Patent Publication Number: US-7220149-B2

Title: Communication plug with balanced wiring to reduce differential to common mode crosstalk

Description:
RELATED APPLICATIONS  
     The present application claims priority from U.S. Provisional Patent Application Ser. Nos. 60/633,783, filed Dec. 7, 2004, entitled Communication Plug with Balanced Wiring to Minimize Differential to Common Mode Crosstalk and from U.S. Provisional Patent Application Ser. No. 60/648,002, filed Jan. 28, 2005, entitled CONTROLLED MODE CONVERSION PLUG FOR REDUCED ALIEN CROSSTALK, the disclosures of which are hereby incorporated herein in their entireties. 
    
    
     FIELD OF THE INVENTION  
     The present invention relates generally to communication connectors and more particularly to near-end crosstalk (NEXT) compensation in communication connectors. 
     BACKGROUND OF THE INVENTION  
     In an electrical communication system, it is sometimes advantageous to transmit information signals (video, audio, data) over a pair of wires (hereinafter “wire-pair” or “differential pair”) rather than a single wire, wherein the transmitted signal comprises the voltage difference between the wires without regard to the absolute voltages present. Each wire in a wire-pair is susceptible to picking up electrical noise from sources such as lightning, automobile spark plugs and radio stations to name but a few. Because this type of noise is common to both wires within a pair, the differential signal is typically not disturbed. This is a fundamental reason for having closely spaced differential pairs. 
     Of greater concern, however, is the electrical noise that is picked up from nearby wires or pairs of wires that may extend in the same general direction for long distances and not cancel differentially on the victim pair. This is referred to as differential crosstalk. Particularly, in a communication system where a modular plug often used with a computer is to mate with a modular jack, the electrical wires (conductors) within the jack and/or plug also can produce near-end crosstalk (NEXT) (i.e., the crosstalk measured at an input location corresponding to a source at the same location). This crosstalk occurs from closely-positioned wires over a short distance. In all of the above situations, undesirable signals are present on the electrical conductors that can interfere with the information signal. As long as the same noise signal is added to each wire in the wire-pair, the voltage difference between the wires will remain about the same and differential cross-talk does not exist. 
     Crosstalk can be classified as either differential crosstalk, as described above, in which the crosstalk signal appears as a difference in voltage between two conductors of a differential pair, or common mode crosstalk, in which the crosstalk signal appears common to both conductors of a differential pair. Differential crosstalk or common mode crosstalk appearing in a communication channel can result from sources that are either differential mode or common mode in nature. 
     U.S. Pat. No. 5,997,358 to Adriaenssens et al. (hereinafter “the &#39;358 patent”) describes a two-stage scheme for compensating differential to differential NEXT for a plug-jack combination (the entire contents of the &#39;358 patent are hereby incorporated herein by reference, as are U.S. Pat. Nos. 5,915,989; 6,042,427; 6,050,843; and 6,270,381). Connectors described in the &#39;358 patent can reduce the internal NEXT (original crosstalk) between the electrical wire pairs of a modular plug by adding a fabricated or artificial crosstalk, usually in the jack, at one or more stages, thereby canceling or reducing the overall crosstalk for the plug-jack combination. The fabricated crosstalk is referred to herein as a compensation crosstalk. This idea can often be implemented by crossing the path of one of the differential pairs within the connector relative to the path of another differential pair within the connector twice, thereby providing two stages of NEXT compensation for that pair-to-pair relationship. This scheme can be more efficient at reducing the NEXT than a scheme in which the compensation is added at a single stage, especially when the second and subsequent stages of compensation include a time delay that is selected to account for differences in phase between the offending and compensating crosstalk. This type of arrangement can include capacitive and/or inductive elements that introduce multi-stage crosstalk compensation, and is typically employed in jack lead frames and PWB structures within jacks. These configurations can allow connectors to meet “Category 6” performance standards set forth in ANSI/EIA/TIA 568, which are primary component standards for mated plugs and jacks for transmission frequencies up to 250 MHz. 
