User`s guide

74 Agilent InfiniiVision 2000 X-Series Oscilloscopes User's Guide
4 Math Waveforms
Because the frequency span goes from ≈ 0 to the Nyquist frequency, the
best way to prevent aliasing is to make sure that the frequency span is
greater than the frequencies of significant energy present in the input
signal.
FFT Spectral Leakage
The FFT operation assumes that the time record repeats. Unless there is
an integral number of cycles of the sampled waveform in the record, a
discontinuity is created at the end of the record. This is referred to as
leakage. In order to minimize spectral leakage, windows that approach
zero smoothly at the beginning and end of the signal are employed as
filters to the FFT. The FFT Menu provides four windows: Hanning, Flat
Top, Rectangular, and Blackman-Harris. For more information on leakage,
see Agilent Application Note 243, The Fundamentals of Signal Analysis at
"http://cp.literature.agilent.com/litweb/pdf/5952-8898E.pdf."
Units for Math Waveforms
Units for each input channel can be set to Volts or Amps using the Units
softkey in the channel's Probe Menu. Units for math function waveforms
are:
A scale unit of U (undefined) will be displayed for math functions when
two source channels are used and they are set to dissimilar units and the
combination of units cannot be resolved.
Math function Units
add or subtract V or A
multiply
V
2
, A
2
, or W (Volt-Amp)
FFT dB* (decibels). See also "FFT Units" on
page 72.
* When the FFT source is channel 1, 2, 3 or 4, FFT units will be displayed in dBV when channel
units is set to Volts and channel impedance is set to 1 M
Ω. FFT units will be displayed in dBm
when channel units is set to Volts and channel impedance is set to 50
Ω. FFT units will be
displayed as dB for all other FFT sources or when a source channel's units has been set to Amps.