student observation manualvemu.org/uploads/lecture_notes/20_01_2020_793958863.pdf · 2020. 1....

ANALOG COMMUNICATION SYSTEMS LAB

II/IV B. TECH., II SEMESTER

STUDENT OBSERVATION MANUAL

DEPARTMENT

OF

ELECTRONICS & COMMUNICATION ENGINEERING

VEMU INSTITUTE OF TECHNOLOGY Tirupati - Chittoor Highway Road, P. Kothakota, Chittoor- 517 112.

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY ANANTAPUR

VEMU INSTITUTE OF TECHNOLOGY

DEPT. OF ELECTRONICS AND COMMUNICATION ENGINEERING

Vision of the institute

To be a premier institute for professional education producing dynamic and vibrant force of

technocrat with competent skills, innovative ideas and leadership qualities to serve the society

with ethical and benevolent approach.

Mission of the institute

Mission_1: To create a learning environment with state-of-the art infrastructure, well equipped

laboratories, research facilities and qualified senior faculty to impart high quality technical

education.

Mission_2: To facilitate the learners to foster innovative ideas, inculcate competent research and

consultancy skills through Industry-Institute Interaction.

Mission_3: To develop hard work, honesty, leadership qualities and sense of direction in rural

youth by providing value based education.

Vision of the Department

To become a centre of excellence in the field of Electronics and Communication Engineering and

produce graduates with Technical Skills, Research & Consultancy Competencies, Life-long

Learning and Professional Ethics to meet the challenges of the Industry and Society.

Mission of the Department

Mission_1: To enrich Technical Skills of students through Effective Teaching and Learning

practices for exchange of ideas and dissemination of knowledge.

Mission_2: To enable the students with research and consultancy skill sets through state-of-the

art laboratories, industry interaction and training on core & multidisciplinary technologies.

Mission_3: To develop and instill creative thinking, Life-long learning, leadership qualities,

Professional Ethics and social responsibilities among students by providing value based

education.

Programme Educational Objectives ( PEOs)

PEO_1: To prepare the graduates to be able to plan, analyze and provide innovative ideas to

investigate complex engineering problems of industry in the field of Electronics and

Communication Engineering using contemporary design and simulation tools.

PEO_2: To provide students with solid fundamentals in core and multidisciplinary domain for

successful implementation of engineering products and also to pursue higher studies.

PEO_3: To inculcate learners with professional and ethical attitude, effective communication

skills, teamwork skills, and an ability to relate engineering issues to broader social context at

work place.

Programme Outcome (POs)

PO_1: Engineering knowledge: Apply the knowledge of mathematics, science, engineering

fundamentals, and an engineering specialization to the solution of complex engineering problems.

PO_2: Problem analysis: Identify, formulate, review research literature, and analyze complex

engineering problems reaching substantiated conclusions using first principles of mathematics,

natural sciences, and engineering sciences.

PO_3: Design/development of solutions: Design solutions for complex engineering problems

and design system components or processes that meet the specified needs with appropriate

consideration for the public health and safety, and the cultural, societal, and environmental

considerations.

PO_4: Conduct investigations of complex problems: Use research-based knowledge and

research methods including design of experiments, analysis and interpretation of data, and

synthesis of the information to provide valid conclusions.

PO_5: Modern tool usage: Create, select, and apply appropriate techniques, resources, and

modern engineering and IT tools including prediction and modeling to complex engineering

activities with an understanding of the limitations.

PO_6: The engineer and society: Apply reasoning informed by the contextual knowledge to

assess societal, health, safety, legal and cultural issues and the consequent responsibilities relevant

to the professional engineering practice.

PO_7: Environment and sustainability: Understand the impact of the professional engineering

solutions in societal and environmental contexts, and demonstrate the knowledge of, and need for

sustainable development.

PO_8: Ethics: Apply ethical principles and commit to professional ethics and responsibilities and

norms of the engineering practice.

PO_9: Individual and team work: Function effectively as an individual, and as a member or

leader in diverse teams, and in multidisciplinary settings.

PO_10: Communication: Communicate effectively on complex engineering activities with the

engineering community and with society at large, such as, being able to comprehend and write

effective reports and design documentation, make effective presentations, and give and receive

clear instructions.

PO_11: Project management and finance: Demonstrate knowledge and understanding of the

engineering and management principles and apply these to one’s own work, as a member and

leader in a team, to manage projects and in multidisciplinary environments.

PO_12: Life-long learning: Recognize the need for, and have the preparation and ability to

engage in independent and life-long learning in the broadest context of technological change.

Programme Specific Outcome (PSOs)

PSO_1: Higher Education: Qualify in competitive examinations for pursuing higher education

by applying the fundamental concepts of Electronics and Communication Engineering domains

such as Analog & Digital Electronics, Signal Processing, Communication & Networking,

Embedded Systems, VLSI Design and Control Systems etc..

PSO_2: Employment: Get employed in allied industries through their proficiency in program

specific domain knowledge, specialized software packages and Computer programming or

become an entrepreneur.

(15A04407) ANALOG COMMUNICATION SYSTEMS LAB

B.Tech II-II Sem. (E.C.E.)

Course Outcomes:

C228.1: Analyze behavior of analog modulations systems in the time domain

C228.2: Analyze behavior of pulse modulations systems in the time domain

C228.3: Illustrate the characteristics of radio receiver and antenna measurements

List of Experiments: (All Experiments are to be conducted)

1. Amplitude modulation and demodulation.

2. Frequency modulation and demodulation.

3. a. Characteristics of Mixer.

b. Pre-emphasis & de-emphasis.

