Rohde & Schwarz R&S FSL3 - Page 37

Measuring the Spectra of Complex Signals R&S FSL
1300.2519.12 2.12 E-11
Distortion free Dynamic Range
(1 MHz carrier offset
)
-120
-110
-100
-90
-80
-70
-60
-50
-40
-60 -50 -40 -30 -20 -10
Mixer level /dBm
D
y
n
r a
n g
e
/
d
B
T.O.I.
Thermal Noise
+ Phase Noise
RWB = 1 kHz
RWB = 100 Hz
RWB = 10 Hz
Fig. 2-8 Intermodulation–free range of the R&S FSL as a function of level at the input mixer and the
set resolution bandwidth (useful signal offset = 1 MHz, DANL = –145 dBm /Hz, TOI = 15 dBm; typical
values at 2 GHz)
The optimum mixer level, i.e. the level at which the intermodulation distance is at its maximum, depends
on the bandwidth. At a resolution bandwidth of 10 Hz, it is approx. –35 dBm and at 1 kHz increases to
approx. –30 dBm.
Phase noise has a considerable influence on the intermodulation–free range at carrier offsets between
10 and 100 kHz (Fig. 2-9). At greater bandwidths, the influence of the phase noise is greater than it
would be with small bandwidths. The optimum mixer level at the bandwidths under consideration
becomes almost independent of bandwidth and is approx. –40 dBm.
Distortion free Dynamic Range
(10 to 100 kHz carrier offset
)
-120
-110
-100
-90
-80
-70
-60
-50
-40
-60 -50 -40 -30 -20 -10
Mixer level /dBm
D y
n
. r
a n
g
e
/ d
B
RBW = 1 kHz
Thermal Noise
+ Phase Noise
TOI
RBW = 100 Hz
RBW = 10 Hz
Fig. 2-9 Intermodulation–free dynamic range of the R&S FSL as a function of level at the input
mixer and of the selected resolution bandwidth (useful signal offset = 10 to 100 kHz, DANL = –145 dBm
/Hz, TOI = 15 dBm; typical values at 2 GHz).