This document provides information about the Analog Communications course offered at Matrusri Engineering College. It includes the course objectives, outcomes, syllabus, lesson plan and introduction. The key points are: - The course objectives are to analyze analog communication systems and understand various analog modulation techniques, noise performance and AM/FM receivers. - The syllabus covers topics like linear modulation schemes, angle modulation schemes, transmitters and receivers, noise sources and types, and analog pulse modulation schemes. - The lesson plan provides details of topics to be covered in each unit, including frequency modulation, phase modulation, and modulation/demodulation techniques. - The introductions provide an overview of the topics to be discussed in each

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SUBJECT NAME: ANALOG COMMUNICATIONS
FACULTY NAME: Dr. M.NARESH
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MATRUSRI
ENGINEERING COLLEGE

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
COURSE OUTCOMES:
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
UNIT I- Linear Modulation schemes: Need for modulation,
conventional Amplitude Modulation (AM). Double side band
suppressed carrier (DSB –SC)modulation ,Hilbert transform,
properties of Hilbert transform. Pre-envelop. Complex envelope
representation of band pass signals, In-phase and Quadrature
component representation of band pass signals. Low pass
representation of band pass systems. Single side band (SSB)
modulation and Vestigial-sideband (VSB) modulation. Modulation
and demodulation of all the modulation schemes, COSTAS loop.
UNIT II- Angle modulation schemes: Frequency Modulation (FM)
and Phase modulation (PM), Concept of instantaneous phase and
frequency. Types of FM modulation: Narrow band FM and wide
band FM. FM spectrum in terms of Bessel functions. Direct and
indirect (Armstrong's) methods of FM generation. Balanced
discriminator, Foster–Seeley discriminator ,Zero crossing detector
and Ratio detector for FM demodulation. Amplitude Limiter in FM.
MATRUSRI
ENGINEERING COLLEGE

4. UNIT IV- Analog pulse modulation schemes: Sampling of
continuous time signals. Sampling of low pass and band pass signals.
Types of sampling. Pulse Amplitude Modulation (PAM) generation
and demodulation. Pulse time modulation schemes: PWM and PPM
generation and detection. Time Division Multiplexing.
UNIT III- Transmitters and Receivers: Classification of
transmitters. High level and low level AM transmitters. FM
transmitters. Principle of operation of Tuned radio frequency (TRF)
and super heterodyne receivers. Selection of RF amplifier. Choice of
Intermediate frequency. Image frequency and its rejection ratio
Receiver characteristics: Sensitivity, Selectivity, Fidelity, Double
spotting, Automatic Gain Control.
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UNIT V- Noise Sources and types: Atmospheric noise, Shot noise
and thermal noise. Noise temperature. Noise in two-port network:
noise figure, equivalent noise temperature and noise bandwidth.
Noise figure and equivalent noise temperature of cascade stages.
Narrow band noise representation. S/N ratio and Figure of merit
calculations in AM, DSB-SC, SSB and FM systems, Pre-Emphasis and
De-Emphasis

5. TEXT BOOKS /REFERENCES
TEXT BOOKS:
1. Simon Haykin, “Communication Systems,” 2/e, Wiley India, 2011.,
2. B.P. Lathi, Zhi Ding, “Modern Digital and Analog Communication
Systems”, 4/e, Oxford University Press, 2016
3. P. Ramakrishna Rao, “Analog Communication,” 1/e, TMH, 2011.
REFERENCES:
1.Taub, Schilling, “Principles of Communication Systems”, Tata
McGraw‐Hill, 4th Edition, 2013.
2. John G. Proakis, Masond, Salehi, “Fundamentals of Communication
Systems”, PEA, 1st Edition,2006
MATRUSRI
ENGINEERING COLLEGE

6. LESSON PLAN:
UNIT II- Angle modulation schemes
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ENGINEERING COLLEGE
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
TOTAL 11