4. Pulse amplitude modulation & demodulation.

5. Pulse width modulation & demodulation

6. Pulse position modulation & demodulation.

7. Radio receiver measurements – sensitivity selectivity and fidelity. 8. Measurement of half power beam width (HPBW) and gain of a half wave dipole

Antenna.

9. Measurement of radiation pattern of a loop antenna in principal planes.

Equipment required for the Laboratory:

1. Regulated Power Supply equipments 0 – 30 V

2. CROs 0 – 20 M Hz.

3. Function Generators 0 – 3 M Hz

4. RF Signal Generators 0 – 1000 M Hz

5. Multimeters

6. Required electronic components (active and passive) for the design of experiments

from 1 - 7

7. Radio Receiver Demo kits or Trainers.

8. RF power meter frequency range 0 – 1000 MHz 9. Spectrum Analyzer

10. Dipole antennas (2 Nos.) 850 MHz – 1GHz

11. Loop antenna (1 no.) 850 MHz – 1GHz

VEMU INSTITUTE OF TECHNOLOGY::P.KOTHAKOTA NEAR PAKALA, CHITTOOR-517112

(Approved by AICTE, New Delhi & Affiliated to JNTUA, Anantapuramu) Department of Electronics &Communication Engineering

LIST OF EXPERIMENTS TO BE CONDUCTED

PART-A

List of Experiments: (All Experiments are to be conducted)

1. Amplitude modulation and demodulation.

2. Frequency modulation and demodulation.

3. a. Characteristics of Mixer.

b. Pre-emphasis & de-emphasis.

4. Pulse amplitude modulation & demodulation.

5. Pulse width modulation & demodulation

6. Pulse position modulation & demodulation.

7. Radio receiver measurements – sensitivity selectivity and fidelity.

8. Measurement of half power beam width (HPBW) and gain of a half wave

dipole Antenna.

9. Measurement of radiation pattern of a loop antenna in principal planes.

PART-B

ADVANCED EXPERIMENTS

1. Digital Phase Detector.

2. Balanced modulator and synchronous detector.

CONTENTS

S.NO. NAME OF THE EXPERIMENT PAGE

NO

1. AMPLITUDE MODULATION & DEMODULATION 1-5

2. FREQUENCY MODULATION & DEMODULATION 6-9

3(a) CHARACTERISTICS OF MIXER 10-13

3(b) PRE-EMPHASIS & DE-EMPHASIS 14-17

4. PULSE AMPLITUDE MODULATION AND DEMODULATION 18-21

5. PULSE WIDTH MODULATION AND DEMODULATION 22-25

6. PULSE POSITION MODULATION & DEMODULATION 26-29

7. RADIO RECEIVER MEASUREMENTS – SENSITIVITY,

SELECTIVITY AND FIDELITY

30-35

8. MEASUREMENT OF HALF POWER BEAM WIDTH (HPBW)

AND GAIN OF A HALF WAVE DIPOLE ANTENNA

36-39

9. MEASUREMENT OF RADIATION PATTERN OF A LOOP

ANTENNA IN PRINCIPLE PLANES

40-43


10. DIGITAL PHASE DETECTOR 44-46

11. BALANCED MODULATOR & SYNCHRONOUS DETECTOR 47-50

DOS & DONTS IN LABORATORY

1. While entering the Laboratory, the students should follow the dress code

(Wear shoes, White Apron & Female students should tie their hair back).

2. The students should bring their observation note book, practical manual,

record note book, calculator, necessary stationary items and graph sheets if

any for the lab classes without which the students will not be allowed for

doing the practical.

3. All the equipments and components should be handled with utmost care. Any

breakage/damage will be charged.

4. If any damage/breakage is noticed, it should be reported to the instructor

immediately.

5. If a student notices any short circuits, improper wiring and unusual smells

immediately the same thing is to be brought to the notice of technician/lab in

charge.

6. At the end of practical class the apparatus should be returned to the lab

technician and take back the indent slip.

7. Each experiment after completion should be written in the observation note

book and should be corrected by the lab in charge on the same day of the

practical class.

8. Each experiment should be written in the record note book only after getting

signature from the lab in charge in the observation note book.

9. Record should be submitted in the successive lab session after completion of

the experiment.

10. 100% attendance should be maintained for the practical classes.

PRECAUTIONS

1. Avoid loose connections.

2. Make sure that the connections are correct.

3. Take readings without parallax error.

4. Do not apply stress on the components.

5. Do not use the components beyond their specifications.

SCHEME OF EVALUVATION

S NO

DATE

NAME OF EXPERIMENT

MARKS AWARDED

Sign. Obser.

(10M)

Viva voce

(10M)

Total

(20M)

1 Amplitude Modulation & Demodulation

2 Frequency Modulation & Demodulation

3(a) Characteristics of Mixer

3(b) Pre-Emphasis & De-Emphasis

4 Pulse Amplitude Modulation and

Demodulation

5 Pulse Width Modulation and Demodulation

6 Pulse Position Modulation & Demodulation

7 Radio Receiver Measurements –

Sensitivity, Selectivity and Fidelity

8 Measurement Of Half Power Beam

Width (HPBW) and Gain of A Half

Wave Dipole Antenna

9 Measurement of Radiation Pattern of A

Loop Antenna in Principle Planes

10 Sampling Theorem Verification


1. Digital Phase Detector

2. Balanced Modulator and Synchronous

Detector

Signature of Lab In-charge

ANALOG COMMUNICATION SYSTEMS LAB II B.Tech II SEMESTER

VEMU INSTITUTE OF TECHNOLOGY, DEPARTMENT OF ECE Page 1

3. CIRCUIT DIAGRAM:

1. AMPLITUDE MODULATION & DEMODULATION

Aim: To generate amplitude modulated wave and determine the percentage modulation. To ge

nerate demodulated wave using envelope detector and plot the graph.

