An electromagnetic advantage, which involves two transverse sections of the pair of electric conductors with pre-cuts of different depths having practically the same dielectric cross section, helping keep the impedance constant and thus reduce return loss.
A mechanical advantage, which involves the two faces produced from the pre-cut continuing to be in contact, helping give the pair of conductors greater resistance to compression, i.e. the usual compression over the life of the data transmission line -2- according to the present invention during production, transport, installation and service. However, when separating the two electric conductors (-200-, -200'-) in order to apply said conductors to the corresponding connection terminal, either traction must be applied by pulling the two electric conductors (-200-, -200'-) in opposite directions in the direction of the common axis between the centres of the electric conductors (-200-, -200'-), or a shearing force must be applied by pulling the two electric conductors (-200-, -200'-) in opposite directions in the direction perpendicular to said common axis. In these cases, only the section not affected by the cut will act, reducing the effort required for the operation.

The combination of a longitudinal perforation -4- and at least one or two pre-cuts (-30-, -30'-) allows, if required, the two electric conductors (-200-, -200'-) to retain the insulating covering -20- around each conductor after the separation, protecting said conductors. Moreover, each conductor remains reasonably centred relative to the outer contours of the insulating covering -20-, helping guide said conductor to the connection terminal when the conductor is inserted into the cavity of said terminal.
The configuration described above will also apply both to pairs of conductors that are not shielded and to pairs that are shielded as illustrated in Fig. 11 according to a fourth embodiment. The main difference between a non-shielded pair and a shielded pair, apart from the existence of the shield -5-, is that the shielding normally requires a greater thickness of insulator covering (and a lower dielectric constant) to maintain the impedance for conductors with the same cross section. Furthermore, the shield -5- of the shielded pair must have been opened or removed beforehand in the zone where the separation of the two conductors of the pair will take place. Moreover, the shielding in this configuration according to the present invention may also allow the twisting operation to be eliminated. The usefulness of twisting is centred on keeping the two conductors together (if they are individual elements) in order to keep the impedance constant. The existence of the individual shield -5- will be sufficient to maintain the required levels of crosstalk.
The mechanical advantages of the configuration described above allows different embodiments to be provided, as will be illustrated below, while maintaining the same object of a high-performance data transmission line in which its pairs of conductors have a high degree of structural consistency along the length thereof, maintaining the dimensions of the two conductors of the pair, those of the insulators thereof, and also the relative positioning therebetween, while keeping the twisting, if any, uniform.
According to a fifth embodiment according to the present invention illustrated in Fig. 12, the data transmission line -2- comprises electric conductors (-201-, -201'-) of elliptical cross section (that is, not circular), allowing the total dimension (distance d₆) of the data transmission line -2- according to the present invention to be reduced along the common axis between the centres of the conductors (-201-, -201'-) relative to the total dimension (distance d₂) of the data transmission line -2- of the embodiment of Fig. 10. Alternatively, the data transmission line -2- according to the present invention comprises electric conductors (-201-, -201'-) of oval cross section (not illustrated).
To evaluate the possible reduction of dimensions and materials, comparative electromagnetic simulations have been carried out. One case to illustrate the advantages of the above embodiment is based on a conventional pair non-individually shielded electric conductors of 100 ohm, having a conductor cross section with an AWG (American wire gauge) value of 23, taken as a reference. Each conductor of elliptical cross section like the one illustrated in Fig. 12, with a ratio of 1.21 between the larger and smaller diameters, required a conductor cross section that was 19 % smaller. In addition, the greater diameter of the pair of conductors reduced by 22 %, which significantly reduces the total diameter of the balanced pair data transmission line -2- according to the present invention. Other cases which allow greater ratios between the larger and smaller diameters of each conductor allow greater reductions in dimensions, material and, consequently, in the final cost of the product.
Fig. 13 shows a sixth embodiment similar to that of Fig. 12, that is, comprising electric conductors (-201-, -201'-) of elliptical cross section, allowing the total dimension (distance D₁) of the data transmission line -2- according to the present invention to be reduced along the common axis between the centres of the conductors (-201-, -201'-) compared with the total dimension (distance D) of the data transmission line -2- of the embodiment of Fig. 11. In the case of Fig. 13, as mentioned earlier, the shielding -5- normally requires a greater thickness of insulating covering (and a lower dielectric constant) to maintain the impedance for conductors with the same cross section.
As explained above, one of the main problems of a data transmission cable of the prior art which comprises at least one balanced pair of electric conductors individually covered with their respective dielectric insulating material and arranged adjacently to one another longitudinally, is the possibility that the two conductors may separate at some point along the length of the pair. Said separation at some point along the length of the pair may cause an isolated variation in the impedance and, thus, an increase in return loss. In addition, as explained above, said small deviations of position in the case of non-circular electric conductors are usually more likely to occur and involve more significant variations in the transmission behaviour of the cable than for relative variations of position between electric conductors of circular cross section. Moreover, the isolated separations between the electric conductors of a particular pair may also be produced repeatedly at different points along the same pair, causing significant increases in return loss and, in addition, increases in attenuation, lowering the performance of the pair and of the cable.
One of the technical advantages of the fifth embodiment of Fig. 15 according to the present invention, that is, a pair of electric conductors (-201-, -201'-) of elliptical cross section covered by the same insulating covering -20-, is that it would allow a constant misalignment to be maintained as illustrated in Fig. 14 (linear displacement of the longitudinal axes in the direction perpendicular to the straight line between the two centres of the electric conductors) and Fig. 15 (axial displacement of the longitudinal axes of the conductors relative to one another) in the case of conductors of elliptical cross section. In such cases the attenuation efficiency would be lower but the remaining parameters could be kept constant.
