Rohde & Schwarz FPL1000 Series, Руководство пользователя

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The Spectrum Application (RF Measurements)
R&S
®
FPL1000
261 User Manual 1178.3370.02 ─ 03
The video bandwidth (VBW) is set as a function of the channel bandwidth (see formula
above) and the smallest possible VBW with regard to the available step size is
selected.
Detector
The RMS detector correctly indicates the power irrespective of the characteristics of
the signal to be measured. The whole IF envelope is used to calculate the power for
each measurement point. The IF envelope is digitized using a sampling frequency
which is at least five times the resolution bandwidth which has been selected. Based
on the sample values, the power is calculated for each measurement point using the
following formula:


 
N
i
i RMS
s
N
P
1
2
1
Where:
s
i
= linear digitized video voltage at the output of the A/D converter
N = number of A/D converter values per measurement point
P
RMS
= power represented by a measurement point
When the power has been calculated, the power units are converted into decibels and
the value is displayed as a measurement point.
In principle, the sample detector would be possible as well. Due to the limited number
of measurement points used to calculate the power in the channel, the sample detector
would yield less stable results.
The RMS detector can be set for the defined channel settings automatically. Use the
"Adjust Settings" function in the "Ch Power" menu or the "General Settings" tab of the
"ACLR Setup" dialog box (see
"Optimized Settings ( Adjust Settings )" on page 266).
You can set the detector manually in the "Traces" configuration dialog box, see "
Detector " on page 467.
Trace Averaging
Avoid averaging, which is often performed to stabilize the measurement results but
leads to a level indication that is too low. The reduction in the displayed power
depends on the number of averages and the signal characteristics in the channel to be
measured.
The "Adjust Settings" function switches off trace averaging. You can deactivate the
trace averaging manually in the "Traces" configuration dialog box, see
" Average Mode
" on page 468.
Reference Level
To achieve an optimum dynamic range, set the reference level so that the signal is as
close to the reference level as possible without forcing an overload message. How-
ever, if the signal-to-noise ratio becomes too small, the dynamic range is also limited.
The measurement bandwidth for channel power measurements is significantly smaller
Measurements and Results