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R&S
RT-ZD40
This has resulted in a difference of opinion as to which of the following two sig-
nals should be output by the probe:
1. The initial signal that is not loaded by the probe (V
the signal at the test point without the probe being connected.
2. The input signal that is additionally loaded with the input impedance of the
probe (V
) and that is actually present between the probe tips.
in
Both approaches are physically correct and have their individual advantages and
disadvantages. In theory, it is even possible to mathematically convert the two
measurement results into each other, but only by performing a complex transfor-
mation to and from the frequency domain. Probe manufacturers will use one or
the other of these two approaches.
Rohde & Schwarz has decided in favor of the user-friendly approach. In our opin-
ion, most users want to know the signal present in the DUT before it was altered
by the influence caused by the probe. After all, users want to characterize their
own DUTs, not the Rohde & Schwarz probe.
As long as measurements are carried out in a 100 Ω (or a comparable) environ-
ment, the signal displayed on the oscilloscope screen is always a direct represen-
tation of the unloaded signal VS, as can be seen in
Fig. 5-8: Unloaded and loaded input signal and step response (for RT-ZS30)
User Manual 1410.5363.02 ─ 03
Measurement Principles
Probing Philosophy
) and that corresponds to
S
figure
5-8.
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