Unit- 2 Angle Modulation.ppt

Analog Communication

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SUBJECT NAME: ANALOG COMMUNICATIONS
FACULTY NAME: Dr. M.NARESH
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2. ANALOG COMMUNICATIONS
COURSE OBJECTIVES:
1. To Analyze the Analog communication system requirements
2.To understand the Generation and Detection of various analog modulation
techniques
3.To Analyze the noise performance of analog modulation techniques
4.To understand AM and FM Receivers.
5. To Understand the Pulse modulation techniques
COURSEOUTCOMES:
CO1: Describe basic concepts of linear and non-linear modulation and
demodulation schemes
CO2: Compare analog modulation schemes in terms of modulation index,
transmission bandwidth, TX power etc.
CO3: Explaining various aspects of sampling theorem to produce various
pulse modulation schemes
CO4: Appreciate the structures of various AM and FM transmitters and
receivers and understand design parameters.
CO5: Estimate electronic noise parameters on various analog modulation
schemes.
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3. SYLLABUS
UNITI-LinearModulationschemes:Needformodulation,
conventionalAmplitudeModulation(AM).Doublesideband
suppressedcarrier(DSB–SC)modulation,Hilberttransform,
propertiesofHilberttransform.Pre-envelop.Complexenvelope
representationofbandpasssignals,In-phaseandQuadrature
componentrepresentationofbandpasssignals.Lowpass
representationofbandpasssystems.Singlesideband(SSB)
modulationandVestigial-sideband(VSB)modulation.Modulation
anddemodulationofallthemodulationschemes,COSTASloop.
UNITII-Anglemodulationschemes:FrequencyModulation(FM)
andPhasemodulation(PM),Conceptofinstantaneousphaseand
frequency.TypesofFMmodulation:NarrowbandFMandwide
bandFM.FMspectrumintermsofBesselfunctions.Directand
indirect(Armstrong's)methodsofFMgeneration.Balanced
discriminator,Foster–Seeleydiscriminator,Zerocrossingdetector
andRatiodetectorforFMdemodulation.AmplitudeLimiterinFM.
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4. UNITIV-Analogpulsemodulationschemes:Samplingof
continuoustimesignals.Samplingoflowpassandbandpasssignals.
Typesofsampling.PulseAmplitudeModulation(PAM)generation
anddemodulation.Pulsetimemodulationschemes:PWMandPPM
generationanddetection.TimeDivisionMultiplexing.
UNITIII-TransmittersandReceivers:Classificationof
transmitters.HighlevelandlowlevelAMtransmitters.FM
transmitters.PrincipleofoperationofTunedradiofrequency(TRF)
andsuperheterodynereceivers.SelectionofRFamplifier.Choiceof
Intermediatefrequency.Imagefrequencyanditsrejectionratio
Receivercharacteristics:Sensitivity,Selectivity,Fidelity,Double
spotting,AutomaticGainControl.
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UNITV-NoiseSourcesandtypes:Atmosphericnoise,Shotnoise
andthermalnoise.Noisetemperature.Noiseintwo-portnetwork:
noisefigure,equivalentnoisetemperatureandnoisebandwidth.
Noisefigureandequivalentnoisetemperatureofcascadestages.
Narrowbandnoiserepresentation.S/NratioandFigureofmerit
calculationsinAM,DSB-SC,SSBandFMsystems,Pre-Emphasisand
De-Emphasis

