108 34410A/11A/L4411A User’s Guide
4 Measurement Tutorial
On the following page, the first figure shows the Fourier Integral of two very
different pulses: one of broad width (200
μs); the other narrow (6.7 μs). The
second figure is an approximation of the shape of the input frequency
response of the 34410A/11A/L4411A.
Comparing these two figures along the frequency axis, notice that
the spectrum of the narrow pulse significantly exceeds the
effective bandwidth of the instrument. The net result is a less accurate
measurement of the narrow, high–frequency pulse.
In contrast, the frequency spectrum of the broad pulse has fallen off
significantly below the multimeter’s 300 kHz (approximately) band–width, so
measurements of this pulse are more accurate.
Reducing the prf increases the density of lines in the Fourier spectrum, and
increases the portion of the input signal’s spectral energy within the
multimeter’s bandwidth, which improves accuracy.
In summary, error in rms measurements arise when there is significant input
signal energy at frequencies above the multimeter’s bandwidth.
UG_ED5.book Page 108 Thursday, March 1, 2012 11:28 AM
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