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1、抽样定理实验报告实验十一抽样定理学生姓名学号*专业班级*学院*完成时间*年*月adership: Luo Mingjun, rectification time: before September 25th, insist for a long time) 1, 2, to further improve research, solve thoroughly, not solid, the effect is not obvious The major issues and enterprises it is a matter of security bureau year developme
2、nt, the vital interests of the problem, determine the research topic, by members of the Party led research Basic research to see the truth, to the truth, do not say hello, not pre arranged After the investigation to submit the research report 3, insist on grassroots party members take the lead in im
3、plementing the line In the construction of work style building long-term mechanism views and , more mines and enterprises, solve the masses of grassroots leaders, mine is not enough 4, contact a crowd Combined with the grassroots cadres contact farmers，? activities and each cadres to contact a peopl
4、e, by一、实验目的1、了解电信号的采样方法与过程以及信号恢复的方法。2、验证抽样定理。二、实验仪器1、20M双踪示波器一台。、信号与系统实验箱。2三、原理说明1、离散时间信号可以从离散信号源获得，也可以从连续时间信号抽样而得。抽样信号可以看成连续信号和一组开关函数的乘积。是一组周期性窄脉冲，见图，ftf, , ts, , ts, , ts111-b T称为抽样周期，其倒数称抽样频率。f, SsTSs, , ttTs,图11-1矩形抽样脉冲对抽样信号进行傅里叶分析可知，抽样信号的频率包括了原连续信号以及无限 个经过平移的原信号频率。平移的频率等于抽样频率及其谐波频率、”。当抽样信 号是 f2
5、f3fsss,sinx周期性窄脉冲时，平移后的频率幅度按规律衰减。抽样信号的频谱是 原信号频谱x周期的延拓，它占有的频带要比原信号频谱宽得多。2、正如测得了足够的实验数据以后，我们可以在坐标纸上把一系列数据点连 起来，得到一条光滑的曲线一样，抽样信号在一定条件下也可以恢复到原信号。只 要用一截止频率等于原信号频谱中最高频率f的低通滤波器，滤除高频分量，经滤 波后得到的信号包含了原n信号频谱的全部内容，故在低通滤波器输出可以得到恢复后的原信号。3、但原信号得以恢复的条件是f, 2Bf,其中为抽样频率，B为原信号占有的频带ssf,2B宽度。而为最低抽样频率乂称“奈奎斯特抽样率”。当时，抽样信号的频
6、 f, 2Bsmin谱会发生混迭，从发生混迭后的频谱中我们无法用低通滤波器获得原信号频谱 的全部内容。f,2B在实际使用中，仅包含有限频率的信号是极少的。因此即使，恢复后的信 号失真还sf, 2Bf, 2B是难免的。图11-2画出了当抽样频率（不混叠时）及当抽样频率（混叠 ss时）两种悄况下冲激抽样信号的频谱。（a）连续信号的频谱F, , , f, , t1t, 00mm adership： Luo Mingjun, rectification time: before September 25th, insist for a long time） s contact farmers7 act
7、ivities and each cadres to contact a people, bycadred enterprises, solve the masses of grassroots leaders, mine is not enough 4, contact a crowd Combined with the grassroots term mechanism views and , more mines an-g longt 3, insist on grassroots party members take the lead in implementing the line
8、In the construction of work style buildinarch to see the truth, to the truth, do not say hello, not pre arranged After the investigation to submit the research reporrese ar development, the vital interests of the problem, determine the research topic, by members of the Party led research Basicsolve
9、thoroughly, not solid, the effect is not obvious The major issues and enterprises it is a matter of security bureau ye 1, 2, to further improve research, 2实验十一抽样定理b()高抽样频率时的抽样信号及频谱(不混叠)，2,smF, , ,sf, , tlsTst, OT, sOssmm()低抽样频率时的抽样信号及频谱(混叠),2, csm图11-2抽样过程中出现的三种惜况实验中选用三种抽样频率对连续信号进行抽样，以验证抽f, 2B, f, 2
10、B, f, 2Bsss样定理一一要使信号采样后能不失真地还原，抽样频率必须大于信号频率中最 高频率的fs两倍。4、为了实现对连续信号的抽样和抽样信号的复原，可用实验原理框图11 -3的 方案。除选用足够高的抽样频率外，常采用前置低通滤波器来防止原信号频谱宽而 造成抽样后信号频谱的混叠。但这也会造成失真。如实验选用的信号频带较窄，则 可不设前置低通滤波器。本实验就是如此。抽低通信号样滤波输入门抽样脉冲图11-3抽样定理实验方框图四、实验内容及步骤1、按下总电源开关，将函数信号发生器产生的正弦波或三角波，送入抽样 器，即用跳线将函数信号发生器的输出端与本实验模块的输入端相连，观察经抽样 后的正弦波
11、或三角波信号。正弦波的频率一般不超过lKHz（三角波要更低一些）， 幅度（峰值）为2V左右，为便于观察，抽样信号频率一般选择50HZ, 400HZ的范围， 而抽样脉冲的频率则是通过电位器W501来调节的。2、若使用外接信号源，应将外接信号源的地与本实验箱的地相连，并将信号 源的输出端接入本实验模块的输入端。3、各测试点的波形分别为：GND :接地端；TP501:输入信号的波形；TP502:本地输出的抽样脉冲；TP503:经反相后的抽样脉冲；TP504:抽样信号输出；adership: Luo Mingjun, rectification time: before September 25th,
12、 insist for a long time） contact a people, bys to ders, mine is not enough 4, contact a crowd Combined with the grassroots cadres contact farmers7 activities and each cadregrassroots, the people, promoting harmony activities notice , more mines and enterprises, solve the masses of grassroots lea ter
13、m mechanism views and and , more mines an-g longt. 3, insist on grassroots party members take the lead in implementing the line In the construction of work style buildinarch to see the truth, to the truth, do not say hello, not pre arranged After the investigation to submit the research reporrese ar development, the vital interests of the problem, determine the research topic, by members of the Party led research Basicsolve thoroughly, not solid, the effect is not obvious The major issues and enterprises it is a matter of security bureau ye 1, 2, to further improve research, 4