R&S ESCI Analyzer - MEAS
1166.6004.12 4.157 E-1
Frequency span The frequency span must at least cover the channels to be measured plus
a measurement margin of 10%.
For channel power measurement, the span is 1.1 x channel bandwidth.
Note: If the frequency span is large in comparison with the channel
bandwidth (or the adjacent-channel bandwidths) being examined, 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.
We therefore strongly recommend that the formulas mentioned be taken
into consideration when selecting the frequency span.
Resolution bandwidth To ensure both an acceptable measurement speed and the required
(RBW) selection (to suppress spectral components outside the channel to be
measured, especially of the adjacent 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 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 in the neighbourhood of the adjacent
channels normally has a constant level. For standard NADC/IS136 this is
not possible for example, since the spectrum of the transmit signal
penetrates into the adjacent channels and a too large resolution bandwidth
causes a too low selection of the channel filter. The adjacent-channel
power would thus be measured too high.
With the exception of the IS95 CDMA standards, the ADJUST SETTINGS
softkey sets the resolution bandwidth (RBW) as a function of the channel
bandwidth:
RBW ≤ 1/40 of channel bandwidth.
The maximum possible resolution bandwidth (with respect to the
requirement RBW ≤ 1/40) resulting 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 would
cause signal averaging and thus result in a too low indication of the power
(-2.51 dB at very low video bandwidths). The video bandwidth should
therefore be selected at least three times the resolution bandwidth.
The ADJUST SETTINGS softkey sets the video bandwidth (VBW) as a
function of the channel bandwidth as follows:
VBW ≥ 3 × RBW.
The smallest possible VBW with regard to the available step size will be
selected.
Detector The ADJUST SETTINGS softkey selects the RMS detector.
The RMS detector is selected since it correctly indicates the power
irrespective of the characteristics of the signal to be measured. In principle,
the sample detector would be possible as well. Due to the limited number
of trace pixels used to calculate the power in the channel, the sample
detector would yield less stable results. Averaging, which is often
performed to stabilize the measurement results, leads to a too low level
indication and should therefore be avoided. The reduction in the displayed
power depends on the number of averages and the signal characteristics
in the channel to be measured.
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