Patent Publication Number: US-2009229850-A1

Title: Cable For High Speed Data Communications

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the invention is data processing, or, more specifically, cables for high speed data communications, methods for manufacturing such cables, and methods of transmitting signals on such cables. 
     2. Description of Related Art 
     High speed data communications over shielded cables are an important component to large high-end servers and digital communications systems. While optical cables provide long distance drive capability, copper cables are typically preferred in environments that require a shorter distance cable due to a significant cost savings opportunity. A typical copper cable used in environments requiring a shorter distance cable, is a twinaxial cable. A twinaxial cable is a coaxial cable that includes two insulated, inner conductors and a shield wrapped around the insulated inner conductors. Twinaxial cables are used for half-duplex, balanced transmission, high-speed data communications. In the current art however, twinaxial cables used in data communications environments are limited in performance due to a bandstop effect that attenuates signals transmitted through the conductive shield at a particular band of frequencies. Because only the signals in the frequency band are typically subject to the bandstop effect, a non-linear attenuation of signals transmitted through the conductive shield occurs. That is, signals within that particular frequency band are attenuated more than signals outside that frequency band. Such non-linear attenuation of the signals transmitted through the conductive shield is often difficult to correct without the use of high-end electronic components, which increases the overall cost of the communications system. Even so, such high-end electronic components may be in fact unable to correct the non-linear attenuation of the signals transmitted through the conductive shield. 
     For further explanation of typical twinaxial cables, therefore,  FIG. 1  sets forth a perspective view of a typical twinaxial cable ( 1   00 ). The exemplary typical twinaxial cable ( 100 ) of  FIG. 1  includes two conductors ( 106 ,  108 ) and two dielectrics ( 110 ,  112 ) surrounding the conductors. The conductors ( 106 ,  108 ) and the dielectrics ( 110 ,  112 ) are generally parallel to each other and a longitudinal axis ( 105 ). That is, the conductors ( 106 ,  108 ) and the dielectrics ( 110 ,  112 ) are not twisted about the longitudinal axis ( 105 ). 
     The typical twinaxial cable ( 100 ) of  FIG. 1  also includes a shield ( 114 ). The shield, when wrapped around the conductors of a cable, acts as a Faraday cage to reduce electrical noise from affecting signals transmitted on the cable and to reduce electromagnetic radiation from the cable that may interfere with other electrical devices. The shield also minimizes capacitively coupled noise from other electrical sources, such as nearby cables carrying electrical signals. In typical twinaxial cable, the shield has a constant width, that is, the shield does not have a variable width. The shield ( 114 ) of  FIG. 1  is wrapped around the conductors ( 106 ,  108 ). The shield ( 114 ) includes wraps ( 101 - 103 ) about the longitudinal axis ( 105 ), each wrap overlapping the previous wrap. A wrap is a  360  degree turn of the shield around the longitudinal axis ( 105 ). The typical twinaxial cable of  FIG. 1  includes three wraps ( 101 - 103 ), but readers of skill in the art will recognize that the shield may be wrapped around the inner conductors and the dielectric layers any number of times in dependence upon the length of the cable. Wrap ( 101 ) is shaded for purposes of explanation. Each wrap ( 101 - 103 ) overlaps the previous wrap. That is, wrap ( 101 ) is overlapped by wrap ( 102 ) and wrap ( 102 ) is overlapped by wrap ( 103 ). The overlap ( 104 ) created by the overlapped wraps is continuous along and about the longitudinal axis ( 105 ) of the cable ( 100 ). 
     The wraps ( 101 - 103 ) of the shield ( 114 ) create an overlap ( 104 ) of the shield that forms an electromagnetic bandgap structure (‘EBG structure’) that acts as the bandstop filter. An EBG structure is a periodic structure in which propagation of electromagnetic waves is not allowed within a stopband. A stopband is a range of frequencies in which a cable attenuates a signal. In the cable of  FIG. 1 , when the conductors ( 106 ,  108 ) carry current from a source to a load, part of the current is returned on the shield ( 114 ). The current on the shield ( 114 ) encounters the continuous overlap ( 104 ) of the shield ( 114 ) which creates in the current return path an impedance discontinuity—a discontinuity in the characteristic impedance of the cable. The impedance discontinuity in the current return path at the overlap ( 104 ) created by the wraps ( 101 - 103 ) acts as a bandstop filter that attenuates signals at frequencies in a stopband. 
