advanced communication lab manual

EC 707 Advanced communication Laboratory Dept. of Electronics & Communication Engineering

EC010 707- ADVANCED COMMUNICATION LAB SEVENTH SEMESTER

ELECTRONICS AND COMMUNICATION DEPARTMENTSYLLABUS – 2010 ONWARDS

By

AJAL.A.JASSOCIATE PROFESSOR – ECE DEPARTMENT MAIL: [email protected]

Mob: 8907305642

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mailto:[email protected]


TABLE OF CONTENTS

EXP.No.

Topic Page No.

1. BASK Generator using analog switch

2. BFSK Generator using analog switch

3. BPSK Generator using analog switch

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MATLAB EXPERIMENTS

4.Mean square estimation of signals

5. BASK

6. BFSK

7. BPSK

5 MICROWAVE EXPERIMENTS

8.Klystron characteristics

9.Frequency and wavelength measurement

10.VSWR measurement

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EXPERIMENT NO:1BASK GENERATOR USING ANALOG SWITCH

AIM: To design and set up a BFSK modulator using analog switch CD 4016

Components and equipments required

IC CD 4016, IC 7404, CRO, Function Generator

Theory

The CD4016 is a quad bilateral switch intended for the transmission or

multiplexing of analog or digital signals. The internal diagram is shown below:

Internal diagram of CD4016 IC

Binary Amplitude Shift Keying (BASK) is one of the digital modulation

techniques in which the amplitude of carrier is switched according to the binary

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data. This digital modulation scheme is used to transmit digital data over optical

fiber, point to point military communication applications, etc. Binary 1 is

represented by a short pulse of light and binary 0 by the absence of

light. Amplitude Shift Keying modulation process are relatively inexpensive and

easy to implement. The main disadvantage of ASK is that it is sensitive to

atmospheric noise, distortions and propagation conditions. Here is the practical

circuit diagram of amplitude shift keying modulator using CD4016 IC. CD4016 is

a switching IC with four embedded switches.

CIRCUIT DIAGRAM

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PIN DIAGRAM OF IC 7404

WORKING:

• Sine wave is obtained from a function generator.• Two switches inside the quad analog switch CD4016 are used in the circuit.• When the binary data is 1, the 1st switch is enabled and the 2nd switch is disabled using not gate arrangement. Hence we get sine wave output.• When the binary data is 0, the 1st switch is disabled and the 2nd switch is enabled using not gate arrangement. Hence the input of pin-4 is ground, we get 0 output.

Procedure1. Construct the circuit shown in Fig.2. Study the pin configuration of 4016 and 7404.3. Experiment with varying the modulating signal frequency and amplitude. Record the modulating signal frequency and amplitude. Observe the input and output waveforms.4. Save the screen shots showing the BASK waveforms.

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WAVEFORM

RESULT

Set up the circuit and obtained the BASK waveform on CRO

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EXPERIMETN NO:2

BFSK GENERATOR USING ANALOG SWITCH

AIM:

To design and set up a BFSK modulator using analog switch

COMPONENTS REQUIRED:

IC CD 4016,IC 7404, CRO, Function Generator

THEORY:

In binary frequency shift keying the carrier is shifted between two preset

frequencies according to binary input. When CLK is set a logic high the signal

with frequency f1 is obtained at the output and when the CLK is at logic 0 the

signal with frequency f2 is obtained at output .Thus Binary FSK is obtained at the

output.

The CD4016 is a quard bilateral switch intended for the transmission or

multiplexing of analog or digital signals.

CIRCUIT DIAGRAM:

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PROCEDURE

1.Set up the circuit part by part and verify their function

2. Connect the parts together and observe output waveform on CRO screen

WAVEFORM:

RESULT

Set up the circuit and obtained the BFSK waveform on CRO

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EXPERIMENT NO:3

BPSK GENERATOR USING CD4016

AIM:

To set up a Binary Phase Shift Keying Circuit using CD 4016 analog switch

COMPONENTS REQUIRED: Analog Switch CD 4016, 741,7404, Signal Generator, etc.

THEORY:

In BPSK modulating system phase of the carrier wave is inverted according to the

logic level of the input data. When the data is at logic1 level, the sinusoid has one

fixed phase and when the data is at the other level, the phase of the sinusoid

changes. BPSK and BFSK signal have a constant envelope and hence they are less

susceptible to noise.

Two switches inside the quad analog switch CD 4016 are used in the circuit.

Op-amp is used to invert the phase of the input sine wave. The sine wave can be

obtained from a function generator .

PROCEDURE:

The circuit is set up as shown in figure after verifying that all the

components are in good condition. Sine wave and clock are fed to the function

generator. Output wave form is observed on the CRO.

