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Chapter 7. Coaxial Cable Test
7.1
Properties of Coaxial Cables
The coaxial cable offers numerous benefits. It is hardly influenced by electromagnetic
disturbances and supports high bandwidths. Thus, many customers prefer using the coaxial
cable for their cable TV and data applications.
A typical coaxial cable consists of:
•
Center Conductor: This conductor usually consists of a fairly heavy, solid and yet
flexible wire. Stranded wire is also used. Though solid conductors are preferred for
permanent installation, a cable with stranded wires is more flexible and easier to
connect to devices.
•
Insulation: Also referred to as dielectric layer. It ensures electrical insulation and
keeps the inner and outer conductors in precise coaxial alignment.
•
Outer Conductor or Shield: This layer protects the inner conductor from external
electrical perturbations. The shield can consist of wire mesh, metal foil or a
combination of both. This shield makes the coaxial cable extremely impervious to
electromagnetic disturbances.
•
Sheath: A robust sheath made of plastic or Teflon protects the coaxial cable from
mechanical damage.
Coaxial cables differ by their impedance (in ohm), which indicates the cable's resistance of
the current. Thus, a coaxial cable of type RG-59 and RG-6 typically has an impedance of 75
ohm, whereas a RG-58 cable has 50 ohm.
7.2
Troubleshooting Coaxial Cables
Use only high-grade connectors and tools to properly seal coaxial cable networks. If cable
has an error, check the following failure points:
Faulty connection: Check if neutral conductor is properly separated from shield.
•
•
Cable Short Circuit: Could occur if cable has been improperly connected to near
and far end. In case of a short circuit, check the resistance values indicated on the
tester. A value of 0 (zero) indicates that the fault is located at the near end of the
cable, whereas a value of ~ 20 ohm points to the far end.
•
Cable Interruption: Occurs frequently. In this case, check out the length
measurement result. A value of 0 (zero) for cable length points to a fault located at
the near end.
LanTEK III
User Manual
161809 Iss 2
Page71
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