COMTECH

COMMUNICATION SYSTEMS
ANANT
SATVIK
PRIYANKA
 This is an overview to introduce you to
some COMMUNICATION basics.

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COMMUNICATION SYSTEMS
Table of Contents

Introduction
1

2 Basics of Classification of Communication

Modulation
3

4 Communication Channels

5
Exit
Optical Fibers

7

INTRODUCTION

C OMMUNI A I I T NS E OF I ORMA I A
C TON S RA F R NF TON ND
ME S GE F
SA ROM ONE POI T A HE W RE I
NT O NOT R HE T
RE C S I A I E LGI E F
A HE N N NT L I BL ORM.
 I MODE C
N RN OMMUNI A I S S E T
C TON Y T M HE
I ORMA I I FRS C E E I O E E T C L
NF TON S I T ONVRT D NT L C RI A
SGNA S A T N S ND E E T C L Y PROV NG
I L ND HE E L C RI A L IDI
S E RE I BI I Y A F C LT T C
PE D, LA LT ND A I I Y O OMMUNI A E CT
OVR L
E ONG DI T NC S OR e . T ., RA O,
S A E .F .g .V DI
T L PHONE C
EE OMMUNI A I e c
C TON t .
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INTRODUCTION
Page 1 of 1

Basics of classification of communication
MAIN POINTS
 ACCORDING TO NATURE OF
INFORMATION SOURCE
 ACCORDING TO MODE OF
TRANSNISSION
 ACCORDING TO TRNSMISSION
CHANNEL
 ACCORDING TO TYPES OF
MODULATION
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Page 1 of 5

1. According to NATURE OF INFORMATION SOURCE.

Picture
Transmission
Speech
e.g. T.V.
Transmissio
n
E.g. RADIO
Data
Facsimile Transmission
Transmission. .
e.g. FAX e.g.
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NEWSPAPER
Page 2 of 5

2. According to MODE OF TRANSMISSION.

Analog
Digital
Communicatio
Communication
n
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Page 3 of 5


3. According to TRANSMISSION CHANNEL

Line
Space
Communication
Communication

Two Wire
communication Line
Coaxial Cable
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Optical Fibre Cable
Page 4 of 5


4. According to TYPE OF MODULATION

PULSED CARRIER
WAVES
SINUSOIDAL
CARRIER WAVES
Pulse Amplitude
Modulation (PAM)
Amplitude
Modulation (AM)
Pulse Time
Modulation (PTM)
Optical Fibre Cable
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Pulse Code
Two Wire
Modulation (PCM)
communication Line
Page 5 of 5

MODULATION
An Important Step Of Communication System

There is always a need of translating the
original Low frequency BASEBAND
message signals into high frequency waves
before transmission so that
 The translated signal continues to possess the
information contained in the original signal.
 The length of the antenna (= wavelength /4 )
is reduced to minimum.
 The effective power radiated by antenna is
maximized.
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 The signals transmitting the signals of same
frequency can be distinguished without any
harm to data.
MODULATION
Page 1 of 3

MODULATION
CONTINOUS OR SINUSOIDAL WAVE MODULATION
The three types of wave modulation are explained as follows :

 Amplitude Modulation (AM): The amplitude of carrier signal
varies in accordance with the modulating signal.

Amplitude of Carrier Wave α Amplitude of Modulating Wave

 Frequency Modulation (FM): Frequency of carrier signal signal
varies in accordance with modulating signal.

Frequency of Carrier Wave α Amplitude of Modulating

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Voltage
MODULATION
Page 2 of 3

MODULATION
PULSE MODULATION
When carrier waves are in form of pulses, digital communication
becomes more relevant. The common Pulse Modulations are ;

• PULSE AMPLITUDE MODULATION :
Pulse Amplitude increases or decreases with the changing
modulating sinusoidal voltage.
• PULSE DURATION MODULATION :
The pulse duration or the width of the original signal is constant
but it is large when the amplitude of the signal is also large.
iii) PULSE POSITION MODULATION :
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In ppm the position of the pulse have to be shifted . It is more if
amplitude is high. Modulated signal varies according to voltage.
MODULATION
Page 3 of 3

COMMUNICATION CHANNELS
Contents

There are two types of communications –
 Space
 Line

The c m unic ion pr es ut ing t
om at oc s iliz he
phy ic s e ar
s al pac ound t earh is t m ed
he t er
as S pace C ommunication.
Ther ar t ee m odes ofs e
e e hr pac
c m unic ion(pr
om at opagation).
 Ground Wav Pr
e opagat ion.
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 Spac Wav Pr
e e opagation
 Sk Wav Pr
y e opagat
ion
Page 1 of 10

1. GROUND WAVE PROPAGATION
This mode of propagation can exist when the
transmitting and receiving antenna are close
to the surface of earth.
As ground wave passes over the surface of
the earth, it is weakened as a result of
energy absorbed by the earth. Due to these
losses, ground waves are not suited for very
long range communication. These losses are
frequency dependent and are higher for high
frequencies ( ~ 500-1500kHz ).
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Page 2 of 10

