A. CAT5e: The Foundation for Many KVM

Applications

Category 5e (CAT5e) represents an enhanced iteration of the Category 5 standard, engineered to support data transfer speeds of up to 1 Gigabit per second (Gbps) over distances up to 100 meters, with a specified bandwidth of 100 MHz. 6 This cable type remains widely adopted in both residential and commercial networking environments, primarily due to its cost-effectiveness and its proven capacity to reliably support Gigabit Ethernet speeds. 6 CAT5e cables typically utilize 24 AWG (American Wire Gauge) copper conductors.17 The four twisted pairs within a CAT5e cable commonly feature twist rates ranging from 1.5 to 2 twists per centimeter (cm). 15 A crucial design aspect is the intentional variation of these twist rates among the individual pairs, a technique employed to effectively minimize crosstalk, which is the unwanted signal coupling between adjacent wire pairs.16 CAT5e is available in both UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair) configurations, providing adaptability to different installation environments based on their susceptibility to electromagnetic interference (EMI). 10 Notably, CAT5e cables are frequently identified as a suitable, and often preferred, medium for KVM extension, particularly for analog KVM systems. 24

B.

CAT6/6A:

Advancem

ents for

Digital

Data

Category 6 (CAT6) cabling supports data transfer speeds of 1 Gbps over its full 100-meter length. However, it can achieve higher speeds, specifically 10 Gbps, over shorter distances, typically ranging from 37 to 55 meters.12 The standard bandwidth for CAT6 is 250 MHz.10 CAT6 cables are characterized by tighter twist rates, generally exceeding 2 twists per centimeter, compared to CAT5e. They often incorporate an internal nylon spline that physically separates the four twisted pairs, a design feature aimed at further reducing internal crosstalk. 15 Conductors in CAT6 cables are typically 23 or 24 AWG. 12 Category 6 Augmented (CAT6A) significantly extends electrical specifications , supporting a bandwidth of 500 MHz. This allows for full 10 Gbps Ethernet performance over the entire 100- meter cable run. 10 CAT6A cables tend to have a larger overall diameter (averaging 0.29–0.35 inches) compared to CAT6 (0.21–0.24 inches). 10 This increased size and weight are attributed to enhanced shielding or greater separation between pairs, specifically designed to minimize Alien Crosstalk (ANEXT), which is interference from adjacent cables. 10 CAT6A typically uses 23 AWG copper conductors.1 2 Both CAT6 and CAT6A are designed to be backwards- compatible with CAT5e, ensuring interoperabilit y within existing network infrastructure s. 10

CAT7:

Designed

for High-

Frequency

Digital

Performa

nce

Category 7 (CAT7), also known as Class F cabling, is engineered to support 10 Gbps Ethernet and frequencies up to 600 MHz. 5 Its distinctive construction is S/FTP (Screened/Foi led Twisted Pair). This means each of the four individual twisted pairs is wrapped in its own foil shield, and there is an additional overall outer screen braid encompassin g all four pairs. 5 This multi-layered shielding provides extremely high levels of crosstalk performance and superior noise immunity. 5 Physically, this extensive shielding and tighter construction make CAT7 cables noticeably thicker and more rigid than lower category cables. 5 CAT7 conductors are typically 22 or 23 AWG. 12 While precise twists-per- centimeter values for CAT7 are not as commonly standardized or published as for CAT5e/6, the standard implicitly requires significantly tighter twisting to achieve its demanding high- frequency digital performance and crosstalk suppression targets. 26 CAT7 is officially rated for 10 Gbps transmission over the full 100-meter length. 5 Laboratory testing has demonstrated even higher capabilities, with some high-quality CAT7 cables transmitting 40 Gbps at 50 meters and even 100 Gbps at 15 meters, although these are not official standard ratings. 5 Its substantial bandwidth (600 MHz) is specifically designed for highly demanding digital applications, such as large data centers and telecommuni cations infrastructure where high- speed data transfer and minimal interference are paramount. 5 A critical distinction for CAT7 is its standardizati on status: it is an ISO/IEC 11801 standard 10 but is not recognized or endorsed by the ANSI/TIA 568 telecommuni cations cabling standard in the United States. 6 This lack of broad industry endorsement means that the specifications and performance of "Category 7" cabling can vary considerably between different manufacturer s. 6 Furthermore, CAT7 cables were originally designed to use proprietary GG45 or TERA connectors, rather than the ubiquitous RJ-45 (8P8C) Ethernet connector. 5 Although GG45 connectors are backward compatible with RJ-45, the limited adoption of CAT7 has made these proprietary connectors difficult to source. 5 This non- conformity with established cabling standards and connector types significantly contributed to CAT7's unpopularity and spurred the development of the more widely adopted CAT6A standard. 29 Many industry observers now consider CAT7 an "effectively dead standard" for general networking applications due to its proprietary nature and the subsequent emergence of more practical and widely supported alternatives like CAT6A and CAT8. 29 Higher category cables, particularly CAT6/6A and CAT7, achieve their superior performance metrics through specific design choices such as tighter twist rates, thicker sheaths, and extensive shielding. 5 These design decisions are fundamentall y driven by the need to reduce crosstalk (Near-End Crosstalk (NEXT) and Alien Crosstalk (AXT)) and enhance the signal-to- noise ratio for high- frequency digital data transmission. 15 The tighter twisting, for instance, is specifically engineered to ensure that both wires within a pair are exposed equally to external noise, enabling differential receivers to effectively cancel out common- mode interference. 1 6 While these characteristic s are unequivocally beneficial for digital data, they can inadvertently introduce or exacerbate problems for analog signals. Analog signals rely on the precise reproduction of continuous waveforms and accurate timing, rather than the interpretation of discrete bits. This fundamental difference means that design optimizations for digital performance can become detrimental to analog signal integrity, forming a central tenet of the argument presented here. CAT7's recognition by ISO/IEC, coupled with its notable absence of endorsement from the widely adopted TIA/EIA standards in North America, creates a unique situation. 6 Furthermore, its original design incorporated proprietary connectors (GG45/TERA) instead of the industry- standard RJ- 45. 5 This lack of broad industry standardizati on and the choice of proprietary connectors severely limited CAT7's market adoption, contributing to its designation as an "effectively dead standard" for general networking. 29 For analog KVM extension, this non- standard nature introduces significant practical challenges. These include inconsistent performance characteristic s across different manufacturer s 6 , difficulties in sourcing compatible components 29 and potential interoperabilit y issues with standard KVM extender hardware that is typically designed for TIA/EIA compliant cables. 25 This practical complexity and uncertainty further weaken the case for using CAT7 in analog KVM applications, even before considering its electrical performance characteristic s.

