EC1020 Communication Engineering Lab · PDF fileSYLLABUS OF EC1020 COMMUNICATION ENGINEERING...

DEPARTMENT OFELECTRONICS AND COMMUNICATION ENGINEERING

EC1020 COMMUNICATION ENGINEERING LABORATORY MANUAL

FACULTY OF ENGINEERING AND TECHNOLOGY

SRM UNIVERISTY

S.R.M. NAGAR, KATTANKULATHUR – 603203.

KANCHEEPURAM DISTRICT

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC1020 Communication Engineering Lab

Laboratory Manual

Course Team

Mr.S.Bashyam

Mrs. G. Kalaimagal

Mr.M.Aravindan

Mrs. M. NeelaveniAmmal

Mrs. S. Sudarvizhi

Mrs.S.Kolangiammal

Mrs. S. VasanthadevSuryakala

Mrs.G.Suganthibrindha

Mrs. P. Malarvezhi

Mrs. S. Krithiga

Mr. G. ElavelVisuvanathan

June 2015

Revision: 00

SYLLABUS OF EC1020 COMMUNICATION ENGINEERING LAB

Course Number and Title EC1020 COMMUNICATION ENGINEERING LAB

Credits / Contact Hours 2/45

Instructor NameMrs. S. Kolangiammal

Textbooks, References • John O. Attia, “PSPICE and MATLAB for Electronics: An integrated approach”, CRC press,

2002. • LAB MANUAL, Department of ECE, SRM University.

Purpose

The experiments in this laboratory enable the students to gather basic knowledge on communication systems. Different experiments are performed which forms the fundamental blocks of any communication system used now‐a‐days. Experiments are performed using electronic instrument, such as oscilloscopes, signal generators, spectrum analyzers, and network analyzers. Certain experiments are simulated using MATLAB and P‐SPICE simulation software.

Prerequisites Co‐requisites Nil EC1018

Required, Elective orSelected Elective (as per Table 5.1a)

Required

Instructional Objectives

1. To practice the basic theories of analog communication system.

2. To provide hands‐on experience to the students, so that they are able to apply theoretical concepts in practice.

3. To use computer simulation tools such as P‐SPICE, or MATLAB to carry out design experiments as it is a key analysis tool of engineering design.

4. To give a specific design problem to the students, which after completion they will verify using the simulation software or hardware implementation.

Student Outcomes from Criterion 3 covered by this Course

Student Outcome a b C d e f g h i j k

X X X X X X X X

Mapping of instructional objectives with student outcome

1‐4 1‐4 1‐4

1‐4 3,4 3,4 4 3,4

List of Topics Covered

1. AM modulator and Demodulator.

2. DSB‐SC modulator and Demodulator.

3. SSB Modulation and Demodulation in MATLAB.

4. FM modulator and Demodulator.

5. PAM modulator and Demodulator.

6. TDM Multiplexer and Demultiplexer.

7. FDM Multiplexer and Demultiplexer.

8. Pre emphasis and De‐emphasis in FM.

9. Simulation experiments using P‐SPICE and MATLAB.

a) AM modulator with AWGN noise in MATLAB.

b) Pre‐emphasis and De‐emphasis in FM using P‐SPICE.

S.R.M University

Faculty of Engineering and Technology

Department of Electronics and Communication Engineering

Sub Code : EC1020 Semester : V Sub Title : Communication Engineering Lab Course Time : Jun‐Dec ‘15 Pre‐ requisite : NIL Co‐ requisite : EC1018 COMMUNICATION THEORY

Program Outcome

b. Graduate will demonstrate the ability to identify, formulate and solve engineering problems Experiment 1: AM modulation and demodulation Experiment 2: Frequency modulation c. Graduate will demonstrate the ability to design and conduct experiments, analyse and interpret data. Experiment 1: Amplitude modulation and demodulatation Experiment 2: Frequency Modulation Experiment 3: PAM modulation and Demodulation Experiment 5: Pre‐emphasis and De‐emphasis in FM d.Graduates will demonstrate the ability to design a system, component or process as per needs and specifications Experiment 6: Amplitude Modulation with AWGN noise in MATLAB Experiment 7: Pre‐emphasis and De‐emphasis using PSPICE e.Graduates will demonstrate the ability to visualize and work on laboratory and multi‐disciplinary tasks. Experiment 1: Amplitude modulation and demodulation Experiment 2: Frequency Modulation Experiment 3: PAM modulation and Demodulation Experiment 5: Pre‐emphasis and De‐emphasis in FM f. Graduate will demonstrate the skills to use modern engineering tools, software’s and equipment to analyse problems. Experiment 6: Amplitude Modulator with AWGN noise in MATLAB Experiment 7: Pre‐emphasis and De‐emphasis using PSPICE Experiment 8:FM Modulation in MATLAB Experiment 9:DSB‐SC modulation in MATLAB Experiment 10:SSB‐SC Modulation and demodulation in MATLAB i.Graduate will show the understanding of impact of engineering solutions on the society and also will be aware of contemporary issues. Experiment 6: Amplitude Modulator with AWGN noise in MATLAB Experiment 7: Pre‐emphasis and De‐emphasis using PSPICE Experiment 8:FM Modulation in MATLAB

Experiment 9: DSB‐SC modulation in MATLAB Experiment 10: SSB‐SC Modulation and demodulation in MATLAB j. Graduate will develop confidence for self education and ability for life‐long learning. Experiment 6: Amplitude Modulator with AWGN noise in MATLAB Experiment 7: Pre‐emphasis and De‐emphasis using PSPICE Experiment 8: FM Modulation in MATLAB Experiment 9: DSB‐SC modulation in MATLAB Experiment 10: SSB‐SC Modulation and demodulation in MATLAB k. Graduate will show the ability to participate and try to succeed in competitive examinations Experiment 6: Amplitude Modulator with AWGN noise in MATLAB Experiment 7: Pre‐emphasis and De‐emphasis using PSPICE Experiment 8: FM Modulation in MATLAB Experiment 9: DSB‐SC modulation in MATLAB Experiment 10: SSB‐SC Modulation and demodulation in MATLAB

S.R.M University




S. No. Experiments Detail Equipments/Software Required Components Required

1 AM Modulator and demodulator

Regulated power supply,CRO, AFO

Resistors, capacitors Semiconductors: BC108,OA79

2 FM modulator Regulated power supply,CRO, AFO

Resistors: As per design Capacitors: As per design Semiconductors: IC NE 566

3 PAM modulator and Demodulator AFO, CRO

Resistors: As per design Capacitors: As per design Semiconductors: BC107

4 TDM Multiplexer and De‐multiplexer Using Trainer Kit

TDM‐TRAINER KIT,CRO ‐

5 Pre‐emphasis and De‐emphasis in FM

Regulated power supply AFO, CRO, Decade Inductance box.

Resistors: As per design Capacitors: 0.1µF, 0.01µF Semiconductors: Q2N2222

6 AM modulator with AWGN noise in MATLAB. MATLAB. ‐

7 Pre‐emphasis and De‐emphasis in FM using P‐SPICE.

P‐SPICE ‐

8 FM modulation in MATLAB MATLAB ‐

9 DSB‐SC modulation in MATLAB MATLAB ‐

10 SSB –SC modulation and Demodulation in MATLAB

MATLAB ‐

S.R.M University




Program Educational Objective

PEO1: Graduates will perform as a successful Professional engineer in related fields of Electronics and Communication Engineering.

PEO2: Graduates will pursue higher education and/or engage themselves in continuous professional development to meet global standards.

PEO3: Graduates will work as a team in diverse fields and gradually move into leadership positions.

PEO4: Graduates will understand current professional issues, apply latest technologies and come out with innovative solutions for the betterment of the nation and society.

Student Outcomes

b √ √

c √ √

d √ √ √

e √ √ √ √

f √ √ √

i √ √ √

j √ √ √ √

k √ √ √ √

Academic Course Description

SRM UniversityFaculty of Engineering and Technology


EC1020 Communication Engineering Laboratory Fifth Semester, 2015‐16 (OddSemester)

Course (catalog) description

This course provides the foundation education in communication engineering lab.

The experiments in this laboratory enable the students to gather basic knowledge

on communication systems. Different experiments are performed which forms the

fundamental blocks of any communication system used now a day. Experiments

are performed using electronic instrument, such as oscilloscopes, signal

generators, spectrum analyzers, and network analyzers. Certain experiments are

simulated using MATLAB and P‐SPICE simulation software.

Compulsory/Elective course: Compulsory

Credit hours: 2 credits

Laboratory

Communication EngineeringLaboratory (TP10L4) , Computing Laboratory (TP10L1), RF Laboratory (TP13L4)

Course coordinator(s)

S.Kolangiammal, Assistant Professor (Ordinary Grade), Department of ECE

INSTRUCTOR(S)

Name of the instructor

Class handling

Office location

Office phone

Email (@ktr.srmuniv.ac.i

n) Consultations

Mr. S. Bashyam X1 TP103A 2075 bashyam.s Day 4‐12.45PM to 1.20PM

Mrs Kalaimagal X2 TP1103A 2062 Kalaimagal.g Day 3‐12.45PM

to 1.20PM

Mr.M.Aravindan X3 TP1103A 2063 Aravindan.m Day 1‐12.45PM

to 1.20PM Mrs. M. NeelaveniAmmal X4 TP12S4 2087 Neelaveniammal.m Day 5‐12.45PM

to 1.20PM .

Ms. S. Sudarvizhi X5 TP1003A 2059 sudarvizhi.s Day 5‐12.45PM

to 1.20PM . Mrs.S.Kolangiammal Y1 TP1003

A 2059 kolangiammal.s Day 5‐12.45PM to 1.20PM

Mrs.S.VasanthadevSuryakala Y2 TP1003

A 2059 vasanthadevsuryakala.s

Day 5‐12.45PM to 1.20PM .

Mrs.G.Suganthi brindha Y3 TP10S8 ‐ Suganthibrindha.g Day 1‐12.45PM

to 1.20PM .

Mrs. P. Malarvizhi Y4 TP1203A 2064 malarvizhi.p Day 1‐12.45PM

to 1.20PM .

Mrs. S. Krithiga Y5 TP1203A 2064 Krithiga.s Day 1‐12.45PM

to 1.20PM . Mr. G. Elavel Visuvanathan Y6 TP10S4 ‐ ElavelVisuvanathan

.g Day 5‐12.45PM to 1.20PM .

RELATIONSHIP TO OTHER COURSES

Pre‐requisites : NIL

Assumed knowledge : BJT – Basic device operation and characteristics Signal generators – sinusoidal and non‐sinusoidal generators

Following courses : EC1025 Digital communication lab

Text book(s) and/or required materials:

Lab manual; additional materials posted on SRM web.

References

1. Communication Engineering Lab MANUAL, Department of ECE, SRM University

2. John O Atta “PSPICE AND MATLAB for electronics: AN Integrated approach”, CRC press 2002

Computer usage

To carry out AM and Pre emphasis and deemphasis experiments using

discrete electronic components, Software’s like MATLAB and PSPICE are used to

simulate the circuit operations

Hardware Laboratory Usage

Each laboratory station is equipped with breadboards, a power supply, CRO

and Function generators. Students work in groups of three, but maintain individual

laboratory notebooks and submit individual records.

