Patent Application
20180075949
The present invention relates to data communication cables that have an extended frequency range of at least 2 Ghz.
In all transmission lines, the electrical parameters are determined by the physical dimensions and electrical properties of the components. It is common to have periodic or random variations in those properties that induce inconsistencies in the electrical transmission parameters. Within the frequency range of prior cable standards, several design approaches and prior art have been developed in an attempt in order to reduce the effect of those variations.
Insertion loss and return loss characteristics can have abrupt changes at specific frequencies that are related to the electrical wave interacting with the periodicity of the transmission line variations. If the signal wavelengths are sufficiently longer than the perturbations in the cable construction, then the effect of frequency dependent electrical parameters is much less evident or non-existent. However, if the signal wavelengths are in the same range as the cable perturbations, then the effect on the signal transmission is much more pronounced at those specific signal wavelengths that correlate with the dimension of the transmission line anomalies.
A particular source of anomalies in cable performance occurs when the pairs are assembled together.
Another example is a cable with individually shielded pairs, with each pair being surrounded by a metal shield layer. The manufacturing processes cause periodic variations in spacing from conductor to conductor as well as spacing of the conductors to the pair shield. These variations cause anomalies in the insertion loss and return loss measurement as shown in
The process of manufacturing a completed cable causes periodic mechanical perturbations. It is known that tension consistency and care in handling of the cable components is important. It was also discovered that one of the effects caused by the twisting action is the unintended spiral that is induced in the cable components by the twisting action. The spiral length is the same as the twist length. In rotating machinery, it is also common to have a slightly different path of the wire from the payoff spool through the machine as it turns. The periodic changing path in the wire results in having different sections of the components which bend and flex differently than other sections. The difference in bending leads to slight periodic differences in the mechanical structure in the cable and is one cause for anomalies in electrical measurement results.
In
For shielded pairs, surrounding the pairs with a metallic tape is known to provide electrical isolation from one pair to the next pair. However, metallic tapes are generally not of sufficient tightness in order to provide the pair dimensional integrity to avoid electrical anomalies in the final cable test results.
However the metallic spiral shield wrap construction with a relatively short spiral alone was not found to provide the necessary shielding effectiveness. It was discovered that a combination shield could be employed such that a metallic tape wrap with a shorter lay length is applied over metallic wrap with a long lay length or in a longitudinal fashion. Note that a lay length is traditionally defined as the axial distance necessary for one pair of insulated conductors to complete a full 360 degree rotation when twisting about one another, such that a tight twist will result in a shorter lay length while a looser twist will result in a longer lay length. A preferred arrangement is to have the conductive surface of the inner tape facing away from the pair and the shorter lay metallic tape with a metallic conductive surface on both sides to provide electrical contact with the inner longitudinal tape and to adjacent similar shielded pairs in the assembled cable.
Cabling twist length can be chosen to be below about 0.5 wavelengths of the highest frequency of operation in order to move the cabling process and design electrical anomalies beyond the frequency of interest. However, at frequencies in the range of 2,000 MHz this approach has drawbacks due to the additional path length of the pairs within the shorter spiral length of each pair as well as a crushing action caused by the short lay lengths in the cable. This generally leads to problems in meeting specifications for cable propagation delay and insertion loss. However, with the design options provided by the pair wrapping, much longer cable lay lengths can be utilized, avoiding the problems caused by short cable lay lengths.
For the new extended frequency electrical requirements, the prior art does not solve all the problems found in designing and manufacturing such a cable, and some of the prior art techniques cause, rather than solve, problems at these extended frequency ranges.
Pretwisting (U.S. Pat. No. 5,767,441—Brorein '441) was introduced to eliminate the random effect of conductor to conductor spacing, but It is to appreciated that this arrangement also generates its own problems in the new frequency ranges of interest. The random conductor to conductor spacing caused undesirable effects in the electrical parameter of return loss. Although this technology is widely used in the data communication cable industry, it was discovered that the pretwisting of the conductor also results in degradation of electrical properties, such as return losses, due to conductor deformation effects. Those effects are now visible in the extended frequency range of interest.
Bonded pair technology (U.S. Pat. No. 6,222,129—Siekierka et al. '129) is a technology which controls the return loss parameters of a twisted pair by maintaining the conductor to conductor spacing. The main advantage of bonded pairs is to prevent the need for pretwisting of the conductor. However, such bonding does not control the spacing of the wires in the pair to pair shield or to an overall cable shield, so other means must be employed to establish and control the electrical properties defined by the interaction of the pairs to the cable shield components.
For non-shielded pairs, tightly wrapping or coating the two wires of a pair with a dielectric material is one means for establishing and maintaining the mechanical integrity of the pair.
With respect to category 8 cables, it is to appreciated that such cables increase the frequency of operation for category cables to 2 GHz or more. This change reduces the electrical wavelength in the cable so that mechanical perturbations in the cable are longer than the electrical wavelength.
