frequency spectrum

Altera_Forum · ‎05-25-2010

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?

Altera_Forum · ‎05-25-2010

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 · ‎05-27-2010

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"?