R&S FSL WLAN TX Measurements (Option K91 / K91n)
1300.2519.12 4.413 E-11
IQ measurements can be run in split screen mode (allowing both the Magnitude Capture Buffer
display and the selected IQ measurement results to be displayed simultaneously) or in full screen
mode (with either the Magnitude Capture Buffer display or the selected IQ measurement results
displayed).
• frequency sweep measurements
The frequency sweep measurements use different signal data to IQ measurements and as such it is
not possible to run an IQ measurement and then view the results in the frequency sweep
measurements and vice–versa. Also because each of the frequency sweep measurements uses
different settings to obtain signal data it is not possible to run a frequency sweep measurement and
view the results of another frequency sweep measurement.
All frequency sweep measurements are run in full screen mode.
Further information
This section provides background information on measurements and displayed information. For details
on signal processing refer to chapter "Advanced Measurement Examples", section "Measurement
Examples of the WLAN TX Measurements Option (K91/K91n)".
Rise / fall time measurement
The rise/fall time is calculated according to the following algorithm:
• Apply a moving average filter over the burst power (adjustable average length)
• If Ref Pow Max is set: Search maximum power P
max
over the whole burst. Set P
ref
=P
max
• If Ref Pow Mean is set: Calculate mean power P
mean
of the whole burst. Set P
ref
=P
mean
• Rise time
– Search the first crossing of 0.5xP
ref
from the left.
– Search backwards for the 10% crossing 0.1xP
ref
and note t
10
.
– Search forward for the 90% crossing 0.9xP
ref
and note t
90
.
– Return T
rise
=t
90
–t
10
.
• Fall time
– Search the first crossing of 0.5xP
ref
from the right.
– search forwards for the 10% crossing 0.1xP
ref
and note t
10
.
– search backwards for the 90% crossing 0.9xP
ref
and note t
90
.
– Return T
fall
=t
10
–t
90
.
Since the single carrier modes of 802.11b, g use linear modulation formats like BPSK or QPSK, the
transmit signal power varies between symbol sampling times. These power variations are determined
by the transmit filter, which is not defined in the standard. The R&S FSL–K91 allows fine tuning of the
PVT measurements on signals with high crest factors by an adjustable moving average filter and two
different reference power settings.
The reference power equals the 100% setting for the rise / fall time calculation. Either the maximum
burst power or the mean burst power can be chosen as reference power. Using the mean burst power,
rarely power peaks within the burst does not influence the rise / fall time measurement.
The moving average filter smoothes the power trace and thus eliminates the modulation. While a long
average length leads to more stable measurement results, it naturally increases the rise / fall times
compared to no averaging.
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