R&M Data Center Handbook

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If for visualization some noise is added, it becomes obvious that at faster data-transmission rates, the sensitivity to
interference increases tremendously. As a result, the sensitivity to interference in the EMC area gets increasingly
higher as the data-transmission rate increases.
During 2008, a group of cable suppliers, including R&M, came together to compare the EMC behavior of various
cabling types in a neutral environment. To ensure the independence and objectivity of the results, a 3rd party test
laboratory was commissioned with the investigation, specifically the “Gesellschaft für Hochfrequenz Messtechnik
GHMT” (“Organization for High Frequency Testing”) located in the German town of Bexbach. The goal of the
study was to answer the following questions concerning the selection of the cabling system:
• Which parameters must be estimated in order to draw meaningful conclusions about the EMC behavior
of shielded and unshielded cabling systems
• Which special measures are necessary when using shielded or unshielded cabling in order to ensure
operation that conforms to legal requirements and standards
• How does the EMC behavior of shielded and unshielded cabling compare during the operation of 1G and
10GBase-T
The basic idea was not to pit shielded and unshielded systems against each other, but rather to clearly indicate
the basic conditions that must be adhered to in order to ensure problem-free operation of 10GBase-T that is in
conformance with legal requirements. By doing so, assistance can be offered to planners and end customers so
they can avoid confusion and uncertainty when selecting a cabling system.
The results presented are exclusively those from the independent EMC study carried out by GHMT; the interpretation
of the results and conclusions drawn are, however, based on analyses by R&M.
Equipment under test and test set-up
The examination of six cabling systems was planned:
• 1x unshielded Cat 6
• 2x unshielded Cat 6A
• 3x shielded Cat 6A with shielded twisted pairs (foil) and different degrees of coverage of the braided
shield (U-FTP without braided shield, S-STP “light” with moderate braided shield, S-STP with good
braided shield).
The Figure below shows the results from the antecedent measurements according to ISO/IEC 11801 (2008-04).
The values given are the margin vs. the Class E A limits, with the exception of coupling attenuation, which is given
as an absolute value.
Cable parameters in accordance with ISO/IEC 11801 (2008-04)
Surprisingly, the transmission parameters (IL, NEXT, PS NEXT, TCL and RL) of the Cat 6A UTP systems are at a
similar level as those from the shielded systems. Except with the older Cat 6 system, the values are more or less
comparable to each other. Noticeable is that the PS ANEXT requirements are barely reached, if at all, by the
unshielded systems. As soon as shielding is present, the ANEXT values are improved 30 to 40 dB so much that
they no longer present a problem.
R&M Data Center Handbook V2.0 © 08/2011 Reichle & De-Massari AG Page 149 of 156