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 Fourier transform (FFT) was developed
as a special algorithm that speeds up the discrete Fourier transform (DFT)
by reducing the large number of calculations that are required by DFTs.
Because an FFT runs 10 to 100 times faster than the traditional DFT,Fourier
transform calculations typically use FFTs in place of DFTs.
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
10-28
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