5.3. 1 Amplitude modulation and demodulation 1. Amplitude modulation(AM) Amplitude modulation To multiply a high frequency signal(carrier) with the measurand (modulating signal)so that the carrier amplitude is varied with the measurand xm(t)=x(t)cos 2yfot the Fourier transform pair x(O)y(t)eX()*Y() accordingly, we have x()osx1x()*6(+)+1x(0)*(/-f)(6255.3.1 Amplitude modulation and demodulation 1. Amplitude modulation(AM) Amplitude modulation: To multiply a high￾frequency signal (carrier) with the measurand (modulating signal) so that the carrier amplitude is varied with the measurand. x t x t f t m 2 0 ( ) = ( )cos  the Fourier transform pair: x(t) y(t)  X ( f ) *Y( f ) ,accordingly, we have: ( ) ( ) ( ) ( ) 0 0 * 0 2 1 ( ) * 2 1 x t cos 2f t  X f  f + f + X f  f − f (5.25)