MAYURBHANJ SCHOOL OF ENGINEERING � LAXMIPOSI ,BARIPADA,757107

• DEPARTMENT- E&TC ENGG.
• SEMISTAR- 5^TH
• SUBJECT-A & D Communication
• CHAPTER – 2 – Amplitude Modulation System
• NAME OF TOPIC – Amplitude modulation, Expression of AM, SSB, DSB
• PREPARED BY - U S Panda (Sr. Lect. E & TC Engineering)
• AY – 2021-2022, WINTER-2021

Content

• What Is Modulation?
• Why Do We Need Modulation?
• Type of Modulation
• AMPLITUDE MODULATION
• Mathematical Equations of AM
• Modulation Index
• Type of Amplitude Modulation
• Balance Modulator
• Amplitude Demodulation
• Type of Amplitude Demodulation
• Envelope Detector
• Synchronous Detector
• Application of AM
• References

What Is Modulation?

• Modulation is define as the process by which some characteristics , usually amplitude, frequency or phase, of a carrier is varied in accordance with instantaneous value of some other voltage , called the modulating voltage.

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• It is the process of transmission of information signal (low frequency signal) using a high frequency Carrier signal

Why Do We Need Modulation?

• If we transmit the information signal directly. Signals from different

transmitters will get mixed up.

• Baseband signals or low frequency signals could not transmitted without modulation.
• Antenna height :=λ/4

c=νλ

λ=c/ν

• signal transmission with minimum noise.

Type of Modulation

AMPLITUDE MODULATION

• The amplitude of the carrier is changing in accordance with the

instantaneous value of modulating signal

• Information is contain in the envelope

Mathematical Equations of AM

• Carrier Signal C(t)=

Ac sin(2π f_ct) or Ac sin(ω_ct)

• Modulating Message Signal m(t)=

Am sin(2π f_mt) or Am sin(ω_mt)

• The AM Signal s_AM (t) =

(Ac + Am sin(ω_mt) ) sin(ω_ct)

Modulation Index

μ = 1

μ > 1

• The amount of modulation in AM signal is given by its modulation index:

 μ= Αm /Ac

• When Am =Ac ,μ =1 or 100% modulation.

Over-modulation, i.e. Am>Ac , should be avoided

because it will create distortions

​

μ < 1

Type of Amplitude Modulation

• Double Sideband with full carrier (DSB-FC):The transmission of such a signal which contains a carrier along with two sidebands, can be termed as Double Sideband Full Carrier system, or simply DSB-FC. most widely used AM.

• Double Sideband Suppressed Carrier (DSB-SC):If this carrier is suppressed and the saved power is distributed to the two sidebands, then such a process is called as Double Sideband Suppressed Carrier system or simply DSBSC.

• Single Sideband with suppressed carrier(SSB-SC): The process of suppressing one of the sidebands, along with the carrier and transmitting a single sideband is called as Single Sideband Suppressed Carrier system, or simply SSB-SC or SSB.

• Vestigial Sideband(VSB): Modification of SSB

Balance Modulator

The balanced modulators are used to suppress the unwanted carrier in an AM

wave.

The carrier and modulating signals are applied to the inputs of the balanced modulator and we get the DSB signal with suppressed carrier at the output of the balanced modulator.

Thus the output consists of the upper and lower side bands only.

Balance Modulator using diodes:

Balance Modulator using Modulators:

Amplitude Demodulation

Demodulation extracting the baseband message from the carrier.

Type of Amplitude Demodulation

• Envelop Detector

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• Square Law Detector

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• Synchronous Detector or Coherent Detection

Envelope Detector

Synchronous Detector

Application of AM

• Entertainment - AM Radio (music, talk radio)
• Business - CB Radio to relay shipment progress, conference calls with other branches via telephone or speakerphone
• Government - Police officers keeping contact with the station, or

relaying the information and location of a suspect

• Personal - Cell phones or walkie-talkies for chatting with friends
• Military - Using undetectable radio signals to communicate with other soldiers, or voice commands to control weapons

References

• Communication system by-Sanjay Sharma
• https://en.wikipedia.org/wiki/Amplitude_modulation
• en.wikipedia.org/wiki/Demodulation
• Communication system Fourth Edition by Simon Haykin, from

chapter 2

• Google//AM pdf
• byjus.com/physics/modulation-need-modulation/

Thank You