Microwave & Optical Communication Lab Manual - SRM

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EC0322 MICROWAVE AND OPTICAL COMMUNICATION LAB

LABORATORY MANUAL

SEMESTER VI

DEPARTMENT OF

ELECTRONICS AND COMMUNICATION ENGINEERING

SRM UNIVERISTY (Under SECTION 3 of the UGC Act, 1956)

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

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Department of Electronics and Communication Engineering

EC0322 MICROWAVE AND OPTICAL COMMUNICATION LAB

Laboratory Manual

Course Team

Mrs. S. Vasantha Dev Suryakala Mrs. M. Sangeetha Mrs. P. Aruna Priya Mrs P. Malarvizhi Mr. R. Ramesh Dr. Shanthi prince

January 2011

Revision: 1

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L T P C

EC0322 MICROWAVE AND OPTICAL COMMUNICATION LAB 0 0 3 2

Prerequisite : nil

PURPOSE To know and understand how communication is being established at microwave frequencies and using fiber in optical communication. INSTRUCTIONAL OBJECTIVES 1. To have a detailed practical study on microwave equipments 2. To study the optical devices and to use in the appropriate application LIST OF EXPERIMENTS

MICROWAVE EXPERIMENTS 1. Characteristics of Reflex Klystron 2. Study of power distribution in Directional coupler, E & H plane and Magic tee. 3. Wavelength and Frequency measurement. 4. Impedance measurement by slotted line method. 5. Gain and Radiation pattern of Horn antenna. 6. Design of Micro strip antenna.

OPTICAL COMMUNICATION EXPERIMENTS 1. D. C. Characteristics of LED and PIN photo diode. 2. D. C. Characteristics of Laser diode. 3. Measurement of Numerical aperture, Propagation and Bending Loss in fiber. 4. Fiber Optic Analog Link. 5. Fiber Optic Digital Link.

SPICE SIMULATION 1. Frequency response of RF amplifier. 2. Frequency response of IF amplifier. 3. Amplitude modulation

TOTAL 45

REFERENCE: 1) Laboratory Manual, ECE Department, SRM University.

2) Basic Microwave Techniques and Laboratory Manual by Sisodia and Raghuvanshi

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EC0322 – Microwave and Optical Communication Lab

Course designed by Department of Electronics & Communication Engineering 1 Program

outcome a B c d e f g h i j k

x x x 2 Category General

(G) Basic

Sciences (B)

Engineering Sciences and

Technical Arts(E)

Professional Subjects(P)

x 3

Broad area (for ‘P’category)

Communication Signal Processing Electronics VLSI Embedded

x

4 Staff responsible for preparing the syllabus Mrs.Shanthi Prince

Mrs.Neelaveni ammal Mrs.J.Manjula 5 Date of preparation

December 2006

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S.R.M University

Faculty of Engineering and Technology

Department of Electronics and Communication Engineering Sub Code : EC0322 Semester : VI Sub Title : Microwave and Optical Communication Lab Course Time : Jan–May’11 Pre_requisite : NIL Co_requisite : EC0302 Microwave and RF Design

EC0304 Optical Communication and Networks

Program Outcome

c. Graduate will demonstrate the ability to design and conduct experiments, analyze and interpret data. Experiment 1:Characteristics of Reflex Klystron Experiment 2: Study of Power distribution in Directional coupler, Experiment 3:Study of Power distribution in E&H Plane Tee Experiment 4: Study of Power distribution in Magic Tee Experiment 5: i) Wavelength and frequency measurement ii)Impedance measurement by slotted line method Experiment 6: Gain and radiation pattern of Horn antenna. Experiment 7: Design of Micro strip antenna d .Graduates will demonstrate the ability to design a system, component or process as per needs and specifications Experiment11:Setting up of Fiber Optic Analog link Experiment 12:Setting up of Fiber Optic Digital link f .Graduate will demonstrate the skills to use modern engineering tools, software’s and equipment to analyze problems. Experiment 13:Frequency response of RF amplifier Experiment 14:Frequency response of IF amplifier

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Sub Code : EC0322 Semester : VI Sub Title : Microwave and Optical Communication Lab Course Time : Jan–May’11 Pre_requisite : NIL Co_requisite : EC0302 Microwave and RF Design. EC0304 Optical Communication and Networks

Program Educational Objectives vs Program Outcome

Program Outcomes

Program Educational Objectives 1. To prepare students to compete for a successful career in their chosen profession through global education standards.

2. To enable the students to aptly to apply their acquired knowledge in basic sciences and mathematics in solving engineering problems.

3. To produce skill full graduates to analyze, design and develop a system/component/process for the required needs under the realistic constraints.

4.To train the students to approach ethically any multidisciplinary engineering challenges with economic, environmental and social contexts

5. To create an awareness among students about the need for life long learning to succeed in their professional career.

c. Graduate will demonstrate the ability to design and conduct experiments, analyze and interpret data

X X

d. Graduate will demonstrate the ability to design a system, component or process as per needs and specification

X X X

f.Graduate will demonstrate the skills to use modern engineering tools, software’s and equipment to analyze problems

X X

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Sub Code : EC0322 Semester : VI Sub Title : Microwave and Optical Communication Lab Course Time : Jan– May’11 Pre Requisite : Nil Course Requisite : EC0302 Microwave and RF Design EC0304 Optical Communication And Networks

Instructional Objective and Program Outcome S.No. Instructional

Objective Program Outcome Experiment Details

1 To have a detailed practical study of microwave equipments

c. Graduate will demonstrate the ability to design and conduct experiments, analyze and interpret data

Experiment 1:Characteristics of Reflex Klystron Experiment 2: Study of Power distribution in Directional coupler, Experiment 3:Study of Power distribution in E&H Plane Tee Experiment 4: Study of Power distribution in Magic Tee Experiment 5: i) Wavelength and frequency measurement ii)Impedance measurement by slotted line method Experiment 6: Gain and radiation pattern of Horn antenna. Experiment 7: Design of Micro strip antenna

2 To study the optical devices and to use in the appropriate application

c. Graduate will demonstrate the ability to design and conduct experiments, analyze and interpret data d Graduates will demonstrate the ability to design a system, component or process as per needs and specifications f Graduate will demonstrate the skills to use modern engineering tools, software’s and equipment to analyze problems.

Experiment 8: DC Characteristics of LED and PIN Photodiode Experiment 9: DC Characteristics of Laser diode Experiment10:Measurement of Numerical aperture, propagation and bending loss in fiber Experiment11:Setting up of Fiber Optic Analog link Experiment 12:Setting up of Fiber Optic Digital link Experiment 13:Frequency response of RF amplifier Experiment 14:Frequency response of IF amplifier

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EC0322 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 prelab and postlab report format is as follows:

1. A neat thorough prelab must be presented to your Staff 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 staff 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 Staff 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 staff 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 staff 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 staff incharge of both the sections. Habitually late students (i.e., students late more than 15

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minutes more than once) will receive 10 point reductions in their grades for each occurrence following the first.

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 Staff Incharge will ask pertinent questions to individual members of a team at random. Labs will be graded as per the following grading policy:

Pre-Lab Work 20.00%

In-Lab Performance 30.00%

Post Lab Work 20.00%

Laboratory Report 30.00%

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 75%. The remaining 25% 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.

9. Precautions:

Microwave experiments

a) During operation of Klystron, repeller does not carry any current and as such it

may severely be damaged by electron bombardment. To protect repeller from such

damage, the repeller negative voltage is always applied before anode voltage.

b) The repeller voltage should be varied in one direction to avoid hysteresis.

c) The heater voltage should be applied first and cooling should be provided

simultaneously. After some time other voltages should be applied

d) While measuring power, the frequency meter should be detuned each time because

there is a (attenuation) dip in the output power when the frequency is tuned.

e) To avoid loading of the klystron an isolator/attenuation should invariably be used

between klystron and the rest of the set-up.

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SRM UNIVERSITY

Department of Electronics and Communication Engineering

EC0322 Microwave and Optical Communication Lab

Laboratory Report Cover Sheet

EVEN SEM – 2011

Name: ______________________________________ Section: Tick One M ( ) TU ( ) W ( ) Th ( ) Fr ( )

Venue: _______________________________________

Title of Lab: ________________________________________

Preparation Verification

Staff Name & Signature: ______________________

______________________

Experiment Completion Verification


______________________

Date, Time: ______________________

Particulars Max Marks Marks Obtained Pre-lab Work 20 Lab Procedure 30 Post lab Work 20 Lab Report 30 Total 100

Report Verification


______________________

Date, Time: ______________________

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STUDY OF MICROWAVE COMPONENTS

RECTANGULAR WAVE GUIDE Wave guides are manufactured to the highest mechanical and electrical standards and mechanical tolerances. L and S band wave guides are fabricated by precision brazing of brass-plates and all other wave guides are in extrusion quality. W.G. sections of specified length can be supplied with flanges, painted outside and silver or gold plated in side. SPECIFICATIONS X Band EIA No. : WR - 90 Frequency : 8.2 - 12.4 GHZ Width : 2.286cm Height : 1.1016cm Width : 2.54 cm Height : 1.27cm ± Tol. (µm) : 7.6 Material : Brass/Copper. FIXED ATTENUATORS Series 5000 fixed Attenuators are meant for inserting a known attenuation in a wave guide system. These consists of a lossy vane inserted in a section of wave guide, flanged on both ends. These are useful for isolation of wave guide circuits, padding and extending the range of measuring equipments. Fixed Attenuators are available for 3,6 or 10 dB attenuation values, but any attenuation valve between 0 and 30dB can be provided.

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SPECIFICATIONS Model No: X-5000 /Frequency : 8.12 - 12.4 GHZ /Attenuation (dB) : 3,6,10/Callibration Accuracy : ± 0.2dB/Avg Power : 2W/Max VSWR : 1.10/Max Insertion Loss (dB) : 0.2/W.G. Type: WG – 90/Flange Type (UG/U) : 39. A precision built probe carriage has a centimeter scale with a vernier reading of 0.1mm least count and a dial gauge can be mounted easily if precise readings are required. Model No. : X - 6051 Freq (GHz) : 8.2 - 12.4 Max Residual VSWR : 1.01 WG type (WR-) : 90 Flange Type (UG-/U) : 39 TUNABLE PROBE Model 6055 Tunable probe is designed for use with model 6051 slotted sections. These are meant for exploring the energy of the EF in a suitably fabricated section of wave guide. The depth of penetration into a wave guide - section is adjustable by the knob of the probe. The tip pick up the RF power from the line and this power is rectified by crystal detector, which is then fed to the VSWR meter or indicating instrument. /Model No. : X6055 /Freq (Ghz) : 8.2 - 12.4 /output Connector : BNC(F) /Detector : IN23. WAVE GUIDE DETECTOR MOUNT (TUNABLE) Model 4051 Tunable Detector Mount is simple and easy to use instrument for detecting microwave power through a suitable detector. It consists of a detector crystal mounted in a section of a Wave guide and shorting plunger for matching purpose. The output from the crystal may be fed to an indicating instrument. In K and R bands detector mounts the plunger is driven by a micrometer.

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Model No. : X - 4051 Freq. Range (GHz) : 8.2 - 12.4 O/P Connector : BNC (F) Wave guide type (WR-) : 90 Flange Type (UG/U) : 39 Detector : IN23 KLYSTRON MOUNT Model 2051 Klystron mounts are meant for mounting corresponding Klystrons such as 2K25, 723A/B, 726A or RK - 5976 etc. These consists of a section of wave guide flanged on one end and terminated with a movable short on the other end. An octal base with cable is provided for Klystron. Model No. : X – 2051/ Freq. Range (GHz) 8.2 - 12.4/ WG Type (WR-) : 90 Flange Type (UG-/U): 39 CIRCULATORS Model 6021 and 6022 are T and Y types of three port circulators respectively. These are precisely machined and assembled to get the desired specifications. Circulators are matched three port devices and these are meant for allowing Microwave energy to flow in clockwise direction with negligible loss but almost no transmission in the anti-clockwise direction. Model No. : X - 6021 Frequency Range (GHz) : 8.6 - 10.6 or 10.2 - 12.2 Min. Isolation (dB) : 20 Max. Insertion Loss (dB) : 0.4 Max. VSWR : 1.20 SLIDE SCREW TUNERS Model 4041 slide screw tuners are used for matching purposes by changing the penetration and position of a screw in the slot provided in the centre of the wave guide.

