Basic FAQ for FFT Analyzer

Power spectrum refers to the power of a time signal x (t), obtained by performing FFT analysis to determine the power for each frequency bandwidth (i.e., frequency resolution Δ f), and graphing it with frequency on the horizontal axis.

In the FFT analyzer, it is calculated as follows. If the Fourier spectrum of the signal x (t) is X (f), then the power spectrum P (f) is;

(* denotes the complex conjugate)

（1）

It is required. (1) From the formula, the power spectrum shows that [1] the phase information of the original signal x (t) is lost, [2] it has the dimension of the square of the amplitude, that is, if the physical unit of the signal x (t) is EU (V), it becomes EU ² (V ²), and so on.

 

As a specific example, if the input signal is given by (2) as x (t), the power spectrum will be A² /2 (= (A / √2) ², the square of the effective value).

 

（2）

Also, since the power spectrum corresponds to the square of the amplitude, the square root of this is called the linear spectrum (or amplitude spectrum), which means the effective value in each frequency bandwidth. Similarly, the linear spectrum of equation (2) x (t) will be 0.707 A (0.707 = 1/ √2).

Power Spectrum (Glossary of Basic Terms for FFT Analyzer)