Patent Grant
7196271
This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/364,158 filed Mar. 13, 2002, entitled “Very High Frequency Quad Pair Cable Wit Asymmetric Cross Web or Two T-Shaped Cross Webs”, by Cornibert, et al. The entirety of the aforementioned application is hereby incorporated by reference.
The present invention relates to data cables employing twisted pairs of insulated conductors as the transmission medium, and to cable splines for use in the data cables.
High performance twisted pair cables have become popular for a variety of reasons. Such cables are comparatively easy to handle, install, terminate and use. They also are capable of meeting high performance standards.
Commonly, multiple twisted pairs are used in these types of cables. In each pair, the wires are twisted together in a helical fashion forming a balanced transmission line. When twisted pairs are placed in close proximity, such as in a cable, electrical energy may be transferred from one pair of the cable to another. Such energy transfer between pairs is undesirable and is referred to as crosstalk. Crosstalk causes interference to the information being transmitted through the twisted pair and can reduce the data transmission rate and can cause an increase in the bit error rate. The Telecommunications Industry Association (TIA) and Electronics Industry Association (EIA) have defined standards for crosstalk in a data communications cable such as the Category 6 cable standard ANSI/TIA/EIA-568-B.2-1, published Jun. 20, 2002 by TIA. The International Electrotechnical Commission (IEC) has also defined standards for data communications cable crosstalk, such as ISO/IEC 11801, which includes the international equivalent to ANSI/TIA/EIA-568-B.2-1.
One popular cable type meeting the above specifications is foil shielded twisted pair (FTP) cable. FTP cable is popular for local area network (LAN) applications because it has good noise immunity and a low level of radiated emissions.
Another popular cable type meeting the above specifications is unshielded twisted pair (UTP) cable. Because it does not include shield conductors, UTP cable is preferred by installers and plant managers as it is easily installed and terminated. The requirements for modern state of the art transmission systems require both FTP and UTP cables to meet very stringent requirements. Thus, FTP and UTP cables produced today have a very high degree of balance and impedance regularity. In order to achieve this balance and regularity, the manufacturing process of FTP and UTP cables may include twisters that apply a back torsion to each wire prior to the twisting operation. Therefore, FTP and UTP cables have very high impedance regularities due to the randomization of eventual eccentricities in a twisted wire pair during manufacturing.
Crosstalk is primarily capacitively coupled or inductively coupled energy passing between adjacent twisted pairs within a cable. Among the factors that determine the amount of energy coupled between the wires in adjacent twisted pairs, the center-to-center distance between the wires in the adjacent twisted pairs is very important. The center-to-center distance is defined herein to be the distance between the center of one twisted pair to the center of an adjacent twisted pair. The center of a twisted pair may be taken as the point equidistant from and on the line passing through the center of each of the individual wires in the pair. The magnitude of both capacitively coupled and inductively coupled crosstalk varies inversely with the center-to-center distance between wires, approximately following an inverse square law. Increasing the distance between twisted pairs will thus reduce the level of crosstalk interference. Another factor affecting the strength of the coupling between two twisted pairs is the medium through which the wires couple and the electromagnetic properties of that medium. Examples of these properties include conductivity, permittivity, permeability, and loss tangent. Yet another important factor relating to the level of crosstalk is the distance over which the wires run parallel to each other. Twisted pairs that have longer parallel runs will have higher levels of crosstalk occurring between them.
In twisted pairs, the twist lay length is the longitudinal distance between twists of the wire. The direction of the twist is known as the twist direction. If adjacent twisted pairs have the same twist lay length, then the coupling is longitudinally additive. In other words, the crosstalk tends to be higher between pairs having substantially the same twist lay length. In addition, cables with the same twist lay length tend to interlink. Interlinking occurs when two adjacent twisted pairs are pressed together filling any interstitial spaces between the wires comprising the twisted pairs. Interlinking will cause a decrease in the center-to-center distance between the wires in adjacent twisted pairs and can cause a periodic coupling of two or more twisted pairs. This can lead to an increase in crosstalk among the wires in adjacent twisted pairs within the cable.