Class / Lab schedule : one 100 minutes lab session per week, for 10‐14 weeks

Group Schedule X1 DAY 1 – 7, 8 & DAY 2 ‐ 3,4 X2 DAY 3 – 7, 8 & DAY 4 ‐ 7,8 X3 DAY 3 – 7, 8 & DAY 5 ‐ 3,4 X4 DAY 2 – 3, 4 & DAY 3 ‐ 7,8 X5 DAY 2 – 3, 4 & DAY 5 ‐ 7,8 Y1 DAY 2 – 7, 8 & DAY 5 ‐ 3,4 Y2 DAY 2 – 7, 8 & DAY 3 ‐ 3,4 Y3 DAY 3 – 3, 4 & DAY 4 ‐ 7,8 Y4 DAY 3 – 3, 4 & DAY 5 ‐ 7,8 Y5 DAY 4 – 7, 8 & DAY 5 ‐ 3,4 Y6 DAY 1 – 7, 8 & DAY 4 ‐ 1,2

Professional component General ‐ 0% Basic Sciences ‐ 0% Engineering sciences & Technical arts ‐ 0% Professional subject ‐ 100%

Broad area: Communication | Signal Processing | Electronics | VLSI | Embedded

Mapping of Instructional Objectives with Program Outcome This course provides the foundation education in communication systems. Through lecture, laboratory, and out‐of‐class assignments, students are provided learning experiences that enable them to:

Correlates to Student Outcome

H M L

1.To practice the basic theories of analog communication system.

b,c,d,e I,j,k

2. To provide hands‐on experience to the students, so that they are able to apply theoretical concepts in practice.

b,c,d,e,f,I,k j

3.To use computer simulation tools such as P‐SPICE, or Matlab to carry out design experiments as it is a key analysis tool of engineering design.

b,c.d,e.f.i,j,,k

4.To give a specific design problem to the students, which after completion they will verify using the simulation software or hardware implementation

b,c,d,i e,f,j,k

H: High correlation, M: Medium correlation, L: Low correlation

COURSE TOPICS

S.No. Lab Experiments Sessions

Using discrete components and/or BC107/BC108/Q2N2222/IC566

1 AM modulation and Demodulation. 1

2 FM modulation 2

3 PAM modulation and Demodulation. 3

4 TDM Multiplexer and Demultiplexer Using Trainer Kit 4

5 Pre emphasis and De‐emphasis in FM. 5

Simulation experiments using MATLAB& P‐SPICE.

6 AM modulator with AWGN noise in MATLAB. 6

7 Pre‐emphasis and De‐emphasis in FM using P‐SPICE. 7

8 FM Modulation in MATLAB 8

9 DSB‐SC modulation in MATLAB 9

10 SSB modulation and Demodulation in MATLAB 10

Mapping of Instructional Objective with experiments:

List of Experiments IO#1 IO#2 IO#3 IO#4 AM modulation and Demodulation.

X X X

FM modulation X X X PAM modulation and Demodulation.

X X X

TDM Multiplexer andDemultiplexer Using Trainer Kit

X X

Pre emphasis and De‐emphasis in FM.

X X X

AM modulator with AWGN noise in Matlab.

X X X X

Pre‐emphasis and De‐emphasis in FM using P‐SPICE.

X X X X

FM Modulation in MATLAB X X X X

DSB‐SC modulation in MATLAB X X X X

SSB modulatIion and Demodulation in MATLAB

X X X X

EVALUATION METHODS

Internal Assessment Marks: 60 End Semester Examination Marks: 40

Carrying out lab work & Report

: 30

Mini Project : 5 Attendance : 05 Model Exam : 20

Circuit diagram / Program : 10 Design / Calculation : 05 Procedure/Algorithm : 05 Tabulation / Graph : 10 Result : 05 Viva‐Voce : 05

Prepared by:

Mrs.S.Kolangiammal, Assistant Professor (OG), Department of ECE

Dated: 26 june 2015

Revision No.: 00 Date of revision: NA Revised by: NA

LABORATORY POLICIES AND REPORT FORMAT

Reports are due at the beginning of the lab period. The reports are intended to be a complete documentation of the work done in preparation for and during the lab. The report should be complete so that someone else familiar with electronic design could use it to verify your work. The prelab and postlab report format is as follows:

1. A neat thorough prelab must be presented to your faculty Incharge at the beginning of your scheduled lab period. Lab reports should be submitted on A4 paper. Your report is a professional presentation of your work in the lab. Neatness, organization, and completeness will be rewarded. Points will be deducted for any part that is not clear.

2. In this laboratory students will work in teams of three. However, the lab reports will be written individually. Please use the following format for your lab reports.

a. Cover Page: Include your name, Subject Code, Section No., Experiment No. and Date.

b. Objectives: Enumerate 3 or 4 of the topics that you think the lab will teach you. DO NOT REPEAT the wording in the lab manual procedures. There should be one or two sentences per objective. Remember, you should write about what you will learn, not what you will do.

c. Design: This part contains all the steps required to arrive at your final circuit. This should include diagrams, tables, equations, explanations, etc. Be sure to reproduce any tables you completed for the lab. This section should also include a clear written description of your design process. Simply including a circuit schematic is not sufficient.

d. Questions: Specific questions (Prelab and Postlab) asked in the lab should be answered here. Retype the questions presented in the lab and then formally answer them.

3. Your work must be original and prepared independently. However, if you need any guidance or have any questions or problems, please do not hesitate to approach your faculty incharge during office hours. Copying any prelab/postlab will result in a grade of 0. The incident will be formally reported to the University and the students should follow the dress code in the Lab session.

4. Each laboratory exercise (circuit) must be completed and demonstrated to your faculty Incharge in order to receive working circuit credit. This is the procedure to follow:

a. Circuit works: If the circuit works during the lab period (3 hours), call your faculty incharge, and he/she will sign and date it.. This is the end of this lab, and you will get a complete grade for this portion of the lab.

b. Circuit does not work: If the circuit does not work, you must make use of the open times for the lab room to complete your circuit. When your circuit is ready, contact your faculty incharge to set up a time when the two of you can meet to check your circuit.

5. Attendance at your regularly scheduled lab period is required. An

unexpected absence will result in loss of credit for your lab. If for valid reason a student misses a lab, or makes a reasonable request in advance of the class meeting, it is permissible for the student to do the lab in a different section later in the week if approved by the faculty incharge of both the sections. Habitually late students (i.e., students late more than 15 minutes more than once) will receive 10 point reductions in their grades for each occurrence following the first. Student attendance less than 75% is detention.

6. Final grade in this course will be based on laboratory assignments. All labs

have an equal weight in the final grade. Grading will be based on pre‐lab work, laboratory reports, post‐lab and in‐lab performance (i.e., completing lab, answering laboratory related questions, etc.,).The faculty Incharge will ask pertinent questions to individual members of a team at random. Labs will be graded as per the following grading policy:

Attendance ‐ 05%

Lab Performance ‐ 10%

Prelab ‐ 05%

Post Lab ‐ 05%

Report ‐ 10%

Student Contribution ‐ 05%

Model Exam ‐ 20%

Final exam ‐ 40%

7. Reports Due Dates: Reports are due one week after completion of the corresponding lab.

8. Systems of Tests: Regular laboratory class work over the full semester will carry a weightage of 60%. The remaining 40% weightage will be given by conducting an end semester practical examination for every individual student if possible or by conducting a 1 to 1 ½ hours duration common written test for all students, based on all the experiment carried out in the semester.

General Procedures

a) Properlyplace the components in the breadboard as per circuit diagram, and identify the different input and outputs of the circuit before making connection.

b) Know the biasing voltage required for different devices and connect power supply voltage.

c) Note down the readings obtained from the CRO or Measuring devices in the observation book.

d) Plot the graph on a linear graph or semi log graph and verify its characteristics using model graph.

e) After the completion of the experiments switch off the power supply and return the components.

ADDENDUM Student Outcomes ofB.Tech ECE program:

(a) an ability to apply knowledge of mathematics, science, and engineering (b) an ability to design and conduct experiments, as well as to analyze and interpret data (c) an ability to design a system, component, or process to meet desired needs within realistic constraints such as economic, environmental, social, political, ethical, health and safety, manufacturability, and sustainability (d) an ability to function on multidisciplinary teams (e) an ability to identify, formulate, and solve engineering problems (f) an understanding of professional and ethical responsibility (g) an ability to communicate effectively (h) the broad education necessary to understand the impact of engineering solutions in a global, economic, environmental, and societal context (i) a recognition of the need for, and an ability to engage in life‐long learning (j) a knowledge of contemporary issues (k) an ability to use the techniques, skills, and modern engineering tools necessary for engineering practice. Program Educational Objectives

PEO1: Graduates will perform as a successful professional engineer in related fields of Electronics and Communication Engineering.

PEO2: Graduates will pursue higher education and/or engage themselves in continuous professional development to meet global standards.

PEO3: Graduates will work as a team in diverse fields and gradually move into leadership positions.

PEO4: Graduates will understand current professional issues, apply latest technologies and come out with innovative solutions for the betterment of the nation and society.

ATTESTATION FROM COURSE TEACHERS

NAME OF THE INSTRUCTOR SIGNATURE

Mr. S. Bashyam

Mrs Kalaimagal

Mr.M.Aravindan

Mrs. M. NeelaveniAmmal

Ms. S. Sudarvizhi

Mrs.S.Kolangiammal

Mrs.S.VasanthadevSuryakala

Mrs.G.Suganthibrindha

Mrs. P. Malarvizhi

Mrs. S. Krithiga

Mr. G. ElavelVisuvanathan

Course Coordinator Academic Coordinator Professor In‐Charge HOD/ECE (S.Kolangiammal) (Mrs.N. Saraswathy) (Dr.B. Ramachandran) (Dr.S. Malarvizhi)

PREFACE

The EC1020 Communication Engineering Lab is designed to help students understand the

basic principles of communication techniques as well as giving them the insight on design,

simulation and hardware implementation of circuits. The main aim is to provide hands‐on

experience to the students so that they are able to put theoretical concepts to practice.

The content of this course consists of two parts, ‘simulation’ and ‘hardwired’. Computer

simulation is stressed upon as it is a key analysis tool of engineering design. “OrCADPspice”

and MATLAB software is used for simulation of communication experiments

Students will carry out design experiments as a part of the experiments list provided in this

lab manual. Students will be given a specific design problem, which after completion they

will verify using the simulation software or hardwired implementation.

LIST OF EXPERIMENTS

Exp. No Title

1 AM modulation and Demodulation.

2 FM modulation

3 PAM modulation and Demodulation

4 TDM Multiplexer and Demultiplexer using trainer kit

5 Pre emphasis and De‐emphasis in FM.

6 AM modulator with AWGN noise in MATLAB.

7 Pre‐emphasis and De‐emphasis in FM using P‐SPICE.

8 FM Modulation in MATLAB

9 DSB‐SC Modulation in MATLAB

10 SSB‐SC modulation and Demodulation in MATLAB

LABORATORY ORIENTATION

I. OVERALL PURPOSE

The laboratory portion of this course is designed to give the student practical

experience in working with operational amplifiers. The laboratory integrate the

theory taught in the lectures with practical design, and should help the student to

apply his or her knowledge of analog electronics.

II. GENERAL COMMENTS

Every week before lab, each student should read over the laboratory design or

experiment and work out the various calculations, etc. that are outlined. The student

should refer to the text as prescribed in the course description for the fundamental

theory.

Your grade will reflect how well you have prepared for the lab.

III LABORATORY AND EQUIPMENT MAINTENANCE is the responsibility of not only

the laboratory staff, but also the students. A concerted effort to keep the equipment

in excellent condition and the working environment well‐organized will result in a

productive and safe laboratory. There are useful guides one should follow to avoid

the pitfalls in electronic instrumentation and measurement. Above all, keep in mind

that safety is first!

IV. LABORATORY NOTEBOOK

Each student should maintain a laboratory notebook according to the following

guidelines:

1. Obtain a printed material whose pages are consecutively numbered.

2. Write name, register number, course number and name, section number,

lab location, semester, and staff’s name on the cover.