5. TEXT BOOKS /REFERENCES
TEXTBOOKS:
1.SimonHaykin,“CommunicationSystems,”2/e,WileyIndia,2011.,
2. B.P. Lathi, ZhiDing, “Modern Digital and Analog Communication
Systems”, 4/e, Oxford University Press, 2016
3.P.RamakrishnaRao,“AnalogCommunication,”1/e,TMH,2011.
REFERENCES:
1.Taub,Schilling,“PrinciplesofCommunicationSystems”,Tata
McGraw‐Hill,4thEdition,2013.
2.JohnG.Proakis,Masond,Salehi,“FundamentalsofCommunication
Systems”,PEA,1stEdition,2006
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6. LESSON PLAN:
UNIT II-Angle modulation schemes
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S. No. Topic(S)
No.
of Hrs
Relevant
COs
Text Book/
Reference
Book
1.
Angle modulation schemes: Frequency Modulation
(FM)
2 CO1 T1,T2,T3
2.
Phase modulation (PM), 1 CO1,CO2 T1,T2,T3
3.
Concept of instantaneous phase and frequency 1 CO2 T1,T2,T3
4.
Types of FM modulation: Narrow band FM 1 C01,CO2 T1,T2,T3
5.
wide band FM 1 C01,CO2 T1,T2,T3
6.
FM spectrum in terms of Bessel functions 1 CO2 T1,T2,T3
7.
Direct and indirect (Armstrong's) methods of FM
generation
1 CO1 T1,T2,T3
8.
Balanced discriminator, Foster–Seeley discriminator 1 CO1 T1,T2,T3
9.
Zero crossing detector and Ratio detector for FM
demodulation
1 CO1 T1,T2,T3
10.
Amplitude Limiter in FM 1 CO1 T1,T2,T3
TOTAL11

7. PRE-REQUISITES FOR THIS COURSE:
PTSP III-SEM 3-Credits
ES215EC :SS IV-SEM 3-Credits
EXTERNAL SOURCES FOR ADDITIONAL LEARNING:
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Description Proposed ActionsRelevance With POs
Relevance
With PSOs
Modulation &
Demodulation of all
Techniques including
multiplexing .
Communication Lab PO3, PO4, PO5 PSO2
CONTENT BEYOND SYLLABUS:
S. No. Topic Relevance with POs and
PSOs
1.Advanced Communication system PSO1

8. INTRODUCTION:
Analyzethebasicconceptsoffrequencymodulationlikesingletone,spectrumanalysis
offrequencymodulatedwaveandtransmissionbandwidthofFM.Understandthe
conceptsofnarrowbandfrequencymodulation,widebandfrequencymodulationand
preemphasisanddeemphasiscircuitsinFM.discussthegenerationoffrequency
modulationwavesbydirectmethodandindirectmethodanddetectionmethodslike
balancedfrequencydiscriminator,fosterseeleydiscriminator,phaselockedloopetc.,
OUTCOMES:
1.Analyzethebasicconceptsoffrequencymodulationlikesingletone,spectrumanalysisof
frequencymodulatedwaveandtransmissionbandwidthofFM.
2.Understandtheconceptsofnarrowbandfrequencymodulation,widebandfrequency
modulationandpreemphasisanddeemphasiscircuitsinFM.
3.Discussthegenerationoffrequencymodulationwavesbydirectmethodandindirect
methodanddetectionmethodslikebalancedfrequencydiscriminator,fosterseeley
discriminator,phaselockedloopetc.,
UNIT II-Angle modulation schemes
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9. INTRODUCTION:
2.1 Angle modulation schemes: frequency modulation and phase modulation
2.2 concept of instantaneous phase and frequency.
2.3 Types of FM modulation: narrow band FM and wide band FM.
2.4 FM spectrum in terms of Bessel functions.
2.5 Direct and indirect (Armstrong's) methods of FM generation.
2.6 Balanced discriminator, foster–seeleydiscriminator , ratio detector
2.7 zero crossing detector for FM demodulation.
2.8 Amplitude limiter in FM.
UNIT II-Angle modulation schemes
OUTCOMES:
Analyze generation and detection of FM signal and comparison between amplitude and
angle modulation schemes.
MATRUSRI
ENGINEERING COLLEGE