Until Category 8 cables, the periodicity length of manufacturing operations is longer than the electrical wavelength. However, this changes with Category 8 cables.
When frequencies greater than 2 GHz are required, even shorter periodicity lengths are required and this, in turn, substantially increases the electrical delay and insertion loss effects.
Other cable designs have performance above 2 GHz, but the industry desires to have a cable construction that is very similar to the existing Category 6 and 7 constructions. Such similarity of construction allows ease of adapting cable connectors, termination practices, installation ease and familiarity, etc.
The periodicity length in the cable is accompanied by an insertion loss notch at the frequency corresponding to the length. A return loss spike accompanies the insertion loss notch. With conventional equipment, even equipment with updated design and controls, the periodic perturbations cause insertion loss and return loss results that do not meet the cable specifications.
The inventors have discovered that the root cause for the electrical problems result from one or more minor inconsistencies in the mechanical structure of the cable, over its entire axial length, which are normally caused by the associated manufacturing equipment, e.g., cabling of the cable core assembly during manufacture of the cable.
Wherefore, it is an object of the present invention to overcome the above mentioned shortcomings and drawbacks associated with the prior art.
The foregoing and other features and advantages will be apparent from the following description of exemplary embodiments of the disclosure, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure.
It is an object of the present invention in one embodiment to provide a dielectric material or wrap which binds, wraps or otherwise immobilizes the (two) first and second insulated conductors of a twisted-pair, in order to prevent relative movement between the two insulated conductors.
It is a further object of the invention in one embodiment to provide a metallic material which binds, wraps, or otherwise immobilizes the two insulated conductors, of a twisted pair, and also provides effective shielding from one pair to another pair.
A further object of the present invention is to wrap the insulated conductors of the twisted pairs, with a longer lay length, with a material which increases the propagation delay of the insulated conductors in order to compensate for the propagation delays which occur in the twisted pairs with the shorter lay length(s).
Yet another object of the present invention is to utilize materials which have different dielectric constant(s) so as to equalize the propagation delay among the twisted pairs in the cable. That is, lower dielectric constant materials, such as foamed insulation, may be utilize as the conductor insulation for the twisted pairs with the shorter lay length(s) while higher dielectric constant materials, such as using solid insulation, may be utilize as the conductor insulation for the twisted pairs with the longer lay length(s). In addition, the twisted pair or pairs having the longer lay length(s) may be wrapped with a material having a high dielectric constant in order to equalize the propagation delay among the twisted pairs of the cable.
A novel way of assembling cable for Category 8 requirements is to assemble twisted pairs, in a longitudinal direction or fashion. Thus, the twisted pairs extend along a longitudinal along a common axis. A key to this approach is to provide a wrap or layer over the shielded pairs that creates a mechanically robust structure for the assembly of longitudinal components within.
The advantage of this arrangement is that there generally are not any mechanical perturbations caused by a cabling together of the 4 pairs with their shield tapes, since there is no cabling action upon the core at this stage of manufacture.
Thereafter, once the cable assembly is complete with a final wrap or layer over the assembly, it is much less susceptible to subsequent twisting to form the desired spiral of the twisted pairs, so a wide range of cable lay lengths is thus available.
For cables with a metal shield over each pair, the pair shield tapes can be applied longitudinally, placed in predetermined positions and held in place by the core wrap/layer. This cabling method could also be used when the pairs within the core are either unwrapped or wrapped.
As a result of conventional cabling operations, if the cable lay length is greater than about 5 to 7 inches for example, the inventors have discovered that such components, because of the long and loose spiral of the cable core, tend to ‘fall apart’ before the subsequent manufacturing operations.
However, with the completed core with a wrap/layer, the range of cable lay lengths extend from essentially infinity down to a very few inches (i.e., 1.5-4 inches for example). Of course the insertion loss and electrical delay problems still exist with short cable lay lengths, but this construction allows cable lay lengths up to 8 to 20 inches. Such long lay lengths are not generally practical with conventional cabling processes. And these longer lay lengths improve insertion loss and electrical delay compared to conventional processes. For installation integrity and use, such long cable lengths can be sufficient, but not attainable with conventional processes due to the dimensional and structure instability of the long lay core.
Another advantage with this approach is that when used with shielded pairs, the overlaps of metal shield tapes over each pair can have a specific orientation, and be held in that orientation by the core wrap/layer while in a longitudinal configuration. One specific example is to apply the tapes such they each of the overlaps face away from the center of the common axis. According to this arrangement, any signal leakage that escapes the overlap tapes has minimal effect on electrical crosstalk from pair to pair. Another example is to only have the overlap at specific locations in order to provide a balance of electrical crosstalk between the pairs, or between adjacent cables. It is the core wrap/layer design that allows this flexibility of tape placement in a core with a longitudinal configuration. This tape orientation is maintained in subsequent operations, since the wrap/layer allows the elements to twist together as an assembly.