Apparatus Required:

1. Amplitude Modulation and Demodulation Trainer

2. Function Generator

3. Oscilloscope

4. Connecting Wires

5. Probes



1. AIM: To generate Amplitude modulated signal and determine the modulation index

2. APPARATUS REQUIRED:

1. Amplitude Modulation and Demodulation Trainer kit

2. Oscilloscope (osc-503; 30MHz))

4. Connecting Wires

5. BNC Probes

4. CIRCUIT OPERATION: Modulation is defined as the process of changing the characteristics of a

high frequency carrier signal in accordance with a low frequency message signal. The base band

signal is referred to as the modulating signal or message signal and the output of the modulation

process is called as the modulation signal. Amplitude modulation is defined as the process of

changing the amplitude of the carrier signal in accordance with the base band signal.

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

following two requirements are satisfied

(1). the carrier frequency fc must be much greater than the highest frequency components fm of

the message signal m (t) i.e. fc >> fm

(2) The modulation index must be less than unity. if the modulation index is greater than unity,

the carrier wave becomes over modulated

5. PROCEDURE:

1. As the circuit is already wired, the circuit has to be traced according to circuit diagram.

2. Connect the trainer to the main and switch on the power supply.

3. Measure the output voltage of the regulated power supply circuit +_ 12 V

4. Observe the output of RF and AF signal generator using CRO and note the RF voltage

approximately

300 Vp-p of 1 MHz frequency and AF voltage as 10 Vp-p of 2 KHz frequency

Modulation: 1. Now connect RF and AF signals to the respective input of modulator as shown in figure.

2. Initially check both the signals at zero levels

3. Connect one of the input of oscillator to modulator output and other input to AC signal



Calculations:

Adjust RF signal amplitude of AF signal and observe the amplitude modulated wave at output.

Note the percentage modulation for different values of signal

Percentage modulation = B-A/B+A*100

B=Minimum amplitude

A=Maximum amplitude

Observe 100% amplitude modulation and over modulation by varying amplitude of AF signal.

Demodulation:

1. Now connect the modulator output to the demodulator input as shown in figure

2. Observe the demodulated signal at output of demodulator at approximately 50% modulation

using oscilloscope.

3. Compare it with the original AF signal.

4. If the detected signal is same as the AF signal applied then there is no information is lost in the

process of modulation.

5. If AM wave is to be observed of differ external signal generator to the modulator and observe

the amplitude modulated wave at different frequencies.



6. EXPECTED WAVE FORMS:



7. RESULT:

AF INPUT:

Amplitude____________ VP-P & Frequency _______________KHz.

RF INPUT:


MODULATION INDEX:

Case I: In Under modulation ma=_________________

Case II: In over modulation ma= __________________

8. CONCLUSIONS:

1. Amplitude of the carrier is varied in accordance with the instantaneous values of the modulating

signal.

2. The modulating signal can be recovered faithfully when carrier is either under or critically

modulated.

3. In the case of envelope detractor, the detection of modulating signal mainly depends on Resistor,

Capacitor & Modulation index.

9. VIVA QUESTIONS:

1. Define modulation and write need for modulation.

2. Write the expression for AM signal in the case of single tone, multi tone & band of frequencies?

3. Draw the spectrum of the AM signal in the case of single tone, multi tone & band of frequencies?

4. Write the power and current relation in AM signal?

5. What is BW and power efficiency of AM signal?



3. CIRCUIT DIAGRAM:

FM modulator:

FM demodulator:



2. FREQUENCY MODULATION & DEMODULATION

1. AIM: 1.To generate frequency modulated signal and determine the modulation index and

bandwidth for various values of amplitude and frequency of modulating signal.

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


1. Physitech Frequency Modulation and Demodulation Trainer (phy-138)

2. Function Generator (phy-103m, 20 to 20MHz)

3. Oscilloscope (osc-503; 30MHz))

4. Connecting Wires

5. BNC Probes

4. CIRCUIT OPERATION:

Frequency modulation:

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

amplitude of the modulating signal, is called "Frequency Modulation".

S(t) = Ac cos (wct +ө(t))

Where ө(t) = km ᶴ m(t) dt Km is the frequency sensitivity

MODULATION INDEX:

In FM modulation index is the ratio of frequency deviation (fd) to modulating frequency (fm).

It is denoted by m or β

Β = FD / FM

5. PROCEDURE:

1. Switch on the FM experimental board.

2. Connect Oscilloscope to the FM O/P and observe that carrier frequency at that point without

any A.F. input.

3. Connect around 3 KHz to 7 KHz sine wave (A.F. signal) with 2.4 V AF signal to the input of

the frequency modulator (At AF input).

4. Now observe the frequency modulation output on the 1st channel of on CRO and

Adjust the amplitude of the AF signal to get clear frequency modulated wave form.



6. MODEL WAVEFORMS:

5. Vary the modulating frequency (A.F Signal) and amplitude and observe the effects on the

modulated waveform.

6. Connect the FM o/p to the FM i/p of De-modulator.

7. Vary the potentiometer provided in the demodulator section.

8. Observe the output at demodulation o/p on second channel of CRO.

9. Draw the demodulated wave form

7. RESULT:

AF INPUT:


RF INPUT:


8. CONCLUSIONS:

1. Frequency of the carrier signal is varied in accordance with the message signal.

2. Modulation index in WBFM is greater than 1.



9. VIVA QUESTIONS:

1. Write the expression for FM signal in the case of single tone, multi tone & band of frequencies?

2. Draw the line spectrum of FM signal the case of single tone.

3. Define frequency deviation and write the Carlson formula.

4. Compare NBFM and WBFM.

5. Compare AM and FM.



3. CIRCUIT DIAGRAM:



3(a). CHARACTERISTICS OF MIXER

1. AIM: To observe the characteristics of a Frequency Mixer and to measure its conversion gain.


1. Physitech Frequency mixer trainer kit.

2. Function generator - (2)

3. C R O

4. B N C Probes

5. Connecting wires


A mixer is a non linear circuit with two input signals and one output signal. The output signal

is a distorted combination of the two input signals. Let the two input frequencies, given be F x and

because of non linear distortion, the output signal contains signal frequencies and their harmonics. In

addition to the harmonics, a frequency signal with frequency = (Fx-Fy) and also appear across output

terminals.

