G. H. RAISONI COLLEGE OF ENGINEERING, NAGPUR
Department of Electronics & Communication Engineering
Branch:-6thSemester[Electronics And Telecommunication]
Subject: - Communication Electronics
List of Experiment
Sr.
No.
Name of Experiment
Experiments on Analog Communication:1.
Generation of Amplitude Modulation using transistor BC 548 and compare the results
with simulation results in MATLAB. Calculation of modulation index for different
values of modulating amplitude.
2.
Generation of Amplitude Demodulation using Envelop Detector and write MATLAB
code for demodulation.
3.
Generation of Frequency Modulation using IC 8038 function generator and compare the
results with simulation results in MATLAB.
4.
To perform Frequency Demodulation using IC 565 PLL and compare the results with
simulation results in MATLAB.
5.
Generation of Pre-emphasis circuit on breadboard system & to plot pre-emphasis curve.
6.
Generation of De-emphasis circuit on breadboard system & to plot pre-emphasis curve.
7.
Generation of DSB-SC using IC 1496 on breadboard and compare the results with
simulation results in MATLAB.
8.
To study FM radio receivers.
9.
Generation of FSK using XR 2206IC. And observation of mark and space frequencies.
And perform the simulation in MATLAB.
Experiments on Digital Communication:10.
11.
12.
13.
14.
15.
16.
17.
18.
Generation of PWM signal using IC 555 on breadboard. And Verify Simulation in
Micro-cap.
Generation of PPM signal using IC 555 on breadboard. And Verify Simulation in
Micro-cap.
To perform Time Division Multiplexing on breadboard system .
To perform Pulse Width Demodulation on breadboard and Verify Simulation in Microcap.
Generation of Pulse Position Demodulation on breadboard. And Verify Simulation in
Micro-cap.
Generation of Pulse Amplitude De-Modulation on breadboard. And Verify Simulation
in Micro-cap.
To perform Phase Shift Keying and verify the results on CRO.
To perform Phase Shift Keying demodulation and verify the results on CRO.
To perform Quadrature Phase Shift Keying and verify the results on CRO.
19.
20.
21.
Generation of PAM signal using switching CMOS IC 4016 on breadboard and
observation of single polarity and dual polarity waveforms on Digital Storage
Oscilloscope.
Simulation of Pulse Code Modulation In MATLAB.
Observation of Frequency spectrum of Amplitude Modulation on Spectrum Analyzer
Experiment No.: - 01
Aim:- Generation of Amplitude Modulation using transistor BC 548 and compare the
results with simulation results in MATLAB.Calculation of modulation index for
different values of modulating amplitude.
Equipments required:CRO, CRO probes, Function Generator (2 nos.), Power supply, Breadboard, connecting
wires.
Components:- Transistor: - BC548/549 (1 nos.),Resistor: - 330Ω (2 nos.),
Inductor: - 1mH (1 nos.)
Theory:In amplitude modulation, the amplitude of the carrier voltage varies in accordance with
the instantaneous value of modulating voltage. Let the modulating voltage be given by
expression,
Vm = Vm cos wmt
Where wm is angular frequency of the signal & Vm is the amplitude. Let the carrier
voltage be given by expression,
Vc = Vc coswct
On Amplitude Modulation, The instantaneous value of modulated carrier voltage is given
by,
V = V(t) cos wct
V(t)=Vc + ka Vm cos wmt
V=Vc[1+ ma cos wm t] cos wct
Where ma is modulation index and the modulation index is defined as the ratio of
maximum amplitude of modulating signal to maximum amplitude of carrier signal.
ma= K Vm / Vc
% modulation is defined as,
%ma=Vm/Vc
Circuit Diagram: -
Simulation Result In MATLAB: -
Procedure: 1. Assemble components and make connections on the breadboard.
2. Adjust the function generator to obtain the sine wave of frequencies 2 KHz and 1
MHz respectively.
3. Apply the sine wave of modulating signal and carrier signal to the ckt.
4. Observe the resulting amplitude modulated signal on CRO.
5. Calculate Vmax and Vmin from the obtained AM wave and hence calculate
modulation index.
6. Vary amplitude of modulating signal to get overmodulation, 100% modulation
and undermodulation condition.
7. Draw the waveform for overmodulated, 100% modulated, and undermodulated
AM wave on graph paper.
8. Write a MATLAB program to generate AM wave.
9. Take the printouts of simulation results.
10. Note the similarity /Differences in the observations and comment on
the results.
Observation Table: Table (1):
Sr.No.
Voltage signal
Frequency
Amplitude (Vs )
Modulating signal
Carrier signal
Table (2):
Sr. No.
Vmax
Vmin
Result: When Vm = ………
When Vm = ………
When Vm = ………
ma =……….
ma =……….
ma =……….
Modulation
index
% of
modulation
index
Conclusion: Thus the amplitude-modulated signal is generated and modulation index for different
values of modulating amplitudes is calculated. The program to generate AM wave is
written in MATLAB and the two results were compared.
Viva Questions: 1. What are the advantages of AM over FM?
2. What are the advantages of FM over AM?
3. What are the disadvantages of over modulation?
4. What is the bandwidth of Am signal?
Experiment No: - 2
Aim: - Generation of AM demodulator using envelope detector and to write MATLAB
code for amplitude demodulation.
Equipment Required: -CRO, Probes, Connecting wires.
Components: - Diode OA79 (1 no.), Resistor 10 K (1 no.), capacitor 0.1 µF (1 no.)