10. CONTENTS:
2.1 Angle modulation schemes:
frequency modulation and
phase modulation
OUTCOMES:
Discuss the Basic definition Of FM AND PM
.
MODULE-I
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11. Angle modulation : Angle modulation is the process by which the angle (frequency
or phase) of the carrier signal is changed in accordance with the instantaneous
amplitude of modulating or message signal.
Classified into two types such as
1. Frequency modulation (FM)
2.Phase modulation (PM)
2.1 Angle modulation schemes
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Used for :
1. Commercial radio broadcasting
2. Television sound transmission
3. Two way mobile radio
4. Cellular radio
5. Microwave and satellite communication system
Advantages over AM:
1.Freedomfrominterference:allnaturalandexternalnoiseconsistofamplitude
variations,thusreceiverusuallycannotdistinguishbetweenamplitudeofnoiseor
desiredsignal.AMisnoisythanFM.
2.Operateinveryhighfrequencyband(VHF):88MHz-108MHz
3.Cantransmitmusicalprogramswithhigherdegreeoffidelity

12. 1.FREQUENCY MODULATION:
InFMthecarrieramplitude remains constant,thecarrier
frequency varies with the amplitude of modulating signal.
The amount of change in carrier frequency produced by the modulating signal is
known as frequency deviation.
f
i(t)=f
c+k
fm(t)
2.1 Angle modulation schemes
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f
i(t)=f
c+k
fm(t)

13. 2.Phase modulation(PM):
The process by which changing the phase of carrier signal in accordance with the
instantaneous of message signal. The amplitude remains constant after the modulation
process.
2.1 Angle modulation schemes
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14. CONTENTS:
2.2 concept of instantaneous phase and frequency.
OUTCOMES:
Analyzethebasicconceptsoffrequencymodulationlikesingletone,spectrumanalysis
offrequencymodulatedwaveandtransmissionbandwidthofFM.
.
MODULE-2
MATRUSRI
ENGINEERING COLLEGE

15. Duringtheprocessoffrequencymodulationsthefrequencyofcarriersignalischanged
inaccordancewiththeinstantaneousamplitudeofmessagesignal.Thereforethe
frequencyofcarrieraftermodulationiswrittenas
To find the instantaneous phase angle of modulated signal, integrate equation above
w.r.to ‘t’:
2.2 concept of instantaneous phase and frequency
MATRUSRI
ENGINEERING COLLEGE tAtm
mmcos
Message signal
Carrier signal  tAtc
cccos
1.Frequency modulation: tAKtAK
mmfCmfci
 cos   t
AK
tdttAKdt
m
m
mf
CmmfCii


 sincos  
Thus, we get the FM wave as:)sincos(cos)( t
AK
tAActS
m
m
mf
CCiFM


  )sincos()( ttAtS
mfCCFM
 m
mf
f
AK


Where Modulation index

16. 2.PHASE MODULATION(PM):
Where = phase angle of carrier signal. It is changed in accordance with the amplitude
of the message signal;
2.2 concept of instantaneous phase and frequency
MATRUSRI
ENGINEERING COLLEGE tAtm
mmcos  tAtc
cccos  tAKtAK
mmpmp
 cos)( )coscos()(
)coscos()(
tmtAtS
tAKtAtS
mpCCpm
mmpCCpm




After phase modulation the instantaneous voltage will be
Where m
p= Modulation index of phase modulation
Kpis a constant and called deviation sensitivities of
the phase

17. FREQUENCY DEVIATION:
∆F is the relative placement of carrier frequency (Hz) w. r. t its un-modulated value.
Given as:
2.2 concept of instantaneous phase and frequency
MATRUSRI
ENGINEERING COLLEGEmfC
AK
max mfC
AK
min mfCCd
AK
minmax
 mf
d
AKf 


2 m
f
mf
f
f
AKf




;

18. Relationship between FM and PM:
2.2 concept of instantaneous phase and frequency
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Relationship between FM and PM

19. CONTENTS:
2.3 Types of FM modulation:
Narrow band FM and
wide band FM.
OUTCOMES:
Understand the concepts of narrow band frequency modulation, wide band frequency
modulation.
MODULE-3
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ENGINEERING COLLEGE

20. Types of FM Modulation:
NBFM (Narrow Band FM):
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE)sincos()( ttAtS
mfCCFM