A Mixer circuit finds its application in a super heterodyne receiver in converting a RF signal

into an IF signal with help of a local oscillator. If RF signal frequency RF is 1000 KHz, by choosing

local oscillator frequency to 1455KHZ the difference frequency becomes 455 KHz, which is the

intermediate frequency for radio receiver. Other frequencies such as 1455 kHz, 1000 kHz and 2455

kHz can be filtered out with help of low pass filter. But for getting the clear output without distortion

low frequencies in the range of 85 kHz -115 kHz.



5. MODEL WAVEFORMS:



6. Procedure:

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

2. Apply 99 kHz signal to the base of the transistor and 100 kHz, signal to the emitter of the

transistor.

3. Observe a sinusoidal signal with 1kHz frequency across output terminals

4. Vary Base signal frequency and note down O/P amplitude. The output reaches to a Maximum

value at a particular frequency.

Calculate conversion gain.

Conversion gain = (O/P Voltage)/ (Base signal voltage)

5. Plot conversion for gain and base signal frequency.

7. RESULT:

INPUT 1

AMPLITUDE_______________V P-P& FREQUENCY______________KHz

INPUT 2

AMPLITUDE_______________ V P-P &FREQUENCY______________ KHz

MIXER OUTPUT:

AMPLITUDE_______________ V P-P &FREQUENCY______________ KHz

8.CONCLUSIONS:

1.Mixer generates sum or difference frequencies

2.It can be used in heterodyne receivers.

9. VIVA QUESTIONS:

1. What is need of mixer in heterodyne receivers?

2. What is linear and non linear operation in mixer?

3. How the sum and difference frequencies are generated using mixer circuit?

4. what is the need of filter in mixer circuit?

5.which type of filters are used in mixer?



3. CIRCUIT DIAGRAMS:



3(b). PRE-EMPHASIS & DE-EMPHASIS

1. AIM:

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

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


1. Resistors (10 K, 33K,1K)-----Each one

2. Capacitors (10F, 0.1-F)

3. Transistor BC547

4 Function generators---------------------- 01

5. CRO-----------------------------------------01

6. Connecting Wires

7. Connecting wires.


The noise has an effect on the higher modulating frequencies than on the lower ones. Thus, if

the higher frequencies were artificially boosted at the transmitter and correspondingly cut at the

receiver, an improvement in noise immunity could be expected, thereby increasing the SNR ratio.

This boosting of the higher modulating frequencies at the transmitter is known as pre-emphasis and

the compensation at the receiver is called de-emphasis.



5. Tabular column: Pre-emphasis:

De-emphasis:

S.NO

Frequency

(KHz)

Input voltage

Vin (V)

Output voltage Vo

(V)

Gain (dB)= Vin/ Vo

20 log Vin/ Vo

1.

2.

3.

4.

5.

6.

7.

8.

S.NO

Frequency

(KHz)

Input voltage

Vin (V)

Output voltage Vo

(V)

Gain (dB)= Vin/ Vo

20 log Vin/ Vo

1.

2.

3.

4.

5.

6.

7.

8.



6. Procedure:

1. Study theory of operation thoroughly

2. Connect the trainer to mains and switch on the power supply

3. Measure the output of required power supply 12 V

4. Observe the output of AF Generator using frequency range of 0.66 Vp-p provided to select the

frequency range

5. Connect the AF signal to the required amplitude level

6. Adjust the AF signal to required amplitude level

7. Plot the graph between frequency output voltage

8. Plot the graph and note the frequency at which the output voltage is 70.7% of input voltage and

compare with theoretical frequency

9. Repeat the steps from 5 to 10 for the de-emphasis network

10. Theoretical frequency is given by 1/ 2πRC

8. RESULT:

Time Constant of Pre-Emphasis & De-Emphasis τ = ___________Sec

Cut off frequency of Pre-Emphasis & De-Emphasis fc = _________KHz

9.CONCLUSION:

It is used to imporove signal to noise ratio at audio frequency range in FM system.

10. VIVA QUESTIONS:

1. What is need of pre emphasis and de emphasis in FM system?

2. What is time constant of pre emphasis and de emphasis in audio applications?

3. Pre emphasis and De emphasis in are not used in AM system Why?

4. What are the cutoff frequencies of pre emphasis and de emphasis?

5. Write the transfer function pre emphasis and de emphasis?



3. CIRCUIT DIAGRAM:



4. PULSE AMPLITUDE MODULATION AND DEMODULATION

1. AIM: To generate the Pulse Amplitude modulated signal and demodulated signals.


1. Pulse amplitude modulation trainer.

2. Signal generator

3. CRO

4. BNC probes, CONNECTING WIRES.

4. Circuit Operation:

PAM is the simplest form of the data modulation. The amplitude of uniformly spaced

pulses is varied in proportion to the corresponding sample values of a continuous message m(t).A

PAM waveform consists of a sequence of list-topped pulses. The amplitude of each pulse corresponds

to the value of the message signal x(t) at the leading edge of the pulse.

The pulse amplitude modulation is the process in which the amplitude of regularity spaced

rectangular pulses vary with the instantaneous sample values of a continuous message signal in a one-

one fashion.

