APPLICATIONS
4. M e a s u r e m e n t o f noise ( F i g . 6)
If t h e noise indeces o f A a n d B are expressed b y F j a n d
F
3
r e s p e c t i v e l y , t h e a m o u n t o f a t t e n u a t i o n is expressed
b y L
2 /
and t h e gain
Gi
o f A is s u f f i c i e n t l y large,
F j •=
R
t
l
L
2
~
F
t
2 L a
' ( F
1
» - )
L
2
" - L
2
' G
F t j a n d F t
2
are F t (overall noise f i g u r e ) w h e r e L
2
is L
2
'
a n d L
2
"
M e a s u r e m e n t o f noise s h o u l d be p e r f o r m e d a f t e r check-
ing t h e c i r c u i t s y s t e m .
Fig. 6
10
Signal generator
or
noise generator
Amplifier
under test
Variable
attenuator
Auxiliary
amplifier
AC voltmeter
RA-920