     Alien NEXT is the differential crosstalk that occurs between communication channels. Obviously, physical separation between jacks will help and/or typical crosstalk approaches may be employed. However, a problem case may be “pair  3 ” of one channel crosstalking to “pair  3 ” of another channel, even if the pair  3  plug and jack wires in each channel are remote from each other and the only coupling occurs between the routed cabling. To reduce this form of alien NEXT, shielded systems containing shielded twisted pairs or foiled twisted pair configurations may be used. However, the inclusion of shields can increase cost of the system. Another approach to reduce or minimize alien NEXT utilizes spatial separation of cables within a channel and/or spatial separation between the jacks in a channel. However, this is typically impractical because bundling of cables and patch cords is common practice due to “real estate” constraints and ease of wire management. 
     In spite of recent strides made in improving mated connector (i.e., plug-jack) performance, and in particular reducing crosstalk at elevated frequencies (e.g., 500 MHz—see U.S. patent application Ser. No. 10/845,104, entitled NEXT High Frequency Improvement by Using Frequency Dependent Effective Capacitance, filed May 4, 2004, the disclosure of which is hereby incorporated herein by reference), many connectors that rely on either these teachings or those of the &#39;358 patent can still exhibit unacceptably high alien NEXT at very high frequencies (e.g., 500 MHz). As such, it would be desirable to provide connectors with reduced alien NEXT at very high frequencies. 
     SUMMARY OF THE INVENTION  
     The present invention provides communications connectors, in particular communications plugs, that may have improved crosstalk performance. As a first aspect, embodiments of the present invention are directed to a communications plug, comprising: a mounting substrate; a plurality of pairs of output terminals; and first, second, third and fourth pairs of conductors. The first, second and fourth pairs of the output terminals are arranged in immediately adjacent relationship, and a third pair of output terminals includes output terminals that are separated from each other such that a first output terminal of the third pair is positioned between the first and second pairs of output terminals, and such that a second output terminal of the third pair is positioned between the first and fourth pairs of output terminals. Each of the first, second, third and fourth pairs of conductors engages the mounting substrate and is attached for electrical communication with a respective one of the output terminals. The third pair of conductors has at least two locations in which the conductors of the pair cross each other, and is arranged such that, between the crossover locations, the third pair of conductors forms an expanded loop that brings segments of the third conductor into closer proximity to the second and fourth pairs of conductors than to the first pair of conductors. In this configuration, the plug (which in some embodiments is a communications plug) may exhibit a reduced tendency for differential to common mode crosstalk conversion, particularly between the third pair of conductors and the second and fourth pairs of conductors, which can improve alien NEXT performance between channels, particularly at elevated frequencies. 
     As a second aspect, embodiments of the present invention are directed to a communications plug, comprising: a mounting substrate; a plurality of pairs of output terminals; and first, second, third and fourth pairs of conductors. The first, second and fourth pairs of the output terminals are arranged in immediately adjacent relationship, and a third pair of output terminals includes output terminals that are separated from each other such that a first output terminal of the third pair is positioned between the first and second pairs of output terminals, and such that a second output terminal of the third pair is positioned between the first and fourth pairs of output terminals. Each of the first, second, third and fourth pairs of conductors engages the mounting substrate and is attached for electrical communication with a respective one of the output terminals. The third pair of conductors has at least two locations in which the conductors of the pair cross each other. The third pair of conductors is arranged such that, between the crossover locations, the third pair of conductors forms an expanded loop that brings segments of the third conductor into relative proximity to the first, second and fourth pairs of conductors. The positioning of the second, third and fourth pairs of conductors substantially prevents the conversion of differential mode crosstalk to common mode crosstalk between (a) the second and third pairs of conductors and (b) the third and fourth pairs of conductors. This configuration can reduce the alien NEXT experienced between a plug-jack combination, especially at elevated frequencies. 
     As a third aspect, the present invention is directed to a mounting substrate for a communications plug. The mounting substrate includes: a body formed of a dielectric material; a spreading member mounted to an upper surface of the body, the spreading member being configured to receive respective conductors on opposite sides thereof, and capture members mounted to opposing edge portions of the upper surface of the body. Each of the capture members is configured to receive a pair of conductors and maintain the pairs of conductors at a given distance from conductors received in the spreading member channels. This configuration can position the respective conductors such that alien NEXT performance is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         FIG. 1  is a stylized partial perspective view of the blades and conductors of a prior art plug. 
         FIG. 2  is a stylized partial perspective view of blades and conductors of embodiments of plugs of the present invention. 