Theory: Envelope detector is also called as linear diode detector. The envelope detector operates
over linear region of the dynamic current voltage characteristic of the diode. Envelope
detector utilizes the rectification characteristics of a diode. The modulated carrier voltage
is applied to the series combination of diode and the load impendence consisting of
resistor R in shunt with capacitor C. During the positive half cycle the diode conducts
thereby charging the capacitor C to the peak value of the carrier voltage. During the
negative half cycle the diode does not conduct and hence discharges the capacitor
through R. Thus the output voltage is spiky in nature but it almost traces the envelope of
the modulated carrier voltage and hence it is nothing but original modulating voltage. The
departure of this output voltage from the envelope may be reduced by proper choice of R
and C depending upon the modulation frequency and depth of modulation.
Circuit Diagram: -
Fig: Circuit diagram of Envelop Detector
Procedure: (1)
(2)
(3)
(4)
(5)
Assemble the components on the breadboard as shown in the circuit diagram.
Apply the amplitude modulated signal to the input side.
Observe the output on CRO.
Draw the Amplitude modulated signal and demodulated on graph paper.
Write the MATLAB code for AM demodulation.
Simulation Result: Amplitude modulated signal
4
2
e
d
ut
i
pl
m
A
0
-2
-4
0
100
200
300
0
100
200
300
4
400
500
600
Time
Demodulated signal
700
800
900
700
800
900
2
e
d
ut
i
pl
m
A
0
-2
-4
400
500
Time
600
Observations: AM signal:
Carrier frequency=
Vmax=
Vmin=
Demodulated Signal:
Frequency=
Amplitude=
Result: The demodulated signal at the output of envelope detector was found to be equal to the
modulating signal.
Viva Questions: (1) Why envelope detector is also called as linear diode detector?
(2) How by proper choice of R and C the performance of the envelope detector can
be improved?
Experiment No.3
Aim: -A) Generation of Frequency modulation using XR 8038.
B) Program to generate FM in MATLAB.
Equipments Required:- Breadboard ,CRO , function generator, power supply,
CRO probes, connecting wires.
Components:-IC:-XR 3038, Resistors:-100K(2),5.6KΩ,Capacitors :-0.1µf(NO. 2)
Theory:Frequency modulation consists in varying the frequency of the carrier voltage in
accordance with the instantaneous value of the modulating voltage.Thus the amplitude of
the carrier does not change due to frequency modulation. Let the modulating voltage be
given by expression:
Vm=Vm coswmt.
Where wmis angular frequency of the signal & Vm is the amplitude. Let the carrier
voltage be given by expression,
Vc=Vcsin ( wct+θ)
On frequency modulation, the instantaneous value of modulated carrier voltage is given
by,
Vc=Vcsinφ
Where φ=wct+θ;
ϕ=wct+kfVm1/wmsinwmt+θ1;
Hence the frequency modulated carrier voltage is given by,
V=Vcsin[wct+kfVm/wm sinwmt]
The modulation index is defined as the ratio of frequency deviation to frequency of
modulating signal mf=d/fm where deviation f(fmax=fmin)/2.
Procedure:1.
2.
3.
4.
5.
Study the circuit diagram provided in the manual.
Study the pin configuration of IC-XR8038.
Adjust the function generator to obtain the sine wave of frequency 1KHZ.
Apply the sine wave modulating signal to the circuit.
Adjust the amplitude & frequency of modulating signal to get the frequency
modulated output.
6. From the carrier sidebands chart find the highest order sideband corresponding to
obtained modulation index.
7. Change the amplitude of modulating signal & repeat step 5 & 6.
8. Draw the waveform on graph paper.
9. Write a MATLAB program to generate FM signal.
10. Take the print out of the simulation result.
Circuit Diagram:-12v
R0
5.6K
R3
100K
4
7
5
6
2
XR8038
8
10
C1
0.1 f
V1
R1
5.6K
11
12
FM
O/P
R4
100K
C2
0.1 f
-12v
IC 8038
Sine Adjust
1
14
NC
Sine out
2
13
NC
Triangle out
3
12
Sine
Adjust
Duty
Cycle/Freque
ncy Adjust
4
11
5
Vcc
F.M. Bias
6
7
10
9
8
GND
Timing
Capacitor
Square
out
Sweep
Out
Observation:Table1:Sr no.
1
2
Signal
Modulating Signal
Carrier Signal
Amplitude
Frequency
Result:- when Vm=….then B.W.=
Conclusion:Thus by changing the amplitude of modulating signal the amount of deviation will
change, but it remains constant for any change in modulating signal frequency. Any
slight change in deviation for change in modulating frequency was due to the change in
amplitude of generator output.
Viva Questions:1)What is frequency deviation in FM?
2)What are the advantages of FM over AM?
3)What is Carson’s rule for BW calculation of FM signal?
Experiment No.4
Aim;-To perform Frequency Demodulation using IC 565 PLL and compare the results
with simulation results in MATLAB.
Equipment required:IC 565, Function generation ,CRO.
Component required:R1=560 (2 NO.),R2=10K ,C1=470Pf,C2=0.001µf,C3=0.1µf,C4=0.01µf.
Theory:The process of FM Demodulation is to exact the original modulating voltage from the
frequency modulated voltage. This detection should be done efficiently and linearly.
Further it is desirable that the detector circuit should be in sensitive to amplitude changes
and should not be too critical in its adjustment and operation.
The FM demodulator performs the detection process in two steps:-1)it converts the
frequency modulated voltage into corresponding amplitude modulated voltage using one
or more tuned circuits .2)it rectifies this amplitude modulated voltage in linear diode
demodulator to extract the original modulation frequency voltage. The FM demodulator
may be of the following types:
i)
The slope demodulator.
ii)
The balanced slope demodulator.
iii)
Phase difference discriminator
iv)
Ratio detector
v)
Foster seeley discriminator
vi)
PLL.
PLL -Phase-locked loop principal has been used in application such as FM modulation
,FM demodulator FSK. The PLL IC 565 is used as FM Demodulator IC and it performs
its demodulation operation.
