ac labwithoutreadings

ANALOG COMMUNICATIONS

LAB MANUAL (STUDENT COPY)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING GUDLAVALLERU ENGINEERING COLLEGE

SESHADRI RAO KNOWLEDGE VILLAGE::GUDLAVALLERU

INDEX

S.NO. NAME OF THE EXPERIMENT PAGE NO.

USING SOFTWARE (MATLAB, COMMUNICATION TOOL BOX)

Introduction to MATLAB 1-12

1 Amplitude Modulation & Demodulation 13-17

2 AM-DSBSC Modulation And Demodulation 18-22

3 Frequency Modulation and Demodulation 23-25

USING SOFTWARE (MATLAB, SIMULINK)

Introduction to SIMULINK 26-35


5 DSB-SC Modulation and Demodulation 39-41

6 Frequency Modulation 42-43

USING HARDWARE


8 Diode Detector Characteristics 51-53

9 Frequency Modulation And Demodulation 54-58

10 Balanced Modulator 59-62

11 Pre-Emphasis & De-Emphasis 63-67

12 Synchronous Detector 68-71

13 SSB System 72-76

14 Spectrum Analysis of AM And FM Signal Using

Spectrum Analyzer 77-79

ADDITIONAL EXPERIMENTS (USING SOFTWARE)

1 Pulse Width Modulation 80-81

2 Phase Locked Loop 82-86

ADDITIONAL EXPERIMENTS (USING HARDWARE)

3 Characteristics of Mixer 87-90

4 Phase Locked Loop 91-93

5 Squelch Circuit 94-97

6 Frequency Synthesizer 98-100

APPENDIX -A 101-104

APPENDIX -B 105-128

REFERENCES 129

Analog Communication Lab

(Software Experiments)

Simulation Using MATLAB

Analog Communication Lab

(Hardware Experiments)

Additional Experiments

(Using Software)

Additional Experiments

(Using Hardware)

APPENDIX

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

ANALOG COMMUNICATIONS LAB 1

INTRODUCTION TO MATLAB The name MATLAB stands for matrix laboratory. MATLAB® is a high-

performance language for technical computing. It integrates computation,

visualization, and programming in an easy-to-use environment where problems

and solutions are expressed in familiar mathematical notation.MATLAB is an

interactive system whose basic data element is an array that does not require

dimensioning. This allows you to solve many technical computing problems,

especially those with matrix and vector formulations, in a fraction of the time it

would take to write a program in a scalar noninteractive language such as C or

Fortran.

Typical uses include

Math and computation

Algorithm development

Data acquisition

Modeling, simulation, and prototyping

Data analysis, exploration, and visualization

Scientific and engineering graphics

Application development, including graphical user interface building

To start MATLAB on a Microsoft Windows platform, select the Start ->

Programs -> MATLAB 7.0.1 -> MATLAB 7.0.1, or double-click the MATLAB

shortcut icon on your Windows desktop. The shortcut was automatically created

when you installed MATLAB. If you have trouble starting MATLAB, see

troubleshooting information in the Installation Guide for Windows.

When you start MATLAB, it displays the MATLAB desktop, a set of tools

(graphical user interfaces or GUIs) for managing files, variables, and applications

associated with MATLAB.



The toolbar in the desktop provides easy access to frequently used operations.

Position the cursor over a button for a second or two and a tooltip appears that

describes the item.

The Command Window is one of the main tools you use to enter data, run

MATLAB functions and other M-files, and display results.

Use the Help browser to search and view documentation and

demonstrations for MATLAB and all other installed MathWorks products.

MATLAB automatically installs the documentation and demos for a product when



you install that product. The Help browser is an HTML browser integrated with

the MATLAB desktop.

To open the Help browser, click the Help button in the desktop toolbar,

type helpbrowser in the Command Window, or use the Help menu in any tool.

There are two panes:

Working with Matlab:

In MATLAB, a matrix is a rectangular array of numbers. Special meaning

is sometimes attached to 1-by-1 matrices, which are scalars, and to matrices with

only one row or column, which are vectors. MATLAB has other ways of storing

both numeric and nonnumeric data, but in the beginning, it is usually best to think



of everything as a matrix. The operations in MATLAB are designed to be as

natural as possible. Where other programming languages work with numbers

one at a time, MATLAB allows you to work with entire matrices quickly and

easily.

To do work in MATLAB, you type commands at the command prompt.

Often these commands will look like standard arithmetic. Or function calls similar

to many other computer languages. By doing this, you can assign sequences to

variables and then manipulate them many ways. You can even write your own

functions and programs using MATLAB's control structures. The following

sections will describe the most commonly used commands on MATLAB and give

simple examples using them.

Expressions:

Like most other programming languages, MATLAB provides mathematical

expressions, but unlike most programming languages, these expressions involve

entire matrices. The building blocks of expressions are

Variables

Numbers

Operators

Variables:

MATLAB does not require any type declarations or dimension statements.

When MATLAB encounters a new variable name, it automatically creates the

variable and allocates the appropriate amount of storage. If the variable already

exists, MATLAB changes its contents and, if necessary, allocates new

storage.Variable names consist of a letter, followed by any number of letters,

digits, or underscores. MATLAB uses only the first 31 characters of a variable

name. MATLAB is case sensitive; it distinguishes between uppercase and

lowercase letters. A and a are not the same variable. To view the matrix

assigned to any variable, simply enter the variable name.

You can assign the values to variables by typing in equations. For example, if

you type



>>x=5

MATLAB creates a 1-by-1 matrix named xand stores the value 5 in its single

element. The output produced by the MATLAB

x =

5

MATLAB uses ans for any expression you don't assign to a variable. For

instance, if you type

>> 5

to MATLAB, MATLAB will return

ans =

5

and assign the value 5 to the variable ans. Thus, ans will always be assigned to

the most recently calculated value you didn't assign to anything else.

Numbers:

MATLAB uses conventional decimal notation, with an optional decimal point and

leading plus or minus sign, for numbers. Scientific notation uses the letter e to

specify a power-of-ten scale factor. Imaginary numbers use either i or j as a

suffix. Some examples of legal numbers are

3 -99 0.0001

9.6397238 1.60210e-20 6.02252e23

1i -3.14159j 3e5i

All numbers are stored internally using the long format specified by the

IEEE floating-point standard. Floating-point numbers have a finite precision of

roughly 16 significant decimal digits and a finite range of roughly 10-308 to

10+308.



Operators:

Expressions use familiar arithmetic operators and precedence rules.

Symbol Operation

+ Addition

- Subtraction

* Multiplication

/ Division

\ Left division

^ Power

' Complex conjugate transpose

( ) Specify evaluation order

>>x= 1:4will return

x =

1 2 3 4

You can optionally give the colon a step size. For instance,

>>x=8:-1:5 will give

x =

8 7 6 5

and

>> x = 0:0.25: 1.25will return

x =

0 0.25 0.5 0.75 1.0 1.25

The colon is a subtle and powerful operator, and we'll see more uses of it later.

Flow Control:

MATLAB has several flow control constructs:

if, else, and elseif



switch and case

for

while etc… …

if, else, and elseif:

The if statement evaluates a logical expression and executes a group of

statements when the expression is true. The optional elseif and else keywords

provide for the execution of alternate groups of statements. An end keyword,

which matches the if, terminates the last group of statements. The groups of

statements are delineated by the four keywords -- no braces or brackets are

involved.

The basic command looks like if a > 0

x=a^2;

end

This command will assign x to be the value of a squared, if a is positive.

Again, note that it has to have an end to indicate which commands are actually

part of the if. In addition, you can define an else clause which is executed if the

condition you gave the if is not true. We could expand our example above to be

if a>0

x = a^2;

else

x = -a^2

end

For this version, if we had already set a to be 2, then x would get the

value 4, but if a was -3, x would be -9. Note that we only need one end, which

comes after all the clauses of the if. Finally, we can expand the if to include

several possible conditions. If the first condition isn't satisfied, it looks for the

next, and so on, until it either finds an else, or finds the end. We could change

our example to get

if a>0

x = a^2;

else if a == 0



x = i;

else

x = -a^2

end

For this command, it will see if a is positive, then if a is not positive, it will check if

a is zero, finally it will do the else clause. So, if a positive, x will be a squared, if

a is 0, x will be i, and if a is negative,

then x will be the negative of a squared. Again, note we only have a single end

after all the clauses.

For:

The for loop repeats a group of statements a fixed, predetermined number of

times. A matching end delineates the statements.

. It is functionally very similar to the for function in C. For example, typing

for i= 1:4

end

will cause MATLAB to make the variable i count from 1 to 4, and print its value

for each step. So, you would see

i = 1

i = 2

i = 3

i = 4

Every command must have a matching end statement to indicate which

commands should be executed several times. You can have nested for loops.

For example, typing

Form = 1:3

for n= 1:3

x(m,n)=m+n*i;

end

end

will define x to be the matrix

x =



1.0000 + 1.0000i 1.0000 + 2.0000i 1.0000 + 3.0000i

2.0000 + 1.0000i 2.0000 + 9.0000i 2.0000 + 3.0000i

3.0000 + 1.0000i 3.0000 + 2.0000i 3.0000 + 3.0000i

The indentations in the for structure are optional, but they make it easier to figure

out what the commands are doing.

While:

The while command allows you to execute a group of commands until

some condition is no longer true. These commands appear between the while

and its matching end statement. For instance, if we want to keep squaring x until

it is greater than a million,

we would type

while x < 1000000

x = x^2;

end

Scripts and Functions:

MATLAB is a powerful programming language as well as an interactive

computational environment. Files that contain code in the MATLAB language are

called M-files. You create M-files using a text editor, then use them as you would

any other MATLAB function or command.

There are two kinds of M-files: Scripts, which do not accept input arguments or

return output arguments. They operate on data in the workspace. Functions,

which can accept input arguments and return output arguments. Internal

variables are local to the function.

