Improving Level Performance
R&S
®
SMA100B
162
User Manual 1178.3834.02 ─ 03
Depending on the R&S NRP power sensor type, the manual setting of the filter length
varies in resolution:
●
Resolution = 1 for the R&S NRPxx family
●
Resolution = 2
n
for R&S NRP-Zxx power sensors, with n = 1 to 16
Follow the following general recommendation to find out the
optimum filter length
:
●
Always start a measurement in auto mode ("Filter > Auto").
Check if the measurement results are sufficient.
●
If the power is not constant, select the filter length manually ("Filter > User").
Trigger the "Auto Once" function to search for the optimum filter length for the cur-
rent measurement conditions.
The estimated value is indicated as filter length.
●
If the target measurement accuracy value is known, select "Filter > Fixed Noise".
The averaging factor is selected automatically and so that the sensor's intrinsic
noise (two standard deviations) does not exceed the specified noise content.
●
Different sensor types achieve the same filtering result with different filter and time
window lengths.
The time window length depends on the sensor type:
–
For most sensors, it is fixed to 20 ms.
–
For the R&S NRP-Z81 sensor, it is 10
μ
s.
The R&S NRP-Z81 uses filter length that is 1000 times larger than the filter
length for other sensors.
About zeroing
Activates the auto zero function.
Zeroing calibrates the external power sensor by adjusting its reading at zero signal
power. For this purpose, the RF power source must be switched off or disconnected
from the sensor. If a Rohde
&
Schwarz power sensor receives an input power during
the zeroing process, it aborts zeroing and generates an error message. Zeroing takes
a few seconds, depending on the sensor model. Refer to the documentation of your
power sensor for more information.
Tips for zeroing
When to perform zeroing:
●
During warm up after switching on or connecting the instrument
●
After a substantial change of the ambient temperature
●
After fastening the power sensor module to an RF connector at high temperature
●
After several hours of operation
●
When low-power signals are to be measured, e.g. less than 10
dB above the lower
measurement limit.
●
Switch off the RF power source for zeroing, but do not disconnect it from the power
sensor. This proceeding keeps the thermal equilibrium, and the zeroing process
also compensates the noise that superimposes the measured signal (e.g. from a
broadband amplifier).
Using Power Sensors
