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COURSE MATERIAL

ANALOG COMMUNICATIONS
SUBJECT
(19A04403T)

UNIT 2

COURSE B.Tech

SEMESTER 22

ELECTRONICS & COMMUNICATION

DEPARTMENT
ENGINEERING

PREPARED BY Mrs KANAKA DURGA DEVI P M

(Faculty Name/s) Assistant Professor

VERSION V-5

PREPARED /REVISED DATE 31-03-2021

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TABLE OF CONTENTS – UNIT 2

SNO CONTENTS PAGE

1 COURSE OBJECTIVES 1

2 PREREQUISITES 1

3 SYLLABUS 1

4 COURSE OUTCOMES 1

5 CO - PO/PSO MAPPING 1

6 LESSON PLAN 2

7 ACTIVITY BASED LEARNING 2

8 LECTURE NOTES 2

2.1 INTRODUCTION:Angle Modulation 2

2.2 Single-Tone Frequency Modulation 5

2.3 Transmission Bandwidth of FM waves: 15

2.4 Generation of NBFM,WBFM Waves 18

Generation of FM 25
2.5
2.6 FM Transmitter 27

2.7 Comparison of AM and FM (Advantages of FM ) 28

2.8. Foster Seely discriminator 29

2.9 Preemphasis and Deemphasis 29

2.10 FM DEMODULATORS 32

9 PRACTICE QUIZ 34

10 ASSIGNMENTS 36

11 PART A QUESTIONS & ANSWERS (2 MARKS QUESTIONS) 36

12 PART B QUESTIONS 37

13 SUPPORTIVE ONLINE CERTIFICATION COURSES 38

14 REAL TIME APPLICATIONS 38

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15 CONTENTS BEYOND THE SYLLABUS 38

16 PRESCRIBED TEXT BOOKS & REFERENCE BOOKS 38

17 MINI PROJECT SUGGESTION 39

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1. COURSE OBJECTIVES
The objectives of this course is to
1. To introduce various modulation and demodulation techniques of analog
communication systems.
2. To analyze different parameters of analog communication techniques .
3. Know Noise Figure in AM & FM receiver systems.
4. Understand functions of various stages of AM,FM transmitters and know
characteristics of AM & FM receivers.
5. Underststand the concepts of information theory.

2. PREREQUISITES
Students should have knowledge on
1. Basic of Signals and systems
2. Basic mathematics

3. SYLLABUS
UNIT II
Angle Modulation &Demodulation: Concept of instantaneous
frequency, Generalized concept of angle modulation, Bandwidth of angle
modulated waves – Narrow band frequency modulation (NBFM); and Wide
band FM (WBFM), Phase modulation, Verification of Frequency modulation
bandwidth relationship, Features of angle modulation, Generation of FM waves
– Indirect method, Direct generation; Demodulation of FM, Band pass limiter,
Practical frequency demodulators, Small error analysis, Pre-emphasis, & De-
emphasis filters, FM receiver, FM Capture Effect, Illustrative Problems

4. COURSE OUTCOMES
1. Understand the concepts of Analog modulation and demodulation
techniques. (L1)
2. Understand importance Pre-emphasis &de-emphasis circuits in FM
modulation (L1)
3. Apply the concepts to solve problems in Angle modulation Schemes.(L2)
4. Analyse frequency spectra of modulated signals used in various angle
Modulation(L3)
5. Co-PO / PSO Mapping
PO PO PO PO PO PO PO PO1 PO1 PSO PSO
PO5 PO8 P10
1 2 3 4 6 7 9 1 2 1 2

CO1 3 3 2 2

CO2 3 3 2 2

CO3 3 3 2 2

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CO4 3 3 2 2

CO5 3 3 2 2

6. LESSON PLAN
LECTURE WEEK TOPICS TO BE COVERED REFERENCES

Generalized concept of angle modulation Concept of

T1
1 instantaneous frequency

Narrow band frequency modulation (NBFM); and Wide band FM T1, R1

2 1
(WBFM),
Phase modulation T1, R1
3

4 Verification of Frequency modulation bandwidth relationship T1, R1

T1, R2
5 Generation of FM waves – Indirect method, Direct generation
T1, R1
6 Demodulation of FM
2
T1, R1
7 Pre-emphasis, & De-emphasis filters

8 T1, R1
FM receiver, FM Capture Effect
T1, R1
9 COMPARISION OF AM &FM ,APPLICATION OF FM

10 Illustrative Problems T1, R1

3
11 Discussion of objective type questions & Short answer questions T1,R1

12 Discussion of Previous year university questions in question papers T1,R1

7. ACTIVITY BASED LEARNING

1. Through project based teaching learning to apply the theoretical concepts.
2. Through worksheets is used to facilitate project based learning by
strengthening the fundamental concepts during classroom teaching.
8. LECTURE NOTES
2.1.INTRODUCTION
Angle modulation is a method of analog modulation in which either the
phase or frequency of the carrier wave is varied according to the message
signal. In this method of modulation the amplitude of the carrier wave is
maintained constant.
Angle Modulation is a method of modulation in which either Frequency or
Phase of the carrier wave is varied according to the message signal.
In general form, an angle modulated signal can represented as

s(t)  Ac cos[θ (t)] ...2.1

Where Ac is the amplitude of the carrier wave and θ(t) is the angle of the
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modulated carrier and also the function of the message signal.

The instantaneous frequency of the angle modulated signal, s(t) is given by

1 dθ (t)

fi (t)  ...2.2
2π dt

The modulated signal, s(t) is normally considered as a rotating phasor of length

Ac and angle θ(t). The angular velocity of such a phasor is dθ(t)/dt , measured
in radians per second.

An un-modulated carrier has the angle θ(t) defined as

θ (t )  2π fct  φc .....2.3

Where fc is the carrier signal frequency and φc is the value of θ(t) at t = 0.

The angle modulated signal has the angle, θ(t) defined by

θ (t )  2π fc t  φ (t) ......4

There are two commonly used methods of angle modulation:

1. Frequency Modulation, and

2. Phase Modulation.
2.1.1.Phase Modulation (PM):

In phase modulation the angle is varied linearly with the message signal m(t) as
:

θ (t)  2π fct  k p m(t) .....2.5

where kp is the phase sensitivity of the modulator in radians per volt. Thus the
phase modulated signal is defined as


s(t)  Ac cos 2πfct  k p m(t)  ... 2.6

2.1.2 .Frequency Modulation (FM):

In frequency modulation the instantaneous frequency fi(t) is varied linearly with

message signal, m(t) as:
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f i (t )  fc  k f m(t) ....2.7

where kf is the frequency sensitivity of the modulator in hertz per volt. The
instantaneous angle can now be defined as

θ (t)  2π fct  2π k f ∫t m(t)dt ....2.8

0
and thus the frequency modulated signal is given by

s(t)  Ac cos 2π fct  2π k f ∫

t m(t)dt ... 2.9

The PM and FM waveforms for the sinusoidal message signal are shown in the
fig-2.1.

