Exercise 2 Cable Identification

Exercise 2 Cable Identification

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Objectives for Exercise 2 ■ At the end of this Exercise, you will be able

to: – Describe the construction of coaxial cable. – Explain the difference between shielded and unshielded twisted-pair cable.

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Objectives (continued) ■

Describe cable impedance and explain the difference between impedance and resistance.

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Discuss the sources of electromagnetic interference and ways to minimize its effects.

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Types of Cables Used In Networks ■

Copper Cables

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Fiber Optic Cable

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Factors Affecting Copper Cable Performance ■

Impedance

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Electrical Interference

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Cable Impedance ■

Resistance

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Reactance

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Cable Resistance ■

Opposes current flow.

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Is measured in ohms.

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Can be measured with an ohmmeter.

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Is directly proportional to cable length.

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Cable Reactance ■

Opposes changes in voltage or current.

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Is rated in ohms but cannot be measured with an ohmmeter.

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Is the result of capacitance and inductance between conductors.

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Determined by their diameter and spacing.

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Impedance ■ Impedance is the vector sum of

resistance and reactance. Im ped an c e

Resistance

Reactance

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Electrical Interference ■

Degrades data signals.

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Can result in data errors.

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Types of electrical interference: – Crosstalk – EMI/RFI

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Interference Protection Techniques ■

Cancellation – Twisted wire pairs create out of phase magnetic fields which tend to cancel each other.

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Shielding – Grounded metal braid or foil surrounding a conductor protects it from external radiation.

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Crosstalk Between Conductors The interference generated when a magnetic field from one wire induces current into another wire. ■ Fields of opposite phase tend to cancel each other. Insulation ■

Electromagnetic Fields

Copper Conductor

+ -

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EMI/RFI Results from the cable being placed in an external magnetic field. ■ Shielding blocks external magnet interference. ■

Conductor Magnetic Field Grounded Shield

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Types of Copper Network Cables ■

Coaxial Cables

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Unshielded Twisted Pair (UTP)

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Shielded Twisted Pair (STP )

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Coaxial Cable Coaxial cable is comprised of : ■ Central conductor ■ Dielectric material ■ Copper braid Braided Shield ■ PVC jacket. PVC Jacket

Conductor

Dielectric

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Coaxial Cable Characteristics ■

The center conductor and the braided shield make up the two paths of a signal circuit.

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Two types of coaxial cable used in networks are: – RG-6 (10Base5) Thicknet cable. – RG-58 (10Base2) Thinnet cable.

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Unshielded Twisted Pair

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Unshielded Twisted Pair Characteristics Typical impedance is 100 ohms. ■ Contains four pairs of 22 or 24 gauge solid copper wire. ■ Relatively small diameter of 0.17” makes it easy to install. ■ Has no physical shielding. ■ Uses cancellation effect to reduce crosstalk and EMI/RFI noise. ■

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Categories of UTP Cables Category 1 - Not Rated ■ Category 2 - Telephone Wiring ■ Category 3 - 10Base-T Ethernet ■ Category 4 - 16 Mbs Token Ring ■ Category 5 - 100Base-T Ethernet ■

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Shielded Twisted Pair (STP)

Shield Drain Wire

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Shielded Twisted Pair Characteristics ■

Available for: – 100 ohm 10Base-T – 150 ohm Token Ring

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Utilize both shielding and cancellation interference techniques.

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Typical Fiber Optic Cable

Jacket Buffer Cladding Core

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Fiber Optic Cable Characteristics Immune to electrical interference ■ Extremely secure ■ Very low loss ■ Very expensive to install and maintain ■ Requires electrical-optical-electrical signal conversion ■

Now it’s your turn...

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