Therefore, adjacent twisted pairs within a cable are given unique twist lay lengths and the same twist directions. The use of unique twist lay lengths serves to decrease the level of crosstalk between adjacent twisted pairs. However, it causes the coupling strength between each possible pair of twisted-pairs in a cable to be different.
Additionally, if each adjacent twisted pairs in cable has a unique twist lay length and/or twist direction, other problems may occur. In particular, during use mechanical stress may interlink adjacent twisted pairs.
In order to obtain yet better crosstalk performance in FTP and UTP cables, for example, to meet performance standards such as the Category 6 standard, some have introduced an interior support or spline for the data cable, such as disclosed by Gaeris et al. in U.S. Pat. No. 5,789,711, issued Aug. 4, 1998, and by Gareis in U.S. Pat. No. 6,297,454, issued Oct. 2, 2001. Additional examples of such interior support for data cables are given by Prudhon in U.S. Pat. No. 5,952,615, issued Sep. 14, 1999, and also by Blouin et al. in U.S. Pat. No. 6,365,836, issued Apr. 2, 2002. Such splines serve to separate adjacent twisted pair cables and prevent interlinking of twisted pairs.
Conventional splines have the basic cross form, such as shown in
The conventional cable configuration of
During the stranding operation, the walls 104 of cable spline 101 may be stressed and thinned, allowing the twisted pairs 102 to move tangentially to the circumference of the cable in addition to radially, away from the center of the cable. This movement is undesirable, as it causes crosstalk and attenuation variation. Due to the latter, impedance also varies, exhibiting some roughness. Variation in crosstalk over time and distance is influenced by variations in center to center distance caused by tangential displacements of the twisted pairs over time and distance. The tangential displacement varies the spacing between pairs. Radial displacement predominantly affects attenuation. Variation in radial displacement cause attenuation variation, also called attenuation roughness, as the distance from the center of each twisted pair to the jacket varies. Both of these variations also incidentally have an impact upon impedance roughness.
In conventional cables, the loss factor or loss tangent of the jacketing material also has a substantial impact upon the attenuation figure of data grade cables. Attenuation increases with proximity of the transmission media to the jacket. For this reason, data cables not having an interior support such as disclosed by Gaeris et al. generally have loose fitting jackets. The looseness of the jacket reduces the attenuation figure of the cable, but introduces other disadvantages. For example, the loose fitting jacket permits the geometric relationship between the individual twisted pairs as well as the center-to-center distance to vary, thus varying impedance and crosstalk performance.
In FTP cable, the effect of the loss tangent of the jacketing material is substantially mitigated by the shield. The shielding characteristics of the foil surrounding the twisted pairs determine the effect upon different frequencies. This shielding characteristic is best described by the transfer impedance. However, measurement of the transfer impedance is difficult, especially at higher frequencies.
The performance of shielded cable can be substantially improved by individually shielding the twisted pairs. However, such cables commonly designated as STP (Individually Shielded Twisted Pairs) wires are impractical, as they require a substantial amount of time and specialized equipment or tools for termination. Additionally, the cables themselves are relatively large in diameter due to the added bulk of the shield. Bulkier cables exhibit poor flammability performance, and also occupy more space in ducts and on cross connects than less bulky cables.
The cable spline structures disclosed by Blouin et al. in U.S. Pat. No. 6,365,836, issued Apr. 2, 2002, solves the problem of attenuation due to loss tangent by increasing the distance between the twisted pairs and the cable jacket. The cable splines disclosed by Blouin, cross sections of which are shown in
While the structure described in Blouin solves the problems associated with loss tangent and controlling attenuation variation, it is still desirable to further reduce the losses due to crosstalk between twisted pairs. One method of reducing the crosstalk between twisted pairs is described by Gareis in U.S. Pat. No. 6,297,454.
