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1、第第4 4章章 连连续续信信号号与与系系统统 的的频频域域分分析析信信号号与与系系统统分分析析2)()(jFtf 线性 奇偶性 对称性3 尺度变换 时移特性 频移特性)()()()(2211 jFtfjFtf)()()()(22112211 jFajFatfatfa 1a2a45)sgn(2121)(tt )(21 jt1)()(jt2)sgn()sgn(2121)(tt j221)(221 s noic s()()(f tt df tjtt dtdtetfjFtj )()()()RXj()|()|jF je)()()(22 XRjF )()(arctan)(RX)(tf)()(RR )()-
2、(jFjF)()(XX )()-(6 dtttfjdtttfjF)(sin)()(cos)()()()(jXR )()(tftf ,0)(X则则)()(RjF)()(tftf ,0)(R则则)()(jXjF)(tf)()()(*jFjFtf 7()F jt()()fFjt82()f)(tSa)2()(aStg2 )(2)(2 aStg)(2)(22 gtSa)()(2 gtSa9)()(jFtf)(1)(ajFaatf 01022)(tf)(jF2t20)2(2jF210t)2(tf044)2j(F2124410)2(tft)()(,1 jFtfa 当当102()tf22()F j2()ft1
3、22()F j 0)()(tjejF )()(jFtf0)()(0tjejFttf 0)()(0tjejFttf )()(jejF)()(jejF 0-tje )(1)(ajFeabatfabj 为为常常数数0t11)()()(21tftftf 165()()f tg t)5()(22 tgtf5632()()jSaSFaej)(tf jeSa5)3(6 jeSa5)(2 120)()(0tjejFttf )()(jFtf)()(00 jFtfetj为为常常数数0 13)5(tf)(5 jFej【例例5 5】已已知知信信号号 的的傅傅里里叶叶变变换换是是 ，求求信信号号 的的傅傅里里叶叶变变换
4、换。解解:由由已已知知利利用用时时移移特特性性据据尺尺度度变变换换性性质质由由频频移移特特性性注注意意：当当使使用用多多个个性性质质时时，要要注注意意性性质质使使用用的的顺顺序序)(tf)(jF)53(2 tfetj)()(jFtf0)()(0tjejFttf )(1)(ajFaatf)53(tf)()(00 jFtfetj)53(2 tfetj)3(3135 jFej)32(31325 jFej14381020103 )m(15000 68109.103103 )m(3 f8103 15图图6 6 实实现现频频谱谱搬搬移移的的原原理理图图0001122cos()jtjttee001122()()F jF j)()(jFtf)(0 jF0()jtef ttjtjetfetfttf00)(21)(21)cos()(0 1617为为实实现现有有效效、可可靠靠、远远距距离离的的传传输输，需需要要进进行行调调制制)(21)(21)cos()(000 jFjFttf1819)()()()(22112211 jFajFatfatfa )()()(*jFjFtf )(2)(fjtF)(1)(ajFaatf 0)()(0tjejFttf )()(00 jFtfetj)()(jFtf20