Depends upon the Modulation index ,Frequency modulation classified into 2 types:
1.NBFM (Narrow Band FM) if
2.WBFM (Wide Band FM)1
f
 1
f
 1
f
 )2sin2cos()( tftfAtS
mfCCFM
 








sin
1cos
""2sin.
,3.01:sin
)]2sin().2sin()2sincos().2[cos()(
tbefLet
radceNBFM
tftftftfAtS
mf
f
mfCmfCCFM )]2sin().2sin([)]2[cos()(: tftfAtfAtSThen
cmfcccFM


21. MATRUSRI
ENGINEERING COLLEGE
2.3 TYPES OF FM MODULATION
NBFM (Narrow Band FM):
NBPM (Narrow Band PM): )])(2sin
2
))(2sin
2
)]2[cos()(
)])(2sin))(2[sin
2
)]2[cos()(
)]2sin().2cos([)]2[cos()(
tff
A
tff
A
tfAtS
tfftff
A
tfAtS
tftfAtfAtS
cmc
pc
mc
Pc
ccPM
cmcmc
Pc
ccPM
cmPcccPM











 )])(2cos
2
))(2cos
2
)]2[cos()(
)])(2cos))(2[cos
2
)]2[cos()(
)]2sin().2sin([)]2[cos()(
tff
A
tff
A
tfAtS
tfftff
A
tfAtS
tftfAtfAtS
cmc
fc
mc
fc
ccFM
cmcmc
fc
ccFM
cmfcccFM













22. Spectrum of NBFM:
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE)])(2sin
2
))(2cos
2
)]2[cos()( tff
A
tff
A
tfAtS
cmc
fc
mc
fc
ccFM
 





23. WBFM (WIDE BAND FM):
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE1
f
 )2sin2cos()( tftfAtS
mfCCFM
 ])(2cos[)(.)(
]).(Re[.)(
]).(.Re[.)(
)22(
22
0













n
mcfncW BFM
n
tnffj
fnc
n
tnj
fn
tfj
c
tnffJAtS
eJAtS
eJeAtS
mc
c






24. CONTENTS:
2.4 FM spectrum in terms of Bessel functions.
OUTCOMES:
Understand the concepts FM Bessel function
MODULE-4
MATRUSRI
ENGINEERING COLLEGE

25. 2.4 FM spectrum in terms of Bessel functions
WBFM (WIDE Band FM):Bessel Function
MATRUSRI
ENGINEERING COLLEGE







])2cos(cos).()2cos().([
])cos(cos).()cos().([cos)()(
)(2cos).()(
22
110
tJtJA
tJtJAtJAtS
tnffJAtS
mcmcc
mcmccccW BFM
m
n
cncFM


 

])2cos(cos)2).[cos((
])cos()).[cos((cos)()(
2
10
ttJA
ttJAtJAtS
mcmcc
mcmccccW BFM



26. WBFM with Bessel Function:
Properties of BESSELS Functions:
2.4 FM spectrum in terms of Bessel functions
MATRUSRI
ENGINEERING COLLEGE)(
2
)()(.5
0)(
""arg.4
0)(,2/)(,1)(;
!
2/
)(
)1(.3
1)(.2
)()1()(.1
11
10
2










nnn
n
on
n
n
n
n
n
n
n
J
n
JJ
JLt
nevaluesofForl
JJJ
n
J
lueofForsmallva
J
JJ

















 

])2cos(cos)2).[cos((
])cos()).[cos((cos)()(
2
10
ttJA
ttJAtJAtS
mcmcc
mcmccccW BFM



27. Power Calculation:
2.4 FM Power calculation & Bandwidth
MATRUSRI
ENGINEERING COLLEGER
JA
R
JA
PerCarrierPow
PPPPTotalpower
c
c
C
mcmcct
2
)(2
)(
)(
....)2()(
2
0
2
2
0


















 2
)([
2
)(.;
2
)(
2
)(
2
2
2
2
1
2
2
1
2
2
1
2
c
t
n
n
c
sidebandct
c
c
mc
c
mc
A
P
J
A
PPP
JisAAvg
JA
P
JA
P
















