The Spectrum Application (RF Measurements)
R&S
®
FPL1000
260
User Manual 1178.3370.02 ─ 03
●
Bandwidth of one of adjacent-channels ADJ, ALT1 or ALT2, whichever is furthest
away from the transmission channels
"(No. of transmission channels – 1) * (transmission channel s 2) * (adjacent-
channel s adjacent-channel bandwidth) + measurement margin"
The measurement margin is approximately 10
% of the value obtained by adding the
channel spacing and the channel bandwidth.
Resolution Bandwidth (RBW)
It is important to suppress spectral components outside the channel to be measured,
especially of the adjacent channels. At the same time, you expect an acceptable mea-
surement speed. To fulfill both these requirements, the appropriate resolution band-
width is essential. As a general approach, set the resolution bandwidth to values
between 1
% and 4
% of the channel bandwidth.
If the spectrum within the channel to be measured and the spectrum around the chan-
nel has a flat characteristic, you can select a larger resolution bandwidth. In the stan-
dard setting, e.g. for standard 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
near the adjacent channels normally has a constant level.
You can optimize the resolution bandwidth for the defined channel settings. 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 )"
You can set the RBW manually in the "Bandwidth" configuration dialog box, see
Except for the IS95 CDMA standards, the "Adjust Settings" function sets the resolution
bandwidth (RBW) as a function of the channel bandwidth:
"RBW" ≤
1/40 of "Channel Bandwidth"
The maximum resolution bandwidth (concerning the requirement RBW ≤
1/40) result-
ing from the available RBW steps (1, 3) is selected.
Video Bandwidth (VBW)
For a correct power measurement, the video signal must not be limited in bandwidth. A
restricted bandwidth of the logarithmic video signal causes signal averaging and thus
results in a too low indication of the power (-2.51
dB at very low video bandwidths).
Thus, select the video bandwidth at least three times the resolution bandwidth:
VBW ≥3
* RBW
For FFT sweeps, instead of increasing the VBW, you can also select the trace average
mode "Power" to ensure correct power measurements (see
on page 468). Note that in power measurements this setting affects the VBW regard-
less of whether or not a trace is actually averaged.
The video bandwidth 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 )"
You can set the VBW manually in the "Bandwidth" configuration dialog box, see
Measurements and Results
