Twisted Pair Cabling:
Unshielded Twisted Pair
Unshielded Twisted Pair (UTP)
has been designed for use in voice applications and local area
networks. Because of the comparatively low cost this cable is
widely used and is available in several different performance
categories (Categories 3, 4, 5 and 6). Over 99% of our copper
installations are UTP versus shielded twisted pair (STP),
which is rarely used.
Electromagnetic interference is present in all types of cabling
to some degree. There are two basic types of electromagnetic
interference (EMI) that cable engineers worry
about-electromagnetic emissions and electromagnetic immunity.
Emissions refer to energy that is radiated by the cable, and
immunity is the ability of the cable to reject outside signals.
In local area networks (LANs), failure to properly manage EMI
can have an adverse effect on the integrity of the signal being
transmitted.
In an
unshielded cable, careful design of the cable and the associated
electronic equipment results in a "balance" of the currents in
the two conductors of a pair. That is, the currents in the two
conductors are equal in magnitude but flowing in opposite
directions. Proper installation and termination of the cable is
also critical to maintaining this balance.
In a
balanced system, there is very little radiation of EMI since the
external field from one conductor is effectively canceled by the
external field from the other conductor of the pair. Generally,
the more twists per foot of cable, the better the cable is
electrically balanced. Category 5 cable has
more twists per foot than Category 3 or 4
cables and, therefore, offers better protection from EMI
problems.
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