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These consists of a section of wave guide flanged on both ends and a thin slot is provided in the broad wall of the Wave guide. A carriage carrying the screw, is provided over the slot. A VSWR upto 20 can be tuned to a value less than 1.02 at certain frequency. Model No. : X – 4041/ Freq. Range (GHz) : 8.2 - 12.4/WG Type (WR-) : 90 Flange type (UG/U) : 39 MULTIHOLE DIRECTIONAL COUPLERS Model 6000 series Multihole directional couplers are useful for sampling a part of Microwave energy for monitoring purposes and for measuring reflections and impedance. These consists of a section of Wave guide with addition of a second parallel section of wave guide thus making it a four port network. However the fourth port is terminated with a matched load. These two parallel sections are coupled to each other through many holes, almost to give uniform coupling; minimum frequency sensitivity and high directivity. These are available in 3,6,10,20 and 40dB coupling. Model No. : X - 6003 Frequency Range (GHz) : 8.2 - 12.4 Coupling (dB) : 3,10,20,40 Directivity (dB) : 35 Wave guide type (WR-) : 90 Flange type (UG/U) : 39 E PLANE TEE Model 3061 E - plane tee are series type T - junction and consists of three section of wave guide joined together in order to divide or compare power levels. The signal entering the first port of this T - junction will be equally dividing at second and third ports of the same magnitude but in opposite phase. Model No. : X - 3061 Frequency Range (GHz) : 8.2 - 12.4 WG Type (WR-) : 90 Flange Type (UG/U) : 39

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H - PLANT TEE Model 3065 H - Plane Tee are shunt type T - junction for use in conjunction with VSWR meters, frequency - meters and other detector devices. Like in E-plane tee, the signal fed through first port of H - plane Tee will be equally divided in magnitude at second and third ports but in same phase. Model No. : X - 3065 Frequency Range (GHz) : 8.2 - 12.4 WG Type (WR-) : 90 Flange Type (UG-/U) : 39 MAGIC TEE Model 3045 E - H Tee consists of a section of wave guide in both series and shunt wave guide arms, mounted at the exact midpoint of main arm. Both ends of the section of wave guide and both arms are flanged on their ends. These Tees are employed in balanced mixers, AFC circuits and impedance measurement circuits etc. This becomes a four terminal device where one terminal is isolated from the input terminal. Model No. : X - 3045 Frequency Range (GHz) : 8.2 - 12.4 WG Type (WR-) : 90 Flange Type (UR-/U) : 39 MOVABLE SHORT Model 4081 movable shorts consists of a section of waveguide, flanged on one end and terminated with a movable shorting plunger on the other end. By means of this non contacting type plunger, a reflection co-efficient of almost unity may be obtained. Model No. : X - 4081 Frequency Range (GHz) : 8.2 - 12.4 WG Type (WR-) : 90 Flange Type (UG-/U) : 39

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MATCHED TERMINATION Model 4000 are low power and non-reflective type of terminations. It consists of a small and highly dissipative taper flap mounted inside the centre of a section of wave guide. Matched Terminations are useful for USWR measurement of various waveguide components. These are also employed as dummy and as a precise reference loads with Tee junctions, directional couplers and other similar dividing devices. Model No. : X - 4000, Freq. Range (GHz) : 8.2 - 12.4 Max VSWR : 1.04 AV Power : 2W, WG Type (WR-) 90, Flange Type (UG-/U) : 39 PYRAMIDAL WAVEGUIDE HORN ANTENNA Model 5041 pyramidal Wave guide Horn antenna consists of waveguide joined to pyramidal section fabricated from brass sheet. The pyramidal section shapes the energy to concentrate in a specified beam. Wave guide horns are used as feed horns as radiators for reflectors and lenses and as a pickup antenna for receiving microwave power. Model No. : X - 5041 Frequency Range (GHz) : 8.2 - 12.4 Max VSWR : 1.20 WG Type (WR-) : 90 Flange Type (UG-/U) : 39 GUNN OSCILLATORS Model 2151 Gunn Oscillators are solid state microwave energy generators. These consists of waveguide cavity flanged on one end and micrometer driven plunger fitted on the other end. A gunn-diode is mounted inside the Wave guide with BNC (F) connector for DC bias. Each Gunn oscillator is supplied with calibration certificate giving frequency vs micrometer reading. Model No. : X - 2152, Freq : 8.2 - 12.4 GHz, Min output power : 10 MW WG Type (WR-) : 90 Flange Type (UG-/U) : 39

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PIN MODULATORS Model 451 pin modulators are designed to modulate the CW output of Gunn Oscillators. It is operated by the square pulses derived from the UHF(F) connector of the Gunn power supply. These consists of a pin diode mounted inside a section of Wave guide flanged on it’s both end. A fixed attenuation vane is mounted inside at the input to protect the oscillator. Model No. : X - 451 Frequency Range (GHz) : 8.3 - 12.4 Max RF Power : 1W WG Type (WR-) : 90 Flange Type (GHz) : 39 GUNN POWER SUPPLY Model X-110 Gunn Power supply comprises of an regulated DC power supply and a square wave generator, designed to operate Gunn-Oscillator model 2151 or 2152, and pin modulators model 451 respectively. The DC voltage is variable from 0 - 10V. The front panel meter monitors the gunn voltage and the current drawn by the Gunn diode. The square wave of generator is variable from 0 - 10V. in amplitude and 900 - 1100 Hz in frequency. The power supply has been so designed to protect Gunn diode from reverse voltage application over transient and low frequency oscillations by the negative resistance of the Gunn-diode. SPECIFICATIONS Amplifier Type : High gain tuned at one frequency Frequency : 1000 Hz ± 2% Sensitivity : 0.1 microvolt at 200 for full scale Band width : 25 - 30 cps Range : 70dB min in 10 dB steps Scale selector : Normal Expand Gain control : ‘Coarse’ & ‘Fine’ Mains power : 230V, 50Hz

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ISOLATORS The three port circulators Model 6021 may be converted into isolators by terminating one of its port into matched load. these will work over the frequency range of circulators. These are well matched devices offering low forward insertion loss and high reverse isolation. Model No. : X - 6022 Frequency Range (GHz) : 8.6 - 10.6 or 10.2 - 12.2 Min Isolation (dB) : 20 Max Insertion Loss (dB) : 0.4 Max VSWR : 1.20

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CONTENTS

Lab: 1 Mode Characteristics of Reflex Klystron 1 1.1Objective 1.2 Hardware Required 1.3 Introduction 1.4 Prelab Questions 1.5 Precautions 1.6 Experiment 1.6.1 Procedure 1.6.2 Calculations 1.6.3 Block Diagram 1.6.4 Model Graph 1.6.5 Tabulation 1.7 Post Lab Questions 1.8 Result Lab: 2.1 Study of Power Distribution in Directional Coupler 2.1.1Objective 2.1.2 Hardware Required 2.1.3 Introduction 2.1.4 Prelab Questions 2.1.5 Experiment 2.1.5.1 Procedure 2.1.5.2 Formula 2.1.5.3 Block Diagram 2.1.6 Post Lab Questions 2.1.7 Result Lab: 2.2 Study of Power Distribution In E Plane & H Plane and Magic Tee 2.2 .1 Objective 2.2.2 Hardware Required 2.2.3 Introduction 2.2.4 PreLab Questions 2.2.5 Experiment 2.2.5.1 Procedure 2.2.5.2 Block Diagram 2.2.5.3 Tabulation: 2.2.6 Post Lab Questions 2.2.7 Result Lab :3 Wavelength and Frequency Measurement 3.1 Objective 3.2 Hardware Required 3.3 Introduction 3.4 Pre Lab Questions 3.5 Experiment 3.5.1 Procedure 3.5.2 Calculation 3.5.3 Block Diagram 3.5.4 Tabulation 3.6 Post Lab Questions 3.7 Result

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Lab: 4 Impedence Measurement By Slotted Line Method 4.1 Objective 4.2 Hardware Required 4.3 Introduction 4.4 Prelab Questions 4.5 Experiment 4.5.1 Procedure 4.5.2 Formula 4.5.3 Block Diagram 4.6 Postlab Questions 4.7 Result Lab : 5 Gain and Radiation Pattern of Horn Antenna 5.1 Objective 5.2 Hardware Required 5.3 Introduction 5.4 Prelab Questions 5.5 Precautions 5.6 Experiment 5.6.1 Procedure 5.6.2 Block Diagram 5.6.3 Tabulation 5.7 Post Lab 5.8 Result Lab: 6 Design of Microstrip Antenna 6.1 Objective 6.2 Hardware Required 6.3 Introduction 6.4 Prelab Questions 6.5 Experiment 6.5.1 Procedure 6.5.2 Tabulation 6.5.3 Radiation Pattern 6.6 Postlab Questions 6.7 Result Lab: 7.1 DC Characteristics Of LED 7.1.1 Objective 7.1.2 Hardware Required 7.1.3 Introduction 7.1.4 Prelab Questions 7.1.5 Experiment 7.1.5.1 Procedure 7.1.5.2 Tabulation 7.1.5.3 Model Graph 7.1.6 Post Lab 7.1.7 Result Lab: 7.2 DC Characteristics of Pin Photodiode 7.2.1 Objective 7.2.2 Hardware Required 7.2.3 Introduction 7.2.4 Prelab Questions

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7.2.5 Precaution 7.2.6 Experiment 7.2.6.1 Procedure 7.2.6.2 Tabulation 7.2.6.3 Model Graph 7.2.7 Postlab Questions 7.2.8 Result

Lab: 8 DC Characteristics of Laser Diode 8.1 Objective 8.2 Hardware Required 8.3 Introduction 8.4 Pre Lab Questions 8.5 Precaution 8.6 Experiment 8.6.1 Procedure 8.6.2 Tabulation 8.6.3 Model Graph 8.7 Postlab Questions 8.8 Result

Lab: 9.1 Measurement of Numerical Aperture of Optical Fiber 9.1.1 Objective 9.1.2 Hardware Required 9.1.3 Introduction 9.1.4 Prelab Questions 9.1.5 Procedure 9.1.6 Tabulation 9.1.7 Post Lab Questions 9.1.8 Result Lab: 9.2 Measurement Of Propagation Loss In Optical Fiber 9.2.1Objective 9.2.2 Hardware Requirement 9.2.3 Introduction: 9.2.4 Prelab Questions 9.2.5 Procedure 9.2.6 Tabulation 9.2.7 Result Lab: 9.3 Measurement Of Bending Loss In A Optical Fiber 9.3.1 Objective 9.3.2 Hardware Requirements

9.3.3 Introduction 9.3.4 Prelab Questions 9.3.5 Experiment 9.3.5.1 Procedure 9.3.5.2 Tabulation 9.3. 6 Post Lab Question 9.3.7 Result Lab: 10 Setting Up a Fiber Optic Analog Link 10.1 Objective: 10.2 Hardware Required:

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10.3 Introduction: 10.4 Prelab Questions 10.5 Procedure: 10.6 Layout Diagram 10.7 Postlab Questions 10.8 Result Lab: 11 Setting Up a Fiber Optic Digital Link 11.1 Objective: 11.2 Hardware Required: 11.3 Introduction: 11.4 Prelab Questions 11.5 Procedure: 11.6 Layout Diagram 11.7 Postlab Questions 11.8 Result Lab :12 RF Amplifier 12.1 Objective 12.2 Software Required 12.3 Introduction 12.4 Prelab Questions 12.5 Procedure 12.6 Circuit Diagram 12.7 Netlist 12.8 Simulated Output 12.9 Postlab Questions 12.10 Result Lab: 13 Frequency Response of If Amplifier 13.1 Objective 13.2 Software Required 13.3 Introduction 13.4 Prelab Questions 13.5 Procedure 13.6 Circuit Diagram 13.7 Netlist 13.8 Simulated Output 13.9 Post Lab Questions 13.10 Result Lab: 14 Amplitude Modulation 14.1 Objective 14.2 Software Required 14.3 Introduction 14.4 Prelab Questions 14.5 Procedure 14.6 Circuit Diagram 14.7 Netlist 14.8 Output 14.9 Post Lab Questions 14.10 Result Appendix

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EXPT NO: 1

MODE CHARACTERISTICS OF REFLEX KLYSTRON

1.1 OBJECTIVE

1. To study and plot the reflex klystron output and frequency characteristics. 2. To find mode number, transit time, electronic tuning range (ETR) and

Electronic tuning sensitivity (ETS) 1.2 HARDWARE REQUIRED Klystron Power Supply, Klystron with mount, Isolator, Frequency meter, Variable Attenuator, Slotted section with Probe carriage, CRO, Movable Short. 1.3 INTRODUCTION Klystron is a microwave vacuum tube employing velocity modulation. These electrons move towards the repeller (ie) the electrons leaving the cavity during the positive half cycle are accelerated while those during negative half cycle are decelerated. The faster ones penetrate further while slower ones penetrate lesser in the field of repeller voltage. But, faster electrons leaving the cavity take longer time to return and hence catch up with slower ones. In the cavity the electrons bunch and interact with the voltage between the cavity grids. It consists of an electron gun producing a collimated electron beam. It bunches pass through grids at time the grid potentials is such that electrons are decelerated they give by energy. The electrons are then collected by positive cavity wall near cathode. To protect repeller from damage, repeller voltage is applied before accelerating voltage. Transit time is defined as the time taken for the electron to travel in to the reflector space and back to the gap. t1=n+3/4, n is an integer. It depends on beam and reflector voltages. Several combinations of beam – reflector voltages provide oscillations for the particular value of n. Each value of n corresponds to a different mode. Modes corresponding n=2 and n=3 are often used for optimum efficiency. ETR – Electronic tuning range i.e, the frequency band from one end of the mode to another is calculated by ETR = f1max – f1min (GHz) for N1 mode f1max, f1min → half power frequencies

ETS – Electronic tuning sensitivity

ETS = min1max1

min1max1

VVff

−−

(MHz/V)

f1max, f1min → half power frequencies V1max, V1min→ corresponding repeller voltages for a particular mode.

