advanced communication lab 10ecl67 b.e - vi semester lab

QMP 7.1 D/F

Channabasaveshwara Institute of Technology

(An ISO 9001:2008 Certified Institution)

NH 206 (B.H. Road), Gubbi, Tumkur – 572 216. Karnataka.

Department of Electronics & Communication Engineering

Advanced Communication Lab

10ECL67

B.E - VI Semester

Lab Manual 2015-16

Name : _____________________________________

USN : _____________________________________

Batch : __________________ Section : ___________

Channabasaveshwara Institute of Technology

(An ISO 9001:2008 Certified Institution)


Department of Electronics and Communication Engineering

Advanced Communication Lab

Version 1.0

February 2016

Prepared by: Reviewed by:

Pradeep N R Nagaraja P

Vidyarani K R Associate Professor

Harish S

Tejaswini S

Yashaswini T

Approved by:

Prof. Rajendra

Professor & Head,

Dept. of ECE

Channabasaveshwara Institute of Technology (An ISO 9001:2008 Certified Institution)


DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

SYLLABUS

Advanced Communication LAB

Subject Code : 10ECL67 IA Marks : 25

No. of Practical Hrs/Week : 03 Exam Hours : 03

Total no. of Practical Hrs.: 42 Exam Marks : 50

LIST OF EXPERIMENTS USING DISCRETE COMPONENTS and LABVIEW – 2009

can be used for verification and testing.

1. TDM of two band limited signals.

2. ASK and FSK generation and detection

3. PSK generation and detection

4. DPSK generation and detection

5. QPSK generation and detection

6. PCM generation and detection using a CODEC Chip

7. Measurement of losses in a given optical fiber (propagation loss, bending loss)

and numerical aperture

8. Analog and Digital (with TDM) communication link using optical fiber.

9. Measurement of frequency, guide wavelength, power, VSWR and attenuation in a

microwave test bench

10. Measurement of directivity and gain of antennas: Standard dipole (or printed

dipole), microstrip patch antenna and Yagi antenna (printed).

11. Determination of coupling and isolation characteristics of a stripline (or

microstrip) directional coupler

12. (a) Measurement of resonance characteristics of a microstrip ring resonator and

determination of dielectric constant of the substrate.

(b) Measurement of power division and isolation characteristics of a microstrip 3

dB power divider.

QMP 7.1 D/D

‘Instructions to the Candidates’‘Instructions to the Candidates’‘Instructions to the Candidates’‘Instructions to the Candidates’

• Student should come with thorough preparation for the experiment to be

conducted.

• Student should take prior permission from the concerned faculty before

availing the leave.

• Student should come with proper dress code and to be present on time

in the laboratory.

• Student will not be permitted to attend the laboratory unless they bring

the practical record fully completed in all respects pertaining to the

experiment conducted in the previous class.

• Student will not be permitted to attend the laboratory unless they bring

the observation book fully completed in all respects pertaining to the

experiment to be conducted in present class.

• Experiment should be started conducting only after the staff-in-charge

has checked the circuit diagram.

• All the calculations should be made in the observation book. Specimen

calculations for one set of readings have to be shown in the practical

record.

• Wherever graphs to be drawn, A-4 size graphs only should be used and

the same should be firmly attached in the practical record.

• Practical record and observation book should be neatly maintained.

• Student should obtain the signature of the staff-in-charge in the

observation book after completing each experiment.

• Theory related to each experiment should be written in the practical

record before procedure in your own words with appropriate references.

Channabasaveshwara Institute of Technology (An ISO 9001:2008 Certified Institution)


Department of Electronics and Communication Engineering

----------------------------------------------------------------------------------------------

Advanced Communication Lab Course Objective and Outcome

----------------------------------------------------------------------------------------------

OBJECTIVES

The objectives of this course are;

To aware the simulation tools like Labview.

To get better understanding of digital modulation techniques, microstrip technology

and concept of optical fibre communication losses.

To design suitable modulator and demodulator for given application.

To understand the different advanced modulator techniques and their importance in

real time applications like QPSK,DPSK etc.

Implementation and realization of Time Division Multiplexing modulation and

demodulation.

Understanding and obtaining the radiation pattern of microwave antennas.

OUTCOMES

After completing the Advance Communication Lab, students will be able to

Understand the clearly the concepts related to Digital Modulation techniques.

Understand the various concepts related to microstrip components.

Understand the importance of various Linear Integrated Circuits.

Under the design of digital modulation techniques.

Understand the various optical fibre communication losses that occur in real time.

CONTENTS

Sl.

No. Name of the Experiment

Page

No.

First cycle

1 Amplitude Shift Keying 02

2 a) Ring Resonator

b) Power Divider

06

10

3 Binary Phase shift Keying 12

4 Study of losses in Optical Fiber cable 16

5 Differential Phase Shift Keying 22

6 Quadrature Phase Shift Keying 24

Second cycle

7 Frequency Shift Keying 28

8 Time Division Multiplexing 32

9 Analog and Digital Communication Link using Optical Fiber 36

10 Measurement of frequency, Guided Wavelength and VSWR 40

11 Radiation Patterns of Microstrip Antennas 42

12 Directional Coupler 46

13 PCM generation and detection using a CODEC chip 48

Additional Experiments

Sample Viva Questions

References

Question Bank

INDEX PAGEINDEX PAGEINDEX PAGEINDEX PAGE

Sl.

No Name of the Experiment

Date

Man

ual

Marks

(M

ax .

25

)

Reco

rd

M

arks

(M

ax.

10

)

Sig

natu

re

(S

tud

en

t)

Sig

natu

re

(Facu

lty)

Conduction Repetition Submission of

Record

1

2

3

4

5

6

7

8

9

10

11

12

13

Average

10ECL67-Advanced Communication Lab 2015-16

Dept. of ECE, CIT, Gubbi Page No. 1

Circuit Diagram-1: ASK modulator and demodulator

Design:

Let Vc = 5 volts peak-to-peak, Vm =10 volts peak-to-peak, fm = 500 Hz, fc =50 kHz.