CIRCUIT DIAGRAM:

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Design

An inverting Amplifier with unity gain is used.

Gain = -Rf/Ri = 1.

ie. Rf = Ri

Take Rf = Ri = 4.7K

Waveform

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PROCEDURE

1.Set up the circuit part by part and verify their function

2. Connect the parts together and observe output waveform on CRO screen

RESULT

Set up the circuit and obtained the BPSK wave on CRO

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MATLAB EXPERIMENTS

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EXPERIMENT NO:4

MEAN SQUARE ESTIMATION OF SIGNALS

Aim: Write a matlab program to estimate the mean square error of signals

Theory :

In statistics and signal processing, a minimum mean square error (MMSE)

estimator describes the approach which minimizes the mean square error (MSE),

which is a common measure of estimator quality. Let X be an unknown random

variable, and let Y be a known random variable (the measurement). An estimator

is any function of the measurement Y, and its MSE is given by

where the expectation is taken over both X and Y.

The MMSE estimator is then defined as the estimator achieving minimal MSE.In

many cases, it is not possible to determine a closed form for the MMSE estimator.

In these cases, one possibility is to seek the technique minimizing the MSE within

a particular class, such as the class of linear estimators.

Matlab code

%Mean Square Error Estimation of signals

clc;

clear all;

N=100;

%Input signal

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http://en.wikipedia.org/wiki/Mean_squared_error

http://en.wikipedia.org/wiki/Estimator

http://en.wikipedia.org/wiki/Mean_square_error

http://en.wikipedia.org/wiki/Signal_processing

http://en.wikipedia.org/wiki/Statistics


f=1000;

t=0:0.00001:0.001;

X_Tra= 10*sin(2*pi*f*t);

% Adding White Gaussian noise by the channel

SNR=0.01;

X_Noise=AWGN(X_Tra,SNR);

% plot(X_Noise);

X_Rec=X_Noise;

%Cost = (Received signal - Estimated signal).^2

Error_UnCor = sum((X_Rec - X_Tra).^2)/N;

X_Fil= filter([0.33 0.33 0.33],1,X_Rec);

% plot(X_Fil);

Error_Cor=sum((X_Fil - X_Tra).^2)/N;

figure;

subplot(311);

plot(X_Tra);

subplot(312);

plot(X_Rec);

subplot(313);

plot(X_Fil)

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OBSERVATION

RESULT

The program for the estimation of mean square error of signal was

executed and output was varified

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EXPERIMENT NO:5

BINARY AMPLITUDE SHIFT KEYING

AIM:To generate Binary amplitude shift keyed (BASK) signal using MATLAB

THEORY:Generation of BASK Amplitude shift keying - BASK - is a modulation

process, which imparts to a sinusoid two or more discrete amplitude levels. These are related to the number of levels adopted by the digital message. For a binary message sequence there are two levels, one of which is typically zero. The data rate is a sub-multiple of the carrier frequency. Thus the modulated waveform consists of bursts of a sinusoid. One of the disadvantages of BASK, compared with FSK and PSK, for example, is that it has not got a constant envelope. This makes its processing (eg, power amplification) more difficult, since linearity becomes an important factor. However, it does make for ease of demodulation with an envelope detector.

Program:

clcclear alla=input('enter the binary sequence');l=length(a);i=0; for d=1:l i=i:.01:i+(2*pi); subplot(3,1,1); plot(i,a(d)); ylim ([0 2]) xlabel('time'); ylabel('amplitude'); title('modulating signal'); hold on; c=sin(i); subplot(3,1,2); plot(i,c); xlabel('time');

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ylabel('amplitude'); title('carrier'); if a(d) ==1 y=c; else y=0; end; hold on; subplot(3,1,3); plot(i,y); xlabel('time'); ylabel('amplitude'); title('Bask signal'); hold on; i=i+(2*pi);end; OBSERVATION

RESULT

Matlab program for BASK was executed and output was varified

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EXPERIMENT NO:6

BINARY FREQUENCY SHIFT KEYING

AIM:

To generate Binary amplitude shift keyed (BASK) signal using MATLAB

PROGRAM

clear all;clc;close all;x=input('enter the sequence');l=length(x);for d=1:l p=c:.01:(c+(2*pi)); s=sin(p); s1=sin(2*pi); subplot(2,1,1); plot(p,s); title('carrier frequency'); xlabel('t'); ylabel('amp'); hold on; if(x(d)==1) y=s1; else y=s; end subplot(2,1,2); plot(p,y); title('BFSK'); xlabel('time'); ylabel('amplitude'); c=c+(2*pi); hold on:end

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RESULT

Matlab program for BFSK was executed and output was varified

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EXPERIMENT NO:7

BINARY PHASE SHIFT KEYING

AIM:

