Source: http://www.google.es/patents/US7534964
Timestamp: 2017-12-11 04:31:10
Document Index: 112022324

Matched Legal Cases: ['§ 120', '§ 120', '§ 120', '§ 120', '§ 120', '§ 120', '§ 120', '§ 120']

Patente US7534964 - Data cable with cross-twist cabled core profile - Google Patentes
Cables including a plurality of twisted pairs of insulated conductors and a jacket surrounding the plurality of twisted pairs of insulated conductors, the jacket including a plurality of protrusions extending away from an inner circumferential surface of the jacket toward a center of the cable. The plurality...http://www.google.es/patents/US7534964?utm_source=gb-gplus-sharePatente US7534964 - Data cable with cross-twist cabled core profile
Número de publicación US7534964 B2
Número de solicitud US 12/143,388
También publicado como CA2677681A1, CA2677681C, US7405360, US20070193769, US20080251276, WO2008100714A1
Número de publicación 12143388, 143388, US 7534964 B2, US 7534964B2, US-B2-7534964, US7534964 B2, US7534964B2
Inventores William T Clark, Galen M Gareis
Citas de patentes (107), Citada por (23), Clasificaciones (6), Eventos legales (2)
US 7534964 B2
Cables including a plurality of twisted pairs of insulated conductors and a jacket surrounding the plurality of twisted pairs of insulated conductors, the jacket including a plurality of protrusions extending away from an inner circumferential surface of the jacket toward a center of the cable. The plurality of protrusions are configured so as to hold the plurality of twisted pairs away from the inner circumferential surface of the jacket, and may provide an air gap between the plurality of twisted pairs of insulated conductors and the inner circumferential surface of the jacket.
This application is a continuation of and claims priority under 35 U.S.C. § 120 to U.S. application Ser. No. 11/673,357 entitled “Data Cable with Cross-Twist Cabled Core Profile” filed on Feb. 9, 2007, now U.S. Pat. No. 7,405,360, which is a continuation-in-part of and claims priority under 35 U.S.C. § 120 to U.S. application Ser. No. 11/584,825 entitled “Data Cable with Cross-Twist Cabled Core Profile,” filed on Oct. 23, 2006 and, which is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 11/445,448, entitled “Data Cable with Cross-Twist Cabled Core, ” filed on Jun. 1, 2006 and now abandoned, which is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 11/197,718 entitled “Data Cable With Cross-Twist Cabled Core Profile,” filed on Aug. 4, 2005, now U.S. Pat. No. 7,135,641, which is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 10/705,672 entitled “Data Cable With Cross-Twist Cabled Core Profile,” filed on Nov. 10, 2003, now U.S. Pat. No. 7,154,043 which is a continuation-in-part of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 10/430,365 entitled “Enhanced Data Cable With Cross-Twist Cabled Core Profile,” filed May 5, 2003, now abandoned, which is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 09/532,837 entitled “Enhanced Data Cable With Cross-Twist Cabled Core Profile,” filed on Mar. 21, 2000, now U.S. Pat. No. 6,596,944 which is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. application Ser. No. 08/841,440, filed Apr. 22, 1997 entitled “Making Enhanced Data Cable with Cross-Twist Cabled Core Profile” (as amended) now U.S. Pat. No. 6,074,503, each of which is herein incorporated by reference in its entirety.
Cables intended for installation in the air handling spaces (i.e. plenums, ducts, etc.) of buildings are specifically required by NEC or CEC to pass the flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FT6. The UL-910 and the FT6 represent the top of the fire rating hierarchy established by the NEC and CEC respectively. Cables possessing this rating, generically known as “plenum” or “plenum rated”, may be substituted for cables having a lower rating (i.e. CMR, CM, CMX, FT4, FT1 or their equivalents), while lower rated cables may not be used where plenum rated cable is required. Cables conforming to NEC or CEC requirements are characterized as possessing superior resistance to ignitability, greater resistant to contribute to flame spread and generate lower levels of smoke during fires than cables having a lower fire rating. Conventional designs of data grade telecommunications cables for installation in plenum chambers have a low smoke generating jacket material, e.g. of a PVC formulation or a fluoropolymer material, surrounding a core of twisted conductor pairs, each conductor individually insulated with a fluorinated ethylene propylene (FEP) insulation layer. Cable produced as described above satisfies recognized plenum test requirements such as the “peak smoke” and “average smoke” requirements of the Underwriters Laboratories, Inc., UL910 Steiner test and/or Canadian Standards Association CSA-FT6 (Plenum Flame Test) while also achieving desired electrical performance in accordance with EIA/TIA-568A for high frequency signal transmission.