     The attenuation of the signals transmitted through the cable ( 100 ) may be visually represented on a graph of the insertion loss of the cable ( 100 ). For further explanation, therefore,  FIG. 2  sets forth a graph of the insertion loss of a typical twinaxial cable. Insertion loss is the signal loss in a cable that results from inserting the cable between a source and a load. The insertion loss depicted in the graph of  FIG. 2  is the insertion loss of a typical twinaxial cable, such as the twinaxial cable described above with respect to  FIG. 1 . In the graph of  FIG. 2 , the signal ( 119 ) is attenuated ( 118 ) within a stopband ( 120 ) of frequencies ( 116 ) ranging from seven to nine gigahertz (‘GHz’). The stopband ( 120 ) has a center frequency ( 121 ) that varies in dependence upon the composition of the shield, the width of the shield, the wrap rate that the shield is wrapped around the conductors and dielectrics, and other factors as will occur to those of skill in the art. In typical twinaxial cable, the shield has a constant width. The center frequency ( 121 ) of  FIG. 2  is approximately 8 GHz. Although the exemplary stopband of  FIG. 2  is described as ranging in frequency from seven to nine GHz, readers of skill in the art will recognize that the stopband may include other frequencies, ranging from 3 GHz, for example, to greater than 9 GHz. 
     The attenuation ( 118 ) of the signal ( 119 ) in  FIG. 2  peaks at approximately −60 decibels (‘dB’) for signals with frequencies ( 116 ) in the range of approximately 8 GHz. The magnitude of the attenuation ( 118 ) of the signal ( 119 ) is dependent upon the length of the cable. The effect of the EBG structure, the attenuation of a signal, increases as the length of the EBG structure increases. A longer cable having a wrapped shield has a longer EBG structure and, therefore, a greater attenuation on a signal than a shorter cable having a shield wrapped at the same wrap rate. That is, the longer the cable, the greater the attenuation of the signal. 
     Typical twinaxial cables for high speed data communications, therefore, have certain drawbacks. Typical twinaxial cables have a bandstop filter created by overlapped wraps of a shield that attenuates signals at frequencies in a stopband. The attenuation of the signal increases as the length of the cable increases and limits data communications at frequencies in the stopband. 
     SUMMARY OF THE INVENTION 
     A cable for high speed data communications and methods for manufacturing such cable are disclosed, the cable including a first inner conductor enclosed by a first dielectric layer and a second inner conductor enclosed by a second dielectric layer. The cable also includes conductive shield material wrapped in a rotational direction at a wrap rate along and about the longitudinal axis around the inner conductors and the dielectric layers, including overlapped wraps of the conductive shield material along and about the longitudinal axis, an inner surface of the conductive shield material roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material. 
     Methods of transmitting signals on for high speed data communications are also disclosed that include transmitting a balanced signal characterized by a frequency in the range of 7-9 gigahertz on a cable, the cable comprising, the cable including a first inner conductor enclosed by a first dielectric layer and a second inner conductor enclosed by a second dielectric layer. The cable also includes conductive shield material wrapped in a rotational direction at a wrap rate along and about the longitudinal axis around the inner conductors and the dielectric layers, including overlapped wraps of the conductive shield material along and about the longitudinal axis, an inner surface of the conductive shield material roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular descriptions of exemplary embodiments of the invention as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts of exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  sets forth a perspective view of a typical prior art twinaxial cable. 
         FIG. 2  sets forth a graph of the insertion loss of a typical prior art twinaxial cable. 
         FIG. 3  sets forth a perspective view of an exemplary cable for high speed data communications according to embodiments of the present invention. 
         FIG. 4  sets forth a perspective view of a further exemplary cable for high speed data communications according to embodiments of the present invention. 
         FIG. 5  sets forth a graph of the insertion loss of an exemplary cable for high speed data communications according to embodiments of the present invention. 
         FIG. 6  sets forth a flow chart illustrating an exemplary method of manufacturing a cable for high speed data communications according to embodiments of the present invention. 