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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ENGINEERING COLLEGE
Description Proposed Actions Relevance 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:
Analyze the basic concepts of frequency modulation like single tone , spectrum analysis
of frequency modulated wave and transmission bandwidth of FM. Understand the
concepts of narrow band frequency modulation, wide band frequency modulation and
pre emphasis and de emphasis circuits in FM. discuss the generation of frequency
modulation waves by direct method and indirect method and detection methods like
balanced frequency discriminator, foster seeley discriminator, phase locked loop etc.,
OUTCOMES:
1. Analyze the basic concepts of frequency modulation like single tone , spectrum analysis of
frequency modulated wave and transmission bandwidth of FM.
2. Understand the concepts of narrow band frequency modulation, wide band frequency
modulation and pre emphasis and de emphasis circuits in FM.
3. Discuss the generation of frequency modulation waves by direct method and indirect
method and detection methods like balanced frequency discriminator, foster seeley
discriminator, phase locked loop etc.,
UNIT II- Angle modulation schemes
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ENGINEERING COLLEGE

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–seeley discriminator , 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
MATRUSRI
ENGINEERING COLLEGE

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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ENGINEERING COLLEGE
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.Freedom from interference: all natural and external noise consist of amplitude
variations, thus receiver usually cannot distinguish between amplitude of noise or
desired signal. AM is noisy than FM.
2. Operate in very high frequency band (VHF): 88MHz-108MHz
3. Can transmit musical programs with higher degree of fidelity

12. 1.FREQUENCY MODULATION:
In FM the carrier amplitude remains constant, the carrier
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.
fi(t)=fc+kfm(t)
2.1 Angle modulation schemes
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fi(t)=fc+kfm(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:
Analyze the basic concepts of frequency modulation like single tone , spectrum analysis
of frequency modulated wave and transmission bandwidth of FM.
.
MODULE-2
MATRUSRI
ENGINEERING COLLEGE

15. During the process of frequency modulations the frequency of carrier signal is changed
in accordance with the instantaneous amplitude of message signal .Therefore the
frequency of carrier after modulation is written as
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
  t
A
t
m m
m 
cos

Message signal
Carrier signal   t
A
t
c c
c 
cos

1.Frequency modulation:
  t
A
K
t
A
K m
m
f
C
m
f
c
i 


 cos




  t
A
K
t
dt
t
A
K
dt m
m
m
f
C
m
m
f
C
i
i 





 sin
cos 



 

Thus, we get the FM wave as:
)
sin
cos(
cos
)
( t
A
K
t
A
Ac
t
S m
m
m
f
C
C
i
FM 


 


)
sin
cos(
)
( t
t
A
t
S m
f
C
C
FM 

 

m
m
f
f
A
K

 
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
  t
A
t
m m
m 
cos

  t
A
t
c c
c 
cos


t
A
K
t
A
K m
m
p
m
p 
 cos
)
( 

)
cos
cos(
)
(
)
cos
cos(
)
(
t
m
t
A
t
S
t
A
K
t
A
t
S
m
p
C
C
pm
m
m
p
C
C
pm








After phase modulation the instantaneous voltage will be
Where mp = Modulation index of phase modulation
Kp is 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 COLLEGE
m
f
C A
K

 
max m
f
C A
K

 
min
m
f
C
C
d A
K




 min
max 




m
f
d
A
K
f 




2
m
f
m
f
f
f
A
K
f





;

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

20. Types of FM Modulation:
NBFM (Narrow Band FM):
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE
)
sin
cos(
)
( t
t
A
t
S m
f
C
C
FM 

 

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

)
2
sin
2
cos(
)
( t
f
t
f
A
t
S m
f
C
C
FM 

 




















sin
1
cos
"
"
2
sin
.
,
3
.
0
1
:
sin
)]
2
sin(
).
2
sin(
)
2
sin
cos(
).
2
[cos(
)
(
tbe
f
Let
rad
ceNBFM
t
f
t
f
t
f
t
f
A
t
S
m
f
f
m
f
C
m
f
C
C
FM
)]
2
sin(
).
2
sin(
[
)]
2
[cos(
)
(
: t
f
t
f
A
t
f
A
t
S
Then c
m
f
c
c
c
FM 


 