Aspects and embodiments of the invention are directed to cables for data transmission that have constructions that may reduce alien crosstalk and/or may improve data transmission performance of the cable as compared to conventional cables. In one embodiment, a cable comprises a cable core including a plurality of twisted pairs of insulated conductors including a first twisted pair and a second twisted pair, each twisted pair comprising two insulated conductors twisted together in a helical manner, a jacket surrounding the plurality of twisted pairs of insulated conductors, and an element disposed between cable core and the jacket along a length of the cable, the element providing an air gap between the jacket and the cable core. The element may comprise, for example, one or more dielectric helixed splines (made of any of a variety of materials, including, for example, a fluoropolymer) or a conductive rod. The element(s) may be disposed about a circumference of the cable core or may be helically wrapped about the cable core. In one example, the cable core may further comprises a separator disposed among the plurality of twisted pairs of insulated conductors so as to separate at least one the plurality of twisted pairs from others of the plurality of twisted pairs. In one example, the cable core, the jacket and the element are helically twisted together with a cable twist lay that is within a range of about 2 to 6 inches.
Aspects and embodiments of the invention are directed to twisted pair communication cables that may exhibit superior transmission properties through the use of structures which may reduce alien crosstalk, internal crosstalk and signal attenuation in the twisted pairs. Various illustrative embodiments and aspects thereof are described in detail below with reference to the accompanying figures. It is to be appreciated that this invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, elements and features discussed in connection with one embodiment are not intended to be excluded from a similar role in other embodiments. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Referring to FIG. 2, there is illustrated a portion of one embodiment of a cable including an extruded core 101 having a profile described below cabled into the cable with four twisted pairs 103. Although the following description will refer primarily to a cable that is constructed to include four twisted pairs of insulated conductors and a core having a unique profile, it is to be appreciated that the invention is not limited to the number of pairs or the profile used in this embodiment. The inventive principles can be applied to cables including greater or fewer numbers of twisted pairs and different core profiles. Also, although this embodiment of the invention is described and illustrated in connection with twisted pair data communication media, other high-speed data communication media can be used in constructions of cable according to the invention. In addition, it is to be appreciated that the term “core” is used synonymously herein with the term “separator” and is intended to refer to an element that may be included in a jacketed cable to separate at least one transmission medium (e.g., a twisted pair of insulated conductors) from at least one other transmission medium and/or from the cable jacket.
As shown in FIG. 2, according to one embodiment of the invention, the extruded core profile may have an initial shape of a “+”, providing four spaces or channels 105, one between each pair of fins 102 of the core 101. Each channel 105 carries one twisted pair 103 placed within the channel 105 during the cabling operation. The illustrated core 101 and profile should not be considered limiting. The core 101 may be made by some other process than extrusion and may have a different initial shape or number of channels 105. For example, as illustrated in FIG. 2, the core may be provided with an optional central channel 107 that may carry, for example, an optical fiber element or strength element 109. In addition, in some examples, more than one twisted pair 103 may be placed in each channel 105.
As discussed above, the core 101 may have a variety of different profiles and may be conductive or non-conductive. According to one embodiment, the core 101 may further include features that may facilitate removal of the core 101 from the cable. For example, referring to FIG. 5, the core 101 may be provided with narrowed, or notched, sections 111, which are referred to herein as “pinch points.” At the notched sections, or pinch points, a diameter or size of the core 101 is reduced compared with the normal size of the core 101 (at the non-pinch point sections of the core). Thus, the pinch points 111 provide points at which it may be relatively easy to break the core 101. The pinch points 111 may act as “perforations” along the length of the core, facilitating snapping of the core at these points, which in turn may facilitate removal of sections of the core 101 from the cable. This may be advantageous for being able to easily snap the core to facilitate terminating the cable with, for example, a telephone or data jack or plug. In one example, the pinch points 111 may be placed at intervals of approximately 0.5 inches along the length of the cable. The pinch points 111 should be small enough such that the twisted pairs may ride over the pinch points 111 substantially without dipping closer together through the notched sections 111. In one example, the pinch points may be formed during extrusion of the core by stretching the core for a relatively short period of time each time it is desired to form a pinch point 111. Stretching the core during extrusion results in “thinned” or narrowed sections being created in the core, which form the pinch points 111.