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PRELAB QUESTIONS 1 What is the effect of cavity gap on electron bunching? 2 Explain mode in reflex klystron. 3 Higher order mode occurs at ____________ repeller voltage. 4 When is the output power of reflex klystron maximum? 5 What is transit time?

1.5 PRECAUTIONS 1. During operation of Klystron, repeller does not carry any current and as such it

may severely be damaged by electron bombardment. To protect repeller from such damage, the repeller negative voltage is always applied before anode voltage.

2. The repeller voltage should be varied in one direction to avoid hysterisis. 3. While measuring output power frequency meter should be detuned each time. 4. An isolator or attenuator should be used between klystron and other equipment in

the set up to avoid loading of the klystron. 5. Before switching on power supply the control knobs of klystron power supply

should be kept as below.

Meter switch : off Mode switch : AM Beam voltage knob : fully anticlockwise (min) Reflector voltage : fully clockwise (max) AM – Amplitude : fully clockwise (max) AM - Frequency knob : mid position.

1.6 EXPERIMENT 1.6.1 PROCEDURE

1. Assemble the components as shown in fig. 2. After following the necessary precautions, the Klystron Power Supply is switched

ON. 3. Adjust the variable attenuator to obtain maximum output.. 4. Vary the repeller voltage from it’s maximum negative value and increase it in steps of

1V and record output power and frequency. 5. Measure the frequency by tuning the frequency meter corresponding to a dip in the

output voltage each time. 6. The frequency meter is detuned before measuring the output power each time. 7. Plot the mode characteristics of Reflex Klystron. (i.e. Output Voltage Vs Repeller

voltage and Frequency Vs Repeller voltage)

1.6.2 CALCULATIONS

(i) Knowing mode top voltages of two adjacent modes, mode numbers of the modes is computed from the equation,

4/3

4/3)1(

2

1

1

2

+++

==n

nVV

NN

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where V1 and V2 are the values of repeller voltages required to operate the klystron in

mode numbers N1 and N2.

(ii) Knowing mode number, transit time of each mode is calculated from

01

1

011

)4/3(fN

fnt =

+= seconds

f01 → frequency of microwave operation in one mode.

(iii) ETR – Electronic tuning range i.e, the frequency band from one end of the mode to another is calculated by

ETR = f1max – f1min for N1 mode (GHz) f1max – f1min → half power frequencies

(iv) ETS – Electronic tuning sensitivity

ETS = min1max1

min1max1

VVff

−−

(MHz/V)

f1max, f1min → half power frequency V1max, V1min→ corresponding repeller voltages for a particular mode.

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1.6.3 BLOCK DIAGRAM:

Fig 1 Mode Characteristics of Reflex Klystron 1.6.4 MODEL GRAPH:

Klystron Power Supply

Klystron with Mount Isolator

Frequency Meter

Variable Attenuator

Detector Mount

C.R.O

27

1.6.5 TABULATION:

Mode Frequency (GHz) Repeller voltage (V) Output Voltage (mV)

1

2

3

1.7 POST LAB QUESTIONS:

1. What is the effect of transit time? 2. List two basic configurations of Klystron tubes. 3. Why only discrete modes of operation are possible in reflex klystron. 4. Which mode number is most frequently used? Why? 5. Velocity modulation of electrons can result in density modulation of the same.

Comment. 1.8 RESULT The mode characteristics of reflex klystron has been studied and plotted. Transit time, ETR and ETS are determined for each mode of operation.

Modes Transit Time(µs) ETR (GHz) ETS (MHz/V) Mode 1 Mode 2 Mode 3

28

Lab Report

Each individual will be required to submit a lab report. Use the format specified in the

"Lab Report Requirements" document available on the class web page. Be sure to include the following items in your lab report:

Lab cover sheet with staff verification for circuit diagram Answer the pre-lab questions Complete paper design for all three designs including K-maps and minimized

equations and the truth table for each of the output signals. Answer the post-lab questions

Grading

Pre-lab Work 20 points Lab Performance 30 points Post-lab Work 20 points Lab report 30 points

For the lab performance - at a minimum, demonstrate the operation of all the circuits to your staff incharge

29

NO: 2.1

STUDY OF POWER DISTRIBUTION IN DIRECTIONAL COUPLER

2.1.1 OBJECTIVE To study the power distribution in various ports of directional coupler and measure the following parameters:

i) Insertion loss ii) Coupling factor iii) Directivity

2.1.2 HARDWARE REQUIRED Klystron power supply, Klystron with mount, Isolator, variable attenuator,, CRO, Directional Coupler, Matched termination. 2.1.3 INTRODUCTION A directional coupler is a useful hybrid waveguide joint, which couple power in an auxiliary waveguide arm in one direction. It is a four-port device but one of the ports is terminated into a matched load. Ref figure 1. Characteristics of a Directional Coupler

An ideal directional coupler has the following characteristics i) If power is fed into port (1) the power is coupled in ports (2) and (3) i.e.,

power flows in the forward direction of the auxiliary arm port (3) but no power couples in port (4) i.e., in backward direction similarly power fed in (2) couples into ports (1) and (4) and not in (3).

ii) All the four ports are matched, i.e. if three of them are terminated in matched loads, the fourth is automatically terminated in a matched load.

iii) If power couples in reverse direction, power fed in (1) appears in ports (2) and (4) and nothing in (3), then such type of coupler is known as backward directional coupler. The conclusion is that in the auxiliary section the power is coupled in only one direction.

We will measure coupling coefficient, directivity and the main line insertion loss as a

function of frequency.

30

Fig 1 Directional coupler as a three – port device:

Unidirectional coupler

2.1.4 PRELAB QUESTIONS

1. How does power couple in a reverse coupler. 2. Give the applications of directional coupler 3. What is the purpose of measuring directivity, coupling factor? 4. Give the S matrix for directional coupler 5. What is the relation between directivity and isolation?

2.1.5 EXPERIMENT 2.1.5.1 PROCEDURE: INSERTION LOSS

1. Set the equipment by connecting detector mount to the input end(without directional coupler).

2. Set mode 3 and obverse the input voltage Vi. Do not alter till the end of the experiment.

3. Insert the directional coupler; terminate port 4 with matched termination. 4. Connect detector mount to port 2 and measure V12. 5. Calculate insertion loss as per the formula.

COUPLING FACTOR

1. To measure coupling factor, terminate port 2 with matched termination, connect detector mount to port 4 and measure V14.

2. Calculate coupling factor as per the formula

DIRECTIVITY:

1. Set up the equipment as shown in fig Terminate port 2 with matched termination and connect detector mount to port 4.

2. Measure the voltage at port 4 and note it as V14. 3. Connect the directional coupler in reverse direction. ie, port 2 – input, port 1 –

matched termination, port 4 – detector mount

31

4. Measure the voltage as V24 5. Calculate directivity D as per the formula

2.1.5.2 OBSERVATIONS AND CALCULATIONS: Observations Vi =

V12 =

V14 =

V24 =

INSERTION LOSS (L) L = 20 log10 (Vi/V12) dB COUPLING FACTOR (C) C = 20 log 10 (Vi/V14) dB DIRECTIVITY (D) D = 20 log10 (V14 / V24) dB 2.1.5.3 BLOCK DIAGRAM Mode 3 set up: Input Voltage Vi = -----------------(v)

32

DIRECTIVITY MEASUREMENT

1

2 1

34

Insertion Loss (V12) measurement

Coupling Factor (V14) measurement

4

2

33

2.1.6 POST LAB QUESTIONS:

1. Explain how back power is zero in a directional coupler with neat diagram. 2. What is multihole directional coupler. 3. List the performance of a directional coupler. 4. What factors determine parameters of directional coupler 5. List one practical application where DC is used.

2.1.7 RESULT: Thus the power distribution in various ports of a directional coupler was studied and the following parameters are calculated.

Coupling factor Directivity Insertion loss

Lab Report

Each individual will be required to submit a lab report. Use the format specified in the "Lab Report Requirements" document available on the class web page. Be sure to include the following items in your lab report:



Grading


For the lab performance - at a minimum, demonstrate the operation of all the circuits to your staff in charge

34

EXPT NO: 2.2. STUDY OF POWER DISTRIBUTION IN E PLANE &

H PLANE AND MAGIC TEE

2.2.1 OBJECTIVE To determine isolations and coupling coefficients for E, H plane Tee and Magic Tee junctions. 2.2.2 HARDWARE REQUIRED Klystron power supply, Klystron with mount, isolator, variable attenuator, Magic Tee, Matched termination, detector mount, CRO. 2.2.3 INTRODUCTION H Plane Tee Fig 1 shows the sketch of H plane tee. It is clear from the sketch that an auxiliary waveguide arm is fastened perpendicular to the narrow wall of a main guide, thus it is a three port device in which axis of the auxiliary or side arm is parallel to the planes of the magnetic field of the main of the main guide and the coupling from the main guide to the branch guide is by means of magnetic fields. Therefore, it is also known as H plane tee. The perpendicular arm is generally taken as input and other two arms are in shunt to the input and hence it is also called as shunt tee. Because of symmetry of the tee; equivalent circuit of H plane, when power enters the auxiliary arm, and the two main arms 1 and 2 are terminated in identical loads, the power supplied to each load is equal and in phase with one another. Thus H plane tee is an `adder’. E Plane Tee Fig 2 shows the sketch of E plane tee. It is clear from the sketch of the E plane tee that an auxiliary waveguide arm is fastened to the broader wall of the main guide. Thus it is also a three port device in which the auxiliary arm axis in parallel to the plane of the electric fields of the main guide, and the coupling from the main guide to the auxiliary guide is by means of electric fields. Therefore, it is also known as E plane tee. It is clear that it causes load connected to its branches to appear in series. So it is often referred to as a series tee. E plane tee divides the power equally and 180 out of phase. Thus E plane Tee is a subtractor/differentiator Magic Tee An interesting type of T junction is the hybrid tee, commonly known as `magic tee’ which is shown in fig 3. The device as can be seen from fig is a combination of the E arm and H plane tees. Arm3, the H arm forms an H plane tee and arm 4, the E arm, forms an E plane tee in combination with arms 1 and 2. The central lines of the two tees coincide and define the plane of symmetry, that is, if arms 1 and 2 are of equal length, the part of structure on one side of the symmetry plane shown by shaded area is the mirror image of that on the other. Arms1 and 2 are sometimes called as the side or collinear arms.

