Rohde & Schwarz URV5-Z4 - Page 49

3.7
Checking
the
Preggencxinespgnse
of
RP
Probes
Due
to
the
narrow
tolerances
of
the
RF
probes,
frequency
response
measurements
are
extremely
difficult
and
should
therefore
only
be
carried
out
with
suitable
test
sets.
-
.
Similar
to
power
meters,
all
RF
probes
are
calibrated
to
the
rms
value
of
the
voltage
corresponding
to
the
incident
power:
V
=
J
z
x
Pi
The power P1 can be determined with the aid of corresponding
test
sets.
The
connections
of
the
insertion
units
and
of
the
probe
for
these
measurements
are
shown
in
Fig.
3-5.
Since
-
unlike
microwave
power
meters
-
all
RF
probes
measure
voltages,
the
following
should
be
observed:
1.
The
reflection
coefficient
of
the
connected
terminations
(probes
and
insertion
units)
causes
a
measurement
error
of
the
same
amount
due
to
the
VSWR
on
the
test
line.
A
reflection
cogfficient
of
1%
for
instance
causes
a
measurement
error
of
2.
The
distortion
of
the
test
signal
causes
at
higher
voltages
measurement
errors
of
the
same
order
of
magnitude.
This
is
due
to
the
characteristic
of
the
detector,
which
at
high
voltages
provides
for
a
peak
evaluation
of
the
input
signal.
Therefore,
either
a
low-distortion
generator
(d
<
0.5%)
must
be
used
for
the
frequency
response
measurements
or
the
measurements
be
carried
out
at
low
level.
With
an
input
voltage
of
30
mVrms
(300
mvrms
for
the
100-V
insertion
units)
this
effect
can
be
neglected.
394.8010.02
3.29
8-3
3.7 Checking The Frequenz Response
of er
probes
Due to the narrow tolerances of the RF
probes,
frequency response
measurements are extremely difficult and should therefore only
be
carried out Voith suitable test Sets.
.
Similar to power meters, all RF probes are calíbrated to
Value of the voltage corresponding to the incident power:
the ums
ı:
v /Zxpj.
The power Pi can be determined
Voith the ad of corresponding
test Sets. The
connections of the inser ton Units and of the
probe for these
measurements are show in Fig. 3-5.
Since - unlike
microwave power meters - all
voltages, the
following should be observed:
RF probes measure
1.
The reflectíon coefficíent of the connected terminators
(probes and Insertion Units) causes a measurement error of the
same account due to the VSWR on the test line. A reflection
coefficíent of 1% for instance causes* a measurement error of
-1%.
2.
The distor ton of the Test Signal causes at higher voltages
measurement errors of the same Order of magnitude. This is due
to the characteristic of the detector, which at high voltages
provides for a peak evaluation of the Input Signal. Therefore,
either a low-distortion generator (d < 0.5%) must be used for
the frequency response measurements er the measurements be
carried out at los . level. Voith an Input voltage of 30 1"vrms
(300 'Wrms for the 100-V inser ton Units) this effect can be
neglected.
394.8010.02
3.29
E-3