3. Record data by pen, not pencil. Do not use eraser.

4. Sign and date each page that has data.

5. Log all events, whether positive or negative, in the lab. This includes not

only data, but also problems encountered, equipment use, equipment

settings, measurement technique, or any departure from the procedure

suggested by the lab manual.

6. Record instruments, their settings, and methods used to acquire data.

7. Label the axes of a graph with variable names, units, origin, and scales.

8. Demonstrate to the lab staff your understanding and achievement of the

lab objectives.

9. Have the lab staff sign and date all data groups before completing each

laboratory session. It is the responsibility of both the staff and the student

to make sure that the data is within expectation before the student leaves

each lab session.

V. PRE‐LAB WORK

There are pre‐lab works for each experiment. The prework must be completed in the

logbook before entering the laboratory. The prework usually consists of some

questions that is closely related to the experimental work and is intended to prepare

you for the lab. The labs are designed so that a student who has done the prework

should be able to complete the lab in the allotted time. If you find that you are

having difficulties completing labs then it is probably a good idea for you to do all of

the theoretical work (in addition to the assigned prework) for the experiment before

entering the lab.

To ensure that you can complete the experimental tasks within the allocated lab

session, you could collect all the parts and components from the Lab stores and build

the circuits on breadboards before starting the actual lab. Therefore you have more

time on testing in the lab session.

VI. LABORATORY REPORTS

Lab reports will be submitted by each student at the beginning of the following lab

period. The report will be graded on clarity, legibility, and content, neither on length

nor on the quality of the artwork. Although the data is measured jointly, the text and

analysis of the report must be original work and may not be copied.

REPORT FORMAT:

TITLE PAGE:

EXPERIMENT #

EXPERIMENT NAME

DATE

REPORT CONTENT:

I. OBJECTIVES (5 sentences max.)

II. EQUIPMENT (1 paragraph max.)

‐ include pertinent theory for experiment

III. DESIGN

IV. EXPERIMENT

‐ include schematic of all circuits built

‐ include names and values of all components actually used

‐ include all data recorded (tables, plots, printouts, observations)

V. POSTLAB QUESTIONS

‐ answer all the questions in the postlab component available at the end of each experiment in the laboratory manual.

‐ thepostlab questions are closely related to the experimental work you had done in the lab.

VI. SUMMARY

VII. EQUIPMENT AND LABORATORY MAINTENANCE

Be responsible for equipment and laboratory maintenance. For example:

1. Keep the lab and benches neat and organized.

2. Use the equipment properly. For example, use only the probes that have

been compensated for your oscilloscope with your oscilloscope. An

oscilloscope and its matched probes are labeled by the same number to help

you keep using them together. Do not take the sleeve off the sensitive probe

tip and use the probe tip directly (e.g., by inserting the probe tip directly into

a hole on a breadboard). Many probes have been permanently damaged

when used this way because a) the fragile tip is broken by the severe probing

strain, b) the probe accidentally falls to the ground, breaking the fragile tip,

or c) the probe sleeve is lost after it is removed from the probe tip. A short

hook‐up wire hooked to the probe will allow fine probing without using the

probe tip directly.

3. Return instruments, manuals, tools, components, cables, etc., to the proper

storage location.

4. Bring defective equipment to the lab staff or laboratory maintenance staff for

repair.

5. Notify the lab staff when the stock is about to run out of a certain

component.

VIII. USEFUL LABORATORY PRACTICES

In general, keep the following points in mind:

1. Identify lab objectives. An experiment should not be treated as a cookbook

procedure. Find a rationale behind each step.

2. Come to the lab prepared. Preview the experiment as homework.

3. Keep a lab notebook to record all activities during all lab sessions.

4. Finish as much as possible before leaving. This includes acquiring data,

interpreting data, answering questions, and revolving uncertainties.

5. All data are real. If data look unbelievable, check all the steps carefully.

Consult the lab staff.

6. Safety is first. Change instrument settings slowly. Observe the effect of the

most recent change before proceeding with more change. Set

voltage/current/power limit. It is important that right from the beginning of

your lab work you consider the possible interactions between measuring

instruments and the device under test. For example:

7. The input impedance of meters can cause measurement error in high

impedance circuits.

8. The input capacitance of scopes, scope probes, or connecting cables may

have important high frequency loading effects.

9. When using an oscilloscope to make accurate waveform or frequency

response measurements with a x10 probe, make sure the probe is properly

compensated.

10. Learn to use the current limiting features of the laboratory power supplies to

protest the device under test from possible damage under short circuit

conditions.

11. Make sure to have low impedance ground connections between the test

instruments and your “breadboard”. Avoid groundloops!

The list could go on much longer. It represents the pitfalls of doing electronics in the

real world.

IX. SAFETY PRECAUTIONS AND LABORATORY RULES

To be responsible for your own safety and keep the laboratory in a good order, you

must comply with the rules below.

Solid footwear must be worn by all students inside the laboratory. Staffs are

required by the university to ensure that everyone in the laboratory is

wearing solid footwear. Students with bare feet, thongs, sandals, or other

forms of open footwear will not be allowed into the laboratory.

No smoking, drinking, or eating is permitted in the laboratory (this includes

chewing gum and confectionaries).

Always have your circuits checked by a demonstrator before switching on,

and always switch the power off immediately after taking measurements.

Act sensibly and tidy up after yourself.

/There is a safety switch on each bench which switches power to (and

protects) the GPO's (general purpose outlets/power points).

Under no circumstances should you attempt to remove any of the panels on

the bench. There is a 220 volt supply behind them which could be lethal.

You should not take equipment from another bench. If something is faulty (or

missing) ask the lab staff for assistance.

SAFETY

Safety in the electrical laboratory, as everywhere else, is a matter of the knowledge

of potential hazards, following safety precautions, and common sense. Observing

safety precautionsare important due to pronounced hazards in any

electrical/computer engineering laboratory. Death is usually certain when 0.1

ampere or more flows through the head or upper thorax and have been fatal to

persons with coronary conditions. The current depends on body resistance, the

resistance between body and ground, and the voltage source. If the skin is wet, the

heart is weak, the body contact with ground is large and direct, then 40 volts could

be fatal. Therefore, never take a chance on "low" voltage. When working in a

laboratory, injuries such as burns, broken bones, sprains, or damage to eyes are

possible and precautions must be taken to avoid these as well as the much less

common fatal electrical shock. Make sure that you have handy emergency phone

numbers to call for assistance if necessary. If any safety questions arise, consult the

lab demonstrator or technical assistant/technician for guidance and instructions.

Observing proper safety precautions is important when working in the laboratory to

prevent harm to yourself or others. The most common hazard is the electric shock

which can be fatal if one is not careful.

ELECTRIC SHOCK

Shock is caused by passing an electric current through the human body. The severity

depends mainly on the amount of current and is less function of the applied voltage.

The threshold of electric shock is about 1 mA which usually gives an unpleasant

tingling. For currents above 10 mA, severe muscle pain occurs and the victim can't

let go of the conductor due to muscle spasm. Current between 100 mA and 200 mA

(50 Hz AC) causes ventricular fibrillation of the heart and is most likely to be lethal.

What is the voltage required for a fatal current to flow? This depends on the skin

resistance. Wet skin can have a resistance as low as 150 Ohm and dry skin may have

a resistance of 15 kOhm. Arms and legs have a resistance of about 100 Ohm and the

trunk 200 Ohm. This implies that 240 V can cause about 500 mA to flow in the body

if the skin is wet and thus be fatal. In addition skin resistance falls quickly at the point

of contact, so it is important to break the contact as quickly as possible to prevent

the current from rising to lethal levels.

EQUIPMENT GROUNDING

Grounding is very important. Improper grounding can be the source of errors, noise

and a lot of trouble. Here we will focus on equipment grounding as a protection

against electrical shocks. Electric instruments and appliances have equipments

casings that are electrically insulated from the wires that carry the power. The

isolation is provided by the insulation of the wires. However, if the wire insulation

gets damaged and makes contact to the casing, the casing will be at the high voltage

supplied by the wires. If the user touches the instrument he or she will feel the high

voltage. If, while standing on a wet floor, a user simultaneously comes in contact

with the instrument case and a pipe or faucet connected to ground, a sizable current

can flow through him or her. However, if the case is connected to the ground by use

of a third (ground) wire; the current will flow from the hot wire directly to the

ground and bypass the user.

Equipment with a three wire cord is thus much safer to use. The ground wire (3rd

wire) which is connected to metal case is also connected to the earth ground (usually

a pipe or bar in the ground) through the wall plug outlet.

Always observe the following safety precautions when working in the laboratory:

1. Do not work alone while working with high voltages or on energized electrical

equipment or electrically operated machinery like a drill.

2. Power must be switched off whenever an experiment or project is being

assembled, disassembled, or modified. Discharge any high voltage points to

grounds with a well‐insulated jumper.

3. Remember that capacitors can store dangerous quantities of energy.

4. Make measurements on live circuits or discharge capacitors with well insulated

probes keeping one hand behind your back or in your pocket. Do not allow any

part of your body to contact any part of the circuit or equipment connected to

the circuit.

5. After switching power off, discharge any capacitors that were in the circuit. Do

not trust supposedly discharged capacitors. Certain types of capacitors can build

up a residual charge after being discharged. Use a shorting bar across the

capacitor, and keep it connected until ready for use. If you use electrolytic

capacitors, do not:

put excessive voltage across them

put ac across them

connect them in reverse polarity

6. Take extreme care when using tools that can cause short circuits if accidental

contact is made to other circuit elements. Only tools with insulated handles

should be used.

7. If a person comes in contact with a high voltage, immediately shut off power. Do

not attempt to remove a person in contact with a high voltage unless you are

insulated from them. If the victim is not breathing, apply CPR immediately

continuing until he/she is revived, and have someone dial emergency numbers

for assistance.

8. Check wire current carrying capacity if you will be using high currents. Also make

sure your leads are rated to withstand the voltages you are using. This includes

instrument leads.

9. Avoid simultaneous touching of any metal chassis used as an enclosure for your

circuits and any pipes in the laboratory that may make contact with the earth,

such as a water pipe. Use a floating voltmeter to measure the voltage from

ground to the chassis to see if a hazardous potential difference exists.

10. Make sure that the lab instruments are at ground potential by using the ground

terminal supplied on the instrument. Never handle wet, damp, or ungrounded

electrical equipment.

11. Never touch electrical equipment while standing on a damp or metal floor.

12. Wearing a ring or watch can be hazardous in an electrical lab since such items

make good electrodes for the human body.

13. When using rotating machinery, place neckties or necklaces inside your shirt or,

better yet, remove them.

14. Never open field circuits of D‐C motors because the resulting dangerously high

speeds may cause a "mechanical explosion".

15. Keep your eyes away from arcing points. High intensity arcs may seriously impair

your vision or a shower of molten copper may cause permanent eye injury.

16. Never operate the black circuit breakers on the main and branch circuit panels.

17. In an emergency all power in the laboratory can be switched off by depressing

the large red button on the main breaker panel. Locate it. It is to be used for

emergencies only.

18. Chairs and stools should be kept under benches when not in use. Sit upright on

chairs or stools keeping the feet on the floor. Be alert for wet floors near the

stools.

19. Horseplay, running, or practical jokes must not occur in the laboratory.

20. Never use water on an electrical fire. If possible switch power off, then use CO2

or a dry type fire extinguisher. Locate extinguishers and read operating

instructions before an emergency occurs.

21. Never plunge for a falling part of a live circuit such as leads or measuring

equipment.

22. Never touch even one wire of a circuit; it may be hot.

23. Avoid heat dissipating surfaces of high wattage resistors and loads because they

can cause severe burns.

