python – Why function sampled in time frequency is not repeating?
I’m reading my lecture and found this figure:
sampled signal in frequency domain
So, I get the continuous function after sampling, in frequency domain, should repeat the pattern of the original continuous function. But in my Python code I just get one square where it should be a
lot more squares repeating. I’m new to signals (I’m not engineer, it’s an additional course) so I’m a little confused with my code. Am I missing something? Sorry if it is something dumb or concept misunderstanding.
def g(t): if t == 0: return 1 return np.sin(1.5*np.pi*t) / (1.5*np.pi*t) if __name__ == '__main__': n = 40 fs = 100 # 0.01 t = np.arange(-n, n, 1.0/fs) y = [g(i) for i in t] plt.plot(t, y) plt.xlim(-5, 5) plt.show() # Impulse train n = 40 T = 1.0/2.5 tn = np.arange(-n, n, T) # y2 = [1 for i in range(len(tn))] nT = tn*T y2 = [g(i) for i in nT] # Sampled g plt.stem(nT, y2, 'r', markerfmt="C3o", use_line_collection=True) plt.xlim(-0.9, 0.9) plt.show() fft_s = fft(y2) plt.plot(fftshift(fftfreq(len(fft_s ))), fftshift(np.abs(fft_s ))) plt.show()
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