In addition to suffering from the previously described problems of loss tangent, the cable spline disclosed by Gareis also introduces problems due to its shape. The elliptical shape of the cable introduces difficulties in spooling the cable, and also during installation. For example, it is desirable to spool cables as tightly as possible; to spool cables tightly, it is necessary to control their position during the spooling process. This process is made difficult when the cable does not have a circular cross-section, and may require additional time or equipment. In addition, non-circular cables may require special treatment during installation or greater pull strength due to having a preferential bend axis.
Additionally, it is desirable to further improve the cross-talk properties over the cables and cable splines previously discussed.
The present invention provides an improved high performance data cable and an improved data cable spline.
According to one aspect of the invention, a cable separator spline comprises a plurality of longitudinally extending walls joined along a central axis of the spline, and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls, wherein the pair of longitudinally extending walls includes a first wall substantially thicker than a second wall.
According to another aspect of the invention, a cable separator spline assembly comprises a plurality of longitudinally extending walls joined along a central axis of the spline, and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls, wherein a pair of opposing longitudinally extending walls have defined through them a common gap defining two separate sub-splines having T-shaped cross-sections.
According to yet another aspect of the invention, a high performance data cable comprises: a plurality of twisted pairs of insulated conductors; a cable separator spline having a plurality of longitudinally extending walls joined along a central axis of the spline, and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls,wherein the pair of longitudinally extending walls includes a first wall substantially thicker than a second wall.
According to yet another aspect of the invention, a high performance data cable comprises: a plurality of twisted pairs of insulated conductors and a cable separator spline assembly, which comprises a plurality of longitudinally extending walls joined along a central axis of the spline and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls, wherein a pair of opposing longitudinally extending walls have defined through them a common gap defining two separate sub-splines having T-shaped cross-sections.
According to yet another aspect of the invention, a high performance data cable comprises: a plurality of twisted pairs of insulated conductors; a jacket; a plurality of longitudinally extending walls connected to the jacket and extending substantially toward the center of the data cable; and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls, wherein the pair of longitudinally extending walls includes a first wall substantially thicker than a second wall.
According to yet another aspect of the invention, a cable separator comprises a plurality of longitudinally extending walls, and a plurality of longitudinally extending channels, each longitudinally extending channel defined by a pair of the longitudinally extending walls, wherein the pair of longitudinally extending walls includes a first wall substantially thicker than a second wall.
The accompanying drawings, are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
The present invention will be better understood upon reading the following detailed description of embodiments of aspects thereof in connection with the figures.
The invention provides for improved crosstalk characteristics by introducing a cable spline which retains a wire in a channel and reduces attenuation due to loss tangent, while allowing for a greater separation between twisted pairs which have stronger electromagnetic coupling. The invention also provides for a cable spline assembly have the properties described above, and which additionally provides for more shielding between strongly coupled twisted pairs as well as easier installation of the cable.
Yet another embodiment of the invention is shown in
Another embodiment of the invention is shown in
The spine assembly of
In addition to the arrangements discussed above, the subsplines having T-shaped cross-sections may also be constructed of folded layers of shielding tape. An example of such a spline-assembly is shown in
In addition to using a single layer of shielding to separate and insulate the two sub-splines having T-shaped cross-sections, other shielding arrangements are possible.
Another possible shielding arrangement for use with the invention is depicted in
According to the present invention, many different material variations are possible in each of the embodiments previously discussed.
The spline used in each of the foregoing embodiments may be formed of variety of different materials. In general, it is desirable to use a material which has a low loss tangent. Suitable material include polyolefins such as polyethylene or polypropylene, as well as copolymers of each of those materials. Additionally, the material used in the construction of the cable spline may include fire-retardant additives such as chlorinated or brominated additives with antimony oxide or aluminum or magnesium hydroxides. Other examples of materials which may be used include low dielectric loss fluoropolymers such as fluorinated ethylene propylene (FEP) or ethylene-chlorotrifluoro-ethylene (such as VATAR™, produced by Ausimont). To reduce the use of material and further reduce dielectric loss, or allow the use of higher loss materials, the materials may be foamed. Foamed material can further improve overall attenuation and both attenuation and impedance roughness because air or other foaming gasses such as nitrogen generally have lower dielectric loss than the unfoamed material.