28. BANDWIDTH:
The theoretical bandwidth is “infinity”
According to the Carson’s Rule, for large band width of β, the band width of FM
slightly greater than the total frequency execution “2??????f”
2.4 FM Power calculation & Bandwidth
MATRUSRI
ENGINEERING COLLEGE
. )1(2
)1(2
)
1
1(2
)1(2
)22
)(2









m
m
m
m
m
m
m
m
mm
mm
f
f
fBW
fBW
fBW
or
f
f
fBW
ffBW
ffBW



29. CONTENTS:
2.5. Generation of FM wave
.OUTCOMES:
Discuss the generation of frequency modulation waves by direct method and indirect
method
MODULE-5
MATRUSRI
ENGINEERING COLLEGE

30. GENERATION OF FM WAVE:
1. Direct method
A. Direct FM VARACTOR diode modulation
b. Fm reactance modulator
c. Frequency stabilized reactance modulator
d. CROSS BY DIRECT FM transmitter
E. PLL
2. In -Direct method : ARMSTRONG METHOD
2.5. Generation of FM wave
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ENGINEERING COLLEGE
DETECTION OF FM WAVE:
1.Slope Detector
2.FoosterseelyDetector
3.Ratio FM Detector
4.Zero crossing
5.QuadratureFM Demodulator
6.PLL Non linear and Linear methods

31. GENERATION OF FM WAVE: Direct method:
2.5. Generation of FM wave
MATRUSRI
ENGINEERING COLLEGE )()(
2
)(
2
1)](1()(
)](1[
)(
)(1[2
1
)(
)((2
1
)(,,0)(,
2
1
00
0
0
0
0
2
1
0
0
2
1
0
0
0
00
00
00
0
tmkfftm
c
kf
ftm
c
k
tm
c
k
ftf
tm
c
k
f
tf
tm
c
k
CL
tf
tkmCL
tfthenfreqtmwhen
CL
f
i
i
i
i












32. GENERATION OF FM WAVE: IN-DIRECT METHOD:
2.5. Generation of FM wave
MATRUSRI
ENGINEERING COLLEGE
First Generate NBFM then convert into WBFM]sincos[)(
.....]sincos[[
]sincos[.)(
.....)(
]sincos[)(
0
2
1
02
2
22
2
11102
1
tntnAtV
AfterBPF
ttAa
ttAatV
VaVaVatV
ttAtV
mc
mcc
mcc
mcc










33. CONTENTS:
2.5. Detection of FM
OUTCOMES:
Discuss the Detection of frequency modulation waves by detection methods like
balanced frequency discriminator, foster seeleydiscriminator,
.
MODULE-6
MATRUSRI
ENGINEERING COLLEGE

34. 2.6. Detection of FM wave
MATRUSRI
ENGINEERING COLLEGE
Simple Slope Detector:

35. SIMPLE SLOPE DETECTOR :
It can be seen from the diagram that changes in the slope of the filter, reflect into the linearity of the
demodulation process. The linearity is very dependent not only on the filter slope as it falls away, but
also the tuning of the receiver -it is necessary to tune the receiver off frequency and to a pint where
the filter characteristic is relatively linear.
The final stage in the process is to demodulate the amplitude modulation and this can be achieved
using a simple diode circuit. One of the most obvious disadvantages of this simple approach is the
fact that both amplitude and frequency variations in the incoming signal appear at the output.
However the amplitude variations can be removed by placing a limiter before the detector.
A variety of FM slope detector circuits may be used, but the one below shows one possible circuit
with the applicable waveforms. The input signal is a frequency modulated signal. It is applied to the
tuned transformer (T1, C1, C2 combination) which is offset from the centre carrier frequency. This
converts the incoming signal from just FM to one that has amplitude modulation superimposed upon
the signal.
This amplitude signal is applied to a simple diode detector circuit, D1. Here the diode provides the
rectification, while C3 removes any unwanted high frequency components, and R1 provides a load.
2.6. Detection of FM wave
MATRUSRI
ENGINEERING COLLEGE