Assume hfe= 30, VBEsat= 0.7 volts, VCEsat= 0.3 volts, Ic=1 mA, Ic = Ie.

Vc peak = VCEsat + IeRe

2.5 = 0.3 + (1 m)Re, => Re = 2.2 kΩ

Vm peak = RbIb+VBEsat+IeRe

5 = RbIb + 0.7 + 2.2, where Ib=Ic/hfe

then Rbmax = 63 kΩ , Choose Rb = 22 k Ω

Envelope Detector:

1/fm>RdCd>1/fc, hence 2ms>RdCd>20µs

Let RdCd =50/fc=1 ms

Assume Cd=0.01 µF, then Rd=100 kΩ

Tabular column:

Vc in volts fc in Hz Vm in volts fm in Hz Error in detection in ms



Experiment No. 1 Date: __ /__ / _____

AMPLITUDE SHIFT KEYING

Aim: To generate ASK signal and to demodulate it.

Apparatus Required:

Sl. No. Apparatus Range Quantity

1 Op-Amp IC 741 1

2 Transistor SL 100 1

3 Diode OA 79 1

4 Resistors As Per the design

5 Potentiometer 10KΩ 1

6 Capacitor 0.01µF 1

Procedure:

1. Connections are made as shown in the circuit diagram-1.

2. Apply a square wave modulating signal of 500 Hz (1000bits/sec) of 10VP-P

3. Apply a sine wave carrier signal of 50 kHz of 5V peak-to-peak amplitude.

4. Observe ASK waveform at point A.

5. Demodulate the ASK signal using the envelope detector.

6. To find minimum frequency of carrier signal for proper detection:

After Step 5 start reducing the frequency of the sine wave carrier signal from 50 kHz

gradually. At a particular frequency of carrier signal, the demodulated signal does not

tally with the modulating square wave. Note the carrier frequency just before the

mismatch.

10ECL67-Advanced Communication Lab

Dept. of ECE, CIT, Gubbi

ASK modulation and demodulation waveforms

nced Communication Lab

ASK modulation and demodulation waveforms :

2015-16

Page No. 3



LabVIEW Block Diagram:

Result:

Error = ….….…. ms

Minimum frequency for proper detection: ………….Hz



Circuit Diagram-2: To measure the characteristics of microstrip Resonator

Calculation and observation:

λ1 = c/f

λ2 = c/f

The effective dielectric constant of any material can be found using the formula:

Where, h= height of the known sample(substrate used for ring resonator)

w= width of ring resonator

The effective dielectric constant of the unknown material can be found using the relation

πdm = λ1/ Є

where dm = diameter of the ring resonator

Є1 = effective dielectric constant o

Є2 = effective dielectric constant of unknown material

Now Using equation (3) find the dielectric constant Є


o measure the characteristics of microstrip esonator


c/f1 …….(1)

= c/f2 …….(2)


………(3)


width of ring resonator


/ Є1 = λ2/ Є2 ………….(4)

= diameter of the ring resonator

= effective dielectric constant of known material

effective dielectric constant of unknown material

Now Using equation (3) find the dielectric constant Єr of the unknown material

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Page No. 5

o measure the characteristics of microstrip Ring




of the unknown material




(a) RING RESONATOR

Aim: To conduct an experiment to measure resonance characteristics of a micro strip

ring resonator and to determine the dielectric constant of the substrate.

Components required:

Sl No Apparatus Range Quantity 1 Power supply - 1

2 Transmission line 50 Ω

3 Ring resonator - 1

4 Terminators 50 Ω 1

5 Oscilloscope /

VSWR meter - 1

Procedure:

Part (a)

1. Set up the system as shown in circuit diagram-2.

2. Keeping the voltage at minimum, switch on the power supply.

3. Insert a 50 Ω transmission line and check for the output at the end of the system

using a CRO/ VSWR meter

4. Vary the power supply voltage and check the output for different VCO

frequencies. Set the frequency to the maximum output voltage.

5. Replace the 50 Ω transmission lines with ring resonator.

6. Vary the supply voltage, tabulate VCO frequency vs. output.

7. Plot a graph frequency vs. output and find the resonant frequency

Part (b)

1. Select a VCO frequency (say f1) where there is a measurable output. Note down

the magnitude /power level of the output.

2. Place the unknown dielectric material on top of the ring resonator. Ensure that

there is no air gap between dielectric piece and the resonator surface.

3. Observe the change in magnitude /power level at the output.

4. Now reduce the supply voltage till maximum power level (before inserting the

dielectric) is achieved. This is the new resonance condition due to the insertion of

new dielectric material (eg: Teflon)

5. Note down the VCO frequency (say f2)

6. Calculate the dielectric constant of the unknown material by using the formula



Tabular Column:

f1 λ1 f2 λ2 Effective dielectric constant of the unknown

material, Єr



Sample calculation:

For the known material:

f1 = 5GHz, h=0.762 mm w=1.836 mm Єr1 = 3.2

λ1 = c/f1 = 3 x 10 10 / 5 x 10 09 = 6 cm

Єeff 1 = Є1 = [(3.2 +1) /2] + [(3.2 -1) /2] [1+(12x0.762/1.836)]-1/2

= 2.717

For the unknown material

f2= 4.6 GHz h=0.762 mm w=1.836 mm Єr2 = ?