21. MATRUSRI
ENGINEERING COLLEGE
2.3 TYPES OF FM MODULATION
NBFM (Narrow Band FM):
NBPM (Narrow Band PM):
)]
)
(
2
sin
2
)
)
(
2
sin
2
)]
2
[cos(
)
(
)]
)
(
2
sin
)
)
(
2
[sin
2
)]
2
[cos(
)
(
)]
2
sin(
).
2
cos(
[
)]
2
[cos(
)
(
t
f
f
A
t
f
f
A
t
f
A
t
S
t
f
f
t
f
f
A
t
f
A
t
S
t
f
t
f
A
t
f
A
t
S
c
m
c
p
c
m
c
P
c
c
c
PM
c
m
c
m
c
P
c
c
c
PM
c
m
P
c
c
c
PM

























)]
)
(
2
cos
2
)
)
(
2
cos
2
)]
2
[cos(
)
(
)]
)
(
2
cos
)
)
(
2
[cos
2
)]
2
[cos(
)
(
)]
2
sin(
).
2
sin(
[
)]
2
[cos(
)
(
t
f
f
A
t
f
f
A
t
f
A
t
S
t
f
f
t
f
f
A
t
f
A
t
S
t
f
t
f
A
t
f
A
t
S
c
m
c
f
c
m
c
f
c
c
c
FM
c
m
c
m
c
f
c
c
c
FM
c
m
f
c
c
c
FM


























22. Spectrum of NBFM:
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE
)]
)
(
2
sin
2
)
)
(
2
cos
2
)]
2
[cos(
)
( t
f
f
A
t
f
f
A
t
f
A
t
S c
m
c
f
c
m
c
f
c
c
c
FM 



 





23. WBFM (WIDE BAND FM):
2.3 Types of FM modulation
MATRUSRI
ENGINEERING COLLEGE
1

f

)
2
sin
2
cos(
)
( t
f
t
f
A
t
S m
f
C
C
FM 

 

]
)
(
2
cos[
)
(
.
)
(
]
).
(
Re[
.
)
(
]
).
(
.
Re[
.
)
(
)
2
2
(
2
2 0

















n m
c
f
n
c
WBFM
n
t
nf
f
j
f
n
c
n
t
n
j
f
n
t
f
j
c
t
nf
f
J
A
t
S
e
J
A
t
S
e
J
e
A
t
S
m
c
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





















]
)
2
cos(
cos
).
(
)
2
cos(
).
(
[
]
)
cos(
cos
).
(
)
cos(
).
(
[
cos
)
(
)
(
)
(
2
cos
).
(
)
(
2
2
1
1
0
t
J
t
J
A
t
J
t
J
A
t
J
A
t
S
t
nf
f
J
A
t
S
m
c
m
c
c
m
c
m
c
c
c
c
WBFM
m
n
c
n
c
FM





























]
)
2
cos(
cos
)
2
).[cos(
(
]
)
cos(
)
).[cos(
(
cos
)
(
)
(
2
1
0
t
t
J
A
t
t
J
A
t
J
A
t
S
m
c
m
c
c
m
c
m
c
c
c
c
WBFM













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
1
1
1
0
2















n
n
n
n
o
n
n
n
n
n
n
n
n
J
n
J
J
J
Lt
n
evaluesof
Forl
J
J
J
n
J
lueof
Forsmallva
J
J
J






































]
)
2
cos(
cos
)
2
).[cos(
(
]
)
cos(
)
).[cos(
(
cos
)
(
)
(
2
1
0
t
t
J
A
t
t
J
A
t
J
A
t
S
m
c
m
c
c
m
c
m
c
c
c
c
WBFM













27. Power Calculation:
2.4 FM Power calculation & Bandwidth
MATRUSRI
ENGINEERING COLLEGE
R
J
A
R
J
A
P
er
CarrierPow
P
P
P
P
Totalpower
c
c
C
m
c
m
c
c
t
2
)
(
2
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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 “2𝜟f”
2.4 FM Power calculation & Bandwidth
MATRUSRI
ENGINEERING COLLEGE
.
)
1
(
2
)
1
(
2
)
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(
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(
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f
f
BW



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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DETECTION OF FM WAVE:
1. Slope Detector
2. Fooster seely Detector
3. Ratio FM Detector
4. Zero crossing
5. Quadrature FM Demodulator
6. PLL Non linear and Linear methods

