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Not All Modular Patch Cords Are Created Equal!

Often over-looked as a secondary contributor to network per-formance, modular patch cords actually represent one of the largest sources of performance variation in high performance cabling systems. Much like the weakest link in a chain, a patch cord with poor transmission characteristics can degrade system performance significantly, even when used with the best performing outlets and cable. Low quality patch cords may reduce initial installation costs, but they can compromise network performance and reliability and eventually cost much more over the life of a system.

So how does one determine which patch cords are poor performers? Most patch cords look substantially the same, however, small differences in conductor position within the plug can cause large differences in crosstalk performance. The modular plug is susceptible to signal interference due to the close spacing of the blades and tight parallel array of conductors at the nose of the plug. Additionally, cable pairs must be straightened for plug termination. Excessive un-twisting of pairs during this process contributes to excessive pair-to-pair signal coupling between the conductors (i.e., crosstalk).

Even for skilled cable assemblers, ensuring proper cable preparation, precise placement of conductors, and correct plug termination for every single modular cord can be challenging. How can a manufacturer ensure that all category 6 cords shippped will provide acceptable per-formance? Tight quality control and use of high performance cable and modular plug components are a good start. The only real way to guarantee modular cord performance, however, is to test every modular cord across all pairs combinations, in both directions after assembly.

Chart 1: Number of Cords out of 40 that passed Category 6

To demonstrate the variability in patch cord assembly and performance, Siemon developed an objective modular patch cord test to measure the most difficult parameter to control - NEXT. NEXT was measured using a test configuration similar to that specified in the latest ANSI/TIA/EIA-568-B.2-1 category 6 Draft 9 (June 16, 2001). The test set-up consisted of patch cord adapters mated directly to a standard handheld field tester. The tester was calibrated prior to testing to ensure accurate measurements. The test adapters used performed at the center of the allowable TIA range specified for crosstalk for all six pair combinations. By centering test adapter performance, un-acceptable test results indicated a patch cord was not compliant with the current de-embedded NEXT plug range specified by Draft 9.

The Siemon Company tested its standard category 6 MC6™ patch cords against 6 different competitive brands. All cords, including Siemon's, were randomly purchased through distribution. A total of twenty 3ft (.09m) and twenty 15ft (4.6m) patch cords of each brand were evaluated for NEXT performance on all six pair combinations in both directions, providing a total of 12 measurements per cord. Patch cords were compared based on the minimum margin of the worst case pair throughout the entire frequency range of 1 to 250 MHz.

Only Siemon and one other manufacturer passed all 40 cords (see Chart 1). A significant number of cords from five other manufacturers failed. The performance gap between acceptable patch cords and failures results from inconsistency in the assembly process. 100% factory transmission testing is critical to ensure the quality of the assembly process. Without 100% trans-mission testing during production, poor performing cords are not detected and eventually end up in customer installations.

Chart 2: Difference between Best and Worst Patch Cord NEXT

Another method of demonstrating the variation between manufacturing processes was to compare the range of margin between the best and worst patch cord within any one group. The data in Chart 2 shows that the manufacturers with failures had greater performance variation between their patch cords than Siemon. Large patch cord NEXT variation will result in inconsistent network performance. The uniform performance of Siemon MC6™ patch cords ensures customers receive consistent channel and network performance.

The Siemon Company achieves superior category 6 patch cord performance by using the same stringent test method and criteria used in this test. Siemon's investment in modular cord quality assurance is unparalleled in the industry, and the results are clear - our customers get the highest quality patch cords available. Not every patch cord is created equal, so make sure you get the best by specifying patch cords that are 100% factory transmission tested.

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