R&S FSH
Spectrum Analyzer Mode
Performing Spectrum Measurements
Operating Manual 1173.6275.12 - 30
63
The predefined standards are the same as for channel power measurements (3GPP
WCDMA, cdmaOne and CDMA2000 1x systems). However, you can also customize
the settings to set up the R&S FSH for other radio communication standards. You can
define the settings directly on the R&S FSH or define and manage them using the
R&S FSH4View software.
When customizing settings, make sure to consider the following points to get valid and
accurate measurement results:
● Reference level
Make sure not to overload the R&S FSH as the power is measured with a
resolution bandwidth that is small in comparison with the signal bandwidth. As with
Channel Power measurements, automatically set the reference to an optimal level
with the "Level Adjust" softkey.
● Setting the span
The frequency span must at least cover the carriers and the adjacent channels
plus a measurement margin of about 10 % to get valid results.
If the span is automatically calculated by the R&S FSH with the "Auto Span"
function, the span is calculated as follows:
(No. of transmission channels - 1) x transmission channel s
2 x transmission channel ban measurement margin
with the measurement margin being approx. 10 % of the value obtained by adding
the channel spacing and the channel bandwidth.
Selecting the frequency span
If the frequency span is too 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.
● Setting the resolution bandwidth:
The RBW should not be too high or too small to get both an acceptable
measurement speed and a suppression of spectral components outside the
channels. As a rule of thumb, it is recommended to set it to about 1 % to 4 % of the
channel bandwidth.
You can select a larger resolution bandwidth if the spectrum within the channel to
be measured and around it has a flat characteristic. In the standard setting, e.g. for
standard cdmaOne 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.