The present invention also relates to a cable comprising: a plurality of twisted pairs, and each of the plurality of twisted pairs comprising first and second insulated conductors; the plurality of twisted pairs being assembled with one another to form a cable core assembly; and the cable having at least one of a hoop wrap having at least one of sufficiently short lay length or a sufficient hoop strength so as to increase mechanical strength and integrity of the cable to prevent degradation caused by periodicity of deformations induced by cabling action during assembly of the cable.
The foregoing and other features and advantages will be apparent from the following more particular description of exemplary embodiments of the disclosure, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various embodiments of the invention and together with the general description of the invention given above and the detailed description of the drawings given below, serve to explain the principles of the invention. The invention will now be described, by way of example, with reference to the accompanying drawings in which:
The following non-limiting examples further illustrate the various embodiments described herein.
It was surprisingly discovered by the inventors that the pretwisting operation itself—such as in accordance with the teachings of Brorein '441 briefly discussed above—induces a specific periodicity in the twisted pairs 14, 16, 18 or 20 that results in significant electrical performance anomalies. The conductor pretwist length is often determined for conventional cable designs as a percent of the pair twist length. However, in order to prevent electrical anomalies at extended frequency ranges that are caused by conductor deformation during the twisting action, it was discovered that the pretwist length′ for each one of the first and the second insulated conductors 24, 26 must be less than the 1/2 wavelength of the highest frequency of the intended operation.
It is important to provide pretwisting of each conductor at a twist rate within certain bounds in order to prevent undesirable interactions.
For pairs without an individual pair shield, it was discovered that an electrical crosstalk resonance occurs at high frequencies that are not visible in the frequency ranges of the previous cable standards. The resonance length occurs at a distance where the number of electrical lay lengths in one pair compared to another differs by one.
It has also been found that the tightness and the strength of the pair wrapping has distinct effects on the mechanical stability and electrical performance of the pair. Moreover, the lay length and the hoop strength of the at least one wrapping is an important parameter of the cable.
For non-shielded pairs, tightly wrapping the two wires of a pair with a dielectric material or wrap is one means or mechanism for establishing and maintaining the mechanical strength and integrity of the pair of insulated conductors of the twisted pair and preventing the two (i.e., the first and the second) insulated conductors from becoming sufficiently separated from one another during, for example, subsequent manufacture, handing and/or installation of the cable. It is also discovered that the twisted pairs with the shorter twist lengths have a higher degree of mechanical integrity and strength, due to the relatively short twist length of the two wires or insulated conductors, than a twisted pair with a relatively long twist length. In view of this, the inventors have determined that it is generally necessary for at least the two insulated conductors, of the twisted pair with the longest twist or lay length, to be tightly wrapped or coated with a (e.g., dielectric or metallic) wrap. The lay length of the pair wrap is preferably from 0.33 to 1.5 inches to provide hoop strength.
It was discovered that a difference in an electrical delay, along the length of the cable, needs to be controlled in order to meet the electrical requirements of the cable since the difference in the lay lengths of unshielded twisted pairs must be larger than in conventional cables in order to control the crosstalk resonance of the cable. It is to be appreciated that the twisted pairs with the shorter lay lengths, which have a relatively long electrical path, have more delay than twisted pairs with longer lay lengths, which have a relatively shorter electrical path. In order to compensate for the delay in the twisted pairs with the shorter lay lengths, the longer lay lengths are preferably wrapped with a dielectric material or wrap which thereby increases the propagation delay of the pair to the pair, compared to not wrapping the twisted pair with any (dielectric) material or wrap. By wrapping at least the twisted pair, and preferably both twisted pairs, having the longer lay lengths and leaving the one, or both of the twisted pairs, having the shorter lay lengths unwrapped, the propagation delay differences, between the longer lay lengths and the shorter lay lengths, are thereby reduced and the desired balance of electrical properties can be achieved to meet the pair to pair differential time delay requirements as well as provide control for the mechanical structure of the pair.
It was also discovered that for non-shielded pairs in an overall shielded construction, there is an insertion loss interaction with the cable shield that depends on the lay length of the non-shielded pair. It was noted that a significant increase in insertion loss occurs when the electrical wavelength of the signal in the cable is about ¼ or less of the lay length of the twisted pair. Accordingly, in order to provide a smooth curve for insertion loss, the lay length of the twisted pair should be sufficiently short, e.g., be less than about ¼ the wavelength of the highest frequency of operation.
One problem with avoiding the crosstalk resonances is that the lay length differences between the twisted pairs of the cables is much larger than found in cables designed for operation at lower frequencies. The ratio of the shortest lay length to the longest lay length, in a four (4) twisted pair cable, can approach 3 to 4, for example, where a conventional cable may have a ratio of the shortest lay length to the longest lay length of 2 or less, for example.