Scripts:

When you invoke a script, MATLAB simply executes the commands found in the

file. Scripts can operate on existing data in the workspace, or they can create

new data on which to operate. Although scripts do not return output arguments,

any variables that they create remain in the workspace, to be used in subsequent

computations.



Functions:

Functions are M-files that can accept input arguments and return output

arguments. The names of the M-file and of the function should be the same.

Functions operate on variables within their own workspace, separate from the

workspace you access at the MATLAB command prompt.

Procedure:

1. Open the MATLAB® software by double clicking its icon .

2. MATLAB® logo will appear and after few moments Command Prompt will

appear.

3. Go to the File Menu and select a New M- file. (File ?New?M-file) or in the left

hand corner a blank white paper icon will be there. Click it once.



4. A blank M- file will appear with a title ‘untitled’



5. Now start typing your program. After completing, save the M- file with

appropriate name. Toexecute the program Press F5 or go to Debug Menu and

select Run.

6. After execution output will appear in the Command window .If there is an error

then with an

alarm, type of error will appear in red color.

7. Rectify the error if any and go to Debug Menu and select Run.



1. AMPLITUDE MODULATION AND DEMODULATION

Aim:

A. To generate the amplitude modulated signal(AM wave) by using given

message signal and carrier signals in MATLAB software

B. To demodule the AM wave using envelope detector principle

Hardware and software requirements:

Personal computer(PC)

MATLAB Software 7.0.4

Theory:

In amplitude modulation, the amplitude of the carrier voltage varies in

accordance with the instantaneous value of modulating voltage. Let the

modulating voltage be given by expression,

Vm = Vmcoswmt

Where wm is angular frequency of the signal &Vm is the amplitude. Let the

carriervoltage be given by expression,

Vc = Vccoswct

On Amplitude Modulation, The instantaneous value of modulated carrier voltage

is given by,

V = V(t) coswct

V(t)=Vc + kaVmcoswmt

V=Vc[1+ ma coswm t] coswct

Where ma is modulation index and the modulation index is defined as the ratio of

maximum amplitude of modulating signal to maximum amplitude of carrier signal.

ma= Vm / Vc

The demodulation circuit is used to recover the message signal from the

incoming AM wave at the receiver. An envelope detector is a simple and yet

highly effective device that is well suited for the demodulation of AM wave, for

which the percentage modulation is less than 100%.Ideally, an envelop detector

produces an output signal that follows the envelop of the input signal wave form



exactly; hence, the name. Some version of this circuit is used in almost all

commercial AM radio receivers.

PROGRAM:

AM without functions:

clc

clearall

closeall

t=linspace(0,0.02,10000);%defining time range for the signal

fc=5000;%frequency of carrier signal

fm=200;%frequency of message signaql

fs=40000;%sampling frequency---------fs>=2(fc+BW)

Am=5;%amplitude of the message signal

Ac=10;%amplitude of the carrier signal

m=Am/Ac%modulation index for the AM wave

wc=2*pi*fc*t;%carrier frequency in radians

wm=2*pi*fm*t;%message frequency in radians

ec=Ac*sin(wc);%carrier signal

em=Am*sin(wm);%messagesignal

y=Ac*(1+m*sin(wm)).*sin(wc);%amplitude modulated signal

z=y.*ec; %in synchronous detection the AM signal is

multiplied with carrier signal and passed through LPF

z1=conv(z,exp(-t/0.000795));% the LPF filter response in time domain is given

by exp(-t/RC), the cut off frequency for filter should be fm=200

%F=1/(2*pi*R*C), replacing F=200, and

%assuming R=1k ohm then C=0.795MICROFARAD

%so RC=0.000795

%we will get the demodulated signal by convolving the AM signal with LPF

response

l=10000;

subplot(4,1,1),plot(t(1:l),em(1:l))



xlabel('time(sec)');

ylabel('amplitude in volts(V)');

title('MODULATING SIGNAL');

subplot(4,1,2),plot(t(1:l/2),ec(1:l/2))



title('CARRIER SIGNAL');

subplot(4,1,3),plot(t(1:l),y(1:l))



title('AMPLITUDE MODULATED SIGNAL');

subplot(4,1,4),plot(t(1:l),z1(1:l))



title('DEMODULATED SIGNAL');

Model Waveforms:



AM with functions:

clc

clearall

closeall



fm=200;%frequency of message signal









y=ammod(em,fc,fs,0,Ac);%amplitude modulated signal

z=amdemod(y,fc,fs,0,Ac);%demodulated AM signal

l=100000;










axis([0 0.02 -20 20])%setting axis dimensions





title('AMPLITUDE MODULATED SIGNAL');

subplot(4,1,4),plot(t(1:l),z(1:l))




Model Waveforms:

Result:



2. AM-DSBSC MODULATION AND DEMODULATION

Aim:

A. To generate the AM-DSBSC modulated signal(DSBSC wave) by using

given message signal and carrier signals in MATLAB software

B. To demodule the DSBSC wave using synchronous detector




Theory:

The amplitude-modulated signal is simple to produce but has two practical

drawbacks inapplication to many real communications systems: the bandwidth of

the AM signal is twice that of the modulating signal and most of the power is

transmitted in the carrier, not in the information bearing sidebands. To overcome

these problems with AM, versions on AM have been developed. These other

versions of the AM are used in applications were bandwidth must be conserved

or power used more effectively.

If the carrier could somehow be removed or reduced, the transmitted

signal would consistof two information-bearing sidebands, and the total

transmitted power would be information. When the carrier is reduced, this is

called as double sideband suppressedcarrier AM or DSB-SC. Instead of two

third of the power in the carrier, nearly all being the available power is used in

sidebands.

PROGRAM:

AM-DSBSC without functions:

clc

clearall

closeall





fm=1000;%frequency of message signaql




m=Am/Ac;%modulation index for the AM wave





y=em.*ec;

z=y.*ec; %in synchronous detection the AM signal is multiplied with carrier signal

and passed through LPF

z1=conv(z,exp(-t/0.000159));% the LPF filter response in time domain is given by

exp(-t/RC), the cut off frequency for filter should be fm=200

%F=1/(2*pi*R*C), replacing F=200, and

%assuming R=1k ohm then C=0.159MICROFARAD

%so RC=0.000159

%we will get the demodulated signal by

%convolving the AM signal with LPF response

l=100000;

subplot(4,1,1),plot(t(1:l/2),em(1:l/2))








subplot(4,1,3),plot(t(1:l/2),y(1:l/2))





title('DSBSC MODULATED SIGNAL');

subplot(4,1,4),plot(t(1:l),z1(1:l))




Model waveforms:

AM-DSBSC with functions:

clc

clearall

closeall



fm=200;%frequency of message signal











y=modulate(em,fc,fs,'amdsb-sc');%amplitude modulated signal

z=demod(y,fc,fs,'amdsb-sc');%demodulated AM signal

l=10000;










axis([0 0.02 -5 5])%setting axis dimensions



title('DSBSC MODULATED SIGNAL');

subplot(4,1,4),plot(t(1:l),z(1:l))






Model Waveforms:

Result:

The AM-DSBSC wave is generated for the given message and carrier

signals and the message signal is recovered from the modulated wave using

synchronous detector.



3. FREQUENCY MODULATION AND DEMODULATION

Aim:

A. To generate frequency modulated signal and observe the characteristics of

FM wave using MATLAB software.

B. To demodulate a Frequency Modulated signal usingMATLAB software




Theory:

Frequency modulation consists in varying the frequency of the carrier

voltage inaccordance with the instantaneous value of the modulating

voltage.Thus the amplitude ofthe carrier does not change due to frequency

modulation. Let the modulating voltage begiven by expression:

Vm=Vmcoswmt.

Where wmis angular frequency of the signal &Vmis the amplitude. Let the

carriervoltage be given by expression,

On frequency modulation, the instantaneous value of modulated carrier voltage is

given by,

Hence the frequency modulated carrier voltage is given by,

The modulation index is defined as the ratio of frequency deviation to frequency

of modulating signal mf=d/fm where deviation d=(fmax-fmin)/2.



FM with functions:

clc

clearall

closeall

Fs = 8000; % Sampling rate of signal

Fc = 100; % Carrier frequency

t = linspace(0,1,10000); % Sampling times

x = sin(2*pi*10*t) % Channel 1

dev = 50; % Frequency deviation in modulated signal

y = fmmod(x,Fc,Fs,dev); % Modulate both channels.

z = fmdemod(y,Fc,Fs,dev); % Demodulate both channels.

subplot(411),plot(t,x)




subplot(412),plot(t,sin(2*pi*Fc*t))




subplot(413),plot(t,y)



title('FREQUENCY MODULATED SIGNAL');

subplot(414),plot(t,z)






Model waveforms:

Result:



INTRODUCTION TO SIMULINK

Introduction:

Simulink is a software package that enables you to model, simulate, and

analyze systems whose outputs change over time. Such systems are often

referred to as dynamic systems. Simulink can be used to explore the behavior of

a wide range of real-world dynamic systems, including electrical circuits, shock

absorbers, braking systems, and many other electrical, mechanical, and

thermodynamic systems. This section explains how Simulink works.

Simulating a dynamic system is a two-step process with Simulink. First, a

user creates a block diagram, using the Simulink model editor, that graphically

depicts time-dependent mathematical relationships among the system's inputs,

states, and outputs. The user then commands Simulink to simulate the system

represented by the model from a specified start time to a specified stop time.

In general, block and lines can be used to describe many "models of

computations." One example would be a flow chart. A flow chart consists of

blocks and lines, but one cannot describe general dynamic systems using flow

chart semantics.

The term "time-based block diagram" is used to distinguish block

diagrams that describe dynamic systems from that of other forms of block

diagrams. In Simulink, we use the term block diagram (or model) to refer to a

time-based block diagram unless the context requires explicit distinction.

