FFT / PSD out of rpm vs amplitude data

I have obtained an experimental data which contains rpm Vs amplitude (m/s^2) values for a particular engine order (3. Engine order). The amplitudes are both positive and negative. From engine order and rpm, I can calculate the frequency and represent the experimental values as Freq Vs amplitude. How can I make a FFT and PSD out of it. The amplitude data has both positive and negative values.I am a starter in matlab and have very little idea as to how to go about. Thank you for your help.

Answer 1

[Wayne King]

If I understood your post correctly, you have amplitudes as a function of revolutions/minute. If you take the Fourier transform of that data you will have complex amplitudes as a function of the dual units -- minutes/revolution. Is that what you want? If so you can use periodogram.m if you have the Signal Processing Toolbox. Or just use fft() if you do not have the Signal Processing Toolbox.