komunikasi analog

8/13/2019 Komunikasi Analog

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V. Chandra Sekar Oxford University Press 2013


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Communication Basics

Communication deals with the principle of transferring

information from one place to another.

It involves transmission and reception, and processing of

information between these two locations. The source could be in continuous form as in the case of

analog communication and as discrete signals as in the case of

digital communication.

Short distance transmission of information is called basebandtransmission.

Oxford University Press 2013


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Communication Basics

For long distance transmission, information has to be

impressed upon an high frequency component to beable to reach the reception end of communication.

The high frequency component is termed as a carrier

and the entire process is called modulation.



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Need For Modulation

To translate the frequency of a low-pass signal to a higher

band so that the spectrum of the transmitted bandpass signal

matches the bandpass characteristics of the channel.

For efficient transmission, it has been found that the antennadimension has to be of the same order of magnitude as the

wavelength of the signal being transmitted.

Since C=f for a typical low-frequency signal of 2 kHz, the

wavelength works out to be 150 km. Even assuming the

height of the Antenna half the wavelength, the height works

out to be 75 km, which is impracticable.



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Need For Modulation

To enable transmission of a signal from several

message sources simultaneously through a singlechannel employing frequency division multiplexing.

To improve noise and interference immunity in

transmission over a noise channel by expanding the

bandwidth of the transmitted signal.



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Frequency Translation

The modulation process shifts the modulatingfrequency to a higher frequency, which in turndepends on the carrier frequency, thus producing

upper and lower sidebands. Hence, signals are upconverted from low frequencies

to high frequencies and downconverted from highfrequencies to low frequencies in the receiver.

The process of converting a frequency or a band offrequencies to another location in the frequencyspectrum is calledfrequency translation.



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Types Of Modulation

Depending on whether the amplitude, frequency, or phase ofthe carrier is varied in accordance with the modulation signal,we classify the modulation as

Amplitude modulation

Frequency modulation

Phase modulation.

The method of converting information into pulse form andthen transmitting it over a long distance is calledpulsemodulation.



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Transmitter

The message as it arrives may not be suitable for direct

transmission. It may be voice signal, music, picture, or data. The

signals, which are not of electrical nature, have to be converted

into electrical signals. This is the role of transmitter. Typical block

diagram is illustrated below.



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Receiver

A receiver is meant to receive the electromagnetic signal which

carries the information. It is tuned to receive the required

information at a predetermined frequency. The output of the

receiver is usually fed into a transducer which converts the

information into understandable signal.



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Multiplexing

When it is required to transmit more signals on the same channel,

baseband transmission fails, as in the case of audio signals being

broadcast from different stations on the same channel.

To encounter this problem either frequency division multiplexing

or time division multiplexing is employed.

This method of transmitting several channels simultaneously is

known asfrequency division multiplexing (FDM).

In Time Division Multiplexing (TDM)several signals are

transmitted over a time interval. Each signal is allotted a time slot

and it gets repeated cyclically. The only difference compared to

FDM is that the signals are to be sampled before sending.



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Signals An Introduction



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Signals:

Any function that carries information.

Shows how a parameter varies with anotherparameter.

Will be dealing with signals with time or frequency as

an independent variable

Signals



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Signals are classified as:

Continuous and discrete.

Causal and Non causal.

Even and Odd.

Deterministic and Random

Real and complex

Energy and power type

Signals



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Discrete Signals



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Continuous Signals



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Causal Signals



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Even & Odd Signals



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( )sinsin ( ) ,

tc t

t

=


Special Signals


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Sgn(t) = 1, t > 0

= -1, t < 0


Signum Signals


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Impulse or Delta signal

( ) 1

( ) ( ) ( )

t

and v t t dt v t

=

=



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Classification Of Systems

Discrete time and Continuous Time systems.

Time Invariant and Time varying systems

Causal and Non Causal system

Instantaneous and Dynamic systems

Stable and Unstable systems



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Fourier Series & Transform

1. Fourier series:

- Any periodic of function of time x(t) having a fundamental

period T and frequency 1/T can be represented as an infinite

series of sinusoidal waveforms of fundamental and itsharmonic frequencies.

2. If a function is x(t), its Fourier series is given by:

0

1 1

( 0 cos(2 ) sin(2 )n nn n

x t a a fnt b fnt

= =

= + +



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Where:

2

0

2

2

2

1( )

2 2( ) cos

2( ) sin(2 )

T

T

T

n

T

n

a x t dt

T

nta x t dt

T T

b x t nt dt T

=

=

= =



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Fourier Transform

To represent aperiodic function Fourier transform is used

Unlike Fourier series, this representation will be continuous in

frequency domain

It is given by:

Also x(t) can be obtained from X(f) as:

x(t) =

2( ) ( ) j ftX f x t e dt

=

dfefX ftj 2)(



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Laplace Transform

1. It converts time domain signal into frequency domain a plane called s plane having

as the real part and as the imaginary part.