PAM is of two types:

1. Double polarity PAM - This is the PAM wave which consists of both positive and Negative

pulses.

2. Single polarity PAM - This consists of PAM wave of only either negative or positive pulses. In

this the fixed dc level added to the signal to ensure single polarity signal.



5. MODEL WAVEFORMS:



6. PROCEDURE:

1. Refer the block diagram and carryout the connections and switch settings.

2. Connect the power supply with proper polarity to the kit DCL-08 and switch it on.

3. Select 16 KHz sampling frequencies by jumper JP1.

4. Connect the 1 KHz, 2Vp-p sine wave signal generated on board to PAM IN POST.

5. Observe the amplitude pulse modulation output at PAM OUT POST.

6. Short the following posts with connecting chords provided as shown in block diagram

PAM OUT and PAM IN,PAM OUT and FIN IN

7. Keep the amplifier gain control potentiometer is to be maximum completely clockwise.

8. Observe the pulse amplitude demodulated signal at FIL OUT, which is same as the input signal.

9. Repeat the experiment for different input signals and sampling frequencies.

7 . RESULT:

Message Signal:

Amplitude_______________V P-P & Frequency______________KHz

Carrier Signal:

Amplitude_______________ V P-P & Frequency______________ KHz

PAM Signal:


Demodulated Signal:


8. CONCLUSIONS:

1. Amplitude of the discrete signal is varied in accordance with the message signal.

2. PAM can be used in PCM

9. VIVA QUESTIONS:

1. What are different sampling techniques are used to generate PAM signal?

2. What is the BW of PAM signal?

3. What is Aperture affect in PAM?

4. What is the minimum sampling frequency required to generate PAM?

5. What are the applications of PAM?



3. CIRCUIT DIAGRAM:



5. PULSE WIDTH MODULATION AND DEMODULATION

1. AIM: To generate the pulse width modulated and demodulated signals


1. Pulse width modulation and Demodulation Trainer.

2. CRO

3. BNC probes and Connecting Wires


In PWM, the samples of the message signal are used to vary the duration of the individual

pulses. Width may be varied by varying the time of occurrence of leading edge, the trailing edge or

both the edges of the pulse in accordance with modulating wave. It is also called Pulse Duration

Modulation.

Pulse Width Modulation

PWM controls the variation of duty cycle of square wave (with fundamental frequency )

according to the input modulating signal .Here the amplitude variation of the modulation signal is

reflected in the ON period variation of square wave. Hence, it is a technique of V to T conversion.

Pulse Width Demodulation

The input signal is demodulated, so the ON time of the signal is changing according to the

modulating signal .In this demodulation technique during ON time of PWM signal one counter is

enabled .At the end of ON time, counter gives a particular count, which directly corresponds to the

amplitude of input signal. Then this count is fed to DAC. The output of DAC corresponds to the

amplitude of the input signal. Thus train of varying pulse widths gives varying count values and

accordingly DAC give outputs, which is directly proportional to amplitude of input signal. This is

then filtered to get original signal .Thus at the output we get the original modulating signal extracted

from PWM wave.



5. MODEL WAVEFORMS:



6. PROCEDURE:

1. Switch on pulse width modulation and Demodulation trainer

2. Observe the clock generator output and modulating signal output

3. Connect the Clock output to the clock input terminal of PWM modulation.

Observe the same clock on channel of a dual trace CRO.

4. Trigger the CRO with respect to CH1

5. Apply the available DC voltage of 8V to 12 V from any external RPS

6. Observe the PWM output on CH2.

7. If we observe the modulating signal is given to the observe how the PWM

signal are varying for AC modulating signal.

8. In this case we have to trigger the CRO with respect to modulating voltage.

8. RESULT:

Message Signal:


Carrier Signal:


PWM Signal:

Amplitude_______________ V P-P

Demodulated Signal:


9. CONCLUSIONS:

1. Width of the discrete signal is varied in accordance with the message signal.

2. PWM can be used to control the speed of the electric motor.

10. VIVA QUESTIONS:

1. What are different techniques to generate PWM?

2. What is the difference between discrete and continuous wave modulation?

3. What is the minimum sampling frequency of PWM?

4. Compare PAM, PPM &PWM.

5. What are the applications of PWM?



3. CIRCUIT DIAGRAM:

Pulse Position Modulation -(PPM)-Modulation :

Pulse Position Modulation (PPM)-De Modulation :

PPM Input

AF Input

Clk Input



6. PULSE POSITION MODULATION & DEMODULATION

1. AIM: To generate pulse position modulation and demodulation signals and to study the effect of

amplitude of the modulating signal on output.


1. Pulse position modulation and demodulation trainer.

2. CRO

3. BNC probes and Connecting Wires


In Pulse Position Modulation, both the pulse amplitude and pulse duration are held constant but

the position of the pulse is varied in proportional to the sampled values of the message signal. Pulse

time modulation is a class of signaling technique that encodes the sample values of an analog signal

on to the time axis of a digital signal and it is analogous to angle modulation techniques. The two

main types PTM are PWM and PPM. In PPM the analog sample value determines the position of a

narrow pulse relative to the clocking time. In PPM rise time of pulse decides the channel bandwidth.

It has low noise interference.

Modulating a digital signal's pulse position is straightforward. Each delay between pulses is

represented by a zero or a one. A small delay is represented by zero; a long delay is represented by

one. The duration of delay varies according to the system's requirements. For example, in a Sony

infrared remote protocol that uses PPM, a short delay of 1.2 meters per second is represented by zero,

and a longer delay of 1.8 meters per second is represented by one.PPM is very sensitive to external

interferences. Although interference is usually impossible to detect, it can cause complete data

corruption. Therefore, PPM is not used in cable communications, which are subject to

electromagnetic interference. PPM is, however, used in fiber optic cables, which are not subject to

interference.



