Specifications

69
When we add a preamplifier to our analyzer, the system noise figure and
sensitivity improve. However, we have accounted for the 2.5 dB factor in our
definition of NF
SA(N)
, so the graph of system noise figure becomes that of
Figure 5-8. We determine system noise figure for noise the same way that we
did previously for a sinusoidal signal.
NF
SA
– G
pre
+ 3 dB
NF
SA
– G
pre
+ 2 dB
NF
SA
– G
pre
+ 1 dB
NF
SA
– G
pre
System Noise
Figure (dB)
NF
pre
+ 3 dB
NF
pre
+ 2 dB
NF
pre
+ 1 dB
NF
pre
NF
pre
+ G
pre
– NF
SA
(dB)
–10 –5 0 +5 +10
Figure 5-8. System noise figure for noise signals