24. Keep clear of rotating machinery.

Precautionary steps before starting an experiment so as not to waste time

allocated

a) Read materials related to experiment beforehand as preparation for pre‐lab quiz

and experimental calculation.

b) Make sure that apparatus to be used are in good condition. Seek help from

technicians or the lab demonstrator in charge should any problem arises.

Power supply is working properly ieImax (maximum current) LED

indicator is disable. Maximum current will retard the dial movement and

eventually damage the equipment. Two factors that will light up the LED

indicator are short circuit and insufficient supply of current by the

equipment itself. To monitor and maintain a constant power supply, the

equipment must be connected to circuit during voltage measurement.

DMM are not to be used simultaneously with oscilloscope to avert wrong

results.

Digital millimetre (DMM) with low battery indicated is not to be used. By

proper connection, check fuses functionality (especially important for

current measurement). Comprehend the use of DMM for various

functions. Verify measurements obtained with theoretical values

calculated as it is quite often where 2 decimal point reading and 3

decimal point reading are very much deviated.

The functionality of voltage waveform generators are to be understood.

Make sure that frequency desired is displayed by selecting appropriate

multiplier knob. Improper settings (ie selected knob is not set at

minimum (in direction of CAL – calibrate) at the bottom of knob) might

result in misleading values and hence incorrect results. Avoid connecting

oscilloscope together with DMM as this will lead to erroneous result.

Make sure both analog and digital oscilloscopes are properly calibrated by

positioning sweep variables for VOLT / DIV in direction of CAL. Calibration

can also be achieved by standalone operation where coaxial cable

connects CH1 to bottom left hand terminal of oscilloscope. This

procedure also verifies coaxial cable continuity.

c) Internal circuitry configuration of breadboard or Vero board should be at

students’ fingertips (ie holes are connected horizontally not vertically for the

main part with engravings disconnecting in‐line holes).

d) Students should be rest assured that measured values (theoretical values) of

discrete components retrieved ie resistor, capacitor and inductor are in

accordance the required ones.

e) Continuity check of connecter or wire using DMM should be performed prior to

proceeding an experiment. Minimize wires usage to avert mistakes.

CONTENTS

EXP 1 : AMPLITUDE MODULATION AND DEMODULATION 1

1.1 OBJECTIVE:

1.2 HARDWARE REQUIRED:

1.3 THEORY:

1.3.1 AMPLITUDE MODULATI0ON

1.3.2 AMPLITUDE DEMODULATION

1.4 AM MODULATION CIRCUIT DIAGRAM

1.5 MODEL GRAPH

1.6 AM DEMODULATION CIRCUIT DIAGRAM

1.7 PRE LAB QUESTIONS:

1.8 LAB PROCEDURE:

1.9 LAB RESULT:

1.10 POST LAB QUESTIONS:

EXP 2 : FREQUENCY MODULATION 9

2.1 OBJECTIVE

2.2 HARDWARE REQUIRED

2.3 THEORY

2.3.1 FREQUENCY MODULATION USING IC 566

2.4 DESIGN:

2.5 FM MODULATOR CIRCUIT DIAGRAM

2.6 IC 566 PIN DIAGRAM

2.7 PRELAB QUESTIONS

2.8 LAB PROCEDURE

2.9 LAB RESULT

2.10 POST LAB QUESTIONS

EXP 3 :PULSE AMPLITUDE MODULATION AND DEMODULATION 16

3.1 OBJECTIVE:


3.3 THEORY:

3.4 DESIGN:

3.5 PAM MODULATOR AND DEMODULATOR CIRCUIT:

3.6 MODEL GRAPH:


3.8 LAB PROCEDURE:

3.9 LAB RESULT:


EXP4. TIME‐DIVISION MULTIPLEX1NG AND DEMULTIPLEXING 23

4.1. OBJECTIVE

4.2. HARDWARE REQUIRED

4.3. THEORY

4.4 BLOCK DIAGRAM

4.5 MODEL GRAPH:


4.7 LAB PROCEDURE:

4.8. LAB RESULT

4.9. POST LAB QUESTIONS

EXP 5: PRE –EMPHASIS AND DE‐EMPHASIS IN FM 30

5.1 OBJECTIVE:


5.3 THEORY:

5.3.1 PRE‐EMPHASIS:

5.3.2 DE‐EMPHASIS:

5.4 DESIGN:

5.5 PRE – EMPHASIS CIRCUIT DIAGRAM:

5.6 DE – EMPHASIS CIRCUIT DIAGRAM:

5.7 MODEL GRAPH:


5.9 LAB PROCEDURE:

5.10 LAB RESULT:


EXP 6: AM MODULATOR WITH AWGN NOISE IN MATLAB 39

6.1 OBJECTIVE

6.2 SOFTWARE REQUIRED:

6.3 MATLAB® INTRODUCTION

6.4 ALGORITHM:

6.5 PROGRAM FOR AMPLITUDE MODULATION


6.7 LAB PROCEDURE:

6.8 MODEL GRAPH

6.9 LAB RESULT:


EXP 7.PRE –EMPHASIS AND DE‐EMPHASIS IN FM USING PSPICE 47

7.1 OBJECTIVE

7.2 SOFTWARE REQUIRED

7.3 ABOUT PSPICE:

7.4 PRE‐EMPHASIS CIRCUIT DIAGRAM

7.5 DE‐EMPHASIS CIRCUIT DIAGRAM

7.6 PRE‐EMPHASIS PROGRAM:

7.7 DE‐EMPHASIS PROGRAM:

7.8 MODEL GRAPH

7.9 PRELAB QUESTIONS:

7.10 LAB PROCEDURE:

7.11 LAB RESULT:


EXP 8.FM MODULATION IN MATLAB 59

8.1 OBJECTIVE



8.4 THEORY

8.4.1 FREQUENCY DIVISION MULTIPLEXING

8.4.2 DE‐MULTIPLEXING:

8.5 ALGORITHM:


8.7 LAB PROCEDURE:

8.8 MODEL GRAPH

8.9 LAB RESULT:

8.10 POSTLAB QUESTIONS:

EXP 9.DSB‐SC MODULATION IN MATLAB 66

9.1 OBJECTIVE



9.4 THEORY:

9.4.1 GENERATION

9.4.2 DEMODULATION

9.5 ALGORITHM:

9.6. PRE LAB QUESTIONS:

9.7 LAB PROCEDURE:

9.8 MODEL GRAPH

9.9 LAB RESULT:


EXP. 10. SSB‐SC MODULATION AND DEMODULATION IN MATLAB 75

10.1 OBJECTIVE



10.4 Theory:

10.5 ALGORITHM:


10.7 LAB PROCEDURE:

10.8 MODEL GRAPH

10.9 LAB RESULT:


DEPARTMENT OF ECE Faculty of Engineering and Technology, SRMUniversity

SRM Nagar, Kattankulathur – 603203, Kancheepuram District, Tamilnadu

EC1020 COMMUNICATION ENGINEERING LAB LABORATORY REPORT COVER PAGE

Name of the Student : _____________________________________________

Register No. : ________________

Class : III Year / V Semester / B.Tech / ECE / ___ Section

Academic Year : 2015‐16

Expt. No. &Title : _____________________________________________

Date of Experiment : ___________

Due Date : ___________

Submission Date : ___________

Instructor(s) :

Particulars Max. Marks

Marks Obtained

Pre‐Lab 5

Experimental Data & Analysis (using hardware setup & simulation)

10

Graphs & Conclusion 5

Post‐Lab 5

Promptness, Neatness and Organization 5

Total Marks 30

Remarks :

Name / Sign / Stamp with date

1

1.AMPLITUDE MODULATION AND DEMODULATION

1.1 OBJECTIVE:

To construct an amplitude modulator circuit using transistor with Vc=50mv , Vm=8v to satisfy

under modulation condition and generate amplitude modulated signal.Calculate the

modulation index and also demodulate using envelope detector and reconstruct the

modulating signal.


S.No Equipment/Component name Specifications/Value Quantity

1 Cathode Ray Oscilloscope (0 – 20MHz) 1

2 Audio Frequency Oscillator (0‐2) MHz 2

3 Regulated power supply (0 ‐30V), 1A 1

4 Resistors 1.5K Ω

10 K Ω

20 K Ω

100 K Ω

2

3

1

2

5 capacitors 0.1 µf

0.01 µf

0.001 µf

22 µf

1

1

3

1

6 Semiconductor Device(Transistor) BC108 1

7 Semiconductor Device( Diode) OA79 1

1.3 THEORY:

Modulation is defined as the process by which some characteristics of a

carrier signal is varied in accordance with a modulating signal. The base band signal

is referred to as the modulating signal and the output of the modulation process is

called as the modulation signal.

2

1.3.1 AMPLITUDE MODULATION

Amplitude modulation is defined as the process in which amplitude of the

carrier wave is varied in accordance with the instantaneous values of the modulating

signal. The envelope of the modulating wave has the same shape as the base band

signal provided the following two requirements are satisfied

1. The carrier frequency fc must be much greater then the highest frequency

components fm of the message signal m (t)

i.e. fc >>fm

2. The modulation index must be less than unity. If the modulation index is

greater than unity, the carrier wave becomes over modulated.

1.3.2 AMPLITUDE DEMODULATION

The process of detection provides a means of recovering the modulating

Signal from modulating signal. Demodulation is the reverse process of modulation.

The envelope detector circuit is employed to separate the carrier wave and eliminate

the side bands. Since the envelope of an AM wave has the same shape as the

message, independent of the carrier frequency and phase, demodulation can be

accomplished by extracting envelope.

An increased time constant RC results in a marginal output follows the

modulation envelope. A further increase in time constant the discharge curve

become horizontal if the rate of modulation envelope during negative half cycle of

the modulation voltage is faster than the rate of voltage RC combination ,the output

fails to follow the modulation resulting distorted output is called as diagonal clipping

: this will occur even high modulation index.

The depth of modulation at the detector output greater than unity and circuit

impedance is less than circuit load (Rl>Zm) results in clipping of negative peaks of

modulating signal. It is called “negative clipping “

SPECIFICATIONS

R1 = R2 = R5 = 10KΩ; R3 = 1.5KΩ; R4 = 20KΩ; C1 = 0.01µF; C2 = 0.001µF;

C3 = 0.1 µf; Vc = 50mV; fc = 500KHZ; Vm = 8V; fm = 1KHZ; VCC = 30V;

3

1.4 AM MODULATION CIRCUIT DIAGRAM

Fig. 1.1 AM Modulator Circuit

4

1.5 MODEL GRAPH

Fig. 1.2 AM Modulated Waveform

SPECIFICATIONS

C1=0.001μf, C2=22 μf, C3=0.001μf, R1=100KΩ and R2=100KΩ.

1.6 AM DEMODULATION CIRCUIT DIAGRAM

Fig. 1.3 AM Demodulator Circuit

5


1. Define Modulation.

2. Why Modulation is necessary for communication system.

3. What is Baseband signal?

4. Differentiate analog and Digital Modulation.

5. Define Amplitude Modulation and Demodulation?

6. Mention the degrees of Modulation.

7. What is Pilot Carrier?

8. Write an expression for the total power of the Amplitude Modulated wave.

9. What is the efficiency of AM signal?

10. What are the applications of AM system?

1.8 LAB PROCEDURE:

I). AMPLITUDE MODULATION

1. The circuit connection is made as shown in the circuit.

2. The power supply is connected to the collector of the transistor.

3. Set the input signal fm as 1KHz and 8volt sinusoidal signal in AFO

4. Set the carrier signal fc as 500KHz and 50 millivolt sinusoidal signal in AFO

5. The AmplitudeModulated Output is taken from the collector of the

Transistor.

