Fluke CableAnalyzer DSP-4000 Series, User Manual

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DSP-4000 Series
Users Manual
7-2
Cables are designed to perform best in specific applications. For example, power
cables are designed to minimize power losses at frequencies of 50 Hz or 60 Hz.
LAN cables are designed to minimize signal distortion at higher frequencies.
Two types of cables are designed for use with LAN systems: twisted pair cable
and coaxial cable.
Twisted Pair Cable
Twisted pair cable consists of wire pairs that are twisted together, as shown in
Figure 7-1. The wires are twisted to minimize crosstalk between the cable pairs.
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Figure 7-1. Twisted Pair Cable Construction
Each cable pair forms a complete electrical path for signal transmission. The
currents flowing through the wires in each pair are equal, but flow in opposite
directions. These currents produce electromagnetic fields that could transmit
electrical noise to nearby wires. However, the fields surrounding the two wires
have opposite polarities. Twisting the wires together causes the fields to cancel
out, which minimizes the electrical noise, or crosstalk, generated by each cable
pair.
There are two types of twisted pair cable: shielded twisted pair (STP) and
unshielded twisted pair (UTP). STP cable, which may also be referred to as ScTP
(screened twisted pair) or FTP (foil-screened twisted pair), contains a conductive
shield that is electrically grounded to protect the wires inside from electrical noise.
STP cable is more expensive and more difficult to install than UTP.