How to perform FT on XY Graph data?

[djcdun]

Hello,

I have my data in two 1D arrays (X and Y) and plotted in an XY Graph.  I did not use a waveform because it was not a time signal, it was a spatial one with an uneven interval.  Briefly, the experiment measured the output of an amplifier as the position of a mirror was varied through several millimeters.  I need the fourier transform of this plot but cannot figure out how to do it in labview.
I've uploaded the raw data file which is a tab delimited txt file.  If this is transposed and displayed in an XY graph you will retrieve the curve I need to FT.  As the X data is on the order of 1E-10 I am expecting reciprocal space, X', to be on the order of 1E+10.

Please help, I have been playing about with FFT.vi and signal processing VI's all day and cannot seem to get anywhere. 

[ejkaiser]

Your time stepping dt seems to be 3.3e-14, so you can expect a frequency range of 1.5e13.

Cheers

Edgar

[altenbach]

FFT assumes that your data is equally spaced in X, but you said that you have uneven intervals (if I understand you right).

There is a tool for unevenly sampled data: Unevenly Sampled Signal Spectrum VI

You could also resample your data into a even grid using interpolation.

A waveform graph does not imply time data, you can call the axis anything you want. The only requirement is that the data has a constant x-increment. If it does, you can di a plain FFT on the Y array and calculate df from dx and N.

EDIT: looking at your data: for all practical purpose it is sampled equally in time, the differences are due to the limited decimal resolution. the delta is randomly either 3.3E-14 or 3.4E-14, depending on where you look. You could just use an average delta.

[altenbach]

Here's a quick draft using waveform graphs (using a simple approximation for dx. As mentions you might want to average over the entire x range instead.:

 

I am also only showing the magnitude. Modify if you are interested in the real or imaginary parts, or both.

[djcdun]

Perfect!  Thank you, I see it was much simpler than I had convinced myself it was.