R&S FSQ Signal Analyzer - Rohde & Schwarz

R&S FSQ Getting Started
Measurements on Modulated Signals
Optimum Level Setting for ACP Measurements on W-CDMA Signals
The dynamic range for ACPR measurements is limited by the thermal noise floor,
the phase noise and the intermodulation (spectral regrowth) of the R&S FSQ. The
power values produced by the R&S FSQ due to these factors accumulate linearly.
They depend on the applied level at the input mixer. The three factors are shown in
the figure below for the adjacent channel (5 MHz carrier offset)
A CLR /dBc
-50
-55
-60
-65
-70
-75
-80
-85
-90
phase
noise
thermal
noise
total
A CLR
spectral
regrowth
-20 -15 -10 -5 0
M ixer level / dB m
Fig. 2.34 The R&S FSQ’s dynamic range for adjacent channel power measurements on W-CDMA
uplink signals is a function of the mixer level.
The level of the W-CDMA signal at the input mixer is shown on the horizontal axis,
i.e. the measured signal level minus the selected RF attenuation. The individual
components which contribute to the power in the adjacent channel and the resulting
relative level (total ACPR) in the adjacent channel are displayed on the vertical axis.
The optimum mixer level is –10 dBm. The relative adjacent channel power (ACPR)
at an optimum mixer level is –77,5 dBc. Since, at a given signal level, the mixer level
is set in 5 dB steps with the 5 dB RF attenuator, the optimum 5 dB range is shown in
the figure: it spreads from –13 dBm to –8 dBm. The obtainable dynamic range in this
range is 76 dB.
To set the attenuation parameter manually, the following method is recommended:
• Set the RF attenuation so that the mixer level (= measured channel power – RF
attenuation) is between -13 dBm and -8 dBm.
• Set the reference level to the largest possible value where no overload (IFOVLD)
is indicated.
This method is automated with the R&S FSQ’s ADJUST REF LEVEL function.
Especially in remote control mode, e.g. in production environments, it is best to correctly
set the attenuation parameters prior to the measurement, as the time required
for automatic setting can be saved.
To measure the R&S FSQ’s intrinsic dynamic range for W-CDMA adjacent channel
power measurements, a filter which suppresses the adjacent channel power
is required at the output of the transmitter. A SAW filter with a bandwidth of 4
MHz, for example, can be used.
2.50 Operating Manual 1313.9681.12 - 01