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R&S
RT-ZS60
4.2.1.3
RF Resistance R
R
and R
(summarized R
RF1
RF2
range from 20 MHz to 2 GHz. Due to the constantly high input impedance of
300 Ω over the whole range, the loading of high-frequency signals in 50 Ω envi-
ronments is very small.
4.2.1.4
Input Capacitance C
The input capacitance C
quencies above 2 GHz. C
The minimum input impedance |Z
inductance and the connection type. An overview is given in
4.3
Probing Philosophy
The previous sections made clear that probes exert a load on the signal to be
measured and change its characteristic. The signal at the test point where the
probe makes contact (V
before the probe was connected (V
with all real probes – independent of type and manufacturer.
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.
User Manual 1418.7342.02 ─ 03
and R
RF1
RF2
) determine the input impedance in the frequency
RF
and Minimum Input Impedance |Z
in
causes the input impedance to decrease for high fre-
in
is very low - Typically under 300 fF.
in
| mainly depends on the the connection
min
) is therefore different from the signal that was present
in
). This effect cannot be avoided and occurs
S
Measurement Principles
Probing Philosophy
min
table
4-2.
) and that corresponds to
S
|
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