Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
50Operating Manual 1176.7649.02 ─ 04
3.8.3 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)
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If "Ref Pow Max" is set: Search maximum power Pmax over the whole burst. Set
Pref=Pmax
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If "Ref Pow Mean" is set: Calculate mean power Pmean of the whole burst. Set
Pref=Pmean
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Rise time
– Search the first crossing of 0.5xPref from the left.
– Search backwards for the 10 % crossing 0.1xPref and note t10.
– Search forward for the 90 % crossing 0.9xPref and note t90.
– Return Trise=t90-t10.
●
Fall time
– Search the first crossing of 0.5xPref from the right.
– Search forwards for the 10 % crossing 0.1xPref and note t10.
– Search backwards for the 90 % crossing 0.9xPref and note t90.
– Return Tfall=t10-t90.
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 stand-
ard. The R&S FSV-K91/91n allows fine tuning of the PVT measurements on signals
with high crest factors by an adjustable moving average filter and two different refer-
ence 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 modula-
tion. While a long average length leads to more stable measurement results, it natu-
rally increases the rise/fall times compared to no averaging.
3.9 Measurement Settings and Result Displays
The WLAN option provides two main measurement types:
Frequency sweep measurements
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Spectrum mask (see "Spectrum Mask (IEEE 802.11ac, b, g (Single Carrier)) /
Spectrum IEEE/ETSI (IEEE 802.11a, g, j, n (OFDM), p)" on page 78 softkey)
●
Spectrum ACP/ACPR (see "Spectrum ACPR (IEEE 802.11a, ac, g (OFDM Turbo
Mode), n, p)/ Spectrum ACP (IEEE 802.11b)/ ACP Rel/Abs (IEEE 802.11j)"
on page 80
Measurement Settings and Result Displays