HP 54750A, User Manual, Page: 280 / 478

General Purpose Oscilloscope Menus
FFT Menu
Other FFT measurements
There are a number of time domain measurements that you can make on FFT
waveforms:
Tmin
Tmax
Vp-p
Vmin
Vmax
The Tmax measurement is particularly useful because it returns the
frequency of the highest peak on the display .
FFT basics
The F ourier series states that any waveform that repeats in time can be
represented by a dc term plus a series of cosine and sine waves . The F ourier
series was developed in 1807 by the French mathematician, Jean Baptiste
F ourier , to solve thermodynamics problems . A more general form of the
F ourier series , called the F ourier transform, was developed later . It allows any
time domain signal, whether it is periodic or single shot, to be transformed
into the frequency domain. The fast F ourier transform (FFT) was developed
as a special algorithm that speeds up the discrete F ourier transform (DFT)
by reducing the large number of calculations that are required by DFT s .
Because an FFT runs 10 to 100 times faster than the traditional DFT , F ourier
transform calculations typically use FFT s in place of DFT s .
Oscilloscopes operate in the time domain and display waveforms with the
vertical axis representing amplitude and the horizontal axis representing time .
Because FFT s are frequency domain functions , the horizontal axis on the
display changes to represent frequency when you select FFT s .
Figure 10-3 illustrates what an FFT does . An FFT transforms a time record of
N samples into a frequency record of N points from 0 Hz to Fs , where Fs is
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