36. .
2.6. Demodulation of FM wave
MATRUSRI
ENGINEERING COLLEGE
Single Tuned FM Detector
Balanced slope Detector:

37. Operation of Balanced slope Detector:
Thebalancedslopedetectorisalsoknownasthetravisdetector(afteritsinventor),
thetriple-tuneddiscriminator(forobviousreasons),andastheamplitude
discriminator(erroneously).Thecircuitusestwoslopedetectors.Theyareconnected
backtoback,totheoppositeendsofacenter-tappedtransformer,andhencefed180°
outofphase.ThetopsecondarycircuitistunedabovetheIFbyanamountwhich,inFM
receiverswithadeviationof75khz,is100khz.Thebottomcircuitissimilarlytuned
belowtheIFbythesameamount.Eachtunedcircuitisconnectedtoadiodedetector
withanRCload.Theoutputistakenfromacrosstheseriescombinationofthetwoloads,
sothatitisthesumoftheindividualoutputs.
Letf
cbetheIFtowhichtheprimarycircuitistuned,andletf
c+δfandf
c–δfbethe
resonantfrequenciesoftheuppersecondaryandlowersecondarycircuitsT’andT”,
respectively.Whentheinputfrequencyisinstantaneouslyequaltof
c,thevoltageacross
T’,thatis,theinputtodiodeD
1,willhaveavaluesomewhatlessthanthemaximum
available,sincef
cissomewhatbelowtheresonantfrequencyofT’.Asimilarcondition
existsacrossT”.Infact,sincef
cisjustasfarfromf
c+δfasitisfromf
c–δf,thevoltages
appliedtothetwodiodeswillbeidentical.Thedcoutputvoltageswillalsobeidentical,
andthusthedetectoroutputwillbezero,sincetheoutputofD
1ispositiveandthatof
D
2isnegative.
2.6. Demodulation of FM wave
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38. Now consider the instantaneous frequency to be equal to fc + δf. Since T’ is tuned to this frequency,
the output of D1 will be quite large. On the other hand, the output of D2 will be very small, since the
frequency fc + δf is quite a long way from fc –δf. Similarly, when the input frequency is
instantaneously equal to fc –δf, the output of D2 will be a large negative voltage, and that of D1 a
small positive voltage. Thus in the first case the overall output will be positive and maximum, and in
the second it will be negative and maximum.
When the instantaneous frequency is between these two extremes, the output will have some
intermediate value. It will then be positive or negative, depending on which side of fc the input
frequency happens to lie. Finally, if the input frequency goes outside the range described, the output
will fall because of the behavior of the tuned circuit response. The required s-shaped frequency-
modulation characteristic (as shown in figure 6-35) is obtained.
Although this detector is considerably more efficient than the previous one, it is even trickier to align,
because there are now three different frequencies to which the various tuned circuits of the
transformer must be adjusted. Amplitude limiting is still not provided, and the linearity, although
better than that of the single slope detector FM demodulation, is still not good enough.
2.6. Detection of FM wave
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39. 2.6. Demodulation of FM wave
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40. FOSTER SEELY DISCRIMINATOR:
ItusesatunedRFtransformertoconvertfrequencychangesintoamplitudechanges.Atransformer,
tunedtothecarrierfrequency,isconnectedtotworectifierdiodes.Thecircuitresemblesafull-wave
bridgerectifier.Iftheinputequalsthecarrierfrequency,thetwohalvesofthetunedtransformer
circuitproducethesamerectifiedvoltageandtheoutputiszero.Asthefrequencyoftheinput
changes,thebalancebetweenthetwohalvesofthetransformersecondarychanges,andtheresultis
avoltageproportionaltothefrequencydeviationofthecarrier.
Foster–Seeleydiscriminatorsaresensitivetobothfrequencyandamplitudevariations,unlikesome
detectors.Thereforealimiteramplifierstagemustbeusedbeforethedetector,toremoveamplitude
variationsinthesignalwhichwouldbedetectedasnoise.Thelimiteractsasaclass-Aamplifieratlower
amplitudes;athigheramplitudesitbecomesasaturatedamplifierwhichclipsoffthepeaksandlimitsthe
amplitude.
2.6. Demodulation of FM wave
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41. The ratio detector is a type of detector circuit, commonly used in radio receivers for demodulating
frequency modulated (FM) signal.
The ratio detector is a variant of the Foster-Seeley discriminator, but one diode conducts in an
opposite direction, and using a tertiary winding in the preceding transformer. The output in this case
is taken between the sum of the diode voltages and the center tap.
The output across the diodes is connected to a large value capacitor, forming a dynamic limiter. The
ratio detector has the advantage over the Foster-Seeley discriminator that it does not respond to
amplitude modulation (AM) signals, thus potentially saving a limiter stage; however, the output is
only 50% of the output of a discriminator for the same input signal. The ratio detector has wider
bandwidth, but more distortion than the Foster-Seeley discriminator.
2.6. Demodulation of FM wave
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RATIO DETECTOR

