模拟调制信号调制解调与时频域分析资料

1、简明通信原理实验报告五 实验5Matlab 实验二 模拟调制信号调制解调与时频域分析一、实验内容：1、 运行样例程序，观察 AM、FM 信号的时域波形、频谱和解调后的信号波形，对仿真结果进行分析说明。从频谱图 FM 信号带宽，并与用卡森公式计算得到的带宽进行比较。2、设基带信号为 m(t)=sin(2000t)+2cos(1000t)，载波频率为 20KHz，修改样例程序，并仿照样例程序编写 DSB-SC、SSB 调制（上边带或下边带）与解调程序，绘制 AM、FM、DSB-SC 和 SSB（上边带或下边带）信号的时域波形、频谱以及解调后的信号波形，对仿真结果进行分析说明，要求指出 SSB 信号

2、是上边带还是下边带。二、实验结果：样例1 11：AM 调制与解调程序% 用Matlab产生一个频率为10Hz、功率为1的余弦信号m(t)，设载频为100Hz，载波分量幅度A=2。close all; clear all;dt = 0.001; % 采样间隔fm = 10; % 信号最高频率fc = 100; % 载频T = 4; % 信号时长fs = 1/dt; % 采样频率t = 0:dt:T-dt; % 时域采样点mt = sqrt(2)*cos(2*pi*fm*t); % 调制信号A = 2;s_am = (A+mt).*cos(2*pi*fc*t); % 普通调幅信号B = 2*fm;

3、 % 信号带宽figure(1)subplot(311)plot(t,s_am);hold onplot(t,A+mt,'r-');title('AM信号及调制信号波形');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信号幅度谱');xlabel('f');% AM 解调rt = s_am.*cos(2*pi*fc*t); % 相干解

4、调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('相干解调后的信号波形与输入信号的比较');xlabel('t');12：AM 调制与解调波形分析：AM 信号的频谱是双边带抑制载波调幅信号（DSB-SC）的频谱加上离散的载波分量。包络反应了基带信号的变化规律，频谱由载波分量和上下对称的两个边带组成。样例2：FM 调制与解调2.1、FM 调制与解调程序% 设输

5、入信号为m(t)=cos2*pi*t，载频为10Hz，调频器的压控振荡系数为5Hz/V，载波平均功率为1W，画出该调频信号的波形，求出该调频信号的幅度谱，用鉴频器解调该调频信号，并与输入信号比较；close all; clear all;kf = 5;dt = 0.001; % 采样间隔fm = 1; % 信号最高频率fc = 10; % 载频T = 5; % 信号时长fs = 1/dt; % 采样频率t = 0:dt:T-dt; % 时域采样点mt = cos(2*pi*fm*t); % 调制信号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); % 调频信号figure(1)subplot(311)plot(t,s_fm);hold onplot(t,mt,'r-');title('FM信号及其调制信号波形');xlabel('t');subplot(312)f,sf = myt2f(s_fm,fs);plot(f,abs(sf),'r-')axis(-25 25 0 max(abs(sf);title('FM信号幅度谱');xlabel('f');% FM解调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('调频信号微分后包络');2.2、FM 调制与解调波形分析：调制信号波形过零点的密度与m(t)成正比，幅度保持不变。3、基带信号为 m(t)=sin(2000t)+2cos(1000t)，载波频率为 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信号的包络不再与基带信号形状相同，频谱中不再有载波分量带宽与AM相同，为基带信号2倍。SSB（下边带）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带宽仅为AM一半，只有上边带或下边带。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