矿大通信原理课件CH 5.1 模拟调制

1、CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1 1 这里：控制信号称为调制信号，被控制信号称为载波。2. 调制的必要性/目的CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2 210 l 如： mlMHzfmlKHzfc1,10103103,3010,10103103,3784538 fc B. 提高信道的利用率CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3 3530KHz1600KHz300 90003. 模拟调制的分

2、类 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4 44.1 模拟幅度调制 tttAtStAtStmcmc coscos0已已调调信信号号载载波波信信号号为为为为待待传传信信号号（调调制制信信号号）设设CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin5 5数学表达式CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin6 6h(t)m(t)cosctSm(t) 01coscos00 ，令令AttmttAmtSccm频域表达式Com

3、municationCommunicationCUMT LIShiyinCUMT LIShiyin7 7h(t)m(t)cosctSm(t)频域表达式频域表达式 HMMSccm 21 ttmtScm cos Mtmccct cos 2121FFtftf4. 1.1 常规调幅（AM） CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin8 8 ttmtAttmtScccAM coscoscos0 ccAMAS 0 ccMM 21m(t)cos ctSAM(t)A0m(t) tmAtm 0波形图CommunicationCommunication

4、CUMT LIShiyinCUMT LIShiyin9 9OOttcosc(t) tSAMOtt tmA 0 tmfmmcf mcf mAMfB2 解调CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1010 tSAM tmA 0 tSAM AM 特点CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin11 11功率分配mcf mcf mAMfB2 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1212 0)(tm scAMApp

5、tmAtSP2)(22202得得 ttmtAtSccAM coscos0 5. 1.2 抑制载波双边带调幅（DSB） CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1313m(t)A0cosctsAM(t) ttmtmtSccAM coscos0 ttmtScDSBcos DSB信号的波形和频谱CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1414cosw0tOtOcc AMS0m 0m MH H OtOt tSAMOt载波反相点载波反相点tSDSB DSBSAM信号的波形和频谱

6、 ttmtmtSccAM coscos0 ccccAMMMmS 210 ttmtScDSB cos ccDSBMMS 21结论 MH H CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1515缺点与措施LPFcosctm0(t) tSp ttmtScDSB cos ttStScDSBp cos tmtm210 tcostmtcostmcc2122CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1616缺点与措施CommunicationCommunicationCUMT LIShi

7、yinCUMT LIShiyin1717DSB信号的缺点：信号的缺点：占用频带宽，占用频带宽，BDSB=2m 。(含有两个完全相同的边带含有两个完全相同的边带) 克服措施：克服措施：将只传输一个边带将只传输一个边带 单单边带调制边带调制 DSBSmAMfB2 上边带上边带下边带下边带 ccDSBMMS 2121mcf mcf SSBCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1818滤波特性CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1919形成SSB信号的滤波特性H()10

8、ccH()0cc1(a)(b)hSSB(t)m(t)cosctSSSB(t)SSB信号频谱CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2020SSB信号的频谱M()HHSM()ccOO 上边带 下边带 下边带 上边带ccO上边带频谱Occ下边带频谱SSB信号的数学式CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2121 DSBSmcf mcf SSBSSSB频谱频谱 ccSSBH , 0, 1 SSBDSBSSBHSS ttmttmtsccSSB sin21cos21 结论Co

9、mmunicationCommunicationCUMT LIShiyinCUMT LIShiyin2222VSBCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2323CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2424DSB、 SSB和VSB信号的频谱M()2B2BODSB()ccO(a)(b)SSB()OccccVSB()O(c)(d)实现CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2525 HcVSBcVSBHH 常常数数，滤波法产生残留边带信号滤波法产生残留边带信号hVSB(t)m(t)cosctSVSB(t)残留边带滤波器必须满足残留边带滤波器必须满足特性特性滚将特性CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2626cOcHVSB()HVSB(c)cOcHVSB(c)HVSB(c) HVSB