FFT, 2 Sines with Hamming window.

Cuthbert Nyack
The use of a window in conjunction with the FFT reduces the variation in the spectrum that occurs when an integer or nonteger number of periods is sampled. A broadening of the spectrum is the price paid for this reduction in variation.

eg parameters (4.0, 4.2, 0.0, 70.00, 512, 10, 185, 10.0, 150.0, 0.04)
This is the case of 1 sinusoid, varying T2 shows little variation in the spectrum of the signal. On the other hand it is no longer possible to get a spectrum consisting of a single line.

eg parameters (4.0, 4.2, 1.0, 129.25, 512, 10, 185, 10.0, 150.0, 0.04) show that in order to distinguish 2 sinusoids of equal amplitude separated by 0.2rad/s, then the sampling interval > 100s. For a separation of 0.1rad/s an even longer interval is required.

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COPYRIGHT 2007 Cuthbert Nyack.