5. OUTPUT WAVEFORMS:



6. PROCEDURE:

1. Switch on PPM modulator and demodulator trainer.

2. Connect the clock input to the Pin 2 of IC 555.

3. Connect the AF output to the pin 5 of IC 555.

4. Observe the PPM Output at pin 3 of second IC 555 on CRO.

5. Connect the PPM Output to the PPM Input of PPM demodulation.

6. Observe the demodulated Output on CRO.

7. RESULT:

Message Signal:


Carrier Signal:


PPM Signal:

Amplitude_______________ V P-P

Demodulated Signal:


8. CONCLUSIONS:

1. Position of the discrete signal is varied in accordance with the message signal.

2. PPM can be obtained from PWM.

9. VIVA QUESTIONS:

1. Define PPM?

2. What is the minimum sampling frequency of PPM?

3. What is the difference between discrete and continuous wave modulation?

4. What are the applications of PPM?

5. What are the merits & demerits of PTM over PAM?



3. CIRCUIT DIAGRAM:



7. RADIO RECEIVER MEASUREMENTS – SENSITIVITY, SELECTIVITY AND FIDELITY

1. AIM: To study the Sensitivity, Selectivity and Fidelity of a radio receiver.

2. EQUIPMENT REQUIRED:

1. Trainer Kit

2. CRO

3. Probes

4. Patch cards


Sensitivity:

The sensitivity of a receiver is its ability to amplify weak signals. The sensitivity of a receiver is the

minimum voltage required at the input of the receiver to produce the original signal.

It is often defined in terms of the voltage that must be applied to the receiver input terminals to give a

standard output power, measured at the output terminal.

For an AM broadcast receivers, several relevant quantities have been standardized. The most

important factors determining sensitivity of a receiver is the Gain of the receiver.

Selectivity:

A parallel tuned circuit has its greatest impendence at resonance and decreased at higher and lower

frequencies. If a tuned circuit is induced in the circuit design of an amplifier, it results in the

amplifiers, which offers more gain at the frequency of resonance and reduced amplification above

and below this frequency. This is called selectivity.

The radio receiver is tuned to a frequency of 820 KHz and at this frequency the amplifer

provides a gain of five.

5. PROCEDURE:

Sensitivity:

1. Refer to the figure and carry out the following connections

2. Connect the output of function generator section (ACL-AM) outpost to the input of balance

modulator (ACL-AM) signal post.

3. Connect the output of VCO (ACL-AM) outpost to the input of balance modulator (ACL-AM)

carrier in post.

4. Connect the power supply with proper polarity to the kit ACL-AM & ACC-AP, while

connecting. Ensure that power supply is OFF.



6. TABULAR COLUMN:

For sensitivity:

Carrier

Freq.(KHz) VCO

600 700 800 900 1000 1100 1200 1300

Local OSC.

Freq.(KHz) 1050 1150 1250 1350 1450 1550 1650 1750

Output of

Mixer(V)



Function generator:

Sine wave about 0.5 VP-P Frequency about 1KHz

VCO level about 2 VP-P Frequency about 600 KHz

Switch on 1500 KHz

Balanced modulator:

Carrier null completely rotates clockwise or counter clockwise so that the modulator is

unbalanced and an AM signal without suppressed carrier is obtained across the output which

amplitude is 200 VP-P.

Local Oscillator:

ACL-AD is 1050 KHz, 2 V

5. Connect load oscillator outpost to LOIN of micro-mixer section.

6. Connect balance modulator-1 OUT to RFIN of micro-section in ACL-AD.

7. Connect the mixer output to IFIN of first IF amplifier in ACL-AD , connect IF OUT of first IFIN1

and IF OUT 2 of first IF to IN2 of second IF amplifier.

8. Observe the modulated signal envelope which corresponds to the waveform of the modulating

signal at output of the balanced modulator of ACC-AM. Connect the oscilloscope to the IN &

OUT POST of envelope detector and detect the AM signal.

9. Check that detected signal follows the behavior of AM signal envelope, vary the amplitude of

the balanced modulator output and check the corresponding variations of demodulated signal.

10. Adjust the input to RFIN POST by varying the output of AM in such a way that you should get

minimum detected output of about 0.3 V at the output of envelope detector.

11. Take the readings as per the table mentioned below for various carrier frequencies&

corresponding local oscillator frequency settings.

7. PROCEDURE:

Selectivity:

1. Refer to the figure and carry out the following connections

2. Connect the output of function generator section (ACL-AM) outpost to the input of balance

modulator (ACL-AM) signal inpost.

3. Connect the output of VCO (ACL-AM) outpost to the input of balance modulator (ACL-AM)

carrier in post.

4. Connect the power supply with proper polarity to the kit ACL-AM & ACC-AW, while

connecting. Ensure that power supply is OFF.

5. Switch on the power supply and carryout the following presetting.



Function generator:

Sine wave about 0.5 VP-P Frequency about 1KHz

VCO level about 2 VP-P Frequency about 850 KHz

Switch on 1500 KHz

Balanced modulator:

Carrier null completely rotates clockwise or counter clockwise so that the modulator is unbalanced

and an AM signal without suppressed carrier is obtained across the output which amplitude is 50mm

VP-P.

Local Oscillator:

ACL-AD is 1300 KHz, 2 V

1. Connect load oscillator outpost to LOIN of micro-mixer section.

2. Connect balance modulator-1 OUT to RFIN of micro-section in ACL-AD.

3. Connect the mixer output to IFIN of first IF amplifier in ACL-AD , connect IF OUT of first IF

and IF W and IF OUT 2 of first IF to IN2 of second IF amplifier.