         FIG. 3  is a top perspective view of an embodiment of a communications plug according to the present invention with its housing removed. 
         FIG. 3A  is a top perspective view of the mounting sled of the plug of  FIG. 3 . 
         FIG. 4  is a bottom perspective view of the plug of  FIG. 3 . 
         FIG. 5  is a top perspective view of another embodiment of a communications plug according to the present invention with its housing removed. 
         FIG. 6  is a side view of the plug of  FIG. 3 . 
         FIG. 7  is a top perspective view of another embodiment of a communications plug according to the present invention with its housing removed. 
         FIG. 8  is a perspective view of another embodiment of a mounting sled for a communication plug according to the present invention. 
         FIG. 9  is an exploded perspective view of the plug of  FIG. 3  showing the housing. 
         FIG. 10  is a top perspective view of the plug of  FIG. 3  with the housing in place. 
         FIG. 11  is a graph plotting differential to common mode NEXT as a function of frequency for conventional and experimental communication plugs according to the embodiment of  FIG. 3 , wherein the NEXT of interest is between conductor pairs  3  and  2 . 
         FIG. 12  is a graph plotting differential to common mode NEXT as a function of frequency for conventional and experimental communication plugs according to the embodiment of  FIG. 3 , wherein the NEXT of interest is between conductor pairs  3  and  4 . 
         FIG. 13  is a graph plotting differential to common mode NEXT as a function of frequency for conventional and experimental communication plugs according to the embodiment of  FIG. 5 , wherein the NEXT of interest is between conductor pairs  3  and  2 . 
         FIG. 14  is a graph plotting differential to common mode NEXT as a function of frequency for conventional and experimental communication plugs according to the embodiment of  FIG. 5 , wherein the NEXT of interest is between conductor pairs  3  and  4 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION  
     The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be limited to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     This invention is directed to communications connectors, with a primary example of such being a communications plug. As used herein, the terms “forward”, “forwardly”, and “front” and derivatives thereof refer to the direction defined by a vector extending from the center of the plug toward the free end of the plug, ie., away from a cable attached to the plug. Conversely, the terms “rearward”, “rearwardly”, and derivatives thereof refer to the direction directly opposite the forward direction; the rearward direction is defined by a vector that extends from the center of the plug toward the cable. The terms “lateral,” “laterally”, and derivatives thereof refer to the direction generally parallel with the plane defined by the conductors as they align at the forward end of the plug and extending away from a plane bisecting the plug in the center. The terms “medial,” “inward,” “inboard,” and derivatives thereof refer to the direction that is the converse of the lateral direction, i.e., the direction parallel with the plane defined by the conductors and extending from the periphery of the plug toward the aforementioned bisecting plane. Where used, the terms “attached”, “connected”, “interconnected”, “contacting”, “coupled”, “mounted” and the like can mean either direct or indirect attachment or contact between elements, unless stated otherwise. 
     Turning now to the figures,  FIG. 1  illustrates a typical wiring layout for a prior art communication plug  10  having four pairs of twisted wires  20   a ,  20   b ,  22   a ,  22   b ,  24   a ,  24   b ,  26   a ,  26   b . As is conventional pursuant to TIA  568 B plug wiring standards, wire pair  1  (wires  20   a ,  20   b ) is in the center of the plug  10  (connected to blades  12   a ,  12   b ), wire pair  2  (wires  22   a ,  22   b ) occupies the right side of the plug  10  (connected to blades  14   a ,  14   b ), wire pair  4  (wires  26   a ,  26   b ) occupies the left side of the plug  10  (connected to blades  18   a ,  18   b ), and wire pair  3  (wires  24   a ,  24   b ) straddles wire pair  1  (connected to blades  16   a ,  16   b ). As is conventional, each of these pairs of wires is twisted, with the lay lengths of the twists of these pairs being slightly different. Because wire pair  3  straddles wire pair  1 , the tip of pair  3  (i.e., blade  16   b  and wire  24   b ) is closer to both conductors  22   a ,  22   b  and blades  14   a ,  14   b  of pair  2  (especially in the blade region) than is the ring of pair  3  (ie., blade  16   a  and wire  24   a ). Similarly, blade  16   a  and wire  24   a  are closer to both conductors  26   a ,  26   b  and blades  18   a ,  18   b  of pair  4  than are blade  16   b  and wire  24   b , especially in the blade region. Consequently, the blades  16   a ,  16   b  and wires  24   a ,  24   b  of pair  3  are spatially unbalanced relative to the end pairs  2  and  4 , particularly in the plug blades and the region approaching the blades. 