6. Calculate Emax and Emin from the Output waveform.

7. Calculate modulation index using the formula.

Emax – Emin

Modulation index (m)% = ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ X 100

Emax + Emin

8. Plot the input signals and obtained AM output waveforms in the graph sheet

6

OBSERVATION:

Modulating signal Carrier signal

Signal

Type

Time

Period Frequency Amplitude

Signal

Type

Time

Period Frequency Amplitude

Sine

wave

Sine

wave

Modulated Output

Signal Type Emin Emax Modulation index

AM

II).AMPLITUDE DEMODULATION

1. The circuit connections are made as shown in the circuit diagram.

2. The amplitude modulated signal from AM generator is given as input to the

demodulator circuit.

3. The demodulated output is observed on the CRO

4. Plot the obtained AM demodulated output waveforms in the graph sheet

OBSERVATION:

Demodulated output

Signal

Type

Time Period Frequency Amplitude

Sine wave

7

1.9 LAB RESULT:

Thus the amplitude modulation and demodulation were performed and the

modulation index for various modulating voltage were calculated.

8


1. What will happen, if modulation index is greater than 100%?

2. What happens to AM signal if ma<1 & ma=1?

3. A 1500Hz signal which has amplitude of 25 V amplitude modulates a 50 MHz

carrier which when unmodulated has amplitude of 75V. What frequencies

would shown up in the spectrum of AM wave?

4. A complex modulating waveform consisting of a sine wave of amplitude 4 V

and frequency 1 kHz plus a cosine wave of amplitude 6 V and frequency 3 kHz

amplitude modulates 500 kHz and 10Vpeak carrier voltage. Plot the spectrum

of modulated wave.

5. A commercial AM station is broadcasting with an average transmitted carrier

power of 10kW; the modulation index is 0.707 for a sinusoidal message signal.

Find the transmission power and efficiency.

9

2. FREQUENCY MODULATION

2.1 OBJECTIVE

To design a VCO circuit using IC NE566 to generate triangular and square waveforms

for a frequency of 93 KHz. With this generated waveform as carrier signal and baseband

signal of 1V with a frequency of 5 KHz as a input signal, obtain the frequency modulated

waveform and also calculate its modulation index .

2.2 HARDWARE REQUIRED





4 Resistors 5.6K Ω

2.7K Ω

3.9K Ω

1

1

1


0.001 µf

1

2

6 VCO IC IC NE566 1

2.3 THEORY

Frequency modulation is a process of changing the frequency of a carrier

wave in accordance with the slowly varying base band signal. The main advantage of

this modulation is that it can provide better discrimination against noise.

2.3.1 FREQUENCY MODULATION USING IC 566

The IC 566 is a general purpose voltage controlled oscillator which may be

used to generate square and triangular waves, the frequency of which is a very linear

function of a control voltage. The frequency is also a function of an external resistor

and capacitor.

10

Applications of IC 566

1. FM modulation

2. Signal generation

3. Function generation

4. Frequency shift keying

5. Tone generation

The Schmitt trigger circuit present in this IC is used to switch the current

source between charge and discharge capacitor and triangular voltage developed

across the capacitor and the square wave from the Schmitt trigger are provide as

the output of the buffer amplifier.

The R2 and R3 combination is a voltage divider, the voltage VC must be in the

range ¾ VCC< VC < VCC. The modulating voltage must be less than ¾ VCC. The frequency

fc can be calculated using the formula

fc =

2.4 DESIGN:

Let R1 = 2.7KΩ and C1 = 0.001µF

For VCC = 12v

Vc(at pin no.5) = = = 10.493 volts

fc =

fc = 93.02 KHz

11

2.5 FM MODULATOR CIRCUIT DIAGRAM

Fig. 2.1 FM Modulator Circuits using VCO

2.6 IC 566 PIN DIAGRAM

Fig.2.2 IC 566 Pin diagram

13


1. What are the different methods of generating FM signal?

2. Compare FM with AM technique.

3. Give the Carson’s rule to calculate bandwidth of the system.

4. What is the commercial FM frequency range?

5. What is the difference between FM and FSK technique?

2.8 LAB PROCEDURE

(1) Frequency Modulation

1. Give the circuit connections as per the circuit diagram.

2. Without input signal, note down the time period Tc of the output signal (at pin

no. 3 or pin no.4)

3. Set the input signal fm as 5 KHz and 1volt sinusoidal signal in AFO

4. Observe the FM output waveforms at pin no. 3 (square wave) and pin no. 4

(triangular wave).

5. Note down the Tmin and Tmax from the output FM waveform. (preferably at pin

no.4 to note down readings easily)

6. Calculate fmax=1/Tmin and fmin= 1/Tmax

7. Calculate frequency deviation ∆f= (fmax‐fmin)/2

8. Calculate the modulation index m=∆f/fm

9. Plot the input signal and obtained FM output waveforms in the graph sheet

OBSERVATION

Without input signal Tc= fc =

With input signal

Amplitude Tmin fmax Tmax fmin frequeny deviation

∆f

modulation index

m

14

2.9 LAB RESULT

Thus the frequency modulation using IC NE566 was performed and the

modulation index was calculated.

15

2.10 POST LAB QUESTIONS

1. How FM wave can be converted to PM wave?

2. Write down the significance of Bessel functions in FM modulation.

3. List the applications of FM technique.

4. What is the difference between ratio detector and foster seeley discriminator

circuit?

5 Define frequency deviation.

6. Design a VCO circuit with IC NE 566 to generate an output signal with

frequency 125 KHz. Assuming C=0.001µF, Control voltage Vc =10.5V and

Vcc=12V

16

3.PULSE AMPLITUDE MODULATION AND DEMODULATION

3.1 OBJECTIVE:

To modulate a carrier square wave signal has a duty cycle 50% with sinusoidal

signal amplitude of 1.5V and a frequency less than 1KHz using transistor as a switch

circuit and reconstruct the message signal by using a low pass filter.





3 Resistors 10K Ω

1K Ω

3.3K Ω

1

1

1

4 capacitors 0.1 µf 2

5 Semiconductor Device(Transistor) BC107 1

3.3 THEORY:

The simple pulse modulation technique called Pulse Amplitude

Modulation (PAM) proved to be more power efficient than the PWM and consumes

constant power for individual pulses like PPM. In PAM the amplitude of the

individual pulses are varied according to the amplitude of the modulating signals.

The PAM modulator and demodulator circuits simple compared to other kind of

modulation and demodulation techniques. There are two kinds of PAM one in which

the pulses have the same polarity and the other in which the pulses can have both

positive and negative polarity according to the amplitude of the modulating signal.

Pulse amplitude modulation is a scheme, which alters the amplitude of

regularly spaced rectangular pulses in accordance with the instantaneous values of a

continuous message signal. Then amplitude of the modulated pulses represents the

amplitude of the intelligence.

17

A train of very short pulses of constant amplitude and fast repetition rate is

chosen the amplitude of these pulse is made to vary in accordance with that of a

slower modulating signal the result is that of multiplying the train by the modulating

signal the envelope of the pulse height corresponds to the modulating wave.

The demodulated PAM waves, the signal is passed through a low pass filter

having a cut –off frequencies equal to the highest frequency in the modulating

signal. At the output of the filter is available the modulating signal along with the DC

component.

PAM has the same signal to noise ratio as AM and so it is not employed in

practical circuits. To implement PAM is to use transistor in switching mode

technique. The flow of current from collector to emitter in a bipolar junction

transistor is controlled by the voltage at its base.

Pulse amplitude modulation is kind of digital modulation technique in which

analog message signal is sampled at constant frequency –carrier frequency .A pulse

of specified duration is used to sample the message signal. When the pulse is on, the

message is sampled and when it is off no message is sampled. This is a basic step in

the digitization of analog message signals. The circuits to be implemented in this

experiment do a kind of natural sampling.

The message is fed as input to a switch and the switch ON/OFF time is

controlled by the pulses at sampling frequency. The flow of current from collector to

emitter in a bipolar junction transistor is controlled by the voltage at its base.

The demodulation of PAM waveform can be implemented by using a low

pass filter which passes message signal frequencies but blocks the carrier signal.

3.4 DESIGN:

(I) Design a pulse amplitude modulator using transistor as switch:

The flow of current from collector to emitter in a bipolar junction transistor is

controlled by the voltage at its base, choose the transistor BC107 and apply the

sinusoidal message signal of frequency fm< 1 KHz and amplitude Em= 1.5Vpp at the

18

collector .Apply a carrier at the transistor base through a resistor 10KΩ.The carrier

pulse amplitude is set as Ec=3Vpp and frequency fc =10KHz.

(II)Design of pulse amplitude demodulator:

Demodulation is done using RC filter .Design the Low pass filter as per the given

equation, R=3.3KΩ is obtained from PAM modulated frequency (fH ) as taken as

cut off frequency for RC filter(LPF) with standard value of capacitance C=0.1µF.

fH=1/2πRC

R=1/2π fHC

3.5 PAM Modulator and Demodulator circuit:

Fig 3.1 PAM Modulator and Demodulator circuit

3.6 MODEL GRAPH:

Fig. 3.2 PAM Modulated Waveform

19

Fig. 3.3 Pulse Amplitude Demodulated Waveform


1. What is PAM?

2. Write the transmission bandwidth of PAM signal?

3. What are the functions of reconstruction filter?

4. What is the purpose of Equalizer in PAM demodulator?

5. Draw Flat‐top and natural sampling of PAM with respect to input signal.

3.8 LAB PROCEDURE:

(I) PULSE AMPLITUDE MODULATION:

1. Connect the circuit as shown in circuit diagram.

2. Set the Carrier square wave of 3Vpp at 10 KHz using an AFO.

3. Set the modulating signal of 1.5Vpp, 500 Hz by using another AFO.

4. Observe the PAM modulated output wave from CRO across 1KΩ load resistor

5. Plot the graph of the modulating signal, Carrier signal and PAM modulated

waveforms.

20

OBSERVATION:

Modulating signal Carrier signal

Signal

Type

Time

Period

Frequency Amplitude Signal

Type

Time

Period

Frequency Amplitude

Sine

wave

Square

wave

Modulated Output

Signal Type Time Period Frequency Amplitude

PAM

(II) PULSE AMPLITUDE DEMODULATION:

1. Connect modulator circuit output to RC filter circuit (LPF).

2. Measure the amplitude and frequency of the demodulated signal from the

CRO and verify with that of the modulating input .

3. Plot the demodulated waveform.

OBSERVATION:

Demodulated output

Signal Type Time Period

Frequency

Amplitude

Sine wave

21

3.9 LAB RESULT:

Thus the pulse amplitude modulation and demodulation was performed and

its corresponding waveforms are plotted.

22


1 Mention the applications of PAM signal.

2 Compare PAM signal with other Pulse modulation.

3 Which device is used to track PAM frequency variations in the clock recovery

circuit?

4 What kind of switches is commonly used in PAM multiplexers?

5 What are the advantage and disadvantages of PAM?

6 Consider an analog signal x(t)= 30cos(2000πt)+5sin(6000πt)+10cos(12000πt).

Find the Nyquist rate and Nyquist interval of this signal.

7 For the analog signal x(t)= 3cos (100πt),the signal is sampled at the

rate of fs=75Hz, what is the discrete time signal obtained after sampling?

23

4. TIME‐DIVISION MULTIPLEX1NG AND DEMULTIPLEXING

4.1. OBJECTIVE

To generate the two different signals with the following specifications:

Amplitude Frequency

Signal 1: 4V 500Hz

Signal 2: 5V 1 KHz

Transmit both the signals simultaneously in different time slots in the same channel.

Recover the individual signal at the receiver end and observe the amplitude and time

period of the individual signal.

4.2. HARDWARE REQUIRED:



2 TDM Trainer kit ST2102 1

4.3. THEORY

An important feature of pulse‐amplitude modulation is conservation of time.

