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34
October 2014
Press
F4
to switch between dB and Vrms.
Press
F5
to zoom in/out, options including multiplied *1, *2, *5, *10.
Adjust the "
Horizontal
" knob in horizontal control zone to move the
waveform and the shown frequency of M Pos is the exact frequency of
the cursor point in the middle of spectrum.
Press
F1
to turn off FFT and then press
math menu
to go back to
WAVE MATH menu.
►
Selecting an FFT Window
The FFT feature provides four windows. Each one is a trade-off between
frequency resolution and magnitude accuracy. What you want to measure
and your source signal characteristics help you to determine which window
to use. Use the following guidelines to select the best window.
Type
Characteristics
Window
Rectangle
This is the best type of window for resolving
frequencies that are very close to the same value
but worst for accurately measuring the amplitude
of those frequencies. It is the best type for
measuring the frequency spectrum of non
repetitive signals and measuring frequency
components near DC.
Use rectangle for measuring transients or bursts
where the signal level before and after the event
are nearly equal. Also, use this window for
equal-amplitude sine waves with frequencies
that are very close and for broadband random
noise with a relatively slow varying spectrum.
Hamming
This is a very good window for resolving
frequencies that are very close to the same value
with somewhat improved amplitude accuracy
over the rectangle window. It has a slightly
better frequency resolution than the Hamming.
Use Hamming for measuring sine, periodic and
narrow band random noise. This window works
on transients or bursts where the signal levels
before and after the event are significantly
different.