The embodiments disclosed above envisage the use of constant insulating covering thicknesses in the perimeter zones outside the join zone of the pair. However, the concept of a single insulator around the two conductors allows variations in said thickness according to the embodiments which will be explained below.
Fig. 16 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 10 in which the thickness (d₁') of the insulating covering -20- is reduced in the direction perpendicular to the common axis between the centres of the electric conductors (-200-, -200'-), compared with the thickness (d₁) of the embodiment of Fig. 10. Thus, the total upward dimension (d₃') of the transmission line -2- of Fig. 16 has been reduced compared with the total upward dimension (d₃) of the data transmission line -2- of Fig. 10.
Fig. 17 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 10 in which the thickness (d₁') of the insulating covering -20- is reduced in the direction of the common axis between the centres of the electric conductors (-200-, -200'-), compared with the thickness (d₁) of the embodiment of Fig. 10. Thus, the total widthways dimension (d₂') of the data transmission line -2- of Fig. 17 has been reduced compared with the total widthways dimension (d₂) of the data transmission line -2- of Fig. 10.
Fig. 18 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 12 in which the thickness (d₅') of the insulating covering -20- is reduced in the direction perpendicular to the common axis between the centres of the electric conductors (-201-, -201'-), compared with the thickness (d₅) of the embodiment of Fig. 12. Thus, the total upward dimension (d₇') of the data transmission line -2- of Fig. 18 has been reduced compared with the total upward dimension (d₇) of the data transmission line -2- of Fig. 12.
Fig. 19 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 12 in which the thickness (d₄') of the insulating covering -20- is reduced in the direction of the common axis between the centres of the electric conductors (-201-, -201'-), compared with the thickness (d₄) of the embodiment of Fig. 12. Thus, the total widthways dimension (d₆') of the data transmission line -2- of Fig. 19 has been reduced compared with the total widthways dimension (d₆) of the data transmission line -2- of Fig. 12.
In the above embodiments in which the thickness of the insulation around the conductor has been reduced, the external dimensions of the balanced pair data transmission line -2- according to the present invention and the quantities of material (conductor and insulator) are consequently reduced, which will entail a reduction in the cost of the pair while maintaining the electromagnetic performance. The reduction in the external dimensions of the data transmission line -2- of the type according to the present invention will also involve a reduction of the external dimensions of the cable which uses one or more of said pairs. The consequence will be a reduction of the material required for possible shielding of the entire data transmission line -2- according to the present invention and of the material required for the outer covering. The end result is a balanced pair data transmission line with a lower total cost. The reduction in the external dimensions is also an advantage in itself, as it makes it possible to use smaller ducts for the same number of cables or to increase the number of cables which can be housed in a given duct.
Alternatively, this could be done in the opposite direction, that is, by increasing the thickness of the insulating covering -20-, and although this would involve use of more insulating material, it would still allow for an improvement in the crosstalk between pairs.
The use of individual shielding of the pair has other implications and allows for other embodiments which involve a reduction in the thickness of the insulating covering -20-, as will be explained below.
The different cases allow the dielectric constant between the conductor and shield to be reduced, allowing the outer dimensions of the balanced pair data transmission line according to the present invention to be reduced, with the advantages already mentioned.
Fig. 20 is a view in cross section of the data transmission line -2- of Fig. 11, additionally comprising two longitudinal apertures (-6-, -6'-) for propagating air, each aperture being arranged on either side of the data transmission line -2- of the present invention in the direction of the common axis between the centres of the electric conductors (-200-, -200'-) and between the outer surface of the insulating covering -20- and a portion of the shielding means -5-. Thus, the total widthways dimension (D') of the data transmission line -2- of Fig. 20 is reduced compared with the total widthways dimension (D) of the data transmission line -2- of Fig. 11.
Fig. 21 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 11, additionally comprising four longitudinal apertures (-61-, -61'-, -62-, -62'-) for propagating air arranged in pairs on either side of said line -2- in the direction of the common axis between the centres of the electric conductors (-200-, -200'-) and between the outer surface of the insulating covering -20- and a portion of the shielding means -5-. Thus, the total widthways dimension (D") of the data transmission line -2- of Fig. 21 is reduced compared with the total widthways dimension (D) of the data transmission line -2- of Fig. 11.
Fig. 22 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 13, additionally comprising two longitudinal apertures (-6-, -6'-) for propagating air arranged each one respectively on either side of said data transmission line -2- in the direction of the common axis between the centres of the electric conductors (-201-, -201'-) and between the outer surface of the insulating covering -20- and a portion of the shielding means -5-. Thus, the total widthways dimension (D₁') of the data transmission line -2- of Fig. 22 is reduced compared with the total widthways dimension (D₁) of the data transmission line -2- of Fig. 13.
Fig. 23 is a view in cross section of the embodiment of the data transmission line -2- of Fig. 13, additionally comprising four longitudinal apertures (-61-, -61'-, -62-, -62'-) for propagating air arranged in pairs on either side respectively of said data transmission line -2- in the direction of the common axis between the centres of the electric conductors (-201-, -201'-) and between the outer surface of the insulating covering -20- and a portion of the shielding means -5-. Thus, the total widthways dimension (D₁") of the data transmission line -2- of Fig. 23 is reduced compared with the total widthways dimension (D₁) of the data transmission line -2- of Fig. 13.
From what is shown in Fig. 16 to 23, it can be deduced that the concept described here allows for a variable thickness of insulating covering -20- in the zone outside the join zone, which will enable various advantages depending on how it is applied.
The use of an optimised data transmission line -2- according to the present invention for high frequencies will allow for a reduction in the cross section of the conductors of the pair and, thus, a reduction in the weight and cost thereof. Said reduction, however, may be limited by other determining factors:

the electrical resistance requirements for DC voltage, expressed in accordance with international standards
the ability to support PoE (Power over Ethernet) applications, PoE being a technology which incorporates electrical supply to communications infrastructure in accordance with the known Ethernet standard, also detailed in international standards
compatibility with the dimensions of the terminals of the connectors used.

In general, the two conductors of the optimised balanced pair data transmission line according to the present invention are characterised by having elongate shapes, which may be the same or different, with substantially parallel larger axes and smaller axes with substantially aligned axes, and by having opposite faces of which the radii of curvature will be greater than the radius of the circle of the same area as the respective conductor. This will produce a greater concentration of the electric field lines, which will produce less insertion loss and less crosstalk.
For all the embodiments described according to the present invention, the electric conductors according to the present invention may each be made of a highly electrically conductive material such as copper or aluminium, which can also be covered by a thin layer of some other highly conductive material, such as tin, to improve anti-corrosion behaviour or to improve contact with the connectors situated at the beginning and end of the cable in a typical installation.
The insulating covering -20- may be prepared with a polymer of low dielectric constant (to minimise insertion loss or attenuation), which may be solid or cellular, and which includes air bubbles with the object of further reducing the dielectric constant as air is characterised by a dielectric constant (of close to 1) which is less than that of the polymers used for this application. Normally, the insulating covering -20- according to the present invention will have a constant thickness around the conductor.
Each of the pair of conductors of which a data transmission line -2- according to the present invention may be composed will be used to transmit a differential signal, the signals in both conductors usually being out of phase by 180º, this type of cable being referred to and/or known as balanced cables or also as 'balanced pair'.
In addition, a data transmission line -2- according to the present invention may be comprised of other lines -2- of the same type inside a data transmission cable, the most common configuration being that with four balanced pair data transmission lines -2- according to the present invention, which is equivalent to four conventional pairs according to the prior art. In this case, a central insulator may be used to position each balanced data transmission line -2- appropriately and to reduce the crosstalk therebetween.
The shielding means or shield -5- described in the above embodiments may be formed of a conductive tape, normally of aluminium, on a tape made of a dielectric material, such as polyester, and may also include a drain wire to improve the conductivity of the shielding. Alternatively or as a complement thereto, the outer shielding may consist of a copper mesh.
In addition or alternatively, shielding may be provided for the set of data transmission lines -2- according to the present invention comprised within the same data transmission cable, by using a conductive tape, normally of aluminium, on a tape of dielectric material, such as polyester, which surrounds, with some overlap, each of the data transmission lines -2-.
The data transmission line -2- according to the present invention will optimise the above-mentioned parameters at frequencies from 1 MHz to 2 GHz or more depending on the application of the cable which will comprise at least said data transmission line -2- according to the present invention.
In addition, the data transmission line -2- according to the present invention may comprise said conductors arranged in parallel inside said insulating covering -20-. Alternatively, said conductors may be twisted together uniformly along the length of said conductors inside said insulating covering -20-.
In the case of twisted conductors, it will be useful to perform the twisting operation before proceeding to the process of extruding the insulating covering -20- on the conductors. Thus, a rigid support will allow the twisting to be produced in a more consistent way than by performing said process on the insulators, which are not very hard. The process of twisting and co-extruding the two conductors also offers a reduction in manufacturing costs by reducing the number of operations compared with the conventional process of extruding each individual conductor and twisting in a subsequent operation. In addition, in the case of a twisted pair there will be an improvement in terms of the return loss. The significant reduction in the length of the pair along the larger axis thereof, without significantly altering the smaller axis, will produce a pair with a more circular cross section, allowing the shielding tape to be fitted closer to the insulator over the entire length of the pair, which will produce less variability in the impedance.