That is, for a given message signal, transmission of the associated PAM wave

engages the communication channel for only a fraction of the sampling interval on a

periodic basis. Hence, some of the time interval between adjacent pulses of the PAM

wave is cleared for use by the other independent message signals on a time‐shared

basis. By this, we obtain a time‐division multiplex system (TDM), which enables the

joint utilization of a common channel by a plurality of independent message signals

without mutual interference.

Each input message signal is first restricted in bandwidth by a low‐pass pre‐

alias filter to remove the frequencies that are nonessential to an adequate signal

representation. The pre‐alias filter outputs are then applied to a commutator, which

is usually, implemented using electronic switching circuitry. The function of the

commutator is two‐fold: (1) to take a narrow sample of each of the N input messages

24

at a rate fs that is slightly higher than 2W, where W is the cut‐off frequency of the

pre‐alias filter, and (2) to sequentially interleave these N samples inside a sampling

interval Ts = 1/fs. Indeed, this latter function is the essence of the time‐division

multiplexing operation. Following the commutation process, the multiplexed signal is

applied to a pulse‐amplitude modulator, the purpose of which is to transform the

multiplexed signal into a form suitable for transmission over the communication

channel.

At the receiving end of the system, the received signal is applied to a pulse‐

amplitude demodulator, which performs the reverse operation of the pulse

amplitude modulator. The short pulses produced at the pulse demodulator output

are distributed to the appropriate low‐pass reconstruction filters by means of a

decommutator, which operates in synchronism with the commutator in the

transmitter. . This synchronization is essential for satisfactory operation of the TDM

system, and provisions have to be made for it.

4.4BLOCK DIAGRAM

Fig 4.1 TDM Trainer Kit –ST2102 Block Diagram

25

4.5 MODEL GRAPH:

TRANSMITTER SECTION

Fig.4.2 TDM Multiplexed Signal

26

RECEIVER SECTION

Fig. 4.3 TDM Demultiplexed Signal


1 In what situation multiplexing is used?

2 Mention the types of multiplexing?

3 Why sync pulse is required in TDM?

4 What are the functions of commutator switch?

5 Give the advantages of multiplexing.

27

4.7 LAB PROCEDURE:

1. Signals from the function generator are given to the channels (CH0 ... CH3)

present in the transmitter using patch chords. Note down the amplitude and

time period of each signal.

2. Measure the amplitude and time period at the transmitter output point.

3. Using a patch chord, connect transmitter output to receiver input.

4. For synchronization purpose, connect the transmitter clock and receiver clock

and also transmitter CH0 and receiver CH0.

5. See the output before the filter and after the filter for all the channels

connected.

OBSERVATION:

Transmitter Section Receiver Section

Signal 1 Demultiplexed Signal 1

Amplitude Time Period Amplitude Time Period

Signal 2 Demultiplexed Signal 2


Transmitter Output Filtered Demultiplexed Signal 1


Filtered Demultiplexed Signal 1

Amplitude Time Period

28

4.8. LAB RESULT

Two signals has been transmitted simultaneously in different time slots over the

same channel and it has been recovered in the receiver end.

29


1. How is synchronization achieved in TDM?

2. What is the limitation of synchronous TDM?

3. How to overcome the limitation in synchronous TDM?

4. Define bandwidth expansion factor.

5. What is the difference between TDM and FDM?

6. Two signals g1(t) and g2(t) are to be transmitted over a common channel by

means of time division multiplexing. The highest frequency of g1(t) is 1 KHz and

that g2(t) is 1.5 KHz. What is the minimum value of the permissible sampling

rate? Justify your answer.

30

5. PRE –EMPHASIS AND DE‐EMPHASIS CIRCUITS USING FM

5.1 OBJECTIVE:

To design a pre emphasis circuit to boost the input signal level for a FM

transmitter for a cut off frequency of 1KHz. Attenuate the boosted high frequency

signals at the receiver side using a deemphasis circuit with a cutoff frequency of

1.6KHz. Analyze the frequency response characteristics of pre emphasis and de

emphasis circuits.






4 Resistors 1K Ω

2K Ω

10K Ω

68K Ω

100K Ω

1

1

2

1

1


0.001 µf

2

3

6 Semiconductor Device(Transistor) Q2N2222 1

7 Decade Inductance Box 0.3H 1

5.3 THEORY:

During the transmission over a channel, the received signal contains interference

(high frequency noise). For demodulated FM signals, the interference power

increases as the frequency goes up. Thus, de‐emphasis is applied to the

31

demodulated signal to decrease the power of the interference in high frequency.

However, in order to keep the high frequency component of the demodulated

message, pre‐emphasis must be applied to the message before going through the

FM modulator.

5.3.1 PRE‐EMPHASIS:

Pre‐emphasis refers to boosting the relative amplitudes of the modulating voltage

for higher audio frequencies. Pre‐emphasis is done at the transmitting side of the

frequency modulator.

Signals with higher modulation frequencies have lower SNR. In order to

compensate this, the high frequency signals are emphasised or boosted in amplitude

at the transmitter section of a communication system prior to the modulation

process. That is, the pre‐ emphasis network allows the high frequency modulating

signal to modulate the carrier at higher level, this causes more frequency deviation.

The circuit consist of a transistor, resistor and an inductor. It is basically a

high pass filter or Differentiator. A pre‐emphasis circuit produces a constant increase

in the amplitude of the modulating signal with an increase in frequency.

The cut off frequency is determined by the RC or L/R time constant of the

network. Normally, the cut off frequency occurs at the frequency where capacitive

reactance or inductive reactance equals R.

The cut off frequency is given by the formula

fc = R/(2π L)

By the use of an active pre‐emphasis network we can reduce the signal loss and

distortion with the increase of SNR. Also the output amplitude of the network

increases with frequencies above cut off frequency.

5.3.2 DE‐EMPHASIS:

De‐emphasis is the complement of pre‐emphasis, in the antinoise system called

emphasis. This circuit is used to attenuate the high frequency signal that is boosted

at the transmitter section.The circuit is placed at the receiving side. It acts as a low

pass filter. The cut off frequency is given by the formula

fc = 1/(2πRC)

32

The circuit consists of a passive network consisting of a resistor and a capacitor. It is

basically a low pass filter or integrator. The pre‐ emphasis network in front of the

FM modulator and a de‐emphasis network at the output of the FM demodulator

improves the Signal to Noise Ratio for higher modulating signal frequencies, thus

producing a more uniform SNR at the output of demodulator.

5.4 DESIGN:

PRE EMPHASIS


fc = R/(2π L)

Let fc =1KHz

Assume R=2KΩ

Therefore L = R/(2π fc)

L = 2000/(2*3.14*1000)

L = 0.3H

DE EMPHASIS


fc = 1/(2π RC)

Let fc =1.6KHz

Assume R=10KΩ

Therefore C1 = 1/(2π fc R)

C1 =1/(2*3.14*1600*10000)

C1 =0.01µF

33

5.5 PRE – EMPHASIS CIRCUIT DIAGRAM:

Fig. 5.1 Pre Emphasis Circuit

5.6 DE – EMPHASIS CIRCUIT DIAGRAM:

Fig. 5.2 De Emphasis Circuit

34

5.7 MODEL GRAPH:

Fig 5.3 Pre emphasis and De emphasis Characteristics Curve


1. What is meant by threshold effect?

2. What is pre‐emphasis?

3. How the threshold effect can be avoided?

4. What is fidelity?

5. What is sensitivity and selectivity?

5.9 LAB PROCEDURE:

1. The circuit connections are made as shown in the circuit diagram for the pre‐

emphasis and de‐emphasis circuits.

35

2. A power supply of 10V is given to the pre‐ emphasis circuit.

3. Set the input voltage at 2V, 1 KHz for pre emphasis and 1V,1KHz for de

emphasis using AFO .

4. For this constant value of input voltage the values of the frequency is varied

and the output voltage is noted on the CRO.

5. A graph is plotted between gain and frequency in a semilog graph sheet for

both pre emphasis and de emphasis outputs.

OBSERVATION FOR PRE‐EMPHASIS:

Vi=

Frequency(Hz) Vo Gain= Vo/Vi Gain in dB=20log(Vo/Vi)

37

OBSERVATION FOR DE‐EMPHASIS:

Vi=

Frequency(Hz) Vo Gain= Vo/ Vi Gain in dB =20log(Vo/Vi)

38

5.10 LAB RESULT:

The characteristics of pre‐ emphasis and de‐ emphasis circuits were studied and a

graph was drawn between gain (in db) and frequency.

39


1. What is de‐emphasis?

2. How to reduce the noise during transmission in FM ?

3. What should be the time constant for the de emphasis circuit?

4. Why pre‐emphasis is done after modulation?

5. List some applications of pre‐emphasis circuit.

6. Design a circuit to boost the baseband signal amplitude in the FM transmitter

for the cut off frequency fc =2KHz as shown in the figure below.

40

6. AM MODULATION WITH AWGN NOISE IN MATLAB

6.1 OBJECTIVE

To write and simulate a MATLAB program for amplitude modulation with

vc>vm , fc>fm and add an additive white Gaussian noise with SNR=10dB and analyze

by varying the SNR value.


MATLAB, Computer installed with Windows XP or higher Version.


MATLAB® is a programming language and numerical computing environment.

The name MATLAB® is an acronym for “Matrix Laboratory”. As it name suggests it

allows easy manipulation of matrix and vectors. Plotting functions and data is made

easy with MATLAB®. It has a good Graphic User Interface and conversion of matlab

files to C/C++ is possible. It has several toolboxes that possess specific functions for

specific applications. For example Image Processing, Neural Networks, CDMA

toolboxes are name a few. An additional package, Simulink, adds graphical

multidomain simulation and Model‐Based Design for dynamic and embedded

systems. Simulink contains Blocksets that is analogous to Toolboxes. It was created

by Mathworks Incorporation, USA. Writing MATLAB programs for modulation

applications require knowledge on very few functions and operators. The operators

mostly used are arithmetic operators and matrix operators. To know more type in

the command prompt ‘help ops’. MATLAB will give a list in that to know on specific

operator say addition type in the command prompt ‘help plus’. MATLAB will give

how to use and other relevant information.

Commonly used graphical functions are plot, figure, subplot, title, and

mathematical functions are sin and cos only. The mathematical functions sin and cos

are self‐explanatory. The graphical function figure will create a new window and

then subsequent graphical commands can be applied. The plot function usually takes

two vectors and plot data points according to given vector data. Subplot function is

used when two or more plots are drawn on the same figure. As title function

41

suggests it helps to write title of the graph in the figure. For further details type ‘help

plot’ or ‘help subplot’ in the command prompt and learn the syntax.

6.4 ALGORITHM:

1. Create a vector ‘t’ (time) that varies from zero to two or three cycles.

2. Create a message signal with single sine frequency or combination of few sine

frequencies. All the frequency used in message signal should be less than the

carrier frequency likewise amplitude of message signals should be less than

carrier amplitude.[AmSin(2πfmt)]

3. Create a carrier signal. [AcSin(2πfct)]

4. Create the modulated signal using the AM equation

Am [(1+maSin(2πfmt)]Sin(2πfct)

5. Introduce AWGN noise and observe the changes in the amplitude modulated

signal.

6. Plot the message signal, carrier signal, and amplitude modulated signal with

AWGN noise.

