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HP 416A - Page 16

HP 416A
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circuit.
The
inductance
in
the
parallel
=
resonant
circuit
is
center-tap
ped
.
The
other
filter
(
Filter
2)
i
ncludes
two
coupled
parallel-resonant
circuits.
The
out
-
pu
t
of
Filter
2
is
tied
t o
the
midpoint
of
the
inducta
nce
in
the
Filter
1
parallel
-
resonant
circuit.
Typical
configurations
for
such
a
combina
ti
on
of
filters
and
the
ph
ase
shif
ts
that
occu
r
in
their
circuits
are
indicated
in
Fig
. 3 . Si
nusoidal
voltages
E1
an
d
E2
are
in
phase
at
the
inputs
to
each
filter.
In
Filter
1,
the
ph
ase
of
sin
usoid
Ei
i s
shifted
90°
by
the
inductance
in
the
series
arm
,
and
another
90°
by
the
mutual
inductance
between.
the
series
and
parallel
-
resonant
sections
.
Thus
t
he
v
oltage
across
the
parallel
-
resonant
circuit
is
shifted
180°
with
re
sp
ect
to
in
put
sinusoid
E
1
.
In
Filter
2,
the
phase
of
sinusoid
E2
is
s
hifted
90°
by
the
m
utu
a l
inductance
between
the
two
parallel
-
resonant
cir
-
cuits
,
and
t
her
efore
jE2
is
applied
to
the
center
tap
of
the
inductor
in
Filter
1.
Sinu
s oi
ds
Ei
a
nd
E 2,
after
the
phase
shifts
described
above
,
are
combined
at
the
terminals
of
the
Fil
ter
1
parallel
-
resonant
circuit
,
and
the
two
resultant
voltages
(sin
usoid
A
and
sinusoid
B)
are
1T
-
26
out
of
phase
.
By
means
of
this
circuit
, a
ph
ase
angle
may
be
derived
which
is
related
to
the
ratio
of
the
in
-
pu
t v
olt
ages.
The
Model
416A
uses
a
scheme
similar
to
the
foregoing
to
obtain
two
voltages
w h
ich
are
out
of
phase
by
ff
-
26.
These
voltages
are
used
in
the
triggering
of
subsequent
circuits
that
convert
the
two
voltages
to
square
-
waves
which
are
app
l
ied
to
the
meter
circuit.
The
sum
of
these
two
waveforms
is
another
sq
u
are
wave
whic
h
is
proportional
to
e,
and
the
meter
scales
are
so
calibrated
that
with
a
cur
rent
proportional
to
8
flowing
in
the
meter
circuit,
an
indication
wil
l
be
given
w
hich
is
proportional
to
the
square
root
of
tan
e,
The
ratio
of th e
reflecte
d
to
the
incident
voltage
in
the
transmission
system
und
er
measurement
is
eq
ua l
to
t
he
square
root
of
tan
8 .
General
=-
T
he
circuit
of
the
Model
4
16
A
is
shown
i n
block
diagram
form
in
Fig.
4
and
sc
hematically
in
the
sche
matic
diagram
at
the
back
of
this
book
.
From
externa
l
square=
law
detectors
,
the
Model
416A
Ratio
Meter
ac
=
c
ept
s
two
1 =
kc
voltages
,
one
proportional
to
the
inciden
t
power
in
a
trans
-
mission
system
a
nd
the
other
proportional
to
the
r e
flected
power
.
The
Model
416
A
input
circuits
am
plify
and
deliver
each
voltage
to
a 1 -
kc
band
-
pass
filter
.
Filter
l
(incide
nt
voltage)
i
ncludes
a
series
resonant
circuit
coupled
to a p
aralle
l -
resona
nt
circu
i
t,
and
Filter
2
(reflected
v
oltage)
in
-
cludes
two
coupled
parallel
-
re
sonant
circuits
.
Filter
2
delivers
an
output
voltage
11
/2
out
of
phase
wit
h
the
outpu
t
of
Filter
1.
The
ou
t
put
from
Filter
2
is
a
pplied
to
the
center
tap
of
the
inducta
nce
of
the
Fi
lte
r 1
parallel
=
resonant
circuit
,
and
the
two
voltages
are
added
as
shown
in
Fig
. 5.
The
resultant
voltages
are
always
f(
- 28
ou
t
of
phase.
Under
a
condition
of
100%
reflection
,
when
the
reflecte
d
and
incide
nt
voltages
are
of
equal
amplitude
,
angle
e
is
71/4
,
and
the
resultant
volta
ges
be
i n g
Tf-28
out
of
phase
therefore
are
71
/2
out
of
phase
wit
h
respect
to
ea
c h
other
.
Under
a
condition
of
less
than
100%
reflection
,
the
ph
ase
angle
('if
-2
6)
is
greater
than
1f
/2
.
The
phase
angle
of
t
he
resu
lt
a
nt
vo
ltages
under
a
condition
of
50%
reflection
is
shown
in
F
ig
. 5 .
-
7-

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