42. 2.6. Demodulation of FM wave
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Discrimination method

43. CONTENTS:
2.7 zero crossing detector for FM demodulation
2.8 amplitude limiter in FM
phased lock loop (PLL)
OUTCOMES:
Discuss the Detection of frequency modulation by phase locked loop etc.,
.
MODULE-7
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44. 2.7 zero crossing detector for FM demodulation.
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45. The limiter is a form of clipping device, a circuit whose output tends to remain constant
despite changes in the input signal. Most limiters behave in this fashion, provided that
the input voltage remains within a certain range.
2.8 Amplitude limiter in FM
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Amplitude limiter in FM

46. Aphase-lockedlooporphaselockloop(PLL)isacontrolsystemthatgeneratesan
outputsignalwhosephaseisrelatedtothephaseofaninputsignal.Thereareseveral
differenttypes;thesimplestisanelectroniccircuitconsistingofavariablefrequency
oscillatorandaphasedetectorinafeedbacklooptheoscillatorgeneratesaperiodic
signal,andthephasedetectorcomparesthephaseofthatsignalwiththephaseofthe
inputperiodicsignal,adjustingtheoscillatortokeepthephasesmatched.
Phased Lock Loop (PLL)
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Sout ( t ) Sf ( t )
Sphase( t )
Voltage Controlled
Oscillator (VCO)
SVCO ( t ) = AVCO ·sin [ 0 t +  0( t )]
Sf ( t ) = Af ·cos [ c t +  ( t )]
SVCO ( t )
Phase
Detector
Low-pass
filter

47. 1. Draw and explain Armstrong method of generation of FM signal.
2. Derive the expression for a single tone FM signal in terms of Bessel function jn(β). Hence, obtain
the spectrum of FM signal.
3. Obtain mathematical representation of FM and PM.
4. An FM wave is represented by v=12sin (6X 10
8
t+5 sin 1250t). Find the carrier and modulating
frequencies, the modulation index and maximum deviation of FM wave. Is it narrow band or
wideband FM? What power this FM will dissipate in a 10ohm resistor?
5. Explain the different FM types?
Assignment Question
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48. Short answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1.Derive an expression for single tone FM wave. L1 CO2
2.State Carson’s rule of FM bandwidth L1 CO2
3.Differentiate between NBFM and WBFM. L1 CO2
4.Compare AM & FM and list out the applications . L1 CO2
5.What is the need of limiter circuit in FM receiver? L1 CO2

49. Long answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1.Explain the Armstrong method of FM generation L2 CO2
2.Describe the balanced slope detection o0f FM
demodulation?
L4 CO2
3.An FM wave is represented by V=12sin (6X 10
8
t+5 sin
1250t). Find the carrier and modulating frequencies, the
modulation index and maximum deviation of FM wave. Is it
narrow band or wideband FM? What power this FM will
dissipate in a 10ohm resistor?
L2
CO2
4.Draw the circuit of Foster-seelydiscriminator and explain
how it can be used in the detection of FM signal.
L2 CO2
5.Explain with Appropriate theory and block diagrams the
working of an FM demodulator using PLL.
L2 CO2

50. THE-END
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