λ2 = c/f2 = 3 x 10 10 / 4.6 x 10 09 = 6. 52 cm

Using the values of λ1 and λ2 in equation 4 calculate the effective dielectric constant of

the unknown material

λ1/ Є1 = λ2/ Є2

6/2.712 = 6.52 / Є2

Є2 = 2.947

Using this value in equation (3)

Єeff 2 = Є2 =2.947= [(Єr +1) /2] + ([(Єr -1) /2] [1+(12x0.762/1.836)]-1/2 )

The effective dielectric constant of the unknown material, Єr2 =2.59

Result:



Circuit Diagram-3: Setup to measure the characteristics of

divider

Calculation and observations:

With VSWR meter:

Isolation in dB = P

Power division in dB at arm 3 = P

Power division in dB at arm 2 = P

With CRO:

Isolation between port 2 and 3= 20 log (V

Coupling factor in dB at arm 3 = 20 log (V

Coupling factor in dB at arm 2 = 20 log (V

Tabulation: I/P at port 1

O/P at port 2

O/P at port 3


Setup to measure the characteristics of microstrip power

divider

Calculation and observations:

Isolation in dB = P3- P2

Power division in dB at arm 3 = P3- P1

Power division in dB at arm 2 = P2- P1

between port 2 and 3= 20 log (V3/ V2)

Coupling factor in dB at arm 3 = 20 log (V3/ V1)

Coupling factor in dB at arm 2 = 20 log (V2/ V1)

O/P at port 3

Isolation between port 2&3

Coupling factor at arm 2

Couplingfactor at arm 3

Figure 1

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Page No. 9

microstrip power

Coupling factor at

Figure 12.4 Power Divider



(b) POWER DIVIDER

Aim: To conduct an experiment to measure power division and isolation characteristics

of micro strip 3dB power divider.



2 Transmission line 50 Ω

3 Power divider - 1

4 Terminators 50 Ω 1

5 Oscilloscope /

VSWR meter - 1

Procedure:




using a CRO/ VSWR meter


frequencies. Set the frequency to the maximum output voltage.

5. Replace the 50 Ω transmission lines with the Wilkinson power divider.

6. Tabulate the output at ports 2 and 3

7. Calculate insertion loss and coupling factoring each coupled arm

8. Calculate the isolation between ports 2 and 3 by feeding the input to port 2 and

measure output at port 3 by terminating port 1.

Result:



Circuit Diagram-4: BPSK modulator and demodulator

Design:

Let Vc = 5 volts peak-to-peak, Vm =10 volts peak-to-peak, fm = 500 Hz, fc =50 kHz.

Assume hfe= 30, VBEsat= 0.7 volts, VCEsat= 0.3 volts, Ic=1 mA, Ic = Ie.


2.5 = 0.3 + (1 m)Re, => Re = 2.2 kΩ


5 = RbIb + 0.7 + 2.2, where Ib=Ic/hfe

Then Rbmax = 63 kΩ , Choose Rb = 22 k Ω

Envelope Detector:

1/fm>RdCd>1/fc, hence 2ms>RdCd>20µs


Assume Cd=0.01 µF, then Rd=100 k Ω

Tabular Column:

Vc in volts fc in Hz Vm in volts fm in Hz Error in detection in ms




BINARY PHASE SHIFT KEYING

Aim: To generate PSK signal and to demodulate the PSK signal.

Apparatus Required:

Sl. No. Apparatus Range Quantity 1 IC 1458 2

2 Transistor

SL 100

SK 100

1

1

3 Diode OA 79 1

4 Resistors As Per Design 16


6 Capacitor As Per Design 3

Procedure:


2. Apply square wave modulating signal of 500 Hz (1000bits/sec) of 10 VP-P.

3. Apply a sine wave carrier signal of 50 kHz of 5V peak amplitude.

4. Observe BPSK waveform at point A.

5. Demodulate the BPSK signal using the coherent detector (Adder + Envelope

Detector). The error in the demodulated wave can be minimized by adjusting the

Vref using 10k pot.



BPSK modulation and demodulation waveforms


BPSK modulation and demodulation waveforms:

2015-16

Page No. 13



BPSK Block Diagram:

Result:

Error = …….… ms

Minimum frequency for proper detection: ………….Hz.



Circuit Diagram-5: Falcon fiber-optic kit set up for bending loss measurement

Block Diagram Representation:

EQUIPMENTS:

Link-B Kit with power supply patch chords

20 MHz Dual Channel Oscilloscope

1MHz Function Generator

1 & 3 Meter Fiber Cable




STUDY OF LOSSES IN OPTICAL FIBER

Aim: To measure the losses in optical fiber.

Apparatus Required:

Sl. No. Apparatus Range Quantity 1 Link-B Kit 2

2 Link-B Kit

Power Supply 1

3 Fiber Cable

1 Meter

0.5 m cable

1

1

4

Numerical

Aperture

measurement

Jig

Procedure to measure Attenuation (Falcon kit):

1. Make connections as shown in circuit diagram–5 Connect the power supply cables

with proper polarity to Link-B kit, While connecting this, ensure that the power

supply is OFF.

2. Keep SW9 towards TX1 position for SFH756.

3. Keep Jumpers & SW8 positions as shown. Keep Intensity control pot P2 towards

minimum position. Switch ON the Power Supply.

4. Apply 2Vpp sinusoidal signal of 1 kHz from the function generator to the IN port

of Analog Buffer.

5. Connect the output port Out of Analog Buffer to the port TX IN of Transmitter.

6. Connect the fiber from TX1 to RX2.

7. Observe the detected signal at port ANALOG OUT on oscilloscope. Adjust intensity

to get 2Vpp amplitude at the Analog out. This voltage is V1.

8. Now replace 0.5 meter fiber by 1 meter fiber between same LED and Detector. Do

not disturb any settings. Again take the peak voltage reading and let it be V2.

If α is the attenuation of the Fiber then,

αdB =(10/L1-L2)log10(V2/V1)

where α = dB/Km

L1= Fiber Length for V1

L2= Fiber length for V2

This α is for peak wavelength of 660nm



Circuit Diagram-6: Set up to measure NA

NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION.