Simulink block diagrams define time-based relationships between signals

and state variables. The solution of a block diagram is obtained by evaluating

these relationships over time, where time starts at a user specified "start time"

and ends at a user specified "stop time." Each evaluation of these relationships is

referred to as a time step. Signals represent quantities that change over time and

are defined for all points in time between the block diagram's start and stop time.

The relationships between signals and state variables are defined by a set of

equations represented by blocks. Each block consists of a set of equations (block

methods). These equations define a relationship between the input signals,



output signals and the state variables. Inherent in the definition of a equation is

the notion of parameters, which are the coefficients found within the equation.

Starting Simulink

To start Simulink, you must first start MATLAB. You can then start

Simulink in two ways:

• Click the Simulink icon on the MATLAB toolbar.

• Enter the simulink command at the MATLAB prompt.

On Microsoft Windows platforms, starting Simulink displays the Simulink

Library Browser.



SIMULINK EDITOR:

When you open a Simulink model or library, Simulink displays the model

or library in an instance of the Simulink Editor.

Editor Components:

The Simulink Editor includes the following components.

Menu Bar

The Simulink menu bar contains commands for creating, editing, viewing,

printing, and simulating models. The menu commands apply to the model

displayed in the editor. See Creating a Model and Running Simulations for more

information.

Toolbar

The toolbar allows you to execute Simulink's most frequently used

Simulink commands with a click of a mouse button. For example, to open a

Simulink model, click the open folder icon on the toolbar. Letting the mouse

cursor hover over a toolbar button or control causes a tooltip to appear. The

tooltip describes the purpose of the button or control. You can hide the toolbar by

clearing the Toolbar option on the Simulink View menu.



Canvas

The canvas displays the model's block diagram. The canvas allows you to

edit the block diagram. You can use your system's mouse and keyboard to

create and connect blocks, selelect and move blocks, edit block labels, display

block dialog boxes, and so on. See Working with Blocks for more information.

Context Menus

Simulink displays a context-sensitive menu when you click the right mouse

button over the canvas. The contents of the menu depend on whether a block is

selected. If a block is selected, the menu displays commands that apply only to

the selected block. If no block is selected, the menu displays commands that

apply to a model or library as a whole.

Status Bar

The status bar appears only in the Windows version of the Simulink Editor.

When a simulation is running, the status bar displays the status of the simulation,

including the current simulation time and the name of the current solver. You can

display or hide the status bar by selecting or clearing the Status Bar option on the

Simulink View menu.

Building a Model

This example shows you how to build a model using many of the model-

building commands and actions you will use to build your own models.

The model integrates a sine wave and displays the result along with the

sine wave. The block diagram of the model looks like this.



To create a new model , click the New Model button on the Library

Browser's toolbar.

Simulink opens a new model window.

To create this model, you need to copy blocks into the model from the following

Simulink block libraries:

• Sources library (the Sine Wave block)

• Sinks library (the Scope block)

• Continuous library (the Integrator block)

• Signal Routing library (the Mux block)

To copy the Sine Wave block from the Library Browser, first expand the Library

Browser tree to display the blocks in the Sources library. Do this by clicking the



Sources node to display the Sources library blocks. Finally, click the Sine Wave

node to select the Sine Wave block.

Here is how the Library Browser should look after you have done this

Now drag a copy of the Sine Wave block from the browser and drop it in the

model window.

Copy the rest of the blocks in a similar manner from their respective

libraries into the model window. You can move a block from one place in the

model window to another by dragging the block. You can move a block a short

distance by selecting the block, then pressing the arrow keys.

With all the blocks copied into the model window, the model should look

something like this.



If you examine the blocks, you see an angle bracket on the right of the

Sine Wave block and two on the left of the Mux block. The > symbol pointing out

of a block is an output port; if the symbol points to a block, it is an input port. A

signal travels out of an output port and into an input port of another block through

a connecting line. When the blocks are connected, the port symbols disappear.

Now it's time to connect the blocks. Connect the Sine Wave block to the

top input port of the Mux block. Position the pointer over the output port on the

right side of the Sine Wave block. Notice that the cursor shape changes to

crosshairs.

Hold down the mouse button and move the cursor to the top input port of

the Mux block.

Notice that the line is dashed while the mouse button is down and that the cursor

shape changes to double-lined crosshairs as it approaches the Mux block.



Now release the mouse button. The blocks are connected. You can also

connect the line to the block by releasing the mouse button while the pointer is

over the block. If you do, the line is connected to the input port closest to the

cursor's position.

If you look again at the model at the beginning of this section, you'll notice

that most of the lines connect output ports of blocks to input ports of other blocks.

However, one line connects a line to the input port of another block. This line,

called a branch line, connects the Sine Wave output to the Integrator block, and

carries the same signal that passes from the Sine Wave block to the Mux block.

Drawing a branch line is slightly different from drawing the line you just drew. To

weld a connection to an existing line, follow these steps:

1. First, position the pointer on the line between the Sine Wave and the Mux

block.

2. Press and hold down the Ctrl key (or click the right mouse button).Press

the mouse button, then drag the pointer to the Integrator block's input port

or over the Integrator block itself.



3. Release the mouse button. Simulink draws a line between the starting point and

the Integrator block's input port.

Finish making block connections. When you're done, your model should look something

like this.

Controlling Execution of a Simulation

The Simulink graphical interface includes menu commands and toolbar buttons

that enable you to start, stop, and pause a simulation.

Starting a Simulation

To start execution of a model, select Start from the model editor's Simulation

menu or click the Start button on the model's toolbar.



You can also use the keyboard shortcut, Ctrl+T, to start the simulation.

Note: A common mistake that new Simulink users make is to start a simulation while the

Simulink block library is the active window. Make sure your model window is the active

window before starting a simulation.

Simulink starts executing the model at the start time specified on the

Configuration Parameters dialog box. Execution continues until the simulation reaches

the final time step specified on the Configuration Parameters dialog box, an error occurs,

or you pause or terminate the simulation.

While the simulation is running, a progress bar at the bottom of the model

window shows how far the simulation has progressed. A Stop command replaces the

Start command on the Simulation menu. A Pause command appears on the menu and

replaces the Start button on the model toolbar.

Your computer beeps to signal the completion of the simulation.

Ending a Simulink Session

Terminate a Simulink session by closing all Simulink windows.

Terminate a MATLAB session by choosing one the File menu and Exit

MATLAB.



4. Amplitude Modulation & Demodulation

Aim:

To generate amplitude modulated wave using simulink and demodulate

the modulated wave.

Software Required:

MATLAB 7.0.4

Simulink

Theory:

Amplitude Modulation is defined as a process in which the amplitude of

the carrier wave c(t) is varied linearly with the instantaneous amplitude of the

message signal m(t).The standard form of an amplitude modulated (AM) wave is

defined by

( ) ( ) ( )[ ]tftmKAtscac

π2cos1+=

Where aK is a constant called the amplitude sensitivity of the modulator.

Basically amplitude modulated signal is generated by product

modulator.The inputs to the product modulator are message signal and carrier

signal. Demodulation is the process of extracting the baseband message signal

from the carrier so that it may be processed at the receiver. For that purpose

various methods are used like diode detector method, product detector

method, filter detector etc. The same has been implemented on simulink model.

Low pass filter has been implemented to extract the carrier from the modulated

signal. Low pass filter (LPF), filters out the high frequency component and allows

the low frequency component to pass. Since the carrier signal is of relatively

much higher frequency than that of message signal, carrier signal is attenuated

while the message signal is received at the receiver.



Circuit diagram:

Procedure:

1. open the MATLAB window and then select a simulink

2. select Create a new blank model and open the Simulink Library browser

3. select Signal generator from sources of simulink and drag it to the New

model

4. Select the sine wave as message signal and set the input voltage signal to

5Vp-p and signal frequency to 500Hz

5. Again select the signal generator then sine wave. Give the name as

Carrier signal. Set the carrier voltage 8Vp-p,frequency 1KHz

6. Select constant from commonly used block of simulink

7. Select Add, Product Blocks from Math Operations

8. All the above blocks connect as per the diagram shown to get the

Amplitude modulation signal. observe the output in scope

9. For demodulation select Analog Filter Design block from Filter Designs

Library Links of Simulink

10. Connect the filter output to the scope and observe the results



Model Waveform:

Results:



5. DSB-SC MODULATION AND DEMODULATION

Aim:

To generate DSB-SC Modulated wave using simulink and demodulate the

modulated signal

Software Required:

MATLAB 7.0.4

SIMULINK

Theory:

In the double-sideband suppressed-carrier transmission (DSB-SC) modulation,

unlike AM, the wave carrier is not transmitted; thus, a great percentage of power

that is dedicated to it is distributed between the sidebands, which imply an

increase of the cover in DSB-SC, compared to AM, for the same power used.

The DSB-SC modulator output as follows

The coherent DSB-SC requires a synchronized local oscillator and works on

following

principle.

A low pass filter filters out the message signal from above.



Circuit diagram:

Procedure:




model

4. Select the sine wave as message signal and set the input voltage signal to

5Vp-p and signal frequency to 500Hz

5. Again select the signal generator then sine wave. Give the name as

Carrier signal. Set the carrier voltage 8Vp-p,frequency 1KHz

6. Select Product Block from Math Operations

7. All the above blocks connect as per the diagram shown to get the

Amplitude modulation signal. observe the output in scope

8. For demodulation select Analog Filter Design block from Filter Designs

Library Links of Simulink

9. Connect the filter output to the scope and observe the results



Model waveform:

Result:



6. Frequency Modulation

Aim:

To generate frequency modulated signal using communication block set of

SIMULINK

Software Required:

MATLAB 7.0.4

SIMULINK

Theory:

In Frequency Modulation (FM), the amplitude of the sinusoidal carrier wave was

modulated in AM, this time the instantaneous frequency of a sinusoidal carrier

wave will be modified proportionally to the variation of amplitude of the message

signal.

