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Altera_Forum
Honored Contributor I
862 Views

frequency spectrum

Hallo, 

I worked with the Altera FFT Megafunction.At the output i have an imaginery and a real part. but the output (sourcereal and sourceim)in the simulator is time-dependent. How can i get the frequency-spectrum for the signal? and how can i analyse the output, if its right or wrong?
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Altera_Forum
Honored Contributor I
52 Views

The I/Q of fft is the frequency domain. 

so just plot the absolute value of output.  

 

IQ = I + jQ; 

power = 20* log10(abs(IQ)); %dB 

f = linspace(-.5*Fs,.5*Fs,fft_points) % if centered on dc else 

%f = linspace(0,1*Fs,fft_points); 

 

%Fs = fft clock frequency 

plot(f,power)
Altera_Forum
Honored Contributor I
52 Views

So If i have a 1024 fft i take the last 1024 values of the real and imaginery part and set them as an array in i and q? What means "centered on dc"?

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