31. GENERATION OF FM WAVE: Direct method:
2.5. Generation of FM wave
MATRUSRI
ENGINEERING COLLEGE
)
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2
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



32. GENERATION OF FM WAVE: IN-DIRECT METHOD:
2.5. Generation of FM wave
MATRUSRI
ENGINEERING COLLEGE
First Generate NBFM then convert into WBFM
]
sin
cos[
)
(
.....
]
sin
cos[
[
]
sin
cos[
.
)
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






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

34. 2.6. Detection of FM wave
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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
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ENGINEERING COLLEGE

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

37. Operation of Balanced slope Detector:
The balanced slope detector is also known as the travis detector (after its inventor),
the triple-tuned discriminator (for obvious reasons), and as the amplitude
discriminator (erroneously). The circuit uses two slope detectors. They are connected
back to back, to the opposite ends of a center-tapped transformer, and hence fed 180°
out of phase. The top secondary circuit is tuned above the IF by an amount which, in FM
receivers with a deviation of 75 khz, is 100 khz. The bottom circuit is similarly tuned
below the IF by the same amount. Each tuned circuit is connected to a diode detector
with an RC load. The output is taken from across the series combination of the two loads,
so that it is the sum of the individual outputs.
Let fc be the IF to which the primary circuit is tuned, and let fc + δf and fc – δf be the
resonant frequencies of the upper secondary and lower secondary circuits T’ and T”,
respectively. When the input frequency is instantaneously equal to fc, the voltage across
T’, that is, the input to diode D1, will have a value somewhat less than the maximum
available, since fc is somewhat below the resonant frequency of T’. A similar condition
exists across T”. In fact, since fc is just as far from fc + δf as it is from fc – δf, the voltages
applied to the two diodes will be identical. The dc output voltages will also be identical,
and thus the detector output will be zero, since the output of D1 is positive and that of
D2 is negative.
2.6. Demodulation of FM wave
MATRUSRI
ENGINEERING COLLEGE

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
MATRUSRI
ENGINEERING COLLEGE

39. 2.6. Demodulation of FM wave
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ENGINEERING COLLEGE

40. FOSTER SEELY DISCRIMINATOR:
It uses a tuned RF transformer to convert frequency changes into amplitude changes. A transformer,
tuned to the carrier frequency, is connected to two rectifier diodes. The circuit resembles a full-wave
bridge rectifier. If the input equals the carrier frequency, the two halves of the tuned transformer
circuit produce the same rectified voltage and the output is zero. As the frequency of the input
changes, the balance between the two halves of the transformer secondary changes, and the result is
a voltage proportional to the frequency deviation of the carrier.
Foster–Seeley discriminators are sensitive to both frequency and amplitude variations, unlike some
detectors. Therefore a limiter amplifier stage must be used before the detector, to remove amplitude
variations in the signal which would be detected as noise. The limiter acts as a class-A amplifier at lower
amplitudes; at higher amplitudes it becomes a saturated amplifier which clips off the peaks and limits the
amplitude.
2.6. Demodulation of FM wave
MATRUSRI
ENGINEERING COLLEGE

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
MATRUSRI
ENGINEERING COLLEGE

44. 2.7 zero crossing detector for FM demodulation.
MATRUSRI
ENGINEERING COLLEGE

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
MATRUSRI
ENGINEERING COLLEGE
Amplitude limiter in FM

46. A phase-locked loop or phase lock loop (PLL) is a control system that generates an
output signal whose phase is related to the phase of an input signal. There are several
different types; the simplest is an electronic circuit consisting of a variable frequency
oscillator and a phase detector in a feed back loop the oscillator generates a periodic
signal, and the phase detector compares the phase of that signal with the phase of the
input periodic signal, adjusting the oscillator to keep the phases matched.
Phased Lock Loop (PLL)
MATRUSRI
ENGINEERING COLLEGE
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 108 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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ENGINEERING COLLEGE

48. Short answer questions
Questions & Answers
MATRUSRI
ENGINEERING COLLEGE
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
MATRUSRI
ENGINEERING COLLEGE
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 108 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-seely discriminator 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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