Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2003-01-28
2004-09-07
Mayo, III, William H. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S1130AS
Reexamination Certificate
active
06787697
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cable channel filler or spline and to a cable having the channel filler or spline. More particularly, the present invention relates to a cable channel filler having a shield, formed from a foil tape, embedded therein and having a plurality of shield legs with the shield legs forming a plurality of channel filler/cable pockets.
BACKGROUND OF THE INVENTION
Electronic cables provide a highway through which much of today's digital information travels. Many of the cables which transmit digital information utilize a plurality of twisted pair cables. These twisted pair cables, to satisfy high-speed digital requirements, need to transmit information at high frequencies. Unfortunately, high frequencies, generally transmitted at extremely low voltages, are susceptible to electronic interference. For instance, near end cross-talk between twisted pairs within the same cable, referred to in the industry as NEXT, can interfere with high frequency sign al transmission.
To control NEXT in unshielded twisted pair (UTP) cables, the industry typically resorts to extremely short lay lengths and/or a central channel filler member that acts to physically separate the twisted pairs in order to improve crosstalk performance. The ultimate control for crosstalk is to individually shield the twisted pairs (ISTP) and electrically isolate them from one another by grounding the common shield plane. Though effective, these cables are typically quite expensive to purchase and install.
U.S. Pat. Nos. 5,789,711, 5,969,295 and 5,519,173 each describe methods used to physically separate twisted pairs with a shaped central filler in UTP or screen twisted pair cables. These configurations provide some isolation due to physical separation of the UTP's, but do not provide the benefit of a conductive isolating member between the pairs.
U.S. Pat. No. 5,952,615 describes the embodiment of an ISTP cable that utilizes a central rod filler surrounded with a shield, and an overall shield to fully isolate each twisted pair. This configuration typically requires that the shielding members be grounded and is contrary to my UTP invention. In addition, one embodiment proposes two metal tapes inside the fins of the central rod filler configures in a cruciform shape. This configuration of the two metal tapes is not desirable in that it allows the possibility of electromagnetic leakage between the joining point of the two tapes. In addition, the close proximity of the shield surrounding the entire circumference of the twisted pairs adversely affects the impedance and attenuation of the cable's twisted pairs. To maintain required impedance and attenuation values, the ISTP design requires that additional insulation material and copper volume be added to the twisted pairs, increasing the size and cost of the cable, both undesirable. Also, the proximity of the shield adversely affects the stability of electrical parameters such as impedance, attenuation and return loss.
U.S. Pat. No. 3,819,443 describes a shielding member comprised of laminated strips of metal and plastic materials that are cut, bent and assembled to define radial branches of a shielding member. This configuration also has many of the same problems previously described. The assembly of the tapes allows a channel for electromagnetic leakage to be transmitted from opposite pairs.
SUMMARY OF THE INVENTION
Our cable improves the isolation of a plurality of twisted pairs from each other by having a channel filler with a plurality of longitudinally extending tubular pockets and an internal metal shield. In some instances, it is preferred that the channel filler cable pockets have a cross-sectional area that is equal to or greater than the diameter of the envelope area of the wire(s) or cable(s) that are to be placed in each of the pockets. The metal shield is embedded in the channel filler to isolate each of the channel filler pockets. The channel filler shield is preferably a single tape that is folded to the conformity of the shape of the channel filler and extends into and is embedded by each of the pocket legs. The single shield tape is folded to provide a plurality of fins or legs so that there is a shield leg for each of the channel filler pocket legs. We also provide an improved two tape shield. In the two tape shield a first shield tape is folded to provide the plurality of shield legs and the second shield tape provides one shield leg. The second shield leg has 20-50%—at least {fraction (1/16)} inch of one side thereof being encased by a folded over portion of one of the first shield tape legs.
A communication cable manufactured using the channel filler of our invention generally has an unshielded twisted pair cable in each pocket. Then the twisted pair containing channel filler is jacketed.
The present invention and the advantages thereof will become more apparent upon consideration of the following detailed description when taken in conjunction with the accompanying drawings
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Schaffstein Andrew David
Stipes Jason
Barnes & Thornburg LLP
Belden Wire & Cable Company
Conte James B.
Mayo III William H.
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