35

The name `magic Tee’ is derived from the manner in which power divides among various arms. If power is fed into arm3, the electric field divides equally between arms 1 and 2 and the fields are in phase. Because of symmetry of the T junction, no net electric field parallel to the narrow dimension of the waveguide is excited in arm 4. Thus no power is coupled in port 4. Reciprocity demands no coupling in port 3 if power is fed in 4. Another property that results from the symmetry of the junction is, if power is fed in E or H arm, it is equally divided between arms 1 and 2. 2.2.4 PRE LAB QUESTIONS:

1. What is Tee junction? Give two examples 2. What is the other name for Hybrid ring? 3. Name some wave guide components used to change the direction of the guide through

an arbitrary angle 4. What is the S matrix of H plane Tee junction. 5. List some Applications of magic Tee.

2.2.5 EXPERIMENT 2.2.5.1 PROCEDURE: E Plane & H Plane Tee and Magic Tee Isolation & Coupling Coefficient

1. Energize the microwave source and set mode 3. 2. Note down the input voltage as Vi (mv) (should not alter the setting) 3. Now connect the magic tee/E-Plane/H-Plane Tee. 4. Determine the corresponding voltages Vj (mv) for each pair of ports by connecting

one port to the source and measuring the output at other port while the remaining ports are connected to matched termination.

5. Determine the isolation and coupling coefficients for the given Tee using the following formula.

Isolation between port 1 and 2 is I12 = 20 log10 (V1 / V2) dB, and when matched load and detector are

interchanged I13 = 20 log10 (V1 / V3) dB The coupling coefficient by the formula C = 10-α / 20 Where α is the attenuation in db between the input (i) and detector (j) arm when the third arm is terminated in a matched load. Thus α = 10 log Pi / Pj dB where Pi is the power delivered to ‘i’ arm and Pj is the power detected in arm j. For example, when the attenuation measured between arms 1 and 2 is 3 db when arm 3 terminated in matched load, then the coupling coefficient between arms 1 and 2, C12 = 10-α / 20 = 10-3 / 20 = 0.708 db

36

E PlaneTee

H Plane Tee

Magic Tee

37

2.2.5.2 BLOCK DIARGAM Characteristics of E&H Plane Tee

2.2.5.3 TABULATION: E-Plane & H – Plane Tee

Vin = ---------mv

Nature of Tee Voltage (mv) I/P O/P

Isolation (Iij) dB

Coupling Coefficient Cij = 10Iij/20

E-Plane

1st arm

2nd C12

3rd C13

3rd arm

2nd C32

1st C31

H = Plane

1st arm

2nd C12

3rd C13

3rd arm

2nd C32

1st C31

38

2.2.5.3 TABULATION: Magic Tee

Magic Tee orientation Vi (mv) Vj (mv) Iij (dB) Cij

Input Arm-i

Output arm-j

1 2 3 4

I12 C12 I13 C13 I14 C14

2 1 3 4

I21

I23 I24

3 4 1 2

I34

I31 I32

4 3 1 2

I43

I41 I42

39

2.2.6 POST LAB QUESTIONS:

1. Microwave components used to connect branch waveguide to the main waveguide or transmission line are known as_______

2. What are series and shunt Tee. 3. How to construct a Magic Tee 4. Why phase change of 180 degree is observed in series tee in electric foeld and not in

shunt Tee. 5. Why does power equally divide between two collinear arms.

2.2.7 RESULT: Thus the power distribution in various ports of E, H and magic tee was studied . Isolations and coupling factor are determined. Lab Report




Grading



40

EXPT NO: 3

MEASUREMENT OF GUIDE WAVELENGTH AND SOURCE FREQUENCY

3.1 OBJECTIVE To measure the guide wavelength and frequency of a given microwave signal using slotted section with probe carriage. 3.2 HARDWARE REQUIRED Klystron power supply, Klystron with mount, Isolator, Frequency meter, variable attenuator, slotted section with probe carriage, slide screw tuner, matched termination, VSWR meter, CRO. 3.3 INTRODUCTION Standing waves result from the simultaneous presence of waves traveling in opposite direction in the waveguide. The ratio of the maximum of the standing - wave pattern to the minimum is defined as the standing wave ratio, designated by ρ. Thus

Standing wave ratio = currentorvoltageMinimumcurrentorvoltageMaximum

(ie) ρ = min

max

min

max

II

VV

=

The standing wave in a waveguide is due to improper termination. The standing wave ratio results from the fact that the two traveling wave components either add in phase at some points or subtract at other points. The distance between 2 successive maxima or minima is λ/2. The standing wave is unity for a purely traveling wave and is infinity for a purely standing wave. When the standing wave ratio is unity, there is no reflected line and the line is called a flat line. The SWR, cannot be defined on a lossy line as standing wave pattern changes from one position to another. On a low-loss line, SWR is constant for a defined region. For a loss less line, the ratio stays the same throughout. Since the reflected wave is defined as the product of an incident wave and its reflection coefficient, the SWR ρ is related to the reflection coefficient Γ by

ρ = Γ−

Γ+

11

and vice versa Γ = 11

+−

ρρ . This relation is used for determining the

reflection coefficient from the SWR, which is usually found from the Smith chart. Since |Γ| ≤1, the SWR is a positive real number and never less than unity, ρ ≥ 1. 3.4 PRE LAB QUESTIONS: 1. Can you measure VSWR of a circuit using magic Tee? If yes give outline in brief. 2. What is slotted section with line carriage? 3. What is the main purpose of slotted section with line carriage? 4. What is a VSWR meter? 5. Waveguides are mainly used in microwaves because_________________________

41


1. The equipments are setup as per the block diagram 2. Keep the attenuation minimum and set mode 3, after taking necessary precaution 3. With the load end terminated determine the frequency in the frequency meter. 4. Replace the termination with movable short and detune the frequency meter. 5. Move the probe along the slotted line and note down the successive minimum

positions as d1 and d2. 6. Find the guide wavelength using formula given 7. Find the frequency from the formula 8. Verify the frequency obtained with the frequency obtained in the frequency meter. 9. Repeat the procedure at different frequency settings.

3.5.2. CALCULATION i) Guide wavelength:

λg /2 = (d2-d1) λg =2(d2-d1) ii) Frequency:

f λg = 22

11cg

cλλ

+

λc = Cutoff wavelength 2a, where a is inner broad dimension of the waveguide c = 3 * 10^8 m/sec

3.5.3 BLOCK DIAGRAM



Frequency Meter

Variable Attenuator

Slotted Section

with Probe Carriage

Tunable Probe

Load

Mat

ched

Te

rmi

CRO/VSWR Meter

Matched Termination

42

3.5.4 TABULATION

S.No Frequency Setting

d1 cm

d2 cm

λg cm

fM fλg

3.6 POST LAB QUESTIONS: 1. What is tunable detector? 2. When VSWR occur in microwave communication? How it is measured? 3. In measuring VSWR, the attenuation of the receiver should be___/ Why? 3.7 RESULT:

Thus the frequency and wavelength of a given microwave signal was determined and found to be

Wavelength λ _____________

Frequency f _____________

LAB REPORT Each individual will be required to submit a lab report. Use the format specified in the


Lab cover sheet with staff verification for circuit diagram Answer the pre-lab questions Tabulate the experimental results, do the calculations and plot the required graphs Answer the post-lab questions

GRADING



43

EXPT NO: 4

IMPEDENCE MEASUREMENT BY SLOTTED LINE METHOD

4.1 OBJECTIVE To measure the impedance of an unknown load using slotted Line. 4.2 HARDWARE REQUIRED Klystron Power supply, Klystron with mount, Isolator, Frequency meter, Variable attenuator, Slotted section, Movable Short, CRO. 4.3 INTRODUCTION The simplest method for measurement of impedance at microwave frequencies is as follows. The unknown impedance is connected at the end of a slotted co axial line. Microwave power is fed from the other end of coaxial line. Unknown impedance reflects a part of this power. This reflection coefficient is measured by probing the standing wave fields in the slotted line by a suitable arrangements. The reflection coefficient is given by

P = oL

oL

ZZZZ

+−

ZL - Load impedance at any point ZO - Characteristics impedance of waveguide at operating frequency Thus if P is measured & ZO is known, ZL can be found. In general ZL is complex, both magnitude and phase of P is needed. The magnitude of P may be found from VSWR measurement.

11

+−−

=VSWR

VSWRP

The phase of P may be found by measuring the distance of first voltage minima from the load. Thus the measurement of impedance involves the measurements of VSWR and the distance of the voltage minima from the load. These measurements may be carried out by using a slotted line and probe arrangement. 4.4 PRELAB QUESTIONS

1. What are the types of methods used in microwave frequencies to measure impedance? 2. Relation-ship between S & P. 3. Define VSWR. 4. Microwave impedance measurement at different frequencies can be achieved with the

help of ______ 5. A loaded cavity has a lower value of Q factor than an unloaded cavity. Comment.

44


1 Assemble the components as per the circuit diagram

2 After making initial adjustments, mode3 is set up for operations

3 The frequency of the excited wave is found by adjusting the frequency meter for a dip in the output meter. Thereafter detune the frequency meter slightly

4 The VSWR is found for the given load (horn), by measuring Vmax and Vmin.

5 Probe carriage is moved to one reference point. With load-end terminated with the

given load, the first minima(X) is noted from the reference point.

6 The given load is replaced with short-circuit, the first minima(Y) or d1 is noted down from the same reference point. Moving the carriage further determine the successive minima(d2). i.e., With load - end short circuited, two successive minimas (d1 and d2)are found out by moving the probe carriage along the slotted waveguide line.

7 Find the shift (X-Y). Depending on whether the carriage is moved towards the load

or source, it will be positive or negative.

8 The impedance of the unknown load is found using smith chart and verified using formula.

Calculation of Impedance using Smith Chart

1 Determine VSWR of the given load from the measurement 2 Draw a VSWR Circle 3 Calculate the shift βΛl in terms of wavelength. 4 Locate the shift point from (0,0) moving clockwise (if βΛl is negative) or

anticlockwise(if βΛl is positive) on the circumference. 5 Join the point to the centre of smith chart. 6 The intersection of VSWR circle and the line gives the normalized load

impedence(ZL) Theoretical Calculations: Load impedance (ZL) is calculated from the product of normalized impedance and characteristic impedance of slotted line.

45

4.5.2 OBSERVATIONS AND FORMULA Observations

fo = For the Load Vmax = Vmin = X = (First minima from the ref. point) For the Short Y = d1 = (First minima from the ref. point) d2 = (successive minima) FORMULA: Characteristic impedance Zo

2

1

120

−

=

fofc

zoπ

Α−Α−

=)tan(()(tan)(1

ljVSWRlVSWRjZZ oL β

β

o360×

−=Α

g

YXlλ

β

fc → Cutoff frequency

fc = c/λc

λc → Cut off wavelength

λc = 2a

a → inner broad dimension of waveguide

λg = 2(d1 – d2)

VSWR = Vmax/Vmin

46

4.5.3 BLOCK DIAGRAM IMPEDANCE MEASUREMENT



Frequency Meter

Variable Attenuator

Slotted Section with

Probe Carriage

Movable short/ Load

Tunable probe

CRO

47

4.6 POSTLAB QUESTIONS

1. How will you measure the impedance of the unknown load in the microwave setup bench?

2. What are the application of smith chart? 3. What is the input impedance of the shorted line and open line?

4.7 RESULT The impedance of an unknown load was calculated the value was found out to be From smith chart: From theoretical calculations: LAB REPORT



GRADING



48

EXPT NO : 5

GAIN AND RADIATION PATTERN OF HORN ANTENNA 5.1 OBJECTIVE To obtain Gain and Radiation pattern of a Horn Antenna. 5.2 HARDWARE REQUIRED Klystron Power Supply, Klystron with mount , Isolator, Frequency meter, Fixed Attenuator Detector, Parabolic Reflector, CRO. 5.3 INTRODUCTION A horn antenna may be regarded as a flared out or opened out wave guide. A wave guide is capable of radiating radiation into open space provided the same is excited at one end and opened at the other end. However, the radiation is much greater through wave guide than the 2 wire transmission line. To overcome reflection and diffraction in the wave guide, the mouth of the waveguide is opened out which assumes the shape of a electromagnetic horn. If the wave guide is terminated by any type of horn, the abrupt discontinuity existed is replaced by a gradual transformation, then all the energy incident in forward direction in the waveguide will now be radiated, provided the impedance matching is proper. This improves directivity and reduces diffraction. If flaring is done only in one direction, then sectorial horn is produced. If flaring is done along both the walls, then pyramidal horn is obtained. By flaring the walls of the circular waveguide, a concial horn is formed. The fields inside the waveguide propagate in the same manner as in free space, but on reaching the mouth of the waveguide, these propagating fields continue to propagate in the same general direction but also starts spreading laterally and the wave front eventually becomes spherical. However this may be treated as transition region where the change over from the guided propagation to free space propagation occurs. Since the waveguide impedance & free space impedance are not equal, hence to avoid standing wave ratio, flaring of walls of waveguide is done which besides matching of impedance also provide concentrated radiation pattern(ie)greater directivity and narrower beam width. It is the flared structure that is given the name electro magnetic horn radiator. The function is to produce a uniform phase front with a larger aperture in comparison to waveguide and thus directivity is greater. If flare angle is very large, the wavefront on the mouth of the horn will be curved rather than plane. This will result in non-uniform phase distribution over the aperture, resulting in increased beam width and reduced directivity, and vice versa occurs if the flare angle is very small. The directivity of the horn antenna is given as D = 7.5 A/λ2 where A area of horn mouth opening. Horn antennas are extensively used at microwave frequencies under the condition that power gain needed is moderate.