Turning now to
When comparing the lay lengths L of any two pairs 14, 16, 18 or 20 of the cable 12 in order to determine the resonance length, the percentage difference between the two pairs 14, 16, 18 or 20 becomes larger as the absolute value of the pair lay lengths L increase. For the two twisted pairs with the shorter lay length, e.g., the first and the second twisted pairs 14 and 16, a percentage difference of only about 23% is needed to ensure a short enough resonance length, e.g., the second pair 16 has a lay length L of 0.43 inches which is 23% greater than the lay length L of 0.35 inches of the first pair 14. However, for controlling the resonance length of the long pairs, a percentage difference of 40% is required, since the lay lengths L start from a larger value, e.g., the third pair 18 has a lay length L of 0.6 inches which is 23% greater than the lay length L of 0.43 inches for the second pair 16, while a percentage difference of 50% is required between the third and the fourth pairs 18 and 20, e.g., the fourth pair 20 has a lay length L of 0.9 inches which is 50% longer than the lay length L of 0.6 inches for the third pair 18.
According to the present invention, the percentage difference of the lay length L of the (second) twisted pair 16, with the second shortest lay length, and the lay length L of the (first) twisted pair 14, with the shortest lay length, is between about 10-25%. The percentage difference of the lay length L of the (third) twisted pair 18, with the second longest lay length, and the lay length L of the (second) twisted pair 16, with the second shortest lay length L, is between about 25-45%. The percentage difference of the lay length L of the (fourth) twisted pair 20 with the longest lay length and the lay length L of the (third) twisted pair 18 with the second longest lay length is between about 45-70%.
It is to be appreciated that the four (4) lay lengths L, in a four (4) pair cable 12, are not established by equally dividing up the differences in lay lengths L among the four (4) twisted pairs 14, 16, 18 or 20 of the cable 12, or equally dividing the ratio of the longest and shortest pair lay lengths L among the four (4) twisted pairs 14, 16, 18 or 20 of the cable 12, or an empirically established sequencing of the lay lengths within the cable 12 within conventional bounds of maximum and minimum lay lengths. A fundamental requirement is to place bounds on the resonance length between any two twisted pairs 14, 16, 18 or 20 of the four (4) pair cable 12.
For a cable 12 with non-shielded pairs, it is important that no combination of pairs within the cable 12 have a resonance length longer than about 2 inches, which is about ½ wavelength of the highest frequency of operation for the frequency range of the cable 12, namely, 2 GHz for the cable 12 according to the present invention.
It is to borne in mind that this wide range of lay lengths L and the different path lengths induced by spiral of the wires in the twisted pair 14, 16, 18 or 20, at those different lay lengths L, adds problems in maintaining the twisted pair 14, 16, 18 or 20 to twisted pair 14, 16, 18 or 20 signal propagation delay, as required by the applicable standards.
A first technique for addressing the signal propagation delays of the various twisted pairs 14, 16, 18 or 20 is to encase or surround each of the first and the second conductors 24, 26, which form one of the twisted pairs 14, 16, 18 or 20, in an appropriate conductor insulation 25. For example, at least the first and the second conductors 24, 26 which are to be twisted together in order to form the twisted pair which has the shortest lay length, e.g., the first twisted pair 14, or to form the twisted pair which has the second shortest lay length, e.g., the second twisted pair 16 shown in
By appropriate selection of the dielectric material or wrap for forming the conductor insulation 25, which surrounds and/or encases each of the first and the second conductors 24, 26 that form each twisted pair 14, 16, 18 or 20, the propagation delay differences of the various twisted pairs 14, 16, 18 or 20, which have different lay lengths L, can be easily readily and easily compensation for so that any electric signal, which travels along each one of the twisted pairs 14, 16, 18 or 20, will generally have the same propagation velocity.
In order to compensate further for the propagation delay differences of the various twisted pairs 14, 16, 18 or 20, which have different lay lengths L, the conductors 24, 26 of at least the longest lay length (fourth) twisted pair 20 or possibly, the conductors 24, 26 of both of the two longest lay length (third and fourth) twisted pairs 18, 20 are wrapped together by a dielectric layer (e.g., a polyester film) or wrap 22 as shown in
That is, the dielectric layers or wraps 22 which have a relatively low dielectric constant, for example, are appropriate materials for wrapping or otherwise binding the two insulated conductors 24, 26 of the first and the second twisted pairs 14, 16—and possibly the third twisted pair 18—with one another in order to assist with maintaining the mechanical strength and integrity of the twisted pairs, during subsequent handing thereof, while also assisting with increasing the velocity of signals traveling along the insulated conductors 24, 26 of those twisted pairs 14, 16 or 18. For the longer lay lengths L, the dielectric layers or wraps 22 which have a relatively high dielectric constant are appropriate materials for wrapping or otherwise binding the two insulated conductors 24, 26 of the third and the fourth twisted pairs 20, 18—and possibly the second twisted pair 16—with one another to assist with maintaining the mechanical strength and integrity of the twisted pairs 20, 18 or 16, during subsequent handing thereof, and also assist with decreasing the velocity of any electrical signal(s) traveling along the insulated conductors 24, 26 of those twisted pairs 20, 18 or 16.