Circuit diagram:-
10k
0.01
f
Fm
i/p
7
8
560
4
5
10
565
1
11
590
6
7
2
12
5
4
Audio
o/p
470pf
-5v
Procedure:1) The output of FM is forward to the input of demodulator.
2) Set deviation control R1fully clockwise for maximum deviation .Also set the
generation frequency control to be 200HZ.
3) Connect your oscilloscope to pin 7 of the 565 phase locked loop .set the time/cm
control to 2ms/cm and the vertical input to 0.5v/cm.At this point ,you may or may not
have an audio output signal displayed on the oscilloscope. You must adjust the 565 PLL
to the correct operating frequency .To do this adjust R2 until you obtain a sine wave
output on the oscilloscope.
4) Using the generation frequency control and R the deviation control, verify that the
output of the phase locked loop is directly proportional to the modulating signal.
Result:The demodulated signal was found equal to the modulating signal.
Viva Question:
1. What is Frequency Discriminator?
2. What is the advantage of using PPL for FM Demodulation?
Experiment No.: -5
Aim: Generation of pre-emphasis circuit on breadboard system & to plot pre-emphasis
curve.
Equipment Required: Breadboard system, dual channel CRO, function generator,
CRO probes, connecting wires.
Components:
Resistors of 10 K, 2.7 K. Capacitor of 0.1 µf. Inductor 0.2 mH.
Theory:
The noise has greater effects on higher modulating frequencies than on 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 signal-to-noise ratio.
Frequency modulation is more immune to noise than amplitude modulation & is
significantly more immune than phase modulation. Natural tendency of audio is that the
amplitude of high frequency signal is lower as compared to amplitude of low frequency
signal.
The S/N ratio reduces as the audio frequency increases. In turn the S/N ratio is not same
over the entire spectrum of audio signals. Thus in order to reduce the effect of noise the
higher frequency signals are boosted before transmission. This is called pre-emphasis.
When these signals are recovered at the receiver in order to restore the original
amplitudes of higher frequency signals they are suppressed. This is known as deemphasis.
Circuit Diagram:-
Procedure:1.
2.
3.
4.
5.
Assemble components and make connections on breadboard as shown in fig.
Apply AF input.
Observe the waveform on CRO.
Vary the AF i/p frequency between 20-20KHZ.
Observe the variation of o/p amplitude with respect to input frequency.
6. Plot the graph between gain and frequency.
Observation:Sr no.
Fin
Vin
Vout
Gain=Vout/Vin
Result:
As the I/P frequency increases the O/P amplitude increases in case of pre-emphasis.
Conclusion:The gain offered by the pre-emphasis circuit increases with increase in frequency.
Viva Questions:
1. Why FM is more immune to noise than AM?
2. What is pre-emphasis?
3. What are the applications of pre-emphasis?
Experiment No.: -6
Aim: Generation of De-emphasis circuit on breadboard system & to plot De-emphasis
curve.
Equipment Required: Breadboard system, dual channel CRO, function generator,
CRO probes, connecting wires.
Components:
Resistors of 10 K, 2.7 K. Capacitor of 0.1 µf. Inductor 0.2 mH.
Theory:
The noise has greater effects on higher modulating frequencies than on 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 signal-to-noise ratio. Frequency modulation is more immune to noise than
amplitude modulation & is significantly more immune than phase modulation. Natural
tendency of audio is that the amplitude of high frequency signal is lower as compared to
amplitude of low frequency signal. The S/N ratio reduces as the audio frequency
increases. In turn the S/N ratio is not same over the entire spectrum of audio signals. Thus
in order to reduce the effect of noise the higher frequency signals is boosted before
transmission. This is called pre-emphasis. When these signals are recovered at the
receiver in order to restore the original amplitudes of higher frequency signals they are
suppressed. This is known as de-emphasis.
Circuit Diagram:-
Procedure:1. Assemble components and make connections on breadboard as shown in fig.
2. Apply AF input.
3. Observe the waveform on CRO.
4. Vary the AF i/p frequency between 20-20KHZ.
5. Observe the variation of o/p amplitude w.r.t. i/p signal frequency.
6. Plot the graph between gain and frequency.
Observation:Sr
no.
Fin
Vin
Vout
Gain=Vout/Vin
Result:
As the i/p frequency increases the o/p amplitude decreases in case of de-emphasis.
Conclusion:The gain offered by the de-emphasis circuit decreases with increase in frequency .Thus
suppressing the high frequency component there by improving the signal to noise ratio
for higher frequencies.
Viva Questions:
1. How do pre-emphasis and de-emphasis affects the S/N ratio of audio frequencies?
2. What is de-emphasis?
3. What are the application of de-emphasis?
Experiment No.:- 7
Aim: - Generation of DSB-SC using IC 1496 on breadboard and compare the results
with simulation results in MATLAB
Equipment Required:- Function Generator, CRO, Connecting wires.
Components: - IC 1496 (1 nos.), Resistors: 1KΩ (3 nos.), 100Ω (2 nos.)
Theory: -
The amplitude-modulated signal is simple to produce but has two practical drawbacks in
application to many real communications systems: the bandwidth of the AM signal is
twice that of the modulating signal and most of the power is transmitted in the carrier, not
in the information bearing sidebands. To overcome these problems with AM, versions on
AM have been developed. These other versions of the AM are used in applications were
bandwidth must be conserved or power used more effectively.
If the carrier could somehow be removed or reduced, the transmitted signal would consist
of two information-bearing sidebands, and the total transmitted power would be
information. When the carrier is reduced, this is called as double sideband suppressed
carrier AM or DSB-SC. Instead of two third of the power in the carrier, nearly all being
the available power is used in sidebands.