49

PYRAMIDAL HORN ANTENNA

5.4 PRELAB QUESTIONS 1. List some of the types of antennas used in microwaves. 2. Why is a paraboloid preferred to horn at microwave frequencies? 3. Write the formula for directivity & power gain of horn antenna. 4. What are the different types of horn antenna used in microwave frequencies? 5. Comment on the radiation pattern of a practical antenna and a theoretical one. 5.5 PRECAUTIONS

1. Power flowing out of horns may damage retina of the eye so do not see directly inside the horn antenna


1. Setup the equipments as shown in fig. Keeping the axis of both antennas in same axis line

2. Energize the microwave source, and set mode3 determine input power at transmitting antenna end by connecting detector mount.

3. Connect the Receiving antenna. 4. Measure the power received at different transmitter-receiver antenna distances. 5. Make a plot of gain pattern with distance of the receiving antenna. 6. Fix the receiver antenna distance at an optimum, turn the receiving horn to the left

in 5° steps upto atleast 60° and note the corresponding output voltage. 7. Repeat the above step but this time turning the receiver to the right and note down

the readings. 8. Draw a relative power pattern on the polar graph ie, Output power versus

reception angle. 9. From the plot obtain the 3 dB beam width.

50

5.6.2 BLOCK DIAGRAM

51

Beam Width

3 dB

52

Gain Vs. Separation distance

5.6.3 TABULATION INPUT VOLTAGE VT = __________mv S. No Separation Distance (cm) Output voltage VR (mv) Gain (dB) = 20 log

(VR/VT) 1 2 3 4 5 6 Separation distance = ___________cm

Angle (degree s) VR (mv) Gain (dB) = 20 log (VR/VT) Clock wise Anticlock wise Clock wise Anticlock wise

0 5 10 15 . . . . . .

80 85 90

53

5.7 POST LAB

1. How to find an antenna Beam width? 2. Why measured values of gain and band width do not tally with theoretical values. 3. Why is the maximum signal detected when the transmitting and the receiving units

are axially aligned. Explain 4. When a reflectormeter is employed in the radiation of signals, how does it affect the

VSWR at the transmitter and the receiver. 5. List some important applications of antenna

5.8 RESULT Thus the Gain Vs. separation distance and directional pattern of the given antenna were drawn. LAB REPORT



GRADING


For the lab performance - at a minimum, demonstrate the operation of all the circuits to your staff in charge

54

EXPT NO: 6 DESIGN OF MICROSTRIP ANTENNA

6.1 OBJECTIVE To Study the gain and radiation pattern of horn antenna. 6.2 HARDWARE REEQUIRED Antenna Trainer kit Microstrip antennas CRO 6.3 INTRODUCTION

A microstrip antenna is basically a conductor printed on top of a layer of substrate with a backing ground plane as shown in figure .

The length of the radiating conductor or patch is made approximatelyλg/2, so the patch starts to radiate. In this experiment the patch will be fed by a microstrip transmission line, which usually has a 50Ώ impedance. The antenna is usually fed at the radiating edge along the width (W) as it gives good polarisation, however the disadvantages are the spurious radiation and the need for impedance matching. This is because the typical edge resistance of a microstrip antenna ranges from 150 Ώ to 300 Ώ . The design of a microstrip antenna begins by determining the substrate used for the antenna and then the dimensions of the patch. Due to the fringing fields along the radiating edges of the antenna there is a line extension associated with the patch, which is given by the formula [3]:

The effective dielectric constant (∑eff) due to the air dielectric boundary is given by [3]:

55

1

PRELAB QUESTIONS

1. What is a Microstrip antenna? 2. What are the advantages of MMIC? 3. What is an antenna. Why an oscillating dipole radiates in space isotropically?

EXPERIMENT

PROCEDURE

1. Setup the equipments as shown in fig. Keeping the axis of both antennas in same axis line

2. Energize the microwave source, and set mode 3 determine input power at transmitting antenna end by connecting detector mount.

3. Connect the transmitting antenna back. Turn the receiving horn to the left in 5° steps upto atleast 60° and note the corresponding voltage.

4. Repeat the above step but this time turning the receiver to the right and notedown the readings.

5. Draw a relative power pattern ie, o/p vs angle. 6. From diagram 3 dB beam width is determined.

6.5.3 TABULATION

INPUT VOLTAGE VT =

Angle (degree s) VR (mv) Gain (dB) = 20 log (VR/VT) Clock wise Anticlock wise Clock wise Anticlock wise

56

6.5.4 RADIATION PATTERN

POSTLAB QUESTIONS

1. When a reflector is employed in the radiation of signals, how does it affect the VSWR

at the transmitter and signal at the detector. 2. What is an isotropic radiator 3. Define directivity and Beam width

RESULT

Thus the Gain and Radiation pattern of Horn antenna is obtained LAB REPORT



GRADING


For the lab performance - at a minimum, demonstrate the operation of all the circuits to your staff in charge.

57

EXPT. NO: 7.1 D.C. CHARACTERISTICS OF LED

OBJECTIVE

To study the Voltage Vs Current (V-I) and Power Vs Current ( P-I) characteristics of the given LED.

HARDWARE REQUIRED 1. OFT Power Supply 2. A digital multi-meter 3. LED Module 4. Benchmark Fiber Optic Power Meter 5. Bare fiber adaptor-Plastic 6. 1.25m Plastic fiber

7.1.3 INTRODUCTION

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.

The LED is based on the semiconductor diode. When a diode is forward biased

(switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. Symbol of LED

Like a normal diode, the LED consists of a chip of semiconducting material

impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.

58

The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.

LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.

LEDs must have a resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is 12V or less. 7.1.4 PRELAB QUESTIONS

1. How to change the colour of an LED? 2. What are the two different types of LED structures? 3. What do you know about the spectral width of LED? 4. Give the expression that relates bandgap energy and wavelength. 5. How does an LED differ from a normal PN junction diode.

LED Module Setup

7.1.5 EXPERIMENT 7.1.5.1 PROCEDURE Connect the OFT power supply properly to the module using the DIN-DIN cable provided with the power supply. Turn the multi-turn pot to its minimum position and switch ON the module.

59

1 Measure the voltage across the resistor R1 (180 ohms and calculate the current through the LED lf which is given as

i. 1f = V1/180

2 Now measure the voltage VLED across the LED and note down.

3 Remove the dummy adaptor cap from the power meter PD exposing the large area

photo-detector. Mount the bare fiber adaptor-plastic over the PD. Carefully hold the LED source very close to the photo-detector window perpendicular to it to couple all the optical power output P of the LED. Calculate the power in mW and note it down which is given as

P0 (mW) = 10 P(dBm)/10

4 Turn the potentiometer clockwise direction slightly towards the maximum till you get a convenient reading V and repeat the steps 1 to 3 and tabulate.

4. Repeat step 4 till the potentiometer reaches its maximum position and plot the graph for VLED VS If and If VS P0). The graphs should be similar to the one shown in fig.1 and fig. 2 respectively.

5. Calculate the E-O conversion efficiency `η’ of the LED from the plotted graph `If’ VS P0 which is given as

η = P0 / If

6. Unscrew the self locking cap in the LED without removing it completely and insert the 1.25 m plastic fiber into the cap. Now tighten the cap. Remove the ST adaptor from the power meter PD and mount the Bare fiber adaptor – plastic on to the PD. Insert the other end of the plastic fiber to this adaptor Repeat above experiment but the optical measurement with a plastic fiber and plastic fiber adaptor in Power meter, instead of measuring it was explained in step 3.

Plot the optical power values and what do you see in the plots and what happens to the E-O conversion efficiency? 7.1.5.2 TABULATION Wavelength of the LED: _____________nm

S. No. V1 V

If mA

VLED V

P dBm

P0 mW

0.1 0.2 0.3 .. .. ..

1.1 1.2 1.3

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7.1.5.3 MODEL GRAPH

Figure 1. Voltage Vs Current graph

Figure 2. Power Vs Current graph

7.1.6 POST LAB

1. List the specifications of good LED materials. 2. What is lambertian pattern? 3. Discuss about fiber LED coupling. 4. On what factor does the speed of LED depend on? 5. What is OLED?

7.1.7 RESULT Thus the DC characteristics of LED has been studied and plotted.

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LAB REPORT



GRADING


For the lab performance - at a minimum, demonstrate the operation of all the circuits

to your staff incharge

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EXPT. NO: 7.2

D.C. CHARACTERISTICS OF PIN PHOTODIODE

7.2.1 OBJECTIVE To study the characteristics of the given Photo Detector at zero-bias, Forward Bias and Reverse Bias conditions. 7.2.2 HARDWARE NEEDED

1. OFT power supply 2. A digital multi-meter 3. PD Module 4. Benchmark Fiber Optic Power Source 5. Benchmark Fiber Optic Power Meter 6. 1m Patch cord (PSTO-PC-1) 7. 1 M.10K resistors 8. 10K, 6.8K, 4.7K, 3.3K, 3.9K & 2.2K resistors (for reverse bias) 9. Ambient light arrester

7.2.3 INTRODUCTION

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.

Photodiodes are similar to regular semiconductor diodes except that they may be

either exposed (to detect vacuum UV or X-rays) or packaged with a window or optical fiber connection to allow light to reach the sensitive part of the device. Many diodes designed for use specifically as a photodiode will also use a PIN junction rather than the typical PN junction.

A photodiode is a PN junction or PIN structure. When a photon of sufficient energy

strikes the diode, it excites an electron, thereby creating a mobile electron and a positively charged electron hole. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced. Photovoltaic mode

When used in zero bias or photovoltaic mode, the flow of photocurrent out of the device is restricted and a voltage builds up. The diode becomes forward biased and "dark current" begins to flow across the junction in the direction opposite to the photocurrent. This mode is responsible for the photovoltaic effect, which is the basis for solar cells—in fact, a solar cell is just a large area photodiode. Photoconductive mode

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In this mode the diode is often reverse biased, dramatically reducing the response time at the expense of increased noise. This increases the width of the depletion layer, which decreases the junction's capacitance resulting in faster response times. The reverse bias induces only a small amount of current (known as saturation or back current) along its direction while the photocurrent remains virtually the same. The photocurrent is linearly proportional to the illuminance. Critical performance parameters of a photodiode include: responsivity

The ratio of generated photocurrent to incident light power, typically expressed in A/W when used in photoconductive mode. The responsivity may also be expressed as a quantum efficiency, or the ratio of the number of photogenerated carriers to incident photons and thus a unitless quantity.

dark current

The current through the photodiode in the absence of light, when it is operated in photoconductive mode. The dark current includes photocurrent generated by background radiation and the saturation current of the semiconductor junction. Dark current must be accounted for by calibration if a photodiode is used to make an accurate optical power measurement, and it is also a source of noise when a photodiode is used in an optical communication system. noise-equivalent power

(NEP) The minimum input optical power to generate photocurrent, equal to the rms noise current in a 1 hertz bandwidth. The related characteristic detectivity (D) is the inverse of NEP, 1/NEP; The NEP is roughly the minimum detectable input power of a photodiode.