     This imbalance typically effectively occurs from the point of contact with a connecting jack through the plug blades and the connecting wires back into the plug  10 . The magnitude of the imbalance depends on the distance into the plug  10  that the wires  24   a ,  24   b  of pair  3  remain separated before returning to the twisted configuration that is characteristic of a twisted pair. The imbalance between (a) pair  3  and pair  2  and (b) pair  3  and pair  4  can convert a differential mode signal on pair  3  to common mode crosstalk on pairs  2  and  4  in the plug  10 . Although this conversion from differential to common mode crosstalk can occur across the frequency band below 250 MHz, the resulting channel alien NEXT generated is typically minimal. However, it has been discovered in connection with the present invention that at elevated transmission frequencies (e.g., up to 500 MHz), the conversion of differential to common mode crosstalk can have a substantial detrimental impact on channel alien NEXT levels and, likely, the ability of the channel to meet FCC emission level limits, particularly at elevated transmission frequencies. 
     The imbalance typically experienced in conventional plugs  10  can be addressed by plugs of the present invention, embodiments of which are illustrated in  FIGS. 2–9 . These plugs can substantially reduce the amount of differential to common mode crosstalk conversion that occurs compared with prior art connectors. Generally speaking, it has been discovered that by reducing the differential to common mode crosstalk conversion in a plug, better alien NEXT performance can be achieved, particularly at elevated frequencies (i.e., above 250 MHz). 
     Referring now to  FIG. 2 , a stylized embodiment of a plug of the present invention, designated broadly at  30 , is illustrated therein. The plug  30  includes eight blades  32   a ,  32   b ,  34   a ,  34   b ,  36   a ,  36   b ,  38   a ,  38   b  and eight conductors  40   a ,  40   b ,  42   a ,  42   b ,  44   a ,  44   b ,  46   a ,  46   b  twisted into pairs and attached to the blades in the same pairings as set forth above for the plug  10  of  FIG. 1 . Notably, the conductors of pair  3  (ie., conductors  44   a ,  44   b ) are arranged such that, after a first crossover point  45  adjacent the blade region, the conductors  44   a ,  44   b  form an expanded loop  48  that terminates at a second crossover point  52  (where typical twisting of conductors of pair  3  occurs). The expanded loop  48  includes segments  50   a ,  50   b  that are positioned adjacent to conductor pair  2  (conductors  42   a ,  42   b ) and conductor pair  4  (conductors  46   a ,  46   b ), respectively, and that are spaced apart from conductor pair  1  (conductors  40   a ,  40   b ). In this configuration, the spatial imbalance between (a) pairs  2  and  3  and (b) pairs  3  and  4  caused by the positions of the blades and wire attachments thereto can be overcome. As a result, the conversion of differential crosstalk to common mode crosstalk ordinarily occurring in the plug  10  of  FIG. 1  can be prevented or substantially reduced, with the result that alien NEXT performance of the plug  30  can be improved. 
     This configuration may be suitable for use in a variety of communication connectors, including plugs, patch panels, and the like. The configuration may be particularly suitable for use in a communications plug, such as that illustrated in  FIGS. 3 ,  3 A,  4  and  6  and designated broadly at  60 . The plug  60  includes a mounting sled  64  that mounts terminating blades (not shown in  FIGS. 3 ,  4  and  6 ) and maintains conductors  40   a – 46   b  in their desired arrangement prior to their merging into a cable  61 . The mounting sled  64 , which is typically formed of a polymeric material such as acrylonitrile-butadiene-styrene copolymer (ABS), includes a relatively flat body  66 . A spreading member  68  extends upwardly from a central portion of the body  66 . The spreading member  68  defines two channels  70  on lateral sides thereof; each of the channels  70  is configured to receive one of the conductors  44   a ,  44   b  of pair  3 . The sled  64  also includes a pair of wings  72  on opposed lateral portions thereof. Each of the wings  72  extends upwardly and outwardly from the body  66  and defines a channel  76  that receives a twisted pair of conductors, i.e., either conductors  42   a ,  42   b  (pair  2 ) or conductors  46   a ,  46   b  (pair  4 ). A slot  74  is present in the body  66  below the spreading member  68  (see  FIGS. 3A and 4 ). The slot  74  is sized to receive the conductors  40   a ,  40   b  of pair  1 . An alignment projection  78  is located on each rear side edge of the body  66 . Also, an X-shaped guide  73  (see  FIG. 3A ) extends rearwardly from the spreading member  68 . The guide  73  includes an upper vane  73   a , a lower vane  73   b , and lateral vanes  73   c ,  73   d ; these vanes receive pairs of conductors as they exit the cable  61  and guide them to their respective locations on the sled  64 . 