Circuit Diagram: +12
100
Carrier Signal
100K
1K
8
4
Modulating
signal
1
5
10
XR1496
1
3
2
14
C2
0.1 f
1K
-12v
1K
12
6
1µF
O/P
Simulation Results:Modulating signal
1
0.5
e
d
ut
i
pl
m
A
0
-0.5
-1
0
100
200
300
400
500
Time
DSB-SC signal
600
700
800
900
0
100
200
300
400
500
Time
600
700
800
900
1
0.5
e
d
ut
i
pl
m
A
0
-0.5
-1
Procedure: 1. Assemble components and make connections of the breadboard.
2. Adjust the function generator to obtain the sine wave of frequencies 2 KHz and 1
MHz respectively.
3. Apply the sine wave of modulating signal and carrier signal to the ckt.
4. Observe the resulting DSB-SC signal on CRO.
5. Draw the time domain and frequency domain representation of DSB-SC on graph
paper.
Observation: Table(1)-
Sr. No.
Signals
Modulating signal
Carrier signal
Frequency
Amplitude in Vs
Result & Conclusion: The Balanced modulator IC 1496 can be used for the generation of DSB-SC signal. The
frequency domain representation of DSB-SC signal shows that DSB-SC signal do not
contain the carrier component and it consists of two symmetrically placed sidebands.
Viva Questions: 1. What is the bandwidth of the DSB-SC signal?
2. How SSB signal could be generated from DSB-SC signal?
3. What is ring modulator?
Experiment No.8
Aim:-Study of FM radio receiver.
Equipments Required:FM receiver kit.
Block diagram:-
RF
amplifier
Frequency
Mixer
Loud
Speaker
IF
amplifier
Limiter
FM
Detector
AF
amplifier
Local
Oscillator
Theory: The block diagram of FM radio receiver is shown in the diagram. The constituent stages
of the FM receiver are as follows.
(1) R.F.Amplifier: It increases the level of the signal level appreciably before the signal is
fed to the mixer and it also helps images frequency rejection. In FM broadcast the signal
bandwidth is large being 150 KHz therefore the RF amplifier must be designed to handle
this large bandwidth.
(2) Frequency mixer: It performs the usual function of mixing or heterodyning the signal
frequency voltage and the local oscillator voltage to produce the difference voltage and
frequency voltage which is the intermediate frequency voltage. Since FM broadcast takes
place either in VHF or UHF band single transistor frequency converter is not used.
Separate local oscillator is always used and another transistor serves as a frequency
mixer. The IF used in FM receiver is higher than that in AM. Typical value of
intermediate frequency is 12MHz. This high IF helps in image rejection.
(3) Local oscillator: A separate local oscillator is always used. At ultrahigh frequencies it
is preferred to keep the local oscillator frequency smaller than the signal frequency by an
amount equal to the IF.
(4) IF amplifier: A multistage IF amplifier is used to provide large gain. Further this IF
amplifier should be designed to have high overall bandwidth of the order of 150 KHz.
Double tuned circuits may be used but it is preferred particularly at the higher frequencies
in the UHF range, to use stagger tuned single tuned circuit which are found to produce
more gain bandwidth product than the conventional double tuned circuits.
(5) Limiter: The IF amplifier is followed by limiter which limits the IF voltage to
predetermined level and thus removes all amplitude variations which may be incidentally
caused due to changes in the transmission path or by manmade static or natural static.
(6) FM detector: This extracts the original audio modulation frequency voltage from the
frequency modulated carrier voltage. A discriminator is used as a frequency detector.
(7) Audio amplifier: The output of the FM detector is fed to an audio frequency small
signal amplifier and one or more audio frequency large signal amplifiers. The output
audio voltage is then fed to the loud speaker. In FM broadcast, the maximum modulating
frequency permitted is 15 KHz and hence the audio frequency must be designed to
accommodate such large bandwidth. Similarly the loud speaker must be capable of
reproducing all high frequency tones up to 15 KHz. Often two or more loud speaker are
used each reproducing a limited range of frequencies.
Viva Question:
1. What is Super heterodyne principle?
2. What are the functions of RF amplifier?
Experiment No.:-9
Aim:-A) Generation of Frequency shift keying using XR 2206 and observe the mark
and space frequencies .
B) Program to generate FSK signal in MATLAB.
Requirements:- Breadboard , CRO dual channel, function generator, power supply,
CRO probes, connecting wires.
Components:-IC:-XR2206, Resistors:-22K,1K(2),100K(2),220ΩCapacitors-1µf,10µf
Theory:Frequency shift keying is the digital system of frequency modulation .Digital signal
generated in system like telegraphy is not transmitted as it is instead they are transmitted
using keying techniques .In FSK the nominal unmodulated carrier frequency
.Corresponding to mark condition and space condition is transmitted for logic level 1 and
logic level 0 respectively.
Circuit Diagram:-12v
Sine out
16
NC
2
15
NC
3
22k
-12v
4
5
0.1 f
R3
1K
1K
R1
100K
1
R1
100
XR
2
2
0
6
14
R3
220
13
12
6
11
7
10
8
9
-12v
NC
R4
C1
10 f
Sq.wave
o/p
Simulation result in MATLAB:-
Procedure:1.
2.
3.
4.
5.
6.
Assemble components and make connection on breadboard as shown in fig.
Get it checked before turn on the power supply .
Apply square wave input.
Observe the waveform on CRO & note down mark & space frequencies.
Write a MATLAB program to generate FSK signal.
Take the print out of the simulation result.
Observation:The standard mark frequency f(mark)= 1/R1C3
Space frequency f(space)= 1/R2C3
Observe I/P square wave
Frequency=
Amplitude =
Observe O/P sine wave
Mark frequency=
Space frequency=
Result:Mark frequency is ……. And Space frequency is ……
Conclusion: Mark frequency is greater than space frequency. FSK system is used for digital data
transmission.
Viva question:1) What is FSK?
2) What are mark and space frequencies?
3) Which component in the circuit governs the mark and space frequencies?