When a photodiode is used in an optical communication system, these parameters contribute to the sensitivity of the optical receiver, which is the minimum input power required for the receiver to achieve a specified bit error ratio 7.2.4 PRELAB QUESTIONS

1. What is photo detector? 2. List some of the operating performance and requirements of optical detectors. 3. What is impact ionization? 4. Draw the simple model of a photo detector receiver. 5. What is the figure of merit of a photodetector?

7.2.5 PRECAUTION Before switching between the bias modes, it is recommended to switch OFF the PD module and the power supply. This ensures that the voltages are not reversed or applied quickly to the PD. Failure to do so may result in permanent damage to PD and its power supply.

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7.2.6 EXPERIMENT 7.2.6.1 PROCEDURE Photo-detector at Zero bias Connect of OFF power supply to the module using the DIN-DIN cable provided with the power supply. Set the bias switch to the zero bias configuration (Bias switch moved to the top most position). Turn the bias voltage varying pot in the PD module to its minimum position and switch ON the module. The zero bias LED lights up. The module at the zero bias configuration is shown in Fig.1. The photodiode is given no bias voltage. The current induced by the photo-detector due to the incident optical power on to it, flows through the load resistor.

Figure 1 : PD with zero bias configuration

1. Put 1 M ohm resistor across VL. 2. Connect the ST connector end of the patch cord supplied with the module to the

power source. 3. Set the Power source in CW mode and to give maximum output power (refer

Benchmark power source manual on how to adjust the power). Connect 1m patch cord between source and meter (use bare fiber adaptor – plastic at the power meter end) and measure this optical power P and adjust the power in source such that it reads-18dBm approx. Note down this power.

4. Slightly unscrew the black colored cap of the PD to loosen it without removing it from the connector assembly. Remove the patch cord from the power meter and gently push the fiber into the black cap until it is held in place. Now tighten the black cap by screwing it back. The fiber will now be held firmly in place. Now measure the voltage across V1.

5. Vary the optical power P from -18dBm approx in steps of 5dBm.To reduce the power more than what the power source can attenuate remove the ST connector of the patch cord slightly that is connected to the power source. This gives the natural attenuation. Ensure that this loose connector is not disturbed while connecting and removing the patch cord between meter and PD. May be you can stick the cable on to the table with a sticking tape near the source. Tabulate the readings as follows:

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7.2.6.2 TABULATION

S.No. Power P dBm

Power P0 µW VL Volts

Iz µA

IZ = VL/1 x 106

1. Plot the graph P vs IZ The graph should be similar to the one shown in fig.2 7.2.6.3 MODEL GRAPH

Figure 2 Power Vs Current graph Photo-detector at Forward bias Connect the OFT power supply to the module using the DIN-DIN cable provided with the power supply. Set the bias switch to the forward bias configuration (Bias switch moved tot eh middle position). Turn the bias voltage varying pot in the PD module to its minimum position and switch ON the module. The forward bias LED lights up.

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The module at the forward bias configuration switches the photodiode to a basic configuration as shown in Fig.3. The photodiode is given forward bias voltage.

Figure 3 : PD with forward bias configuration

1. Put 10K resistor across VL. 2. Adjust the potentiometer and fix the bias voltage at 10V 3. Connect the ST connector end of the patch cord supplied with the module to the


Benchmark power source manual on how to adjust the power). Connect 1m patch cord between source and meter (use bare fiber adaptor – plastic at the power meter end) and measure this optical power P and adjust the power in source such that it reads – 18dBm approx. Note down this power.

5. Slightly unscrew the black colored cap of the PD to loosen it, without removing it from the connector assembly. Remove the patch cord from the power meter and gently push the fiber into the black cap until it is held in place. Now tighten the black cap by screwing it back. The fiber will now be held firmly in place. Now measure the voltage VL.

6. Vary the optical power P from – 18 dBm to -40 dBm approx in steps of 5dBm. To reduce the power more than what the power source can attenuate, remove the ST connector of the patch cord slightly that is connected to the power source. This gives the natural attenuation. Ensure that this loose connector is not disturbed while connecting and removing the patch cord between meter and PD. May be you can stick the cable on to the table with a sticking tape near the source. Tabulate the readings as follows:

Forward Voltage: -------------- V If = VL/10 x 103

S.No. Power P

dBm Power P0

µW VL V

If Ma

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Figure 4 Power Vs Current graph

7. Plot the graph P vs If. The sample graph is shown in fig.4

8. Now fix the power launched as – 20 dBm.

9. Vary the bias voltage from 2V to 10V by adjusting the potentiometer and measure VL.

10. Tabulate the values and plot the graph VBIAS VS IL. The sample graph is shown in

Fig.5 Incident Power = ----------------dBm

S.No. Bias Voltage

VBIAS V VL V

If mA

Fig. 5 Voltage Vs. Current graph

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Photo-detector at Reverse Bias Connect the OFT power supply to the module using the DIN-DIN cable provided with the power supply. Set the bias switch to the reverse bias configuration (Bias switch moved to the bottom most position). Turn the bias voltage varying pot in the PD module to its minimum position and switch ON the module. The reverse bias LED lights up. The module at the reverse bias configuration switches the photodiode to a basic configuration as shown in Fig.6. The photodiode is given reverse bias voltage. The current induced by the photodiode due to the incident optical power on to it, flows through the load resistor.

Figure 6: PD with reverse bias configuration

1. Put 10K resistor across VL. 2. Adjust the potentiometer and fix the bias voltage at 10V. 3. Connect the ST connector end of the patch cord supplied with the module to the


Benchmark power source manual on how to adjust the power). Connect 1m patch cord between source and meter (use bare fiber adaptor plastic at the power meter end) and measure this optical power P and adjust the power in source such that it reads – 18dBm approx. Note down this power.

5. Slightly unscrew the black colored cap of the PD to loosen it, without removing it from the connector assembly. Remove the patch cord from the power meter and gently push the fiber into the black cap until it is held in place. Now tighten the black cap by screwing it back. The fiber will now be held firmly in place. Now measure the voltage VL.

6. Vary the optical power P from – 18dBm to -40dBm approx in steps of 5dBm. To reduce the power more than what the power source can attenuate, remove the ST connector of the patch cord slightly that is connected to the power source. This gives the natural attenuation. Ensure that this loose connector is not disturbed while connecting and removing the patch cord between meter and PD. May be you can stick the cable on to the table with a sticking tape near the source. Tabulate the readings as follows:

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Reverse Voltage = _______________V Ir = VL/10 x 103

S.No. Power P dBm

Power P µW

VL V

IR mA

7. Plot the graph P vs IR. The sample graph is shown in figure 7.

Figure 7 Power Vs Current graph

8. Now fix the power launched as – 20 dBm. 9. Vary the bias voltage from 2V to 10V by adjusting the potentiometer and measure VL. 10. Tabulate the values

Incident Power = _____________ dBm

S.No. Bias voltage VBIAS( V)

VL (V)

IR (mA)

Rλ (A/W)

η (%)

11. For each value of the bias voltage and current calculate the value of the responsivity

from the formula. Are all the Rλ values approximately same? What do you infer from this? Rλ = VL/(RL* PS) A/W

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where PS is the power in W.

12. From the average value of Rλ calculate the value of the quantum efficiency from the

formula η = Rλ h ν / e x 100%

where h = 6.64 x 10-34 JS, is the Planck’s constant ν = C/λ = 3 x 108 / 850 x 10-9 Hz , is frequency of the incident photons e = 1.6 x 10-19 Coulombs, is the electric charge Repeat the above steps for various values of RL 6.8K, 4.7K, 3.9K & 2.2K. Leakage Characteristics of Photo-detector

One among the important characteristics of a photodiode is its leakage characteristics when it is reverse biased. Since the leakage current through the photo-detector is normally very less, increased bias voltage and higher value of RL is used in the module at the reverse bias configuration. The basic configuration of the PD module in leakage characteristics is shown in Fig.8

Figure 8: PD with leakage characteristics Caution Before switching between the bias modes, it is recommended to switch OFF the PD module and the power supply. This ensures that the voltages are not reversed or applied quickly to the PD. Failure to do so may result in permanent damage to PD and its power supply. Connect the OFT power supply to the module using the DIN-DIN cable provided with the power supply. Set the bias switch to the reverse bias configuration (Bias switch moved to the bottom most position). Turn the bias voltage varying pot in the PD module to its minimum position and switch ON the module. The reverse bias LED lights up.

1. Put 10 M resistors across VL. 2. Adjust the potentiometer and fix the bias voltage as 10V.

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3. Screw in the free end of the ambient light arrester unit supplied with the module to the PD. This is done to avoid ambient light falling on the Photodiode.

4. Measure the voltage VL. 5. Repeat the above procedure for various values of bias voltage and tabulate. 6. Plot the graph using Vbias and Idark and the sample graph is shown in fig.9

Idark = VL / RL|| Rm A

where Rm is the multi-meter input impedance which is normally 10Mohm.

S.No. Vbias (Volts)

VL (Volts)

Idark (nA)

Figure 9. Voltage Vs Dark Current graph POSTLABQUESTIONS

1. Photo detector is a square law device. Justify. 2. What is quantum efficiency? 3. What is dark current? 4. Define noise equivalent power. 5. What is the cutoff wavelength of a photodetector ? Give the expression.

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RESULT Thus the V-I characteristics of PIN photodiode has been studied and following parameters are determined. Rλ = η =

LAB REPORT



GRADING


For the lab performance - at a minimum, demonstrate the operation of all the circuits to your staff incharge.

73

EXPT. NO 8 DC CHARACTERISTICS OF LASER DIODE

8.1 OBJECTIVE To study the V-I and P-I characteristics of LASER diode. 8.2 HARDWARE REQUIRED

1. OFT power supply (OFT power supply can be used for LD module) 2. A digital multi-meter 3. Benchmark LD unit 4. Benchmark LD drive module with its accessories 5. Benchmark Fiber Optic Power meter with ST adaptor 6. Mounting Posts

8.3 INTRODUCTION

A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electric current. These devices are sometimes referred to as injection laser diodes to distinguish them from (optically) pumped laser diodes, which are more easily manufactured in the laboratory.

A laser diode, like many other semiconductor devices, is formed by doping a very thin layer on the surface of a crystal wafer. The crystal is doped to produce an n-type region and a p-type region, one above the other, resulting in a p-n junction, or diode. When an electron and a hole are present in the same region, they may recombine or "annihilate" with the result being spontaneous emission — i.e., the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron and hole states involved. (In a conventional semiconductor junction diode, the energy released from the recombination of electrons and holes is carried away as phonons, i.e., lattice vibrations, rather than as photons.) Spontaneous emission gives the laser diode below lasing threshold similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating.

In the absence of stimulated emission (e.g., lasing) conditions, electrons and holes may coexist in proximity to one another, without recombining, for a certain time, termed the "upper-state lifetime" or "recombination time" (about a nanosecond for typical diode laser materials), before they recombine. Then a nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission. This generates another photon of the same frequency, travelling in the same direction, with the same polarization and phase as the first photon. This means that stimulated emission causes gain in an optical wave (of the correct wavelength) in the injection region, and the gain increases as the number of electrons and holes injected across the junction increases. The spontaneous and stimulated emission processes are vastly more efficient in direct bandgap semiconductors than in indirect bandgap semiconductors; therefore silicon is not a common material for laser diodes.

As in other lasers, the gain region is surrounded with an optical cavity to form a laser. In the simplest form of laser diode, an optical waveguide is made on that crystal surface, such that the light is confined to a relatively narrow line. The two ends of the crystal are cleaved to

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form perfectly smooth, parallel edges, forming a Fabry-Perot resonator. Photons emitted into a mode of the waveguide will travel along the waveguide and be reflected several times from each end face before they are emitted. As a light wave passes through the cavity, it is amplified by stimulated emission, but light is also lost due to absorption and by incomplete reflection from the end facets. Finally, if there is more amplification than loss, the diode begins to "lase".

8.4 PRE LAB QUESTIONS

1. What are multiquantum well lasers. 2. List the different types of Laser modes. 3. Expand (Nd: YAG) LASER = __________. 4. Mention the important transition process demonstrated by Einstein for LASER action. 5. In comparison to LED, Laser has-----------------spectral width .