If a cable comprises various data transmission lines according to the present invention, it will be possible to use colours to distinguish each pair of conductors of each data transmission line according to the present invention. The usual coding is for one of the conductors of the pair to be white while the other is blue, green, orange or brown. The process of co-extruding the two conductors may include an injection nozzle for white polymer at one end of the pair and another nozzle at the other end with the desired colour. An alternative is to extrude the entire pair in white and to add a subsequent operation of painting the other colour.
Although the invention has been presented and described with reference to embodiments thereof, these should not be taken to limit the invention; rather, there may be many variable structural or other details which will be obvious to a person skilled in the relevant art after interpreting the subject matter disclosed in the present description, claims and drawings. Thus, all variants and equivalents will be included within the scope of the present invention if they can be considered as comprised within the widest scope of the following claims.

Claims

Balanced pair data transmission line which comprises:
- two electric conductors each having a longitudinal extension body;

- an insulating covering which surrounds both of said electric conductors along the length of their respective bodies, said insulating covering comprising surface depressions on each of the faces of the outer surface of said covering close to the perpendicular line at the centre of the straight line between the two centres of said conductors;

- at least one longitudinal aperture arranged along the central longitudinal axis of the insulating covering between said conductors, keeping both conductors covered by said covering;

- at least one pre-cut arranged on at least one of said surface depressions in the outer surface of the insulating covering.
Balanced pair data transmission line according to claim 1, characterised in that said conductors are arranged in parallel inside said insulating covering.
Balanced pair data transmission line according to claim 1, characterised in that said conductors are twisted together uniformly along the length of said conductors inside said insulating covering.
Balanced pair data transmission line according to any one of claims 1, 2 or 3, characterised in that said conductors have a cross section shaped such that the respective opposite faces thereof are circular arcs.
Balanced pair data transmission line according to claim 4, characterised in that said conductors have a circular cross section.
Balanced pair data transmission line according to any one of claims 1, 2 or 3, characterised in that said conductors have a non-circular cross section.
Balanced pair data transmission line according to claim 6, characterised in that said conductors have a cross section shaped such that the respective opposite faces thereof are elliptical arcs.
Balanced pair data transmission line according to claim 6, characterised in that said conductors have a cross section shaped such that the respective opposite faces thereof are oval arcs.
Balanced pair data transmission line according to any one of the preceding claims, characterised in that it also comprises an external shielding means which covers the set of electric conductors surrounded by said common insulating covering.
Balanced pair data transmission line according to the preceding claim, characterised in that it also comprises at least two longitudinal apertures for propagating air, each arranged on either side of the cable respectively in the direction of the common axis between the centres of the electric conductors and between the outer surface of the insulating covering and a portion of the shielding means
Balanced pair data transmission line according to claim 9, characterised in that it also comprises at least four longitudinal apertures for propagating air arranged in pairs on either side of the cable respectively in the direction of the common axis between the centres of the electric conductors and between the outer surface of the insulating covering and a portion of the shielding means.
Balanced pair data transmission line according to the preceding claims, characterised in that it also comprises an additional pre-cut arranged on at least one other of said surface depressions.
Data transmission cable which comprises at least one balanced pair data transmission line according to claims 1 to 12.