Procedure to measure NA (Falcon kit):

1. Make connections as shown in Circuit Diagram-6. Connect the power supply

cables with proper polarity to link-B kit. While connecting this, ensure that the

power supply is OFF.

2. Keep Intensity control pot P2 towards minimum position.

3. Keep Bias control pot P1 fully clockwise position.

4. Switch ON the power supply.

5. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the

connector. Once the cap is loosened, insert the 1 meter fiber into the cap. Now

tighten the cap by screwing it back.

6. Insert the other end of the fiber into the numerical aperture measurement jig.

Adjust the fiber such that its cut face is perpendicular to the axis of the fiber.

7. Now observe the illuminated circular patch of light on the screen.

8. Measure exactly the distance d and also the vertical and horizontal diameters MR

and PN as indicated

9. Mean radius is calculated using the following formula

r = (MR+PN)/4

10. Find the numerical aperture of the fiber using the formula

NA = Sinθmax = r/√( d2 + r2)

where θmax is the maximum angle at which the light incident is properly

transmitted through the fiber.

Result: Attenuation Loss=

Bending Loss=

Sl. No. No. of turns Output Voltage

Numerical Aperture=



Circuit Diagram-7: DPSK Transmitter

Circuit Diagram-8: DPSK Receiver




DIFFERENTIAL PHASE SHIFT KEYING

Aim: Study of Carrier Modulation Techniques by DPSK.

Apparatus Required:

Sl. No. Apparatus Range Quantity 1 DPSK Kit Kit No. 1

2 Power Supply 1

3 Patch Cards

Procedure for Transmitter:

1. Switch on the power supply.

2. Connect either 300 or 600 bps clock to SEL CLK socket, connect measuring probe of

CRO to SEL CLK and WORDPULSE to observe the selected clock (300bps or 600bps).

3. Connect MARK (Sine) and MARK (SINE) Mux input.

4. Connect NRZ DATA to SEL DATA. Adjust the dip switch to any digital patterns of 8

bits by keeping them for ‘1’ or ‘0’ positions also observe selected data in CRO.

5. Connect DPSK data to Mux input, also observe DPSK data.

Procedure for Receiver:

1. Interconnect the Transmitter and Receiver modules through the interconnecting cable

required.

2. Connect Adder output to BPF input.

3. If external clock is required give from SEL CLK from Tx socket.

4. If External carrier is required, feed it from CARRIER FROM Tx socket.

5. Observe the modulated signal at DPSK IN, DPSK O/P in the CRO. The output should

match the data transmitted from the transmitter.




Result:



Circuit Diagram-9: QPSK Transmitter

Circuit Diagram-10: QPSK Receiver




QUADRATURE PHASE SHIFT KEYING

Aim: Study of Carrier Modulation Techniques by QPSK method.

Apparatus Required:

Sl. No. Apparatus Range Quantity 1 QPSK Kit Kit no. 1

2 Power Supply 1

3 Patch Cards

Procedure for Transmitter:

1. Switch on the power supply from power cord to module given.

2. Connect either 300 or 600 bps clock to SEL CLK Socket, connect measuring probe of

CRO to SEL CLK and WORDPULSE to observe the selected clock (300 or 600 bps).

3. Connect NRZ or EXT DATA to SEL DATA. Adjust the dip switch to any digital patterns

of 8 bits by keeping them for ‘1’ or ‘0’ positions. Observe the selected data in CRO.

4. Separately monitor the selected data, word pulse (WP) by connecting WP to A

Channel of CRO and selected data to B Channel of CRO.

5. Monitor selected data in channel A of CRO and Compare it with B∅ and B1 on

channel B. Observe QPSK output according to phase change on output according to

B∅ and B1.

Procedure for Receiver:

1. Connect Transmitter and Receiver with interconnecting cable required.

2. Check the WP, Sin, Cos, B∅, B1 and QPSK output on Transmitter.

3. Check the QPSK Signal at receiver at pin input SIGNAL.

4. Connecting SIGNAL to Channel A of CRO and verify the waveform by connecting the

Channel B to PRE B∅, PRE B1 and QPSK output. The waveform of PRE B∅ should

correspond to B∅ of Transmitter and the waveform of PRE B1 should correspond to

B1 of Transmitter. The QPSK output should correspond to NRZ (L) of transmitter.



QPSK Waveforms:


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Page No. 25



QPSK Block Diagram:

Result:



Circuit Diagram-11: FSK modulator and demodulator




FREQUENCY SHIFT KEYING

Aim: To generate FSK signal and to demodulate the FSK signal.

Apparatus Required:

Sl.No Apparatus Range Quantity 1 IC 1458 2

2 Transistor

SL 100

SK 100

1

1

3 Diode OA 79 1




Procedure:

1. Connections are made as shown in circuit diagram-11.

2. Apply a square wave modulating signal of 100 Hz (200bits/sec) and 10 VP-P

amplitude.

3. Apply a sine wave carrier signal-1 of 1 kHz, 5V peak to peak amplitude and signal-2

of 50 kHz, 5V peak to peak amplitude.

4. Observe FSK waveform at point A.

5. Demodulate the FSK signal using the coherent detector (Adder + Envelope Detector).

The error in the demodulated waveform can be minimized by adjusting the Vref using

10k POT.



Design:

Let Vc = 5 volts peak-to-peak, V

Assume hfe= 30, VBEsat= 0.7 volts, V


2.5 = 0.3 + (1 m)Re, => R


5 = RbIb + 0.7 + 2.2, where I

then Rbmax = 63 kΩ , Choose R

Envelope Detector:

1/fm>RdCd>1/fc, hence 2ms>R


Assume Cd=0.01 µF, then Rd

Tabular Column:

Vc in volts fc1 in Hz fc2

FSK Waveforms:


peak, Vm =10 volts peak-to-peak, fm = 500 Hz, f

= 0.7 volts, VCEsat= 0.3 volts, Ic=1 mA, Ic = Ie.