Table 1: Ethernet Cable Category Specifications (Relevant to KVM)

II. Understanding Ethernet

Cable Categories: A

Technical Comparison

III.

Why

High

er

Cate

gorie

s

(CAT

7) are

Detri

ment

al for

Anal

og

KVM

Exte

nsion

The design characteristic s that make higher- category Ethernet cables, particularly CAT7, superior for high-speed digital data transmission can paradoxically introduce significant challenges and degradation for analog signals, especially in KVM extension applications. A. Twist Ratios and Physical Length Discrepancie s Twisted pair cabling is fundamental to Ethernet for its ability to cancel out electromagne tic interference (EMI) and reduce crosstalk between neighboring pairs. 22 This is achieved by twisting two conductors of a single circuit together, ensuring that noise sources introduce signals into both wires equally, which can then be cancelled at the receiving end through differential mode transmission. 22 To prevent crosstalk between different pairs within the same cable, manufacturer s intentionally vary the twist rates (or pitch) for each of the four twisted pairs. 16 This variation ensures that conductors from different pairs do not consistently lie parallel to each other over long distances, which would otherwise undo the benefits of twisting and increase interference. 1 6 However, this necessary variation in twist rates among pairs has a direct physical consequence: it means that the actual physical length of the copper wire within each twisted pair will differ, even if the overall cable length is identical. 22 For example, if a cable is 100 meters long, the individual wires within the more tightly twisted pairs will be physically longer than those in less tightly twisted pairs. While specific twist rates are not standardized by IEEE or TIA/EIA, manufacturer s typically design CAT5e cables with 1.5-2 twists per centimeter, while CAT6 cables are more tightly wound with 2 or more twists per centimeter. 15 Higher category cables like CAT7, designed for superior crosstalk performance, necessarily employ even tighter and more varied twist rates. 26 The physical length of a twisted wire can be calculated using principles of helix geometry. If 'H' is the desired end length of the cable and 'D' is the diameter from each wire core center, the length of the wire 'L' for one turn of a helix is given by the formula: L = √(H² + (πD)²). This means that for a given cable length, a tighter twist (smaller pitch) results in a longer actual wire length. 33 For instance, if it takes 13 inches of 24 AWG wire to make 12 inches of cable, this demonstrates the ratio of wire length to cable length due to twisting. 33 The tighter the twist, the greater this difference becomes. B. Delay Skew and Analog Video Degradation The differing physical lengths of the twisted pairs within a single Ethernet cable lead directly to a phenomenon known as "delay skew". 22 Delay skew refers to the variation in signal propagation time between the wire pairs within an Ethernet cable. 36 Since electricity travels at a finite speed, and each pair has a slightly different physical length, the signals transmitted simultaneousl y across these pairs will arrive at the receiving end at different times. 23 For digital data transmission, the ANSI/TIA 568-C.2 standard specifies an acceptable propagation delay skew of less than 50 nanoseconds (ns) over a 100-meter link, with values under 25 ns considered excellent. 36 While this is critical for maintaining timing synchronizati on in high- speed digital networks, where excessive skew can cause timing errors, data corruption, and signal integrity issues 36 , the impact on analog video is distinct and often more visibly problematic. In analog video applications, particularly those transmitting RGB (Red, Green, Blue) component signals, each color component (and often sync signals) travels along its own dedicated twisted pair. 23 When these signals arrive at the display device at different times due to delay skew, the image components do not align correctly when recombined. 2 2 This improper color convergence results in noticeable visual artifacts such as subtle color defects, "ghosting" (faint, displaced copies of the image), and a degradation of overall resolution and color accuracy. 22 This negative effect can be even more pronounced on larger display screens. 41 Cables designed for lower skew, sometimes marketed as "low skew" or "no skew" UTP cables, exist to mitigate this for analog RGB applications. 2 3 However, these cables often achieve reduced skew by allowing less variation in twist pitch, which can, in turn, increase crosstalk—a significant problem for digital data transmission. 