42幅度训 o=0 2原O台n(+O)+O(o-a 载波(/()f()1 3x[F(a)*F2() 已调信号Sn(t)=Am(Ocos(ot+) m(调制信号(基带信号) 设m()冷M(0) WU S(o)=FLs (t]=M(0-0)+M(o+o) 23 4.2 幅度调制 原理 载波 已调信号 m(t)调制信号(基带信号) 设 则 ( ) cos( ) =  +0 s t A t c ( ) ( )cos( ) =  +0 s t Am t t m c m(t)  M () [ ( ) ( )] 2 ( ) [ ( )] m m M c M c A S  = F s t =  − +  + 0 = 0 cos [ ( ) ( )] c c c  t    + +  − [ ( ) ( )] 2 1 ( ) ( ) 1 2 1  2   f t f t  F  F