Instrument Functions
NRP2
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User Manual 1173.9140.02 ─ 07
4.2.4 Measurement ranges
The power sensors of the R&S NRP series avoid range switching. Some of them, like
the thermal ones of the R&S NRP-Z5x series and the wideband power sensors of the
R&S NRP-Z8x series, have only one measurement range. All other sensors feature
two or three measurement ranges. These ranges are called measurement paths
because they are operated in parallel (simultaneously). With automatic range selection,
measurement paths which are neither overdriven nor underdriven are selected for
evaluation. No range switching occurs at all. Adjacent paths overlap by about 6 dB, the
so-called transition region. Therefore, the final result may be composed by the mea-
surement results of two paths within certain power ranges. Transition regions can be
offset from the default settings to meet the demands of signals with high peak-to-aver-
age ratio.
4.2.4.1
Sensor range dialog box
Automatic or manual path selection can be chosen in the "Range" dialog box,
accessed via the "Sensor" menu. No function is available for power sensors that use
only one measurement range.
The "Auto" range function always selects the most suitable paths. With "User def'd
transition" deactivated, the default overlap regions between adjacent paths are consid-
ered. The offset value can be modified at any time during "Auto" range operation, but it
is only considered with an activated "User def'd transition" checkbox.
Only offsets with a negative sign are allowed. This means that transition regions can
only be shifted to lower power levels. Thus, paths can be excluded from evaluation well
before they exhibit noticeable linearity errors with critical signals. Only the most insen-
sitive path cannot be protected by this measure.
The performance of the sensors can effectively be improved by this measure with
respect to linearity errors when applying signals with high peak-to-average ratios. How-
ever, there is a certain downside regarding speed and noise. If an offset value of e.g.
-10 dB is entered, this means that paths can be underdriven by an amount of 10 dB
with respect to the default setting. This way, the amount of inherent sensor noise will
become more evident or the settling time will increase if one counteracts with a higher
averaging number. That is why there is little point in entering offsets less than -10 dB.
As a rule of thumb, linearity errors introduced by signals with high peak-to-average
ratios, are reduced according to the offset value, e.g. by a factor of four when entering
-6 dB.
Manual path selection can be chosen by deactivating the "Auto" checkbox and select-
ing the preferred path in the "Path" selection box. Testing the drive range of an individ-
ual path or avoiding the noise contribution of the adjacent path may be a good reason
for selecting manual operation.
Data acquisition and parameters
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