MODULATION

BY- SANJAY KUMAR0900321088

EN-2(A)

introduction

Modulation is the process by which some characteristics of a carrier is varied in accordance with a modulation wave .

Modulation is the process of putting information onto a high frequency carrier for transmission (frequency translation).

such a modification is achieved by mean of a process called modulation .

In the modulation process, the baseband signle is called “modulating signal” and anther higher frequency signal is called as the “carrier”. The carrier signal will carry the modulating signal to the destination.

Different of Modulation Method

Analog modulation - The modulating signal and

carrier both are analogue signal.

TYPES : Amplitude modulation (AM), Frequency modulation (FM),

Phase modulation (PM)

Figure Types of analog- modulation

Digital modulation - The modulating signal is

a digital signal , but the carrier is an analogue

signal.

TYPES :

Amplitude Shift Keying (ASK),

Frequency Shift keying (FSK),

Phase Shift Keying (PSK)

Amplitude Modulation

Amplitude Modulation is a process of changing the amplitude of a high frequency carrier signal in proportion with the instantaneous value of modulating signal (information).

Amplitude Modulation is the simplest and earliest form of transmitters.

Figure : Amplitude modulation

AM Characteristics

AM is a nonlinear process

Sum and difference frequencies are created that carry the information

modulation index

The ratio between the amplitudes between the amplitudes of the modulating signal and carrier, expressed by the equation:

c

m

E

Em =

Measurement of Modulation Index

Overmodulation When the modulation index is greater than 1,

overmodulation is present

Modulation Index for Multiple Modulating Frequencies

Two or more sine waves of different, uncorrelated frequencies modulating a single carrier is calculated by the equation:

m m12 m2

2

Full-Carrier AM: Frequency Domain

Time domain information can be obtained using an oscilloscope

Frequency domain information can be calculated using Fourier methods, but trigonometric methods are simpler and valid

Sidebands are calculated using the formulas at the right

fusb fc fmf lsb fc fm

E lsb Eusb mEc2

Bandwidth

• Signal bandwidth is an important characteristic of any modulation scheme

• In general, a narrow bandwidth is desirable• Bandwidth is calculated by:

mFB 2

fC fc+fmfc-fm

2fm

applications Amplitude Modulation

AM applications include broadcasting in medium- and high-frequency applications,

CB radio , and

aircraft communications

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