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Cable Tests
Introduction
4
4-5
Twisted Pair Cables
Twisted pair cable is currently the most popular cable in
LAN systems. The 10BASE-T standard for twisted pair
cabling systems is much more popular than coaxial based
Ethernet networks because it is easier to work with and is
inherently more reliable. The 10BASE-T standard is valid
for Unshielded Twisted Pair (UTP) and Shielded Twisted
Pair (ScTP).
UTP cable typically consists of four pairs of 24 AWG
(American Wire Gauge) solid or stranded wire surrounded
by an insulating jacket. ScTP cable adds a foil shield
around the four pairs to improve its noise immunity. The
wires in each pair are twisted around each other, and the
four pairs, in turn, are twisted together inside the cable
sheath. Most UTP and ScTP cables have characteristic
impedance of 100Ω. However, in some countries UTP is
also available in 120Ω. The Cable Tests described in this
chapter are designed to work with 100Ω cabling systems.