In this applet a section of 2 sinusoids from T1 to T2 is sampled and the DTFT and DFT calculated. The variation of the spectra as T1, T2 are changed is illustrated.

eg parameters:-

(3.0, 4.0, 0.01, 6.04, 25, NA, 15, 10.0, 15.0, 0.7) and

(3.0, 4.0, 0.01, 6.93, 25, NA, 15, 200.0, 15.0, 0.7) show the same phenomemon which occurs for a single sinusoid.

To separate the 2 frequencies, then the sampled interval and number of samples must be chosen so that the DFT line separation must be equal to or be a submultiple of the difference between the 2 frequencies. eg:-

(3.0, 3.2, 0.01, 31.02, 80, NA, 45, 10.0, 34.5, 0.2) Sampling frequency = 16rad/s, line separation = 0.2rad/s, frequency separation = 0.2rad/s.

(3.0, 3.4, 0.01, 31.11, 100, NA, 45, 10.0, 34.5, 0.2) Sampling frequency = 20rad/s, line separation = 0.2rad/s, frequency separation = 0.4rad/s.

(3.0, 4.0, 0.01, 31.11, 100, NA, 45, 10.0, 34.5, 0.2) Sampling frequency = 20rad/s, line separation = 0.2rad/s, frequency separation = 1rad/s.

COPYRIGHT © 2007 Cuthbert Nyack.