As mentioned previously, the cables and cable splines of the present invention may contain additional materials to improve isolation and cable performance. For example, conductive materials may be deposited inside or on the surface of the splines. Materials deposited inside the splines may be distributed throughout the spline, or may fill a hollow region such as those embodiments described in connection with
If the spline is covered with or formed of an electrically conductive material, preferably a material also having a high permeability, then the shielding effectiveness of the spline according to the present invention is greater than previously known splines not having a conductive coating. The conductive surfaces of the spline may be longitudinally in contact with a surrounding foil shield. In this way the spline and the foil shield combine to form shielded sectored compartments for each twisted pair. In fact, if the shielding material on or forming the spline has a sufficient thickness to provide shielding equivalent to the shielding effectiveness of the surrounding foil shield, then performance close to STP cable can be attained. Thus, cables can be designed which have geometric characteristics similar or identical to high performance FTP cable while having substantially the electric performance of STP cable.
The foregoing cable employing a conductively coated spline is advantageous in another, unexpected way. By shielding the twisted pairs from the material of the spline, the inventive construction of this embodiment may render the loss tangent of the spline material unimportant. Therefore, the material of the spline may be chosen without regard for its loss tangent, but rather with regard to such considerations as cost, flammability, smoke production and flame spread.
Cable splines including suitable conductive shielding materials can be produced a variety of ways. The surface of a non-conductive polymeric spline can be rendered conductive by using conductive coatings, which could also be polymeric. Another possibility is to use a sufficiently conductive polymer to construct the spline.
One process which can produce a suitable coating is electrolytic metallization. However, the penetration of the coating into the grooves or channels of the spline during production can be difficult. This process tends to produce an accumulation of deposited metal at the tips of the spline arms or flanges. Another possibility would be to deposit the metal in a current less process. The most common metals used for these processes are nickel and copper. Alternatively, the cable spline could be coated by vapor deposition.
As mentioned above, conductivity can be achieved by use of conductive materials for the cable spline material. Moreover, other coatings can be combined with a spline formed of a ferrite-loaded polymer, in order to decrease pair-to-pair coupling. Such a material provides magnetic properties which improve the cross talk isolation. Moreover, if such a spline is additionally metalized at the surface, then the metal coating can be substantially smaller than in the previously described designs.
The shielding layers used in some of the embodiments of the invention may also be constructed of a variety of materials. Examples of these materials include metal foil, metal coated polymer tapes, braided wire coverings, etc.
The present invention has now been described in connection with a number of specific embodiments thereof. However, numerous modifications which are contemplated as falling within the scope of the present invention should now be apparent to those skilled in the art. Therefore, it is intended that the scope of the present invention be limited only by the scope of the claims appended hereto.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3363047 | Grove | Jan 1968 | A |
| 3819443 | Simons et al. | Jun 1974 | A |
| 5132488 | Tessier et al. | Jul 1992 | A |
| 5671313 | Schneider et al. | Sep 1997 | A |
| 5789711 | Gaeris et al. | Aug 1998 | A |
| 5952615 | Prudhon | Sep 1999 | A |
| 6288340 | Arnould | Sep 2001 | B1 |
| 6297454 | Gareis | Oct 2001 | B1 |
| 6365836 | Blouin et al. | Apr 2002 | B1 |
| 6687437 | Starnes et al. | Feb 2004 | B1 |
| 6787697 | Stipes et al. | Sep 2004 | B2 |
| Number | Date | Country |
|---|---|---|
| 1162632 | Dec 2001 | EP |
| WO0154142 | Jul 2001 | WO |
| WO02073634 | Sep 2002 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20040055781 A1 | Mar 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60364158 | Mar 2002 | US |