         FIG. 7  sets forth a flow chart illustrating an exemplary method of transmitting a signal on a cable for high speed data communications according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary cables for high speed data communications, methods for manufacturing such cables, and methods of transmitting signals on such cables according to embodiments of the present invention are described with reference to the accompanying drawings, beginning with  FIG. 3 .  FIG. 3  sets forth a perspective view of a cable for high speed data communications according to embodiments of the present invention. The cable ( 125 ) of  FIG. 3  includes a first inner conductor ( 134 ) enclosed by a first dielectric layer ( 132 ) and a second inner conductor ( 130 ) enclosed by a second dielectric layer ( 128 ). Although the cable ( 125 ) is described as including only two inner conductors, readers of skill in the art will immediately recognize that cables for high speed data communications according to embodiments of the present invention may include any number of inner conductors. In the cable ( 125 ) of  FIG. 3 , the inner conductors ( 134 ,  130 ) also include an optional drain conductor ( 136 ). A drain conductor is a non-insulated conductor electrically connected to the earth potential (‘ground’) and typically electrically connected to conductive shield material ( 126 ). 
     The cable ( 125 ) of  FIG. 3  also includes conductive shield material ( 126 ) wrapped in a rotational direction ( 123 ) at a wrap rate along and about the longitudinal axis ( 122 ) around the inner conductors ( 134 ,  130 ) and the dielectric layers ( 132 ,  128 ), including overlapped wraps ( 127 ,  129 ,  133 ) of the conductive shield material ( 126 ) along and about the longitudinal axis ( 122 ). The wrap rate is the number of times that the conductive shield material is wrapped around the inner conductors per unit of measure along the longitudinal axis. The wrap rate, for example, may be  30  wraps per foot along a two foot cable or  200  wraps per meter along a  15  meter cable. 
     In the example of  FIG. 3 , the inner surface ( 139 ) of the conductive shield material ( 126 ) is roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material ( 126 ). The inner surface ( 139 ) of the conductive shield material ( 126 ) is the surface of the conductive shield material ( 126 ) that faces towards the longitudinal axis ( 122 ). The inner surface ( 139 ) may be roughened using any number of techniques that will occur to those of skill in the art such as, for example, mechanical roughening, machining, microfabrication, sanding, sandblasting, milling, turning, electro-chemical etching, selective plating, laser-machining, plasma sputtering, and so on. 
     In the example of  FIG. 3 , the roughness of the inner surface ( 139 ) of the conductive shield material ( 126 ) varies in intensity along the conductive shield material ( 126 ). In fact, the inner surface ( 139 ) of each of the wraps ( 127 ,  129 ,  133 ) has a different roughness intensity level ( 170 ,  172 ,  174 ) as indicated by the density of the stippling in  FIG. 3 . Readers will note that although the stippling appears on the outside of some parts of the cable in  FIG. 3 , such stippling is shown for explanation and clarity and is intended to represent the roughened inner surface on that portion of the conductive shield material. 
     The roughness intensity level is a measure of the irregularities of a surface of a material such as, for example, the height of the irregularities, the width between the irregularities, the wave and lay of the irregularities, and so on. Such irregularities may be measured in any manner as will occur to those of ordinary skill in the art such as, for example, using an arithmetic average roughness algorithm, root-mean-square roughness algorithm, and so on. In the example of  FIG. 3 , the inner surface ( 139 ) of wrap ( 127 ) has a first roughness intensity level ( 170 ) that is fairly smooth compared to the roughness intensity levels of the other wraps ( 129 ,  133 ). The inner surface ( 139 ) of wrap ( 129 ) has a second roughness intensity level ( 172 ) that is rougher than the inner surface ( 139 ) of wrap ( 127 ) but smoother than the inner surface ( 139 ) of wrap ( 133 ). The inner surface ( 139 ) of wrap ( 133 ) has a third roughness intensity level ( 174 ) that is the roughest compared to the roughness intensity levels of the other wraps ( 127 ,  129 ). 