4. Connect OUT POST of second IF amplifier to IN POST 2 of second amplifier to IN POST of

envelop detector.

5. Connect the post AGC1 to post AGC2 and jumper position as per diagram.

6. Connect the oscilloscope to the IN and OUT post of envelop detector and detect AM signal.

7. Check the defected signal follows the behavior of the AM signal envelop, measure the detected

signal amplitude.

8. RESULT:

Thus sensitivity & selectivity was obtained successfully .

9. CONCLUSIONS:

Sensitivity mainly depends on the gain of the amplifier present in the receiver.

Selectivity mainly depends on the tuning of the amplifier present in the receiver.

10. VIVA QUESTIONS:

1. Define sensitivity, selectivity and fidelity.

2. Define image frequency.

3. What is the IF frequency of AM-MW &FM Receiver?

4. What are different factors to consider to select IF frequency?

5. Compare Tuned Radio Frequency & Super heterodyne Receivers?



11. TABULAR COLUMN:

For selectivity:

Carrier

Freq.(KHz)

VCO

860 870 880 890 900 910 920 930 940 950

Output of

Envelope

Detector(mV)

12. MODEL GRAPHS:



3. BLOCK DIAGRAM:

CPU

Set up arrangement:

RF Signal

Generator

RF Signal

Detector

Display Screen

Buttons

Transmitter Receiver



8. MEASUREMENT OF HALF POWER BEAM WIDTH (HPBW) AND GAIN OF A HALF

WAVE DIPOLE ANTENNA

1. AIM:

To measure the half power beam width (HPBW) and gain of a half wave dipole antenna.


1. Transmitter antenna [wired Dipole]-1

2. Receiver antenna [Yagi- Uda antenna]-1

3. Transmitter input Source [RF out]-1

4. Receiver output Detector [RF input]-1

5. SMA to SMN cables-2

6. Personal Computer with AMS software.


The Half- wave dipole antenna is just a special case of the dipole antenna ,but it is important

to enough that will have its own session .Note that the half wave term means that the length of the

dipole antenna is equal to a half wave length at the frequency of operation.

The small horizontal loop antenna may be rewarded as the magnetic counter part of the short

vertical dipole both loop & dipole have identical fields pattern but with E and H interchanged thus the

horizontal loop is horizontally polarized both small loop and short loop have the same directivity

D=1.5 to quality as a small loop r short loop dipole dimensions should be less.

Let us now proceed to find the fields everywhere around a short dipole. Let the dipole length

‘L’ be placed coincident with the z axis & with its centre at the origin as in fig. The relation of the

electric field components is then as shown it is assumed that the medium surrounding the dipole is air

or vacuum. In delaying with antenna or radiating systems the propagation time is great importance.



5. CALCULATIONS:

1. Antenna test wave length=

2. Near field boundary=

3. Gain=

4. HPBW=

5. Directivity=

6. FNBW=

7. Antenna Resolution=

8. Antenna Factor=

9. Front to back ratio=

6. TABULAR COLUMN:

S.NO Angle in degrees Power(dB)



7. PROCEDURE:

1. Set up the experiment as per shown in figure.

2. Set up the distance between antennas to be around 1 meter.

3. Turn ON the module.

4. Open the AMS-B exe-file, select the corresponding comport and click on run. Now the

software will be in running mode.

5. After switch on the AMS module, press menu key and select appropriate experiment shown

in the list [far field pattern].

6. After selecting the far field pattern select appropriate field pattern (Co-Polarization).

7. Use up and down arrows to select type of antenna.

8. Selected the receiver type of antenna.(Yagi-Uda antenna or Loop antenna)

9. Make the dipole length as displayed on the screen.

10. Set the received antenna to zero degrees and press enter key to start the experiment.

11. Then the reading from 00 to 3600 will be plotted in the software and different types of

parameters will be noted from –AMS-B software.

8. RESULT:

1. Gain= _________ dB

2. HPBW=_________

9. CONCLUSION:

1. The operating bandwidth of the antenna depends on the HPBW.

2. Gain of the practical antenna is calculated with the help of reference antenna.

10. VIVA QUESTIONS:

1. How antenna converts electric energy into electromagnetic energy?

2. Define Front to back ratio& Directivity.

3. Define HNBW & FNBW.

3. What is the gain of dipole antenna?

5. Define antenna factor and antenna resolution.



3. BLOCK DIAGRAM:

CPU

Set up arrangement:

RF Signal

Generator

RF Signal

Detector

Display Screen

Buttons

Transmitter Receiver



9. MEASUREMENT OF RADIATION PATTERN OF A LOOP ANTENNA IN PRINCIPLE

PLANES

1. AIM:

To measure the radiation pattern of a loop antenna in principle planes.

2. EQUIPMENT REQUIRED:

1. Transmitter antenna [wired Dipole]-1

2. Receiver antenna [Loop antenna]-1

3. Transmitter input Source [RF out]-1

4. Receiver output Detector [RF input]-1

5. SMA to SMN cables-2

6. Personal Computer with AMS software.


It is shown that the far field pattern of the square and circular loops of the same and are

identical when the loops are small. As a generalized we may say that the properties depend on the

area that the shape of the loop has no effect when the loop is small. However this is not the case when

the loop is large. The pattern of circular loop of any size is dependent of the angle but it is a function

of Ɵ on the other hand, the pattern of a large square loop is a both Ɵ and angle.

Referring to the pattern in a plane normal to the plane of the loop and parallel to the two

sides as indicated by the line AA1, is simply the pattern of two point sources representing sides 2 to 4

of the loop. The pattern in a plane normal to the plane of the loop and passing through diagonal

corners as indicated by the line BB1 is difference. The complete range in the pattern variation as a

function of angle is obtained in this 45ᶱ interval between AA1 & BB1.