According to another embodiment, the core 101 may comprise a helixed spline, as illustrated in FIG. 6. Such a helixed spline may provide several advantages over conventional round; solid separators such as the separator 200 illustrated FIG. 1. Conventional round, solid fillers are generally inflexible and stiff by nature and displace a relatively large amount of air from the cable. If a conventional cable needed to be flexible, a very soft, often very flammable material was used for the separator or, alternatively, a textile or “slit film” separator was used. These provide little crush resistance or electrical stability if used as central separators in a cable. In addition, the large volume of the conventional separator can make meeting applicable fire safety regulations or the standards for “plenum-rated” cables more difficult. By contrast, a helixed spline core according to embodiments of the invention may provide improved flexibility over a conventional solid, round separator while also providing strength and good dielectric properties.
Referring to FIG. 6, one embodiment of a helixed spline may include a finned or “+-shaped” core (such as is described above) that may be twisted with a very tight twist lay to form the helixed spline. It is to be appreciated that the invention is not limited to the use of a “+-shaped” core to form the helixed spline and any non-round shape may be used, including, for example, a finned core having more or fewer than four fins. The twisted form may have a substantially round profile, as indicated by circle 204 and may be used to provide spacing between transmission media, for example, as a central separator in a cable. However, comparing a helixed spline with a circle 204 of the same diameter as the outer diameter of a conventional solid round separator, the helixed spline may use substantially less material. As a result, the helixed spline may therefore also displace less air from the cable than does a conventional solid separator, for improved electrical properties.
According to one embodiment, a helixed spline such as described above may be formed by extrusion. For example, the helixed spline may be continuously extruded using a die having a shaped head and a material that can be extruded (e.g., an extrudable polymer). In one example, to form a spline that has a “cross-shape” and is twisted with a certain twist lay, as described above, an extrusion die may be used with a crosshead that can be rotated during extrusion to provide the twist lay. In one example, a die may be used that rotates alternately in a clockwise and anticlockwise direction, such that the spline may be extruded with an “S/Z” configuration, as is known in the art.
According to another embodiment, a helixed spline such as described above may be used in as a separation barrier between layers of a multi-layer cable. One embodiment of a multi-layer cable 206 is illustrated in FIG. 7. The cable 206 may include a first layer 210 including a plurality of twisted pairs 103. The first layer may also include one or more separators 208 that may separate ones of the plurality of twisted pairs 103 from others of the plurality of twisted pairs 103. It is to be appreciated that these separators 208 may be helixed splines or may be any of the other core embodiments described herein. The multi-layer cable may further include a second layer 214 comprising another plurality of twisted pairs 103. The second layer may also include one or more separators 208 which may be, for example, helixed splines or any of the separator embodiments discussed above. A helixed spline 212 may be wrapped around the first layer to separate the first layer from the second layer. In this manner, the helixed spline 212 may act as an inner jacket layer, but may use substantially less material than would a conventional inner jacket. In addition, using a helixed spline instead of an inner jacket layer may provide the additional benefit of better electrical characteristics (e.g., decreased attenuation, increased velocity, etc.) due to the air that may be “trapped” between the ridges/fins of the spline, as discussed above.
As discussed above, a cable according to various embodiments of the invention may include a jacket, having a single layer or multiple layers, that may surround the transmission media and any other internal elements (e.g., a separator, binder or shield) making up the cable. In one embodiment, a cable may have a striated or “fluted” jacket that includes one or more protrusions that extend either inwardly toward a center of the cable from an internal circumference of the jacket or outwardly from an exterior circumference of the jacket. These protrusions may increase the distance between the twisted pairs of one cable and the twisted pairs of another adjacent cable and, in the case of inwardly extending protrusions may increase the distance between the twisted pairs and the cable jacket. As a result, such a jacket may provide numerous advantages such as, for example, reducing alien crosstalk (compared to cables with conventional round, smooth jackets) and/or providing a cable having a lower value of signal attenuation (also compared to a conventional cable with a round, smooth jacket) due to the decreased absorption of the signal by the dielectric cable jacket.