23 This highlights a fundamental conflict: design choices that optimize for digital data integrity (e.g., varied, tighter twists to reduce crosstalk) can directly worsen analog video quality by increasing delay skew. For analog KVM, where visual fidelity is paramount, the increased skew inherent in higher- category cables like CAT7, with their even tighter and more varied twists, becomes a distinct disadvantage. C. Capacitance, Impedance, and Analog Signal Integrity Beyond twist ratios and delay skew, the electrical characteristic s of cables, particularly capacitance and impedance, play a critical role in analog signal integrity. Analog signals are continuous waveforms, and their quality is highly susceptible to factors that can alter their shape, amplitude, or timing. 7 Capacitance exists between any two conductors, and in twisted pair cables, there is mutual capacitance between the two wires of a pair. 43 Tighter twisting, while beneficial for crosstalk reduction, can increase the mutual capacitance between the wires within a pair due to their closer proximity. 43 Higher capacitance in a cable can lead to a "rolloff" of high frequencies, effectively acting as a low-pass filter. This is particularly problematic if the driving component has a high output impedance, as the combination forms an RC filter that attenuates higher frequencies. 44 For analog video, this manifests as a loss of fine detail, color smears, or even full color loss, directly impacting picture resolution and clarity. 45 The ability of a cable to store charge (capacitance) directly impacts its fidelity; lower capacitance supports better signal transmission, reducing attenuation and allowing signals to travel longer distances without degradation. 9 Characteristic impedance is another crucial factor. Ethernet cables are designed with a characteristic impedance of 100 ohms. 31 However, traditional analog video signals (e.g., composite video, component video) typically operate with a characteristic impedance of 75 ohms. 41 When the characteristic impedance of the cable does not match the impedance of the source and load circuits, impedance mismatches occur. This causes portions of the signal to be reflected back and forth within the cable, leading to signal loss and degradation. 4 5 While active devices or baluns can be used to convert 75- ohm analog video signals to be transmitted over 100-ohm twisted pair, the quality of this conversion is critical, and poorly constructed baluns can have adverse effects on the signal. 41 CAT7 cables, with their extensive S/FTP shielding (individual foil shields for each pair plus an overall braid shield) 5 , are designed to virtually eliminate external interference and significantly improve noise immunity for high- frequency digital signals. 5 However, this heavy shielding can also contribute to higher mutual capacitance within the cable. 43 While shielding is excellent at preventing EMI, its effectiveness for analog signals can be compromised if it leads to increased capacitance that degrades the signal's frequency response. 7 Some shielded cables may even have "unnecessary design materials that do more harm than good". 56 For analog video, where the signal's "shape" is paramount, the increased capacitance and the challenges of maintaining impedance uniformity across the wide frequency range of an analog video signal can be more detrimental than the benefits of extreme shielding. 7 D. The "Digital-First" Design vs. Analog Requirement s The fundamental issue with using higher- category cables like CAT7 for analog KVM extension lies in their inherent design philosophy. These cables are meticulously engineered for high- speed digital data transmission, where the primary objective is to maintain a low Bit Error Rate (BER) by ensuring clear distinction between discrete voltage levels representing "0"s and "1"s. 8 Digital signals, composed of rapid voltage transitions, are highly susceptible to waveform degradation, and the integrity of these sharp transitions is crucial. 14 Modern digital systems often incorporate error detection and correction codes, and receivers frequently employ signal processing techniques like cable equalization and re- clocking to restore signal integrity and minimize bit errors. 8 In contrast, analog signals are continuous, infinitely variable waveforms. Their integrity depends on the accurate reproduction of their "shape" and amplitude, as even small, undesired voltage variations (noise) can lead to significant errors. 7 Unlike digital systems, real- time analog transmission typically lacks error correction mechanisms. 14 The features that make CAT7 excel in digital environments can be counterprodu ctive for analog signals. For example, the extensive shielding in CAT7 (S/FTP) is designed to provide maximum immunity against external interference and crosstalk for high- frequency digital signals. 5 However, this shielding can increase the cable's mutual capacitance 43 , which, as discussed, can cause high- frequency rolloff and signal degradation for analog video. 9 While shielding does reduce noise, the resulting increase in capacitance can negatively impact the continuous analog waveform's fidelity, leading to a loss of detail or color accuracy. 