To generate Binary Phase shift keyed (BPSK) signal using MATLAB

PROGRAM:

clcclear alla=input('enter the binary sequence');l=length(a);i=0;for d=1:l i=i:.01:i+(2*pi); c=sin(i); subplot(2,1,1); plot(i,c); xlabel('time'); ylabel('amplitude'); title('carrier'); if a(d) ==1 y=c; else y=-c; end; hold on; subplot(2,1,2); plot(i,y); xlabel('time'); ylabel('amplitude'); title('Bpsk signal'); hold on; i=i+(2*pi);end;

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OBSERVATION

RESULT

Matlab program for BFSK was executed and output was varified

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MICROWAVE EXPERIMENTS

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EXPERIMENT NO:8

KLYSTRON CHARACTERISTICS

AIM:

To verify the characteristics of Reflex Klystron tube and to determine

the electronic tuning range

APPARATUS:

1. Klystron Power Supply SKPS-610

2. Klystron Tube 2K-25 with Klystron MOLInt-XM-251

3. Isolator XI-621

4. Frequency Meter XF-710

5. Variable Attenuator XA-520

6. Detector Mount XD-451

7. Wave Guide Stand XU-535

8. VSWR Meter SW-215

9. Oscilloscope

10. BNC Cable

THEORY:

The Reflex Klystron makes the use of velocity modulation to

transform continuous electron beam energy into microwave power.

Electrons emitted from the cathode are accelerated and passed through the

positive resonator towards negative reflector, which retards and, finally,

reflects the electrons and the electron turn back through the resonator.

Suppose an RF- Field exists between the resonator, the electrons traveling

forward will be accelerated or retarded, as the voltage at the resonator

changes in amplitude. The accelerated electrons leave the resonator at an

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increased velocity and the retarded electrons leave at the reduced velocity.

The electrons leaving the resonator will need different time to return, due to

change in velocities. As a result, returning electrons group together in

bunches. As the electron bunches pass through resonator, they interact with

voltage at the resonator grids. If the bunches passes the grid at such time that

the electrons are slowed down by the voltage then energy will be delivered

to the resonator and the Klystron will oscillate. Fig. 2 & 3 shows the

relationship between output power, frequency and reflector voltages.

The frequency is primarily determined by the dimensions of the

resonant cavity. Hence, by changing the volume of resonator, mechanical

tuning of Klystron is possible. Also, a small frequency change can be

obtained by adjusting the reflector voltage. This is called electronic tuning.

PROCEDURE1. Connect the components and equipment as shown in Fig.2. Set the variable attenuator at the minimum position and frequency meter in the maximum position3. keep the control knob of the klystron power supply as below

1.modulation –AM2. AM frequency and amplitude knob- mid position3. FM frequency and amplitude knob- fully anticlock wise

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4.beam voltage knob- fully anticlock wise5. repeller voltage knob –fully clock wise6. meter select- voltage

4. Switch ON the Klystron Power Supply, HT, and Cooling Fan for theKlystron Tube5. set the beam voltage at 240 v6. Keep the control knob of meter select at Rep.7.Vary the repeller voltage to measure the corresponding output voltage

.OBSERVATIONS

REPELLER VOLTAGE(V) OUTPUT VOLTAGE(V)

WAVEFORM

RESULT

The characteristics of Reflex Klystron has been studied and modes have been

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found.

EXPERIMENT NO:9

FREQUENCY AND WAVELENGTH MEASUREMENT

AIM:

To determine the frequency and wavelength in rectangular wave guide working inTE10 mode.

APPARATUS:1. Klystron Power Supply SKPS-6102. Klystron Tube 2K-25 with Klystron MOLInt-XM-23. Klystron Mount XM-254. Isolator XI-6215. Frequency Meter XF-7106. Variable Attenuator XA-5207. Slotted Line SX-6518. Tunable Probe XP-6559. Detector Mount XD-45110. Matched termination XL-40011. Wave Guide Stand XU-53512. Movable Short XT-48113. Oscilloscope14. BNC Cable

For dominant TE10 mode Rectangular waveguide are related as below

1 1 1

Where is free space wave length

is guide wavelength

is cut off wavelengthFor TE 10 mode where a is broader dimension of waveguide.

