SDM_DDM.rar_SDM MATLAB_SDM DDM_matlab sdm_modulation depth_sdm

close all; clear all; clc %%--- Program to find SDM (Sum Depth of modulation) ... %%--- and DDM (Difference depth of modulation) %%--- Used in ILS (Instrument Landing System) Fs=10e3;%15000; fc=3e3; t=(0:Fs)/Fs'; L=1000; x=0.2*sin(2*pi*90*t)+0.2*sin(2*pi*150*t);%+0.02*sin(2*pi*1020*t); am=(1+1*x).*cos(2*pi*fc*t); %ammod(x,fc,Fs);% dam=amdemod(am,fc,Fs); y=am; wid = size(y,1); if(wid==1) y=y(:); end z=y.*(1*cos(2*pi*fc*t))'; [num,den]=butter(5,fc*2/Fs); for i=1:size(y, 2) z(:,i)=filtfilt(num,den,z(:,i))*2; end z=z-0; if(wid==1) z=z'; end dam=z; % dam=dam(1000:5000); [b,a]=butter(1,[80 100]*2/Fs,'bandpass'); dam1=filter(b,a,dam); [b,a]=butter(1,[140 160]*2/Fs,'bandpass'); dam2=filter(b,a,dam); dam1=dam1(1000:5000); dam2=dam2(1000:5000); NFFT=2^nextpow2(L); f=Fs*linspace(0,1,NFFT); am_fft=fft(am,NFFT)/L; dam_fft1=fft(dam1,NFFT)/L; dam_fft2=fft(dam2,NFFT)/L; subplot(411) plot(t,am);axis([0 0.1 -1 1]) hold on; plot(t,x,'r');grid on axis([0 0.1 -2 2]) subplot(412) plot(f,2*abs(am_fft));grid on axis([0 5000 0 1]) subplot(413) plot(dam1(1:1000));grid on hold on plot(dam2(1:1000),'r');grid on subplot(414) plot(f,2*abs(dam_fft1));grid on hold on plot(f,2*abs(dam_fft2),'r'); axis([0 500 0 0.5]) am_max=max(am); am_min=abs(min(am)); dam_max1=max(dam1); dam_min1=abs(min(dam1)); dam_max2=max(dam2); dam_min2=abs(min(dam2)); am_avg=(am_max+am_min)/2; dam_avg_90=(dam_max1+dam_min1)/2; dam_avg_150=(dam_max2+dam_min2)/2; % m1=(am_max-abs(am_min))/(am_max+abs(am_min)) % m2=(dam_max1-dam_min1)/(dam_max1+dam_min1) % m3=(dam_max2-dam_min2)/(dam_max2+dam_min2) sdm=abs(dam_avg_150+dam_avg_90) ddm=abs(-dam_avg_150+dam_avg_90)