110 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.
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