Sunday, May 8, 2011

Amplitude modulation


Amplitude modulation(AM) is the simplest form of modulation .It is an analog-to-analog conversion method. Here the information or AF(Audio Frequency) signal changes the amplitude of the carrier wave without changing its frequency or phase. Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent.
Mathematically,the process can be expressed as

AM      S(t)=[1+nax(t)]cos2πfc t

Where 2πfc t  is the carrier and x(t) is the input signal(caring data),both normalized to unity amplitude.The parameter na, known as the modulation index, is the ratio of the amplitude pf the input signal to the carrier.
The original wave form of AM are given below:

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