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White Paper: The comparison of the performance of screened vs. unscreened cabling systems

A study conducts a practical test to demonstrate the importance of EMC cable parameters in selecting the right cabling system

(PresseBox) (Stolberg, ) The discussion of the pros and cons of various cable designs (unscreened vs. screened) is becoming the focus of attention at an international level to an ever greater extent as new standards for the transmission of 10-Gigabit Ethernet over copper cabling are published and various standards on passive networking are revised and amended.
This was the gist of a new White Paper* prepared by the GHMT (Gesellschaft für Hochfrequenz Mess Technik) AG, a neutral body which works independently of individual manufacturers.

Important parameters that have recently been included in standards, such as the so-called “coupling attenuation” or “alien NEXT” parameters, describe the electromagnetic characteristics of cabling for the first time through the use of normative limit values and – for this reason alone – should therefore be taken into account in the selection of the components used as well as in the planning process.

Furthermore, current standards now take into consideration the fact that generic cabling is no longer used in office buildings “only” and is therefore also exposed to other loads due to mechanical, invasive, chemical and electromagnetic impacts.

The so-called MICE specification in accordance with the new IEC 61918 Ed.1: 2007-12, to which the DIN EN 50173 series of standards also refers, exactly reflects these varying environmental conditions and helps designers and users to choose suitable cabling components for the environment in question.

The study carried out by the GHMT AG shows the effects of the use of screened and unscreened systems with regard to the following topics:
- Cable parameters
- Electromagnetic compatibility
- Supplies of electrical energy
- Unilateral and bilateral earthing.

In a practical test, six different cabling systems were examined for their high-frequency parameters and subjected to typical sources of interference in offices and computer centres such as walky-talkies, mobile phones and fluorescent lamps. Experiments giving a straightforward demonstration of how the systems behave with typical installation methods such as supporting cables on mesh cable trays were also carried out. This allows both cable designs to be compared completely and meaningfully.

Here are the results of the study underlying the test:
- State-of-the-art S/FTP cabling systems can achieve optimum transmission characteristics
- State-of-the-art U/UTP cabling systems can also achieve very good transmission characteristics
- To ensure secure 10 Gbase-T transmission, it is important to be familiar with the prevalent electromagnetic environment and to choose cabling components that also take this environment into account.
- The measurement-based analyses in the lab show considerably better EMC characteristics (emission and immunity) for screened systems than for unscreened cabling systems.
- Screened systems consistently achieve considerably better PS ANEXT and coupling attenuation values than unscreened systems, although the latter showed similarly good or even better LCL values.
- The systems with the best coupling attenuation values also achieved the best EMC values in the (active) immunity tests ? coupling attenuation is THE parameter that is suitable for comparing the EMC characteristics of cabling systems.
- In practical tests, the systems under test were exposed to sources of disturbance that are typical of offices and computer centres, such as walkie-talkies, GSM mobile phones, fluorescent lamps, etc. The results could be directly correlated to the lab measurements ? the values stated for the pertinent MICE environmental classes correlate well with the sources of disturbance present in day-to-day practice.
- It is not possible to ensure interference-free transmission of 10Gbase-T over the U/UTP systems tested even in electromagnetic environments in accordance with the lowest MICE class E1.

The complete White Paper on the study is available free of charge via e-mail under

* The study entitled "The comparison of the performance of screened vs. unscreened cabling systems" was commissioned by LEONI Kerpen, Corning, Dätwyler Cables, Draka, R&M and Tyco Electronics in June 2008 and conducted by the GHMT AG.


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