A. INTRODUCTION

CABLE DEFINITION

• A cable is defined by the National Electrical Code (NEC) as: “ A cable is a factory assembly of two or more insulated conductors having an overall covering”.

• A cable is the term used to describe the complete unit of multiple insulated conductors, strength members, and a cable jacket to keep all the cable elements together.(Kabel ialah medium perantaraan yang digunakan untuk menghubungkan komputer dalam rangkaian.Pemilihan sesuatu kabel adalah berkait rapat dengan topologi rangkaian, protokol dan saiz rangkaian)

CABLE TYPES

• Cable can be divided into two general categories :

a. Copper cables

b. optical fiber cables

COPPER CABLE

• Have conductors that are constructed of some form of copper metal.

• All signals are transmitted across the copper conductors in the form of elektrical energy.

OPTICAL FIBER CABLES

• Have conductors that are constructed of either glass or plastic.

• All signals are transmitted across the glass or plastic conductors in the form of light energy or pulses

• Some of the common types of cables used for communications systems include the following :

a. Unshielded twisted-pair (UTP) cable.

* Category 3

* Category 4

* Category 5

* Category 5e

* Category 6

b. Screened twisted-pair (ScTP) cable

* Category 3

* Category 4

* Category 5

c. Shielded twisted-pair (STP) cable.

* STP

* STP-A

d. Coaxial cable

* RG-58 A/U Thinnet Ethernet

* RG-8 thicknet ethernet

* RG-6 video cable

* RG-11 video cable

* RG-59 video cable

* RG-62

e. Optical Fiber Cable

* 50/125 micrometer multimode

* 62.5/125 micrometer multimode

* Singlemode.

TWISTED-PAIR CABLE

• Twisted-pair cables can be either shielded or unshielded construction.

• The important characteristic of these cables is that the individual conductors are twisted together into pairs.

• The individual pairs typically have different twist rates in the cable to minimize crosstalk coupling between cable pairs.

• Coaxial cable does not use twisted-pair construction because this is a single conductor type of media.

• Optical fiber cable transmits light in the form of light pulses and is not susceptible to electrical noise and crosstalk.

UTP USES

• Unshielded twisted pair (UTP) cabling, because of its 100-year history of use by telephone systems, both indoors and out, is also the most common cable used in computer networking. It is a variant of twisted pair cabling. UTP cables are often called ethernet cables after Ethernet, the most common data networking standard that utilizes UTP cables, although not the most reliable.

UNSHIELDED TWISTED-PAIR (UTP) CABLE

• UTP is the most common type of media used for communications systems and in structured cabling systems.

• UTP cable is used extensively due to its flexibility.

• UTP can be used for voice, low-speed data, high-speed data, audio and paging systems, and building automation and control systems.

• UTP cable can be used in both the horizontal and backbone cabling subsystems.

• For horizontal cables, the number of pairs recommended by industry standards is a four-pair cable

SHIELDED CABLE

• Twisted pair cables are often shielded in attempt to prevent electromagnetic interference.

• Because the shielding is made of metal, it may also serve as a ground.

• However, usually a shielded or a screened twisted pair cable has a special grounding wire added called a drain wire.

• This shielding can be applied to individual pairs, or to the collection of pairs. When shielding is applied to the collection of pairs, this is referred to as screening.

• The shielding must be grounded for the shielding to work.

Shielded Twisted Pair (STP)

• STP cabling includes metal shielding over each individual pair of copper wires. This type of shielding protects cable from external EMI (electromagnetic interferences). e.g. the 150 ohm shielded twisted pair cables defined by the IBM Cabling System specifications and used with token ring networks

Screened Shielded Twisted Pair (S/STP)

• S/STP cabling, also known as Screened Fully shielded Twisted Pair (S/FTP)[1], is both individually shielded (like STP cabling) and also has an outer metal shielding covering the entire group of shielded copper pairs (like S/UTP). This type of cabling offers the best protection from interference from external sources.

Screened Unshielded Twisted Pair (S/UTP)

• S/UTP, also known as Fully shielded (or Foiled) Twisted Pair (FTP), is a screened UTP cable

Advantages

• It is a thin, flexible cable that is easy to string between walls.

• Most modern buildings come with CAT 5 UTP already wired into the wall outlets or at least run between the floors.

• Because UTP is small, it does not quickly fill up wiring ducts.

• UTP costs less per foot than any other type of LAN cable.

Disadvantages

• Twisted pair’s susceptibility to the electromagnetic interference greatly depends on the pair twisting schemes (usually patented by the manufacturers) staying intact during the installation. As a result, twisted pair cables usually have stringent requirements for maximum pulling tension as well as minimum bend radius. This relative fragility of twisted pair cables makes the installation practices an important part of ensuring the cable’s performance.

COAXIAL CABLE

• Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insula-ting spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer (jacket).

• It is used as a high-frequency transmission line to carry a high-frequency or broadband signal.

• Because the electromagnetic field carrying the signal exists (ideally) only in the space between the inner and outer conductors, it cannot interfere with or suffer interference from external electromagnetic fields.

COAXIAL CONNECTORS• From the signal point of view, a connector can be viewed as a short,

rigid cable. • The connector usually has the same impedance as the related cable

and probably has a similar cutoff frequency although its dielectric may be different.

• High-quality connectors are usually gold or rhodium plated, with lower-quality connectors using nickel or tin plating. Silver is occasionally used in some high-end connectors due to its excellent conductivity, but it usually requires extra plating of another metal since silver readily oxidizes in the presence of air.

• One increasing development has been the wider adoption of micro-miniature coaxial cable in the consumer electronics sector in recent years. Wire and cable companies such as Tyco, Sumitomo Electric, Hitachi Cable, Fujikura and LS Cable all manufacture these cables, which can be used in mobile phones.

COAXIAL CABLE USES• Short coaxial cables are commonly used to connect home video equipment,

in ham radio setups, and in measurement electronics. They used to be common for implementing computer networks, in particular Ethernet, but twisted pair cables have replaced them in most applications except in the growing consumer cable modem market for broadband Internet access.

• Long distance coaxial cable is used to connect radio networks and television networks, though this has largely been superseded by other more high-tech methods (fibre optics, T1/E1, satellite). It still carries cable television signals to the majority of television receivers, and this purpose consumes the majority of coaxial cable production.

• Micro coaxial cables are used in a range of consumer devices, military equipment, and also in ultra-sound scanning equipment.

• The most common impedances that are widely used are 50 or 52 ohms, and 75 ohms, although other impedances are available for specific applications. The 50 / 52 ohm cables are widely used for industrial and commercial radio frequency applications (including radio, and telecommunications), although 75 ohms is commonly used for domestic television and radio.

OPTICAL FIBER CABLE