Fig: 2.1 – PM and FM Waveforms with a message signal

Example 2.1:

Find the instantaneous frequency of the following waveforms:

(a) S1(t) = Ac Cos [100π t + 0.25 π ]

(b) S2(t) = Ac Cos [100π t + sin ( 20 π t) ]
(c) S3(t) = Ac Cos [100π t + ( π t2) ]
Solution: Using equations (5.1) and (5.2):

(a) fi(t) = 50 Hz; Instantaneous frequency is constant.

(b) fi(t) = 50 + 10 cos( 20 π t); Maximum value is 60 Hz and minimum value is 40
Hz. Hence, instantaneous frequency oscillates between 40 Hz and 60 Hz.
(c) fi(t) = (50 + t)
The instantaneous frequency is 50 Hz at t=0 and varies linearly at 1 Hz/sec.
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2.1.3. Relation between Frequency Modulation and Phase Modulation:

A frequency modulated signal can be generated using a phase

modulator by first integrating m(t) and using it as an input to a phase
modulator. This is possible by considering FM signal as phase modulated signal in
which the modulating wave is integral of m(t) in place of m(t). This is shown in
the fig-2.2(a). Similarly, a PM signal can be generated by first differentiating m(t)
and then using the resultant signal as the input to a FM modulator, as shown in
fig-2.2(b).

Fig: 2.2 – Scheme for generation of FM and PM Waveforms

2.2.Single-Tone Frequency Modulation:

Consider a sinusoidal modulating signal defined as:

m(t) = Am Cos( 2π fm t) …. (2.10)

Substituting for m(t) in equation (5.9), the instantaneous frequency of the FM

signal is

fi (t )  fc  k f Am cos(2πfmt) = fc+cos (2πfmt)

Where ∆f is called the frequency deviation given by

∆f =kfA m
and the instantaneous angle is

 2πfct  β sin ( 2πfmt) .... 2.11b

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The ratio of frequency deviation ∆f to the modulating frequency is commonly
called as modulation index of the FM signal. We denote it by β=∆f/fm

The resultant FM signal is

s(t )  Ac cos2πfct  β sin(2πfmt )

The frequency deviation factor indicates the amount of frequency change in

the FM signal from the carrier frequency fc on either side of it. Thus FM signal will
have the frequency components between (fc - f ) to (fc + f ). The modulation
index, β represents the phase deviation of the FM signal and is measured in
radians. Depending on the value of β, FM signal can be classified into two
types:

1. Narrow band FM (β << 1) and

2. Wide band FM (β >> 1).

Example-2.2: A sinusoidal wave of amplitude 10volts and frequency of 1 kHz is

applied to an FM generator that has a frequency sensitivity constant of 40
Hz/volt. Determine the frequency deviation and modulating index.

Solution: Message signal Amplitude AM =10 volts

Frequency fm=1000 Hz

Frequency Sensitivity,Kf = 40 Hz/volt

Frequency deviation ,f = KfAm = 400 Hz

Modulation index, β = f / fm = 0.4

(indicates a narrow band FM).

Example-2.3: A modulating signal m(t) =10 Cos(10000πt) modulates a carrier

signal, Ac Cos(2πfct). Find the frequency deviation and modulation index of the
resulting FM signal. Use kf = 5kHz/volt.

Solution: Message signal Amplitude AM =10 volts

Frequency fm=5000 Hz

Frequency Sensitivity,Kf =5K Hz/volt

Frequency deviation ,f = KfAm = 50 K Hz

Modulation index, β = f / fm = 10

(indicates a wide band FM).

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2.2.1.Frequency Domain Representation of Narrow Band FM signal:

Expanding the equation (5.12) using trigonometric identices

s(t)  Ac cos2πfct  β sin(2πfmt)
 Ac cos2πfct cosβ sin(2πfmt)− Ac sin2πfct sinβ sin(2πfmt )

For NBFM, (β << 1), we can approximate,

cosβ sin(2πfmt ) ≈ 1 and sinβ sin(2πfmt ) ≈ β sin(2πfmt )

Hence, s(t)  Ac cos(2πfct) − Ac β sin(2πfct) sin(2πfmt)

Using trigonometric relations;

S(t)= Ac cos(2πfct )+ AC β C0S(2π ( fc + fm ) t) – COS(2π ( fc - fm ) t) ….(2.14)

2

The above equation represents the NBFM signal. This representation is similar to
an AM signal, except that the lower side frequency has negative sign. The
magnitude spectrum of NBFM signal is shown in fig-2.3, which is similar to AM
signal spectrum. The bandwidth of the NBFM signal is 2fm, which is same as AM
signal.

|S(f)|

f −f f f +f
−f −f +f c m c c m

cc m
−f −f
c m

Fig: 2.3 - Magnitude Spectrum of NBFM Waveform.

2.2.2.Frequency Domain Representation of Wide-Band FM signals:

The FM wave for sinusoidal modulation is given by

s(t)  Ac cos2πfct  β sin(2πfmt)

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 Ac cos2πfct cosβ sin(2πfmt)− Ac sin2πfct sinβ sin(2πfmt )

The FM wave can be expressed in terms of complex envelope as:

s(t)  ReAc exp  j2πfct  jβ sin2πfmt 

~
... 2.15
 Res (t) exp j2πfct 
The complex envelope of the FM wave
e

~ ~
s (t )  Ac exp jβ sin2πfmt  and s (t) : periodic function with fm

The complex envelope is a periodic function of time, with a fundamental

frequency equal to the modulation frequency fm. The complex envelope can
be expanded in the form of complex series

~
∑cn exp j2π nfmt  ... 2.16
s (t) 
n

The complex Fourier coefficient, cn equals,

1/2fm

Cn = fm ∫ ~ s(t) exp(-j2 πnfmt)dt

-1/2fm
-
1/2fm

= fm∫ exp(-j β sinj2πfmt)- j2π nfmt)dt

-1/2fm
Substituting x = (2π fm t ), in the above equation we can rewrite
A
c

cn =  ∫π exp j β sin x − nx dx

−π

The nth order Bessel function of the first kind

is defined as

π
J n (β ) ∫ exp ( j β sinx-nx)dx

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-π

Comparing equations (5.18) and (5.19), we getC n = Ac Jn(β)

Substituting in (5.16), the complex envelope is

s (t)  Ac ∑J n (β )exp j 2πnfmt 

n  -∞

Substituting in (5.15), the FM signal can be written as

s(t)  Ac Re ∑J n (β ) exp j2π  fc  nfm t 

n−∞

s(t)  Ac ∑J n (β ) cos2π  fc  nfm t  ...2.21

n−∞

The above equation is the Fourier series representation of the single tone FM wave.

