4.1幅度调制 411常规双边带调幅 DSB-LC(AM a There are 4 types of linear modulation that are a Double sideband large carrier (DSB-LC) D DSB-LC, Double sideband large carrier(AM) s()=[4+n()osy!Re{4+m)m} DSB-SC, Double sideband suppressed carrier SDSB-Lc(O)=TA8(0+0)+8(0-0) LM(o+00)+M(o-OoI m Each type of linear modulation has advantages pa sosa-lc(叫 a DSB-LC is used in broadcast radio 口 VSB in Television D SSB in telecommunication systems 通信原理 通信原理 後照k季 DSB-LC信号的调制 CP4.1.1 DSB-LC的包络检测原理 cP4.1 可以采用包络 ■ DSB-LC系统调制示意图 检测的条件 A+m() 基带信号,调制信号 m(o(modulating signal m()的变化要慢于 己调信号 os(on) (modulated signal) 通信原理 後照大季 通信原理 後照手通信原理 5 4.1 幅度调制 ◼ There are 4 types of linear modulation that are frequently used. They are:  DSB-LC, Double sideband large carrier (AM)  DSB-SC, Double sideband suppressed carrier  SSB, Single sideband  VSB, Vestigal sideband ◼ Each type of linear modulation has advantages in particular applications  DSB-LC is used in broadcast radio  VSB in Television  SSB in telecommunication systems 通信原理 6 4.1.1 常规双边带调幅DSB-LC (AM) ◼ Double sideband large carrier(DSB-LC) ( ) ( ) ( )  ( )  c c s t j t =  A + m t cos  t =Re  A + mt e     2 SDSB−LC() = A ( +c ) + ( −c) + 1 M( +c ) +M( −c) M () 1 SD S B−L C () 4B −c 0  1 2 −2B 0 2 B  4B c A DSB-LC信号的调制 ◼ DSB-LC系统调制示意图 Ac 基带信号, 调制信号 m (t )(modulating signal) cosct 载波 已调信号 (modulated signal) A CP 4.1.1 DSB-LC的包络检测原理 ◼ 可以采用包络 检测的条件 A+m(t) 0 m(t) 的变化要慢于 cos(c t) CP 4.1.1 通信原理 7 通信原理 8