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BLOCK DIAGRAM

PROCEDURE

1. Connect the components and equipment as shown in Fig.2. Set the variable attenuator at the minimum position and frequency meter in the maximum position3. keep the control knobe of the klystron power supply as below

1.modulation –AM2. AM frequency and amplitude knob- mid position3. FM frequency and amplitude knob- fully anticlock wise4.beam voltage knob- fully anticlock wise5. repeller voltage knob –fully clock wise6. meter select- voltage

4. Switch ON the Klystron Power Supply, HT, and Cooling Fan for theKlystron Tube5. set the beam voltage at 240 v ,by adjusting the beam voltage knob6. Tune the plunger of Klystron mount for getting maximum voltage.7.Tune the frequency meter to get a dip on the CRO and note down that frequency from the frequency meter.8. Move the slotted line probe to the left and find the first minimum on CRO,and note down the corresponding scale on slotted line and mark it as d1.9. Again Move the slotted line probe to the left and find the second minimum on CRO,and note down the corresponding scale on slotted line and mark it as d2

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10. Calculate the wavelength as twice the distance between two successive minimum positions ie.

OBSERVATIONS:

Frequency reading from frequency meter =First voltage minima position (d1) =Second voltage minima position (d2) =

RESULT:

The frequency and wave length in a rectangular waveguide working in TE10mode has been and verified with direct reading.

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EXPERIMENT NO:10

VSWR MEASUREMENT

AIM:

To determine the Low VSWR and High VSWR

APPARATUS:1. Klystron Power Supply SKPS-6102. Klystron Tube 2K-25 with Klystron MOLInt-XM-23. Klystron Mount XM-254. Isolator XI-6215. Frequency Meter XF-7106. Variable Attenuator XA-5207. Slotted Line SX-6518. Tunable Probe XP-6559. SS Tuner XT-44110. Detector Mount XD-45111. Wave Guide Stand XU-53512. VSWR Meter SW-21513. Oscilloscope14. BNC Cable

THEORY

The electromagnetic field at any point of transmission line, may be considered asthe sum of two traveling waves the ‘Incident Wave, which propagates from the source tothe load and the reflected wave which propagates towards the generator. The reflected wave is set up by reflection of incident wave from a discontinuity in the line or from the load impedance. The superposition of the two traveling waves, give rise to a standing wave along the line. The maximum field strength is found where the waves are in phase and minimum where the two waves add in opposite phase. The distance between two successive minimum or maximum is half the guide wavelength on the line. The ratio of electrical field strength of reflected and incident wave is called reflection coefficient.

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The voltage standing wave ratio is defined as ratio between maximum andminimum field strength along the line. VSWR is denoted by S and is given as

Where ZL is the load impedance, Z0 is characteristics impedance. The aboveequation gives following equation.

BLOCK DIAGRAM

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PROCEDURE:1. Set up the components and equipments as shown in figure.2. Keep the variable attenuator in the minimum attenuation position.3. Keep the control knobs of VSWR meter as belowRange dB - 40 db/50dbInput Switch - Low ImpedanceMeter Switch - NormalGain (Coarse- Fine) - Mid Position Approx.4. Keep the control knobs of Klystron Power Supply as belowBeam Voltage - OFFMod- Switch - AMBeam Voltage Knob - Fully AnticlockwiseReflector Voltage Knob - Fully ClockwiseAM-Amplitude Knob - Around Fully ClockwiseAM- Frequency Knob - Mid position5. Switch ON the Klystron Power Supply, VSWR meter and Cooling Fan.6. Switch ON the Beam Voltage Switch position and set the beam voltage at 240V.7. Rotate the reflector voltage knob to get deflection in VSWR meter.8. Tune the output by turning the reflector voltage knob, amplitude and frequency of AM Modulation.9. Tune the plunger of Klystron Mount and Probe for maximum deflection in VSWR meter.10. If required, change the range db- switch variable attenuator position and gaincontrol knob to get maximum deflection in the scale of VSWR meter.11. As you move probe along the slotted line, the deflection in VSWR meter willchange.

A. Measurement of Low and Medium VSWR1. Get the maximum square wave on CRO2. Connect the pobe to VSWR meter3. By controlling /turning the gain control knobe of VSWR meter make the

needle to stand on position “1” of SWR scale4. Then move the slotted line knob to the left until the needle

deflects(returns back)5. Note down the value on SWR scale ie the value at which the needle

deflects. this is the low VSWR value.

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B. Measurement of High VSWR(Double Minima Method)

1.get the minimal point on CRO 2. Connect the probe to VSWR meter

3.By controlling /turning the gain control knob of VSWR meter make the needle to point to 3db position of db scale in VSWR meter.move the slotted line knob to the left until the needle is poisioned on “zero” on the db scale. Note down the slotted line scale coinciding to zero position and marke it as d1. 4.By controlling /turning the gain control knob again make the needle point to 3db value5. move the slotted line knob to right until the needle deflects or it passed out of scale. Note down the slotted line scale and mark it as d2.

Where

OBSERVATIONS:

Low VSWRReading on VSWR meter =High VSWRPosition of first minima =Position of second minima =Distance between two minima=

RESULT

Voltage standing wave ratio has been calculated by direct reading and double minima method.

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