Abstract:
A hybrid cable has optical conductors and electrical conductors. The electrical conductors are selected to have varying resistances per unit length, depending upon the distance from a power source at which the conductor is expected to terminate. The use of varying resistance conductors can be used to balance the power supplied to external devices and to lower cable cost, size, and weight.

Description:
PRIORITY APPLICATION 
     This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application No. 61/447,215, filed on Feb. 28, 2011, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     SUMMARY 
     According to a first aspect, a hybrid cable assembly comprises a jacket, at least one first electrical conductor disposed within the jacket, the first electrical conductor having a first resistance per unit length, and at least one second electrical conductor disposed within the jacket, the second electrical conductor having a second resistance per unit length, and a plurality of optical fibers. The first resistance per unit length is greater than the second resistance per unit length. 
     According to a second aspect, a method of connecting a hybrid cable assembly to remote devices comprises providing a cable assembly comprising at least one first electrical conductor pair, the first electrical conductor having a first resistance per unit length; at least one second electrical conductor pair, the second electrical conductor having a second resistance per unit length; and a plurality of optical fibers, wherein the first resistance per unit length is greater than the second resistance per unit length. The method further comprises electrically connecting the cable assembly to a power source; connecting the at least one first electrical conductor pair to a first remote device at a first tap location; and connecting the at least one second electrical conductor pair to a second remote device at a second tap location, the second tap location being downstream from the first tap location in relation to the power source. 
     According to the above aspects, the use of varying resistance conductors can be used to balance the power supplied to external devices and to lower cable cost, size, and weight, as well as providing additional advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system/assembly components and/or method steps, as appropriate, and in which: 
         FIG. 1  is cross-sectional view of a hybrid cable assembly according to a first embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a midspan section of a hybrid cable assembly  10  having both optical fibers and metallic electrical conductors. The cable assembly  10  includes a jacket  20  surrounding a group of optical fibers  30 , a first group of electrical conductors  40 , and a second group of electrical conductors  50 . 
     The cable assembly  10  can be of the type used to provide data communications and power in distributed antenna systems. In such applications, the electrical conductors  40 ,  50  can provide, for example, AC and/or DC power to remote devices such as antenna units (not shown), and the optical fibers  30  can provide voice, data, and other communications signals to the remote devices. The remote antenna units can include active electronics and RF transmitting elements powered by the electrical conductors  40 ,  50 . The cable assembly  10  can be, for example, connected to a source of downloaded communications data and to a source of electrical power connected to an upstream end of the assembly. The data and/or power sources are located in an upstream direction generally indicated by the arrow  60 . A number of remote devices such as remote antenna units may be located downstream from data/power sources in a downstream direction generally indicated by the arrow  62 . 
     In one application, to provide power and data connectivity to remote devices, tap points are cut into the cable jacket  20  and selected optical fibers and electrical conductors are connected to one or more remote devices through the tap points. In  FIG. 1 , a first tap location  70  is formed in the jacket  20  at a first location along the cable assembly  10 , and a second tap location  80  is formed in the cable assembly jacket  20  at location downstream from the first tap location  70 . According to one aspect of the present embodiment, the electrical conductors in the first group  40  have a higher resistance per unit length than the electrical conductors in the second group  50 . The difference in resistance per unit length can be used to compensate for the difference in distance between the power source and the two tap points  70 ,  80 . 
     The first group of conductors  40  can include, for example, one or more pairs of conductors capable of providing AC and/or DC power to remote devices. The conductor pairs can be, for example, metallic, twisted pair conductors. The second group of conductors  50 , and additional groups, if present, can also include twisted pair conductors. 
     The difference in resistance per unit length can be accomplished by, for example, using similar conductive materials in the conductors  40 ,  50 , but using conductors of larger cross-section for the second group  50 . For example, the conductors in the first group  40  can be 20 AWG conductors, and the conductors in the second group  50  can be 16 AWG conductors. Alternatively, more highly conductive materials can be used in the second group  50 . The resistance, measured in for example, ohms per unit length, can be at least ten per cent greater in the first group of conductors  40 . In another embodiment, resistance per unit length, can be at least twenty per cent greater in the first group of conductors  40 . 
     Accordingly, rather than using heavier conductors to provide power to all tap points, smaller and cheaper conductors can be used to provide power to tap locations connected by a shorter conductor length. The overall cost, as well as the size and weight of the assembly  10  can thereby be reduced. Smaller, lighter assemblies are also easier for technicians to install. The resistance of the various conductors  40 ,  50  can also be calculated so that all of the tap points along the assembly receive approximately the same power. 
     According to the present embodiments, power supply to remote devices at different tap locations is passively balanced by the selection of certain conductor types. Active power conditioning at the source is therefore not necessary. In one embodiment, the conductors of various groups can thus be connected at a single terminal. 
     In the arrangement shown in  FIG. 1 , the tap points can be used to connect any number of optical and electrical conductors to one or more devices. The devices can be, for example, opto-electronic devices utilizing both electrical and optical communication signals, as well as electrical power. The exemplary cable assembly  10  includes four optical fibers and four conductors accessed at two tap points. Any number of fibers and tap points may be included, however. 
     Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.