8.5 PRECAUTION

Laser radiation. Avoid direct eye or skin exposure to laser beam while setting up the system or conducting experiments. Always view only the reflected rays while setting up the system or while conducting experiments. Laser Diode (LD) module Setup


1. Setup the LD module as shown in the figure. 2. Keep the potentiometer at the minimum position. Turn ON the power to the module. 3. Measure the voltage V1 between ground and the point. Calculate the current hrough

the LD ILD which is given is ILD = V1/R1 Note: Scientech module R1= 100, Benchmark module R1 = 24

4. Now without changing any voltage or the multi-turn post position, measure the optical power output P of the LD.

Calculate the power in mW which is given as P0(mW) = 10P(dBm)/10

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5. Increase the current through LD by turning the multi-turn pot clockwise direction slightly towards the maximum till you get a convenient reading V1 and repeat the steps 2 to 5 and tabulate them as shown below.

6. Repeat step 4 till multi-run pot reaches its maximum position and plot the graph for VLD VS ILD and ILD VS P0.

7. The threshold current of the LD can be found out from the P-I characteristics graph. Note down the current from the P-I graph at which there is a sharp rise in the optical output power. This is the threshold current of the LD

8.6.2 TABULATION

S.No. V1 Volts

ILD mA

VID Volts

P dBm

P0 mW

1 .

10

8.6.3 MODEL GRAPH

Figure 1 P-I characteristics curve

Figure 2 V-I characteristics curve

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8.7 POSTLAB

1. When light amplification occurs in LASER? 2. Laser is preferred over LED in --------------- fiber. 3. State the threshold conditions for laser oscillations. 4. List some of the major advantages of LASER over LED’s 5. What are the sources of noise in LASER?

8.8 RESULT : The P-I and V-I characteristics of a Laser Diode were studied and plotted the threshold current was found to be _________. LAB REPORT



GRADING



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EXPT NO: 9.1

MEASUREMENT OF NUMERICAL APERTURE OF OPTICAL FIBER 9.1.1 OBJECTIVE:

To measure the numerical aperture of a given optical fiber at 650 nm 9.1.2 HARDWARE REQUIRED: Optical fiber Numerical Aperture measurement Kit 9.1.3 INTRODUCTION:

Numerical aperture (NA) of a fiber is a measure of the acceptance angle of light in the fiber. Light which is launched at angles greater than this maximum acceptable angle does not get coupled to propagating modes in the fiber and therefore does not reach the receiver at the other end of the fiber. The Numerical aperture is useful in the computation of optical power coupled from an optical source to the fiber, from the fiber to a photo detector and between two fibers. 9.1.4 PRELAB QUESTIONS

1. Define angle of acceptance 2. If the angle of acceptance is 30 degree, what is the value of numerical aperture. 3. What is the formula for numerical aperture. 4. What is lens coupling and butt coupling 5. How to relate snell’ s law with Numerical Aperture. DIAGRAM

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9.1.5 PROCEDURE:

1. Insert one end of the fiber into the numerical aperture measurement kit as shown in the figure. Adjust the fiber such that its tip is 10 mm from the screen

2. Gently tighten the screw to hold the fiber firmly in the place. 3. Connect the other end of the fiber to the LED Source through a connector. The fiber

will project a circular patch of red light onto the screen. Let d be the distance between the fiber tip and the screen. Now measure the diameter of the circular patch of red light in two perpendicular directions (BC and DE in figure). The mean radius of the circular patch is given by

X= (DE + BC)/4

4. Carefully measure the distance d between the tip of the fiber and the illuminated screen (OA) as

shown in figure. The Numerical aperture of the fiber is given by

NA= Sin θ = X/(d2 + X2)1/2

5. Repeat steps 1 to 4 for different values of d, compute the average value of Numerical aperture.

9.1.6 TABULATION:

S.No Radius of the

circular path XDistance d NA= Sin θ = X/(d2 + X2)1/2

Average:

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9.1.7 POST LAB QUESTIONS

1. Why do single mode fibers have larger bandwidth as compared to that of multimode fibers?

2. What is pulse dispersion? 3. Define total internal reflection. 4. Can optical fiber conduct electricity? Why? 5. At what wavelength does silica fiber show minimum attenuation? 6. Give the relation between bandwidth and Numerical aperture (NA).

9.1.8 RESULT Thus the numerical aperture of an fiber optic cable is determined. LAB REPORT



GRADING



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EXPT NO: 9.2

MEASUREMENT OF PROPAGATION LOSS IN OPTICAL FIBER

9.2.1 OBJECTIVE

To measure the propagation loss in an optical fiber. 9.2.2 HARDWARE REQUIREMENT: Kit(Fiber link-D) 1m, 3m Fiber Cable Link Patch cords Power supply 9.2.3 INTRODUCTION:

Optical fibers are available in different variety of materials. These materials are usually selected by taking into account their absorption characteristics of different wavelengths of light. Losses are introduced in fiber due to various reasons. As light propagates from one end of fiber to another end, part of it is absorbed in the material exhibiting absorption loss. Also part of the light is reflected back or in some other direction from the impurity particles present in the material contributing to the loss of the signal at the other end of the fiber. It is known as Propagation loss 9.2.3 PRELAB QUESTIONS

1. What are the different types of dispersion 2. What is group velocity dispersion 3. What is the difference between attenuation and dispersion 4. How to increase the signal strength in optical fibers 5. Define attenuation coefficient. 6. What are the reasons for optical signal loss in fiber?

FORMULA:

Propagation loss- Attenuation in dB/m α = ln(Po1/Po2) /(l2-l1)

where Po1---- Output power level (µw) at the end of the fiber of length l1 (m) P02 ---- Output power level (µw) at the end of the fiber of length l2 (m)

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MODEL GRAPH

9.2.4 PROCEDURE:

1. Connect the power supply cables with proper polarity to kit. While connecting this, ensure that the power supply is OFF.

2. Connect the AMP O/P as a constant signal to the TX I/P using a patch cord. 3. You will measure the light output using SIGNAL STRENGTH section of the kit. The

loss will be more for a longer piece of fiber. In order to measure the loss in the fiber you first need a reference of how much light goes into the fiber from the Light transmitter, You will use the short piece of fiber to measure this reference.

4. Switch on the power supply. Connect the short piece of fiber between the TX and RX of the kit. Adjust the transmitter level until the signal strength reads 6, this will be your reference value. Now connect the long piece of fiber instead of the short piece. What reading do you get? Loss in optical fiber system is usually measured in dB. Loss of fiber itself is measured in dB/meter.

5. Subtract the length of the short fiber from the length of the long fiber to get the difference in the fiber lengths (4m-1m). The extra length of 3 m is what created the extra loss you measured. Then take the signal strength reading you obtained for the loss of the long fiber directly from the power meter.

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9.2.6 TABULATION:

S No

Length of the optical fiber cable

(m)

OpticalPower Signal Strength

Propagation Loss

dBm

mW

9.2.7 RESULT Thus the propagation loss in fiber optic cable is measured. LAB REPORT



GRADING



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EXPT NO: 9.3 MEASUREMENT OF BENDING LOSS IN AN OPTICAL FIBER

9.3.1 OBJECTIVE To measure the bending loss of a fiber optic cable 9.3.2 HARDWARE REQUIREMENTS: Kit (Fiber Link-D) 1 m or 3 m fiber cable Spindles to wound the fiber around it Power supply. 9.3.3 INTRODUCTION: Though the fibers are good at bending, each time the fiber is bent, a little light is lost. This experiment will measure how much of this light is lost for different sizes of bends. 9.3.4 PRELAB QUESTIONS

1. What is microbending and macrobending loss? 2. What is total internal reflection? 3. Define Snell’s law 4. Differentiate reflection, refraction and diffraction. MODEL GRAPH

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9.3.5 EXPERIMENT 9.3.5.1 PROCEDURE:

1. Connect the power supply cables with proper polarity to kit. While connecting this, ensure that the power supply is OFF.

2. Connect the AMP O/P as a constant signal to the TX I/P using a patch cord.You will measure the light output using SIGNAL STRENGTH section of the kit.

3. Switch on the power supply. Connect the long piece of fiber between the TX and RX of the kit so there are no sharp bends in the fiber between them

4. Adjust the transmitter level until the signal strength reads 6, this will be your reference value. Now take the portion of the fiber and loop it into the spindle and note the signal strength from the power meter, which give the optical signal power in dBW/m.

5. Repeat it for various diameters of the spindle and for various numbers of bend on the spindle and measure the corresponding signal strength from the optical power meter.

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9.3.5.2 TABULATION: i) No. of turns Vs Signal Strength: Diameter of Spindle: ___________________

S No Bending Signal Strength in mW 1 No Bend 2 1 3 2 4 3

ii) Radius of the Spindle Vs Signal Strength:

S No Radius of spindle Signal Strength in mW

1 2 3 4

9.3. 6 POST LAB QUESTION:

1. How light is propagated inside a fiber? 2. Give the merits and demerits of Optical fiber cable. 3. In optical fiber propagation loss increases or decreases with the increase in length of

the fiber cable?

9.3.7 RESULT Thus the bending loss in fiber optic cable is determined

LAB REPORT



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EXPT NO: 10 SETTING UP A FIBRE OPTIC ANALOG LINK

10.1 OBJECTIVE:

1. To set up an 850nm fiber optic analog link. 2. To observe the linear relationship between the input and received signal. 3. To measure the bandwidth of link 4. To observe the effect of gain control received signal

1.0.2HARDWARE REQUIRED:

1. Optical fiber trainer kit 2. Two channel 20Mhz oscilloscope 3. Function generator(1Hz – 10MHz)

10.3INTRODUCTION:

This experiment is designed to familiarize the user with optical fiber trainer kit. An analog fiber optic link is to be set up in this experiment. The preparation of the optical fiber for coupling light in to it and the coupling of the fiber to the LED and detector are quite important. The LED used is an 850nm LED. The fiber is a multimode fiber with a core diameter of 1000µm. The detector is simple PIN detector.

The LED optical power output is directly proportional to the current driving the LED.

Similarly, for the PIN diode, the current is proportional to the amount of light falling on the detector. Thus, even though the LED and the PIN diode are non-linear devices, the current in the PIN diode is directly proportional to the driving current of the LED. This makes the optical communication system a linear system. 10.4 PRELAB QUESTIONS 1. What is point ot point link? 2. Define link power buget. 3. What is rise time budget? 4.What is the transmission frequency in optical fiber? 5.In Communication link what is the need for repeater? 10.5 PROCEDURE:

1. Set the switch SW8 to the analog position. Switch the power on. The power on switch is located at the top right hand corner.

2. Feed a 1V p-p sinusoidal signal at 1KHZ from a function generator, to the analog in post P11 using the following procedure:

i) Connect a BNC-BNC cable from the function generator to the BNC socketI/03 ii) Connect the signal post I/03 to the analog in post P11 using a patch cord. 3. With this, the signal from the function generator is fed through to the analog in signal

post P11 from theI/03 BNC socket. 4. Connect one end of the 1m fiber to the LED source. 5. Observe the light output at the other end of the fiber.

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6. Feed a 5V p-p rectangular signal at 0.5HZat P11. Observe the signal on the oscilloscope. Now observe the intensity of the light output at the other end of the fiber.

7. Now, feed a 5V p-p sinusoidal signal at 0.5Hz at P11. Observe the variation in the brightness of the light output at the other end of the fiber as a driving signal varies sinusoidally.

8. Thus light intensity is modulated by an input rectangular of sinusoidal signal. 9. Connect the other end of the fiber to the detector PD1 in the optical Rx1 block. 10. Feed a sinusoidal wave of 1KHz, 1V p-p from the function generator of P11. The

PIN detector output signal is available at P32 in the optical Rx1 block. Vary the input signal level driving the LED and observe the received signal at the PIN detector. Plot the received signal peak to peak amplitude with respect to the input signal peak to peak amplitude.

11. The Pin detector signal at P32 is amplified, with amplifier gain controlled by the GAIN potentiometer. With a 3Vp-p input signal at P11, observe P31 as a gain potentiometer is varied.

12. Measure the bandwidth of the link as follows: Apply a 2V p-p sinusoidal signal at P11 and observe the output at P31. Adjust GAIN such that no clipping takes place. Vary the frequency of input signal from 100Hz to 5MHz and measure the amplitude of the received signal. Plot the received signal amplitude as a function of frequency. Note the frequency range for which the response is flat. 10.6 LAYOUT DIAGRAM

88

Fig 1 Gain control

Fig 2 Signal at P31

TABULATION Input : Sine Wave Vi= ___________Vp-p

S.No. Frequency (Hz)

Output Voltage Vo (V)

Gain (dB) G = 20 log (Vo/Vi)

1 2 . .