This observation is important because the lay lengths L, needed to control crosstalk resonances, can be relatively long, but the longer lay lengths also have the interaction with the shield which occurs at lower frequencies. It is to be appreciated that both parameters must be suitably controlled, in the cable design, in order to provide a cable 12 which is suitable for use in the 2 GHz region.
A hoop strength of the dielectric layer or wrap 22, which wraps the pair of insulated conductors 24, 26 together with one another, is affected by the stiffness, the thickness, and the spiral length of the layer or wrap. For instance, a wrapping tape applied with a long lay length, e.g., a lay length substantially extending parallel to the longitudinal axis of the twisted pair 14, 16, 18 or 20, or in a generally longitudinal fashion has a hoop strength of essentially zero. It is to appreciated that an adhesive(s) can be used to adhesively bond the overlapped edges of the wrapping layer or tape with one another and thereby somewhat increase the effective hoop strength of the short or the long lay length wrapping layers or tapes. However, the adhesive layer, bonding the overlapped edges of the wrapping layer or tape to one another, can reduce, or possibly substantially eliminate, the desired electrical continuity and/or grounding function of the wrapping layer or tape.
For cables that contain pairs with a metallic pair shield, the proximity of the metallic shield to the insulated conductors 24, 26 increases the susceptibility to pertubations caused by the cabling process. For shielded pairs, the hoop strength needs to be greater than that of a non-shielded pair in order to maintain the mechanical integrity and the desired electrical properties of the twisted pair. The hoop strength is defined by the wrap material modulus of elasticity, the thickness of the wrap, the angle at which the wrap is applied and the amounts of wrap overlap. For the purpose of wraps on a cable component, the hoop strength is defined as:
HS=M*T*sin(Θ)*(1+O)
Where HS is the hoop strength in kg/mm,
M is the wrap material modulus of elasticity in kg/mm2,
T is the thickness of the wrap in mm,
is the angle of deviation of the applied wrap spiral from the longitudinal axis of the twisted pair, e.g., 14, 16, 18 or 20, or cable core assembly 44, and
Θ is the overlap of the wrap to account for the portions of the wrap that have double thickness.
As an example, a pair of insulated conductors 24, 26 of a non-shielded pair 14, 16, 18 or 20 may be wrapped with a dielectric layer or wrap 22 with a modulus of elasticity of 500 kg/mm2 and a thickness of 12 microns. The twisted pair 14, 16, 18 or 20 in this example is wrapped with a short spiral lay length at an angle of 60 degrees relative to the longitudinal axis of the cable 12 with 25% wrap overlap. Based upon the above formula, the resulting hoop strength is calculated to be 500*0.012*0.866*1.25=6.495 kg/mm2. One technique for increase the hoop strength is to use first and second pairs of metallic wraps, with a modulus of elasticity of about 7000 kg/mm2 and a thickness of 25 microns, for wrapping around the twisted pair 14, 16, 18 or 20. The pair of insulated conductors 24, 26 of the twisted pair 14, 16, 18 or 20, in this example, is wrapped longitudinally with a first tape having 25% overlap that provides substantially no hoop strength. The hoop strength of the first tape would be 7000*0.025*0.0*1.25=0 kg/mm. The second (hoop) wrap is at a relatively short lay length with a 60 degree angle, and a 25% overlap. The hoop strength of second (hoop) wrap, in this example, is 7000*0.025*0.866*1.25=189.5 kg/mm.
It is to appreciated that a typically tape surrounding a pair does not sufficiently control the twisted pairs 14, 16, 18 or 20 or the cable 12 to prevent the electrical performance anomalies. That is, a (hoop) tape or wrap must be sufficiently tightly wrapped around and/or over the two insulated conductors 24, 26 of the twisted pair 14, 16, 18 or 20 or the cable core assembly 44 in order to provide the desired mechanical strength and integrity. The ‘tightness’ of the wrapping, over the two insulated conductors 24, 26 of the twisted pairs 14, 16, 18 or 20, is defined as the ‘extra circumference’ of the wrap compared to the two insulated conductors 24, 26 or wrapped components.