6.5 PROGRAM FOR AMPLITUDE MODULATION

clc;

clear all;

t=0:0.001:1;

vm=5;

vc=10;

fm=2;

fc=25;

m=vm*sin(2*pi*fm*t);

c=vc*sin(2*pi*fc*t);

42

amp=vc+vm*sin(2*pi*fm*t);

am=amp.*sin(2*pi*fc*t);

y=awgn(am,10,'measured');

subplot(4,1,1);

plot(t,m);

xlabel('time');

ylabel('amplitude');

title('message signal');

subplot(4,1,2);

plot(t,C);

xlabel('time');


title('carrier signal');

subplot(4,1,3);

plot(t,AM);

xlabel('time');


title('amplitude modulated signal');

subplot(4,1,4);

plot(t,y);

xlabel('time');


title('amplitude modulated signal with AWGN');

WITH VARYING SNR

clc;

clear all;

t=0:0.001:1;

43

vm=5;

vc=10;

fm=2;

fc=25;

m=vm*sin(2*pi*fm*t);

c=vc*sin(2*pi*fc*t);

amp=vc+vm*sin(2*pi*fm*t);

am=amp.*sin(2*pi*fc*t);

y1=awgn(am,10,'measured');



subplot(4,1,1);

plot(t,am);

xlabel('time');


title('amplitude modulated signal');

subplot(4,1,2);

plot(t,y1);

xlabel('time');


title('amplitude modulated signal with AWGN [snr10]');

subplot(4,1,3);

plot(t,y2);

xlabel('time');


title('amplitude modulated signal with AWGN[snr100]');

subplot(4,1,4);

44

plot(t,y3);

xlabel('time');


title('amplitude modulated signal with AWGN[snr1000]');


1. What is Matlab?

2. What is Matlab working environment?

3. Can we run Matlab without graphics?

4. What is Simulink?

5. What is AWGN noise?

6.7 LAB 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. To execute 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.

45

6.8 MODEL GRAPH

Fig 6.1 High Freq Signal

Fig 6.2 Message Signal

Fig

6.3 Ampitude Modulated Signal with AWGN Channel

46

6.9 LAB RESULT:

Thus the amplitude modulation was simulated with AWGN noise.

47


1. What is the difference between stem and plot functions?

2. What is the use of clean and close statements?

3. Find the answer for the following program code

a=[1 2 3] ; b=[4 5 6]; c=[a;b] ; d=[ a b];

4. Explain Matlab application program interface.

5. Explain briefly Matlab mathematical function library.

48

7. PRE –EMPHASIS AND DE‐EMPHASIS IN FM USING PSPICE

7.1 OBJECTIVE

To simulate the Pre emphasis and De emphasis circuit using PSPICE Program

and verify the output response characteristics.


PSPICE – OrCAD 9.2 lite, Computer installed with Windows XP or higher

Version.

7.3 ABOUT PSPICE:

SPICE is software that stimulates electronic circuits. SPICE can perform

various analyses such as DC analysis, Transient analysis, AC analysis and operating

point measurements. SPICE contains model for common circuit elements active as

well as passive and it is possible of stimulating most electronic circuits. The

abbreviation of SPICE is Stimulation Program with Integrated Circuit Emphasis.

A circuit is described to a computer by using a file called circuit file. The

circuit file contains the circuit details of component and elements, ht information

about the sources and the commands for what to calculate and what to provide as

output. The circuit file is the input file to the SPICE program, which after executing

the commands, produces the result in another file called output file.

The description of analysis of a circuit require specifying the following:

Element values Types of analysis

Nodes Output variables

Circuit elements PSPICE output commands

Element modes Format of output files

Sources Format of circuit files

ELEMENT VALUES:

The elements values are written in standard floating point notation with

optimal scale and unit suffixs

49

Ex: V=Volt, A=Ampere, Hz= Hertz, OHM= ohm

Node voltage:

The voltage of a point with respect to ground references point.

Vname +node ‐node Value

Ex: Vcc 10 30v

The passive component is also indicated as

Rname +node ‐node Values

R1 2 3 10k

Format of circuit files:

The circuit file that can be read by PSPICE may be divided into 5 parts

Title

Circuit description

Analysis description

Output description

.END ( end of statement)

Notes:

1. The first line is the title line and it may contain any type of text.

2. The last line must be the .END command.

3. The order of the remaining lines is not important and does not affect the

results of simulations.

4. If the statement is more than one line, the statements can continue on the

next line. A continuation line is identified by a plus sign(+) in the first column

of the next line

5. The comment line may be included anywhere, precede by an asterisk (*).

Within a statement. A comment is preceded by a semicolon (;).

50

6. The number of blanks between items is not significant. The tabs and commas

are equivalent to blanks. The tabs and commas are equivalent.

7. The statement or comments can be in either lower case or upper case.

8. If you are not sure of any command or statement, the best thing is to run the

circuit file by using that command or statement and see what happened.

PSPICE is user friendly software; it gives an error message in the output file

that identifies a problem.

PRINT statement

.Print dc [output variables]

The print statement used to get the DC outputs. The maximum number of

output variables is 8. .Print statement can be used to print all the desired output

variables. The values of the output variables are printed as a table with each column

corresponding to one output variable.

PLOT statement:

The result from dc analysis van also be obtained in the form of line printer

plots. The plots are drawn by suing characters.

plot dc<output variables>

+[<(lower limit),value><(upper limit), value>]

The plot statement can be used to plot all the desired output variables.

PROBE Statement:

Probe is a graphics post processor/ waveform analyser for PSPICE.

probe

.probe < one or more output variables>

In the first form no output variables is specified, the .probe command writes

all the node voltages and all the element currents in to the probe.dat file. In the

second form where the output variables are specified, only the specified output

variables to the probe.dat file.

51

Run the program by typing filename.cir which should place you in probe with an

empty screen and a message saying that “ all voltages and currents are available”.

That is, data for all node voltages and element currents in the circuit have been

passed from pspice to probe

Select Add_Trace. Functional graphs are called “traces” by probe. At this

point type the names of variables to be traced. Push ENTER to get the trace. Notice

that both axes are cutomatically scaled to suit the curve.

The Zoom feature of probe displays is very useful if you are interested in an

small region of the highlighted. The Zoom in on the peak of the power curve, select

Zoom, and select Specify region which is highlighted.

The cursor feature of probe is very useful to find maxima or minima values.

Select Cursor to go to the cursor submenu.

Once the results of the simulations are processed by the .probe command

the result are available for graphical displays.

Tran statement:

Transient analysis can be performed by the .Tran command

.tran[/op] print_step end_time (no_print_time [step_ceiling]) [UIC]

/op = to print detailed information about the transient analysis operating point

Print_step = it specifies the time increment between the results which are printed in

tabular form into the output file.

End_time = it specifies the final time of the transient calculation.

No_print_time = it specifies a value of time, before which results will not be printed

to probe for graphing.

Step_ceiling = it is the maximum time interval used by the pspice in its internal

calculations which is default by end time/50.

UIC = directs pspice to use initial conditions given to inductors and capacitors in their

defininf L or C statement.

52

Ac source:

The general transient analysis for SIN is

Sin(offset amplitude freq delay damping factor phase)

Frequency response:

.ac sweeptype points fstart fstop

Sweeptype = LIN,DEC,OCT

Fstart = starting frequency must specified in Hz. They also must be positive.

Fstop = ending frequency must specified in Hz. They also must be positive.

Points = it specifies the number of calculations for every power of ten in the

frequency range.

Transfer function:

It can be used to compute the small signal dc gain, the input resistance and

the output resistance of a circuit.

.Tf Vout Vin

.Tf Iout Iin

The .tf command calculates the parameters of Thevenin’s and Norton equivalent

circuit for the circuit file.It automatically prints the output and does not require

.print,.plot or .probe statement.

Dc sweep:

The Dc sweep is also known as dc transfer characteristics. The input variable

is varied over a range of values. For each value of the input variable. The dc

operating and the small signal dc gain are computed by calling the small signal

transfer function.

.dc LIN swname sstart send sinc

.dc oct swname sstart send np

.dc DEC swname sstart send np

53

.dc swname list <value>

Swname = sweep variable name may be V orI

Sstart = start value

Send = end value

Sinc = increment value of the sweep variable. It should be positive.

Np = number of steps.

.Lib statement:

A library file may be referenced in the circuit file by using the following

statement.

.lib fname

Fname = name of the library file.

A library file may contain comments, .model statements, sub circuit

definition, .lib statements and .end statements. No other statements are permitted.

If fname is omitted, pspice looks for the default file EVAL.LIB.

When a .lib command calls for a file, it does not bring the whole text of the

library file into the circuit file. It simply reads those models or sub circuits that are

called by the main circuit file.

54

7.4 PRE‐EMPHASIS CIRCUIT DIAGRAM

Fig 7.1 Pre‐emphasis Circuit

7.5 DE‐EMPHASIS CIRCUIT DIAGRAM:

Fig 7.2 De‐Emphasis Circuit

55

7.6 PRE‐EMPHASIS PROGRAM:

Vm 6 0 AC 1V sin(0 1V 1KHz)

Vcc 1 0 DC 10V

R1 1 3 100K

R2 3 0 68K

L1 1 5 0.3H

R3 5 2 2K

R4 4 0 1K

C1 6 3 0.1uF

C2 2 7 0.01uF

R5 7 0 10k

Q1 2 3 4 Q2N2222

.LIB

.AC DEC 10 10Hz 20KHz

.PROBE

.END

7.7 DE‐EMPHASIS PROGRAM:

Vm 1 0 AC 1V sin(0 1V 1KHz)

R1 1 2 10k

C1 2 0 0.01uF

C2 2 0 0.01uF

.LIB

.AC dec 10 10Hz 20KHz

.PROBE

.END

56

7.8 MODEL GRAPH

Fig 7.3 Preemphasis Output waveform

Fig 7.4 Deemphasisoutputwave form

57

7.9PRELAB QUESTIONS:

1. How to include the file in the circuit file?

2. What is the use of Probe comment?

3. What is threshold effect?

4. Which range of frequency is affected by noise interference?

5. How to include a device which is not already existed in pspice library?

7.10 LAB PROCEDURE:

1. Open the Pspice AD Litesoftware by double clicking its icon.

2. After few moments Command window will appear.

3. Go to the File Menu and select a New text file. (File New text file)

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

5. Now start typing your program. After completing, save the text file as .cir with

appropriate name. To execute the program go to Debug Menu and select Run.


then with an alarm, type of error will appear.


8. If there is no errors, go to Trace menu and click add trace. Enter the output node

voltage and click ok then the output will display.

58

7.11 LAB RESULT:

Thus the net list for the given pre‐emphasis and de‐emphasis circuit was

written and the output waveforms were plotted.

59


1. Which technique is used at the receiver side to reconstruct the original

signal?

2. How to add the arrows in the plot?

3. How to reduce the noise during transmission in FM ?

4. Pre emphasis operation is similar to high pass filter explain how?

5. What is the significance of the 3db down frequency?

6. Write a netlist for the given circuit

60

8.FM MODULATION IN MATLAB

8.1 OBJECTIVE

To write and simulate a MATLAB program to generate frequency modulated

signal with fm=25Hz, fc=400Hz and mf=10.


MATLAB ,Computer installed with Windows XP or higher Version..










systems. Simulink contains Block sets that are analogous to Toolboxes.It was created

by Mathworks Incorporation, USA. MATLAB® has become a defacto programming

language for Engineers.Writing MATLAB programs for modulation applications

require knowledge on very few functions and operators. The operators mostly used

are arithmetic operators and matrix operators. To know more type in the command

prompt ‘help ops’. MATLAB will give a list in that to know on specific operator say

addition type in the command prompt ‘help plus’. MATLAB will give how to use and

other relevant information.


mathematical functions are sin and cos only. The mathematical functions sin and

cosareself‐explanatory. The graphical function figure will create a new window and


two vectors and plot data points according to given vector data. In this case it will

time Vs signal. Subplot function is used when two or more plots are drawn on the

same figure. As title function suggests it helps to write title of the graph in the figure.