     In the cable ( 125 ) of  FIG. 3 , the overlapped wraps ( 127 ,  129 ,  133 ) of the conductive shield material ( 126 ) create a bandstop filter that attenuates signals at frequencies in a stopband. That is, when the inner conductors ( 134 ,  130 ) carry current from a current source to a load, a part of the current is returned on the conductive shield material ( 126 ). The current on the conductive shield material ( 126 ) encounters the continuous overlap ( 131 ) of the conductive shield material ( 126 ) which creates an impedance discontinuity in the current return path. The impedance discontinuity acts as a bandstop filter that attenuates signals at frequencies in a stopband. The stopband is characterized by a center frequency that is dependent upon the composition of the conductive shield material ( 126 ), the width of the conductive shield material ( 126 ), and the wrap rate of the wraps. In the cable ( 125 ) of  FIG. 3 , however, the inner surface ( 139 ) of the conductive shield material ( 126 ) is roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material ( 126 ). Specifically, the roughened inner surface ( 139 ) of the conductive shield material ( 126 ) in  FIG. 3  reduces the attenuation of signals having frequencies in the stopband. The roughened inner surface ( 139 ) of the conductive shield material ( 126 ) reduces the attenuation of signals having frequencies in the stopband by spreading the attenuation across multiple frequencies while decreasing the maximum attenuation of the signals in the stopband. 
     In the cable of  FIG. 3 , the conductive shield material ( 126 ) may be a strip of aluminum foil having a width that is relatively small with respect to the length of the cable ( 125 ). The width of the strip of aluminum foil is relatively small with respect to the length of the cable, such that, when the strip of aluminum is wrapped around the inner conductors and the dielectric layers, at least one overlapped wrap is created. 
     Although the conductive shield material ( 126 ) is described as a strip of aluminum foil, those of skill in the art will recognize that conductive shield material ( 126 ) may be any conductive material capable of being wrapped around the inner conductors of a cable, such as copper or gold. The cable ( 125 ) of  FIG. 3  may also include a non-conductive layer that encloses the conductive shield material ( 126 ) and the twisted first and second inner conductors ( 134 ,  138 ). The non-conductive layer may be any insulating jacket useful in cables for high speed data communications as will occur to those of skill in the art. 
     In the example of  FIG. 3 , readers will note that the inner surface of the conductive shield material is not roughened uniformly. That is, the roughness of the inner surface of the conductive shield material varies in intensity along the conductive shield material. In other embodiments, however, the inner surface of the conductive shield material may be roughened uniformly to reduce non-linear attenuation of signals transmitted through the conductive shield material. For further explanation, consider  FIG. 4  that sets forth a perspective view of a further exemplary cable ( 125 ) for high speed data communications according to embodiments of the present invention. 
     The cable ( 125 ) of  FIG. 4  is similar to the cable described in  FIG. 3 . That is, the cable ( 125 ) of  FIG. 4  includes a first inner conductor ( 134 ) enclosed by a first dielectric layer ( 132 ) and a second inner conductor ( 130 ) enclosed by a second dielectric layer ( 128 ). In the cable ( 125 ) of  FIG. 4 , the inner conductors ( 134 ,  130 ) may also include an optional drain conductor ( 136 ). The cable ( 125 ) of  FIG. 4  also includes conductive shield material ( 126 ) wrapped in a rotational direction ( 123 ) at a wrap rate along and about the longitudinal axis ( 122 ) around the inner conductors ( 134 ,  130 ) and the dielectric layers ( 132 ,  128 ), including overlapped wraps ( 127 ,  129 ,  133 ) of the conductive shield material ( 126 ) along and about the longitudinal axis ( 122 ). The wrap rate is the number of times that the conductive shield material is wrapped around the inner conductors per unit of measure along the longitudinal axis. The wrap rate, for example, may be 30 wraps per foot along a two foot cable or  200  wraps per meter along a 15 meter cable. 
     In the example of  FIG. 4 , the inner surface ( 139 ) of the conductive shield material ( 126 ) is uniformly roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material ( 126 ). That is, each portion of the inner surface ( 139 ) of the conductive shield material ( 126 ) has approximately the same roughness intensity level as measured using an arithmetic mean roughness algorithm, root-mean-square roughness algorithm, or any other algorithm as will occur to those of skill in the art. As mentioned above, the inner surface ( 139 ) may be roughened using any number of techniques that will occur to those of skill in the art such as, for example, mechanical roughening, machining, microfabrication, sanding, sandblasting, milling, turning, electrochemical etching, selective plating, laser-machining, plasma sputtering, and so on. Readers will note that the roughness of the inner surface of the conductive shield material illustrated in  FIG. 4  is indicated by the density of the stippling in  FIG. 4 . Readers will further note that although the stippling appears on the outside of some parts of the cable in  FIG. 4 , such stippling is shown for explanation and clarity and is intended to represent the roughened inner surface on that portion of the conductive shield material. 
