模擬調(diào)制信號調(diào)制解調(diào)與時頻域分析資料

1、簡明通信原理實(shí)驗(yàn)報告五 實(shí)驗(yàn)5Matlab 實(shí)驗(yàn)二 模擬調(diào)制信號調(diào)制解調(diào)與時頻域分析一、實(shí)驗(yàn)內(nèi)容：1、 運(yùn)行樣例程序，觀察 AM、FM 信號的時域波形、頻譜和解調(diào)后的信號波形，對仿真結(jié)果進(jìn)行分析說明。從頻譜圖 FM 信號帶寬，并與用卡森公式計算得到的帶寬進(jìn)行比較。2、設(shè)基帶信號為 m(t)=sin(2000t)+2cos(1000t)，載波頻率為 20KHz，修改樣例程序，并仿照樣例程序編寫 DSB-SC、SSB 調(diào)制（上邊帶或下邊帶）與解調(diào)程序，繪制 AM、FM、DSB-SC 和 SSB（上邊帶或下邊帶）信號的時域波形、頻譜以及解調(diào)后的信號波形，對仿真結(jié)果進(jìn)行分析說明，要求指出 SSB 信號

2、是上邊帶還是下邊帶。二、實(shí)驗(yàn)結(jié)果：樣例1 11：AM 調(diào)制與解調(diào)程序% 用Matlab產(chǎn)生一個頻率為10Hz、功率為1的余弦信號m(t)，設(shè)載頻為100Hz，載波分量幅度A=2。close all; clear all;dt = 0.001; % 采樣間隔fm = 10; % 信號最高頻率fc = 100; % 載頻T = 4; % 信號時長fs = 1/dt; % 采樣頻率t = 0:dt:T-dt; % 時域采樣點(diǎn)mt = sqrt(2)*cos(2*pi*fm*t); % 調(diào)制信號A = 2;s_am = (A+mt).*cos(2*pi*fc*t); % 普通調(diào)幅信號B = 2*fm;

3、 % 信號帶寬figure(1)subplot(311)plot(t,s_am);hold onplot(t,A+mt,'r-');title('AM信號及調(diào)制信號波形');xlabel('t');subplot(312);f,sf = myt2f(s_am,fs);plot(f,abs(sf),'r-')axis(-2*fc 2*fc 0 max(abs(sf);title('AM信號幅度譜');xlabel('f');% AM 解調(diào)rt = s_am.*cos(2*pi*fc*t); % 相干解

4、調(diào)rt = rt-mean(rt);f1,sf1 = myt2f(rt,fs);t0,rt0 = lpf(f1,sf1,B);subplot(313);plot(t0,rt0);hold onplot(t,mt/2,'r-');title('相干解調(diào)后的信號波形與輸入信號的比較');xlabel('t');12：AM 調(diào)制與解調(diào)波形分析：AM 信號的頻譜是雙邊帶抑制載波調(diào)幅信號（DSB-SC）的頻譜加上離散的載波分量。包絡(luò)反應(yīng)了基帶信號的變化規(guī)律，頻譜由載波分量和上下對稱的兩個邊帶組成。樣例2：FM 調(diào)制與解調(diào)2.1、FM 調(diào)制與解調(diào)程序% 設(shè)輸

5、入信號為m(t)=cos2*pi*t，載頻為10Hz，調(diào)頻器的壓控振蕩系數(shù)為5Hz/V，載波平均功率為1W，畫出該調(diào)頻信號的波形，求出該調(diào)頻信號的幅度譜，用鑒頻器解調(diào)該調(diào)頻信號，并與輸入信號比較；close all; clear all;kf = 5;dt = 0.001; % 采樣間隔fm = 1; % 信號最高頻率fc = 10; % 載頻T = 5; % 信號時長fs = 1/dt; % 采樣頻率t = 0:dt:T-dt; % 時域采樣點(diǎn)mt = cos(2*pi*fm*t); % 調(diào)制信號mti = 1/2/pi/fm*sin(2*pi*fm*t);s_fm = sqrt(2)*co

6、s(2*pi*fc*t+2*pi*kf*mti); % 調(diào)頻信號figure(1)subplot(311)plot(t,s_fm);hold onplot(t,mt,'r-');title('FM信號及其調(diào)制信號波形');xlabel('t');subplot(312)f,sf = myt2f(s_fm,fs);plot(f,abs(sf),'r-')axis(-25 25 0 max(abs(sf);title('FM信號幅度譜');xlabel('f');% FM解調(diào)for k = 1:leng

7、th(s_fm)-1rt(k) = (s_fm(k+1)-s_fm(k)/dt;endrt(length(s_fm) = 0;subplot(313)plot(t,rt);hold onplot(t,sqrt(2)*2*pi*kf*mt+sqrt(2)*2*pi*fc,'r-');xlabel('t');ylabel('調(diào)頻信號微分后包絡(luò)');2.2、FM 調(diào)制與解調(diào)波形分析：調(diào)制信號波形過零點(diǎn)的密度與m(t)成正比，幅度保持不變。3、基帶信號為 m(t)=sin(2000t)+2cos(1000t)，載波頻率為 20KHz。AM:close a

