1) Frequency modulation (FM) varies the instantaneous frequency of the carrier signal in proportion to an input modulating signal. This produces sidebands around the carrier frequency.
2) FM is considered superior to amplitude modulation (AM) due to better fidelity, noise immunity, and transmission efficiency. However, FM requires more bandwidth than AM.
3) The modulation index determines the number of significant sidebands and bandwidth occupied. It is defined as the peak frequency deviation divided by the modulating signal frequency.
Comparative Study and Performance Analysis of different Modulation Techniques...Souvik Das
Make a comparative study and performance analysis of different modulation
techniques which shows graphically and comparatively results like Bandwidth,
Energy and Power Efficiency of AM, DSB-SC, SSB and SSB-SC
Modulation
In the modulation process, some characteristic of a high-frequency carrier signal (bandpass), is changed according to the instantaneous amplitude of the information (baseband) signal.
RF Carrier oscillator
To generate the carrier signal.
Usually a crystal-controlled oscillator is used.
Buffer amplifier
Low gain, high input impedance linear amplifier.
To isolate the oscillator from the high power amplifiers.
Modulator : can use either emitter collector modulation
Intermediate and final power amplifiers (pull-push modulators)
Required with low-level transmitters to maintain symmetry in the AM envelope
Coupling network
Matches output impedance of the final amplifier to the transmission line/antenn
Applications are in low-power, low-capacity systems : wireless intercoms, remote control units, pagers and short-range walkie-talkie
Modulating signal is processed similarly as in low-level transmitter except for the addition of power amplifier
Power amplifier
To provide higher power modulating signal necessary to achieve 100% modulation (carrier power is maximum at the high-level modulation point).
Same circuit as low-level transmitter for carrier oscillator, buffer and driver but with addition of power amplifier
Comparative Study and Performance Analysis of different Modulation Techniques...Souvik Das
Make a comparative study and performance analysis of different modulation
techniques which shows graphically and comparatively results like Bandwidth,
Energy and Power Efficiency of AM, DSB-SC, SSB and SSB-SC
Modulation
In the modulation process, some characteristic of a high-frequency carrier signal (bandpass), is changed according to the instantaneous amplitude of the information (baseband) signal.
RF Carrier oscillator
To generate the carrier signal.
Usually a crystal-controlled oscillator is used.
Buffer amplifier
Low gain, high input impedance linear amplifier.
To isolate the oscillator from the high power amplifiers.
Modulator : can use either emitter collector modulation
Intermediate and final power amplifiers (pull-push modulators)
Required with low-level transmitters to maintain symmetry in the AM envelope
Coupling network
Matches output impedance of the final amplifier to the transmission line/antenn
Applications are in low-power, low-capacity systems : wireless intercoms, remote control units, pagers and short-range walkie-talkie
Modulating signal is processed similarly as in low-level transmitter except for the addition of power amplifier
Power amplifier
To provide higher power modulating signal necessary to achieve 100% modulation (carrier power is maximum at the high-level modulation point).
Same circuit as low-level transmitter for carrier oscillator, buffer and driver but with addition of power amplifier
Frequency Modulation In Data TransmissionBise Mond
This presentation includes concepts of FM, generation of FM, transmission, reception, with the concepts of stereo FM and some basic circuitry of receiver and transmitter system.
Introduction to Angle Modulation, Types of Angle Modulation, Frequency Modulation and Phase Modulation Introduction, Generation of FM, Detection of FM, Frequency stereo Multiplexing, Applications, Difference between FM and PM.
. Types of Modulation(Analog)
Phase-Frequency Relationships
FM and PM basics
Frequency deviation
MODULATION INDEX
Classification of FM
Narrow Band FM (NBFM)
generating a narrowband FM signal.
Wide Band FM (WBFM).
Carson’s Rule
Generation of WBFM
Average Power
FM BANDWIDTH
Comparing Frequency Modulation to Phase Modulation
Slide 1
Frequency Modulation (FM)
Slide 2
FM Signal Definition (cont.)
Slide 3
Discrete-Time FM Modulator
Slide 4
Single Tone FM Modulation
Slide 5
Single Tone FM (cont.)
Slide 6
Narrow Band FM
Slide 7
Bandwidth of an FM Signal
Slide 8
Demod. by a Frequency Discriminator
Slide 9
FM Discriminator (cont.)
Slide 10
Discriminator Using Pre-Envelope
Slide 11
Discriminator Using Pre-Envelope (cont.)
Slide 12
Discriminator Using Complex Envelope
Slide 13 Phase-Locked Loop Demodulator
Slide 14
PLL Analysis
Slide 15
PLL Analysis (cont. 1)
Slide 16
PLL Analysis (cont. 2)
Slide 17
Linearized Model for PLL
Slide 18
Proof PLL is a Demod for FM
Slide 19
Comments on PLL Performance
Slide 20
FM PLL vs. Costas Loop Bandwidth
Slide 21
Laboratory Experiments for FM
Slide 21
Experiment 8.1 Spectrum of an FM
Signal
Slide 22
Experiment 8.1 FM Spectrum (cont. 1)
Slide 23
Experiment 8.1 FM Spectrum (cont. 1)
Slide 24
Experiment 8.1 FM Spectrum (cont. 3)
Slide 24
Experiment 8.2 Demodulation by a Discriminator
Slide 25
Experiment 8.2 Discriminator (cont. 1)
Slide 26
Experiment 8.2 Discriminator (cont. 2)
Slide 27
Experiment 8.3 Demodulation by a PLL
Slide 28
Experiment 8.3 PLL (cont.)
Frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
The presentation is made by me. I am a student of EEE, RUET.
Power point presentation of Amplitude modulation from DSBSC.pptxvairaprakash3
The equation of AM wave in simple form is given by,
eAM(t) = Ec sin 2πfct+(mE_c)/2 cos2π(fc + fm)t - (mE_c)/2 cos2π(fc - fm)t
Here, power of the carrier does not convey any information. Most of the power is transmitted in the carrier is not used for carrying information. Hence the carrier is suppressed and only sidebands are transmitted.Therefore, if the carrier is suppressed, only sidebands remain in the spectrum requiring less power.
DSB-SC Contains two side bands i.e USB & LSB
Power efficiency is 100%
% Power saving in DSB-SC w.r.t AM is 66.67%.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
Ethnobotany and Ethnopharmacology:
Ethnobotany in herbal drug evaluation,
Impact of Ethnobotany in traditional medicine,
New development in herbals,
Bio-prospecting tools for drug discovery,
Role of Ethnopharmacology in drug evaluation,
Reverse Pharmacology.
How to Split Bills in the Odoo 17 POS ModuleCeline George
Bills have a main role in point of sale procedure. It will help to track sales, handling payments and giving receipts to customers. Bill splitting also has an important role in POS. For example, If some friends come together for dinner and if they want to divide the bill then it is possible by POS bill splitting. This slide will show how to split bills in odoo 17 POS.
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
We all have good and bad thoughts from time to time and situation to situation. We are bombarded daily with spiraling thoughts(both negative and positive) creating all-consuming feel , making us difficult to manage with associated suffering. Good thoughts are like our Mob Signal (Positive thought) amidst noise(negative thought) in the atmosphere. Negative thoughts like noise outweigh positive thoughts. These thoughts often create unwanted confusion, trouble, stress and frustration in our mind as well as chaos in our physical world. Negative thoughts are also known as “distorted thinking”.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
2. INTRODUCTION
3 properties of an analog signal can be modulated by
information signal:
o Amplitude - - -> produce AM
o Frequency ---> produce FM
o Phase ---> produce PM
FM & PM are forms of angle modulation and often
referred as frequency modulation.
3. FM VS AM
FM is considered to be superior to AM.
Transmission efficiency:
AM use linear amplifier to produced the final RF signal.
FM has constant carrier amplitude so it is not necessary to use
linear amplifier.
Fidelity (capture effect):
The stronger signal will be capture and eliminate the weaker.
In AM, the weaker signal can be heard in the background.
Noise immunity (noise reduction):
Constant carrier amplitude.
FM receiver have limiter circuit
4. Disadvantages of FM
Use too much spectrum space.
Requiring a wider bandwidth
Reduce modulation index to minimize BW but in FM
although we reduced the modulation index, BW is still larger.
typically used at high frequencies (VHF,UHF & microwave
frequencies
More complex circuitry
5. ANGLE MODULATION
Amplitude of the modulated carrier is held constant and either the
phase or the time derivative of the phase of the carrier is varied linearly
with the message signal m(t).
General angle-modulated signal is given by
m( t ) = Vc cos[ωct + θ ( t ) ]
In angle modulation, θ(t) is prescribed as being a function of the
modulating signal
If vm(t) is the modulating signal, angle modulation is expressed as
θ (t ) = F [ vm (t ) ]
vm (t ) = Vm sin(ωmt )
where
ωm = 2π f m
6. FM OR PM ?
FM PM
Instantaneous frequency of the carrier is Phase angle of the carrier is varied
varied from its reference value by from its reference value by an
an amount proportional to the amount proportional to the
modulating signal amplitude modulating signal amplitude
Freq. carrier - - - > directly varied Phase carrier - - - > directly varied
Phase carrier - - -> indirectly varied Freq. carrier - - -> indirectly varied
Both must occur whenever either form of angle modulation is
performed.
7. 2∆f
∆f ∆f
fc-∆f fc fc+∆f f
vm(t) = Vm cos 2πfmt
-Vm 0 +Vm
Figure 4.1 : Frequency deviation
8. MATHEMATICAL ANALYSIS
Instantaneous frequency deviation
Instantaneous change in the frequency of the carrier and is defined
as the first time derivative of the instantaneous phase deviation
instantaneous frequency deviation = θ '(t ) rad/s
θ '(t ) rad/s cycle
or = = = Hz
2π rad/cycle s
Instantaneous frequency
the precise frequency of the carrier at any given instant of time and
is defined as the first time derivative of the instantaneous phase
d
instantaneous frequency = ωi (t ) = [ ωct + θ (t )]
dt
= ωc + θ '(t ) rad/s
9. Substituting 2πfc for ωc gives
instantaneous frequency = fi (t )
rad cycles
and ωi (t ) = 2π fc + θ '(t ) = 2π f c + θ '(t ) rad/s
cycle s
Frequency modulation is angle modulation in which the
instantaneous frequency deviation, θ’(t), is proportional to
the amplitude of the modulating signal, and the
instantaneous phase deviation is proportional to the integral
of the modulating signal voltage.
10. DEVIATION SENSITIVITY
For modulating signal vm(t), the frequency modulation are
frequency modulation = θ’(t) = kfvm(t) rad/s
where kf are constant and are the deviation sensitivities of the
frequency modulator.
Deviation sensitivities are the output-versus-input transfer
function for the modulators, which gave the relationship
between what output parameter changes in respect to
specified changes in the input signal.
frequency modulator,
rad/s ∆ω
kf =
V ∆V
11. FREQUENCY MODULATION
(FM)
Variation of dθ /dt produces Frequency
Modulation
Frequency modulation implies that dθ/dt is
proportional to the modulating signal.
This yields v (t ) = V sin [ ω t + θ (t )]
FM c c
= Vc sin ωc t + ∫ θ '(t )dt
= Vc sin ωc t + ∫ k f vm (t )dt
= Vc sin ωc t + k f Vm ∫ sin ωm (t ) dt
k f Vm
= Vc sin ωc t − cos ωm (t )
ωm
12. Example 4.1
Derive the FM signal using both cosine wave
signal.
v(t ) = Vc cos ( ωc t + θ (t ) )
vm (t ) = Vm cos ( ωmt )
for FM
for PM
(( ))
vFM ((t))= Vc c cosωωc t ∫ kk p vmt()tdt
PM
t = Vcos c t + + f vm ( )
= V cos ( ωω + ∫ kk V cos(ωω )dt )
= V cos ( t t + V cos( t t )
cc c c f p mm m m
= V cos ( ω t + k V ∫ cos(ω t )dt )
c c f m m
k f Vm
= Vc cos ωc t + sin(ωmt )
ωm
13. FM WAVEFORM
Figure 4.2: Phase and Frequency modulation ; (a) carrier signal (b) modulating
signal (c) frequency modulated wave (d) phase modulated wave
14. Carrier amplitude remains constant
Carrier frequency is changed by the modulating signal.
amplitude of the information signal varies, the carrier frequency shift
proportionately.
modulating signal amplitude increases, the carrier frequency increases.
modulating signal amplitude varies, the carrier frequency varies below and
above it normal center or resting, frequency with no modulation.
The amount of the change in carrier frequency produced by the
modulating signal known as frequency deviation fd.
Maximum frequency deviation occurs at the maximum amplitude
of the modulating signal.
The frequency of the modulating signal determines the frequency
deviation rate
15. MODULATION INDEX
Directly proportional to the amplitude of the modulating signal
and inversely proportional to the frequency of the modulating
signal
Ratio of the frequency deviation and the modulating frequency
FM equation : vFM (t ) = Vc sin [ ωct − β cos ωm (t )]
β as modulation index : k f Vm ∆f c
β= =
ωm fm
Example:
Determine the modulation index for FM signal with modulating frequency
is 10KHz deviated by ±10kHz.
Answer : (20KHz/10KHz) = 2 .0 (unitless)
The total frequency change, 10kHz x 2 is called the carrier swing
16. Example:
a simple transmitter with an assigned rest frequency of 100MHz
deviated by a ±25kHz, the carrier changes frequency with modulation
between the limits of 99.975MHz and 100.025MHz
The total frequency change, 25kHz x 2 is called the carrier swing
Table 1 display the transmission band that use FM and the legal
frequency deviation limit for each category
Deviation limits are based on the quality of the intended
transmissions, wider deviation results in higher fidelity
The frequency deviation is a useful parameter for determining the
bandwidth of the FM-signals
17. Table 1 display the transmission band that use FM and the legal
frequency deviation limit for each category
Specifications for transmission of FM signal
18. PERCENT MODULATION
Simply the ratio of the frequency deviation actually
produced to the maximum frequency deviation allowed by
law stated in percent form
∆f actual
% modulation =
∆f max
For example if a given modulating signal produces ±50kHz
frequency deviation, and the law stated that maximum
frequency deviation allowed is ±75kHz, then
50kHz
% modulation = × 100 = 67%
75kHz
19. Example 4.2
A 1 MHz carrier freq with a measured sensitivity of 3
kHz/V is modulated with a 2 V, 4 kHz sinusoid.
Determine
1. the max freq deviation of the carrier
2. the modulation index
3. the modulation index if the modulation voltage is
doubled
4. the modulation index for vm(t)=2cos[2π(8kHz)t)]V
5. express the FM signal mathematically for a cosine
carrier & the cosine-modulating signal of part 4. Carrier
amplitude is 10V
20.
21. FM RADIO FREQUENCY
Commercial radio FM band, 88MHz – 108MHz
Each station allotted to a frequency deviation of
±75kHz (150 carrier swing) and 25kHz of guard
band added above and below the carrier
frequency swing
Total bandwidth is 200kHz
Therefore, maximum of 100 stations can be
made available
23. BESSEL TABLE
,β
Tabulated value for Bessel Function for the first kind of the nth order
24. The first column gives the modulation , while the first row gives the
Bessel function.
The remaining columns indicate the amplitudes of the carrier and the
various pairs of sidebands.
Sidebands with relative magnitude of less than 0.001 have been
eliminated.
Some of the carrier and sideband amplitudes have negative signs. This
means that the signal represented by that amplitude is simply shifted in
phase 180° (phase inversion).
The spectrum of a FM signal varies considerably in bandwidth
depending upon the value of the modulation index. The higher the
modulation index, the wider the bandwidth of the FM signal.
With the increase in the modulation index, the carrier amplitude
decreases while the amplitude of the various sidebands increases. With
some values of modulation index, the carrier can disappear completely.
26. PROPERTIES OF BESSEL
FUNCTION
Property - 1: Property - 3:
∞
For n even,
∑ J n (β ) = 1
2
we have Jn(β) = J-n(β) n =−∞
For n odd,
we have Jn(β) = (-1) J-n(β)
Thus,
Jn(β) = (-1)n J-n (β)
Property - 2:
For small values of the modulation index β, we have
J0(β) ≅ 1
J1(β) ≅ β/2
J3(β) ≅ 0 for n > 2
28. FM BANDWIDTH
The total BW of an FM signal can be determined by knowing the
modulation index and Bessel function.
BW = 2 f m N
N = number of significant sidebands
fm = modulating signal frequency (Hz)
Another way to determine the BW is use Carson’s rule
This rule recognizes only the power in the most significant
sidebands with amplitude greater than 2% of the carrier.
29. Example 4.3
Calculate the bandwidth occupied by a FM signal with a
modulation index of 2 and a highest modulating frequency of
2.5 kHz. Determine bandwidth with table of Bessel functions.
Referring to the table, this produces 4 significant pairs of
sidebands.
BW = 2 × 4 × 2.5
= 20kHz
30. CARSON’S RULE
BW = 2[ f d (max) + f m (max) ]
fd (max) = max. frequency deviation
fm (max) = max. modulating frequency
Carson’s rule always give a lower BW calculated with the
formula BW = 2fmN.
Consider only the power in the most significant sidebands
whose amplitudes are greater than 1% of the carrier.
Rule for the transmission bandwidth of an FM signal
generated by a single of frequency fm as follows:
BT = BW ≅ 2 ∆f + 2 f m = 2 ∆f (1 + 1 )
β
or = 2 fm ( 1 + β )
31. Example 4.4
For an FM modulator with a modulation index β =
1, a modulating signal
vm(t) = Vmsin(2π1000t) and unmodulated carrier
vc(t) = 10sin(2π500kt), determine
d) Number of sets of significant sideband
e) Their amplitude
f) Then draw the frequency spectrum showing their
relative amplitudes
32. Example 4.5
For an FM modulator with a peak freq deviation Δf
= 10kHz, a modulating signal freq fm= 10kHz, Vc
=10V and 500kHz carrier, determine
b) Actual minimum bandwidth from the Bessel
function table
c) Approximate minimum bandwidth using Carson’s
rule
d) Plot the output freq spectrum for the Bessel
approximation
33. DEVIATION RATIO (DR)
Minimum bandwidth is greatest when maximum freq
deviation is obtained with the maximum modulating
signal frequency
Worst case modulation index and is equal to the
maximum peak frequency deviation divided by the
maximum modulating signal frequency
Worst case modulation index produces the widest
output frequency spectrum
Mathematically,
max peak freq deviation ∆f max
DR = =
max mod signal freq f m (max)
34. Example 4.6
• Determine the deviation ratio and bandwidth for
the worst case (widest bandwidth) modulation
index for an FM broadcast band transmitter with a
maximum frequency deviation of 75kHz and a
maximum modulating signal frequency of 15kHz
• Determine the deviation ratio and maximum
bandwidth for an equal modulation index with only
half the peak frequency deviation and modulating
signal frequency
35. POWER IN ANGLE-
MODULATED SIGNAL
The power in an angle-modulated signal is easily computed
P = VC2/2R W
Thus the power contained in the FM signal is independent
of the message signal. This is an important difference
between FM and AM.
The time-average power of an FM signal may also be
obtained from
vFM (t ) = Vc cos(2π f c t + θ (t ))
36. Example 4.7
An FM signal is given as vFM(t)=12cos[(6π106t)
+ 5sin(2π x 1250t)] V. Determine
a. freq of the carrier signal
b. freq of the modulating signal
c. modulation index
d. freq deviation
e. power dissipated in 10 ohm resistor.
37. Example 4.8
Determine the unmodulated carrier power for the
FM modulator given that β =1, Vc=10 V, R = 50
Ω. Then, determine the total power in the angle-
modulated wave.
Solution:
not exactly equal because values in Bessel
table have been rounded off.
38. Example 4.9
An FM signal expressed as v FM (t ) = 1000 cos(2π 10 7 t + 0.5 sin 2π 10 4 t )
is measured in a 50 ohm antenna. Determine the following :-
a. total power
b. modulation index
c. peak freq deviation
d. modulation sensitivity if 200 mV is required to achieve part c
e. amplitude spectrum
f. bandwidth (99%) and approximate bandwidth by Carson’s rule
g. power in the smallest sideband of the 99% BW
h. total information power
39. Example 4.10
An FM signal with 5W carrier power is
fluctuating at the rate of 10000 times per second
from 99.96 MHz to 100.04 MHz. Find
a. carrier freq
b. carrier swing
c. freq deviation
d. modulation index
e. power spectrum
40. Example 4.11
In an FM transmitter, the freq is changing between 100
MHz to 99.98 MHz, 400 times per seconds. The amplitude
of the FM signal is 5 V, determine :-
1. carrier and modulating freq
2. carrier freq swing
3. amplitude spectrum
4. bandwidth by using Bessel Table and Carson’s rule
5. average power at the transmitter if the modulator carrier
power is 5 W.
41. FM SIGNAL GENERATION
They are two basic methods of
generating frequency-Modulated
signals:
Direct Method
Indirect Method
42. DIRECT FM
In a direct FM system the instantaneous frequency is
directly varied with the information signal. To vary the
frequency of the carrier is to use an Oscillator whose
resonant frequency is determined by components that can
be varied. The oscillator frequency is thus changed by the
modulating signal amplitude.
f i = f c + k f vm (t )
• For example, an electronic Oscillator has an output
frequency that depends on energy-storage devices. There
are a wide variety of oscillators whose frequencies depend
on a particular capacitor value. By varying the capacitor
value, the frequency of oscillation varies. If the capacitor
variations are controlled by vm(t), the result is an FM
43. INDIRECT FM
Angle modulation includes frequency modulation FM and
phase modulation PM.
FM and PM are interrelated; one cannot change without the
other changing. The information signal frequency also
deviates the carrier frequency in PM.
Phase modulation produces frequency modulation. Since
the amount of phase shift is varying, the effect is that, as if
the frequency is changed.
Since FM is produced by PM , the later is referred to as
indirect FM.
The information signal is first integrated and then used to
phase modulate a crystal-controlled oscillator, which
provides frequency stability.
44. NOISE AND PHASE SHIFT
The noise amplitude added to an FM signal
introduces a small frequency variation or phase
shift, which changes or distorts the signal.
Noise to signal ratio N/S
N Frequency deviation produced by noise
=
S Maximum allowed deviation
Signal to noise ration S/N
S 1
=
N N
S
45. INTERFERENCE
A major benefit of FM is that interfering signals on the
same frequency will be effectively rejected.
If the signal of one is more than twice the amplitude of the
other, the stronger signal will "capture" the channel and will
totally eliminate the weaker, interfering signal.
This is known as the capture effect in FM.
In FM, the capture effect allows the stronger signal to
dominate while the weaker signal is eliminated.
However, when the strengths of the two FM signals begin
to be nearly the same, the capture effect may cause the
signals to alternate in their domination of the frequency.
46. Despite the fact that FM has superior noise rejection
qualities, noise still interferes with an FM signal. This is
particularly true for the high-frequency components in the
modulating signal.
Since noise is primarily sharp spikes of energy, it contains a
considerable number of harmonics and other high-
frequency components.
These high frequencies can at times be larger in amplitude
than the high-frequency content of the modulating signal.
This causes a form of frequency distortion that can make
the signal unintelligible.
To overcome this problem Most FM system use a
technique known as Pre-emphasis and De-emphasis.