, => Re = 2.2 kΩ

+ 0.7 + 2.2, where Ib=Ic/hfe

= 63 kΩ , Choose Rb = 22 k Ω

, hence 2ms>RdCd>20µs

d=100 k Ω

c2 in Hz Vm in volts fm in Hz detection in ms

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Page No. 29

500 Hz, fc =50 kHz.

= 2.2 kΩ

Error in detection in ms




Result:

Error = ….….…. ms



Circuit diagram-12: TDM of 2 band-limited signals

Design:

Low pass filter:

a) For message signal-1

fc = 1/(2πRC)

Let fc = 300 Hz, and C1 = 0.1µF.

R1 = 1/(2πx300x0.1x10-6)

R1 = 5.305 kΩ ≈ 5.4 kΩ

b) For message signal-2

fc = 1/(2πRC)

Let fc = 500 Hz, and C2 = 0.1µF.

R2 1/(2πx500x0.1x10-6)

R2 = 3.183 kΩ ≈ 3.3 kΩ

5.4 k

3.3 k




TIME DIVISION MULTIPLEXING

Aim: To study Time Division Multiplexing for 2 band-limited signals.

Apparatus Required:

Sl No Apparatus Range Quantity 1 IC CD 4051 2



Procedure:


2. Apply a square wave (TTL) carrier signal of 2 kHz (or >2 kHz) of 5V amplitude.

3. Apply m1(t) and m2(t) whose frequencies are f1 (200 Hz, with DC offset) and f2 (400

Hz, with DC offset).

4. Observe TDM waveform at pin number 3 of IC CD4051.

5. Observe the reconstructed message waveforms m1(t) and m2(t) at pin numbers 13

and 14 of 2nd IC CD4051.

6. The ripples in the demodulated signals can be reduced by increasing the order of the

filter or by increasing the carrier frequency.



TDM Waveforms:




Result:



Circuit Diagram-13: Analog link using fiber


Analog link using fiber-optic link

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Page No. 35




ANALOG AND DIGITAL COMMUNICATION LINK USING OPTICAL FIBER

Aim: The aim of this experiment is to establish analog and digital communication link

using optical fiber

Apparatus Required:

Sl No Apparatus Range Quantity

1 Link B Kit with

power supply - 1

2 Patch chords -

3 Dual trace

Oscilloscope 20MHz 1

4 Fiber cable 1 meter 1

NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION

PROCEDURE:

Make the connection as shown in circuit diagram-13. Before establishing the analog link,

obtain the TDM output from Analog 8:1 Mux.

a) ANALOG LINK

1. Make the connection as shown in the diagram, and adjust the jumper & switch

settings as shown in circuit diagram -13.

2. Keep the intensity control pot P2 towards minimum position.

3. Switch On the power supply.

4. Feed 2 Vpp sinusoidal signal of 1 kHz from the function generator to the IN port of

analog buffer.

5. Connect the OUT port of analog buffer to the TX IN of transmitter.

6. Slightly unscrew the cap of SFH756V (660 nm). Do not remove the cap from the

connector. Once the cap is loosened, insert the 1 meter Fiber into the cap. Now

tighten the cap by screwing it back.

7. Connect the other end of the fiber to the detector SFH350V (photo transistor

detector) carefully as per the instructions given in the above step.

8. Observe the detected signal at ANALOG OUT port on the oscilloscope.. adjust the

intensity control pot P2 so that a signal of a signal of 2 Vpp amplitude is received.

9. To measure the analog bandwidth of the photo transistor, vary the signal

frequency and observe the detected signal at various frequencies.

10. Plot the detected signal against applied signal frequency and determine the 3 dB

bandwidth.



Circuit Diagram-14: Digital link using fiber-optic link



b) DIGITAL LINK

1. Make the connection as shown in the circuit diagram-14, and adjust the jumper &

switch settings as listed below.

2. Switch On the power supply.

3. Connect the OUT port of digital buffer to the port TX IN of transmitter.

4. Connect the fiber to the detector RX1.

5. Observe the detected signal at port TTL OUT on oscilloscope.

6. Press the DIP switch to observe the ON/OFF position of LED.

SWITCH and Jumper Connections Keep all switch faults in OFF position.

Keep switch SW6 towards SINE IN position.

Keep switch SW8 towards TX position.

Keep Switch SW9 towards TX1 position.

Keep Switch SW10 towards TTL position.

Keep Jumper JP1 at TDM OUT position.

Keep Jumper JP2 at 1.024M position.

Keep Jumper JP5 towards +5V position.

Keep Jumper JP6 shorted.

Keep Jumper JP8 towards Pulse position.

Result:



Circuit Diagram-15: Microwave test bench set up

Waveform:

Tabular Column:

Load V max V min VSWR

Horn

Short Circuit

Open Circuit

Match Termination

X1= MSR + (CVD x LC) LC = 0.01 cm λg = 2(X1≈X2)cm = ………….,

λo = (λg x λc) 2

(λg2

+ λc2)

VSWR = Vmax/ Vmin

Load X1 X2 λg λc λ0 f0

GHz

Horn

Short Circuit

Open Circuit

Match

Termination

√

λc=2a a=2.54cm




MEASUREMENT OF FREQUENCY, λg, VSWR

Aim: To measure the frequency, guide wavelength, power and VSWR of a microwave

guide.

Procedure:

1. Set up the microwave bench as shown in circuit diagram-15.

2. With Reflector voltage in maximum position and beam voltage in minimum

position switch on the Klystron power supply (Both main and HT switch) wait until

current reaches 10 to 12mA.

3. Observe the signal at the output of the detector if it is not a square wave then

reduce the reflector voltage until a square wave signal is obtained.

