McGraw-Hill/Irwin Copyright © 2008, The McGraw-Hill Companies, Inc. All rights reserved.

Analogue & Digital Signals

Communications Media

Analogue & Digital Signals

Communications Media

TOPICSTOPICS

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Group MembersGroup Members

Aqeel Aqdus 1421-310023

Muhammad Faisal Akram 1421-310252

BSCS(6th)

PRESTON UNIVERSITY ISLAMABAD

IntroductionIntroduction

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What is Signal?

Types of SignalsTypes of Signals

Analogue Signals

(voice)Digital Signals

(computer oriented data)4

Analogue versus Digital Analogue versus Digital

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Analogue Digital

Analogue SignalsAnalogue Signals

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The term "analog" comes from the word

"analogous" meaning something is similar to

something else.

Signal that is continuous in time and can

assume an infinite number of values in a

given range (continuous in time and value)

Analogue SignalsAnalogue Signals

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In the natural world communication signals

are generally analog for example: Hearing with sound waves Sight with light waves

Analog transmissionAnalog transmission

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Characteristics of Analogue SignalsCharacteristics of Analogue Signals

The three main characteristics of analogue

signals are:FrequencyAmplitude Phase

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FrequencyFrequency

Frequency is the rate of change with respectto time.

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If a signal does not change at all, its frequency is zero.If a signal changes instantaneously, its frequency is infinite.

Frequency and period are the inverse of each other.

Two signals with the same amplitude and phase,but different frequencies

Two signals with the same amplitude and phase,but different frequencies

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Amplitude (A)Amplitude (A)

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A maximum value of the signal over time.

This is the strength of the signal.

The decibel (named in honor of Alexander

Graham Bell) is a popular measure of signal

strength. Sound level Type of Sound

40db normal speech

90db lawn mowers

110db shotgun blast

120db jet engine taking off

120db+ rock concerts

Two signals with the same phase and frequency, but different amplitudes

Two signals with the same phase and frequency, but different amplitudes

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PhasePhase

This is the rate at which the signal changes

its relationship to time, expressed as degree.

Analogue signals are sent via

PSTN.Analogue signals cannot be sent via

the ISDN without being first converted to

digital.

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Three sine waves with the same amplitude and frequency.

but different phases

Three sine waves with the same amplitude and frequency.

but different phases

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Digital SignalsDigital Signals

Discrete change between high and lowphysical property (such as voltage or current) over time.

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Digital SignalsDigital Signals

In the manmade world communication signals

are generally digital for example: Sound: telephone, radio, CD Light: television, computer monitor

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Communications Media Communications Media

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IntroductionIntroduction

Communicationo The message (data

and information) is

communicated via the

signal.o The transmission

medium “carries” the

signal.

Mediao Communication

path through which

data and information can be

transmitted.

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Sender Signal Receiver

Transmission medium

Communication MediaCommunication Media

The most commonly used

data communication media include:Coaxial CableTwisted Pair CableFiber Optic CableMicrowaveSatellite

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Coaxial CableCoaxial Cable

Coaxial cable is a two wire conductor with a

large bandwidth than twisted pair cable(TPC).

It is used in television ,radio and Ethernet

LANs.In voice communication systems, each

coaxial cable supports about 60 speech

channels.

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Coaxial CableCoaxial Cable

Advantages

• Cheap to install

• Conforms to standards

• Widely used

• Greater capacity than UTP to carry more conversations

Disadvantages

• Limited in distance

• Limited in number of connections

• Terminations and connectors must be done properly

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Twisted Pair CableTwisted Pair Cable

A type of cable that consists of two

independently insulated wires twisted around

one another. One wire carries the signal while

the other wire is grounded and absorbs signal

interference. It is light weight, easy to install,

inexpensive and support many different types of

network.

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Unshielded Twisted Pair(UTP) CableUnshielded Twisted Pair(UTP) Cable

Type of cable that consists of two unshielded

wires twisted around each other. Due to its low

cost, UTP cabling is used extensively for local

area networks(LANs) and telephone

connections. 

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Unshielded Twisted Pair(UTP) CableUnshielded Twisted Pair(UTP) Cable

Advantages

• A high installed base

• Cheap to install

• Easy to terminate

Disadvantages

• Very noisy

• Limited in distance

• Suffers from interference

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Shielded Twisted Pair(STP) CableShielded Twisted Pair(STP) Cable

STP is similar to UTP but with each pair

covered by an additional copper jacket or

foil wrapping. This shielding helps protect the

signals on the cables from external interference.

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Most common twisted-pair cablesMost common twisted-pair cables

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Name Type Bandwidth Applications

Cat3 UTP 16 MHz 10BASE-T and 100BASE-T4 Ethernet

Cat4 UTP 20 MHz 16 Mbit/s Token Ring

Cat5 UTP 100 MHz 100BASE-TX & 1000BASE-T  Ethernet

Cat5e UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet

Cat6 UTP 250 MHz 10GBASE-T Ethernet

Fiber Optic CableFiber Optic Cable

Fiber optic cable uses electrical signals to

transmit data. It uses light. In fiber optic cable

light only moves in one direction for two way

communication to take place a second

connection must be made between the two

devices. Fiber optic cable has bandwidth more

than 2 gbps (Gigabytes per Second).

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Fiber Optic CableFiber Optic Cable

Advantages

• High capacity

• Low attenuation

• Can go long distance

Disadvantages

• Costly

• Hard to install

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MicrowaveMicrowave

Microwave transmission is line of sight

transmission. The transmit station must be in

visible contact with the receive station. This sets

a limit on the distance between stations

depending on the local geography. Support at

least 30km distance.

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MicrowaveMicrowave

Advantages

• Medium capacity

• Medium cost

• Can go long distances

Disadvantages

• Noise interference

• Geographical problems due to line of sight requirements

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SatelliteSatellite

In satellite communication, signal transferring between

the sender and receiver is done with the help

of satellite. In this process, the signal which is

basically a beam of modulated microwaves is sent

towards the satellite. Then the satellite amplifies the

signal and sent it back to the receiver’s antenna present

on the earth’s surface. So, all the signal transferring is

happening in space. Thus this type of communication

is known as space communication.

Two satellites which are commonly used in satellite

communication are Active and passive satellites.32

SatelliteSatellite

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Each  communications satellite in geo-stationary

orbit around the earth which can support

thousands of speech channels and about 4 TV

channels simultaneously.

SatelliteSatellite

Advantages

• Low cost per user (for PAY TV)

• High capacity

• Very large coverage

Disadvantages

• High install cost in launching a satellite

• Receive dishes and decoders required

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