2. Laplace transform is given by the expression:

3. The inverse Laplace transform is given by:

( )

( ) ( )

. . ( ) ( )

st

jw t

x x t e dt

i e X x t e dt

+

=

=

1( ) ( )

2

stx t X s e ds

j

=



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Z Transform

Z transform is a polar representation compared to rectangular

representation in Laplace transform

It is for discrete time function

Z transform of a function x(t) is given by:

Inverse Z transform is given by:

In Z transforms a term ROC is defined as region of convergence

where the Z transform of a function has finite value.

[ ] [ ] nX z x n z= 1

[ ] [ ]x n x zZ

=



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Amplitude Modulation



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Amplitude of the carrier is changed in proportion to the

instantaneous amplitude of a message signal

Carrier frequency must be relatively higher than the

message frequency

Modulation index m is the ratio of Em/Ec

Percentage of modulation = m x 100%

Amplitude Modulation



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AM Envelope



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Frequency Spectrum Of AM Wave



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Power Spectrum Of AM



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Suppressed Carrier Systems

Double side band (DSB) system

Single side band system(SSB)

SSB with pilot carrier

Independent side band (ISB) system

Vestigial side band (VSB) system

Other AM Systems



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AM Waveforms For AM, DSB & SSB



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Single Sideband

Advantages:

Lesser power consumption.

Conservation of bandwidth.

Noise reduction. Less fading.

Disadvantages:

Requires complex receiver.

At the receiver, coherent carrier has to be generated.

In case of pilot carrier, at the receiver end it has to be boosted

properly.



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Square law Modulators

Switching Modulators

Transistor ModulatorsLow level

Medium level

High level

AM Modulators



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Balanced Modulators

1. Balanced ring Modulator

2. Balanced bridge Modulator

3. Transistor balanced Modulator4. FET balanced Modulator

SSB Generation

1. The filter method

2. The phase shift method

3. The Third method

Types Of Modulators


D d l t Di t ti &


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AM Demodulators

1. Rectifier detector

2. Envelope detector

Detector Distortions1. Diagonal peak clipping

2. Negative peak clipping

SSB Reception

1. Coherent detection2. Reception with pilot carrier

Demodulators, Distortions &

Reception


AM Transmitters


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AM Transmitters

Low Level AM DSBFC Transmitter



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High Level DSBFC Transmitter



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SSB Transmitter

SSB suppressed carrier Transmitter: BPF is used to remove the other

sideband



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Phase Shift Method


SSB T itt With Pil t


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SSB Transmitter With Pilot

Carrier



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AM Receiver


Super Heterodyne Receiver


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SSB Pilot Receiver


Communication Receiver


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Communication Receiver



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Selectivity

Sensitivity

Dynamic range

Fidelity

Bandwidth

Noise temperature and equivalent noise

temperature


Receiver Parameters

Costas Loop


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Costas Loop



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V. Chandra Sekar



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Angle Modulation



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Angle modulation includes both frequency and phase

modulations.

In Frequency Modulation(FM), the frequency of the

carrier is changed with respect to amplitude of themessage signal

In phase modulation(PM), the phase of the carrier is

changed with respect to amplitude of the message signal

Unlike AM, both FM and PM are nonlinear, hence much

more difficult to implement and analyze.

Introduction


M d l i I d & D i i


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1. Modulation index for FM wave is given by:

Where f is the frequency deviation and fm

is the modulating frequency

2. The expression for an FM wave is:

3. Modulation index for PM wave is given by:

where, is the phase deviation given by:

4. The expression for an PM wave is:

m

f

f

=

( ) cos[2 sin{2 ( )}]FM c mf t A f t f t = +

p mm k E=

pK

p

m

kE

=

( ) cos[2 cos{2 ( )}]PM c m

f t A f t f t = +

Modulation Index & Deviation



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Frequency & Phase Modulator

Phase modulator can be used to generate FM wave and FM modulator can be used to

generate PM wave as shown:


FM & PM Waves


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FM & PM Waves


Narrowband FM


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FM with


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FM with > 10 is called wideband FM

Expression for wideband FM:

f(t) = Jo() cos ct J1(){ cos(c m) t cos(c m) t}+ J2 () { cos

(c- 2m) t + cos (c+ 2m) t} J3 () { cos (c- 3m) t cos (c- 3mt) }

+ -------

The function Jn() is called the Bessel function.

The spectrum is composed of a carrier with an amplitude Jo () and a set

of side bands spaced symmetrically on either side of the carrier at

frequency separation of m, 2m, 3m--- and so on. Unlike AM, FM has an infinite number of side bands along with carrier.

These side bands are separated from the carrier by fm, 2fm, 3fm---------.

Wideband FM


B l F ti A A F ti Of


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Bessel Function As A Function Of



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Bandwidth Requirements For Angle


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Carsons formula for bandwidth of FM system

Band width = 2(f + fm) HZ

For low modulation index, in case of narrow band FM since 2f > fm,

equation reduces to Band width = 2f.

