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Analog Communications Lab
INDEX
Signature of Lab-In-charge HOD
INSTRUCTIONS TO STUDENTS
Turbomachinery Institute Science & Technology 1 Dept. ofECE
S.No Name of the Experimentage
No
Date of
erformance
Date Of
Submission
Assessment
of mar!s
"#ax $%#&
Sign. Of
'acult(
1.Amplitude Modulation &
Demodulation
2. Diode Detector Characteristics
.!re"uency Modulation &
Demodulation
#. $alanced Modulator
%. re'(mphasis & De'emphasis
). Mi*er Characteristics
+. Digital hase Detector
,. hase -oced -oop
/. Synchronous Detector
10 AC Characteristics
11 !re"uency Synthesier
12. S"uelch Circuit
A)erage mar!s
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Students shall read the points given below for understanding the theoretical concepts and Practical applications.
1. Listen carefully to the lecture given by teacher about importance of subject, curriculum philosophy, Learning
structure, skills to be developed, information about equipment, instruments, procedure, method of continuous
assessment, tentative plan of work in Laboratory and total amount of work to be done in a semester.
2. Students shall undergo study visit of the laboratory for types of equipment, instruments and material to be
used, before performing experiments.
3. Read the write up of each experiment to be performed, a day in advance.
4. Organize the work in the group and make a record of all observations.
5. Understand the purpose of experiment and its practical implications.
6. Student should not hesitate to ask any difficulty faced during conduct of practical / exercise.
7. Student shall develop maintenance skills as expected by the industries.
,. Student should develop the habit of pocket discussion / group discussion related to the experiments/
exercises so that exchanges of knowledge / skills could take place.
9. Student should develop habit to submit the practical, exercise continuously and progressively on the
scheduled dates and should get the assessment done.
10. Student shall attempt to develop related hands - on - skills and gain confidence.
11. Student shall focus on development of skills rather than theoretical or codified knowledge.
12. Student shall visit the nearby workshops, workstation, industries, laboratories, technical exhibitions trade fair
etc. even not included in the Lab Manual. In short, students should have exposure to the area of work right in the
student hood.
13. Student shall develop the habit of evolving more ideas, innovations, skills etc. those included in the scope of
the manual.
14. Student shall refer to technical magazines, proceedings of the Seminars, refer websites related to the scope
of the subjects and update their knowledge and skills.
15. The student shall study all the questions given in the laboratory manual and practice to write the answers to
these questions.
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Analog Communications Lab
Exp No* $ Date*
A#LI+,DE #OD,LA+ION DE#OD,LA+ION
AI#* To study the function of Amplitude Modulation & Demodulation 3under modulation4 perfect
modulation & o5er modulation6 and also to calculate the modulation inde*.
AAA+,S E/,IED*
S. No. Component Specification /uantit(
1 Transistor $C10+ 2
2 7esistors
10089 2
#.+89 2
2+0 9 1
9 1
Capacitors#.+:! 2
0.001:! 1# Diode 0A+/ 1
% !unctions enerator 1Mh 2
) 7egulated o;er Supply 30'06< 1
+ $read $oard 1
, Cathode 7ay =scilloscope 0'20M> 1
/ Connecting ?ires Single Strand As 7e"uired
+HEO0*
Modulator sectionillustrates the circuit of modulating amplifier employing a transistor as an acti5e de5ice
in C( mode. 71& 72establish a "uiescent for;ard bias for the transistor. The modulating signal fed at the
emitter section causes the bias to increase or decrease in accordance ;ith the modulating signal. Cis bypass
capacitor for carrier. Thus the carrier signal applied at the base gets amplified more ;hen the amplitude of
the modulating signal is at its ma*imum and less ;hen the amplitude of the modulating signal is small. C2
couples the modulated signal to output of the modulator. Demodulationin5ol5es t;o operations.
i6 7ectification of the modulated signal and
ii6 (limination of 7! components of the rectified signal.
The diode in the circuit diagram of demodulator does half ;a5e rectification. The rectified signal is applied
to a lo; pass filter to e*tract the modulating signal.
