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Using Features for Advanced Applications
3–198
TDS 500C, TDS 600B, & TDS 700C User Manual
9. Read the frequency difference between the cursors from the D: readout. Read
the frequency of the selected cursor relative to the zero frequency point from
the @: readout.
The cursor units will always be in Hz, regardless of the setting in the Time
Units side menu. The first point of the FFT record is the zero frequency
point for the @: readout.
10. Press Function (main) ➞ Paired (side).
11. Use the technique just outlined to place the vertical bar of each paired cursor
to the points along the horizontal axis you are interested in.
12. Read the amplitude between the X of the two paired cursors from the
top-most D: readout. Read the amplitude of the short horizontal bar of the
selected (solid) cursor relative to either 1 V
RMS
(0 dB), ground (0 volts), or
zero phase level
(0 degrees or 0 radians) from the @: readout. Read the
frequency between the long horizontal bars of both paired cursors from the
bottom D: readout.
You can use automated measurements to measure FFT math waveforms. Use the
procedure To Take Automated Measurements found in Waveform Differentiation
on page 3–212.
There are several characteristics of FFTs that affect how they are displayed and
should be interpreted. Read this topic to learn about the FFT frequency domain
record — how the source waveform relates to the record length, frequency
resolution, and frequency range of that record. (The FFT frequency domain
waveform is the FFT math waveform that you display.) Continue reading the
topics that follow to learn how to optimize the oscilloscope setup for good
display of your FFT waveforms.
FFTs May Not Use All of the Waveform Record. The FFT math waveform is a
display of the magnitude or phase data from the FFT frequency domain record. This
frequency domain record is derived from the FFT time domain record, which is
derived from the waveform record. All three records are described below.
To Take Automated
Measurements of an FFT
The FFT Frequency
Domain Record