Average power in sinusoidal wideband FM:

PT= Vc2Jo

2 () /R + 2Vc2/R { J1

2() + J22() + J3

2() + ---------- }

= Vc2/R [ J0

2() + 2 { J12() + J2

2() + J32() + -------------- }]

= Pc[ Jo2

() + 2 { J12

() + J22

() + J32

() + ------------------- }]

where Pcis the unmodulated power Vc2/R.

Bandwidth Requirements For Angle

Modulated Waves



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The expression for sinusoidal FM is:

Kpem(t) = KpEmsin mt = sin mt

where = KpEm, is defined as Peak phase

deviation and is directly proportional to the peak

modulating signal.

Sinusoidal Phase Modulation


Ph R t ti


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Phasor Representation


FM & PM Generation


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FM generation

Varactor diode modulators

Reactance modulators

Modulators using linear integrated circuits

Indirect methods for narrow band and wideband

PM generation:

Varactor diode in direct PM modulators

Direct method with transistor

FM & PM Generation


FM Detectors


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Slope detector

Balance slope detector

Foster Seeley discriminator

Ratio detector

Demodulator using PLL

Quadrature detector

Zero crossing detector

FM Detectors


FM Transmitter


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Crosby Direct FM Transmitter:

FM Transmitter


Indirect FM Transmitter


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Indirect FM Transmitter


FM Receivers


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Super heterodyne Receiver

FM Receivers


Double Superheterodyne Receiver


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Double Superheterodyne Receiver


Ph d L k L


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Phased Lock Loop

It is a feedback system that generates a signal that has a

fixed relation to the phase of a reference signal .

A phase locked loop circuit responds to both the

frequency and phase of the input signals, by changing thefrequency of the voltage controlled oscillator until it

matches to the reference input in both frequency and

phase. Hence it is a negative feedback system except that

the feedback error signal is a phase rather than a current

or voltage signal as usually the case in conventional

feedback system.


PLL Block Diagram (Analog)


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PLL Block Diagram (Analog)



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PLL Block Diagram (Digital)


PLL Applications


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Data and Tape Synchronization

Modems

FSK Modulation FM Demodulation

Frequency Synthesizer

Tone Decoding

Frequency Multiplication and Division

PLL Applications


Direct Digital Synthesis


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Is a powerful technique to generate RF signals.

A direct digital synthesizer operates by storing the

points of a waveform in digital format, and then

recalling them to generate the waveform. The rate at which the synthesizer completes one

waveform then determines the frequency.




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Block Diagram :


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V. Chandra Sekar



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Pulse Modulation


Pulse Modulation


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Pulse Modulation

In analog pulse modulation, the carrier is a periodic

pulse train

The amplitude, position and width of the carrier pulse

train are varied in a continuous manner in accordancewith the corresponding sample value of message

signal.

Thus in Pulse modulation, information is transmitted

basically in analog form, but the transmission takes

place at discrete times. Oxford University Press 2013


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In the case of digital pulse modulation the message signalis represented in a form that is discrete in both time andamplitude

The data is transmitted as a sequence of coded pulse.

This type of modulation is also called pulse codemodulation (PCM).

PCM is the most widely used form in the field ofTelecommunication.

Digital Data transmission provides a higher level of noise

immunity, more flexibility in the band width Power tradeoff possibility of providing more security to

data and ease of implementation using large scaleintegrated circuits.


Predominant Methods Of Pulse


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Pulse width modulation (PWM)

Pulse position modulation (PPM)

Pulse amplitude modulation (PAM)

Pulse code modulation (PCM)

Modulation


Pulse Width Modulation


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Pulse Width Modulation


Pulse Amplitude Modulation


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Pulse Code Modulation (PCM)


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PCM offers a method of over coming some of the disadvantages

of other type of pulse modulation.

In PCM the instantaneous amplitude of the sample is

represented by a binary code resulting in a series of ones and

zeros or mark and space.

All pulses have the same height and same shape

Since only ones and zeros are sent. The receiver has only to

detect the presence or absence of a pulse.

A distorted pulse does not degrade the signal as long as the

pulse can still be recognized. Hence PCM is less sensitive to noise

than wither PAM or PWM

Pulse Code Modulation (PCM)


PCM Transmitter & Receiver


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PCM Transmitter & Receiver


Multiplexing


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When more than one application or connection share thecapacity of one link it is called multiplexing.

This results in better utilization of resources.

A typical example is, many conversations over telephone

line, trunk line, wireless channel, etc.

A few examples of multiplexing are:

TDM- Time division multiplexing

FDM- Frequency division multiplexing

WDM- Wavelength division multiplexing

CDMA- Code division multiple access

Multiplexing


FDM Transmitter


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FDM Transmitter


FDM Receiver


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FDM Receiver


Synchronous TDM Transmitter


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Synchronous TDM Receiver


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Synchronous TDM Receiver


Analog Carrier System Using FDM


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Analog Carrier System Using FDM


Digital Carrier System Using TDM


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