61

For further details type ‘help plot’ or ‘help subplot’ in the command prompt and

learn the syntax.

8.4 ALGORITHM

I.To generate message and carrier signal ,initialize :

fc(carrier frequency),

fm(modulating signal frequency),

t(time axis)

2. Generate message signal as Sin(2πfmt)

3. Generate carrier signal as sin(2πfct).

4. Generate the frequency modulated signal using the FM equation

[sin(2πfct+mfSin(2πfmt) ] where mf stands for modulation index. Choose modulation

index value more than 1.

5.Plot all the signals

62

8.5 PROGRAM

clc;

clearall;

closeall;

fm=25;

fc=400;

mf=10;

t=0:0.0001:0.1;

m=sin(2*pi*fm*t);

subplot(3,1,1);

plot(t,m);

xlabel('Time(s)');

ylabel('Amplitude(V)');

title('Message Signal');

grid on;

c=sin(2*pi*fc*t);

subplot(3,1,2);

plot(t,c);

xlabel('Time(s)');


title('Carrier Signal');

grid on;

y=sin(2*pi*fc*t+(mf.*sin(2*pi*fm*t)));%Frequency changing w.r.t Message signal

subplot(3,1,3);

plot(t,y);

xlabel('Time(s)');


title('Frequency modulated Signal');

grid on;

63


1. An FM signal has an intelligence frequency of 2 kHz and a maximum deviation

of 10 kHz. If its carrier frequency is set at 162 MHz, what is its index of

modulation?

2. Define modulation index for FM.

3. Compare FM and PM.

4. What is capture effect?

5. What is the IF Frequency for FM superheterodyne receiver?

8.7 MODEL GRAPH

Fig 8.1 Message signal

Fig 8.2 Carrier signal

Fig 8.3 Frequency modulated signal

64

8.8 LAB PROCEDURE:


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.



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

select Run.


then with an alarm, type of error will appear in red colour.


65

8.9LAB RESULT:

Thus the Frequency modulation was performed using MATLAB.

66

8.10.POST LAB QUESTIONS:

1. Mention advantages of angle modulation over amplitude modulation

2. What is the bandwidth required for an FM wave in which the modulating

frequency signal is 2 KHz and the maximum frequency deviation is 12 KHz?

3. What is Narrowband FM?

4. Write the functions of limiter?

5. Write short notes on direct method of FM generation.

6. Find the output of the following statement

5^ (2/3) – 25/(2*3)

67

9. DSB‐SC MODULATION IN MATLAB

9.1 OBJECTIVE

To write and simulate MATLAB program for DSB‐SC Modulation in time

domain and using FFT represent the result in frequency domain .












systems. Simulink contains Blocksets that is analogous to Toolboxes. It was created













68



9.4 THEORY:

DSB‐SC is basically an amplitude modulation wave without the carrier,

therefore reducing power waste, giving it a 50% efficiency. This is an increase

compared to normal AM transmission, (DSB) has a maximum efficiency of 33.333%,

since 2/3 of the power is in the carrier which carries no intelligence, and each

sideband carries the same information. Single Side Band (SSB) Suppressed Carrier is

100% efficient.

9.4.1 GENERATION

DSB‐SC is generated by a mixer. This consists of a message signal multiplied by a

carrier signal.

Fig 9.1 Product modulator

69

9.5 ALGORITHM:

1. To generate message and carrier signal, initialize:


fm(modulating signal frequency),

fs(sampling frequency),

2. Generate message signal and carrier signal

3. Multiply message and carrier signal to get DSBSC modulated signal in time

domain.

4. Take fourier transform of DSBSC modulated signal to get the signal in

frequency spectrum.

5. Plot all the signals

70

9.6 PROGRAM:

N = 1024; %N point FFT N>fc to avoid freq domain aliasing

fs = 4096; % Sample frequency

t = (0:N‐1)/fs;

fc = 600; %Carrier Frequency

fm = 80; %Message Frequency

Ec = 20; %Carrier Amplitude

Em = 5; %Messagae Amplitude

xc=Ec*cos(2*pi*fc*t);

xm=Em*cos(2*pi*fm*t);

figure(1)

subplot(2,1,1),plot(t,xc);

title('carrier signal of 600Hz');

xlabel('time (s)');

ylabel('amplitude(V)');

subplot(2,1,2);

plot(t,xm);

title('message signal of 80Hz');

xlabel('time (s)');

ylabel('amplitude(V)');

% DSB‐SC MODULATION

z1= xm.*xc;

figure(2)

subplot(2,1,1),plot(t,z1);

title('DSB‐SC MODULATION IN TIME DOMAIN');

xlabel('time (s)');

ylabel('amplitude (V)');

f = fs * (0 : N/2) / N;%Since the fft result is symmetrical, only the

%positive half is sufficient for spectral representation

M1 = 2/N*abs(fft(z1,N));

subplot(2,1,2); %Frequency Domain Plot

plot(f(1:256),M1(1:256));

title('DSB‐SC MODULATION IN FREQUENCY DOMAIN');

71

xlabel('Frequency (Hz)');

ylabel('amplitude (V)');


1. What is the difference between DSB SC and SSB SC?

2. What are the applications of DSBSC?

3. Write the methods of DSBSC generation.

4. What is the BW for single tone modulating signal with frequency ω?

5. What is the percentage of power saving for DSBSC when compared with AM

having 100% depth of modulation?

9.7 LAB PROCEDURE:



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’.


appropriate name. To execute 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 colour.


72

9.8 MODEL GRAPH

Fig. 9.2 Modulating signal

Fig. 9.3 Carrier signal

73

Fig. 9.4 DSB‐SC Modulated signal in time domain

Fig. 9.5 DSB‐SC Modulated signal in frequency domain

74

9.9 LAB RESULT:

Thus the DSB‐SC modulation was performed using MATLAB.

75


1 Which type of carrier is used in ring modulator?

2. What is the difference between DSB‐FC and DSB‐SC?

3. What are the advantages of DSB SC?

4. What is a Balanced modulator?

5. Write the general equation of DSBSC signal.

6. How will you compute N‐Point DFT using Matlab for N=2096?

76

10.SSB‐SC Modulation and Demodulation in MATLAB

10.1 OBJECTIVE

To write and simulate MATLAB program for SSB‐SC Modulation using Hilbert

Transform in time domain and using FFT represent the result in frequency domain

and hence reconstruct the modulating signal using butterworth filter.












systems. Simulink contains Blocksets that are analogous to Toolboxes. It was created













77



10.4 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. In DSB‐SC it is

observed that there is symmetry in the band structure. So, even if one half is

transmitted, the other half can be recovered at the received. By doing so, the

bandwidth and power of transmission is reduced by half. Depending on which half of

DSB‐SC signal is transmitted, there are two types of SSB modulation

1. Lower Side Band (LSB) Modulation

2. Upper Side Band (USB) Modulation

10.5 ALGORITHM:

1. To generate message and carrier signal, initialize:


(Modulating signal frequency),

fs(sampling frequency),

N( N point DFT‐no of samples)

t(time axis)

(Modulating signal amplitude)

(Carrier signal amplitude)

2. Generate message signal and carrier signal

3. Apply Hilbert transform to the message signal.

4. Write the expression for LSB or USB as per the requirement

LSB =message *carrier (cosine)+Hilbert transform of message*carrier(sine)

USB =message *carrier (cosine)‐Hilbert transform of message*carrier(sine)

78

5. Take fourier transform for LSB or USB to get the desired frequency spectrum for

modulated signal.

6.. For demodulation, multiply LSB with carrier (cosine) and apply butterworth filter to

get demodulated signal or multiply USB with carrier(sine) and apply butterworth

filter to get demodulated signal.

7. Plot all the signals

79

10.6 PROGRAM

N = 1024; fs = 2048; ts = 1/fs; t=(0:N‐1)/fs; fc = 600; % Limit fc<800 to avoid freqdomain aliasing fm = 100; Vm = 1; Vc = 1;

m = Vm*cos(2*pi*fm*t);%Message mh = Vm*cos((2*pi*fm*t)‐pi/2);%Hilbert transform of the messagesignal c=Vc*sin(2*pi*fc*t);

sbu = m.*2.*cos(2*pi*fc*t)‐mh.*2.*sin(2*pi*fc*t);%Expression for USB sbl = m.*2.*cos(2*pi*fc*t)+mh.*2.*sin(2*pi*fc*t);%Expression for LSB

SBU = 2/N*abs(fft(sbu)); %Fourier Transform of USB SBL = 2/N*abs(fft(sbl)); %Fourier Transform of LSB freq = fs * (0 : N/2) / N;

close all; figure(3) subplot(221); plot(10*t(1:200),sbu(1:200),'r');%Time Domain Plot of USB

title('Time Domain Representation === USB'); xlabel('Time(s)'); ylabel('Amplitude(V)'); subplot(222) plot(10*t(1:200),sbl(1:200),'b');%Time Domain Plot of LSB title('Time Domain Representation === LSB'); xlabel('Time(s)'); ylabel('Amplitude(V)');

subplot(223); plot(freq,SBU(1:N/2+1)) title('Frequency Domain Representation'); xlabel('Frequency(Hz)'); ylabel('Amplitude(V)'); legend('USB');

80

subplot(224) plot(freq,SBL(1:N/2+1)); %Frequency domain plot title('Frequency Domain Representation'); xlabel('Frequency(Hz)'); ylabel('Amplitude(V)'); legend('LSB');

figure(4) plot(freq,SBU(1:N/2+1),freq,SBL(1:N/2+1)); title('Frequency Domain Representation'); xlabel('Frequency(Hz)'); ylabel('Amplitude(V)'); legend('USB','LSB');

%Demodulation:

md=sbu.*cos(2*pi*fc*t); [b,a]=butter(2,0.1); mf=filter(b,a,md); figure(5) plot(t,mf) title('Demodulated Signal'); xlabel('Time(s)'); ylabel('Amplitude(V)');

figure(1); plot(t,m); xlabel('Time(s)'); ylabel('Amplitude(V)'); title('message signal'); figure(2); plot(t,c); title('Carrier signal'); xlabel('Time(s)'); ylabel('Amplitude(V)');

81


1. Define SSB‐SC.

2. What are the advantages of signal sideband transmission?

3. What are the disadvantages of single side band transmission?

4. What are the methods for generating SSB‐SC signal?

5. Compare AM with SSBSC

10.8 LAB PROCEDURE:

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


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.



appropriate name. To execute 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.


10.9 MODEL GRAPH

Fig.10.1 Message Signal

82

Fig.10.2 Carrier Signal

Fig. 10.3 Time domain representation of USB

Fig. 10.4 Time domain representation of LSB

83

Fig. 10.5 Frequency domain representation of USB

Fig. 10.6 Frequency domain representation of LSB

Fig. 10.7 Demodulated Signal

84

10.9 LAB RESULT:

Thus the SSB‐SC modulation and demodulation were performed using MATLAB.

85


1. When is the figure of merit of SSB‐SC system is unity?

2. Compare the noise performance of AM receiver with that of

SSB‐ SC receiver.

3. SSB is suitable for speech signals and not for video signals. Why?

4. Mention some applications of SSB‐SC.

5. What do you mean by Hilbert transform and inverse Hilbert Transform? Write

few applications of Hilbert transform?

6. Find Hilbert transform of sine wave having amplitude of 2 V and frequency 50

KHz using Matlab program

EC1020 Communication Engineering Lab · PDF fileSYLLABUS OF EC1020 COMMUNICATION ENGINEERING...

Documents

Transcript of EC1020 Communication Engineering Lab · PDF fileSYLLABUS OF EC1020 COMMUNICATION ENGINEERING...