14 15


1. What is Optical Bandwidth and Electrical Bandwidth? Give their relation. 2. What is the maximum bandwidth the analog link can support 3. What are the important blocks of point to point links? 4. What is the function of Optical receiver?

89

10.8 RESULT Thus the analog Link is established using the Fiber optic Kit. The bandwidth of the link is found to be Optical bandwidth = Electrical bandwidth =

LAB REPORT Each individual will be required to submit a lab report. Use the format specified in the



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90

EXPT NO: 11 SETTING UP A FIBER OPTIC DIGITAL LINK

11.1 OBJECTIVE:

1. To set up a 650nm and 850nm digital link 2. To measure the maximum bit rates supportable on thee links.

11.2 HARDWARE REQUIRED:

Optical fiber trainer kit Two channel 20 MHz oscilloscope Function generator (1Hz – 10MHz)

11.3 INTRODUCTION:

The OFT can be used to set up two fiber optic digital links, one at a wavelength of 650nm and the other at 850nm. Led1, in the optical TX1 block, is an 850nmLED, and LED2, in the optical TX2 block, is a 650nm LED.

PD1, in the optical Rx1 block, is a PIN detector which gives a current proportional to

the optical power falling on the detector. The received signal is amplified and converted to a TTL signal using a comparator. The GAIN control plays a crucial role in this conversion.

PD2, in the optical Rx2 block, is another receiver which directly gives out a TTL

signal. Both the PIN detectors can receive 650nm as well a 850nm signals, though their sensitivity is lower at 650nm.

11.4 PRELAB QUESTIONS

1. What is a TTL signal? 2. Compare Analog and Digital transmitter 3. Define sensitivity 4. What are the modulation formats used in optical Communication 5. What is a Trans impedance receiver.

11.5 PROCEDURE:

1. Set the switch SW8 to the digital position. 2. Connect a 1m optical fiber between LED1 and the PIN diode PD1. 3. Ensure that the shorting plug of jumper JP2 is across the posts B&A1. 4. Feed a TTL signal of about 20KHz from the function generator to post B of S6.

Observe the received analog signal at the amplifier post P31 on channel 1 of the oscilloscope. Note the signal at P31 gets cutoff above 3.5V. Increase and decrease the Gain and observe the effect.

5. Observe the received signal at post A of S26 on channel 2 of the oscilloscope while still observing the signal at P31 on channel 1.

91

6. Set the gain such the signal at P31 is about 2V. Observe the input signal from the function generator on channel 1 and the received TTL signal at post A of S26 on channel 2. vary the frequency of the input signal and obser the output response.

7. Repeat steps 4,5 and6 with 3m fiber. 8. 9. 11.6 LAYOUT DIAGRAM

92

COMPARATOR TO CONVERT RECEIVED SIGNAL INTO A TTL SIGNAL


1. What is a Digital Link 2. What are the advantages of digital link over analog link? 3. What is a high impedance receiver?

11.8 RESULT Thus the Digital link is established in fiber optic link.

93

LAB REPORT



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94

EXPT NO:12 RF AMPLIFIER

OBJECTIVE To perform the PSPICE simulation of RF amplifier circuit .

SOFTWARE REQUIRED ORCAD 9.2 12.3 INTRODUCTION An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high output Power(P1dB) compression, good return loss on the input and output, good gain, and optimum heat dissipation. An RF amplifier has variable resistors which represent impedance. The reactance of an inductor and the capacitance varies as frequency changes. As the frequency increases, inductive reactance increases and capacitive reactance will be equal. The frequency will depend upon the value of the inductor and capacitor. If they are connected as a parallel LC circuit, we have an ideal frequency RF amplifier. Being a high power device and having large gain it gives large output signal power while requiring very small amount of RF power which is normally available from any commercial signal generator. Because of this the power amplifier (or the amplifier chain) itself is commonly known as "The RF source" or sometimes "The Transmitter". The basic applications of RF Power Amplifier includes driving to another high power source, Driving an transmitting antenna, Microwave heating and Exciting resonant cavity structures. Among these applications one for driving transmitter antenna is well known because of the growing field of communication and information technology. The transmitter receivers are not only used for voice and data communication but are also used for weather reporting and forecast (in the form of a RADAR). Microwave or RF heating is an industrial application which is also benefiting our homes in the form of "Microwave Oven". Exciting cavity resonators is quite a research lab and industrial application of an RF source. Particle accelerators utilize RF sources extensively. 12.4 PRELAB QUESTIONS

1. What is PSPICE 2. What is meant by transient analysis 3. List some applications of RF amplifier 4. What are inline amplifiers. 5. What is amplification Bandwidth.

12.5 PROCEDURE

1. Open the Pspice AD Lite software 2. Create a new text file 3. Type the program and save with an extension .cir 4. To execute the program go to debug menu and select run.

95

5. If any errors, modify the netlist accordingly. 6. If no errors, go to trace menu and add the required trace component i.e., 7. output node voltage.

12.6 CIRCUIT DIAGRAM

C3

1n

C20.01uF

C30.01uF

L10.101uH

L20.101uH

R1100K

RE500KR2

100K

R4

100K

Vin

0Adc1VAC

Q1

Q2N2222

RC750K

CE1uF

C3

1nF

R61k

0

VCC

12.7 NETLIST:

VCC 1 0 DC 10V R1 1 3 100K RC 3 0 100K R3 1 7 0.75K R4 5 6 0.100K RL 8 0 1K RE 4 0 0.5K C1 7 2 0.01UF C2 6 0 0.01UF C3 2 8 1NF C4 4 0 1NF C5 6 3 1NF L1 7 2 0.101UF L2 6 0 0.1.132UH Q1 2 3 4 Q2N2222 V1 5 0 AC 50MV SIN(0 59MV 1KHZ) .LIB .TRAN/OP 50NS 5US .AC DEC 10 10HZ 50MEGHZ .PROBE .END

96

12.8 SIMULATED OUTPUT


1. What is AC analysis 2. What is frequency anlaysis 3. Define Fidelity 4. What is delayed AGC 5. What is squelch circuit.

12.10 RESULT Thus the RF amplifier program has been written, compiled and simulated using PSPICE simulator. LAB REPORT



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97

EXPT NO: 13 FREQUENCY RESPONSE OF IF AMPLIFIER

13.1 OBJECTIVE To perform the PSPICE simulation of RF amplifier circuit . 13.2 SOFTWARE REQUIRED ORCAD 9.2 13.3 INTRODUCTION

An NE 592 acts as an IF Amplifier in which dc coupling occurs between mixer and amplifier. It is practical because different supply voltages such as 6v and 12v are used. The voltage at the differential input is about 4.5v. A narrow Band pass filter for the intermediate frequency is achieved using only one crystal as the reactive element. Maximum IF gain is at the crystal series response where the crystal impedance is low.

Unlike the broadband tunable radio-frequency amplifier, the intermediate-frequency

amplifier is designed to operate over a narrow band of frequencies centered about a dedicated fixed frequency (the intermediate frequency); therefore, the intermediate-frequency amplifier can be an extremely efficient stage. If the intermediate frequency is on the order of a few megahertz, the undesirable images may be efficiently rejected, but narrow-band filtering for noise and adjacent-channel-signal rejection is difficult and expensive because of the high ratio of the intermediate frequency to the bandwidth of the intermediate-frequency amplifier. If the intermediate frequency is much smaller, say, on the order of a few hundred kilohertz, then inexpensive and more selective filters are possible that can separate the desired signal from closely packed adjacent signals, but they do not reject images very well. A high-quality double-conversion receiver combines the best of both approaches by cascading both high- and low-frequency intermediate-frequency stages that are separated by a second fixed-frequency mixer.

The superheterodyne structure is common for television, ground-based and satellite

communications, cell phones, ground-based and airborne radar, navigation, and many other receivers. The intermediate-frequency amplifier function is ubiquitous. See Amplifier, Radio-frequency amplifier 13.4 PRELAB QUESTIONS

1. What is the need for Intermediate Frequency conversion. 2. What is heterodyning 3. What is Beat frequency oscillator 4. What is diversity reception

13.5 PROCEDURE

1. Open the Pspice AD Lite software 2. Create a new text file 3. Type the program and save with an extension .cir

98

4. To execute the program go to debug menu and select run. 5. If any errors, modify the netlist accordingly. 6. If no errors, go to trace menu and add the required trace component i.e., 7. output node voltage.


C1

50nF

R122K

RE500KR2

10KVin

0Adc50mV

Q2

Q2N2222

RC1K

CE500nF

C2

1nF

RL1k

VCC

0

C3L3.01uF

13.7 NETLIST

VCC 1 0 DC 6V R1 1 2 22K R2 2 0 10K RC 1 3 1K RE 4 0 500 RL 6 0 1K CE 4 0 50NF C1 2 5 50NF C2 3 6 50NF L 6 0 0.0122MH C 6 0 0.01UH Q1 3 2 Q2N2222 V 5 0 AC 50MV .MODEL TRANS NPN BF=400 .LIB .AC DEC 15 100KHZ 600KHZ .OP .PROBE .END

99

13.8 SIMULATED OUTPUT

13.9 POST LAB QUESTIONS 1. What is the need for heterodyning. 2. What is Image frequency rejection. 3. What is a double conversion receiver 4. What is the need for Beat frequency oscillator 13.10 RESULT

Thus the PSPICE circuit for an IF amplifier is simulated and its frequency response is verified. LAB REPORT



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100

EXPT NO: 14 AMPLITUDE MODULATION

14.1 OBJECTIVE To design and simulate a PSPICE circuit for Amplitude modulation and calculate the modulation index for various levels of modulating voltages. 14.2 SOFTWARE REQUIRED ORCAD 9.2 14.3 INTRODUCTION

Amplitude modulation (AM) is the modulation method used in the AM radio

broadcast band. In this system the intensity, or amplitude, of the carrier wave varies in accordance with the modulating signal. When the carrier is thus modulated, a fraction of the power is converted to sidebands extending above and below the carrier frequency by an amount equal to the highest modulating frequency. If the modulated carrier is rectified (see rectifier) and the carrier frequency filtered out, the modulating signal can be recovered. This form of modulation is not a very efficient way to send information; the power required is relatively large because the carrier, which contains no information, is sent along with the information.

In a variant of amplitude modulation, called single sideband modulation (SSB), the

modulated signal contains only one sideband and no carrier. The information can be demodulated only if the carrier is used as a reference. This is normally accomplished by generating a wave in the receiver at the carrier frequency. SSB modulation is used for long-distance telephony (such as in the amateur radio bands) and telegraphy over land and submarine cables. 14.4 PRELAB QUESTIONS 1. What is the difference of plotting the output using TRAN and AC. 2. Which statement is used to get more than one plot. 3. How much power is transmitted if the modulation index of an AM wave is changed from

1 to 0. 4. What is the application of VSB AM. 14.5 PROCEDURE

• Open the Pspice AD Lite software • Create a new text file • Type the program and save with an extension .cir • To execute the program go to debug menu and select run. • If any errors, modify the netlist accordingly. • If no errors, go to trace menu and add the required trace component i.e., • output node voltage.

101


14.7 NETLIST

VIN 1 0 AC 10MV SIN (0 10MV 1KHZ) VCC 7 0 DC 15V RS 1 2 500 R1 7 3 47K R2 3 0 5K RC 7 4 10K RE 5 0 2K RL 6 0 20K C1 2 3 1UF C2 4 6 1UF CE 5 0 10UF Q1 4 3 5 Q2N2222 .PLOT TRAN V(4) V(6) V(1) .PLOT AC VM(6) VP(6) .TRAN/OP 50 US 2MS AC DEC 10 1HZ 10KHZ .PROBE .END

102

14.8 OUTPUT 14.9 POST LAB QUESTIONS

1. What is meant by transient response 2. Expand SPICE 3. What are the simulation parameters.

14.10 RESULT: Thus a PSIPCE circuit for amplitude modulation is simulated . LAB REPORT



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Microwave & Optical Communication Lab Manual - SRM

Documents

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modern engineering

optical rx1

lab cover

micro strip

d2 x2

circuit diagram

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