Measurement Computing WavePort 312P rev.1.0 - Manual (Page 64)

7-4 Spectrum Analyzer PowerVista/312 User’s Manual
Channel V1 Spectrum
Frequency (Hz)
Volts
73.242 1623.5 383.3 693.4 1003.4 1313.5
0.00
204.34
153.26
102.17
51.09
S1
Figure 7-2. Spectrum for 700 Hz without Hamming.
Channel V1 Spectrum
Frequency (Hz)
Volts
73.242 1623.5 383.3 693.4 1003.4 1313.5
0.00
194.64
145.98
97.32
48.66
S1
Figure 7-3. Spectrum for 700 Hz with Hamming.
7.3.2 The Fast Fourier Transform
The Fast Fourier Transform (FFT) is a mathematical algorithm used to calculate the Discrete Fourier Transform
(DFT) of a time series of points. The DFT’s main weakness is that it necessitates N squared complex
multiplications and N squared complex additions, where N is the number of points in the series. Thus, for large
values of N, a DFT is computationally excessive. From this, it is clear that computational procedures that
reduce the number of additions and multiplications are greatly needed.
In 1965, the first major contribution to this need was presented in a paper by Cooley and Tukey. That
publication led to the development of a variety of efficient algorithms which are collectively referred to as the
FFT. The efficient algorithm used in EasyPower Measure is one based on a commonly used FFT where N by
definition needs to be a power of two.