8、ll; clear all;dt = 0.00001; fm = 1000; fc = 20000;T = 0.04; fs = 1/dt;t = 0:dt:T-dt; mt = sin(2*pi*fm*t)+2*cos(pi*fm*t); A=5;s_am=(A+mt).*cos(2*pi*fc*t);B=2*fm;figure(1);subplot(311)plot(t,s_am);hold onplot(t,A+mt,'r-');title('AMÐźż°µ÷ÖÆ

9、;ÐźŲ¨ÐÎ');xlabel('t'); subplot(312)f,sf=myt2f(s_am,fs);plot(f,abs(sf),'r-');axis(-2*fc 2*fc 0 max(abs(sf);title('AMÐźŷù¶ÈÆ×');xlabel('f'); rt = s_am.*cos(2*pi*fc*t); rt =

10、 rt-mean(rt);f1,sf1 = myt2f(rt,fs);t0,rt0 = lpf(f1,sf1,B);subplot(313);plot(t0,rt0);hold onplot(t,mt/2,'r-');title('Ïà¸É½âµ÷ºóµÄÐźŲ¨ÐÎÓëÊäÈëÐÅ

11、6;ŵıȽÏ');xlabel('t');DSB-SC:close all; clear all;dt = 0.00001; fm = 1000; fc = 20000;T = 0.04; fs = 1/dt;t = 0:dt:T-dt; mt = sin(2*pi*fm*t)+2*cos(pi*fm*t); A=5;s_am=A*mt.*cos(2*pi*fc*t);B=2*fm;figure(1);subplot(311)plot(t,s_am);hold onplot(t,A+mt,

12、9;r-');title('AMÐźż°µ÷ÖÆÐźŲ¨ÐÎ');xlabel('t'); subplot(312)f,sf=myt2f(s_am,fs);plot(f,abs(sf),'r-');axis(-2*fc 2*fc 0 max(abs(sf);title('AMÐźŷù

13、¶ÈÆ×');xlabel('f'); rt = s_am.*cos(2*pi*fc*t); rt = rt-mean(rt);f1,sf1 = myt2f(rt,fs);t0,rt0 = lpf(f1,sf1,B);subplot(313);plot(t0,rt0);hold onplot(t,mt/2,'r-');title('Ïà¸É½âµ÷ºóµÄÐź

14、;Ų¨ÐÎÓëÊäÈëÐźŵıȽÏ');xlabel('t'); DSB信號的包絡(luò)不再與基帶信號形狀相同，頻譜中不再有載波分量帶寬與AM相同，為基帶信號2倍。SSB（下邊帶）close all; clear all;dt = 0.00001; fm = 1000; fc = 20000;T = 0.04; fs = 1/dt;t = 0:dt:T-dt;

15、 Lt=length(t);mt = sin(2*pi*fm*t)+2*cos(pi*fm*t); %A=5;c1=cos(2*pi*fc*t);c2=sin(2*pi*fc*t);s_am=mt(1:Lt).*c1(1:Lt)+imag(hilbert(mt(1:Lt).*c2(1:Lt);B=fm;figure(1);subplot(311)plot(t,s_am);hold onplot(t,mt,'r-');title('AMÐźż°µ÷ÖÆÐ

16、97;ºÅ²¨ÐÎ');xlabel('t'); subplot(312)f,sf=myt2f(s_am,fs);plot(f,abs(sf),'r-');axis(-2*fc 2*fc 0 max(abs(sf);title('AMÐźŷù¶ÈÆ×');xlabel('f'); rt = s_am.*cos(2*pi*fc*t); rt = rt-mean(r

17、t);f1,sf1 = myt2f(rt,fs);t0,rt0 = lpf(f1,sf1,B);subplot(313);plot(t0,rt0);hold onplot(t,mt/2,'r-');title('Ïà¸É½âµ÷ºóµÄÐźŲ¨ÐÎÓëÊäÈëÐźÅ&#

18、181;ıȽÏ');xlabel('t');SSB帶寬僅為AM一半，只有上邊帶或下邊帶。FM:close all; clear all;kf = 5;dt = 0.000001;fm = 1000;fc = 20000;T =0.01;fs = 1/dt; t = 0:dt:T-dt; mt = sin(2*pi*fm*t)+2*cos(pi*fm*t); mti = -1/2/pi/fm*cos(2*pi*fm*t)+2/pi/fm*sin(pi*fm*t);s_fm =sqrt(2)*cos(2*pi*fc*t+2*pi*kf*mti); figure(1)subplot(311)plot(t,s_fm);hold onplot(t,mt,'r-');title('FMÐźż°Æäµ÷ÖÆÐźŲ¨ÐÎ');xlabel('t');subplot