For a dielectric layer or wrap 22, a “dielectric pair minimum circumference” is defined as the shortest perimeter distance in order for the layer or wrap 22 to completely circumscribe both of the two insulated conductors 24, 26 when they are in abutting engagement with one another, i.e., as generally shown by the wrap 22 in
According to the present invention, at least the two insulated conductors 24, 26 of the (fourth) twisted pair 20 with the longest lay length L is bound, wrapped or otherwise immobilized with a dielectric (hoop) layer or wrap 22 so as to prevent, or significantly minimize at the very least, relative movement of the two conductors 24, 26 with respect to one another. If a dielectric layer or wrap is utilized for immobilizing the (fourth) twisted pair 20 with the longest lay length L, then the two insulated conductors 24, 26 of the (third) twisted pair 18 for the second longest lay length may also be bound, wrapped or otherwise immobilized with a dielectric (hoop) layer or wrap 22 so as prevent, or significantly minimize at the very least, relative movement of the two conductors 24, 26 of the (third) twisted pair 18 with the second longest lay length with respect to one another.
For some applications, the two insulated conductors 24, 26 of the (second) twisted pair 16 with the second shortest lay length may also bound, wrapped or otherwise immobilized with a dielectric (hoop) layer or wrap 22 so as prevent, or significantly minimize at the very least, relative movement of the two conductors 24, 26 of the (second) twisted pair 16 with the second shortest lay length with respect to one another. The two insulated conductors 24, 26 of the (first) twisted pair 14 with the shortest lay length may also bound, wrapped or otherwise immobilized with a dielectric (hoop) layer or wrap 22 so as prevent, or significantly minimize at the very least, relative movement of the two conductors 24, 26 of the (first) twisted pair 14 with the shortest lay length with respect to one another.
With respect to the previous embodiment in which each one of the twisted pairs 14, 16, 18 or 20 is wrapped with first and second metallic wraps 30, 32, the inventors have discovered that according to this embodiment the lay lengths for each of the twisted pairs 14, 16, 18 or 20 do not have to vary greatly from one another. For example, the inventors have discovered that percentage difference of the lay length L of the (second) twisted pair 16, with the second shortest lay length, only has to be at least 3-4% greater than the lay length L of the (first) twisted pair 14, with the shortest lay length. The percentage difference of the lay length L of the (third) twisted pair 18, with the second longest lay length, only has to be at least 3-4% greater than the lay length L of the (second) twisted pair 16, with the second shortest lay length L. The percentage difference of the lay length L of the (fourth) twisted pair 20, with the longest lay length, only has to be at least 3-4% greater that the lay length L of the (third) twisted pair 18, with the second longest lay length. For the metallic wraps 30, 32, a “metallic pair minimum circumference” is defined as the shortest perimeter distance in order to completely circularly circumscribe both of the two insulated conductors 24, 26 when they are in abutting engagement with one another, i.e., the metallic pair minimum circumference is circular shaped, as generally shown in
A suitable dielectric layer or wrap 22, which is utilized for wrapping the third and the fourth twisted pairs 18 or 20 having the longer lay lengths, may be, for example, a solid material while the dielectric layer or wrap 22, utilized for wrapping the first and the second twisted pairs 14 or 16 having the two short lay lengths, may be, for example, a foamed material.
It is to be appreciated that each of the two conductors 24, 26 may be first individually pre-twisted, in a conventional manner, to have a desired pretwist prior to the two conductors 24, 26 being twisted with one another to form a twisted pair 14, 16, 18 or 20. Next, both of the pretwisted conductors 24, 26 are then surrounded and encased with a suitable conductor insulation 25 in a conventional manner. Thereafter, the two conductors 24, 26, which have been encased within the suitable conductor insulation 25, are then finally twisted with one another to form a twisted pair which has a desired lay length L and then wrapped with a dielectric layer or wrap 22 (see
It is to be appreciated that the dielectric layer or wrap 22 also assists with straightening of the first and the second insulated conductors 24, 26 and compensates for spiraling which is induced into the first and the second insulated conductors 24, 26, during twisting, to form the twisted pair 14, 16, 18 or 20. The inventors have discovered that the above benefits are only achieved in the event that the dielectric layer or wrap 22 has a length around the first and the second insulated conductors 24, 26 which does not exceed the dielectric pair minimum circumference around the twisted pair 14, 16, 18 or 20 of cables 12 by more than 5%. That is, the circumference of the wrap should be between 100.0% and 105.0% of the dielectric pair minimum circumference in order to maintains the mechanical strength and integrity of the insulated conductors 24, 26 of the twisted pair 14, 16, 18 or 20 and prevents the two insulated conductors 24, 26 from becoming sufficiently separated or spaced apart from one another during subsequent manufacture, handing and/or installation of the cable 12.
According to another embodiment, the hoop wrap which maintains the first and the second insulated conductors 24, 26 in intimate contact and engagement with one another, during subsequent manufacture, handing and/or installation of the twisted pair 14, 16, 18 or 20, is a dielectric material.
