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HP 416A - Page 49

HP 416A
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Spurio
us
Sign
al
F
~
·
- This
er
ro
r
si
gn
al
a
rriv
es at the
forwa
r d deteetor
because
oi
the
impedect
·
~
~
ire
c
tivity
of
the
forward
(incident)
directional
coupler.
A
sample
of
the
v
oha.ge
compone
nt
of
the
refl
e
cted
wave
[( p
LH
EJ]
-[s
coupled
(
af}
into
the
se
c0Eda17
a
rm
of
th
e
forward
direction
al
c
oup
le
r"
1
B
ecause
of
the
imperfect
directi
v
ity
(df)
of
th
e c
oupl
e
r,
som
e
(a
small
part}
of
the
reflected-
wave
voltage
will
reach
the
forward
dete
ct
or.
where
pL
E.
1
::
reflection
coefficient
of
load
:
worst
possib
le
di
rectivity
of
forward
co
up
ler
(.
01)
=
voltage
coup.
ing
coefficie
nt
of
forward
(20
db}
coupler
(.
1)
:
voltage
component
of
inci
dent
wa
ve
,
in
ma
in
gu
i
de
Substituting
approx
i
mate
va
l
ues,
F
1
ha
s a
typic
al
value
of:
pL
(.
01)(.l}Ei
::
l
xl0-
3
pLEi
_S"'"'p_u_r..,.·1_·
o_u_s...,.S,,__ig""--n_a
_l.,_..F:
.z
- T
his
error
signal
results
from
discontinuities
in
the
system,
primarily
at
th
e
fla
nge
jo
i
nt
bet
wee
n
forward
a
nd
reverse
couplers.
T
he
discontinuity
reflection
[(Pc)
(Ei)]
is
re
~re
fle
c
ted
(pg)
at
the
generator,
coupled
(of}
into
the
secondary
arm
of
the
di
rectional
coupler,
and
then
applied
to
the
forward
detector.
The
value
of
F
2
is:
F
2
=
Pc
Pg
a.f
Ei
where
Pc
::
I.umped
refle
ct
ion
c
oefficient
of
discontinuiti
e s
pg
::::
lumpe
d
reflection
coeffic
ient
of
ge
ne
r
ator
Assuming
that
dis
c
ontinuities
may
have
a
reflection
coefficient
of
• 01,
and
the
generator
a
reflection
coefficient
of
.1
, F
2
n1ay
have
a
typical
value
of:
(.
01)
(.1)
(.1)
Ei
:
1x10-
4
Ei
Spurious
Signa
l
F3
-
This
error
signal
results
from
reflections
from
the
forward
(incident)
det
ector.
The
incident
voltage
{Ei)
is
coupled
(of)
by
the
for-
ward
directional
coup
ler
to
the
forward
detector,
and
the
reflection
(pd)
from
the
detector
is
coupled
(af)
back
through
the
coupler
to
the
generator
,
re-reflected
(pg)
by
the
generator
,
and
coupled
(af)
again
by
the
coupler
to
the
forward
detector.
3
The
value
of
F3
is:
F3
=
Pd
Pg
Uf
Ei
where
Pd
::
reflection
coefficient
of
forward
detect.or
(assumed
value,
•
2)
-34-

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