Experiment No.10
Aim:-Generation of Pulse Width Modulation (PWM) signal using IC555.
Equipment required: Breadboard, CRO, function generator, DC power supply, CRO Probes, connecting wires.
Components:-IC:-555, Resistors:-18k (2 no.), Capacitors:-0.01µf (1 no.), 10µf
Theory:-
In Pulse modulation, continuous waveform is sampled at regular intervals and the
information collected at the sampling times together with synchronizing pulse if any is
transmitted.
Pulse width modulation is analog pulse modulation type. In pulse width modulation, each
pulse has fixed amplitude & starting time but the width of each pulse is kept propotional
to the magnitude of the modulating signal. In this system carrier is used as a square wave.
Basically sampling theorem is used for this system ,which states that in any pulse
modulation system if the sampling rate exceeds twice the maximum signal frequency ,the
original signal can be reconstructed in the received with minimal distortion .
Circuit Diagram:-
Simulation Result in Microcap:-
Circuit Description:Pulse width modulation may be generated by applying trigger pulse(at the sampling rate )
to control the starting time of pulse from a monostable multivibrator and feeding the
signal to be sampled to control the duration of the pulses. The circuit diagram of
monostable multivibrator using IC555 is shown in the above figure .Trigger pulses are
applied to pin 2 and the modulating signal is applied to pin 5. Pin 5 is control voltage pin,
which varies the pulse width depending on instantaneous modulating voltage. Observed
the square waveform (PWM wave) at pin no. 3.
Procedure:1.
2.
3.
4.
5.
6.
7.
8.
Study the circuit and pin configuration of IC555.
Assemble components and make connections on the breadboard.
Apply a sine wave modulating signal of around 5V, 80-150HZ to the pin 5.
Observe the waveform on pin no.3 (output pin) on CRO and note down the
amplitude and time period .Note the change in width of pulses .This is the pulse
width modulated wave.
Vary the frequency and the amplitude of the modulating signal and observe the
corresponding changes in the width of pulses.
Design the same circuit using Microcap simulation software, simulate it and
repeat all the observations.
Note the similarly /differences in the observations and comment on the same in
results.
Draw modulating signal ,carrier signal and PWM signal on graph paper.
Observation Table:Modulating wave:Sr no.
Amplitude
Carrier wave:Sr no
Amplitude
Time period
Frequency in HZ
Toff
Frequency in HZ
Ton
Conclusion:Thus the width of the pulses varies in accordance with the instantaneous value of the
modulating signal.
Viva questions:1. Explain pulse duration modulation?
2. Describe the method of demodulation of PWM?
3. What are the drawbacks of PWM over PPM?
Experiment No.11
Aim: - To generate Pulse Position Modulation (PPM) using IC 555 and to simulate the
circuit in micro cap.
Equipment Required: - Breadboard, CRO, Signal generator, CRO probes,
connecting wires.
Components: - IC 555 (1 no.), Resistors:- 18K (2 no), 10k (1 no), 1K (2 no.),
Theory:-
Capacitors- 0.1µF (2 no.), 10 µF (1 no.).
Pulse Position Modulation (PPM) is the type of pulse modulation in which the amplitude
and width of the pulse is kept constant but the position of each pulse in relation to the
position of a recurrent reference pulse is varied by each instantaneous sampled value of
the modulating wave. PPM has the advantage over PWM of requiring constant
transmitter power output but has the disadvantage of dependence on transmitter receiver
synchronization.
PPM may be obtained from PWM. In PWM each pulse has a leading edge and a trailing
edge but the location of the leading edges are fixed whereas those of trailing edges are
not but are dependent on the pulse width, which in turn is dependent on the signal value
at that instant. Thus, we may state that the trailing edges of PWM pulses are position
modulated. Thus PPM may be obtained from PWM by simply getting ride of the leading
edges and flat tops of PWM pulses.
Circuit Diagram: -
Simulation Result: -
Procedure: 1. Study the circuit diagram and the pin configuration of IC 555.
2. Assemble the components on the breadboard to build the circuit of PPM as given
in circuit diagram.
3. Apply sine wave modulating signal to pin number 5 of IC 555 and observe the
same signal on CRO and note down its amplitude and frequency.
4. Observe the PPM signal on CRO.
5. Simulate the circuit to generate PPM in microcap.
6. Draw the modulating signal and PPM signal on graph paper.
Observation Table: Sr.No.
Signal
Amplitude
Frequency
Result:PPM signal is generated using IC 555 and observed on CRO. The same circuit is
simulated in microcap. Both PPM waveforms were compared and were found same.
Conclusion:PPM signal can be generated by first generating PWM by using differentiator and diode
clipper.
Viva Questions: 1) What is the advantage of PPM over PWM?
2) What is the difference between pulse modulation and CW modulation?
Experiment No.:-12
Aim:-A) To construct a Pulse Duration Modulator.
B) To construct 3 channels Time division multiplex generator which uses pulse
duration modulation (PDM).
C) To measure the characteristics of Time Division Multiplexed generator and
verify its operation.
Equipments Requirement:-Dual Trace CRO, Connecting wires.
Components: IC 4017, IC 555, Diode IN 4149 (4 no.), Variable resistor 100k (2 no.), Variable resistor
50K (1 no.), Resistors 1K (1 no.), 1M (1 no.), 100 K (1 no.), 39 K (1no.), Capacitors
22µF (1 no.), 0.01µF (1 no.), Power supply 15V DC.
Theory:Multiplexing is the process of transmitting several separate information channels over the
same communication circuit simultaneously without interference. There are two basic
types of multiplexing time division multiplexing (TDM) and frequency division
multiplexing (FDM).
