User`s guide

FFT Measurement
Operating System Requirements
Refer to "Oscilloscope Compatibility" on page 1-2 for operating system
requirements for FFT operation.
FFT (Function 2) is used to compute the fast Fourier transform using
vertical inputs (1 and 2), or the Function 1 waveform. This function takes
the digitized time record of the specified source and transforms it to the
frequency domain. When the function is selected, the FFT spectrum is
plotted on the oscilloscope display as dBV (dBV or dBm for 54610 and
54615/54616) versus frequency. The readout for the horizontal axis changes
from time to Hertz and the vertical readout changes from volts to dBV (dBV
or dBm for 54610 and 54615/54616). For the 54610 and 54615/54616, when
50Ω input is selected, readout is in dBm; when 1MΩ input is selected,
readout is in dBV. dBV is a unit of measure that is referenced to 1 Vrms. If
the display of the 54600, 54601, 54602, 54603, or 54645 is needed to be in
dBm, the operator must apply an external 50Ω load (10100C or equivalent),
and then perform the following conversion:
dBm = dBV + 13.01
DC Value The FFT computation produces a DC value that is incorrect.
It does not take the offset at center screen into account and is 1.41421
times greater than its actual value. The DC value is not corrected in
order to accurately represent frequency components near DC. All DC
measurements should be performed in normal oscilloscope mode.
Operating the Measurement/Storage Module
FFT Measurement
2–8