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General
Description
The Model
416A Ratio M
e
ter makes possible the rapid
, direct,
and ac-
curate measurement
of the ratio
of
the amplitude
of two voltages
.
The design
of the
circuit is such that
the Model
416A may be
used
in
a reflectometer
system
to measure
the
reflection
coefficient of an u
;::,k
nown
load as a
funct
i
on of fre-
quency over
a wide
band
,
in
a
slotted line system as a
standing wave indicator,
or for
general applications. A d
-
c v
olta
g
e
proportional to the ratio indicated
by the meter
is
provided for
oscilloscope or
recorder operation.
When used
in a reflectometer system
,
the Model 416A combines the
voltages
proportional
to incident and reflected power
,
and displays their ratio
irrespective
of
amplitude var
i
ations which affect
both channels
.
These features
of the ratio meter eliminate
objections
previo
u
sly associated
with reflectometer
systems: ( 1) corrections
required as a
res
u
lt of source
amplitude
variations;
(2) the necessity for makin
g
two
measurements
,
one
of incident
and the other
of reflected power
,
and calculatin
g
their ratio.
When the reflectometer system
signal
source
is an
automati
cally swept oscillator, and an
oscilloscope i
s
con-
nected
t
o the Model
416A
,
an oscilloscope p
:r
esentation
of reflection coefiicient
over
a wide
frequency ran
g
e may
be obtained.
Thus
with
the Model 416A a
straight-forward reflectometer
system
for
fast
production
checks,
broadband
system alignment
,
and
l
abor
a
tory investigations is a
v
ailable.
The Model 416A
is particularly
ad
ap
ted
to the measurement
of
very
low reflection coefficients.
In
addition
to
its application in a
reflectometer
system,
the Model 416A
also is useful as
a
standin
g
wa
v
e indicator
for
conventional
slotted line mea
-
surements.
In this
application
,
a reference
v
olta
g
e derived from the
system
power source
and
applied
to the Model 416A eliminates errors
resulting
from
power source
amplitude
v
ariations which
occur during the measurement.
The Model 416A
meter
i
s equipp
e
d with three
scales
(percent
reflection
,
standing
wave ratio
,
decibel)
and four ran
g
es
.
The
decibel
scale
may be used
with either of the
other two.
By means of t},e
meter multiplier
,
a ran
g
e
of
40 db
is
available
when square
-
law dete
c
tors are
used.
Operation
of the Model 4
1
6A is strai
ght
-
forward. An
RF POWER MONI-
TOR is provided
on the control panel to
g
ive visual i
n
dication of
whether the
level of the
input
signals
is wi thi
n operating limits for
the
instrument.
(Ad
-
justment of
signal power is made at the external power source
.
) Only one
adjustment
of the Mode
l
416A is necessary dur
i
n
g
use.
A condition of
known
ratio is set up
i
n
the system under m
ea
surement
,
and the
SET TO
FULL
SCALE
control on the Mod
e
l 416A panel is then adjusted so
that
the
meter
indicates
exactly
on
the known ratio
.
The Model
416A
i
s
a
r
r
anged so that it
may
be
operated
with
either bar
-
retter or
crystal
detectors
.
A source of approximately
17 ma
.
de (8. 5 ma.
for each
barrett
:::
r
) is provided for use as
bias
current for the
barretters.
A
specially
-
designed
transformer assembly
(Type AC
-
60K)
is
available
(as an
accessory) for use
with barretters
.
The two transformers
in
the assembly
provide an impedance
match between each barretter and its
respective Model
416A input.
I -
C
'-..
[ '
a
'-..
lJ
lJ
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