2. The Relevant Technology Increasingly, applications are being developed that require transmission of high speed and/or high frequency signals. It is generally acknowledged that the medium used to carry the signals is a key factor in the viability of high speed and high frequency transmission. Accordingly, a number of specialized cable geometries have been developed in an attempt to meet the demands for high speed and high frequency signal transmission.

One of the predominant geometries is a coaxial arrangement, wherein the cable employs an inner and outer signal conductor. The conductors are straight, as well as longitudinally coaxial with each other, and are separated by a dielectric, or non- conducting, material. One purpose of the outer conductor, or shield, is to shield the inner conductor from outside interference. However, the inner conductor of the coaxial cable typically radiates a part of its signal into the shield, where the inner conductor signal then interacts with the outside-induced signals. The interacting signals tend to set up random currents in the cable which degrade the quality and speed of the transmitted signal. The problems caused by random currents in coaxial cables become more acute as transmitted signal speeds and frequencies increase. Accordingly, coaxial cable configurations are inherently unsuited to meet the demand for transmission of high speed and high frequency signals.

Not only are coaxial cables prone to random current problems which can inhibit high speed and high frequency signal transmission, but the parallel arrangement of the straight conductors causes difficulties as well. When straight conductors of opposite polarities are located parallel to each other, the conductors act in concert with the dielectric to store electrical energy in the same fashion as a capacitor. The electrical energy stored in the dielectric is released into the signal path as the polarity of the transmitted signal changes.

The stored charge thereby serves to resist current flow through the conductors, and thus

causes the transmitted signal to lose energy. As signal frequencies increase, the signal energy loss caused by this type of geometry becomes increasingly significant; accordingly, the coaxial geometry is only suited for a relatively narrow range of signal frequencies. The aforementioned concerns are not limited to coaxial cables however.

Because capacitance, and its detrimental effect on signal transmission, increases as the distance between conductors decreases, cable geometries that employ a plurality of straight, and closely-spaced, parallel conductors are prone to similar problems.

Furthermore, multiple straight conductors inhibit the mechanical flexibility of the cable.

One configuration that has been developed in an attempt to solve the problems associated with parallel, straight conductors is a double helix arrangement wherein two conductors twist in opposite directions around a central ground conductor. While this type of twisting arrangement has some effect in reducing capacitance, and is therefore preferable to those geometries which employ parallel straight conductors, it is an incomplete solution. As noted earlier, capacitance increases as the distance between conductors decreases. In the typical double helix arrangement, the conductors cross each other at intervals and would touch but for the insulation present on each conductor.

Thus, although the conductors are twisted, they pass very close to each other at numerus points along the cable and therefore are prone to induce undesirable capacitance.

Furthermore, typical double helix geometries make no provision for ensuring that the conductors remain in their proper orientation, with respect to the central conductor.

Finally, because the typical double helix arrangement uses only two conductors, that geometry is necessarily limited to single channel operation.

SUMMARY AND OBJECTS OF THE INVENTION It is a general object of the present invention to provide an improved signal transmission cable to solve the aforementioned problems.

Accordingly, it is an object of the present invention to provide an improved signal transmission cable that is capable of multiple channel operation over a wide range of signal frequencies and signal speeds.

It is a related object of the present invention to provide an improved signal transmission cable that is substantially immune from induced random currents.

It is a similar object of the present invention to provide an improved signal transmission cable which possesses relatively low impedance.

It is finally an object of the present invention to provide an improved signal transmission cable that is mechanically flexible.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In order to more fully understand the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention in its presently understood best mode for making and using the same will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: Figure 1 is a top view of the cable, showing the braid configuration; Figure 2 is a top view of the cable with connectors attached; Figure 3a is a cross-section of the cable, indicating a dual channel conductor arrangement, and showing the conductors in their innermost position; Figure 3b is a cross-section of the cable showing the conductors in their outermost position; Figure 3c is a cross-section of the cable, indicating a single channel conductor arrangement, and showing the conductors in an intermediate position; Figure 4 is a general depiction of the relationship of the cable to the components between which a signal is to be transmitted; and Figure 5 is a partial view of the cable indicating the arrangement of the conductors with respect to the terminals of the connector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an improved signal transmission cable. Figures 1 through 5 shown an improved signal transmission cable according to a preferred embodiment of this invention.

