This presentation gives a brief description about modulation and one of its type i.e amplitude modulation.

1. AMPLITUDE MODULATION
PRESENTED BY:
•Rafat Ansari
•Snehal Ghadge
•Sneha Perla

2. WHAT IS MODULATION?
 Modulation is the basic requirement for transmitting the
message signal through free space.
 It is a process of transmission of information signal(low
frequency audio signal) using a high frequency carrier
signal.
 Modulation is defined as a process by which some
characteristics of a signal called as carrier signal varies
in accordance with the instantaneous value of another
signal called as the modulating signal.
 The information bearing signal is called modulating
signal.
 The signal resulting from the process of modulation is
known as the modulated signal.

3. TYPES OF MODULATION
 Continuous Wave Modulation: The carrier is sinusoidal in
nature. It consist of 3 types:
1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation
 Pulse Modulation: Carrier is pulse type waveform. It
consist of 2 types:
1. Digital Modulation
2. Analog Modulation

4. WHAT IS AMPLITUDE MODULATION?
The process by which the amplitude of a carrier
signal varies in accordance with the instantaneous
value of the modulating signal is called as
Amplitude Modulation.

5. WAVEFORM

6. TIME DOMAIN REPRESENTATION OF AM WAVE
 Let the modulating signal be sinusoidal and be represented
as,
em=Emcosωmt
 Where em=instantaneous amplitude of modulating signal
 Em=Peak modulating amplitude
 ωm=2πfm and fm=frequency of modulating signal.
 Let the carrier signal be also sinusoidal and be represented
as,
ec=Eccosωct
 Where ec=instantaneous amplitude of carrier signal
 Ec=Peak carrier amplitude
 ωc= 2πfc and fc=frequency of carrier signal.

7.  The Amplitude modulated frequency is represented as,
eAM= Acos(2πfct)
 Where A=instantaneous value of envelope of AM wave
and is represented as,
A=Ec+em
=Ec+Emcos (2πfmt)
 Hence the AM wave is given as,
eAM= Acos(2πfct)
=[Ec+Emcos(2πfmt)]cos(2πfct)
=Ec[1+Em/Ec cos(2πfmt)]cos(2πfct)
 Let Em/Ec=m and m is the modulation index
 Hence, the time domain representation of AM wave is,
eAM = Ec[1+mcos(2πfmt)]cos(2πfct)

8. FREQUENCY SPECTRUM OF AM WAVE
 The time domain representation of AM wave is,
eAM =Ec[1+ mcos(2πfmt)]cos(2πfct)
= Ec[1+ mcosωmt]cosωct
=Eccosωct + mEccosωmtcosωct
 We know that,/
2cosAcosB=cos(A+B)+cos(A-B)
eAM = Eccosωct+mEc/2[cos(ωm+ωc)t]+mEc/2[cos(ωm-
ωc)t
carrier upper sideband lower sideband

9. BANDWIDTH OF AM WAVE
BW =fUSB-fLSB
=(fc+fm)-(fc-fm)
=2fm

10. ADVANTAGES AND DISADVANTAGES OF AM
 AM transmitters are less
complex
 AM receivers are simple,
detection is easy.
 AM receivers are cost
efficient. Hence even a
common person can
afford it.
 AM wave can travel
longer distances.
 Low bandwidth
 It is not efficient in terms of
its power usage
 It is not efficient in terms of
its use of bandwidth,
requiring a bandwidth equal
to twice that of the highest
audio frequency
 It is prone to high levels of
noise because most noise is
amplitude based and
obviously AM detectors are
sensitive to it.
Advantages Disadvantages

11. TYPES OF AM RECEIVERS
 Tuned Radio Frequency(TRF) receiver
 Superheterodyne receiver

12. TRF RECEIVERS VS SUPERHETERODYNE
RECEIVERS
 Poor selectivity and low
sensitivity in proportion to
the number of tuned
amplifiers used.
 They are expensive.
 Instability due to large
number of RF stages.
 Gain is non-uniform over
a wide range of
frequencies.
 Better selectivity
 They are less expensive.
 Improved circuit stability.
 Uniform gain over a wide
range of frequencies
Limitations of the TRF receivers Advantages of Superheterodyne
receivers

13. APPLICATIONS OF AM
 Radio broadcasting
 Picture transmission in a TV system.