Applying the Fourier transform to (2.21),

∞
Ac
∑ J n ( β ) δ  f − f c − nf m δf f c  nf m
S(f)  ...2.22
2 n− ∞

The spectrum S(f) is shown in fig-5.4. The above equation indicates the
following:
(i) FM signal has infinite number of side bands at frequencies (f c + nfm).

(ii) Relative amplitudes of all the spectral lines depends on the value of Jn(β).
(iii)The number of significant side bands depends on the modulation
index (β). With (β<<1), only J0(β) and J1(β) are significant. But for (β>>1),
many sidebands exists.
(iv)The average power of an FM wave is P = 0.5Ac2 (based on Bessel
function property).

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|S(f)|
J (β J (β J (β
0 0 2

J (β J−1(β
−1 J (β J (β

1 1

J−2( β

−f f f +2f f
c
f −2f c c
m
−f −f cm

c m −f +f f +f

c m f −f cm

c m

Fig:2.4 - Magnitude Spectrum of Wide Band FM

2.2.3.Bessel’s Function:
Bessel function is an useful function to represent the FM wave spectrum. The
general plots of Bessel functions are shown in fig-2.5 and table (2.1) gives the
values for Bessel function coefficients. Some of the useful properties of Bessel
functions are given below:

(a)J n (β )  (− 1)n J − n (β )for all n (2.23a )

2n
(b) J n 1 (β )  J n −1 (β )  J n (β ) (2.23b)

(c) ∑J n 2 (β )  1 (2.23c)
n  −∞

(β ) ≅ β
(d) For smaller values of β, J 1, J (β ) ≅ and J (β ) ≅0, for n  2

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Fig: 2.5 – Plots of Bessel functions

Table: 2.1 Bessels function

The Spectrum of FM signals for three different values of β are shown in the
fig-2.6In this spectrum the amplitude of the carrier component is kept as a unity
constant. The variation in the amplitudes of all the frequency components is
indicated.

For β = 1, the amplitude of the carrier component is more than the side
band frequencies as shown in fig-2.6a. The amplitude level of the side band
frequencies is decreasing. The dominant components are (f c + fm) and (fc + 2fm).
The amplitude of the frequency components (fc + nfm) for n>2 are negligible.
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For β = 2, the amplitude of the carrier component is considered as unity.
The spectrum is shown in fig-2.6b. The amplitude level of the side band
frequencies is varying. The amplitude levels of the components (f c + fm) and (fc +
2fm) are more than carrier frequency component; whereas the amplitude of the
component (fc + 3fm) is lower than the carrier amplitude. The amplitude of
frequency components (fc + nfm) for n>3 are negligible.

The spectrum for β = 5, is shown in fig-2.6c. The amplitude of the carrier

component is considered as unity. The amplitude level of the side band
frequencies is varying. The amplitude levels of the components (f c + fm), (fc +
3fm), (fc + 4fm) and (fc + 5fm), are more than carrier frequency component;
whereas the amplitude of the component (f c + 2fm) is lower than the carrier
amplitude. The amplitude of frequency components (f c + nfm) for n>8 are
negligible.

Fig: 2.6 – Plots of Spectrum for different values of modulation index.

(Amplitude of carrier component is constant at unity)

Example-2.4:

An FM transmitter has a power output of 10 W. If the index of modulation is 1.0,

determine the power in the various frequency components of the signal.

Solution: The various frequency components of the FM signal are

fc, (fc + fm), (fc + 2fm), (fc + 3fm), and so on.

The power associated with the above frequency components are: (Refer (5.21))

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(J0)2, (J1)2, (J2)2 , and (J3)2 respectively.

From the Bessel function Table, for β = 1;

J0 = 0.77, J1 = 0.44, J2 = 0.11, and J3 = 0.02

Let P = 0.5(Ac)2 = 10 W.

Power associated with fc component is P0 = P (J0)2 = 10 (0.77)2 = 5.929 W.

Similarly, P1 = P (J1)2 = 10 (0.44)2 = 1.936 W.

P2 = P (J2)2 = 10 (0.11)2 = 0.121 W.

P3 = P (J3)2 = 10 (0.02)2 = 0.004 W.

Note: Total power in the FM wave,

Ptotal = P0 + 2P1 + 2P2 + 2P3

= 5.929 + 2(1.936) + 2(.121) + 2(.004) = 10.051 W

Example-2.5:

A 100 MHz un-modulated carrier delivers 100 Watts of power to a load. The
carrier is frequency modulated by a 2 kHz modulating signal causing a
maximum frequency deviation of 8 kHz. This FM signal is coupled to a load
through an ideal Band Pass filter with 100MHz as center frequency and a
variable bandwidth. Determine the power delivered to the load when the filter
bandwidth is:

(a) 2.2 kHz (b) 10.5 kHz (c) 15 kHz (d) 21 kHz

Ans: Modulation index, β = 8 k / 2 k = 4;

From the Bessel function Table- 5.1; for β = 4;

J5 = 0.13, J6 = 0.05, J7 = 0.02

J0 = -0.4, J1 = - 0.07, J2 = 0.36, J3 = 0.43, J4 = 0.28,
Let P = 0.5(Ac)2 =
100 W and

P0 = P (J0)2 = 100 (-0.4) 2 = 16 Watts.

P1 = P (J1)2 =100(-0.07)2=0.490 W.

P2 = P (J2)2 = 100 (0.36)2 = 12.960 W.

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P3 = P (J3)2 = 100 (0.43)2 = 18.490 W.

P4 = P (J4)2 = 100 (0.28)2 = 7.840 W.

P5 = P (J5)2 = 100 (0.13)2 = 1.690 W.

P6 = P (J6)2 = 100 (0.05)2 = 0.250 W.

(a) Filter Bandwidth = 2.2 kHz

The output of band pass filter will contain only one frequency
component fc. Power delivered to the load, Pd = P0 = 16 Watts.

(b) Filter Bandwidth = 10.5 kHz

The output of band pass filter will contain the following frequency
components: fc, (fc + fm), and (fc + 2fm)

Power delivered to the load, Pd = P0 + 2P1 + 2P2 = 42.9 Watts.

(c) Filter Bandwidth = 15 kHz

The output of band pass filter will contain the following frequency
components: fc, (fc + fm), (fc + 2fm), and (fc + 3fm),

Power delivered to the load, Pd = P0 + 2P1 + 2P2 + 2P3 = 79.9 Watts.

(d) Filter Bandwidth = 21 kHz

The output of band pass filter will contain the following frequency
components: fc, (fc + fm), (fc + 2fm), (fc + 3fm), (fc + 4fm), and (fc + 5fm),

Power delivered to the load, Pd = P0 + 2P1 + 2P2 + 2P3 + 2P4 + 2P5 = 98.94 Watts.

Example-2.6:

A carrier wave is frequency modulated using a sinusoidal signal of frequency f m

and amplitude Am. In a certain experiment conducted with f m=1 kHz and
increasing Am, starting from zero, it is found that the carrier component of the
FM wave is reduced to

zero for the first time when Am=2 volts. What is the frequency sensitivity of the
modulator? What is the value of Am for which the carrier component is reduced
to zero for the second time?

Ans: The carrier component will be zero when its coefficient, J 0(β) is zero.

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From Table 5.1: J0(x) = 0 for x= 2.44, 5.53, 8.65.
β = f / fm = kf Am / fm and kf = β fm /Am = (2.40)(1000) / 2 = 1.22 kHz/V

Frequency Sensitivity, kf = 1.22 kHz/V

The carrier component will become zero for second time when β = 5.53.

Therefore, Am = β fm / kf = 5.53 (1000) / 1220 = 4.53 volts

2.3.Transmission Bandwidth of FM waves:

An FM wave consists of infinite number of side bands so that the bandwidth is

theoretically infinite. But, in practice, the FM wave is effectively limited to a finite
number of side band frequencies compatible with a small amount of distortion.
There are many ways to find the bandwidth of the FM wave.

1. Carson’s Rule: In single–tone modulation, for the smaller values of modulation

index the bandwidth is approximated as 2fm. For the higher values of
modulation index, the bandwidth is considered as slightly greater than the total
deviation 2 f. Thus the Bandwidth for sinusoidal modulation is defined as:

BT ≈ 2∆f+2fm
= 2∆f( 1+1/β)

 2(β  1) fm

For non-sinusoidal modulation, a factor called Deviation ratio (D) is considered.

The deviation ratio is defined as the ratio of maximum frequency deviation to
the bandwidth of message signal.

Deviation ratio, D = ( f / W ), where W is the bandwidth of the message

signal and the corresponding bandwidth of the FM signal is ,

BT = 2(D + 1) W ... (2.25)

2. Universal Curve : An accurate method of bandwidth assessment is done by

retaining the maximum number of significant side frequencies with amplitudes
greater than 1% of the un-modulated carrier wave. Thus the bandwidth is
defined as “the 99 percent bandwidth of an FM wave as the separation
between the two frequencies beyond which none of the side-band frequencies
is greater than 1% of the carrier amplitude obtained when the modulation is
removed”.

Transmission Bandwidth -BW = 2 nmax fm , (2.26)

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where fm is the modulation frequency and ‘n’ is the number of pairs of side-
frequencies such that Jn(β) > 0.01. The value of nmax varies with modulation
index and can be determined from the Bessel coefficients. The table 2.2 shows
the number of significant side frequencies for different values of modulation
index.

The transmission bandwidth calculated using this method can be expressed in

the form of a universal curve which is normalised with respect to the frequency
deviation and plotted it versus the modulation index.

Fig: 2.7 – Universal Curve

Table 2.2

From the universal curve, for a given message signal frequency and modulation index
the ratio (B/ f ) is obtained from the curve. Then the bandwidth is calculated as:

BT BT
BT  ( ) f β( ) fm ...2.27

f f

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Example-2.7:

Find the bandwidth of a single tone modulated FM signal described by S(t)=10

cos[2π108t + 6 sin(2π103t)].
Solution:
Comparing the given s(t) with equation-(2.12) we get
Modulation index, β = 6 and
Message signal frequency fm=1000 Hz ,
By Carson’s rule (equation - 2.24),
Transmission Bandwidth, BT = 2(β + 1) fm
BT = 2(7)1000 = 14000 Hz = 14 kHz

Example-2.8:

Q. A carrier wave of frequency 91 MHz is frequency modulated by a sine wave

of amplitude 10 Volts and 15 kHz. The frequency sensitivity of the modulator is 3
kHz/V.

a.Determine the approximate bandwidth of FM wave using Carson’s Rule.

b.Repeat part (a), assuming that the amplitude of the modulating wave is
doubled.
c.Repeat part (a), assuming that the frequency of the modulating wave is
doubled.
Solution:
(a) Modulation index
β=f / fm = kf Am / fm = 3x10/15 = 2
By Carson’s rule; Bandwidth, BT = 2(β + 1) fm = 90 kHz

(b) When the amplitude, Am is doubled,

New Modulation Index, β = f / fm = kf Am / fm = 3x20/15 = 4

Bandwidth, BT = 2(β+1)fm = 150 kHz

(c) when the frequency of the message signal, fm is doubled

New Modulation Index, β = 3x10/30 = 1

Bandwidth, BT = 2(β+1)fm = 120 kHz.

Example-2.9:

Q. Determine the bandwidth of an FM signal, if the maximum value of the

frequency deviation f is fixed at 75kHz for commercial FM broadcasting by radio
and modulation frequency is W= 15 kHz.

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Solution: Frequency deviation, D = ( f / W ) = 5

Transmission Bandwidth, BT = 2(D + 1) W = 12x15 kHz = 180 kHz

Example-2.10:

Consider an FM signal obtained from a modulating signal frequency of 2000 Hz

and maximum Amplitude of 5 volts. The frequency sensitivity of modulator is 2
kHz/V. Find the bandwidth of the FM signal considering only the significant side
band frequencies.

Solution: Frequency Deviation = 10 kHz

Modulation Index, β = f / fm = kf Am / fm = 5;

From table –(2.2) ; 2nmax = 16 for β =5,

Bandwidth, BT = 2 nmax fm = 16x2 kHz = 32 kHz.

Example-2.11: A carrier wave of frequency 91 MHz is frequency modulated by a

sine wave of amplitude 10 Volts and 15 kHz. The frequency sensitivity of the
modulator is 3 kHz/V. Determine the bandwidth by transmitting only those side
frequencies with amplitudes that exceed 1% of the unmodulated carrier wave
amplitude. Use universal curve for this calculation.
Solution:
Frequency Deviation, f = 30 kHz
Modulation Index, β = 3x10/15 = 2

From the Universal curve; for β = 2; (B / f) = 4.3

Bandwidth, B = 4.3 f = 129 kHz

2.4.Generation of FM Waves:
There are two basic methods of generating FM waves: indirect method and
direct method. In indirect method a NBFM wave is generated first and
frequency multiplication is next used to increase the frequency deviation to the
desired level. In direct method, the carrier frequency is directly varied in
accordance with the message signal. To understand the indirect method it is
required to know the generation of NBFM waves and the working of frequency
multipliers.

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Fig: 2.8 – Scheme to generate a NBFM Waveform.

2.4.1.Generation of NBFM wave:

A frequency modulated wave is defined as: (from equation 5.9)

s1 (t)  AC cos2π fC t  φ1 (t ) .... 2.28

Where φ1 (t)  2π k1 ∫0t m(t)dt

s1 (t)  AC cos (2π fC t ) cos[φ1 (t)] - AC sin (2π fC t) sin[φ1 (t)]

Assuming 1 (t) is small, then using cos[ 1 (t)] = 1 and sin[ 1(t) ] = 1(t).

s1 (t)  AC cos (2π fC t) - AC sin (2π fC t) .[φ1 (t)]

s1 (t)  AC cos (2π fC t) - 2π k1 AC sin (2π fC t) . ∫m(t)dt ...2.29

The above equation defines a narrow band FM wave. The generation scheme
of such a narrow band FM wave is shown in the fig.(2.8). The scaling factor,
(2πk1) is taken care of by the product modulator. The part of the FM modulator
shown inside the dotted lines represents a narrow-band phase modulator.

The narrow band FM wave, thus generated will have some higher order
harmonic distortions. This distortions can be limited to negligible levels by
restricting the modulation index to β < 0.5 radians.

2.4.2.Frequency Multiplier:

The frequency multiplier consists of a nonlinear device followed by a

band-pass filter. The nonlinear device used is a memory less device. If the input
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to the nonlinear device is an FM wave with frequency fc,and deviation ,f1 then its

Output v(t) will consist of dc component and ‘n’ frequency modulated waves with

carrier frequencies ,fc,2fc,3fc,….. nfc and frequency deviations a f1,2f1,3,f1,…..nf1

respectively.

The band pass filter is designed in such a way that it passes the FM wave centered at
the frequency, nfc with frequency deviation n f1 and to suppress all other FM
components. Thus the frequency multiplier can be used to generate a wide band FM
wave from a narrow band FM wave.

Fig: 2.9 – Frequency Multiplier

2.4.3.Generation of WBFM using Indirect Method:

In indirect method a NBFM wave is generated first and frequency

multiplication is next used to increase the frequency deviation to the desired
level. The narrow band FM wave is generated using a narrow band phase
modulator and an oscillator. The narrow band FM wave is then passed through
a frequency multiplier to obtain the wide band FM wave, as shown in the
fig:(2.9). The crystal controlled oscillator provides good frequency stability. But
this scheme does not provide both the desired frequency deviation and carrier
frequency at the same time. This problem can be solved by using multiple
stages of frequency multiplier and a mixer stage.

Fig: 2.9 – Generation of WBFM wave

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2.4.4.Generation of WBFM by Armstrong’s Method:

Armstrong method is an indirect method of FM generation. It is used to
generate FM signal having both the desired frequency deviation and the carrier
frequency. In this method, two-stage frequency multiplier and an intermediate
stage of frequency translator is used, as shown in the fig:(2.10). The first multiplier
converts a narrow band FM signal into a wide band signal. The frequency
translator, consisting of a mixer and a crystal controlled oscillator shifts the wide
band signal to higher or lower frequency band. The second multiplier then
increases the frequency deviation and at the same time increases the center
frequency also. The main design criteria in this method are the selection of
multiplier gains and oscillator frequencies. This is explained in the following steps.

Fig: 2.10 – Generation of WBFM wave by Armstrong method

2.4.5. Generation of WBFM using Direct Method:

In direct method of FM generation, the instantaneous frequency of the
carrier wave is directly varied in accordance with the message signal by means
of an voltage controlled oscillator. The frequency determining network in the
oscillator is chosen with high quality factor (Q-factor) and the oscillator is
controlled by the incremental variation of the reactive components in the tank
circuit of the oscillator. A Hartley Oscillator can be used for this purpose.

Fig: 2.11 – Hartley Oscillator (tank circuit) for generation of WBFM wave.

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The portion of the tank circuit in the oscillator is shown in fig:2.11. The capacitive
component of the tank circuit consists of a fixed capacitor shunted by a
voltage-variable capacitor. The resulting capacitance is represented by C(t) in
the figure. The voltage variable capacitor commonly called as varactor or
varicap, is one whose capacitance depends on the voltage applied across its
electrodes. The varactor diode in the reverse bias condition can be used as a
voltage variable capacitor. The larger the voltage applied across the diode,
the smaller the transition capacitance of the diode.

The frequency of oscillation of the Hartley oscillator is given by:

f
i (t)  ...2.30

2π  L1  L2 c(t)

Where the L1 and L2 are the inductances in the tank circuit and the total capacitance,
c(t) is the fixed capacitor and voltage variable capacitor and given by:

c(t)  c0  c cos2πfmt  ...2.31

Let the un-modulated frequency of oscillation be f0. The instantaneous frequency fi(t) is
defined as:
1

−
2
c
f (t)  f 1  cos2πf t ...2.32
i 0 m

c0

where f0  ...2.33

2π  L1  L 2  c0
− 1

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2
c
∴ f (t)  f 1 cos2πf t

i
0 m

c0

c
≅ f 1
0 − cos2πfmt 

2c0

Thus the instantaneous frequency

fi(t) is defined as:

∴ fi (t) ≅ f0  f cos2πfmt  ...2.34

The term, f represents the frequency deviation and the relation with c is given by:

c f

−
... 2.35

2c0 f 0

Thus the output of the oscillator will be an FM wave. But the direct method of
generation has the disadvantage that the carrier frequency will not be stable
as it is not generated from a highly stable oscillator.

Generally, in FM transmitter the frequency stability of the modulator is achieved

by the use of an auxiliary stabilization circuit as shown in the fig.(2.12).

Fig: 2.12 – Frequency stabilized FM modulator.

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The output of the FM generator is applied to a mixer together with the output of
crystal controlled oscillator and the difference is obtained. The mixer output is
applied to a frequency discriminator, which gives an output voltage
proportional to the instantaneous frequency of the FM wave applied to its input.
The discriminator is filtered by a low pass filter and then amplified to provide a
dc voltage. This dc voltage is applied to a voltage controlled oscillator (VCO) to
modify the frequency of the oscillator of the FM generator. The deviations in the
transmitter carrier frequency from its assigned value will cause a change in the
dc voltage in a way such that it restores the carrier frequency to its required
value.
Advantages and disadvantages of FM over AM:
Advantages of FM over AM are:
1. Less radiated power.
2. Low distortion due to improved signal to noise ratio (about 25dB) w.r.t. to
manmade interference.
3. Smaller geographical interference between neighbouring stations.
4. Well defined service areas for given transmitter power.
Disadvantages of FM:
1. Much more Bandwidth (as much as 20 times as much).
2. More complicated receiver and transmitter.

Applications:
Some of the applications of the FM modulation are listed below:
I. FM Radio, 88-108 MHz band, 75 kHz,
II. TV sound broadcast, 25 kHz,
III. 2-way mobile radio, 5 kHz / 2.5 kHz.

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2.5.Generation of FM
The FM systems have some definite advantages.
i) Firstly, the excessive power dissipation due to extreme peaks in the waveform
need not be bothered.
ii) Secondly, the non liner amplitude distortion has no effect on message
transmission, since the information resides in zero crossing of the wave and not
in the amplitude .How ever phase shift or delay distortion is intolerable.
iii) To avoid this problem a limiter circuit is used to clip the spurious amplitude
variation without disturbing the messages.

The frequency modulated signals can be generated in 2 ways:

1. Direct method of FM
2. Indirect method of FM.
The prime requirement of FM generation sis a viable output frequency. The
frequency is directly propositional to the instantaneous amplitude of the
modulating voltage.
The subsidiary requirement of FM generation is that the frequency deviation is
independent of modulating frequency. However if the system does not properly
produce these characteristics, corrections can be introduced during the
modulation process.

2.5.1.Varactor diode modulator

Figure how the characteristics curve of a typical variable capacitance diode

(varactor diode) displaying the capacitance as function of reverse bias.

Fig.2.13. Transfer characteristics of Varactor Diode

Increasing the bias increase the width of PN junction and reduces the
capacitance .It can be mathematically written as

1
C whereV  reverse
V

Bias voltage

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Figure shows the basic circuit for FM generation .Here the varactor diode is
connected across the resonant circuit of an oscillator through a coupling
capacitor of relatively large value .This coupling capacitor isolated the varactor
diode from eh oscillator as far as DC is connected and provide an effective
short circuit at the operation frequencies.

2.14. Basic varactor diode modulator circuit for FM Generation Operation

 The D.C bias to the varactor diode is regulated in such a ways that the
oscillator frequency is not affected by varactor supply fluctuations. The
modulating signal is fed in series with this regulated supply and at any instant
the effective bias to the varactor diode equals the algebraic sum of the d.c
bias volt ‘V’ and the instantaneous values of the modulating signal.
 As a result, the capacitance changes with amplitude of the modulating signal
resulting in frequency modulating of the oscillator output.
 The rate of change of carrier frequency depends on the information signal.
Since the information signal directly controls the frequency of the oscillator the
output is frequency modulated .The chief advanced for this circuit is the use of
two terminal devices but makes its applications limited.
Applications

i) Automatic frequency control

ii) Remote tuning.
Disadvantage of direct method of FM generation

 The direct modulators can’t employ crystal oscillators to obtain high frequency
stability. This problem becomes more accurate when the narrow band FM is
multiplied by appropriate frequency multiplying networks in order to achieve
the desired wide band FM
 This is because crystal frequency cant be varied as required in FM therefore non
crystal oscillators are used which don’t have sufficient stability for use in
commercial system .More over the reactance modulator has to be stabilized
which makes already complex circuitry even more complex.

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2.5.2.Indirect method of FM wave generation

 In this method, first the modulating signal is integrated and then phase
modulated with ethers carrier signal, as a result of which some form for FM signal
is obtained .Later frequency multipliers are used to get the desired wideband
FM.
 To overcome the disadvantage of direct method of FM wave generations, in
the indirect method a stable crystal oscillator is used to generate PM from which
narrow band FM is obtained.
 Then suitable frequency multiplying circuits are used to obtain the desired wide
and FM. This method is called the Armstrong method of FM wave generation.

Fig.2.15.Reactance Tube modulator

2.6.FM Transmitters

The frequency modulated wave can be produced by 2 methods namely;

i) Directly modulated FM transmitter.

ii) Indirectly modulated FM transmitter.

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Fig.2.16. Direct method of FM Generation

2.7.Comparison of AM and FM (Advantages of FM )

i) In AM system there are three frequency components,(the carrier ,LSB and USB
terms) and hence the bandwidth is finite. but FM system has infinite number of
sidebands in addition to a signal carrier. Each sideband is speared by a
frequency, fm hence its B.W is infinite.
ii) In FM, the sidebands at equal distance from f c has equal amplitude s ,ie
sideband distribution is symmetrical about the carrier frequency .The ‘J’
coefficient(Bessel Coefficients) occasionally have negative values signifying a
1800 phase change for the particular pair of side band.
iii) The amplitude of frequency modulated wave in FM is independent of
modulation index, whereas the amplitude of modulated wave in AM is
dependent of modulation index.
iv) In AM, increased modulation index increases the sideband power and there
fore increased the total transmitted power .In FM the total transmitted power
always remains constant but an increase in the modulation index increases the
bandwidth of system.
v) In FM system all transmitted power is useful whereas in AM most of the
transmitted power is used by the carrier .But the carrier does not contains any
useful information .Hence the power is wasted.
vi) Noise is very less in FM, hence there is an increase in the signal to noise ratio.
There are 2 reasons for this
1) There is less noise at frequencies where FM is used.
2) FM receivers use amplitude limiters to remove the amplitude variation caused
by noise, this feature does not exit in AM.
vii) Due to frequency allocations by CCIR (International Radio Consultative
Committee) there are guard bands between FM stations so that the there is less
adjacent channel interface than in AM.
viii) FM system operated in UHF and VHF range of frequencies s and at these
frequencies the space wave is used for propagations, so that the radius of
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reception is limited slightly more than line of sight .It is thus possible to operate
several independent transmitters on the same frequency with considerably less
interference than would be possible with AM.
Comparison of FM & PM

Phase modulation is equivalent to frequency modulation with a modulation

index mp=  m Thus holds only when its modulation is sinusoidal.

The spectrum of PM wave is similar to that of an FM wave.

2.8.Foster Seely discriminator

 The circuit diagram of Foster Seely Discriminator is when in figure It was invented
by Foster Seely hence its name. Because of its circuit conflagration and option it
is also called as center tuned discriminator.
 It is possible to obtain the same ‘S’ shaped response curve from a circuit in
which the primary and secondary winding are both tuned to the center
frewunce4y of the incoming signals .This is derisible because it greatly simplifies
alignment and also the process yields better linearity than slope detection.
 In this discriminator the same diode and load arrangement is used a s I the
balanced slope detection. But the method of ensuring that voltage fed to the
diodes varies linearly with deviation of the input signal.

Fig. 2.17.Foster seley Discriminator

2.9.PREEMPHASIS and DEEMPHASIS

The effect of decreasing SNR as the modulating signal bandwidth grows

exhibited by FM requires pre-emphasis in the modulator and de-emphasis in the
demodulator. What is done is that as the frequency of the modulating signal
increases above some specific frequency, additional gain is applied to the
modulating signal before it is passed to the modulator and is subtracted out
after it is demodulated. The block diagram in Figure 9.12 illustrates where this
occurs. The additional gain in the signal with increasing modulation frequency
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effectively balances out any decrease in SNR as modulation frequency
increases.

Figure2.18.. FM pre-emphasis and de-emphasis.

In the United States the standard that is used starts at 500 Hz and extends
up to 15 kHz. Over this frequency range a total of 17 dB of gain is applied. The
standard curve follows a low-pass-type response curve for the deemphasis
curve.

The 3 dB point can be determined by the time constant of the filter. The
U.S. standard specifies the time constant to be 75 μsec. Therefore, one can
predict the 3 dB point of the filter by the following calculation:
1 1 1 1
   f 3dB    2122 Hz
 RC 2 2 75  10 6

Therefore, at 2.122 kHz, there would be 3 dB of gain applied to the modulating

signal prior to being applied to the modulator, and similarly, there would be 3
dB of attenuation applied to the recovered modulating signal after
demodulation.

The Pre-emphasis and De-emphasis circuits are shown below;

Fig.2.19.Preempasis circuit

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Fig.2.20.Preempasis circuit

The pre-emphasis and de-emphasis circuits are generally a RC high pass filter
and RC low pass filter respectively.

The transfer functions for the above shown high pass and low pass filters are
given as

The product of the transfer functions must be a constant.

The frequency response of the Pre-emphasis filter is shown below

The same for both the filters together can be shown as

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2.10. FM DEMODULATORS
The basic block diagram of a FM receiver is shown in Figure. In FM
receivers, the limiter and discriminator combine to form the central signal
processing required to demodulate the FM signal. The basic idea of a limiter is
to clip the input signal to produce a constant output voltage over a range of
input voltages. When the limiter is adjusted so that the only information
obtained from its output is the zero crossing locations, it is said to be hard
limited. One then just counts the zero crossings to determine the frequency.

Figure2.21. Block diagram of FM receiver.

The basic problem is that discriminators are susceptible to amplitude

variations; by limiting these effects, the frequency deviation alone produces
results. The direct discriminator relies on some method of converting FM
deviation to AM. If there is already AM modulation produced by variations in
the carrier energy, these will pass through and distort the signal.

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For FM, the output signal voltage should vary linearly with the
instantaneous frequency of the modulated waveform. A circuit that responds in
this way is frequency discriminator. It is a device that converts the signal
frequency, but also phase, into an amplitude variation. One type of device that
accomplishes this frequency-to-voltage conversion is the PLL.

2.10.1.Direct Discrimination

One of the oldest and simplest methods of direct FM detection is to use a

slope detector, which uses a high pass filter (HPF) and diode to convert
frequency variations into voltage variations. The detector circuit is tuned such
that the lower end of the diode curve corresponds to the center frequency of
the FM transmission.

As can be seen in Figure, it is useful only in NBFM receivers because if the

FM transmitted signal's deviation is greater than the linear slope of the response
curve, distortion results. In other words, if the bandwidth of the FM transmission is
wider than the linear portion of the HPF response curve, you do not get a good
representation of voltage for frequency variation and, hence, get distortion.

Fig.2.22. Slope detector for FM demodulation.

This circuit works by using the HPF to generate amplitude variations as the
frequency of the FM signal varies. This variation is accomplished by the transfer
characteristic of the HPF. For high deviations, the output of the HPF is low in
amplitude, and for large variations, it is high. This swing is then rectified by the
diode and a varying dc voltage results that corresponds to (discriminates) the
frequency deviations of the input signal.

A good example of a direct FM detector is the zero crossing or pulse

averaging discriminator. This circuit is composed of three main sections, a zero
crossing detector, a monostable multivibrator, and a low-pass filter. More
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advanced versions take advantage of the dual outputs offered by most one-
shots and add a second low-pass filter and utilize a fourth section, a differential
amplifier. The two basic designs are shown in Figure.

Figure : Zero-Crossing Detectors.

The input FM signal is applied to the zero crossing detector, which triggers
the one-shot at each transition of the FM signal. When triggered, the one-shot
produces a DC level on its output or on both outputs in the second case.

The dc level is held for one-half cycle of the input FM signal. In the first
case, the pulse train thus produced is applied to the input of a LPF, which
averages the pulses to produce a dc voltage that represents the modulating
signal. In the second case, the differential amplifier varies its dc output voltage,
moving more positive the more frequently the pulses occur and dropping as the
frequency of occurrence drops, again producing a voltage that represents the
original modulating signal.

9.Practice Quiz:
1. FM bandwidth is approximated using _______ rule.
a)Carson’s
b)Faraday’s
c)Maxwell’s
d) Armstrong’s
2. Which of the following are two methods for generating FM signal?
a)Coherent method ,noncoherent method
b) Product detector, envelope detector
c) Direct method, indirect method
d) Slope detector, Zero crossing detector
3. Which of the following is not a technique for FM demodulation?
a) Slope detection
b) Zero crossing detection
c) Product detector

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d) Phase locked discriminator
4.Which of the following FM demodulator is sometimes known as
pulse averaging discriminator?
a) Slope detection
b) Zero crossing detection
c) Quadrature detection
d) Phase locked discriminator
5. PLL in FM detection stands for ______
a) Phase locked loop
b) Programmable logic loop
c) Phase locked logic
d) Programmable locked loop
5.Carrier swing is defined as
a. The total variation in frequency from the lowest to the highest point
b. Frequency deviation above or below the carrier frequency
c. Width of the side band
d. None of the above
6 The amount of frequency deviation in FM signal depends on
a. Amplitude of the modulating signal
b. Carrier frequency
c. Modulating frequency
d. Transmitter amplifier
7.Pre emphasis is done
a. For boosting of modulating signal voltage
b. For modulating signals at higher frequencies
c. In FM before modulation
d. All of the above
8. De-emphasis is
a. is restoring of original signal power
b. is done at the detector output of the receiver
c. is the inverse process of Pre emphasis
d. All of the above
9. The modulation index of FM is given by
a. μ = frequency deviation/ modulating frequency
b. μ = modulating frequency /frequency deviation
c. μ = modulating frequency/ carrier frequency
d. μ = carrier frequency / modulating frequency
10. What is the required bandwidth according to the Carson’s rule, when a 100
MHz carrier is modulated with a sinusoidal signal at 1KHz, the maximum
frequency deviation being 50 KHz.
a. 1 KHz
b. 50 KHz
c. 102 KHz

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d. 150 KHz

10.Assignments

S.No Question BL CO

Draw the block diagram of Armstrong method of WBFM

1 generation and explain it. 4 1

Describe zero crossing detector and phase locked loop.

2 4 1

Give the expression for FM signal and expand the expression in

3 4 1
terms of Bessel functions

Draw the block diagram of phase shift discriminator and explain

4 the functionality of each block. 1
4

5 Write short note on Pre-Emphasis and De-Emphasis circuits 3 1

11. Part A- Question & Answers

S.No Question& Answers BL CO

1 Define frequency modulation.

Frequency modulation is defined as the process by which the

frequency of the carrier wave is varied in accordance with the 1 1
amplitude of the wave.

2 Define modulation index of frequency modulation.

It is defined as the ratio of maximum frequency deviation to the

1 1
modulating frequency. mf = ∆f/fm

3 . What do you meant by multitone modulation?

Modulation done for the message signal with more than one 4 3
frequency component is called multitone modulation.

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4 Define phase modulation.

Phase modulation is defined as the process of changing the

phase of the carrier signal in accordance with the 4 3
instantaneous amplitude of the message signal.

5 What are the types of Frequency Modulation?

They are Narrow band FM and Wide band FM. If the

modulation index is greater than one then it is wide band FM
4 3
and if the modulation index is less than one then it is Narrow
band FM

6 What is the basic difference between an AM signal and a

narrowband FM signal?

In the case of sinusoidal modulation, the basic difference

between an AM signal and a narrowband FM signal is that the 4 4
algebraic sign of the lower side frequency in the narrow band
FM is reversed.

7 What are the two methods of producing an FM wave?

Basically there are two methods of producing an FM wave.

They are,

i) Direct method

In this method the transmitter originates a wave whose

frequency varies as function of the modulating source. It is used
4 3
for the generation of NBFM

ii) Indirect method

In this method the transmitter originates a wave whose phase is

a function of the modulation. Normally it is used for the
generation of WBFM where WBFM is generated from NBFM

8 Define pre-emphasis and de-emphasis. 2 4

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Pre-emphasis: It artificially emphasizes the high frequency

components before modulation. This equalizes the low
frequency and high frequency portions of the PSD and
complete band is occupied.

De-emphasis: This circuit attenuates the high frequency

components. The attenuation characteristic is exactly
opposite to that of pre-emphasis circuit. De-emphasis restores
the power distribution of the original signal.

The signal to noise ratio is improved because of pre-emphasis

and de-emphasis

9 State the Carson’s rule.

An approximate rule for the transmission bandwidth of an FM

Signal generated by a single tone-modulating signal of 2 4
frequency fm is defined as

BW =2 (∆ω + ωm)

10. How do you get FM using PM system?

The frequency modulated wave can be obtained from PM

system. This is done by integrating the modulating signals before 4 4
applying it to the phase modulators.

12. Part B- Questions

S.No Question BL CO

1 Explain FM generation using indirect method. 1 1

2 Describe zero crossing detector and phase locked loop. 4 3

3 Write short note on Pre-Emphasis and De-Emphasis circuits. 2 3

4 Explain the generation of Narrow band Phase Modulation and 2 3

Narrow band Frequency Modulation with suitable block
diagrams.

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5 The equation for a FM wave is s(t) = 10sin [5.7 x 108 t + 5 sin 12 x 2 3

103 t ]. Calculate: (i) Carrier frequency. (ii) Modulating

frequency. (iii) Modulation index. (vi) Frequency deviation. (v)
Power dissipated in 100 Ω.

6 Give the bandwidth relationship using Carson’s rule in FM. 3 5

7 Draw the phasor diagrams of NBFM & AM and compare 3 5

them.

8 . A carrier is frequency modulated with a sinusoidal of 2 kHz 4 3

resulting in a maximum frequency deviation of 5 kHz.

(i) Find the bandwidth of the modulated signal.

(ii) The amplitude of the modulating sinusoid is increased by a

factor of 3, and its frequency is lowered to 1 kHz. Find the
maximum frequency deviation and the bandwidth of the new
modulated signal.

9 Explain fully the difference between frequency and phase 3 4

modulation, and the modulation index in each case.

10 Explain the working of a ratio detector for FM. 3 4

11 Explain the reactance modulator method of generation of

WBFM. Why is it necessary to use AFC in this method of
generation?

13. Supportive Online Certification Courses

1. Analog Communication By Prof.Goutham Das coordinated by IIT Kharagpur –
12 weeks
2. Principles of communication systems-1by Prof.Aditya Jagannathan,
conducted by IIT Kharagpur – 12 weeks.

14. Real Time Applications

S.No Application CO

1 FM RADIO 3

2 FM TRANSMITTER 3

15. Contents Beyond the Syllabus

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1. Frequency Division Multiplexing.

16. Prescribed Text Books & Reference Books

Text Books:
1. Simon Haykin, “Communication Systems,” Wiley India Edition, 4th Edition,
2011.
2. B. P. Lathi, “Modern Digital and Analog Communication Systems,” 3rd Edition,
Oxford Univ. press, 2006.
3. Sham Shanmugam, “Digital and Analog Communication Systems”, Wiley-
India edition, 2006.(edition).

Reference Books:
1. Bruce Carlson, & Paul B. Crilly, “Communication Systems – An Introduction to
Signals &Noise in Electrical Communication”, 5th Edition, McGraw-Hill
International Edition, 2010.
2.Herbert Taub & Donald L Schilling, “Principles of Communication Systems”, 3rd
Edition, Tata McGraw- Hill, 2009.
3. R.E. Ziemer & W.H. Tranter, “Principles of Communication-Systems
Modulation &
Noise”, 5th edition, Jaico Publishing House 2001.
4. George Kennedy and Bernard Davis, “Electronics & Communication
System”, TMH, 2004. (Edition)

17. Mini Project Suggestion

1. FM Bugger Circuit
Bugger is a device which gives the information of one person to other person in
the remote location. Normally bugger is used for finding out the status of the
person like where he is going, what he is talking etc. This is illegal but most of spy
agencies use this bugger. Here is small circuit with which you can listen to
another people conversation from long distance using the normal FM radio set.
This FM bugger circuit is kept in room where you want listen the conversation.
You can listen to this conversation using the normal FM radio set.
2. FM Remote Encoder/Decoder Circuit

This system uses FM (Frequency Modulation) for transmission. If you press any
push button then corresponding code is generated at transmission section. Here
encoder is used to convert parallel data to serial. This serial data is given to the
FM Tx module to transmit. FM Rx module receives this serial data and fed to the
decoder to produce the corresponding output.

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