Rohde & Schwarz R&S FSP Series, Руководство по эксплуатации

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Operating Manual 1164.4556.12 - 06 2.9
R&S FSP Getting Started
Measuring Signals in the Vicinity of Noise
Fig. 2.13 Change in displayed noise as a function of the selected reference level at bandwidths of
10 kHz and 300 kHz (-30 dBm reference level)
Impact of the resolution bandwidth
The sensitivity of a Spectrum Analyzer also directly depends on the selected band-
width. The highest sensitivity is obtained at the smallest bandwidth (for the
R&S FSP: 10 Hz, for FFT filtering: 1 Hz). If the bandwidth is increased, the reduction
in sensitivity is proportional to the change in bandwidth. The R&S FSP has band-
width settings in 3 and 10 sequence. Increasing the bandwidth by a factor of 3
increases the displayed noise by approx. 5 dB (4.77 dB precisely). If the bandwidth
is increased by a factor of 10, the displayed noise increases by a factor of 10, i.e. 10
dB. Because of the way the resolution filters are designed, the sensitivity of Spec-
trum Analyzers often depends on the selected resolution bandwidth. In data sheets,
the displayed average noise level is often indicated for the smallest available band-
width (for the R&S FSP: 10 Hz). The extra sensitivity obtained if the bandwidth is
reduced may therefore deviate from the values indicated above. The following table
illustrates typical deviations from the noise figure for a resolution bandwidth of 10
kHz which is used as a reference value (= 0 dB).
Fig. 2.14 Change in R&S FSP noise figure at various bandwidths. The reference bandwidth is 10
kHz
-2
0
2
4
6
8
10
12
14
-70 -60 -50 -40 -30 -20
Reference level /dBm
re
l. n
ois
e
le
ve
l /
dB
RBW = 10 kHz
RBW = 300 kHz
-1
0
1
2
3
0,01 0,1 1 10 100 1000
RBW /kHz
Noise figure
offset /dB
digital RBW analog RBW