HP 416A - Page 52

......
ro
. ...
1-<
Q)
(/)
Substituting appro x imate values, R
3
may have a typical value of:
(. 2) pL
2
(.
316)
3
Ei ';' 6. 3 x 10-
3
p L z Ei
Net R eflecte d and In cide n t Signals and Their Ratio - -
F
or t l ~ · e pu rpo s e of ev al uat i ng the e ff ect of spurio u s ~<. g n al s {sw e ~ ? t fr eque n c y
basis ) on the :ra t i o indicated b y t he Mo del 416A m eter, t he n et re fl e cted {S r) and.
n
et inc id ent (. '.\) si gn als may be obtained as follows (assumin g that the signals ad d
in phase}: Desired Error
For
Signal Sign a l
~ r ------,
= PL a.r Ei + R1 + Rz + R3
Sr
-
Su m of
signals at reflected detector
-
s.
=
Sum of
sign a ls
at in cid ent detector
1
Sr
Ei [I
R
=
PL ar
+ l
0
' L
+
Rz
a
+ R3]
E -
i
D.esir.ed ·
S i
gn al
Error
Si gna l
r
s.
1
Fl
+
F
+
F3 J
-
Qf
E i
+
2
1
-
af
E·
l
R
+
R,,
+
R3
Fl
+
Fz
+ F3
" 'i
conve n ie n c e , l et :
(..,
and b
a
=
=
PL
a
E.
a.f
E .
r l
1
C'
..:ir
=
PL
ur
E·
1
(l + a}
Note that a a nd b a. xe
l
small (<< l) a nd t hus
1
+ b
1 - b .
T:he rat io be t ween th e ne t r efl ected and i ncident signal s rn ay be for med
as follows:
PL u r E i (l + a )
af
Ei (J. + b)
Neglect ing t he ab term (ab<< a or b ) ,
S·
1
{l + a) {l - b )
=
p L ( ~r ) ( 1 + a. - b)
a. f
Substitutin g fo r a and b (and R
1
, R
2
, R
3
, Fl' F
2
, F
3
), and rearranging
term s :
+
De s i red
S ig nal
d
r
Approximation of the Error Terms
- 36-