According to one embodiment, the inwardly extending protrusions 218 may be formed such that the twisted pairs 103 may be contained within the inner region 160 and are spaced apart from the inner border of the cable jacket 216 by a distance “s,” as shown in FIG. 9. In one example, s may be on the order of about 0.04 inches which may provide a good tradeoff between size of the cable and electrical performance. However, it is to be appreciated that many other values of s are also possible. With this arrangement, the twisted pairs may be spaced apart from the jacket and therefore, the effects of the cable jacket on the signal propagating through the twisted pairs (e.g., signal attenuation that may be caused by the proximity of the dielectric jacket to the twisted pairs) may be reduced. The protrusions 218 may be viewed as defining one or more spaces or cavities 166 that may exist between the inner circumferential surface 162 of the jacket and the inner region 160 of the cable. In some embodiments, this space 166 may be filled with air. However, it is to be appreciated that other fluids or dielectric materials may be used to fill the space. Since air has a dielectric constant substantially lower than the dielectric constant of most insulating materials used to form the jacket 216, creation of the space 166 by the protrusions 218 may result in the jacket material having a relatively lesser effect (compared with a conventional jacket) on the performance characteristics of the twisted pairs 103. For example, there may be less attenuation of the electromagnetic signals propagating through the twisted pairs due to the increases amount of air surrounding the twisted pairs and the increased distance between the twisted pairs and the bulk of the cable jacket material. In addition, because the jacket 216 may be held further away from the twisted pairs 103 by the protrusions 218, the protrusions may help to reduce alien crosstalk between adjacent or closely spaced cables, for example, in a bundled cable or a conduit in a building.
As illustrated in FIGS. 9-11, various embodiments of the cable jacket 216 may include various numbers of inwardly extending protrusions 218. As will be appreciated by those skilled in the art, there may be a tradeoff between the number of inwardly extending protrusions, which may limit movement of the twisted pairs within the cable, and the amount of dielectric loss due to proximity of the dielectric jacket material to the twisted pairs. As can be seen in FIG. 11, the fewer inwardly extending protrusions that may be provided, the greater the likelihood that one or more twisted pairs may not be confined within the inner region 160. However, it is also to be appreciated that the width, w, of the inwardly extending protrusions may be increased to provide the same or similar confinement of the twisted pairs as would be the case with a larger number of thinner inwardly extending protrusions. In addition, jackets may be formed with a plurality of inwardly extending protrusions having different shapes and/or sizes. For example, some protrusions may be formed with a width, w, or extension, s, from the inner border of the jacket that is different than the width, w, and/or extension (or height), s, of other protrusions in the cable. In one example, provision of a plurality of protrusions having varying extensions (or heights), s, may impart a varying center to the cable. In one embodiment, the protrusions and the jacket may be formed such that the space (or air gap) 166 has a substantially arc shape, as shown, for example, in FIG. 11. For example, selecting a circular jacket with an inner diameter in a range of about 0.100 to 0.500 inches and the number of protrusions to be approximately eight, may result in the inner circumferential surface of the jacket, between any two protrusions, having an arc shape. Of course, it will be appreciated that an arc-shaped surface (and thus air gap) may also be obtained with a different number of protrusions and/or a different jacket diameter, and the invention is not limited to the specific examples given herein. In another example, the protrusions may have a substantially triangular shape with the base of the triangle being adjacent the inner border 162 of the jacket and the tip of the triangle extending inwardly toward the twisted pairs. In this example, if the protrusions are sufficiently closely spaced to one another, the jacket may have a “sawtooth” appearance provided by the protrusions. It is to be appreciated that many other shapes may be possible for the protrusions and that the invention is not limited to the specific examples and/or illustrations given herein. Furthermore, it will be appreciated that the protrusions may be spaced about the inner circumferential surface of the jacket in numerous ways. For example, the protrusions may be evenly spaced, randomly spaced, provided in groups (for example, such that the protrusions within a group may have a first spacing relative to one another and the groups of protrusions may have a second spacing relative to another group), etc., and the invention is not limited to any particular spacing of the protrusions.