With reference to Figure 1, a signal transmission cable according to the present invention is depicted generally as 100. A non-conductive core portion 102 forms the center of the transmission cable 100. In a preferred embodiment, the core portion 102 is composed of a compliant material which serves to ensure that the transmission cable is mechanically flexible.

An even number of equal diameter conductors 104 are spirally wrapped around the core portion 102, as indicated in Figures 1 and 2. In a preferred embodiment, there are two pairs, or a total of four conductors, each conductor being wrapped around the core portion 102 at the rate of about one turn per inch. As indicated in Figure 3a, four conductors enable the same cable to carry two different signals simultaneously; that is, the two pairs of conductors permit dual channel operation. The conductors 104, as indicated in Figures 1,3a, 3b, and 3c, are evenly spaced about the cross-section of the core portion 102, alternatively contacting the core and moving out from the core as they interweave with the spacers 112.

The diameter 108 of the core portion bears a specific, predetermined relation to the diameter 106 of the conductors 104. In a preferred embodiment, the relation is represented by a ratio of about 11 to 1; that is, the diameter 108 of the core portion is about 11 times as great as the diameter 106 of an individual conductor. Maintenance of this relationship serves to ensure a relatively low, constant impedance throughout the length of the transmission cable 100. The relatively low impedance, in turn, facilitates ready transmission of high speed and high frequency signals through the cable. This embodiment thus represents an improvement over those cables which are only capable of single channel transmission over a limited range of signal frequencies and signal speeds.

As indicated in Figures 1 and 2, and Figures 3a-3c, an even number of electrically non-conductive spacers 112 are braided together with the conductors 104, about the core portion 112. In a preferred embodiment, the spacers 112 are present in the same numbers as the conductors 104; the spacers are also made of a compliant material to facilitate mechanical flexibility of the cable 100.

The spacers 112 serve at least two purposes. One purpose of the spacers 112 is to ensure that the conductors 104 remain in position with respect to each other, and with respect to the core portion 102, when the cable is subjected to movement or vibration.

The positioning of the conductors 104 is critical because it ensures that the electrostatic (E) and magnetic (H) fields of the conductors are perpendicular to each other. This relation between E and H desirably minimizes the capacitance between the conductors 104, thereby reducing resistance to signal transmission.

The spacers not only ensure the proper orientation of the conductors 104, but also ensure that the space between the conductors 104 is maximized. Since capacitance diminishes as the distance between conductors increases, the spacers 112 typical of this embodiment serve to substantially minimize any capacitive effect between the conductors 104. This embodiment thus represents an improvement over those cables where the conductors are in close proximity with each other.

In an alternative preferred embodiment, the signal transmission cable 100 is used to carry an audio signal from a first component 120 to a second component 122, as indicated generally in Figure 4. Note that while Figure 4 indicates an amplifier and a speaker, it is contemplated that this embodiment may be utilized to convey audio signals between and among a wide variety of components; Figure 4 thus should not be interpreted as indicating a limitation on the conceivable uses of this embodiment.

With reference to Figures 2 and 5, the signal transmission cable has a connector 114 attached to either end. Each connector 114 has a positive terminal 116 and a negative terminal 118. As indicated in Figure 5, only every other conductor 104 in the ring is connected to the respective negative terminals 118. The remaining conductors are connected to the respective positive terminals 116; all connections are parallel connections. The connectors 114 are adapted to connect the conductors to the first component 120 and the second component 122. Note that the cable and connectors of this embodiment may be packaged as a kit of individual elements for assembly either by the end user or by an intermediary equipment retailer. Such a collection of assembleable components is contemplated as being within the scope of the this invention.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by United States Letters Patent is: