Power Measurements – MEAS Key R&S FSL
1300.2519.12 4.80 E-11
Settings of CP / ACP test parameters
• Frequency span
The frequency span must at least cover the channels to be measured plus a measurement margin
of approx. 10%.
Note: If the frequency span is large in comparison to 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. It is therefore strongly recommended that the
formulas mentioned be taken into consideration when selecting the frequency span.
For channel power measurements the Adjust Settings softkey sets the frequency span as follows:
(No. of transmission channels – 1) x transmission channel spacing + 2 x transmission channel
bandwidth + measurement margin
For adjacent–channel power measurements, the Adjust Settings softkey sets the frequency 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 channels:
(No. of transmission channels – 1) x transmission channel spacing + 2 x (adjacent–channel
spacing + 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 required 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 neighborhood 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:
VBW
3 x RBW
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