According to one embodiment, the inwardly extending protrusions 218 may be helically formed along the inner circumferential surface of the jacket 216 such that the jacket is helically striated along the inner circumferential surface. In this embodiment, one or a few helically formed inwardly extending protrusions may provide a barrier along the longitudinal length of the cable that may maintain the twisted pairs 103 within the inner region 160 that is defined by the end(s) 164 of the protrusions(s) 220. It will be appreciated that a shorter “twist lay” of such helical striations may provide more containment of the twisted pairs at the expense of using more dielectric material to form the projection(s), whereas a longer “twist lay” of the striations may reduce the amount of material used, but may allow one or more twisted pairs to occasionally or periodically contact the inner border 162 of the jacket.
According to another embodiment, the cable jacket may be twisted (referred to as “cabled”) with the twisted pairs (and optional other elements such as a separator, shield or binder) with a given cable lay. In this embodiment, even if the one or more inwardly extending protrusions are formed longitudinally along the length of the cable as straight or substantially straight ridges, the cabling procedure will result in the protrusions forming helical ridges along the inside of the cable jacket with a twist lay equal to the cable lay. Thus, as discussed above in reference to helically formed projection(s), the helical ridges formed one or more protrusions may provide a barrier along the longitudinal length of the cable that may contain the twisted pairs within the inner region. Again, depending on the cable lay, it may be possible for one or more twisted pairs to “dip” between the helical ridges and contact the inner circumferential surface of the jacket. Thus, it will be recognized by those skilled in the art that there may be a tradeoff between a tight (or short) cable lay that allow the projection(s) to better contain the twisted pairs within the inner region and the effects of a shorter cable lay on the performance and material and manufacturing costs of the cable.
According to another embodiment, a cable may be provided with a jacket having one or more outwardly extending protrusions from an outer circumferential surface of the cable. Such a construction may facilitate reduction of alien crosstalk between twisted pairs of nearby cables, as discussed further below. Referring to FIG. 16, there is illustrated an example of cables having a jacket with an exterior striated surface. FIG. 16 illustrates two cables 117 a and 117 b, each cable having jacket 182 with a plurality of outwardly extending protrusions 165 spaced about an outer circumferential surface 163 of the jacket 182. It is to be appreciated that although FIG. 16 illustrates the cables each including four twisted pairs 103 and a separator 101, the invention is not so limited and either or both cables may include more or fewer twisted pairs (or other transmission media) and the separators 101 are optional. In one example, the cables 117 a, 117 b may be helically twisted with a cable lay. In this example, the protrusions 165 may form helical ridges along the length of the cables 117, as shown in FIG. 16. The protrusions 165 may thus serve to further separate one cable 117 a from another 117 b, and may thereby act to reduce alien crosstalk between the twisted pairs of cables 117 a, 117 b.
Referring to FIG. 17, there is illustrated a plurality of cables 117 having externally striated jackets as described above. In one example, the cables 117 may not be twisted with a cable lay. In this example, the protrusions 165 may be constructed such that the protrusions 165 a of the jacket of one cable 117 a may mate with the protrusions 165 b of the jacket 182 of another cable 117 b so as to interlock two corresponding cables 117 a, 117 b together, as illustrated in FIG. 17. This may be particularly useful if multiple cables are to be installed together, for example, in a building conduit, or if two or more cables are to be bundled together to provide a bundled cable. The individual cables 117 may “snap” together, possibly obviating the need for a binder to keep the bundled cable 161 together, or facilitating installation of multiple cables by holding the cables together. This embodiment may also be advantageous in that the cables 117 may be easily separated from one another when necessary.
As discussed above, a goal of cable designers may be to reduce crosstalk in the twisted pairs of a cable because crosstalk may adversely affect the quality and/or speed of data transmission through the twisted pairs. Various embodiments of cable jackets and other elements (e.g., shields or spacers) discussed herein may serve to reduce alien crosstalk. In addition, various embodiments of separators discussed herein may reduce crosstalk between pairs within a single cable. In some embodiments, particularly where the core 101 may be non-conductive, it may be advantageous to provide additional crosstalk isolation between the twisted pairs 103 by varying the twist lays of each twisted pair 103. For example, referring to FIG. 26, the cable 117 may include a first twisted pair 103 a and a second twisted pair 103 b. Each of the twisted pairs 103 a, 103 b includes two metal wires 125 a, 125 b each insulated by an insulating layer 127 a, 127 b. As shown in FIG. 26, the first twisted pair 103 a may have a twist lay length that is shorter than the twist lay length of the second twisted pair 103 b.