Radiation Pattern:

5. TABULAR COLUMN:

S.No Angle in degrees Power(dB)



6. PROCEDURE:

1. Set up the experiment as per shown in figure.

2. Set up the distance between antennas to be around 1 meter.

3. Turn ON the module.

4. Open the AMS-B exe-file, select the corresponding comport and click on run. Now the

software will be in running mode.

5. After switch on the AMS module, press menu key and select appropriate experiment shown

in the list [far field pattern].

6. After selecting the far field pattern select appropriate field pattern (Co-Polarization).

7. Use up and down arrows to select type of antenna.

8. Selected the receiver type of antenna.(Yagi-Uda antenna or Loop antenna)

9. Make the dipole length as displayed on the screen.

10. Set the received antenna to zero degrees and press enter key to start the experiment.

11. Then the reading from 00 to 3600 will be plotted in the software and different types of

parameters will be noted from –AMS-B software.

7. RESULT:

Thus the radiation pattern has been obtained successfully.

9. CONCLUSION:

1. The operating bandwidth of the antenna depends on the HPBW.

2. Gain of the practical antenna is calculated with the help of reference antenna.

10. VIVA QUESTIONS:

1. What are the advantages of loop antenna over dipole antenna?

2. Define Front to back ratio& Directivity.

3. Define HNBW & FNBW.

4. What is the gain of dipole antenna?

5. Define antenna factor and antenna resolution



3. CIRCUIT DIAGRAM:



1. DIGITAL PHASE DETECTOR

1. AIM: To find the phase difference between two signals.


a. Aquila Trainer Kit-AET-26B

b. Dual Trace CRO-1

c. Multimeters-2

d.RPS(0-30V)

e. Patch cords


1. PLL is operated in free running mode at 5KHz by fixing timing resistor Rt=6KΩ & Capacitor

Ct=0.01µf, Two multi meters are connected at Pin no.2&4 to measure the frequencies.

2. The square wave is given to the PLL at pin no.2 and input frequency is varied to operate PLL in

lock range.

3. The phase of input output will differ in the lock range; the input & output of PLL are given to the

XOR Gate to detect the phase difference.

5. PROCEDURE:

1. Switch on the trainer and verify the output of RPS i.e., +5&-5V.

2. Observe the output of square wave generator using CRO &Measure the range with the help of

multimeters, the frequency range should be around 2 KHz to 13 KHz.

3. Calculate the free running frequeny at pin no.4 by varying timing resistor Rt using the formula

fout= 0.3/ Rt Ct, where Ct=0.01µf.

4. Connect two multimeters at pin no.2&pin no.4 of the PLL.

5. The square wave to the input of PLL and short 4&5 pins. Vary the input frequency of the square

wave, If PLL is locked the there exist phase difference between input & output.

6. Connect input &output of PLL to the inputs of XOR gate.

7. Observe the phase difference between input & output.



6. MODEL WAVEFORMS:

7. RESULT:

Free running frequency_______________ KHz & Rt Value______________ KΩ

8. CONCLUSION:

With the help of PLL &XOR gate phase difference between two square waves can be detected.

9. VIVA QUESTIONS:

1. What are the basic blocks in PLL?

2. Define free running mode of PLL.

3. Define lock range of PLL.

4. Why PLL is operated in lock range to detect the phase?

5. Which logic gate is more suitable for detecting phase difference?



3. CIRCUIT DIAGRAM:



2. BALANCED MODULATOR &SYNCHRONOUS DETECTOR

1. AIM: To study the operation of Balanced Modulator &Synchronous Detector


a. Aquila Trainer Kit-AET-59

b. Dual trace CRO

c. Patch cords


1. IC-1496 acts as a multiplier & multiplies two input signals ie., RF & AF signals.

2. When the signal is multiplies, sum & difference frequency will be generated.

3. Synchronous detector contains multiplier followed by a LPF.

4. The multiplier multiplies DSB-SC , RF signal & generates Sum & difference frequency.

5. The difference frequency is equal to the AF signal which will appear at the output of the LPF.

4. PROCEDURE:

1. Switch on the trainer and verify the output of RPS i.e., +12V,-12V &-8V.

2. Observe the output of RF generator using CRO, output should be sine wave of frequency 100KHz

& Amplitude should be 300mVp-p

3. Observe the output of AF generator using CRO, output should be sine wave of frequency 5KHz &

Amplitude should be 8Vp-p

4. Connect output of RF, AF Generators to the input of balanced modulator and connect channel1,

channel2 of CRO to the input & output of balanced modulator respectively.

5. Observe the DSB-SC waveform at the output of balanced modulator with respect to input by

varying null adjusts control.

6. Note down peak to peak voltage of DSB-SC.

7. Connect output of RF generator & balanced modulator to the input of synchronous detector.

8. Observe the output of synchronous detector & it should be same as AF signal.



5. MODEL WAVEFORMS:



6. RESULT:

AF INPUT:


RF INPUT:


BALANCED MODULATOR OUTPUT:


SYNCHRONOUS DETECTOR OUTPUT:


7. CONCLUSION:

1.180 0 Phase shift occurs in DSB signal when ever AF Signal crosses zero.

8. VIVA QUESTIONS:

1. Write the time expression for DSB-SC signal in the case of single tone, multi tone & band of

frequencies?

2. Draw the frequency spectrum of DSB-SC.

3. Write the power relation in DSB-SC signal.

4. What is power efficiency of DSB-SC signal? What is the percentage of power saving in DSB-SC

with respect to AM?

5. Write the applications of DSB-SC.

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