Unevenly Sampled Signal Spectrum (Not in Base Package)

Calculates the power spectrum of a signal that is unevenly spaced in time. Details

XTime is the discrete- and unevenly-spaced times.
X represents the data material at times XTime. There is a one-to-one relation between XTime and X.
Power Spectrum FFT {X} Frequency are the frequency points at which the power spectrum is calculated.
Power Spectrum FFT {X} is the power spectrum, in the sense of the Lomb normalized periodogram.
error returns any error or warning from the VI. Refer to Signal Processing Error Codes for more information about these conditions.

Unevenly Sampled Signal Spectrum Details

The algorithm used is based on the Lomb normalized periodogram. Let the data be given at the time points . In other words,

and

.

Furthermore,

and

.

Then the Lomb normalized periodogram is defined as

,

with

The following diagram shows the Fourier transform of length 256 of a signal that has been sampled at unequal intervals of time. The signal is a combination of sine waves of frequencies 20, 40, 60, and 80 Hz. The duration of the signal is 1 sec. The sampling frequency was chosen as 256 Hz, giving the frequency resolution of 1 Hz.