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71 7
C2
=utput
C1 $ C -1100 >
7! Input $C 10+
72 (
7# C
A! Input
Demo2ulator*
D1
AM Input A! =utput
=A +/ 18
1n!
E3EC+ED 4A5E'O#S*-
OCED,E*
1. Made the connections according to Circuit Diagram.
2. Measure and note do;n the fre"uency & amplitude 3p'p6 of the fi*ed carrier signal.
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Analog Communications Lab
. Measure and note do;n the fre"uency & amplitude 3p'p6 of the fi*ed message signal.
#. Apply fi*ed fre"uency carrier signal to 7! input terminals.
%. Apply modulating signal to A! input terminals.
). ote do;n and trace the modulated signal en5elope on the C7= screen.
+. !ind the modulation inde* by measuring
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/,ES+IONS
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Analog Communications Lab
1. AM is Defined as EEEEEEEEEEEE
2. Dra; its spectrumEEEEEEEEEEE
. Dra; the phase representation of an amplitude modulated ;a5eEEE
#. Modulation inde* is defined asEEEEE
%. The different degrees of modulation EEEEEEE
). ?hat are the limitations of s"uare la; modulator
+. Compare linear and nonlinear modulators
,. Compare base modulation and emitter modulation
/. AM Demodulator is EEEEEEEEEEE
10. Detection process EEEEEEEEE
11. The different types of distortions that occur in an en5elop detector areEEEEEEEEEE
12. (limination of distortions in (n5elope Detector EEEEEEEEEEEEEEEEEE techni"ue ;e use.
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Turbomachinery Institute Science & Technology , Dept. ofECE
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Turbomachinery Institute Science & Technology / Dept. ofECE
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Turbomachinery Institute Science & Technology 10 Dept. of
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Exp No* 6 Date*
DIODE DE+EC+O CHAAC+EIS+ICS
AI#* To perform demodulation of an amplitude modulated signal using
3i6 Simple diode detector and 3ii6 ractical diode detector
AAA+,S E/,IED*
S. No. Component Specification /uantit(
1 Transistor $C10+ 2
2 7esistors
10089 2
#.+89 2
2+0 9 1
9 1
Capacitors
#.+:! 2
0.001:! 1
1
/ otentiometer 1008 9 1
10 Connecting ?ires Single Strand As 7e"uired
+HEO0* Demodulation in5ol5es t;o operationsF
3i6 7ectification of the modulated ;a5e and
3ii6 (limination of 7! components of the rectified modulated ;a5e
Simple Dio2e Detector
The diode is the most common de5ice used in AM demodulator. Signal 3AM modulated signal6 is
applied to anode and output is taen from cathode. Diode operates as half ;a5e rectifier and passes only
positi5e half cycle of the modulated ;a5 e. !urther signal is applied to a parallel combination of resistor
37d6 and capacitor 3Cd6 ;hich acts as a lo; pass filter. This -! allo;s only lo; fre"uency signal to output
and it by passes 7! component to the ground.
This simple diode detector has the disad5antage that the output 5oltage4 in addition to being
proportional to the modulating signal4 also has a dc component4 ;hich represents the a5erage en5elope
amplitude 3i.e. carrier signal6 and a small 7! ripple. >o;e5er these un;anted components are remo5ed in a
practical detector lea5ing only A! signal.
CIC,I+ DIA1A#*
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Analog Communications Lab
E3EC+ED 4A5E'O#S*-
AM Modulated signal
ractical Dio2e Detector*
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ECE
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Analog Communications Lab
In practical diode detector the cathode terminal of the diode is connected to one end of the secondary
of I! transformer. The other end is grounded. Secondary is tuned ;ith the capacitor C1. The capacitors C2
and C are used for 7! filtering.
The modulated signal is applied at the input of I! transformer. The 5oltage applied is negati5e and
hence the cathode of the diode passes is connected to the I! transformer. So the diode passes both the
positi5e and negati5e half cycles. The 7! filtering is done by C2and C. The output is taen at the 5olume
control.
OCED,E*-
1. Connect the circuit as per the circuit diagram and s;itch on the po;er supply. 3 Measure the
po;er supply 5oltage4 12< and '12 fre"uency.. o; connect the modulator output to the simple diode detector input.