7 Furthermore, the impedance characteristic s of cables optimized for digital signals (typically 100 ohms) may not be ideal for analog video signals, which often prefer 75 ohms. 41 While baluns can bridge this impedance difference, they introduce additional components and potential points of failure or signal degradation if not perfectly matched. 41 The design of higher- category cables focuses on maintaining signal integrity for discrete digital pulses, where the timing of transitions and the ability to distinguish between two states are paramount. This is a different challenge from preserving the continuous, nuanced waveform of an analog signal, which is more sensitive to subtle changes in capacitance, inductance, and impedance uniformity across a broad frequency spectrum. 55 Analog KVM extenders, especially older models or those designed for VGA, often operate on principles best suited for CAT5e or CAT6 cabling. 25 These extenders may employ specific balancing and equalization techniques that are calibrated for the known electrical properties of these lower- category cables. Introducing a CAT7 cable, with its significantly different internal geometry, tighter twists, and higher shielding, can disrupt these carefully engineered characteristic s, leading to suboptimal performance or even signal failure. The focus on maximizing bandwidth and reducing crosstalk for digital signals in CAT7 inadvertently creates conditions that are less favorable for the faithful reproduction of analog waveforms. IV. Conclusion The analysis demonstrates that while higher-rated Ethernet cables, specifically CAT7, offer significant advantages for high- speed digital data transmission due to their advanced construction, extensive shielding, and increased bandwidth, these very characteristic s render them suboptimal, and potentially detrimental, for analog KVM extension and switching. The core of the issue lies in the fundamental differences between digital and analog signal transmission requirements. CAT7 cables achieve superior digital performance through design choices like significantly tighter and more varied twist rates for each pair, and comprehensiv e S/FTP shielding. These features, while excellent for minimizing crosstalk and noise in digital networks, lead to: 1. Increa sed Physic al Length Discre pancie s and Delay Skew: The varied and tighter twist rates in CAT7 cables result in greater differe nces in the actual physic al length of the copper condu ctors within each twisted pair. This directly contrib utes to increas ed propag ation delay skew, where the Red, Green, and Blue compo nents of an analog video signal arrive at the receive r at slightly differe nt times. This timing misalig nment manife sts as visible artifact s such as color degrad ation, ghosti ng, and a reducti on in overall image resolut ion and color accura cy on the display . 2. Elevat ed Mutual Capaci tance and Imped ance Misma tch Challe nges: The tighter twistin g and extensi ve multi- layered shieldi ng (S/FTP ) in CAT7 can increas e the mutual capacit ance betwee n the wires within each pair. For analog signals , higher capacit ance can act as a low- pass filter, causin g a "rolloff " of high freque ncies and a loss of fine detail in the video signal. Further more, while Ethern et cables mainta in a 100- ohm charac teristic imped ance, traditio nal analog video signals often require a 75- ohm imped ance. The precise imped ance control and high- freque ncy optimi zation of CAT7, while benefi cial for digital, may not align with the broade r freque ncy respon se and imped ance matchi ng require ments for analog video, potenti ally introdu cing reflecti ons and signal degrad ation. In essence, CAT7 cables are optimized for a "digital- first" world, where the goal is to transmit discrete bits with minimal error. Their design prioritizes factors like bit error rate and high bandwidth for digital data streams. Analog signals, however, demand the faithful reproduction of continuous waveforms, where subtle distortions in timing, capacitance, or impedance can significantly impact visual quality. Analog KVM extenders are often designed and calibrated for the electrical properties of lower- category cables like CAT5e or CAT6, which may have characteristic s more conducive to analog transmission or are better understood by the extender's balancing and equalization circuitry. Therefore, for analog KVM extension and switching, the pursuit of higher- category cabling like CAT7 represents a diminishing return. Its advanced features, instead of improving performance, can introduce specific signal integrity challenges that are less prevalent with CAT5e or CAT6. For reliable and high-quality analog KVM operation, selecting a cable category that aligns with the signal's inherent characteristic s and the extender's design parameters, such as CAT5e or CAT6, is generally more beneficial and cost- effective. The principle that "higher is not always better" holds true when the signal type is analog, emphasizing the critical importance of matching cable design to the specific application and signal requirements.