The Spectrum Application (RF Measurements)
R&S
®
FPL1000
259
User Manual 1178.3370.02 ─ 03
If the sample detector is used, it is best to select the smallest "Sweep Time" possible
for a given span and resolution bandwidth. The minimum time is obtained if the setting
is coupled, that is: the time per measurement is minimal. Extending the measurement
time does not have any advantages. The number of samples for calculating the power
is defined by the number of trace points in the channel.
If the RMS detector is used, the selection of "Sweep Time" s can affect the repeatabil-
ity of the measurement results. Repeatability is increased at longer "Sweep Time" s.
If the RMS detector is used, the number of samples can be estimated as follows:
Since only uncorrelated samples contribute to the RMS value, the number of samples
can be calculated from the "Sweep Time" and the resolution bandwidth.
Samples can be assumed to be uncorrelated if sampling is performed at intervals of 1/
RBW. The number of uncorrelated samples is calculated as follows:
N
decorr
=
SWT * RBW
(N
decorr
means uncorrelated samples)
The number of uncorrelated samples per trace pixel is obtained by dividing N
decorr
by
1001 (= pixels per trace).
The "Sweep Time" can be defined using the softkey in the "Ch Power" menu or in the
"Sweep" configuration dialog box (see
Frequency Span
The frequency span must cover at least the channels to be measured plus a measure-
ment margin of approximately 10 %.
If the frequency span is large in comparison to the channel bandwidth (or the adjacent-
channel bandwidths) being analyzed, only a few points on the trace are available per
channel. The calculated waveform for the used channel filter is less accurate, which
has a negative effect on the measurement accuracy. It is therefore strongly recommen-
ded that you consider the described formulas when you select the frequency span.
The frequency span for the defined channel settings can be optimized. 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 )"
set the frequency span manually in the "Frequency" configuration dialog box.
(See
Chapter 7.4.4, "How To Define the Frequency Range"
For channel power measurements the "Adjust Settings" function sets the frequency
span as follows:
"(No. of transmission channels – 1) x transmission channel s 2 x transmission
channel ban measurement margin"
For adjacent-channel power measurements, the "Adjust Settings" function sets the fre-
quency span as a function of the following parameters:
●
Number of transmission channels
●
Transmission channel spacing
●
Adjacent-channel spacing
Measurements and Results