The FM signal is expressed as

( ) ( )( )tffAtsmcc

πβπ 2sin2cos +=

Where C

A is amplitude of the carrier signal, C

f is the carrier frequency

β is the modulation index of the FM wave

Circuit diagram:



Procedure:




model

4. Select FM modulator from Communication Block set of Simulink Library

Browser

5. Observe FM modulated output in scope

Model waveform:

Results:



1. Amplitude Modulation & Demodulation Aim:

1. To generate amplitude modulated wave and determine the percentage

modulation.

2. To Demodulate the modulated wave using envelope detector.

Apparatus Required:

Name of the

Component/Equipment

Specifications/Range Quantity

Transistor(BC 107)

fT = 300 MHz

Pd = 1W

Ic(max) = 100 mA

1

Diode(0A79) Max Current 35mA 1

Resistors 1KΩ, 2KΩ, 6.8KΩ, 10KΩ 1 each

Capacitor 0.01µF 1

Inductor 130mH 1

CRO 20MHz 1

Function Generator 1MHz 2

Regulated Power Supply 0-30V, 1A 1

Theory:

Amplitude Modulation is defined as a process in which the amplitude of the

carrier wave c(t) is varied linearly with the instantaneous amplitude of the message

signal m(t).The standard form of an amplitude modulated (AM) wave is defined by

( ) ( ) ( )[ ]tftmKAtscac

π2cos1+=

Where aK is a constant called the amplitude sensitivity of the modulator.

The demodulation circuit is used to recover the message signal from the

incoming AM wave at the receiver. An envelope detector is a simple and yet highly

effective device that is well suited for the demodulation of AM wave, for which the

percentage modulation is less than 100%.Ideally, an envelop detector produces an



output signal that follows the envelop of the input signal wave form exactly; hence, the

name. Some version of this circuit is used in almost all commercial AM radio receivers.

The Modulation Index is defined as, m = )(

)(

minmax

minmax

EE

EE

+

−

Where Emax and Emin are the maximum and minimum amplitudes of the

modulated wave.

Circuit Diagrams:

For modulation:

Fig.1. AM modulator



For demodulation:

Fig.2. AM demodulator

Procedure:

1. The circuit is connected as per the circuit diagram shown in Fig.1.

2. Switch on + 12 volts VCC supply.

3. Apply sinusoidal signal of 1 KHz frequency and amplitude 2 Vp-p as modulating

signal, and carrier signal of frequency 11 KHz and amplitude 15 Vp-p.

4. Now slowly increase the amplitude of the modulating signal up to 7V and note down

values of Emax and Emin.

5. Calculate modulation index using equation

6. Repeat step 5 by varying frequency of the modulating signal.

7. Plot the graphs: Modulation index vs Amplitude & Frequency

8. Find the value of R from RC

fm

π2

1= taking C = 0.01µF

9. Connect the circuit diagram as shown in Fig.2.

10. Feed the AM wave to the demodulator circuit and observe the output

11. Note down frequency and amplitude of the demodulated output waveform.

12. Draw the demodulated wave form .,m=1

Observation Table:

Table 1: fm= fc= Ac=

S.No. Vm(Volts) Emax(volts) Emin (Volts) m %m

(m x100)

1

2

3



Table 2: Am= fc = Ac=

S.No. fm(KHz) Emax(volts) Emin(Volts) m %m

(m x100)

1

2

3

Model Waveforms and graphs:



Precautions:

1. Check the connections before giving the power supply

2. Observations should be done carefully.

Result:

Inferences:

Questions:

1. What is the effect of Am and Ac on Amplitude modulated Signal?

2. What is the resonant frequency of the tank circuit?

3. What is the roll of the diode in demodulator circuit?



2. Diode Detector Characteristics

Aim:

To demodulate the modulated wave and to observe the characteristics of diode

detector.

Apparatus Required:

Name of the

Component/Equipment


Diode(0A79) Max Current 35mA 1

Resistor 10KΩ 1

Capacitor 0.1µF 1

CRO 20MHz 1

AM/FM Generator 0.1MHz-110MHz 1


Theory:

The AM signal is applied to a basic half-wave rectifier circuit consisting of diode

and resistor. The diode conducts when the positive half of the AM signals occur. During

the negative half cycles, the diode is reverse-biased and no current flows through it. As a

result, the voltage across resistor is a series of positive pulses whose amplitude varies

with the modulating signal. To recover the original modulating signal a capacitor is

connected across resistor. Its value is critical to good performance. The result is that the

carrier is absent there by leaving the original modulating signal.

Circuit Diagram:

Fig.1. Diode detector



Procedure:

1. Connect the circuit diagram as per Fig.1.

2. Set the input amplitude modulated wave from AM generator.

3. Observe the modulating signal changes by varying the amplitudes of the AM

signal.

4. Note down the Amplitude of the demodulated wave.

5. Plot a graph between Emax Vs Detector wave amplitude as shown in Fig.2

Sample readings:

TABLE 1: Reading of diode detector

S.No. Emax(mV) Emin (mV) Detector O/P

(mV)

1

2

3

4

5

Model Graphs:

Fig.2. Characteristics of Diode detector



Result:

Inferences:

Questions:

1. Classify Amplitude modulation detector or demodulators.

2. Why envelope detector is most popular in commercial receiver circuits?



3. Frequency Modulation and Demodulation

Aim:

a. To generate frequency modulated signal and determine the modulation index

and bandwidth for various values of amplitude and frequency of modulating

signal.

b. To demodulate a Frequency Modulated signal using FM detector.

Apparatus required:

Name of the

Component/Equipment Specifications/Range Quantity

IC 566 Operating voltage –Max-24 Volts

Operating current-Max.12.5 mA 1

IC 8038 Power dissipation – 750mW

Supply voltage - ±18V or 36V total

1

IC 565 Power dissipation -1400mw

Supply voltage - ±12V

1

Resistors 15 K Ω, 10 K Ω, 1.8 K Ω,

39 K Ω, 560 Ω

1,2,1

2,2

Capacitors 470 pF, 0.1µF

100pF , 0.001µF

2,1

1,1 each

CRO 100MHz 1


Regulated Power Supply 0-30 v, 1A 1

Theory:

The process, in which the frequency of the carrier is varied in accordance with

the instantaneous amplitude of the modulating signal, is called “Frequency Modulation”.

The FM signal is expressed as

( ) ( )( )tffAtsmcc

πβπ 2sin2cos +=

Where C

A is amplitude of the carrier signal, C

f is the carrier frequency

β is the modulation index of the FM wave



Circuit Diagrams:

Fig.1. FM Modulator Using IC 566

By using IC 8038:

Fig.2. FM Modulator Circuit



Fig.3. FM Demodulator Circuit

Procedure:

Modulation:

1. The circuit is connected as per the circuit diagram shown in Fig.2( Fig.1 for IC 566)

2. Without giving modulating signal observe the carrier signal at pin no.2 (at pin no.3 for

IC 566). Measure amplitude and frequency of the carrier signal. To obtain carrier

signal of desired frequency, find value of R from f = 1/ (2ΠRC) taking C=100pF.

3. Apply the sinusoidal modulating signal of frequency 4KHz and amplitude 3Vp-p at

pin no.7. ( pin no.5 for IC 566)

Now slowly increase the amplitude of modulating signal and measure fmin and

maximum frequency deviation ∆f at each step. Evaluate the modulating index (mf =

β) using ∆f / fm where ∆f = |fc - fmin|. Calculate Band width. BW = 2 (β + 1)fm = 2(∆f +

fm)

4. Repeat step 4 by varying frequency of the modulating signal.



Demodulation:

1. Connections are made as per circuit diagram shown in Fig.3

2. Check the functioning of PLL (IC 565) by giving square wave to input and

observing the output

3. Frequency of input signal is varied till input and output are locked.

4. Now modulated signal is fed as input and observe the demodulated signal

(output) on CRO.

5. Draw the demodulated wave form.

Observation Table:

Table: 1 fc =

S.No. fm(KHz) Tmax (µsec) fmin(KHz) ∆f(KHz) β BW (KHz)

1

2

Table 2: fm = fc =

S.No. Am (Volts) T (µsec) fmin(KHz) ∆f (KHz) β BW(KHZ)

01

02

Model Waveforms:



Precautions:


2. observations should be done carefully

Result:

Inferences:

Questions:

1. Effect of the modulation index on FM signal?

2. In commercial FM broadcasting, what is highest value of frequency deviation and

audio frequency to be transmitted?



4. Balanced Modulator

Aim:

To generate AM-Double Side Band Suppressed Carrier (DSB-SC) signal.

Apparatus Required:

Name of the


IC 1496 Wide frequency response up to 100 MHz

Internal power dissipation – 500mw(MAX) 1

Resistors

6.8KΩ

10 KΩ, 3.9 KΩ

1KΩ ,51 KΩ

1

2 each

3 each

Capacitors 0.1 µF 4

Variable Resistor

(Linear Pot) 0-50KΩ

1

CRO 100MHz 1


Regulated Power Supply 0-30 v, 1A 1

Theory:

Balanced modulator is used for generating DSB-SC signal. A balanced

modulator consists of two standard amplitude modulators arranged in a balanced

configuration so as to suppress the carrier wave. The two modulators are identical

except the reversal of sign of the modulating signal applied to them.



Circuit Diagram:

Fig.1. Balanced Modulator Circuit

Procedure:


2. An Carrier signal of 1Vp-p amplitude and frequency of 83 KHz is applied as carrier to

pin no.10.

3. An AF signal of 0.5Vp-p amplitude and frequency of 5 KHz is given as message

signal to pin no.1.

4. Observe the DSB-SC waveform at pin no.12.



Observation Table:

Signal AMPLITUDE (Volts) Frequency (Hz)

Message signal

Carrier signal

DSB-SC Signal

Model Waveforms:



Precautions:

1. Check the connections before giving the supply

2. Observations should be done carefully

Results:

Inferences:

Questions:

1. What is the efficiency of the DSB-SC modulating system?

2. What are the applications of balanced modulator?

3. What is the effect of amplitude of message on DSB-Sc signal?



5. Pre-Emphasis & De-Emphasis

Aim:

I) To observe the effects of pre-emphasis on given input signal.

ii) To observe the effects of De-emphasis on given input signal.

