1?t3?3t?2ty(t)?F?Y(?)???e?(t)?2e?(t)?e?(t)22九、带限信号x(t)的频谱如下图所示，试画出x(t)通过下图系统时，系统中A、B、C各点的频
?1???K,??3?K,??4H1(?)??H2(?)???谱密度。图中，。(9)
???0,??3?0,??4X(ω)8-60
解：
x(t)H1(ω)Acos(4t)BH2(ω)Cy(t)6ωFA(?)?X(?)H1(?)
1FB(?)?FA(?)?F?cos(4t)?2?1?FA(?)?????(??4)??(??4)??2?
1??FA(??4)?FA(??4)?2FC(?)?FB(?)H2(?)
FA(ω)FB(ω)FC(ω)8K4K4K4K22K2K2-303ω-7-4-1147ω-7-4047十、已知信号
f(t)??(t?1)??(t?3)，设其设傅立叶变换为
F(?)?j2?，求积分???2F(?)Sa(?)ed?的值。
解： 法一： 设：
Y(?)?2F(?)Sa(?)y(t)?F?1?Y(?)??F?1?F(?)??F?1?2Sa(?)??f(t)?g2(t)
则：
??)Sa(?)ej2?d??2?1??2F(?2?????Y(?)ej2?d??2?y(t)t?2?2?y(2)
ω
y(t)?f(t)?g2(t)???(t?1)??(t?3)????(t?1)??(??1)???????(??1)??(??3)???(t???1)??(t???1)?d???t?1?1???t?2??(t?2)?t?(t)??t?2??(t?2)??t?4??(t?4)d??(t?2)??d??(t)???1t?1t?13d??(t?2)??d??(t?4)3t?1y(2)?4?2?2????2F(?)Sa(?)ej2?d??2???????????f(t)e?j?tdt?j2??Sa(?)e?d??2????j?(t?2)??d????Sa(?)f(t)edt?2??d???????Sa(?)f(t?2)e?j?tdt?2??d?????Sa(?)f(t?2)e?j?t??dt?2??dt?t)?????f(t?2)Sa(?)ej?(?d?所以：
?2??f(t?2)?2?1
??2g2(?t)dt?2?????f(t?2)g2(t)dt?2??1?1dt?4?法四：
f(t)??(t?1)??(t?3)?g4(t?1)F(?)?F?f(t)??F?g4(t?1)??4Sa(2?)e?j?????2F(?)Sa(?)ej2?d???sin(2?)?j??sin(?)j2??2??4e?ed???2????2?sin?j??8?cos??ed?2??????8?sin2?22???cos?d??j8?2?sin2????2cos?sin?d??sin?2??2?8?d??8?Sa(2?)d?2????4?1?2?8?2??Sa(2?)d??2????1??16???g4(t)?dt??4???2???dt?4??2
（按大纲给出各章节所占比例及标注重点、难点）
第一到三章: 30% ，线性系统的判断，模拟图和微分方程已知一个求另一个，信号的运算，卷积运算，非周期信号傅立叶正反变换，傅立叶变换分析法
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