4. Observe the standing wave pattern on SWG (Slotted Wave Guide), note the

maximum and minimum voltage levels of the standing wave pattern of the

connected load.

5. Note the positions of any 2 consecutive minima X1 and X2 (or maxima); twice the

difference between these will give the guide wavelength λg.

Result:

λg =…………… fo =…………….



Circuit Diagram-16: The radiation pattern of microstrip antennas

Tabulation:

Angle

Output on oscilloscope or VSWR meter Output (Clockwise) Output ( AntiClockwise )

0o

5o

10o

15o

20o

25o

30o

35o

DC power

supply

Detector

VCO

Patch

Antenna

Dipole

Antenna

Dipole

Antenna

Patch

Antenna

Active

Filter

230V/50Hz

VSWR

/CRO

Yagi

Antenna

Transmitting

antenna

Test antenna /Receiving

antenna

(Rotatable)

Yagi

Antenna

9 Pin cable for source 9 Pin cable for detector

6 dB

Attenuator

Power

Supply




RADIATION PATTERN OF MICROSTRIP ANTENNAS

Aim: To conduct an experiment to obtain radiation pattern and to measure the

directivity and gain of the following antennas:

1) Standard dipole (or printed dipole)

2) Micro strip patch antenna,

3) Yagi antenna (printed)

Procedure:

1. Set up the system as shown in circuit diagram-16 for a standard dipole antenna.

2. Keeping the voltage at minimum, switch on the power the supply.

3. Vary the power supply voltage and check the output for different VCO frequencies.

The frequency at which the output becomes maximum is the resonant frequency.

4. At the resonant frequency, adjust the distance between the transmitting and receiving

antennas using the formula S=2d2 / λ

where d is the broader dimension of the antenna.

5. Keeping both the antennas in line of sight (0ο at the turn table), tabulate the output

(Et)

6. Rotate the turn table in clock-wise and anti clock-wise for different angles of

deflection and tabulate the output for every angle(Er).

7. Plot a graph of angle vs. output.

8. Find the half power beam width (HPBW) from the points where the power becomes

half (3 dB points or 0.707 V Points)

9. Calculate Directivity and gain of the antenna by using the formula.

10. Repeat the experiment for a patch antenna and a yagi antenna.



An example of a Polar plot:

Calculation and observation

* Directivity of the antenna can be calculated by using the formula.

D=41253 / (HPBW) HPBW is the half power beam width in degrees.

* Gain of the antenna can be calculated using the formula:

Where,

Et and Er are the signal strength measured using an oscilloscope at the transmitting end

and at the receiving end respectively, when there the antennas are in line of sight

S is the actual distance kept between the antennas

λ is the wavelength found using t

Note: For micro strip antenna


An example of a Polar plot:


Directivity of the antenna can be calculated by using the formula.

D=41253 / (HPBW)2

HPBW is the half power beam width in degrees.

* Gain of the antenna can be calculated using the formula:

Gain in dB=10 log G.

are the signal strength measured using an oscilloscope at the transmitting end


S is the actual distance kept between the antennas

λ is the wavelength found using the formula λ= c / f (f= frequency of operation)

Note: For micro strip antenna λ= λo / Єr

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Gain in dB=10 log G.

are the signal strength measured using an oscilloscope at the transmitting end


he formula λ= c / f (f= frequency of operation)



RESULT:



Circuit Diagram-17: To measure the characteristics of microstrip directional coupler


Insertion loss

VSWR meter P1-P2

CRO 20 log(V1/V2)

Tabulation: I/P at port 1

O/P at port 2

O/P at port 3

Input port P1

Isolated port P4

Figure 11.2 Ports of a directional coupler


measure the characteristics of microstrip directional coupler


Coupling factor Isolation Directivity

P1-P3 P1-P4 P

20 log(V1/V3) 20 log(V1/V4) 20 log(V

(a)

O/P at port 4

Insertion loss

Isolation Coupling factor

Transmission

port P2

Coupled

port P3

directional coupler a) Branch line b) Parallel line

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Page No. 45

measure the characteristics of microstrip directional

Directivity

3-P4

20 log(V3/V4)

(b)

Coupling directivity

b) Parallel line




DIRECTIONAL COUPLER

Aim: To conduct an experiment to measure the coupling factor, directivity, isolation

characteristics of the directional coupler.



2 transmission line 50 Ω

3 Directional

coupler 1

4 terminators 50 Ω 2

5 Oscilloscope /

VSWR meter - 1

Procedure:




using a CRO/ VSWR meter.


frequencies.

5. Note down the output for different output frequencies.

6. Replace the 50 Ω transmission line with branch line coupler.

7. Check the output at port 2(throughput), 3(Coupled output), 4(isolated output).

8. Calculate insertion loss, coupling factor and isolation using the formulae given.

Note: The coupled and Isolated ports of branch line Directional Coupler are

respectively Isolated and Coupled ports in Parallel line Directional Coupler

Result:



Circuit Diagram-18: PCM voice coding and



PCM voice coding and CODEC frequency response


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CODEC frequency response




PCM generation and detection using a CODEC Chip

Aim: To study the liberalized a law PCM coding, analog to digital conversion, the reverse

process and the filtering characteristics of the CODEC chip 145502.



2 Link B Kit - 1

3 Patch cords -

4 Function

generator 1MHz 1

5 Dual Trace

Oscilloscope

20MHz

1

Procedure:

1. Make the connections as shown in circuit diagram-18. Connect the power supply

cables with proper polarity to Link B kit. While connecting this, ensure that the

power supply is OFF.

2. Now voice communication can be done between the audio channels using

telephone headset.

3. Observe the effect on the voice signal at various test points.

4. Keep the switch SW6 towards SINE IN position.

5. Feed a sinusoidal signal of 1KHz and the amplitude up to 2Vpp to SINE 1 and

SINE 2 input terminals. This gives an analog input to both the CODECs.

