Matlab hw

% (ExampleAMdemfilt.m) % This program uses triangl.m to illustrate AM modulation % and demodulation ts=1.e-4; t=-0.04:ts:0.04; Ta=0.01; fc=500; m_sig=triangl((t+0.01)/0.01)-triangl((t-0.01)/0.01); Lm_sig=length(m_sig); Lfft=length(t); Lfft=2^ceil(log2(Lfft)); M_fre=fftshift(fft(m_sig,Lfft)); freqm=(-Lfft/2:Lfft/2-1)/(Lfft*ts); B_m=150; %Bandwidth of the signal is B_m Hz. h=fir1(40,[B_m*ts]); % AM signal generated by adding a carrier to DSB-SC s_am=(1+m_sig).*cos(2*pi*fc*t); Lfft=length(t); Lfft=2^ceil(log2(Lfft)+1); S_am=fftshift(fft(s_am,Lfft)); freqs=(-Lfft/2:Lfft/2-1)/(Lfft*ts); % Demodulation begins by using a rectifier s_dem=s_am.*(s_am>0); S_dem=fftshift(fft(s_dem,Lfft)); % Using an ideal LPF with bandwidth 150 Hz s_rec=filter(h,1,s_dem); S_rec=fftshift(fft(s_rec,Lfft)); Trange=[-0.025 0.025 -2 2]; figure(1) subplot(221);td1=plot(t,m_sig); axis(Trange); set(td1,'Linewidth',1.5); xlabel('{\it t} (sec)'); ylabel('{\it m}({\it t})'); title('message signal'); subplot(222);td2=plot(t,s_am); axis(Trange); set(td2,'Linewidth',1.5); xlabel('{\it t} (sec)'); ylabel('{\it s}_{\rm DSB}({\it t})') title('AM modulated signal'); subplot(223);td3=plot(t,s_dem); axis(Trange); set(td3,'Linewidth',1.5); xlabel('{\it t} (sec)'); ylabel('{\it e}({\it t})') title('rectified signal without local carrier'); subplot(224);td4=plot(t,s_rec); Trangelow=[-0.025 0.025 -0.5 1]; axis(Trangelow); set(td4,'Linewidth',1.5); xlabel('{\it t} (sec)'); ylabel('{\it m}_d({\it t})') title('detected signal'); Frange=[-700 700 0 200]; figure(2) subplot(221); fd1=plot(freqm,abs(M_fre)); axis(Frange); set(fd1,'Linewidth',1.5); xlabel('{\it f} (Hz)'); ylabel('{\it M}({\it f})'); title('message spectrum'); subplot(222);fd2=plot(freqs,abs(S_am)); axis(Frange); set(fd2,'Linewidth',1.5); xlabel('{\it f} (Hz)'); ylabel('{\it S}_{rm AM}({\it f})'); title('AM spectrum'); subplot(223);fd3=plot(freqs,abs(S_dem)); axis(Frange); set(fd3,'Linewidth',1.5); xlabel('{\it f} (Hz)'); ylabel('{\it E}({\it f})'); title('rectified spectrum'); subplot(224);fd4=plot(freqs,abs(S_rec)); axis(Frange); set(fd4,'Linewidth',1.5); xlabel('{\it f} (Hz)'); ylabel('{\it M}_d({\it f})'); title('recovered spectrum');