     It can be seen in  FIGS. 3 and 4  that each of the twisted pairs of conductors is maintained in position as it travels over/through the sled  64 . In this configuration, conductors  44   a ,  44   b  form an expanded loop  48  of the variety described above. The segment  50   a  is positioned adjacent the conductors  42   a ,  44   a , and the segment  50   b  is positioned adjacent the conductors  46   a ,  46   b . In this embodiment, the length of the segments  50   a ,  50   b  is typically between about 0.150 and0.250 inch, and they are typically positioned within about 0.030 and 0.040 inch of their respective laterally adjacent wire pairs. The width of the expansion loop  48  (ie., the distance between the segments  50   a ,  50   b ) is typically between about 0.150 and 0.200 inch, which can position the segments  50   a ,  50   b  about 0.050 to 0.080 inch from the conductors  40   a ,  40   b  of pair  1 . These dimensions may be typical for a plug having a length of about 1.0 inch. It will be understood that, although the segments  50   a ,  50   b  are shown as being substantially parallel to closely proximate portions of the conductors of pairs  2  and  4 , segments that are only generally parallel to each other, that are disposed at an oblique angle, or that are skewed relative to each other may also be suitable for use with the present invention. In additional, the loop can be generally square, rectangular, oblong, hexagonal, or any other shape that brings the appropriate portions of the conductors of pair  3  into sufficiently close proximity to the conductors of pairs  2  and  4 . 
     As can be seen in  FIG. 6 , the channels  76  of the wings  72  are sized to receive a twisted wire pair (in this instance, the conductors  42   a ,  42   b ) and to permit them to retain a twisted configuration. However, in other embodiments of plugs, the wings may take different configurations. For example,  FIG. 7  illustrates a plug  90  that includes a wing member  92  that has a tine  94  that extends longitudinally and subdivides the space captured by the wing member  92  into upper and lower channels  96   a ,  96   b , each of which is sized and configured to receive one conductor  42   a ,  42   b . As such, in this configuration the conductors  42   a ,  42   b  do not twist around each other within the wing member  92 . This sled configuration may be desirable to use to fine-tune the differential to differential pair  3  to side pair NEXT of the plug, by shifting the vertical positions of wires  50  relative to channels  96   a ,  96   b.    
     As noted above, the sled  64  of the plug  60  is fashioned such that the conductors  40   a ,  40   b  of pair  1  pass through the slot  74  that is positioned beneath the spreading member  68 . This configuration may facilitate placement of the conductors in the sled  64  when the conductors  44   a ,  44   b  of pair  3  are positioned in the top quadrant of the cable  61  from which they emerge, and the conductors  40   a ,  40   b  of pair  1  are positioned in the bottom quadrant of the cable  61  (see  FIGS. 3 and 4 ), but threading of the conductors  40   a ,  40   b  through a slot when the conductors  40   a ,  40   b  are positioned at the top quadrant of the cable  61  (as will occur at one end of the cable  61  or the other in order that the conductors remain in the same order as they attach to blades) may be difficult. To address this “unfriendly” wiring condition, a plug such as that designated broadly at  80  in  FIG. 5  may be employed. The plug  80  includes a spreading member  82  with a trough  83  having a longitudinally-oriented central channel  84 . The channel  84  receives the twisted conductors  40   a ,  40   b  of pair  1  as they exit the top quadrant of the cable  61 . The conductors  44   a ,  44   b  of pair  3  exiting the cable  61  from the bottom quadrant are routed upwardly to the top side of the sled and to lateral channels  87  of the spreading member  82  in order to form an expanded loop. Once the conductors  44   a ,  44   b  of pair  3  travel past the spreading member  82 , they cross over one another above the conductors  40   a ,  40   b  of pair  1  just before the blade attachment region as shown. 