2. SPACE WAVE PROPAGATION
 T t a mite wa e t a e
he r ns t d v s r v ling in a s r ig line
t a ht ,
d e t r a h t r c iv r e a a e t n p k d
ir c ly e c he e e e nd nd r he ic e
up b t r c iv a e .
y he e e ing nt nna
 T e f c iv r c p io r ng o t b o d a tis
he fe t e e e t n a e f he r a c s
e s nt lly t r g n b t e t t a p nd r a
s e ia he e io e we n he r ns o e nd
t r c iv r whic is c v r d b t line o s htin
he e e e h o e e y he f ig
a c nv nt na s ns . T , t mo e o
o e io l e e hus his d f
c mmunic t n is t r d a l i ne of s i ght
o a io e me s
c om uni c at i on.
m
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Page 3 of 10

3. SKY WAVE PROPAGATION

 A Transmitted wave going up in the sky is
reflected back from the earth’s atmosphere
called ionosphere. The UV and other high
frequency radiations are absorbed by air
which gets ionised and form a layer of
electrons and ions around earth.

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Page 4 of 10

SATELLITE COMMUNICATION
 It is done using satellite which work on the basic principle that the satellite receives
signals from earth stations, amplifies them and transponds then to another
stations.

 Satellites are of two types:

1 Geostationary Satellites: Which are stationary w.r.t. a
station placed on earth.

2. Sun-synchronous satellites: Which rotates around the earth just as
sun does and comes over a fixed
point on earth after about 24 hrs.
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Page 5 of 10

APPLICATIONS OF SATELLITE COMMUNICATION
 REMOTE SENSING: science and art of obtaining
information about an object, acquired by a sensor ,
without actually touching the target of investigation.
 WEATHER FORECASTING
 COMMUNICATION OVER LARGE SCALE

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Page 6 of 10

LINE COMMUNICATION
 Communication where there is a physical
contact between the two ends through wires.
 The principle types of channels used in such
communication are:
3. Two Wire Transmission Lines.
4. Coaxial Cables.
5. Optical Communication.

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Page 7 of 10

LINE COMMUNICATION
1. Two Wire Transmission Lines
 The signal flows through the wires creating
their respective electric and magnetic fields.
 Signals travel as waves in transmission lines.
 Each portion of transmission lines can be
considered as small inductor, resistor, and
capacitor.
 It can be seen in telephone communication in
daily life.
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Page 8 of 10

LINE COMMUNICATION
2. Coaxial Cables
 A COAXIAL CABLE consists of a hollow
outer cylindrical conductor which
surrounds a single inner conductor kept
separated from each by an insulator. It
avoids E.M interference, thus the quality
of transmission is better than in 2-wire line
communication
 The disadvantage of being prone to
electromagnetic interference and
becoming a source of radiation is avoided.
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Page 9 of 10

LINE COMMUNICATION
3. Optical Communication
 Optical Communication is through carrier
optical signals.
 It has advantage over other modes of
communication in points:
1. Wide channel bandwidth and large channel
carrying capacity.
2. Low transmission losses.
3. Signal security and not accessible to
interference.
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Page 10 of 10

OPTICAL FIBRE
INTRODUCTION

For using optical signals, we need to have something that
allows light to travel through in desired direction. So, we use
long thread-like structure called OPTICAL FIBRE which is
generally made up of a Transparent glass, polymer or a
dielectric.

STRUCTURE :A typical optical fibre consists of :

CORE : A Core of glass/silica/plastic with approx diameter of
10-100 micro
meter with refractive index n1.

CLADDING :The core is surrounded by a glass or plastic
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cladding with refractive index n2 such that n2<n1.

OPTICAL FIBRE
BUFFER : For providing safety and strength , a buffer plastic
Page 1 of 3

OPTICAL FIBRE
How Light travels through Optical Fibre ?
Let a light ray is incident on the core of optical fiber
at an angle φi as shown in fig.. A part of it is
reflected and a part of it is refracted at an angle φr
running away from normal (since n1>n2). The angle
φi (and hence θ1 & θ2) are related by
SNELL’s LAW :
n1sinφi = n2sinφr or n1cosθ1 = n2cosθ2

On increasing φi, the refracted ray will come closer to
the core-cladding boundary. At some critical angle
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φc, it becomes parallel to to the boundary.
sinφc = n2/n1
OPTICAL FIBRE
Page 2 of 3

OPTICAL FIBRE
How Light travels through Optical Fibre ?
CONTT.
For φi > φc , there would be no
refracted ray and all incident
light will be totally internally
reflected.This is the condition ,
which is applicable to the Optical fibres .
Due to small diameter of core , Φi > φc. So, light ray
suffers Total Internal Reflection at core-cladding boundary .
Such total reflections confine the light inside the core.
Thus, light travels in the core in a guided manner and hence
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optical fiber is sometimes called as OPTICAL WAVEGUIDE.
OPTICAL FIBRE
Page 3 of 3

BIBLIOGRAPHY
1. NCERT.

3. MICROSOFT ENCARTA.

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5. INTERNET.
BILBLIOGRAPHY
Page 1 of 2

THE
END

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BILBLIOGRAPHY
Page 2 of 2

COMTECH

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