In TDM, several information channels are transmitted over the same communication
circuit simultaneously using a time sharing tech. As an example , PAM waveform is can
be generated that have a very low duty cycle .This means that if a single channel is
transmitted , most of the transmission time would be wasted .instead this time is fully
utilized by transmitting pulse from other PAM signal during the intervals. A PAM –TDM
waveform for 3 channels is shown in fig .The 1st pulse is a synchronizing pulse which is
used at the receiver in demultiplexing. The second pulse amplitude by channel 1, the 3rd
by channel 2 and the 4th by channel 3. This set of pulses is called a frame.
The primary advantages of TDM are that several channels of information can be
transmitted simultaneously over a single cable, a single radio transmitter. Where as
telephone systems uses PCM-TDM.
Circuit Diagram:-
+15 V
+15 V
16
14
100K
5.1M
2
+15 V
100K
4
50K
IC 4017
8
4
7
100K
3
10
15
7
1K
3.9K
2
6
3
555
O/P
0.01µ
Procedure:-
1. Study the circuit configuration given in the manual.
2. Set R1, R2, and R3 to midrange.
3. Connect your oscilloscope to pin 3 the 555 IC. Adjust the triggering control to
obtain a table display. If you cannot stabilize the display, connect the oscilloscope
external trigger input to pin 3 of the 4017 IC. Now switch your oscilloscope to
external triggering. This should trigger the oscilloscope on the TDM waveform
sync pulse.
4. Observe the o/p on CRO. Note that the sync pulse is a relatively short duration
pulse
5. While channels 1, 2, 3 are approximately equal turn potentiometer R1 fully
clockwise.
6. Return R1 to midrange .Now adjust R2 alternately clockwise and counter
clockwise.
7. Return R2 to midrange. Adjust R3 fully clockwise and then fully counter
clockwise.
8. Turn off your experiment.
Results & Conclusion: When the IC 555 o/p goes low, pin no. 13 on the 4017 steps the counter to the next pulse.
In this case R1 becomes the timing resistor, therefore when R1 is adjusted the 1st pulse
duration is changes. This is channel 1.
Also when R2 is adjusted channel 2 pulse duration changes. The same is true for R3 and
channel3 Thus, this circuit is a time division multiplex generator with the i/p signals
being the position of R1, R2 and R3.
Viva Question:1. What is the difference between TDM and FDM?
2. What are the applications of TDM?
Experiment No.:-13
Aim: - To study Pulse Width Demodulation and to observe the changes in demodulated
output with respect to modulating i/p signal.
Equipment Required: -Pulse width modulator, pulse width demodulator, CRO,
Patch cords.
Components: -R1=560 , R2=1K, R3=100 , R4=1K+1M pot, R5=2.7K, R6=10K,
Q1=Q2=BC 148, C1=C2=0.1µF, C3=C4=0.22µF.
Theory: In PWM, the width of the pulses of the carrier pulse train is varied in accordance with the
modulating signal. The pulse width demodulator circuit can be formed by using
transistorized circuit with OP-AMP low pass filter. A PWM i/p signal is applied to the
base of Q1 and demodulated o/p is obtained from OP-AMP o/p. The transistor Q1 works
as a inverter. Hence during the time interval when the PWM is high, the input to the
transistor Q2 is low. Therefore, during this time interval the transistor Q2 is cut-off and
the capacitor C1 gets charged through resistor R4. During the time interval when the
PWM i/p is low the input to the transistor Q2 is high and it gets saturated. The capacitor
C1then discharges very rapidly through Q2. The collector voltage of Q2 during this
interval is then low. Thus the waveform at the collector of Q2 is more or less a saw-tooth
waveform whose envelope is same as the modulating signal. This signal is then passes
through OP-AMP low pass filter to smooth the shape of envelope and finally it gives o/p
whose envelope is nearly equals to the modulating i/p signal.
Circuit Diagram:-
Procedure: 1. Study the circuit provided in the manual switch on the power supply.
2. Apply a PWM i/p to the base of the transistor Q1.
3. Connect one channel of CRO to observe modulating signal and other to
demodulated o/p.
4. First verify and note the PWM i/p signal.
5. Adjust the amplitude and frequency to obtain the demodulated o/p whose
envelope is nearly equals to the modulating signal.
6. Vary the amplitude and frequency of modulating i/p and observe the
corresponding change in demodulated o/p.
Result: The envelope of the sawtooth waveform can be set equals to the modulating signal hence
through OP-AMP IC 741 low pass filter we obtained demodulated o/p equals the
modulating signal the circuit can be used for pulse width demodulator.
Experiment No.:-14
Aim:- To study Pulse Position Demodulation and to observe the changes in
Demodulated output with respect to modulating i/p signal.
Equipment Required: -Pulse Position Modulator, CRO, Patch cords.
Components : -C1=0.1µF, C2=C3=10µF, C4=0.001µF, R1=10K, R2=15K pot,
R3=5.6K, R4=R5=R6=2.7K, IC 3140, IC 555.
Theory: In Pulse Position Modulation the analog AF input signal is converted into the PPM output
which means amplitude and duration of pulse remains constant. While the position of the
pulses relative to reference pulses changes in accordance with the modulating signals.
The pulse position demodulator is a circuit which gives the original modulating signal at
the output. When the pulse position modulated signal is applied at the input side then, the
original signal at the received at the receiver.
The pulse position demodulation circuit consists of two parts. First part is a IC 3140
comparator which gives the AF output with noise. This noise can be eliminated by the
filter using IC 741, which is the second part of the circuit.
IC 3140 is a comparator with two input i.e. pin no. 2 and 3 and output pin no. 6.Output
depends on the input comparision. Pin no.3 is kept at fixed voltage while output of the
PPM is applied at the pin no.2 of IC 3140. Depending on the voltage at the pin no. 2 the
output of the IC 3140 is changing. Since input is a PPM output the output is an AF output
with some noise. This noise is then removed with the help of low pass filter. A pure AF
output thus obtained at the output of the IC 741.