#. =bser5e the A! signal at the output to the simple diode detector at appro*imately %0G
modulation using C7=.
%. Compare it ;ith the original A! and obser5e that the detected signal is same as the A! signal
applied. Thus no information is lost in the process of modulation. 3oteF =nly ;a5e shape and
fre"uency ;ill be same4 amplitude ;ill be attenuated and phase may change6
). To obser5e AM ;a5e at different fre"uencies4 connect A! signal from e*ternal signal generator
to the input of modulator and obser5e demodulated ;a5e at different fre"uencies.
+. 7epeat the e*periment using practical diode detector circuit.
ECA,+IONS*
ES,L+*
Turbomachinery Institute Science & Technology 1 Dept. of
ECE
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A! output
/,ES+IONS
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ECE
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Analog Communications Lab
1. Selecti5ity of recei5er is defined as EEEEEEEEEEEEE
2. Sensiti5ity of a recei5er is defined as EEEEEEEEEEEE
2. The purpose of diode in diode detector circuit is EEEEEEEEEE
. The disad5antages of simple diode detector circuit are EEEEEEE
#. The factors influencing the choice of intermediate fre"uency in recei5ers EEEEE
%. The ad5antages of practical diode detector areEEEEEEEE
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Turbomachinery Institute Science & Technology 1+ Dept. of
ECE
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ECE
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Exp No* 7 Date*
'E/,ENC0 #OD,LA+ION AND DE#OD,LA+ION
AI#*To study the functioning of fre"uency modulation & demodulation and to calculate the modulation
inde*.
AAA+,S E/,IED
S. No. Component Specification /uantit(
1 ICs H7 220)4 -M %)% 1 (ach
2 7esistors
100894 #.+89 2 (ach
1089 1
2209 1
#+89 1
Capacitors
0.01:!40.001:! 2
0. 1:!4 #+0p!4 0.01p! 1
1:!410:! 1# !unctions enerator 1Mh 2
% 7egulated o;er Supply 30'126< 1
) $read $oard 1
+ Cathode 7ay =scilloscope 0'20M> 1
, Connecting ?ires Single Strand As 7e"uired
+HEO0*
1. A! eneratorF
This is an op'amp placed ;ein bridge oscillator. A !(T input "uad =p'Amp 3ICT-0,#6 is used here
to generate lo; fre"uency signals of %00 > and %8> to use as modulating signal. In this
e*periment4 a s;itch is pro5ided to change the fre"uency. 7e"uired amplification is pro5ided to
a5oid loading effect.
2. 7egulated po;er supplyF
This consists of bridge rectifier4 capacitor filters and three terminal regulators to pro5ide re"uired dc
5oltages in the circuit i.e. 1%
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#.+ 10 !B)5
1008 #+8 8
A! IB! !M =B
108
0.1
!
220
0.01 !
1 !B)5
're8uenc( Demo2ulation Circuit Diagram*
%5
108 108!
0.1 !A! Input
),0 18!
A! =utput
),0 #+0!
% !re"uency to use
as carrier signal in this e*periment. AdJustments for Amplitude and !re"uency are pro5ided in panel for
ease of operation.
2. AF Generator:
-o; !re"uency signal of appro*imately %8> is generated using ='AM based ?ein' $ridge oscillator.
IC T- 0,# is used as an acti5e component T- 0,# is !(T input general purpose "uad ='AM integrated
circuit. =ne of the ='AM has been used as amplifier to impro5e signal le5el. !acility is pro5ided to
change output 5oltage.
3. Regulated Power Supply:
This consists of bridge rectifier4 capacitor filters and three terminal regulators to pro5ide re"uired DC
5oltage in the circuit i.e. 1254 ',5 1%0 MA each.