Apparatus Required:

Name of the


Transistor (BC 107)

fT = 300 MHz

Pd = 1W

Ic(max) = 100 mA

1

Resistors 10 KΩ, 7.5 KΩ, 6.8 KΩ 1 each

Capacitors 10 nF

0.1 µF

1

2

CRO 20MHZ 1

Function Generator 1MHZ 1


Theory:

The noise has a effect on the higher modulating frequencies than on the lower

ones. Thus, if the higher frequencies were artificially boosted at the transmitter and

correspondingly cut at the receiver, an improvement in noise immunity could be

expected, there by increasing the SNR ratio. This boosting of the higher modulating

frequencies at the transmitter is known as pre-emphasis and the compensation at the

receiver is called de-emphasis.



Circuit Diagrams:

For Pre-emphasis:

Fig.1. Pre-emphasis circuit

For De-emphasis:

Fig.2. De-emphasis circuit

Procedure:

1. Connect the circuit as per circuit diagram as shown in Fig.1.

2. Apply the sinusoidal signal of amplitude 20mV as input signal to pre emphasis

circuit.

3. Then by increasing the input signal frequency from 500Hz to 20KHz, observe

the output voltage (vo) and calculate gain (20 log (vo/vi).

4. Plot the graph between gain Vs frequency.



5. Repeat above steps 2 to 4 for de-emphasis circuit (shown in Fig.2). by applying

the sinusoidal signal of 5V as input signal

Sample readings:

Table1: Pre-emphasis Vi =

Frequency(KHz) Vo(mV) Gain in dB(20 log Vo/Vi)

0.5

1

2

4

5

6

7

10

15

Table2: De-emphasis Vi =

Frequency(KHz) Vo(Volts) Gain in dB(20 log Vo/Vi)

0.150

1

2

3

5



Graphs:



Precautions:


2. Observation should be done carefully

Result:

Inferences:

Questions:

1. What is the value of time constant used in commercial pre-emphasis

circuit?

2. For which modulated signals pre-emphasis and de-emphasis circuits are

used.

3. On what parameters fc depends?

4. Explain the pre-emphasis and de-emphasis characteristics?



6. Synchronous Detector

Aim:

To demodulate the DSB-SC signal.

Apparatus Required:

Name of the


IC 1496 Maximum voltage - 30 V

power dissipation – 500 mw 1

Resistors

100 Ω,6.8 K Ω , , 22 K Ω

3.9 K Ω

4.7 K Ω

1 K Ω

1 each

2

4

3

Capacitors 0.0047 µF

1 µF

3

3

Theory:

The message signal m(t) is recovered from a DSB-SC wave s(t) by first

multiplying s(t) with locally generated carrier wave and then low-pass filtering as shown

in the block diagram in Fig.1

It is assumed that the local oscillator output in the detector is exactly coherent or

synchronized, in both frequency and phase; with the carrier wave c(t) used to generate

s(t).This method of demodulation is known as coherent detection or synchronous

detection.

Fig.1. Block diagram of synchronous detector



Circuit Diagram:

Fig.2 Synchronous detector Circuit

Procedure:

1. Connect the circuit diagram as shown in Fig.2

2. Apply the RF signal of frequency 83 KHz at pin no.1.

3. Apply modulated (DSB-SC) signal at pin no.8.

4. Observe the synchronous detector output at the pin no.12 on the oscilloscope

(CRO).

Observation Table:

Signal Amplitude (V) Frequency(KHz)

Carrier signal 1 83

Output signal 0.5 4



Model Wave Forms:

Precautions:



Result:

Inferences:



Questions:

1. Write the applications of synchronous detector?

2. What are the drawbacks of synchronous detector?

3. What is the Effect of Carrier signal on output signal?



7. SSB System

Aim:

To generate the SSB modulated wave.

Apparatus Required:

Name of the

Component/Equipment

Specifications Quantity

SSB system trainer board --- 1

CRO 30MHz 1

Theory:

An SSB signal is produced by passing the DSB signal through a highly selective

band pass filter. This filter selects either the upper or the lower sideband. Hence

transmission bandwidth can be cut by half if one sideband is entirely suppressed. This

leads to single-sideband modulation (SSB). In SSB modulation bandwidth saving is

accompanied by a considerable increase in equipment complexity.

Circuit Diagram:

Fig. 1 Single Side Band system



Procedure:

1. Switch on the trainer and measure the output of the regulated power supply i.e.,

±12V and -8V.

2. Observe the output of the RF generator using CRO. There are 2 outputs from the

RF generator, one is direct output and another is 90o out of phase with the direct

output. The output frequency is 100 KHz and the amplitude is ≥ 0.2VPP.

(Potentiometers are provided to vary the output amplitude).

3. Observe the output of the AF generator, using CRO. There are 2 outputs from the

AF generator, one is direct output and another is 90o out of phase with the direct

output. A switch is provided to select the required frequency (2 KHz, 4KHz or 6

KHz). AGC potentiometer is provided to adjust the gain of the oscillator (or to set the

output to good shape). The oscillator output has amplitude ≅ 10VPP. This amplitude

can be varied using the potentiometers provided.

4. Measure and record the RF signal frequency using frequency counter. (or CRO).

5. Set the amplitudes of the RF signals to 0.1 Vp-p and connect direct signal to one

balanced modulator and 90o phase shift signal to another balanced modulator.

6. Select the required frequency (2KHz, 4KHz or 6KHz) of the AF generator with the

help of switch and adjust the AGC potentiometer until the output amplitude is ≅ 10

VPP (when amplitude controls are in maximum condition).

7. Measure and record the AF signal frequency using frequency counter (or CRO).

8. Set the AF signal amplitudes to 8 Vp-p using amplitude control and connect to the

balanced modulators.

9. Observe the outputs of both the balanced modulators simultaneously using Dual

trace oscilloscope and adjust the balance control until desired output wave forms

(DSB-SC).

10. To get SSB lower side band signal, connect balanced modulator output (DSB_SC)

signals to subtract or.

11. Measure and record the SSB signal frequency.

12. Calculate theoretical frequency of SSB (LSB) and compare it with the practical

value.

LSB frequency = RF frequency – AF frequency

13. To get SSB upper side band signal, connect the output of the balanced modulator to

the summer circuit.



14. Measure and record the SSB upper side band signal frequency.

15. Calculate theoretical value of the SSB(USB) frequency and compare it with practical

value. USB frequency = RF frequency + AF frequency

Observations:

Signal Amplitude (volts) Frequency (KHz)

Message signal

Carrier signal

SSB (LSB)

SSB (USB)

Model Waveforms:



Precautions:


2. Observations should be done carefully.

Results:

Inferences:

Question:

1. What are difficulties in practical implementation of SSB-C system?

2. Why SSB-SC is not used in broadcasting?



8. Spectrum Analysis of AM and FM Signal Using

Spectrum Analyzer

Aim:

To observe the spectrum of AM and FM signals and obtain the power levels in

dBm of fundamental frequency components by using spectrum Analyzer.

Apparatus Required:

Name of the Component/Equipment Specifications Quantity

Spectrum analyzer LPT-2250 Spectrum analyzer 1

AM/FM generator 0.1MHz-110MHz 1

CRO 30MHz 1

Theory:

A spectrum analyzer provides a calibrated graphical display on its CRT with

frequency on the horizontal axis and amplitude on the vertical axis. Displayed as vertical

lines against these coordinates are sinusoidal components of which the input signal in

composed. The height represents the absolute magnitude, and horizontal location

represents the frequency. This instrument provide a display of the frequency spectrum

over a given frequency band.

Block diagram:

Fig.1 Block Diagram of Spectrum Analyzer



Procedure:

1. AM signal is given to the spectrum analyzer.

2. Adjust the zero marker to carrier frequency and measure spectrum of AM.

3. For different values of fc and fm, observe the spectrum of AM.

4. Now remove AM signal and give FM signal to the spectrum analyzer.

5. Adjust the zero marker to carrier frequency and observe spectrum of FM.

6. Plot the spectrums of FM and AM.

Observation Table:

Table1: Readings for AM signal

S.No. fc (MHz) fm (KHz) (fm+ fc ) (MHz) (fc - fm) (MHz)

1

Table2: Readings for FM signal

S.No. fc (MHz) fm (KHz) (fm+ fc ) (MHz) (fc - fm) (MHz)

1

Model Graphs:

Fig.2 AM spectrum

Fig. 3 FM spectrum



Precautions:

1. Check the probe connections.


Inferences:

Results:

Questions:

1. Distinguish between CRO and Spectrum analyzer?

2. What are the functions of span/div control and reference level control?



1. PULSE WIDTH MODULATION

Aim:

To write a MATLAB program to simulate the PWM wavefor the given

message signal




Theory:

Pulse width modulation (PWM) encodes a signal into periodic pulses of

equal magnitude but varying width. The width of a pulse at a given point in time is

proportional to the amplitude of the message signal at that time. For example, the

large value of the message yields a narrow pulse.

To implement the PWM, the message signal is compared with the

sawtooth carrier. When the message signal is greater than the carrier, the

comparator output becomes highand vice versa; the heights and lows can be

represented by +1 or-1 respectively.The comparator output will be the pulse

width modulated signal.

Program:

%PWM wave generation

clc;

clearall;

closeall;

t=0:0.001:2;

s=sawtooth(2*pi*10*t+pi);

m=0.75*sin(2*pi*1*t);

n=length(s);

for i=1:n

if (m(i)>=s(i))

pwm(i)=0;



elseif (m(i)<=s(i))

pwm(i)=1;

end

end

subplot(211),plot(t,m,'-r',t,s,'-b');axis([0 2 -1.5 1.5]);

title('message signal with sawtoothcoparison')


ylabel('voltage(V)');

subplot(212),plot(t,pwm,'-k')

axis([0 2 -0.5 1.5]);

title('PWM wave');


ylabel('voltage(V)');

Model Waveforms:



2. PHASE LOCKED LOOP

Aim:

To write the MATLAB program to simulate the operation of PLL circuit.




