Ms.Pallavi Dhok Lecturer, ETC Department

 Modulation  The process by which some characteristics of a carrier wave is varied in accordance with an information-bearing signal.  Continuous-wave modulation Amplitude modulation Frequency modulation  AM modulation family  Amplitude modulation (AM)  Double sideband-suppressed carrier (DSB-SC)  Single sideband (SSB)  Vestigial sideband (VSB)

 Amplitude Modulation is the simplest and earliest form of transmitters  AM applications include broadcasting in medium- and high-frequency applications, CB radio, and aircraft communications

 Carrier wave: is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal. 1. DEFINING AM  A carrier wave whose amplitude is varied in proportion to the instantaneous amplitude of a modulating voltage

nonlinear device: diode or transistor biased in its nonlinear region

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

Double Sideband Suppressed Carrier (DSBSC)

Cont.. When the carrier is reduced, this is called double-sideband suppressed-carrier AM, or DSB-SC. If the carrier could somehow be removed or reduced, the transmitted signal would consist of two information-bearing sidebands, and the total transmitted power would be information

DSB-SC Advantages: – Lower power consumption Disadvantage: Complex detection Applications: – - Analogue TV systems: to transmit colour information – - For transmitting stereo information in FM sound broadcast – at VHF - Complex detection

Single-Sideband (SSB) suppressing the carrier and one of the sidebands

AM: Features and Drawbacks the AM signal is greatly affected by noise impossible to determine absolutely the original signal level conventional AM is not efficient in the use of transmitter power AM is useful where a simple, low-cost receiver and detector is desired