     In the cable ( 125 ) of  FIG. 4 , the overlapped wraps ( 127 ,  129 ,  133 ) of the conductive shield material ( 126 ) create a bandstop filter that attenuates signals at frequencies in a stopband. That is, when the inner conductors ( 134 ,  130 ) carry current from a current source to a load, a part of the current is returned on the conductive shield material ( 126 ). The current on the conductive shield material ( 126 ) encounters the continuous overlap ( 131 ) of the conductive shield material ( 126 ) which creates an impedance discontinuity in the current return path. The impedance discontinuity acts as a bandstop filter that attenuates signals at frequencies in a stopband. The stopband is characterized by a center frequency that is dependent upon the composition of the conductive shield material ( 126 ), the width of the conductive shield material ( 126 ), and the wrap rate of the wraps. In the cable ( 125 ) of  FIG. 4 , however, the inner surface ( 139 ) of the conductive shield material ( 126 ) is uniformly roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material ( 126 ). Specifically, the roughened inner surface ( 139 ) of the conductive shield material ( 126 ) in  FIG. 4  reduces the attenuation of signals having frequencies in the stopband. The roughened inner surface ( 139 ) of the conductive shield material ( 126 ) reduces the attenuation of signals having frequencies in the stopband by spreading the attenuation across multiple frequencies while decreasing the maximum attenuation of the signals in the stopband. 
     The attenuation of the signals transmitted through the cables ( 125 ) illustrated in  FIGS. 3 and 4  may be visually represented on a graph of the insertion loss of the cables ( 126 ). For further explanation,  FIG. 5  sets forth a graph of the insertion loss of an exemplary cable for high speed data communications according to embodiments of the present invention. As mentioned above, the insertion loss is the signal loss in a cable that results from inserting the cable between a source and a load. The insertion loss depicted in the graph of  FIG. 5  is the insertion loss of an exemplary cable for high speed data communications according to embodiments of the present invention, such as the cables described above with respect to  FIGS. 3 and 4 . In the graph of  FIG. 5 , the signal ( 119 ) is attenuated ( 118 ) within a stopband ( 120 ) of frequencies ( 116 ) ranging from seven to nine gigahertz (‘GHz’). The stopband ( 120 ) has a center frequency ( 121 ) that varies in dependence upon the composition of the shield, the width of the shield, the wrap rate that the shield is wrapped around the conductors and dielectrics, and other factors as will occur to those of skill in the art. The center frequency ( 121 ) of  FIG. 5  is approximately 8 GHz. Although the exemplary stopband of  FIG. 5  is described as ranging in frequency from seven to nine GHz, readers of skill in the art will recognize that the stopband may include other frequencies, ranging from 3 GHz, for example, to greater than 9 GHz. 
     In an exemplary cable for high speed data communications according to embodiments of the present invention, the inner surface of the conductive shield material is roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material. When compared to  FIG. 2 , readers will note that the difference between the attenuation of signals within the stopband ( 120 ) of  FIG. 5  and the attenuation of signals outside the stopband ( 120 ) of  FIG. 5  is less than the difference between the attenuation of signals within the stopband ( 120 ) of  FIG. 2  and the attenuation of signals outside the stopband ( 120 ) of  FIG. 2 . In such a manner, the roughened inner surface of the conductive shield material reduces the non-linear attenuation of signals transmitted through the conductive shield material. 
     Although the roughened inner surface reduces non-linear attenuation of signals transmitted through the conductive shield material, readers will note that when compared to the insertion loss graph of  FIG. 2 , the overall attenuation of the signal is greater due to the roughened inner surface of the conductive shield material. Such an overall attenuation illustrated in  FIG. 5  that is more linear than the non-linear attenuation illustrated in  FIG. 2  is advantageous because such linear signal attenuations are more easily and inexpensively corrected by a receiver or transmitter than non-linear signal attenuations. 