Cable Core Wrap
It is to appreciated that for cables 12 with non-shielded pairs 14, 16, 18 or 20, control of the position of the pairs 14, 16, 18 or 20, within the cable assembly, is important. Periodic variations in the spacing, from the twist pair 14, 16, 18 or 20 to the surrounding shield, can cause electrical anomalies, and the process of cabling pairs together can cause periodic dimensional variations to occur. A dielectric core wrap 28 can be applied over the four twisted pairs 14, 16, 18 or 20 and under a surrounding metal shield layer, as shown in
In the event that the (fourth) twisted pair 20 with the longest lay length L is bound, wrapped or otherwise immobilized with a metallic layer, then, according to another embodiment of the present invention, each one of the first, the second, the third and the fourth twisted pairs 14, 16, 18 and 20 are also wrapped with both first and second metallic layers 30, 32, as shown in
According to this embodiment, each one of the first, the second, the third and the fourth twisted pairs 14, 16, 18 or 20 is similarly wrapped with first and second layers 30, 32 of a metallic shield tape, as generally shown in
As noted above, the metallic spiral shield wrap construction over a twisted pair alone was not found to provide the necessary shielding effectiveness from pair to pair. It was discovered that a combination shield, e.g., both the first and the second metal wraps or layers 30, 32 (with the outer layer 32 being a hoop wrap), may be employed such that a second metallic tape wrap 32, with a shorter lay length, is applied over a first metallic tape or wrap 30, with a long lay length L which generally extends in a longitudinal direction along the twisted pair (see
For the core and pair dielectric wraps 22, it is entirely possible and conceivable that a number of filaments may be used in place of a tape to achieve a substantially equivalent hoop strength as the hoop tape or wrap. As an alternate, the metallic overall shield can be applied over the cable core assembly 44 with a hoop strength of about 175 kg/mm or more and a circumference no greater than 5% of the dielectric pair minimum circumference of the two wrapped insulated conductors 24, 26.
For either non-shielded pairs or shielded pairs 14, 16, 18 or 20, a dielectric layer or wrap may be directly applied over the insulated conductors 24, 26 but underneath the wrapping layer of the twisted pair. For non-shielded pairs 14, 16, 18 or 20, a dielectric hoop layer or wrap 22 applied over the cable core assembly 44 of wrapped pairs 14, 16, 18 or 20 may also be included to provide some additional physical separation of the twisted pairs 14, 16, 18 or 20 to the overall metallic shield.
Variable Lay and Wrap Lengths
The prior art includes randomizing of the cable lay lengths to minimize crosstalk, from cable 12 to cable 12 as well as the crosstalk from twisted pair 14, 16, 18 or 20 to twisted pair 14, 16, 18 or 20. However, it was discovered that the interaction of the pair lay and the lay of the first and the second tapes or wraps 30, 32 also results in variations in electrical performance at specific frequencies or within frequency ranges. The interaction of the twisted pair 14, 16, 18 or 20 and the pair wrap can be minimized by randomizing at least one of the pair lay length and/or the lay length of the tape or wrap. It has been found that randomizing the lay length of the tape or wrap by about 5 to 20% over lengths from 2 to 8 meters, for example, minimizes those variations in the twisted pair 14, 16, 18 or 20 to shield interaction.
As generally shown in
As described above, the operation of twisting a group of pairs causes periodic deformations in the core that result in electrical performance problems of insertion loss notches and return loss spikes. Because of the frequency of operation that extends to 2 GHz or more, the twist length (e.g., lay length of the core) must be on the order of 2 inches or less. Such a short lay length causes excess length due to the spiral, resulting in excessive insertion loss and electrical delay.
The inventors have discovered that the frequency of the electrical defects is not related to the actual lay length of the cable core assembly 44, but due to the periodicity of the deformations which occur while initially forming the twisted cable core assembly 44. More importantly, if the cable core assembly 44 is re-twisted to result in a second cable core assembly lay length, the defects and the frequency of the defects from the first cabling action of the cable core assembly 44 still generally remain.
According to one embodiment, the cable core assembly 44 may be optionally reinforced with at least one of a cable core assembly wrap 22 and a cable core assembly reinforcing layer 40, 40′ before the second recabling operation occurs. Most importantly, this chart shows that the insertion loss notch at about 1.1 GHz is generally caused by the initial first cabling operation at the lay length of the first cabling operation. Moreover, this example also shows that the periodic perturbations of about 3.75 inches along the length of cable 12 still remain in the cable 12, even though the actual lay length of the cable core assembly 44 is now longer, e.g., about 6 inches in this instance, as a result of the second cabling operation.
The above demonstrates that the insertion loss notches are a function of the perturbation length periodicity, and not the physical lay length of the twisted pairs 14, 16, 18 or 20 or components of the cable core assembly 44 following the final cabling operation for the cable 12. Such multiple cabling operation may be performed in order to optimize the electrical frequency of the insertion loss notch as well as other attributes of the cable 12 such as overall insertion loss that can be improved by having longer physical cable lay lengths.
