Advanced communication lab manual

EC 707 Advanced communication Laboratory Dept. of Electronics & Communication Engineering
EC010 707- ADVANCED COMMUNICATION LAB
SEVENTH SEMESTER
ELECTRONICS AND COMMUNICATION DEPARTMENT
SYLLABUS – 2010 ONWARDS
By
AJAL.A.J
ASSOCIATE PROFESSOR – ECE DEPARTMENT
MAIL: professorajal@gmail.com
Mob: 8907305642
1

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
4
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
2

EXPERIMENT NO:1
BASK 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
3

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
4

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.
Procedure
1. 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.
5

WAVEFORM
RESULT
Set up the circuit and obtained the BASK waveform on CRO
6

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:
7

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
8

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:
9

Design
An inverting Amplifier with unity gain is used.
Gain = -Rf/Ri = 1.
ie. Rf = Ri
Take Rf = Ri = 4.7K
Waveform
10

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
11

MATLAB EXPERIMENTS
12

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;
13

%Input signal
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)
14

OBSERVATION
RESULT
The program for the estimation of mean square error of signal was
executed and output was varified
15

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:
clc
clear all
a=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);
16

plot(i,c);
xlabel('time');
title('carrier');
if a(d) ==1
y=c;
else
y=0;
end;
hold on;
subplot(3,1,3);
plot(i,y);
xlabel('time');
title('Bask signal');
hold on;
i=i+(2*pi);
end;
OBSERVATION
RESULT
17

Matlab program for BASK was executed and output was varified
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');
c=c+(2*pi);
hold on:
end
18

RESULT
Matlab program for BFSK was executed and output was varified
19

EXPERIMENT NO:7
BINARY PHASE SHIFT KEYING
AIM:
To generate Binary Phase shift keyed (BPSK) signal using MATLAB
PROGRAM:
clc
clear all
a=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');
title('carrier');
if a(d) ==1
y=c;
else
y=-c;
end;
hold on;
subplot(2,1,2);
plot(i,y);
xlabel('time');
title('Bpsk signal');
hold on;
i=i+(2*pi);
20

end;
OBSERVATION
RESULT
Matlab program for BFSK was executed and output was varified
21

MICROWAVE EXPERIMENTS
22

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.
23

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
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.
PROCEDURE
1. Connect the components and equipment as shown in Fig.
24

2. Set the variable attenuator at the minimum position and frequency meter in the
maximum position
3. keep the control knob of the klystron power supply as below
1.modulation –AM
2. AM frequency and amplitude knob- mid position
3. FM frequency and amplitude knob- fully anticlock wise
4.beam voltage knob- fully anticlock wise
5. repeller voltage knob –fully clock wise
6. meter select- voltage
4. Switch ON the Klystron Power Supply, HT, and Cooling Fan for the
Klystron Tube
5. set the beam voltage at 240 v
6. 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
25

RESULT
The characteristics of Reflex Klystron has been studied and modes have been
found.
EXPERIMENT NO:9
FREQUENCY AND WAVELENGTH MEASUREMENT
AIM:
To determine the frequency and wavelength in rectangular wave guide working in
TE10 mode.
APPARATUS:
3. Klystron Mount XM-25
4. Isolator XI-621
7. Slotted Line SX-651
8. Tunable Probe XP-655
10. Matched termination XL-400
12. Movable Short XT-481
13. Oscilloscope
14. 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 wavelength
26

For TE 10 mode where a is broader dimension of waveguide.
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 position
3. keep the control knobe of the klystron power supply as below
1.modulation –AM
2. AM frequency and amplitude knob- mid position
3. FM frequency and amplitude knob- fully anticlock wise
4.beam voltage knob- fully anticlock wise
5. repeller voltage knob –fully clock wise
6. meter select- voltage
4. Switch ON the Klystron Power Supply, HT, and Cooling Fan for the
Klystron Tube
5. set the beam voltage at 240 v ,by adjusting the beam voltage knob
6. 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.
27

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
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 TE10
mode has been and verified with direct reading.
28

EXPERIMENT NO:10
VSWR MEASUREMENT
AIM:
To determine the Low VSWR and High VSWR
APPARATUS:
3. Klystron Mount XM-25
4. Isolator XI-621
7. Slotted Line SX-651
8. Tunable Probe XP-655
9. SS Tuner XT-441
12. VSWR Meter SW-215
13. Oscilloscope
14. BNC Cable
THEORY
The electromagnetic field at any point of transmission line, may be considered as
the 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.
29

The voltage standing wave ratio is defined as ratio between maximum and
minimum 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 above
equation gives following equation.
BLOCK DIAGRAM
30

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 below
Range dB - 40 db/50db
Input Switch - Low Impedance
Meter Switch - Normal
Gain (Coarse- Fine) - Mid Position Approx.
4. Keep the control knobs of Klystron Power Supply as below
Beam Voltage - OFF
Mod- Switch - AM
Beam Voltage Knob - Fully Anticlockwise
Reflector Voltage Knob - Fully Clockwise
AM-Amplitude Knob - Around Fully Clockwise
AM- Frequency Knob - Mid position
5. 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 gain
control 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 will
31

change.
A. Measurement of Low and Medium VSWR
1. Get the maximum square wave on CRO
2. Connect the pobe to VSWR meter
3. By controlling /turning the gain control knobe of VSWR meter make the
needle to stand on position “1” of SWR scale
4. 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.
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 value
5. 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 VSWR
Reading on VSWR meter =
High VSWR
32

Position 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.
33

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