Measurements
R&S
®
FSW
143
User Manual 1173.9411.02 ─ 19
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. This reduces the accuracy of the waveform calculation for the channel filter
used, which has a negative effect on the measurement accuracy. It is therefore
strongly recommended that the formulas mentioned be taken into consideration when
selecting the frequency span.
The frequency span for the defined channel settings can be optimized using 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)"
You can set the frequency span manually in the "Frequency" configuration dialog box,
see
chapter 6.3.3, "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 number of transmission channels, the transmission
channel spacing, the adjacent-channel spacing, and the bandwidth of one of adjacent-
channels ADJ, ALT1 or ALT2, whichever is furthest away from the transmission chan-
nels:
"(No. of transmission channels – 1) x transmission channel s 2 x (adjacent-
channel s adjacent-channel bandwidth) + measurement margin"
The measurement margin is approx. 10 % of the value obtained by adding the channel
spacing and the channel bandwidth.
Resolution Bandwidth (RBW)
To ensure both acceptable measurement speed and the required selection (to sup-
press spectral components outside the channel to be measured, especially of the adja-
cent channels), the resolution bandwidth must not be selected too small or too large.
As a general approach, the resolution bandwidth is to be set to values between 1%
and 4% of the channel bandwidth.
A larger resolution bandwidth can be selected if the spectrum within the channel to be
measured and around it has a flat characteristic. In the standard setting, e.g. for stand-
ard IS95A REV at an adjacent channel bandwidth of 30
kHz, a resolution bandwidth of
30
kHz is used. This yields correct results since the spectrum in the neighborhood of
the adjacent channels normally has a constant level.
The resolution bandwidth for the defined channel settings can be optimized using 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)"
You can set the RBW manually in the "Bandwidth" configuration dialog box, see
Channel Power and Adjacent-Channel Power (ACLR) Measurement
