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HP 416A - Page 11

HP 416A
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Circuit
Des
cri
ption
Introduction
- -
The
Model
416A
Ratio
Meter
is
designed
to
accept
any
two
1-
kc
volt-
ages,
and
to
con
ver
t
and
combine
them
electronically
in
such
manner
that
the
square
root
of
their
ratio
is
indicated
directly
by
the
meter
on
the
instru-
ment
.
Reflection
coefficient
may
be
defined
as
the
ratio
of
the
v
oltage
of
the
reflected
wa
ve
to
the
vo
ltage
of
t
he
incident
wave
,
and
~
herefore
the
Model
416A
is
par
tic
ul
ar
ly
adapted
for
use
in
a
reflectometer
system
to
measure
the
magnitude
of
the
reflection
coefficient
of
components
in
a
microwave
transmission
system
,
A
reflectomet
er
sys
te m
contains
a m i
crowa
ve
oscillator
modulated
at
an
audio
rate
(usually
a 1 -
kc
square
wave
),
By
means
of
two
directional
cou
plers
in
the
line
,
bet
ween
the
source
and
the
load
,
the
incident
and
re
-
flec
te
d
powers
are
sam
pled
and
subsequently
detect
ed
hy
crystal
usually
operated
as
s
qu
a
re
- l
aw
devices
,
Thus
,
two
1-
kc
voltages
,
one
proportional
to
the
i
nc
i
dent
pow
er
and
the
other
to
the
reflected
power
,
are
derived
,
When
the
detectors
used
are
square
-
law
devices
,
the
magnitude
of
the
reflection
coefficient
is
equal
to
t
he
square
root
of
the
ratio
of
these
two
voltages
.·
Whil
e
the
Model
416A
a
lso
may
be
used
i n
the
measurement
of
the
rati
o b
etween
any
tw
o l
··
kc
volta
ges
or to
measure
a
standing
wave
ratio
, .
many
of
the
consi
de
rations
concerning
its
design
were
determined
by
the
re
-
quirements
governing
th e
measurement
of
the
m a
gnitudes
of
reflection
coef
-
fi
c
ie
n
ts
,
and
therefore
the
circuit
will
be
described
in
terms
of
the
measure
-
ment
of
the
magnitude
of
reflect
i
on
coefficients,
Theory
-~
The
ratio
of
t
he
amplitu
des
of
two
si
nusoids
which
are
in
phase
can
be
formed
simply
by
using
an
oscillo
s
cope
.
If
one
si
nuso
i d
is
applied
across
the
horizontal
deflection
pl
a
tes
and
the
oth
er
sinus
o
id
i s
applied
across
the
ver
t
ical
defl
ection
plates
,
the
well
-
known
straig
h
t-
l
ine
L
issa
jous
pattern
results
.
The
pattern
has
the
property
th
a t
the
s
lope
of
the
line
is
a
function
of
the
ratio
of
the
two
voltages
,
In
a
geometrica
l
representation
,
the
rat
io
is
the
s
lop
e
of
the
lo
cus
formed
by
rotating
one
vect
or
by
a n
angle
of·
7f
/ 2
and
addi
ng
the
two
v
ectors
vectorially
.
In
the
time
domain
there
are
operations
which
correspond
to
those
in
the
space
doma
in
.
That
is,
shift
the
phase
of
one
sinusoid
(E2
)
by
an
angle
of
'IT
/2
relati
ve
to
the
other
(E1)
,
the
n
sum
them
(E3),
,
and
measure
the
phase
angle
(e)
between
this
sum
and
the
other
sinusoid
(E1)
(see
Fig.
2).
Tan
( 8 )
is
the
ratio
of
E 2 ,
E1
Phys
ical
realizat
i
on
of
t
hese
operations
i s
achieved
by
combining
the
outputs
of
two
filters
which
are
tuned
to
the
same
frequency.
One
filter
(Filter
1)
includes
a
ser
i
es
-
reso
n
ant
circ
uit
cou
pled
to
a
parallel
-
resonant
- 6-

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