Circuit Diagram:-
Procedure: (1) Study the circuit provided in the manual.
(2) Apply PPM input. Keep the modulating frequency between 70-500 Hz.
(3) Connect the CRO at the output of IC 741 to get a Pulse Position Demodulated
output.
(4) Now vary the frequency and amplitude of modulating i/p & observe the
corresponding change in PPM demodulated output.
(5) Draw the above observation on the graph paper.
Conclusion: By adjusting the amplitude and frequency of the modulating signal and passing through
op-amp 741, low pass filter we obtained demodulated output equals to the modulating
signal.
Viva Questions:1. What are the applications of PPM?
2. What is the concept behind demodulating the PPM signal?
Experiment No.:-16
Aim: - To generate and to observe Phase Shift Keying (PSK) using IC1496.
Equipment Required: PSK kit, Function generator dual channel, CRO, Digital multimeter, IC1496.
Theory: The original source of information, text, speech, the most commonly used coding scheme
is binary sequence such as 0011101011. For transmission purpose this has to be
converted to a continuous electrical waveform, conversion process is referred to as the
modulation .The o/p of the PCM system is also a binary data. If they are to be transmitted
over copper wires, they can be Directly Transmitted as two voltage levels +v and –v. But
if they are to be transmitted through space using antenna, Phase Modulation is used. As
the modulating signal consists of only two levels the modulation technique is known as
Phase Shift Keying.
Phase Shift Keying is a modulation in which the phase of the carrier signal changes with
respect to the digital signal. The binary signal to be transmitted changes the phase of the
sine wave carrier depending upon whether 0 or 1 is transmitted. It is also called as Binary
Phase Shift Keying (BPSK).
The BPSK can be implemented by using a Balanced Modulator. IC1496 is used as a
Balanced Modulator for implementing BPSK. The circuit diagram is shown in the
manual.
The carrier is applied to pin no.8 and Modulating Binary signal is applied to pin no.1 The
BPSK O/P is taken from pin no. 12.IC 1496 internally consists of differential amplifier
configuration .its carrier suppression is rated at a minimum of –5db with a typical value
of –65db at 500khz.
Circuit Diagram:-
8
2
10
3
5
1 IC 1496
4
12
6
14
Procedure: 1) Study the circuit provided on the front panel of kit.
2) Apply the sine wave of 400Hz to pin no. 8.
3) Apply the square wave i.e. non linear binary data minimum 200Hz pin no.1
4) Connect CRO at the o/p i.e. pin no. 12.
5) Switch ON the power supply.
6) Observe the PSK O/P on the CRO.
7) Draw the observed waveform on the graph paper.
Observation Table: Sr. no.
Carrier signal
Amplitude (V)
frequency (KHz)
Modulating signal
Amplitude(V)
Freq(KHz)
Result: -
The carrier signal changes phase as Binary signal changes its state from logic 0 to logic 1.
Viva Questions:-
1. What is the advantage of PSK over FSK?
2. What is the difference between PSK, FSK and ASK?
Experiment No.17
Aim: - To study the phase shift keying demodulator circuit.
Equipments Required: PSK generator, CRO and connecting probes.
Theory: Demodulation of BPSK signal is done with a balanced modulator. The balanced
modulator is constructed using IC for better resolution and sensitivity, while it could be
constructed using diode and transformer. The BPSK signal and carrier signal is applied to
the balanced modulator IC for demodulation of the binary signal that is embedded into
the carrier signal. The key to demodulating BPSK is that a carrier with the correct
frequency and phase relationship must be applied to the balanced modulator along with
the BPSK signal.
Circuit Diagram: Balanced
Modulator
Low Pass
Filter
Data O/P
PSK I/P
Frequency
Multiplier
X2
Band Pass
Filter
Phase Detector
VCO
Frequency
Multiplier
X2
Procedure: (1)
(2)
(3)
(4)
(5)
Study the circuit given on the front panel of the kit.
Provide a PSK signal at the input terminal of the kit.
Connect the CRO probe at the output terminal for the kit.
Switch on the circuit.
Vary the rate of digital data in order to check the output from the CRO, which
reproduces the data that is being transmitted.
Result: The PSK Demodulator circuit gives the original binary transmitted data at the o/p. And as
the bit rate at the I/P of PSK modulator changes the O/P also changes accordingly.
Viva Questions:
1. What is Binary PSK?
2. What is the advantage of QPSK over PSK?
Experiment No.:-18
Aim: - To perform Quadrature Phase Shift Keying and verify the results on CRO.
Equipment Required: -QPSK kit, Function generator dual channel, CRO, Digital
Multimeter.
Theory: -
The Digital symbol outputs of the bit splitter fed to digital modulating inputs of two
balanced modulators. The first bit into the splitter is presented to the upper balanced
modulator & the second bit to the lower one. The reference carrier frequency (fc) is
applied to the input of the Top balanced modulator & to the lower one through 90 degree
phase shifter .The Phase shifter uses the Lag characteristics of resistor, capacitor circuit
to generate a signal, that is designed to lag the input by 90 degree.
The output from the balanced modulators, which will be in Phase with their respective fc
signal for a logic 1 binary input & 180 degree out of phase for logic 0,are fed to a linear
summer.
Linear summing avoids developing sum & difference frequencies normally generated by
a nonlinear circuit used for standard radio modulators. A bypass filter rejects unwanted
signal produced by the summer. The result at the output is a vector sum of the output of
the two balanced modulators.
Circuit Diagram:Data
I/p
011001
Balanced
Modulator
R3
R1
Din
Clock
2
Bit
Spli
tter
I/
P
fc
900
Shifter
QAM O/P
R2
R4
Clock
I/P
Balanced
Modulator
Procedure: 1) Study the circuit provided on the front panel of kit.
2) Apply the carrier signal to the kit at given socket. (1600Hz)
3) Connect CRO at the o/p i.e. pin no. 12.
