FFT giving a huge magnitude of first frequency and pretty much zero after that So I have a (visually) very noisy time series signal and I have applied the fast Fourier transform using numpy's fft function. I am wondering why I am seeing the magnitude of the coefficient for the first frequency very large, actually equal to the number of samples ( 256 samples ) in the data, and the rest of the coefficients very low.

I am assuming this means there there is no periodic signal being extracted from the data, but I wanted to get a second opinion about it. How do I interpret this result? Maybe I am doing something wrong. 

Input Signal:


Frequency Coefficients:


Zoomed Picture:
That's correct. It's simply a property of your signal: your signal has very small "wiggles" with a very large mean value. Your mean value is about 1 and your wiggles are around 0.01 we would expect the first frequency to be about 100 times larger then all the frequencies. 

The first frequency represents the DC component (at 0 Hz), it's simply the sum of the signal.