Theory:

Phase-locked loop (PLL) is a feedback loop which locks two waveforms with

same frequency but shifted in phase. The fundamental use of this loop is in

comparing frequencies of two waveforms and then adjusting the frequency of the

waveform in the loop to equal the input waveform frequency. A block diagram of

the PLL is shown in Figure 1. The heart of the PLL is a phase comparator which

along with a voltage controlled oscillator (VCO), a filter and an amplifier forms the

loop.

Figure 1: Basic Phase-Locked Loop

If the two frequencies are different the output of the phase comparator varies and

changes the input to the VCO to make its output frequency equal to the input

waveform frequency. The locking of the two frequencies is a nonlinear process

but linear approximation can be used to analyse PLL dynamics. In getting the

PLL to lock the proper selection of the filter is essential and it needs some

attention. If the filter design is understood from control theory point-of-view then



the design becomes quite simple. In this short note we will discuss only the

fundamentals of the PLL and how you can use nonlinear simulation and

linearised approximation to get a better understanding of the PLL.

Program:

clc;

closeall;

clearall;

reg1 =0;

reg2 =0;

reg3 = 0;

eta =sqrt(2)/2;

theta =2*pi*1/100;

Kp = [(4*eta*theta)/(1+2*eta*theta+theta^2)];

Ki = [(4*theta^2)/(1+2*eta*theta+theta^2)];

d_phi_1 = 1/20;

n_data = 100;

for nn =1:n_data

phi1= reg1 +d_phi_1;

phi1_reg(nn) = phi1;

s1 =exp(j*2*pi*reg1);

s2 =exp(j*2*pi*reg2);

s1_reg(nn) =s1;

s2_reg(nn) =s2;

t =s1*conj(s2);

phi_error =atan(imag(t)/real(t))/(2*pi);

phi_error_reg(nn) = phi_error;

sum1 =Kp*phi_error + phi_error*Ki+reg3;

reg1_reg(nn) =reg1;

reg2_reg(nn) = reg2;

reg1 =phi1;



reg2=reg2+sum1;

reg3 =reg3+phi_error*Ki;

phi2_reg(nn) =reg2;

end

figure(1)

plot(phi1_reg);

holdon

plot(phi2_reg,'r');

holdoff;

gridon;

title('phase plot');

xlabel('Samples');

ylabel('Phase');

figure(2)

plot(phi_error_reg);

title('phase Error of phase detector');

gridon;

xlabel('samples(n)');

ylabel('Phase error(degrees)');

figure(3)

plot(real(s1_reg));

holdon;

plot(real(s2_reg),'r');

holdoff;

gridon;

title('Input signal & Output signal of VCO');

xlabel('Samples');

ylabel('Amplitude');

axis([0 n_data -1.1 1.1]);



Input &Output Signals Of VCO:

Phase plot:



Phase error of phase detector:

Result:



3. Characteristics of Mixer Aim:

To obtain the characteristics of a mixer circuit.

Apparatus Required:

Name of the


Transistors (BC 107)

fT = 300 MHz

Pd = 1W

Ic(max) = 100 mA

1

Resistors 1 KΩ , 6.8 KΩ, 10KΩ 1 each

Capacitor 0.01µF 1

Inductor 1mH 1

CRO 20MHZ 1


Regulated Power Supply 0-30v, 1A 1

Theory:

The mixer is a nonlinear device having two sets of input terminals and one set of

output terminals. Mixer will have several frequencies present in its output, including the

difference between the two input frequencies and other harmonic components.



Circuit Diagram:

FIG.1. Mixer Circuit

Procedure:

1. Connect the circuit as per the circuit diagram as shown in Fig.1. Assume C=0.1µF

and calculate value of L1 using f=

112

1

CLπ where f=7KHz

2. Apply the input signals at the appropriate terminals in the circuit.

3. Note down the frequency of the output signal, which is same as difference frequency

of given signals.

Observation Table:

Signal Amplitude (Volts) Frequency(KHz)

Input signal1

Input signal 2

Output signal



Waveforms:



Precautions:

1.Check the connections before giving the supply

2.Observations should be done carefully

Result:

Inferences:

Questions:

1. How can we use mixer circuit to generate AM signal?

2. What are the applications of mixer?

3. In which region BJT will be operated?

4. What is the roll of LC circuit?



4. Phase Locked Loop

Aim:

To verify the capture range and lock range for given PLL IC LM 565

Apparatus Required:

Name of the


IC LM 565 Supply voltage ±12V

Power dissipation 1400mw 1

Resistors 12 K Ω 1

Capacitors 10pF

0.01µF

1

2

CRO 20MHZ 1

Function Generator 0- 1MHz 1

Regulated Power Supply 0-30v, 1A 1

Theory:

The best frequency demodulator is the phase locked loop(PLL). A PLL is a frequency or

phase –sensitive feedback control circuit. It used not only in frequency demodulation but

also in frequency synthesizers. All PLLs have three basic elements as illustrated in

Fig.1. A phase detector or mixer is used to compare the input or reference signal with

the output of a

Fig.1. Block diagram of PLL



VCO. The VCO frequency is varied by the dc output voltage from a low pass filter. It is

the output of the phase detector that the low pass filter uses to produce dc control

voltage. This dc control voltage is called the error signal and is also the feedback in this

circuit and will control the VCO.

Circuit Diagram:

Fig.2 PLL Circuit diagram

Procedure:

1. Connect the circuit as shown in Fig. 2.

2. Obtain the free running frequency fo without giving any input signal.

3. Apply the square wave as input signal at pin no.2 and then vary the input signal

frequency. When input signal is locked with VCO output in forward direction then

note down the value of input signal frequency (fC1). Again increase the input

signal frequency and observe the frequency at which the PLL becomes unlocked,

note down the value of input signal frequency (fL2).

4. Again the frequency of input is reduced in backward direction and note down the

frequency of the input signal (fc2) at which input signal is locked with VCO output.



And the frequency of input signal is still reduced, note down the frequency of

input signal (fL1) at which the PLL becomes unlocked.

5. Now by using formulae given calculate lock range and capture range and verify

them experimentally.

Observation Table:

Theoretical(KHz) Practical(KHz)

fo

fL

fC

Formulae and Calculations:

fo (free running frequency) = 1.2/4R1C1 = 1.2/4x1.2K x 0.1µF = 2.5 KHz

fL = lock range = ± 8fo/V, =± 8x2500/24 = ±833 Hz

[where V=+V-(-V)= 12-(-12)=24 volts]

Theoretical lock range is, f= fo ±fL= 2.5±0.833=1.667KHZ to 3.333KHz

fC = capture range =2

1

112

×±

CR

f L

π= ± 60.7Hz

Precautions:



Inferences:

Questions:

1. Write the application of PLL?

2. What is the capture range of PLL.

3. What is the effect of R1 and C1 values and Vcc on output signal?



5. Squelch Circuit

Aim:

To Study the performance characteristics of Squelch Circuit .

Apparatus Required:

Name of the

Component/Equipment


Transistor(BC107)

fT = 300 MHz

Pd = 1W

Ic(max) = 100 mA

2

Resistor 10KΩ, 56KΩ, 1KΩ,2.2KΩ, 1,1,1,2

Capacitor 10µF 2

CRO 20MHz 1

Function generator 0-1MHz 1


Theory:

A squelch circuit also known as a mute circuit. It is designed to keep the receiver

audio turned off until an RF signal appears at the receiver input. The Squelch circuit

provides a means of keeping the audio amplifier turned off during the time that noise is

received in the background when an RF signal appears at the input, the audio amplifier

is enabled. There are two types of squelch circuits used in communication receivers;

they are (i). Amplitude squelch circuit (ii). Noise squelch circuit.



Circuit Diagram:

Fig.1 Squelch Circuit

Procedure:

1. Connect the circuit as shown in Fig.1

2. Set the input signal (say 180mv, 1 KHz) using function generator.

3. Vary the voltage of AGC in different steps and observe corresponding signal

output Voltages (Vo) in CRO and tabulate them.

4. Plot the graph between AGC voltage Vs Gain(dB) as shown in Fig.2



Observation Table:

TABLE 1: Readings of a squelch circuit

S.No. AGC(volts) Vo (mV) Gain=Vo/Vi Gain in

dB=20log(Vo/Vi)

1

2

3

4

5

6

Graphs:

Fig.2. Characteristics of Squelch circuit

Result:

Inferences:



Questions:

1. What is the function of Squelch circuit?

2. What is Amplitude squelch or Gate squelch circuit?

3. What is true noise squelch?



6. Frequency Synthesizer

Aim:

To construct a frequency synthesizer circuit.

Apparatus Required:

Name of the

Component/Equipment


Transistor(BC107)

fT = 300 MHz

Pd = 1W

Ic(max) = 100 mA

1

IC 565 Supply voltage :±12V

Power dissipation :1400mw 1

IC 7490 Max supply Voltage 5.25V

Power supply current 15mA

1

Resistor 2kΩ, 4.7kΩ, 10kΩ, 20kΩ(pot) 1each

Capacitor 10µF, 0.001µF, 0.01µF 1each

CRO 0-20MHz 1

Function generator 0-1MHz 1

Regulated Power Supply

0-30V, 1A

1

Theory:

The frequency divider is inserted between the VCO and the phase comparator of PLL.

Since the output of the divider is locked to the input frequency fin, the VCO is actually

running at a multiple of the input frequency . The desired amount of multiplication can be

obtained by selecting a proper divide– by – N network ,where N is an integer. To obtain

the output frequency fOUT=5fIN, a divide – by – N = 5 network is needed. One must

determine the input frequency range and then adjust the free running fOUT of the VCO by

means of R1 (20kΩpot) and C1 (10µF) so that the output frequency of the divider is

midway within the predetermined input frequency range. The output of the VCO now



should be 5fIN. The output of the VCO now should be adjusted from 1.5 KHz to 15 KHz

by varying potentiometer R1 .this means that the input frequency fin range has to be with

in 300Hz to 3KHz. In addition, the input wave form may be applied to inputs pin2 or pin3.

