# Lect-AM-5_07 - Spectrum of AM: t c t m c A t AM x cos ] cos...

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Unformatted text preview: Spectrum of AM: t c t m c A t AM x cos ] cos 1 [ ) ( + = t m c c A t m c c A t c c A ) cos( ) 2 / 1 ( ) cos( ) 2 / 1 ( cos + +- + = Taking the Fourier transform )} ( ) ( ){ 2 / ( ) ( c f f c f f c A f AM x + +- = )]} ( [ )] ( [ { ) 2 / 1 ( m f c f f m f c f f c A- + +-- + )]} ( [ )] ( [ { ) 2 / 1 ( m f c f f m f c f f c A + + + +- + Along with the carrier there are two frequency components f c-f m is called the LOWER SIDEBAND(LSB) f +f is called the UPPER SIDEBAND(USB) Shows the plot of a 100% modulated message signal. Carrier freq.: 504 KHz ; Message signal freq. : 4.6 KHz POWER EFFICIENCY: Power in the carrier = 2 ) 2 / 1 ( c A Power in the LSB = 2 2 ) 8 / 1 ( 2 2 / ) ( ) 2 / 1 ( c A c A = Power in the USB = 2 2 ) 8 / 1 ( 2 2 / ) ( ) 2 / 1 ( c A c A = Power Efficiency = Sideband power/Total power 2 2 ) 4 / 1 ( 2 ) 2 / 1 ( _______ __________ 2 2 ) 4 / 1 ( c A c A c A + = 2 2 _______ 2 + = When = 1, i.e.., for 100% modulation power efficiency is only 33% Generation Of AM: V 1 (t) R L m(t) A c cos c t V 2 (t) )] ( cos [ ) ( 1 t m t c c A t V + = The switching action of the diode may be approximated by a pulse train, which expressed as a Fourier series is as follows: ] 5 cos ) 5 / 1 ( 3 cos ) 3 / 1 ( )[cos / 2 ( ) 2 / 1 ( ) ( t c t c t c t p g +- + = } cos ) / 2 ( ) 2 / 1 )]{( ( cos [ ) ( 2 t c t m t c c A t V + + = The higher harmonics can be filtered out after passing...
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## This note was uploaded on 09/24/2010 for the course MATHEMATIC AAOC C222 taught by Professor Prof.dilipkumarsatpathi during the Fall '07 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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Lect-AM-5_07 - Spectrum of AM: t c t m c A t AM x cos ] cos...

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