Patent Application
20120067614
A cable that uses a split tube applied over cable elements that require separation and isolation, such as wire pairs and the like. The split tube may be extruded separately from the other cable components, particularly the wire pairs, thereby reducing the risk of damage to the wire pairs during the extrusion process.
As seen in
Conventional cables are typically made by first fabricating the individual components, such as the twisted pairs and other elements. These components are then combined together at an assembly operation, where typically another overall twist is also applied to form the cable core. An overall extruded jacket is then applied. When a conventional cable uses another element, such as the crossweb 40 discussed above, the pairs are separated from the interference of the other pairs within the cable; however the pairs are still susceptible to the transient affects of the overall jacket. Typically, overall jackets are made with poly-vinyl chloride or PVDF compounds loaded with flame retardants and smoke suppressants to meet regulatory flame and smoke requirements for fire safety. These jacket materials often have poor dissipative properties, which cause the signal traveling along the pair to be excessively attenuated. Below is a table listing the typical materials used in communication cable construction. HDPE, FEP and MFA are typically used for the insulation coating on wire and crosswebs, while PVDF and FRPVC are typically used for an overall cable jacket.
Thus, even if a crossweb is used, the pairs are still exposed to the affects of the relatively higher dissipation factor of overall cable jacket.
Moreover, the manufacturing process exposes the wire pairs to risk of damage due to, for example, scraping the outer surface of the pair, unraveling or altering the twist of the pairs and possibly stretching the conductor of the pairs. The affects of these types of damage cause poor performance in required communication cable parameters such as return loss, insertion loss, pair to pair crosstalk and pair balance properties such as transverse conversion loss.
Accordingly, the present invention provides a cable that includes a cable core that has a plurality of twisted wire pairs. Each wire of the pairs is insulated. A separating layer surrounds at least one pair of the plurality of twisted wire pairs. The separating layer may be a tube with a longitudinal split therein. In accordance with one embodiment, the tube may be formed of a dielectric material. In accordance with another embodiment, the tube may be coated with a conductive material. In yet another embodiment of the invention, a shielding layer may be added to the tube. In still another embodiment of the invention, the tube may be a mixture of dielectric and conductive materials.
The present invention also provides a method of constructing a cable that comprises the steps of providing a plurality of wires; extruding insulation over each of the individual wires; twisting the wires into a plurality of wire pairs after the extrusion of insulation of the individual wires; extruding a tube wherein the extrusion of the tube is separate from the extrusion of the insulation over the individual wires; and applying the tube to at least one of the twisted wire pairs.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.
Referring to
Referring to the
A separating layer 230 surrounds at least one wire pair 210, thereby providing a barrier for electrical isolation from the remaining wire pairs. Preferably, each of the wire pairs 210 is surrounded by a separating layer 230 to provide maximum protection against crosstalk. The separating layer 230 is preferably a tube that completely surrounds the wire pair. The tube may include a longitudinal split 240 therein. As seen in
The separating layer or tube 230 is preferably formed of a dielectric material that may be solid or foam and preferably has good dissipative properties. The dielectric material preferably has a dissipation factor less than 0.001. Because the separating layer 230 surrounds each wire pair with a material having good dissipative properties, each pair is protected from the negative affects of the overall cable jacket, that is excessive attenuation of the pair. For example, the tube 230 may be formed of a polyolefin, such as polypropylene or polyethylene, or a fluoropolymer, such as FEP, ECTFE, MFA, PFA and PTFE. The tube 230 may be wrapped around one or more of the wire pairs 210 by inserting the pairs through the longitudinal split 240 of the tube. To avoid damage to the wire pairs 210 and their insulation during extrusion of the cable, the separating tube 230 is preferably extruded separately from the cable 200 and its wire pairs 210. The separating tube 230 is then split. In other words, for the wire pair or pairs that are to be received in the tube 230, they will be extruded separately from the tube or tubes 230. Thus, once the insulation for the wire pairs has been extruded on the individual wires and the wires have been twisted, one or more tubes 230 may be applied to one or more wire pairs, respectively, to provide sufficient crosstalk isolation between the pairs.
As describe above, the tube 230 may be applied to any number of the pairs 210 of the cable including to just one pair or all of the plurality of pairs. By using one or more tubes 230 as barriers between the pairs 210, interference from capacitive coupling is significantly reduced, because the pair or pairs are completely surrounded by the tube. By reducing interference, the electrical characteristics, such as near end crosstalk, insertion loss and return loss of the pairs of cable 200 are significantly improved.
As seen in
Because the tube 330 is formed separately from the remaining components of the cable 300, in the same manner as described above with respect to the first embodiment, the conductive coating 350 may be easily added to the outer surface of the tube 330 before the tube 330 is applied to the wire pair or pairs 210.
Another advantage to using the tube with the conductive coating 350 is the reduced size of the individual insulated conductors in the pair 210. In particular, when the separating layer or tube 330 includes the conductive coating 350, the separating layer or tube 330 preferably has a thickness that is at least 25% of the insulation thickness of the individual conductors in the pair 210. Thus, the overall size of the pair 210 with the tube 330 and coating 350 is smaller than a conventional cable pair of the same impedance.
Because the tube 430 is formed separately from the remaining components of the cable 400, the shielding layer 450 may be easily wrapped around the tube 430. The shielding layer 450 may be foils or screen printed layers containing alloys or mixtures of conductive elements, such as iron oxides, nickel, zinc, silver, carbon and the like. Again, elimination of the cross web 40 significantly reduces the size of the cable. Moreover, the separating tube 430 and shielding layer 450 of the present invention more effectively isolates the wire pairs than a crossweb. That in turn allows less, i.e. not as thick, insulation to be used to insulate each conductor, which also contributes to the overall reduction in size of the cable. That is, like the tube 330, the thickness of the tube 430 is preferably at least 25% of the insulation thickness of the individual conductors, thereby allowing a reduction in the conductor insulation thickness and thus reducing the size or diameter of the pair. By reducing interference, the cable can accommodate high data transmission speeds, such as in 40 Gb/s Ethernet applications, and has an improved performance.
As an alternative to adding the conductive coating, as in the second embodiment, or the shielding layer of the third embodiment to the dielectric tube, a conductive material or particles may be infused into the dielectric material of the tube. That creates a conductive or semi-conductive tube that provides shielding without the added a coating or shielding layer. For example, the separating tube may be formed of a poly-olefin, such as polypropylene or polyethylene, or a fluoropolymer, such as FEP, ECTFE, MFA, PFA and PTFE, that contains conductive particles such as, aluminum, copper, iron oxides, nickel, zinc, silver and metallic coated carbon or graphite nano-fibers.
While particular embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. For example, although four pairs are illustrated, any number of wire pairs may be used with the cable of the present invention. And the tube of any of the embodiments may be applied to one or more of the pairs. Also, the tube of any of the embodiments may be applied to other cable components, including a jacket around the entire cable core.
This application claims priority under 35 U.S.C. §119 to U.S. provisional application No. 61/384,978, the subject matter of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61384978 | Sep 2010 | US |
