Rohde & Schwarz R&S FSP Series, Operating Manual

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R&S FSP Instrument Functions
Analyzer Mode
4.104 Operating Manual 1164.4556.12 - 06
ADJUST REF
LVL
The ADJUST REF LVL softkey adjusts the reference level of the R&S FSP to the
measured total power of the signal. The softkey is activated after the first sweep with
the measurement of the occupied bandwidth has been completed and the total
power of the signal is thus known.
Adjusting the reference level ensures that the signal path of the R&S FSP will not be
overloaded and the dynamic range not limited by too low a reference level.
Since the measurement bandwidth for channel power measurements is significantly
lower than the signal bandwidth, the signal path may be overloaded although the
trace is distinctly below the reference level. If the measured channel power is equal
to the reference level, the signal path cannot be overloaded.
Remote command:
SENS:POW:ACH:PRES:RLEV
ADJUST
SETTINGS
The ADJUST SETTINGS softkey optimizes the instrument settings for the measure-
ment of the occupied bandwidth according to the specified channel bandwidth.
All instrument settings relevant for power measurement within a specific frequency
range are optimized:
• frequency span: 3 × channel bandwidth
• resolution bandwidth: RBW
≤
1/40 of channel bandwidth
• video bandwidth: VBW
≥
3 × RBW
• detector: RMS
The reference level is not influenced by ADJUST SETTINGS . For an optimum
dynamic range it should be selected in a way that the signal maximum is close to the
reference level. The adjustment is carried out only once; if necessary, the instrument
settings may be changed later.
Remote command:
SENS:POW:PRES OBW
Measurement principle
For example, the bandwidth containing 99% of the signal power is to be determined.
The routine first calculates the total power of all displayed points of the trace. In the
next step, the points from the right edge of the trace are summed up until 0.5% of
the total power is reached. Auxiliary marker 1 is positioned at the corresponding fre-
quency. Then the R&S FSP sums up the points from the left edge of the trace until
0.5% of the power is reached. Auxiliary marker 2 is positioned at this point. 99% of
the power is now between the two markers. The distance between the two fre-
quency markers is the occupied bandwidth which is displayed in the marker info
field.
A prerequisite for correct measurement is that only the signal to be measured is vis-
ible on the screen of the R&S FSP. An additional signal would invalidate the mea-
surement.
To ensure correct power measurement especially for noise signals and to obtain the
correct occupied bandwidth, the following settings should be selected:
RBW
<< occupied bandwidth (approx. 1/20 of occupied bandwidth, for voice
communication type. 300 Hz or 1 kHz)
VBW
≥
3 × RBW
Detector RMS or sample
Span
≥
2 to 3 × occupied bandwidth