One approach that is directed at solving the above noted problem is to first cable the cable core assembly 44 at a lay length of about 2 inches or less, for example, in a first cabling direction so that such lay length imparts the electrical problems at frequencies above the range of interest of about 2 GHz. Thereafter, the cable core assembly 44 is then optional provided with an additional (hoop) layer or wrap 22 which provides additional mechanical strength and integrity to the cable core assembly 44. However, due to the very tight twisting action of the cable core assembly 44 at a lay length of about 2 inches, as noted above this cable core assembly 44 still has the problems of electrical insertion loss, electrical delay and possibly some crushing of the components. The additional hoop wrap or layer 22 may comprise a dielectric yarn or tape so that the pitch of the additional wrap or layer 22 is longer than the width of the additional wrap or layer. This allows the metal of the pair metal shield tapes to be exposed to layers that are applied over the wrapping.
Next, the cable core assembly 44 is then re-cabled in a second opposite direction, which results in a longer net lay length of the cable core assembly 44, e.g., a lay length of 6 inches for example, thereby reducing the helical length and improving both the insertion loss and the electrical delay. Such re-cabling may also relax/reduce the crushing effect of the twisted pair(s) 14, 16, 18 or 20 with the short cable lay length(s), further improving the insertion loss of the cable. The improved mechanical strength and integrity of the cable core assembly 44, compared to the individual twisted pairs 14, 16, 18 or 20 within the cable 12, eliminates, or generally minimizes, the effects on the electrical properties due to the second cabling operation.
Because this second cabling/twisting operation is at a longer twist rate, it is also possible that reinforcement of the cable core assembly 44 may be necessary. In addition, at longer twist rates, the mechanical deformation forces induced by the manufacturing equipment are generally less severe.
Example of a Cable Construction
A first example, according with the above described embodiment, is shown in
If desired, one or more adhesive bands or filaments (not shown) may be wrapped around metallic hoop wrap 22, in an opposite helical direction, to assist further with maintaining the structural integrity of those components during subsequent manufacture, handling and installation of the cable 12. Lastly, a conventional exterior cover or jacket 42 surrounds and encases all the components together to form the cable 12.
If desired, one or more adhesive bands or filaments (not shown) may be wrapped around metallic hoop wrap 22, in an opposite helical direction, to assist further with maintaining the structural integrity of those components during subsequent manufacture, handling and installation of the cable 12. Lastly, a conventional exterior cover or jacket 42 surrounds and encases all the components together to form the cable 12.
Next, the cable core assembly 44 is cabled in a first direction so as to have a lay length of about 2 inches or less, 1.8 inches for example, and such lay length imparts the electrical problems at frequencies above the range of interest of about 2 GHz. Following the initial cabling of the cable core assembly 44, the cable core assembly 44 is then wrapped with a metallic hoop wrap 22 in order to immobilized and bind all of the plurality of surrounded twisted pairs 14, 16, 18 or 20 with one another and prevent the respective first and the second insulated conductors 24, 26, of each one of the surrounded twisted pairs 14, 16, 18 or 20, from one separating from one another during subsequent manufacture and handling of the cable. The metallic hoop wrap 22 also assists with shielding of the plurality of twisted pairs 14, 16, 18 or 20 of the cable core assembly 44.
Thereafter, the cable core assembly 44 is then re-cabled in a second opposite direction which results in a longer net lay length of the cable core assembly 44, e.g., a lay length of 6 inches for example, thereby reducing the helical lay length and improving both the insertion loss and the electrical delay. Such re-cabling may also relax/reduce the crushing effect of the twisted pair(s) 14, 16, etc., with the short cable lay length(s), further improving the insertion loss of the cable. The improved mechanical strength and integrity of the cable core assembly 44, compared to the individual twisted pairs 14, 16, 18 or 20 within the cable 12, eliminates, or generally minimizes, the effects on the electrical properties due to the second cabling operation.
If desired, one or more adhesive bands or filaments (not shown) may be wrapped around metallic hoop wrap 22, in an opposite helical direction, to assist further with maintaining the structural integrity of those components during subsequent manufacture, handling and installation of the cable 12. Lastly, a conventional exterior cover or jacket 42 surrounds and encases all the components together to form the cable 12.
According to one embodiment, the two insulated conductors 24, 26 of each of the first, the second, the third and the fourth twisted pairs 14, 16, 18 or 20 has a copper conductor with a diameter which is selected so as to provide no more than 4% of a resistance difference from any twisted pair of the assembly to any other twisted pair of the assembly.
While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/022617 | 3/16/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62133502 | Mar 2015 | US | |
| 62287646 | Jan 2016 | US |
