2.调幅(AM)信号 Amplitude Modulation 乡m(t)带有直流分量 s(t)=m(t)cos at -mo cosa t+m(t)cosa t S(o)=/moS(O-o+So+o I +[M(o-0)+M(o+o) 29 2.调幅(AM)信号 Amplitude Modulation m(t)带有直流分量 s t m t t m c ( ) = ( )cos m t m t t c c cos ( )cos 0 = + ( ) [ ( ) ( )] S m =m0 − c + + c [ ( ) ( )] 2 1 M c M + c + − +