Input – output waveforms forms for fOUT= 5fIN. A small capacitor typically 1000pf is

connected between pin7 and pin8 to eliminate possible oscillations. Also, capacitor C2

should be large enough to stabilize the VCO frequency.

Circuit Diagram:

Fig.1 Frequency synthesizer circuit

Procedure:


2. Measure the free running frequency of PLL (IC565) at pin no.4 with the input

signal set to zero volt.

3. Compare the output with the calculated theoretical value 0.25/RTCT.

4. Set the input signal (say 2 Vp-p, 1KHz square wave form ) using function

generator.

5. Vary the frequency by adjusting the 20KΩ Potentiometer till the PLL(IC565)is

locked.

6. Measure (frequency counter) the frequency of the output signal. It must be 5

times the input signal frequency.

7. Observe and note down the waveform and frequency of various signals using

CRO .



Observation Table:

TABLE 1: Readings of a Frequency Synthesizer

S.No. f i/p (KHz) f o/p (KHz)

1.

2.

Model Wave forms:

Fig.2 Output Wave Forms

Result:

Inferences:

Questions:

1. How to achieve fout = 2 fin ?

2. What is the effect of C1 on the output frequency?



Appendix A

Component/

Equipment

Specifications Pin diagram

Transistor –

BC 107

fT= 300 MHz

IC(max)= 100 mA

Pd=1W,VCEO=45V

hfe (min) = 40

hfe (max) = 450

NE 566

Operating voltage –Max-24 Volts

Operating temperature range –

0.70oC

Operating current-Max.12.5 mA

Max. operating frequency – 1 MHz

The external resistance for

frequency adjustment R1 must have

a value between 2K and 20kΩ

The bias voltage (VC) applied to the

control terminal (pin 5) should be in

the range ¾ V+≤ VC ≤ V+ (V+

supply voltage)

IC 8038

Simultaneous outputs – sine wave

Square wave and Triangle

Low distortion – 1%

High linearity – 01%

Wide frequency range of operation

0.001 Hz to 1.0Mhz

Variable duty cycle – 2% to 98%

Supply voltage - ±18V or 36V total

Power dissipation – 750mW

Input current (pins 4 and 5 ) –

25mA

operating temperature range: 55oC



to +125oC

LM 1496

Operating temperature range →0o to

+70oC

Wide frequency response up to 100

MHz

Dual-in-line package

Carrier feed through

(sinusoidal) – 60mvrms – 40µVrms

(square wave) -300mVPP – (20-

150mVrms)

Internal power dissipation – 500

mw(MAX)

Maximum voltage - 30 V

Bias current – 12mA

LM 565

Supply voltage ±12V

Power dissipation 1400mw

Operating temperature range 55o to

+125oC

VCO maximum operating frequency

500KHz (Co = 2.7PF)

VCO sensitivity (fo=-10KHz) --- 6600

Hz/V

Phase detector sensitivity KD, 0.68

V/radian

SSB Trainer

Board

Consists of

RF generator : - 100 KHz

:Phase shift 90o isavailable

RF generator and 0o phase shifted

signal is also available

Balanced modulator – using MC

1496

Synchronous detector – using MC

__



1496

Radio Receiver

Measurement

Trainer

MW 550kHz to 1.5mHz

Consists of

1. Internal AM generator

2. Internal AF generator

3. Internal RF generator

__

LPT-2250

Spectrum

analyzer

Frequency:

Frequency range: 30 KHz to 1.15

GHz

Frequency resolution: 1KHz

Amplitude:

Input level +20dBm(max.atten.)

Display range 75 dB usable

Ref. level range -30dBm to

+20dBm

__

AM-FM

generator

Frequency range: 100 KHz to 110

MHz (CW mode)

Frequency indication: Digital 4 digit

Frequency accuracy:+/-1 digit (4

digit max.)

RF output:75 mV(rms) max. into

75 ohms

Output control: 0dB/20dB and fine

control

Int.Mod.Freuqency:1KHz

External: Frequency -50Hz to

20KHz

Level – 15V p-p max.

__



µA741

Supply Voltage ±22V

Power Dissipation 500mW

Differential input voltage ±30V

Input voltage ±15V

Operating Temperature -55o to

+125oC

Storage Temperature range -55o to

+150oC

BFW10

N-channel –Depletion JFET

Max Voltage 30V

Idss :8mA

Min Temperature -40oC

Max Temperature 150oC

OA79

Ge-Diode

Max Voltage 45V

Max Current 35mA

7486

Min Supply Voltage 4.75V

Max supply Voltage 5.25V

Output current high -0.4mA

Output current low 80mA

Temperature range 0o to +70oC

7490

Min Supply Voltage 4.75V

Max supply Voltage 5.25V

Output current high -0.4mA

Output current low 80mA

Temperature range 0o to +70oC

Power supply current 15mA



Appendix B

PLOT(X,Y):

Plots vector Y versus vector X. If X or Y is a matrix, then the vector is

plotted versus the rows or columns of the matrix, whichever line up. If X is a

scalar and Y is a vector, length(Y) disconnected points are plotted.

SUBPLOT(m,n,p) or SUBPLOT(mnp):

Breaks the Figure window into an m-by-n matrix of small axes, selects the

p-th axes for for the current plot, and returns the axis handle. The axes are

counted along the top row of the Figure window, then the second row, etc. For

example,

SUBPLOT(2,1,1), PLOT(income)

SUBPLOT(2,1,2), PLOT(outgo)

plots income on the top half of the window and outgo on the bottom half. If the

current axes is nested in a uipanel the panel is used as the parent for the subplot

instead of the current figure.

LINSPACE(a,b,n):

The linspace function generates linearly spaced vectors. It is similar to the

colon operator ":", but gives direct control over the number of points.

y = linspace(a,b,n) generates a row vector y of n points linearly spaced between

and including a and b.

AXIS([xmin xmax ymin ymax]):

Controls axis scaling and appearance.

AXIS([XMIN XMAX YMIN YMAX]) sets scaling for the x- and y-axes on the

current plot.



AMMOD(x,Fc,Fs,ini_phase,carramp):

Uses the message signal x to modulate a carrier signal with frequency Fc

(Hz) using amplitude modulation. The carrier signal and x have sample frequency

Fs (Hz). The modulated signal has initial phase specified by ini_phase.

AMDEMOD(Y,Fc,Fs,INI_PHASE,CARRAMP):Demodulates the amplitude

modulated signal Y from the carrier frequency Fc (Hz). Y and Fc have sample

frequency Fs (Hz).The modulated signal Y has specified initial phase, and

specified carrier amplitude.

MODULATE(x,fc,fs,'method'):

Modulate the real message signal x with a carrier frequency fc and

sampling frequency fs, using one of the options listed below for 'method'. Fs must

satisfy Fs > 2*Fc + BW, where BW is the bandwidth of the modulated signal.

Method Description

‘am’ or ‘amdsb-sc’ Amplitude modulation, double sideband suppressed

carrier

'amssb' Amplitude modulation single side-band

'fm' Frequency modulation

'pm' Phase modulation

'pwm' Pulse width modulation

'ppm' Pulse position modulation



DEMOD(y,fc,fs,'method'):

Demodulates the carrier signal Y with a carrier frequency Fc and sampling

frequency Fs, using the demodulation scheme in METHOD.

FMMOD(X,Fc,Fs,FREQDEV):

Uses the message signal X to modulate the carrier frequency Fc (Hz) and

sample frequency Fs (Hz), where Fs > 2*Fc. FREQDEV (Hz) is the frequency

deviation of the modulated signal.

Method Description

‘am’ or ‘amdsb-sc’ Amplitude demodulation, double sideband

suppressed carrier

'amssb' Amplitude demodulation single side-band

'fm' Frequency demodulation

'pm' Phase demodulation

'pwm' Pulse width demodulation

'ppm' Pulse position demodulation



SIMULINK:

BLOCK NAME LIBRARY DESCRIPTION

Sine / cosine Wave Simulink--

Sources

Generates sine/cosine

wave with required

amplitude, frequency

and phase

constant Simulink--

Sources

Generates constant

value

scope Simulink--Sinks Used to display the

signals

Add,subtract,multiply,divide Simulink--Math

operations

Mathematical

operators

Signal generator Simulink--

Sources

Generates

sine/square/triangular

waves with required

amplitude, frequency

and phase

Analog passband

modulation

Communications

blockset--Analog

passband

modulation

Generates various

analog modulation

waves



Sine wave:

We can generate the sine wave in two ways one is by using the directly sinewave

block and other way is by using the signal generator block

Sine wave block:

The Sine Wave block provides a sinusoid. The block can operate in either time-

based or sample-based mode.

Sine type

Type of sine wave generated by this block, either time- or sample-based. Some

of the other options presented by the Sine Wave dialog box depend on whether

you select time-based or sample-based as the value of Sine type parameter.

Symbol



Time

Specifies whether to use simulation time as the source of values for the sine

wave's time variable or an external source. If you specify an external time source,

the block displays an input port for the time source.

Amplitude

The amplitude of the signal. The default is 1.

Bias

Constant value added to the sine to produce the output of this block.

Frequency

The frequency, in radians/second. The default is 1 rad/s. This parameter

appears only if you choose time-based as the Sine type of the block.

Samples per period

Number of samples per period. This parameter appears only if you choose

sample-based as the Sine type of the block.

Phase

The phase shift, in radians. The default is 0 radians. This parameter appears

only if you choose time-based as the Sine type of the block.

Number of offset samples

The offset (discrete phase shift) in number of sample times. This parameter

appears only if you choose sample-based as the Sine type of the block.



