Fourier Spectral Analysis in Excel

[Frederic C]

Hello,
I am not a mathematician expert, and I would like to do a spectral
(Fourier) analysis of a series of values. For example I have a serie
of 24 values every 15 degrees (over 360 degrees), and I would like to
find out if there are cyclicities in this serie (N=2, 3, ...). I am
not sure how to use the Fourier Analysis in the data analysis tool.
0 7.3
15 4.0
30 5.0
45 5.0
60 4.0
75 5.0
90 6.5
105 5.0
120 4.0
135 5.0
150 4.0
165 4.0
180 4.0
195 4.0
210 5.0
225 6.0
240 3.0
255 4.0
270 6.0
285 4.0
300 7.0
315 5.5
330 5.0
345 5.0
Thanks for your help,

Frederic C.

 

[Dana DeLouis]

In case you don't get a better answer...Excel's built-in Fourier Analysis is
a Radix-2 algorithm. You need 2^n data points. In your case, it will work
with 16, or 32 data points. For what you are doing, I don't believe
zero-padding will give you what you are looking for.
Using something else, here are the absolute values of the fft of your 24
data points to see if you want to pursue this further.
I used the equation for Data Analysis so you can verify the D.C. component.
(the average value). Since your data is not complex, I only included the
upper half of the output. (results are symmetrical). As you can see, the
8th harmonic has the largest value, but I don't think this can be of much
use.

4.8875,
0.2862604829676507,
0.12639798508757286,
0.19566046140042756,
0.15416666666666662,
0.2318477211793163,
0.11094605796411953,
0.16592712344481123,
0.4438820226141176,
0.10145626019847513,
0.10847398269335032,
0.2511756441712853,
0.17916666666666653

HTH.