CIC,I+ DIA1A#*
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ECE
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Analog Communications Lab
4. Modulator:
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Analog Communications Lab
The IC MC 1#/) is used as Modulator in this e*periment. MC 1#/) is a monolithic integrated circuit
balanced modulatorBDemodulator4 is 5ersatile and can be used up to 200 Mh. MultiplierF A balanced
modulator is essentially a multiplier. The output of the MC 1#/) balanced modulator is proportional to the
product of the t;o input signals. If you apply the same sinusoidal signal to both inputs of a ballooned
modulator4 the output ;ill be the s"uare of the input signal AM'DS$BSCF If you use t;o sinusoidal signals
;ith deferent fre"uencies at the t;o inputs of a balanced modulator 3multiplier6 you can produce AMDS$B
SC modulation. This is generally accomplished using a high' fre"uency NcarrierO sinusoid and a lo;er
fre"uency NmodulationO ;a5eform 3such as an audio signal from microphone6. The figure 1.1 is a plot of a
DS$'SC ;a5eform4 this figure is the graph of a 1008> and a % 8> sinusoid multiplied together. !igure
1.2 sho;s the circuit that you ;ill use for this e*periment using MC 1#/) balanced modulatorBdemodulator.
Note: In re!uen"y dou#l$ng I t%e $nput t$&e per$od $' ()* ater re!uen"y dou#l$ng t%e t$&e per$od '%ould
#e %aled.$.e+*),2*.
OCED,E*-
I-Fre!uen"y ou#ler
1. Connect the circuit as per the gi5en circuit diagram.
2. S;itch on the po;er to the trainer it.
. Apply a % 8> signal to both 7! and A! inputs of 0.1
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ES,L+*
/,ES+IONS
1. The t;o ;ays of generating DS$ESC are EEEEEEEE
2. The applications of balanced modulator are EEEEEEEE
. The ad5antages of suppressing the carrier EEEEEEEE
#. The ad5antages of balanced modulator EEEEEEEEEE
%. The ad5antages of 7ing modulator EEEEEEEEEE
). The e*pression for the output 5oltage of a balanced modulator is EEEEEEEEE
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Exp No* ; Date*
E-E#HASIS DE-E#HASIS
AI#* To study the functioning of re'(mphasis and De'(mphasis circuits.
AAA+,S E/,IED*
S. No. Component Specification /uantit(
1 7esistors 189 2
2 Capacitors0.1:! 2
0.001:! 1
!unctions enerator 1Mh 2
# 7egulated o;er Supply 30'06< 1
% $read $oard 1
) Cathode 7ay =scilloscope 0'20M> 1
+ Connecting ?ires Single Strand As 7e"uired
+HEO0*
!re"uency modulation is much immune to noise than amplitude modulation and significantly more
immune than phase modulation. A single noise fre"uency ;ill affect the output of the recei5er only if it falls
;ith in its pass band.
The noise has a greater effect on the higher modulating fre"uencies than on lo;er ones. Thus4 if the
higher fre"uencies ;ere artificially boosted at the transmitter and correspondingly cut at the recei5er4
impro5ement in noise immunity could be e*pected. This booting of the higher fre"uencies4 in accordance
;ith a pre'arranged cur5e4 is termed pre'emphasis4 and the compensation at the recei5er is called de'
emphasis. If the t;o modulating signals ha5e the same initial amplitude4 and one of them is pre'emphasied
to 3say6 t;ice this amplitude4 ;hereas the other is unaffected 3being at a much lo;er fre"uency6 then the
recei5er ;ill naturally ha5e to de'emphasie the first signal by a factor of 24 to ensure that both signals ha5e
the same amplitude in the output of the recei5er. $efore demodulation4 i.e. ;hile susceptible to noise
interference the emphasied signal had t;ice the de5iation it ;ould ha5e had ;ithout pre'emphasis4 and ;as
thus more immune to noise. Alternati5ely4 it is seen that ;hen this signal is de'emphasied any noise
sideband 5oltages are de'emphasied ;ith it4 and therefore ha5e a correspondingly lo;er amplitude than
they ;ould ha5e had ;ithout emphasis again their effect on the output is reduced. The amount of pre'
emphasis in P.S !M broadcasting4 and in the sound transmissions accompanying tele5ision4 has been
standardied at +% microseconds4 ;hereas a number of other ser5ices4 notably CCI7 and Australian T