Hi,
I wanted to use the NI USB 6251 to perform a spectrum analysis, using the SpectrumAnlayzer.2010 example. I made a test using a sinusoidal analog signal and I realized the output spectrum had an anomalous behavior. Using the rectangular window I expected to see a spectrum with about 13 dBm dynamics. That means that the Fourier transform of a rectangular window (a sinc function) shows a difference of 13 dBm between the principal lobe and the nearest lobe. As the Fourier transform of a sinusoidal function is a delta function the final spectrum (the convolution between delta and sinc function), should show a dynamics, i.e.. the difference between the central lobe peak and the nearest lobe peak of 13dBm. However the output shows almost 80 dBm dynamics.
Furthermore, using the Blackman Harris window I expected to see much more dynamics than with a rectangular window but the results show less dynamics.
Does anybody know the reason of that?
XUV