As discussed above, varying the twist lay lengths between the twisted pairs in the cable may help to reduce crosstalk between the twisted pairs. However, the shorter a pair's twist lay length, the longer the “untwisted length” of that pair and thus the greater the signal phase delay added to an electrical signal that propagates through the twisted pair. It is to be understood that the term “untwisted length” herein denotes the electrical length of the twisted pair of conductors when the twisted pair of conductors has no twist lay (i.e., when the twisted pair of conductors is untwisted). Therefore, using different twist lays among the twisted pairs within a cable may cause a variation in the phase delay added to the signals propagating through different ones of the conductors pairs. It is to be appreciated that for this specification the term “skew” is a difference in a phase delay added to the electrical signal for each of the plurality of twisted pairs of the cable. Skew may result from the twisted pairs in a cable having differing twist lays. As discussed above, the TIA/EIA has set specifications that dictate that cables, such as category 5 or category 6 cables, must meet certain skew requirements.
As the dielectric constant of an insulation material covering the conductors of a twisted pair decreases, the velocity of propagation of a signal traveling through the twisted pair of conductors increases and the phase delay added to the signal as it travels through the twisted pair decreases. In other words, the velocity of propagation of the signal through the twisted pair of conductors is inversely proportional to the dielectric constant of the insulation material and the added phase delay is proportional to the dielectric constant of the insulation material. For example, for a so-called “faster” insulation, such as fluoroethylenepropylene (FEP), the propagation velocity of a signal through a twisted pair 103 may be approximately 0.69 c (where c is the speed of light in a vacuum). For a “slower” insulation, such as polyethylene, the propagation velocity of a signal through the twisted pair 103 may be approximately 0.66 c.
This concept may be better understood with reference to FIGS. 28 and 29 which respectively illustrate graphs of measured input impedance versus frequency and return loss versus frequency for twisted pair 1, for example, twisted pair 103 a, in the cable 117. Referring to FIG. 28, the “fitted” characteristic impedance 131 for the twisted pair (over the operating frequency range) may be determined from the measured input impedance 133 over the operating frequency range. Lines 135 indicate the category 5/6 specification range for the input impedance of the twisted pair. As shown in FIG. 28, the measured input impedance 133 falls within the specified range over the operating frequency range of the cable 117. Referring to FIG. 29, there is illustrated a corresponding return loss versus frequency plot for the twisted pair 103 a. The line 137 indicates the category 5/6 specification for return loss over the operating frequency range. As shown in FIG. 29, the measured return loss 139 is above the specified limit (and thus within specification) over the operating frequency range of the cable. Thus, the characteristic impedance could be allowed to deviate further from the desired 100 Ohms, if necessary, to reduce skew. Similarly, the twist lays and insulation thicknesses of the other twisted pairs may be further varied to reduce the skew of the cable while still meeting the impedance specification.
Allowing some deviation in the twisted pair characteristic impedances relative to the nominal impedance value allows for a greater range of insulation diameters. Smaller diameters for a given pair lay results in a lower pair angle and shorter non-twisted pair length. Conversely, larger pair diameters result in a higher pair angles and longer non-twisted pair length. Where a tighter pair lay would normally require an insulation diameter of 0.043″ for 100 ohms, a diameter of 0.041″ would yield a reduced impedance of about 98 ohms. Longer pair lays using the same insulation material would require a lower insulation diameter of about 0.039″ for 100 ohms, and a diameter of 0.041″ would yield about 103 ohms. As shown in FIGS. 28 and 29, allowing this “target” impedance variation from 100 Ohms may not prevent the twisted pairs, and the cable, from meeting the input impedance specification, but may allow improved skew in the cable.
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Clasificación de EE.UU. 174/113.00R, 174/113.0AS, 174/113.00C