4.2.1调幅(AM):原理及波形 调制信号m(t)=0 m(t) SaM (t) 叠加直流4o 滤波器H=1) cos2πfi Ao+m(t) S4w(t)=[A,+m(t]cos2πft=A(t)cos2πft Sw(f)=2[8U+f)+-f]+,Mf+f)+Mf-f】 AAA +M(f) SAM(1) Sau()4.2.1调幅(AM):原理及波形 + m t( ) A0 S t AM ( ) cos 2 c f t ( ) 0 [ ( )]cos2 ( )cos2 AM c c s t A m t f t A t f t = + = ( ) 0 1 ( ) ( ) ( ) ( ) 2 2 AM c c c c A S f f f f f M f f M f f = + + − + + + − 滤波器H(f)=1) 调制信号 m t( ) 0 = 叠加直流A0 O t t O O t O t m(t) A0 +m(t) f t 2 c cos s (t) AM 1 H − f H 0 f f A0 A0 1 2 c f c − f 0 f M ( f ) s ( f ) AM