INTRODUCTION TOANALOG COMMUNICATIONS

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Course objective

At the end of the semester, the learner will be able to:

• Explain the principles of a communication systems

• Discuss the nature of information, different types of signals involved and their characteristics

• Determine the need of modulation and differentiate various type of modulation techniques

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“How do you want to send data/information to someone who is far

from you?”

COMMUNICATION OVER LONG DISTANCES IS NO LONGER A PROBLEM.

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Communication : To transfer information from one place to another

Communication System HistoryCommunication System History

• 1837 – Samuel Morse invented telegraph.• 1858 – First telegraph cable across Atlantic (Canada – Ireland)• 1876 – Alexander Graham Bell invented telephone.• 1988 – Heinrich Hertz introduce electromagnetic field theory.• 1897 – Marconi invented wireless telegraph.• 1906 – Radio communication system was invented.• 1923 – Television was invented.• 1938 – Radar and microwave system was invented for World

War II. • 1956 – First telephone cable was installed across Atlantic.• 1960 – Laser was invented• 1962 – Satellite communication• 1970 – Corning Glass invented optical fiber.• 1985 – Facsimile machine.• 1988 – Installation of fiber optic cable across Pacific and

Atlantic.• 1990 – World Wide Web and Digital Communication.• 1998 – Digital Television.

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• The words "tele", "phon", and "graph" are derived from Greek. – Tele – means ‘at a distance’– Phon – means sound or speech – Graph - means writing or drawing

• Therefore, telecommunication means communication at a distance. This can be done through wires called transmission lines or through atmosphere by a radio link. Other examples include:

– Telephone – speaking at a distance Television – seeing at a distance Telegraph – writing at a distance

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Basic Communication SystemBasic Communication System

TransmitterTransmission

Medium ReceiverInput

TransducerOutput

Transducer

Noise

wired / wirelessmtx(t)

s(t) r(t)

ptx(t)

n(t)

mrx(t)prx(t)

s(t) – Input signal; audio, video, image, data etc.mtx(t) – Modulating signal; input signal that has been converted to electrical signal.ptx(t) – Modulated signal transmit by the transmitter.n(t) – Noise signal.prx(t) – Modulated signal receive by the receiver.mrx(t) – Modulating signal at the receiver.r(t) – Output signal.

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• Input Transducer – convert input signal, s(t) in electrical forms. eg: microphone.

• Transmitter – involve modulation process – convert modulating signal, mtx(t) to modulated signal, ptx(t). And finally transmit the signal.

• Transmission medium – connecting the transmitter and the receiver that enable the modulated signal, ptx(t) propagate through the medium.

• Receiver – receive the modulated signal, prx(t) and then convert the signal to modulating signal, mrx(t) through the process called demodulation.

• Output Transducer – convert the modulating signal, mrx(t) to its original forms (output signal), r(t) that is useful to the users. eg: loud speaker.

Component Function in Basic Component Function in Basic Communication SystemCommunication System

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Transmission Medium (Guided)Transmission Medium (Guided)

Twisted pair

– Unshielded Twisted Pair (UTP)

– Shielded Twisted Pair (STP)

Coaxial

Fiber Optic

Waveguide

Coaxial Cable

•First type of networking media

used

•Available in different types (RG-

6 – Cable TV, RG58/U – Thin Ethernet, RG8 – Thick Ethernet

•Largely replaced by twisted pair for

networks

Unshielded Twisted PairAdvantages

InexpensiveEasy to terminateWidely used, testedSupports many

network types

DisadvantagesSusceptible to

interferenceProne to damage during installation

Distance limitations not understood or

followed

Glass Media

• Core of silica, extruded glass or plastic

• Single-mode is 0.06 of a micron in diameter

• Multimode = 0.5 microns

• Cladding can be Kevlar, fibreglass or even steel

• Outer coating made from fire-proof plastic

Advantages Can be installed over long distances Provides large amounts of

bandwidth Not susceptible to EMI RFI Can not be easily tapped (secure)

Disadvantages

Most expensive media to purchase and install

Rigorous guidelines for installation

Wireless

CHAPTER 1 INTRODUCTION TO COMMUNICATION SYSTEMS

WHAT IS BASEBAND ?

Data

(nonelectrical)

Electrical

Waveform

Without any shift in the range of frequencies of the signalThe signal is in its

original form, not changed by modulation.

Baseband is the original information that is to be Sent.

Modulation

Continuous wave Pulse

PAM

PPM

PWM

PCM

Digital Analog

ASK

FSK

PSK, etc

Linear Exponential

AM

DSB-SC

SSB

VSB

FM

PM

Based on the type of

carrier wave

Based on the type of modulating

signal

Based on the relationship

between modulating

and modulated

signal

TYPE OF MODULATION

Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM)

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TYPE OF MODULATION

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ANALOG AND DIGITAL SIGNAL

The information can be in term of : Analog form such as Human Voice or Music Digital form such as binary-coded number.