4) Switch ON the power supply.
5) Observe the O/P on the CRO.
7) Draw the observed waveform on the graph paper.
Observation Table: Sr. no.
Carrier signal
Amplitude (V)
frequency (KHz)
Modulating signal
Amplitude(V)
Freq(KHz)
Result: The carrier signal changes the phase as the Binary signal changes its state from logic 0 to
logic 1.
Viva Questions:
1. What is the difference between PSK and QPSK?
2. What is DPSK?
Experiment No.19
Aim: - Generation of PAM signal using switching CMOS IC 4016 on breadboard and
observation of single polarity and dual polarity waveforms on Digital Storage
Oscilloscope.
Equipment required:-PAM kit, dual channel CRO, signal generator.
Component required:-R1=39K, R2=18K, R3=R4=10K,R5=10K pot
C1=0.01µf,C2=0.01µf,C3=1µf,IC1=555,IC2=4016 CMOS switch.
Theory:In pulse modulation some characteristics of pulse (carrier) is change in accordance with
the sample of the modulating signal .Such type of modulation is called as Pulse
Modulation. It is applied in many types .But some of common types are Pulse Amplitude
modulation (PAM) ,Pulse width modulation (PWM),and Pulse position modulation
(PPM).If the characteristics of pulse such as amplitude ,duration(width), position is
change in accordance with the modulating signal than it is called as PAM,PDM or PWM
and PPM respectively.
Pulse Amplitude Modulation the amplitude of the pulse is varied in accordance with the
modulating signal then it is called as pulse Amplitude modulation .Its waveform is
shown in fig 1.PAM gives dual polarity (AC type) PAM output called as natural PAM
sampling .But If DC level is introduced to the modulating signal then it results single
polarity PAM.
Circuit Diagram:
+Vcc
+12V
+Vcc
+12V
1K
39K
4
2
6
8
5
I/P
1K
IC 555
16
3
1
2
PAM O/P
0.01µF
13
7
Modulator IC 4016
Procedure:1. Assemble components and make connection on breadboard as shown in fig.
2. Switch on the power supply and note the amplitude and frequency of sample
pulse
internally generated by IC555 connect the same at pin 13 of CMOS IC
by using patch cord.
3. Apply a sine wave modulating signal of around 5-VPp, 70 Hz at the point marked
as I/P 4.Connect dual Channel CRO for at i/p and o/p side.
4. Adjust the amplitude and frequency of modulating i/p to get Dual polarity PAM
output.
5. Note DC voltage V2 given potential divider R3 and R4 now introduced DC
voltage V2 by shorting points A and B by patching repeat. In the above step keep
CRO in DC mode.
6. Vary the input frequency and amplitude of the modulating signal and observe the
corresponding change in PAM output.
Conclusion:As the amplitude of sampling pulse is changed in accordance with the modulating signal
so it is called as pulse amplitude modulation (PAM). By introducing DC voltage it gives
single polarity PAM output.
Viva Questions:1. What is the difference between single polarity and dual polarity PAM signal?
2. How single polarity PAM signal is generated from dual polarity PAM?
Experiment no.20
Aim: -To study the Pulse Code Modulation (PCM) and to simulate PCM in MATLAB.
simulink.
Requirements: -MATLAB software.
Theory:In PCM, the total amplitude range of the signal is divided into a number of standard
levels at equal intervals. These levels are transmitted in a binary code. Hence the actual
number of these standard level is a power of 2 such as 16,32,64,128.The signal is
continuously sampled and quantized ,each sample magnitude being converted to the
nearest standard amplitude .The quantized number is coded using binary code ,converted
into corresponding back-to–front binary number and then sent. If adequate quantizing
levels are used, the result closely resembles the corresponding analog transmission.
MATLAB Simulink Diagram:-
Simulink Results:Input Signal
Output Signal
Viva Questions:
1. What is sampling?
2. What is Quantization?
Experiment No.21
Aim: - Observation of Frequency spectrum of amplitude modulated (AM) signal on
Spectrum Analyzer.
Equipments required:- Spectrum analyzer, patch cords, connecting wires, function
generator, power supply, breadboard.
Components:Transistor BC 548/549 (1 no.), resistor 330 (2 no.), Inductor 1mH (1 no.)
Theory: In amplitude modulation, the amplitude of the carrier voltage varies in accordance with
the instantaneous value of modulating voltage. Let the modulating voltage be given by
expression,
Vm = Vm cos wmt
Where wm is angular frequency of the signal & Vm is the amplitude. Let the carrier
voltage be given by expression,
Vc = Vc coswct
On Amplitude Modulation, The instantaneous value of modulated carrier voltage is given
by,
V = V(t) cos wct
V(t)=Vc + ka Vm cos wmt
V=Vc[1+ ma cos wm t] cos wct
Where ma is modulation index and the modulation index is defined as the ratio of
maximum amplitude of modulating signal to maximum amplitude of carrier signal.
ma= K Vm / Vc
% modulation is defined as,
%ma=Vm/Vc
Circuit Diagram: -
Procedure:1. Assemble components and make the connections on the breadboard.
2. Adjust the function generator to obtain the sine wave of frequencies 2 KHz and 1
MHz respectively.
3. Apply the sine wave of modulating signal and carrier signal to the ckt.
4. Observe the resulting amplitude modulated signal on CRO.
5. Observe the same signal on spectrum analyzer.
6. Draw the frequency spectrum on graph paper.
Result: The sinusoidal voltage on being amplitude modulated by a single sinusoidal modulating
voltage consists of three frequency components- the difference components called as
lower sideband (LSB), the sum component called as upper sideband (USB) and carrier
component. The LSB is mirror image of the USB.
Viva Questions:
1. What is the bandwidth of AM signal?
2. What is the advantage of AM over FM?