Sample time

The sample period. The default is 0. If the sine type is sample-based, the

sample time must be greater than 0. See Specifying Sample Time in the online

documentation for more information.

Interpret vector parameters as 1-D

If selected, column or row matrix values for the Sine Wave block's numeric

parameters result in a vector output signal; otherwise, the block outputs a signal

of the same dimensionality as the parameters. If this option is not selected, the

block always outputs a signal of the same dimensionality as the block's numeric

parameters.

Signal generator:

The Signal Generator block can produce one of three different waveforms:

sine wave, square wave, and sawtooth wave. The signal parameters can be

expressed in Hertz (the default) or radians per second. This figure shows each

signal displayed on a Scope using default parameter values.

The block's Amplitude and Frequency parameters determine the amplitude and

frequency of the output signal. The parameters must be of the same dimensions

after scalar expansion.

Symbol



Wave form

The wave form: a sine wave, square wave, or sawtooth wave. The default is a

sine wave. This parameter cannot be changed while a simulation is running.

Time

Specifies whether to use simulation time as the source of values for the

waveform's time variable or an external signal. If you specify an external time

source, the block displays an input port for the time source.

Amplitude

The signal amplitude. The default is 1.

Frequency

The signal frequency. The default is 1.

Units

The signal units: Hertz or radians/sec. The default is Hertz.




If selected, column or row matrix values for the Amplitude and Frequency

parameters result in a vector output signal.

Constant

The Constant block generates a real or complex constant value. The block

generates scalar (1x1 2-D array), vector (1-D array), or matrix (2-D array) output,

depending on the dimensionality of the Constant value parameter and the setting

of the Interpret vector parameters as 1-D parameter.

The output of the block has the same dimensions and elements as the Constant

value parameter. If you specify a vector for this parameter, and you want the

block to interpret it as a vector (i.e., a 1-D array), select the Interpret vector

parameters as 1-D parameter; otherwise, the block treats the Constant value

parameter as a matrix (i.e., a 2-D array).

Symbol



Constant value

Specify the constant value output by the block. You can enter any MATLAB

expression in this field, including the Boolean keywords, true or false, that

evaluates to a matrix value. The Constant value parameter is converted from its

data type to the specified output data type offline using round-to-nearest and

saturation.


If you select this check box, the Constant block outputs a vector of length N if

the Constant value parameter evaluates to an N-element row or column vector,

i.e., a matrix of dimension 1xN or Nx1.

Sample time

Specify the interval between times that the Constant block's output can change

during simulation (e.g., as a result of tuning its Constant value parameter). The

default sample time is inf, i.e., the block's output can never change. This setting

speeds simulation and generated code by avoiding the need to recompute the

block's output. See Specifying Sample Time in the online documentation for more

information.

Scope

The Scope block displays its input with respect to simulation time. The Scope

block can have multiple axes (one per port); all axes have a common time range

with independent y-axes. The Scope allows you to adjust the amount of time and

the range of input values displayed. You can move and resize the Scope window

and you can modify the Scope's parameter values during the simulation.

Symbol



When you start a simulation, Simulink does not open Scope windows, although it

does write data to connected Scopes. As a result, if you open a Scope after a

simulation, the Scope's input signal or signals will be displayed.

If the signal is continuous, the Scope produces a point-to-point plot. If the signal

is discrete, the Scope produces a stair-step plot.

The Scope provides toolbar buttons that enable you to zoom in on displayed

data, display all the data input to the Scope, preserve axis settings from one

simulation to the next, limit data displayed, and save data to the workspace. The

toolbar buttons are labeled in this figure, which shows the Scope window as it

appears when you open a Scope block.



Number of axes

Set the number of y-axes in this data field. With the exception of the floating

scope, there is no limit to the number of axes the Scope block can contain. All

axes share the same time base (x-axis), but have independent y-axes. Note that

the number of axes is equal to the number of input ports.

Time range

Change the x-axis limits by entering a number or auto in the Time range field.

Entering a number of seconds causes each screen to display the amount of data

that corresponds to that number of seconds. Enter auto to set the x-axis to the

duration of the simulation. Do not enter variable names in these fields.

Sum (Add or subtract)

The Sum block performs addition or subtraction on its inputs. This block can add

or subtract scalar, vector, or matrix inputs. It can also collapse the elements of a

single input vector.

Symbol



The Sum block first converts the input data type(s) to the output data type using

the specified rounding and overflow modes, and then performs the specified

operations.

List of signs

Enter as many plus (+) and minus (-) characters as there are inputs. Addition

is the default operation, so if you only want to add the inputs, enter the number of

input ports. For a single vector input, "+" or "-" will collapse the vector using the

specified operation.

You can manipulate the positions of the input ports on the block by inserting

spacers (|) between the signs in the List of signs parameter. For example, "++|--"

creates an extra space between the second and third input ports.



Sample time (-1 for inherited)

Specify the time interval between samples. To inherit the sample time, set this

parameter to -1. See Specifying Sample Time in the online documentation for

more information.

Product(multiply or divide)

The Product block performs multiplication or division of its inputs.

This block produces outputs using either element-wise or matrix multiplication,

depending on the value of the Multiplication parameter. You specify the

operations with the Number of inputs parameter. Multiply(*) and divide(/)

characters indicate the operations to be performed on the inputs.

Number of inputs

Symbol



Enter the number of inputs or a combination of "*" and "/" symbols. See

Description above for a complete discussion of this parameter.

Multiplication

Specify element-wise or matrix multiplication. See Description above for a

complete discussion of this parameter.

Sample time (-1 for inherited)

Specify the time interval between samples. To inherit the sample time, set this

parameter to -1. See Specifying Sample Time in the online documentation for

more information.

DSB AM (Amplitude modulation and de-modulation)

Modulation

The DSB AM Modulator Passband block modulates using double-

sideband amplitude modulation. The output is a passband representation of the

modulated signal. Both the input and output signals are real sample-based scalar

signals.

if the input is u(t) as a function of time t, then the output is

where: k is the Input signal offset parameter.

fc is the Carrier frequency parameter.

θ is the Initial phase parameter.

Symbol



Input signal offset

The offset factor k. This value should be greater than or equal to the absolute

value of the minimum of the input signal.

Carrier frequency (Hz)

The frequency of the carrier.

Initial phase (rad)

The initial phase of the carrier.

De-modulation

The DSB AM Demodulator Passband block demodulates a signal that was

modulated using double-sideband amplitude modulation. The block uses the

envelope detection method. The input is a passband representation of the


signals.

Symbol



In the course of demodulating, this block uses a filter whose transfer function is

described by the Lowpass filter numerator and Lowpass filter denominator

parameters.

Offset factor

The same as the Input signal offset parameter in the corresponding DSB AM

Modulator Passband block.


The frequency of the carrier in the corresponding DSB AM Modulator

Passband block.

Initial phase (rad)

The initial phase of the carrier in radians.

Lowpass filter numerator

The numerator of the lowpass filter transfer function. It is represented as a

vector that lists the coefficients in order of descending powers of s.

Lowpass filter denominator



The denominator of the lowpass filter transfer function. It is represented as a

vector that lists the coefficients in order of descending powers of s. For an FIR

filter, set this parameter to 1.

Sample time

The sample time of the output signal.

DSB-SC AM (DSB-SC modulation and de-modulation)

Modulation

The DSBSC AM Modulator Passband block modulates using double-sideband

suppressed-carrier amplitude modulation. The output is a passband

representation of the modulated signal. Both the input and output signals are real

sample-based scalar signals.

If the input is u(t) as a function of time t, then the output is

where fc is the Carrier frequency parameter and θ is the Initial phase parameter.

Symbol





Initial phase (rad)


Demodulation

The DSBSC AM Demodulator Passband block demodulates a signal that was

modulated using double-sideband suppressed-carrier amplitude modulation. The

input is a passband representation of the modulated signal. Both the input and

output signals are real sample-based scalar signals.

In the course of demodulating, this block uses a filter whose transfer function is


parameters.

Symbol




The carrier frequency in the corresponding DSBSC AM Modulator Passband

block.








Initial phase (rad)




Sample time

The sample time of the output signal.

FM (DSB-SC modulation and de-modulation)

Modulation

The FM Modulator Passband block modulates using frequency modulation. The

output is a passband representation of the modulated signal. The output signal's

frequency varies with the input signal's amplitude. Both the input and output

signals are real sample-based scalar signals.

If the input is u(t) as a function of time t, then the output is

where:

fc is the Carrier frequency parameter.

θ is the Initial phase parameter.

Kc is the Modulation constant parameter.

Symbol





Initial phase (rad)


Modulation constant (Hertz per volt)

The modulation constant Kc.

Sample time

The sample time of the output signal. It must be a positive number.

Symbol interval

Typically set to Inf.

De-modulation

The FM Demodulator Passband block demodulates a signal that was modulated

using frequency modulation. The input is a passband representation of the


signals.



In the course of demodulating, the block uses a filter whose transfer function is


parameters.

The block uses a voltage-controlled oscillator (VCO) in the demodulation. The

Initial phase parameter gives the initial phase of the VCO.


The carrier frequency in the corresponding FM Modulator Passband block.

Initial phase (rad)

Symbol



The initial phase of the VCO in radians.

Modulation constant (Hertz per volt)

The modulation constant in the corresponding FM Modulator Passband block.








Sample time

The sample time in the corresponding FM Modulator Passband block.



REFERENCES:

• Communication Systems Engineering - by John G. Proakis and

Masoud Salehi, Pearson education

• Electronic Communication Systems - by kennedy, McGraw Hill

Publ.

• Communication Systems - by B.P.Lathi, BS Pub.

• Electronic Commmunication Syatems By Kennedy, Davis

Mc Graw Hill Publ.

• MATLAB User manual 7.0.4

ac labwithoutreadings

Documents

software matlab

matlab desktop

programs matlab

matlab shortcut icon

frequency modulation

dsbsc modulation

pulse width modulation

dsbsc modulation