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R&S
RT-ZZ80
4
Measurement Principles
The R&S RT-ZZ80 transmission line probe provides an electrical connection
between the DUT and the oscilloscope. The probe transfers the voltage of the
electrical signal tapped off the DUT to the oscilloscope, where it is displayed
graphically. Although a probe has a wide variety of specifications, these specifica-
tions can be grouped into two classes of basic requirements:
● High signal integrity of the transferred signal:
With an ideal probe, the output signal that is transferred to the base unit would
be identical to the input signal between the probe tips, and signal integrity
would be extremely high. Every real probe, however, will transfer the input sig-
nal in altered form. A good probe causes only minimum alterations.
How the probe can fulfill this requirement is mainly determined by its band-
width.
● Acceptable loading of the input signal:
Every probe is a load for the signal to be measured. This means that the sig-
nal to be measured changes as soon as the probe is connected. A good
probe should cause a minimum change to the signal, also at higher frequen-
cies.
How the probe can fulfill this requirement is mainly determined by its input
impedance.
The parameters of a probe are usually specified for a minimally short connection
between the probe and the DUT. With longer connections, the connection induc-
tance has a significant effect on the measurement.
The high-frequency behavior of probes is typically characterized in a 50 Ω mea-
surement environment. The probe is connected to a 50 Ω line that is fed by a
source with 50 Ω internal impedance and that is terminated into 50 Ω.
The
figure 4-1
shows the equivalent circuit model of a probe that is connected to
the DUT.
User Manual 1409.7689.02 ─ 02
Measurement Principles
21
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