There are 2 basic type of communication : Analog Communication Digital Communication

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Chapter 1 Introduction to Communication Systems

Example of Analog signal is shown below:

Analog comes in term of Sinusoid (Sine or Cosine wave)

Analog signals are continuous electrical signals that vary in

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Analog Signals

• Human Voice – best example• Ear recognises sounds 20KHz or less• AM Radio – 535KHz to 1605KHz• FM Radio – 88MHz to 108MHz

Chapter 1 Introduction to Communication Systems

Example of Digital Signal is shown below:

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Digital signals

• Represented by Square Wave• All data represented by binary values• Single Binary Digit – Bit• Transmission of contiguous group of bits is a

bit stream• Not all decimal values can be represented by

binary

1 0 1 0 1 0 1 0

Analog or Digital• Analog Message: continuous in amplitude and

over time– AM, FM for voice sound– Traditional TV for analog video– First generation cellular phone (analog mode)– Record player

• Digital message: 0 or 1, or discrete value– VCD, DVD– 2G/3G cellular phone– Data on your disk– Your grade

• Digital age: why digital communication will prevail

Chapter 1 Introduction to Communication Systems

WHAT IS FREQUENCY SPECTRUM ?

IT CONSISTS OF ALL FREQUENCIES CONTAINED IN THE WAVEFORM AND THEIR RESPECTIVE AMPLITUDE IN THE FREQUENCY DOMAIN.

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The Bands

VLF LF MF HF VHF UHF SHF EHF

Su

bm

illim

ete

r R

an

ge

ELF

3MHz 30MHz300MHz 3GHz 30GHz 300GHz

FarInfra-Red

300KHz30KHz 3THz

Radio Optical

3KHz

NearInfra-Red

700nm

1PetaHz

Red

Orange

Yellow

Green

Blue

Indigo

Violet

600nm 400nm500nm

UltravioletX-Ray

1500nm

Frequency SpectrumFrequency Spectrum

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100M

Hz

Waveguide

Coaxial Cable

Twisted Pair

Cable

Infra

red

Visib

le

Ultra

viol

et

Optical Fiber

Extra

H

igh

F

req

uen

cy

EH

FS

up

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Hig

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qu

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ltra H

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Hig

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igh

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Med

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MF

Low

F

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LF

Very L

ow

Fre

qu

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VL

FA

ud

io

Line-of-sight radio

Skywave

radio

Groundwave

radio

Wavelength

Frequencydesignations

Transmission media

Propagation modes

Representativeapplications

Frequency

Laser beam

100km 10km 1km 100m 10m 1m 10cm 1cm 10-6m

Tele

ph

on

eT

ele

gra

ph

Mob

il rad

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F T

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nd

FM

Mob

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d A

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avig

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ban

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Wire

less c

om

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lar, P

ag

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tellite

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row

ave

rela

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arth

-sate

lliteR

ad

ar

Wid

eb

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d d

ata

1kH

z

10kH

z

100kH

z

1M

Hz

10M

Hz

1G

Hz

10G

Hz

1G

0H

z

10

14H

z

10

15H

z

convert from frequency (f) to wavelength

where c = speed of light.

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Chapter 1 Introduction to Communication Systems

WHAT IS BANDWIDTH ?

IT IS THE DIFFERENCE BETWEEN THE HIGHEST FREQUENCIES AND THE LOWEST FREQUENCIES OF THE INPUT SIGNAL FREQUENCIES (fB = 2fm ).

The bandwidth of a communication signal bandwidth of the information signal.

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Chapter 1 Introduction to Communication Systems

EXAMPLE 1:

If human voice frequencies contain signals between 300 Hz and 3000 Hz, a voice frequency channel should have bandwidth equal or greater than 2700 Hz.

a communication channel cannot propagate a signal that contains a frequency that is changing at a rate greater than the Channel Bandwidth.

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Transmission MediumTransmission Medium

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PROPAGATION TECHNIQUES A signal can be propagated in 3 ways: 1. Ground-Wave Propagation Frequency < 2 MHz 2. Sky-Wave Propagation Frequency between 2 MHz and 30

MHz 3. Line-of-Sight Propagation Frequency > 30 MHz

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Ground-Wave Propagation

A propagation of radio frequencies are shown below:

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Sky-Wave Propagation

A propagation of radio frequencies are shown below:

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Line-of-Sight Propagation

A propagation techniques (continued):

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VHF band and up, the propagation tends to straighten out into line-of-sight(LOS)waves

Types of TransmissionTypes of Transmission

• SimplexOne way transmission

• Half-DuplexTwo way transmission but only one user can transmit the signal at one time.

• Full-DuplexTwo way transmission, both users can transmit the signal at the same time.

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Decibel

decibel is a relative unit of measurement used frequently in electronic communications to describe power gain or loss

Equation 1 is commonly referred to as the power ratio form for dB.

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(Eq. 2)

(Eq. 1)

(Eq. 3)

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