     For further explanation  FIG. 6  sets forth a flow chart illustrating an exemplary method of manufacturing a cable for high speed data communications according to embodiments of the present invention. The method of  FIG. 6  includes wrapping ( 138 ), in a rotational direction at a wrap rate along and about a longitudinal axis, conductive shield material around a first inner conductor enclosed by a first dielectric layer and a second inner conductor enclosed by a second dielectric layer, including overlapping wraps of the conductive shield material along and about the longitudinal axis. In the method of  FIG. 6 , an inner surface of the conductive shield material is roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material. In the method of  FIG. 6 , the conductive shield material may be a strip of aluminum foil having a width that is relatively small with respect to the length of the cable. 
     In the method of  FIG. 6 , the overlapped wraps of the conductive shield material create a bandstop filter that attenuates signals at frequencies in a stopband. In the method of  FIG. 6 , the stopband is characterized by a center frequency that is dependent upon the composition of the conductive shield material, the width of the conductive shield material, and the wrap rate. In the method of  FIG. 6 , however, the roughened inner surface of the conductive shield material reduces the attenuation of signals having frequencies in the stopband and increases the attenuation of signal outside of the stopband to reduce the non-linear attenuation of signal transmitted through the conductive shield material. 
     In the method of  FIG. 6 , wrapping ( 138 ) conductive shield material around the inner conductors includes wrapping ( 140 ) conductive shield material around the inner conductors, the dielectric layers, and also a drain conductor. The method of  FIG. 6  also includes enclosing ( 146 ) the conductive shield material and the first and second inner conductors in a non-conductive layer. 
     For further explanation  FIG. 7  sets forth a flow chart illustrating an exemplary method of transmitting a signal on a cable ( 162 ) for high speed data communications according to embodiments of the present invention. The method of  FIG. 7  includes transmitting ( 150 ) a balanced signal ( 148 ) characterized by a frequency in the range of approximately 7-9 gigahertz on a cable ( 162 ). 
     The cable ( 162 ) on which the signal ( 148 ) is transmitted includes a first inner conductor enclosed by a first dielectric layer and a second inner conductor enclosed by a second dielectric layer. The cable ( 162 ) also includes conductive shield material wrapped in a rotational direction at a wrap rate along and about the longitudinal axis around the inner conductors and the dielectric layers. The conductive shield material includes overlapped wraps along and about the longitudinal axis. An inner surface of the conductive shield material is roughened to reduce non-linear attenuation of signals transmitted through the conductive shield material. 
     In method of  FIG. 7  transmitting ( 150 ) a balanced signal on a cable includes transmitting ( 152 ) the balanced signal on the cable where the overlapped wraps of the conductive shield material create a bandstop filter that attenuates signals at frequencies in a stopband. In the method of  FIG. 7 , the roughened inner surface of the conductive shield material reduces the attenuation of signals having frequencies in the stopband and increases the attenuation of signal outside of the stopband to reduce the non-linear attenuation of signal transmitted through the conductive shield material. 
     In the method of  FIG. 7 , transmitting ( 152 ) the balanced signal on the cable includes transmitting ( 154 ) the balanced signal on the cable where the stopband is characterized by a center frequency, and the center frequency is dependent upon the composition of the conductive shield material, the width of the conductive shield material, and the wrap rate. In the method of  FIG. 7 , transmitting ( 150 ) a balanced signal on a cable also includes transmitting ( 158 ) the balanced signal on the cable where the conductive shield material comprises a strip of aluminum foil having a width that is relatively small with respect to the length of the cable. 
     In the method of  FIG. 7 , transmitting ( 150 ) a balanced signal on a cable also includes transmitting ( 156 ) the balanced signal on the cable where conductive shield material wrapped around a first inner conductor enclosed by a first dielectric layer and a second inner conductor enclosed by a second dielectric layer further comprises conductive shield material wrapped around the inner conductors, the dielectric layers, and also a drain conductor. In the method of  FIG. 7 , transmitting ( 150 ) a balanced signal on a cable also includes transmitting ( 158 ) the balanced signal on the cable, where the cable includes a non-conductive layer that encloses the conductive shield material and the first and second inner conductors. 
     It will be understood from the foregoing description that modifications and changes may be made in various embodiments of the present invention without departing from its true spirit. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense. The scope of the present invention is limited only by the language of the following claims.