6. Observe the reconstructed waveform at OUT post of CODEC 1 RX and at OUT post

for CODEC II RX as shown PCM waveform. Compare both the applied input and

the reconstructed signal on the oscilloscope.

7. Observe the signal changes at various test points.

8. Vary the input signal frequency in steps and simultaneously observe the output

signal. Measure the amplitude of the output signal for each input frequency.

9. Find the frequency reading after which the response of the codec drops. This

gives the bandwidth of the codec.

10. Since it works for audio range we should get bandwidth around 3.4KHz.

SWITCH and Jumper Connections Keep all switch faults in OFF position.

Keep switch SW6 towards SINE IN position.

Keep switch SW8 towards TX position.

Keep Switch SW9 towards TX1 position.

Keep Switch SW10 towards TTL position.

Keep Jumper JP1 at TDM OUT position.

Keep Jumper JP2 at 1.024M position.

Keep Jumper JP5 towards +5V position.

Keep Jumper JP6 shorted.

Keep Jumper JP8 towards Pulse position.



PCM Waveforms:


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Page No. 49



Result:



Circuit diagram:

Components required: IC 4016, transistor SL100, resistors, capacitors as per design.

Design: Let Vsample = 1.2 V, VBE(sat) = 0.7V ,VCE(sat) = 0.3V and IC = 1mA, hfe = 40

and VB = 4V (peak amplitude of C(t)) when transistor is driven in to saturation.

Vsample = IcRc + VCE(sat)

1.2 = IcRc + VCE(sat) ⇒ RC = 900Ω ≅ 1KΩ.

VB - IB RB - VBE(sat) = 0

IB = Ic / 40 = 25 uA

RB Max = 132 kΩ Choose RB = 22 kΩ.

Low pass filter design.

fH = 1/(2πRC); assume C and determine R.

Assume the cut off frequency of filter, fH = 150 Hz and C = 0.1 µf, then R = 10 kΩ

22 KΩ



Additional Experiment 1:

Verification of Sampling Theorem using Flat Top Samples

Aim: To design a circuit for generating flat top samples and to verify Sampling theorem.

Procedure:

1. Rig up the circuit as shown in circuit diagram.

2. Apply a low frequency sine wave as the message signal say 100Hz (Apply dc

offset).

3. Apply a high frequency square wave as the carrier signal.

4. Without connecting the capacitor observe the output at pin no 2, the samples are

naturally sampled.

5. Now check the output for different cases by applying the signals at different

frequencies and verify the Nyquist rate.

6. Now connect the capacitor in the circuit and get the sample and hold samples and

flat top sampled output.

7. Connect the sampled output as a input to the demodulator input and reconstruct

the original message signal.



Waveforms:



Result:



Block Diagram:

Tabular column: V in Volts I in mA



Additional Experiment 2:

GUNN DIODE

Aim: To Conduct an experiment to obtain V-I characteristics of GUNN Diode. Theory:

The gunn oscillator is based on negative differential conductivity effecting bulk

semiconductors which has two conduction bands separated by energy gap (greater than

thermal energies). A disturbance at the cathode gives rise to high field region which

travels towards the anode. When this field domain reaches the anode, it disappears and

another domain is formed at the cathode and starts moving towards anode and so on.

The time required for domain to travel form cathode to anode (transit time) gives

oscillation frequency. In the gunn oscillator, the gunn diode is placed in a resonant

cavity. The oscillation frequency is determined by cavity dimensions.

Although gunn oscillator can be amplitude modulated with the bias voltage. We

have used a PIN modulator for square wave modulation of the signal coming from gunn

diode.

A measure of the square wave modulation capability is the modulation depth

i.e., the output ratio between the ON and OFF state.

Procedure:

To find V-I Characteristics of GUNN diode:

1) Set up the microwave bench as shown in block diagram 1.

2) Connect only the GUNN bias signal to the GUNN diode.

3) Witch GUNN bias voltage to minimum position switch ON the power supply.

4) Increase the bias voltage in steps of 1 volt and note down the voltage and

current by alternatively switching the indicator from V to I . Each time note the

value of V and I.

Note: [Up to the threshold voltage current increases with increase in voltage (+ve

resistance) and after threshold current decreases with increase in voltage (-ve

resistance)]

Result :



Sample Viva questions

1. State the difference between Analog systems and digital systems.

2. Explain why digital systems are considered superior to Analog systems.

3. Mention the disadvantages of Analog communication.

4. Explain the basic steps involved in digitizing a signal.

5. Explain ASK operation.

6. State the difference between discrete and digital signals.

7. Define Quantizing.

8. Define Encoding.

9. Explain PCM encoding.

10. State the difference between pulse modulation and digital modulation.

11. Explain FSK circuit operation.

12. Explain different types of channels.

13. Mention the basic blocks of formatting and transmission of base band signals.

14. Mention the difference between broad band transmission and base band

transmission.

15. Explain PSK operation.

16. Define VSWR.

17. Define Characteristics impedance.

18. Define a Wave guide.

19. Give the S-Matrix for an ideal waveguide.

20. What is TDM?

21. What is FDM?

22. Compare TDM and FDM.

23. What are the applications of TDM?

24. What is an optical fiber? What are its advantages?

25. Explain the principle of total internal reflection

26. What is meant by numerical aperture?

27. What is a ring resonator?

28. Define the following: Isolation, Coupling factor, and Insertion loss.

29. Mention the range of microwave frequencies.

30. Explain the operation of a reflex klystron.



References

1. Simon Haykin, “Digital Communications”, John Wiley & Sons, 2008.

2. K. N. Hari Bhat and D. Ganesh Rao, “Digital Communications”, Pearson , 3rd

edition.