     Another embodiment of a mounting sled according to the present invention is illustrated in  FIG. 8  and designated broadly therein at  110 . The sled  110  includes a guide  111  that receives the conductors from the cable as illustrated above (such a guide is described in U.S. Pat. No. 6,250,949 to Lin, the disclosure of which is hereby incorporated herein in its entirety). However, in this embodiment, the spreading member  112  defines two open channels  114  that receive the conductors of pair  3  as they form an expanded loop. The spreading member  112  overlies a slot  116  that receives the conductors of pair  1 . Rather than utilizing lateral wings as illustrated in  FIGS. 3–7  above as the capture members for the conductors of pairs  2  and  4 , the sled  110  has lateral open troughs  118  that capture the conductors of pairs  2  and  4 . 
     Those skilled in this art will recognize that other configurations of capture members for the laterally positioned pairs, including troughs, channels, tunnels, vanes, and the like, that maintain the laterally positioned pairs in their desired locations may also be employed with the present invention. Further, those skilled in this art will recognize that other configurations of spreading members, including channels, troughs, vanes, tunnels and the like, that maintain the expanded loop configuration of pair  3  may also be employed. 
     Any of the plugs and sleds illustrated and described above may be housed within a housing  100  (see  FIGS. 9 and 10 ). The housing  100  has blades  102  mounted therein that electrically connect with the conductors  40   a – 46   b . Once the housing  100  is attached, the plug can be inserted into a jack for use. Typically, the housing  100  will be shaped to enable the plug to function as an RJ11 or RJ45-style plug for insertion into a complementary jack. 
     Those skilled in this art will recognize that the “expanded loop” configuration of the conductors of pair  3  may be applicable to other types of plugs. For example, an expanded loop configuration may be suitable for rigid wire lead frame type plugs (see U.S. Pat. No. 5,989,071 to Larsen et al. and U.S. Pat. No. 5,951,330 to Reichard et al, the disclosures of each of which are hereby incorporated herein in their entireties). Also, the ordinarily skilled artisan should also appreciate that this configuration is not limited to use with plugs with eight conductors; it may also, for example, be suitable for use with sixteen conductors. 
     As noted, plug-jack combinations employing plugs of the present invention may be especially suitable for use with elevated frequencies transmission, and may have acceptable channel alien NEXT performance at somewhat higher frequencies. For example, plug-jack combinations may result in channel alien NEXT of less than —60 dB power sum at 100 MHz, and less than —49.5 dB power sum at 500 MHz. 
     The invention is described further below in the following non-limiting example. 
     EXAMPLE 
     Plugs having the configuration illustrated in  FIGS. 3 and 5  above were constructed of conventional materials. The conductors of pair  3  were formed into an expanded loop having a width of 0.2 inch and segments having a length of about 0.22 inch. This spacing positioned the segments of pair  3  about 0.050 inch from the conductors of pair  1  and about 0.030 inch from the conductors of pairs  2  and  4 . Differential to common mode scattering testing was then conducted on this plug and a conventional plug (Model No. GS8E, available from Systimax Solutions, Inc., Richardson, Tex.). The three plugs were each connected to the same category 6 jack, and modal decomposition tests were performed for differential to common mode conversion between (a) pair  3  and pair  2  and (b) pair  3  and pair  4  using a system and procedures described in U.S. Pat. Nos. 6,407,542; 6,571,187; and 6,647,357 to Conte. 
     The results of the testing are shown in  FIGS. 11–14 .  FIGS. 11 and 12  show the differential to common mode NEXT between pairs  3  and  2  and pairs  3  and  4 , respectively, for the plug configuration of the embodiment shown in  FIG. 3 .  FIGS. 13 and 14  show the differential to common mode NEXT between pairs  3  and  2  and pairs  3  and  4 , respectively, for the plug configuration shown in  FIG. 5 . In each instance, the experimental plug exhibited significantly lower conversion of differential to common mode signal NEXT at virtually all frequencies. The improvement was no less than 5 dB up to 500 MHz. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.