matlab仿真源代码

				%Amplitude Modulation with multitone signal and its spectrum analysis
				%Show the time domain and frquency domain representation of DSB-AM and
				%DSB-SC modulations
				%Saurav R Tuldhar, DOECE/PC/IOE/TU 14th October 2005 
				%Suggestions @->> 059bex438@ioe.edu.np
				
				N = 1024;   %N point FFT N>fc to avoid freq domain aliasing
				fs = 4096; % sample frequency
				t = (0:N-1)/fs;
				
				fc  = 600;  %Carrier Frequency
				fm1 = 20;   %Three message signal frequencies
				fm2 = 80; 
				fm3 = 40; 
				
				Ec  = 20;    %Carrier Amplitude
				Em1 = 5;    %Three message signal amplitudes
				Em2 = 5;
				Em3 = 5;
				% Try changing the message and carrier amplitudes to see the effect in
				% DSB-AM modulation
				
				%---------Double SideBand Full Carrier Modulation (DSB-FC(AM))
				A  =  Ec + Em1*sin(2*pi*fm1*t) + Em2*sin(2*pi*fm2*t) + Em3*sin(2*pi*fm3*t); %Envelope/eliminate the carrier amplitude
				m  = A.*[sin(2*pi*fc*t)];                                                  %to convert DSB-AM to DSB-SC         
				Mf = 2/N*abs(fft(m,N));
				f = fs * (0 : N/2) / N;    %Since the fft result is symmetrical, only the positive half is sufficient for spectral representation
				
				close all;
				
				figure('Name','Time/Fequency domain representations of DSB-AM signals');
				subplot(2,1,1); %Time domain plot
				plot(t(1:N/2),m(1:N/2),t(1:N/2),A(1:N/2),'r',t(1:N/2),-A(1:N/2),'r');
				title('Time Domain Representation');
				xlabel('Time'); ylabel('Modulated signal');
				
				subplot(2,1,2); %Frequency Domain Plot
				plot(f(1:256),Mf(1:256));
				title('Frequency Domain Representation');
				xlabel('Frequency (Hz)'); ylabel('Spectral Magnitude');
				
				%----------Double SideBand Suppressed Carrier DSB-SC----------
				
				A  =   Em1*sin(2*pi*fm1*t) + Em2*sin(2*pi*fm2*t) + Em3*sin(2*pi*fm3*t); %Envelope/eliminate the carrier amplitude
				m  = A.*[sin(2*pi*fc*t)];                                                  %to convert DSB-AM to DSB-SC         
				Mf = 2/N*abs(fft(m,N));
				
				figure('Name','Time/Fequency domain representations of DSB-SC signals');
				subplot(2,1,1); %Time domain plot
				plot(t(1:N/2),m(1:N/2),t(1:N/2),A(1:N/2),'r',t(1:N/2),-A(1:N/2),'r');
				title('Time Domain Representation');
				xlabel('Time'); ylabel('Modulated signal');
				
				subplot(2,1,2); %Frequency Domain Plot
				plot(f(1:256),Mf(1:256));
				title('Frequency Domain Representation');
				xlabel('Frequency (Hz)'); ylabel('Spectral Magnitude');
				text(15,60,'Carrier');
				%--------------------------------------------------------------------