3. K. Sam Shanmugam, “An introduction to Analog and Digital Communication”,

John Wiley India Pvt. Ltd, 2008.

4. John D. Krauss, “Antennas and Wave Propagation, 4th Edition, McGraw-Hill

International edition, 2010.

5. Annapurna Das, Sisir K. Das, “ Microwave Engineering”, Tata McGraw-Hill

Education, 2nd edition, 2000



Question Bank

1. Design and simulate an ASK system to transmit digital data using a suitable carrier.

Demodulate the ASK signal with the help of suitable circuit. Determine the minimum

frequency of carrier for proper detection.

2. Design and simulate the working of FSK with a suitable circuit for _____ Hz and __

Hz carrier signals. Demodulate the FSK signal with the help of suitable circuit.

3. Design and simulate the working of BPSK modulated signal for a given carrier signal

of ______ Hz. Demodulate the BPSK signal to recover the digital data.

4. Design and simulate the working of TDM for PAM signals with _____ Hz and _____

Hz message signals. Also demultiplex the message signals.

5. Conduct a suitable experiment using slotted line carriage to obtain the following for

the given load. a) λg and λo b) VSWR

6. Conduct a suitable experiment using fiber optic trainer kit to determine the numerical

aperture of the optical fiber.

7. Conduct a suitable experiment using fiber optic trainer kit to determine:

a) Attenuation b) Bending loss

8. With the help of suitable circuit demonstrate the working of DPSK encoder and

Decoder for the specified input stream and carrier frequency simulate the same in

software.

9. With the help of a suitable circuit demonstrate the working of QPSK modulator and

demodulator.

10. Conduct an experiment using fiber optic trainer kit to establish analog link with TDM.

11. Conduct an experiment using fiber optic trainer kit to establish digital link and

measure the following: a) Attenuation, b) Bending loss and c) Numerical aperture.

12. Conduct an experiment to obtain the radiation pattern of micro strip patch antenna.

Also calculate the directivity and gain of the antenna.

13. Conduct an experiment to obtain radiation pattern of micro strip dipole antenna. Also

calculate the directivity and gain of the antenna.



14. Conduct an experiment to obtain radiation pattern of micro strip yagi antenna. Also

calculate the directivity and gain of the antenna.

15. Conduct an experiment on a given micro strip directional coupler to determine the

following: a) Isolation b) Coupling factor c) Insertion Loss

16. Conduct an experiment on a given micro strip power divider to determine the

following: a) Isolation b) Coupling factor

17. Conduct an experiment to find the characteristics of micro strip ring resonator. Also

calculate the dielectric constant of the given dielectric material.

18. Conduct an experiment using fiber optic trainer kit to establish digital link for the

realization of PCM technique.

APPENDIX

Introduction to LabVIEW

LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a system-design

platform and development environment for a visual programming

language from National Instruments. Originally released for the Apple Macintosh in 1986,

LabVIEW is commonly used for data acquisition, instrument control, and industrial

automation on a variety of platforms including Microsoft Windows, various versions

of UNIX, Linux and Mac OS X. The latest version of LabVIEW is LabVIEW 2014.

Like C, JAVA, the LabVIEW software is known as ‘G’ language. Its interfacing is GUI

(Graphical User Interfacing) i.e. the complete program is represented in block diagrams

instead of having syntaxes.

Benefits

1. Interfacing to Devices

A key feature of LabVIEW is the extensive support for interfacing to devices such

as instruments, cameras, and other devices. Users can interface hardware by

either writing direct bus commands (USB, GPIB, Serial...) or using high-level,

device-specific drivers that provide native LabVIEW function nodes for controlling

the device.

2. Code Compilation

In terms of performance, LabVIEW includes a compiler that produces native code

for the CPU platform. The graphical code is translated into executable machine

code by interpreting the syntax and by compilation.

3. Large Libraries

Many libraries with a large number of functions for data acquisition, signal

generation, mathematics, statistics, signal conditioning, analysis, etc., along with

numerous graphical interface elements are provided in several LabVIEW package

options. The number of advanced mathematic blocks for functions such as

integration, filters, and other specialized capabilities usually associated with data

capture from hardware sensors is immense.

4. Code re-use

The fully modular character of LabVIEW code allows code reuse without

modifications: as long as the data types of input and output are consistent so

they are interchangeable.

5. Parallel Programming

LabVIEW is an inherently concurrent language, so it is very easy to program

multiple tasks that are performed in parallel by means of multithreading. This is,

for instance, easily done by drawing two or more parallel while loops.

FUNCTIONS IN LabVIEW

1. Acquiring Data and Processing Signals

Measure any sensor on any bus

Perform advanced analysis and signal processing

Display data on custom user interfaces

Log data and generate reports

2. Instrument Control

Automate data collection

Control multiple instruments

Analyze and display signals

3. Automating Test and Validation Systems

Automate the validation or manufacturing test of your product

Control multiple instruments

Analyze and display test results with custom user interfaces

4. Embedded Monitoring and Control Systems

Reuse ANSI C and HDL code

Integrate off-the-shelf hardware

Prototype with FPGA technology

Access specialized tools for medical, robotics, and more

5. Academic Teaching

Apply an interactive, hands-on approach to learning

Combine algorithm design with real-world data measurements

Increase application performance with multicore processing

6. Prototyping

SDR algorithm prototyping

LTE and 802.11 development frameworks

Single design environment for FPGAs

Steps to Create VI in LabVIEW

1. Create a New VI ( File-> New VI) (Blank VI)

This will create a new front panel and block diagram panel.

2. Give the VI a Name.

3. Create your front panel with your necessary controls and indicators.

4. Place the appropriate blocks on block diagram pannel to perform the required

operation.

5. Create the block diagram according to the circuit requirement.

6. Run the VI and view the results in front panel.

advanced communication lab 10ecl67 b.e - vi semester lab

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