It has been a long time since I studied engineering, please forgive my mistakes.
I got data sampled from a digital accelerometer. It is sampled at 20 hz, then collapsed into 1 second epochs. The data is then filtered to remove noise. The system outputs 0 at rest, a lot more during activity.
I'm looking at the fourier transform of the signal, 1024 samples, sampled once per second. I'm seeing this:
Here's a real-imaginary plot of the real-imaginary results of the Fourier transform.
The signal appears to be a helix in frequency domain.The system appears to oscillate around some limit cycle within frequency domain.
Is this possible? Is Fourier transform completely wrong for the digital signal? Should using only the DFT for this kind of analysis? Is my window size wrong ? Am I seeing aliasing due to incorrect window size?
It has been a few years since my last engineering class, and I'd really appreciate any help on the subject. I got 3 books on engineering, signal analysis and transforms, but it takes time for this kind of knowledge to come back to me.