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d.
Check that the SET TO FULL SCALE
control
is not fully
clockwise.
(Completely clockwise is maximum
gai
n
,
and it
is
necessar
y at
the start of the
calibration
procedure
that
some
margin
of
gain be
avai
lable
in the probe
channel.)
e.
Check that the RANGE switch
is
at the 0
DB 100% position.
4.
With no
connection
between
the
slotted
-
line probe and the Model
416A, check that
the
reference
si
g
nal is
within the
Model 416A
operating limits
:
this check includes a check
of
the
level9 of the
signal
and also a check that the modulation frequency
on the signal
is correct
.
NOTE
:
It is
important
that there
be
no
connection
between the
slotted
-
line
probe and the
Model
416A when the
level of
the input
signal is checked and adjusted.
By observing
this
operational
detail
,
danger of overloading
the ratio
meter
and the detectors will be avoided.
Indication that th
e
input
si
g
nal is within frequency
and
v
oltage
limits is
given
by
the
RF POWER MO
N
ITOR (tunin
g
eye) on the
Model 416A.
Input filters in
the
Model 416A are
sharply tuned
to 1
,
000 cycles
.
Therefore
,
re
ga
rdless of
input signal
le
v
el,
no significant
voltage will reach the tuning eye
ci
rcuit unless
the
signal
is
within
±4
0
cycles
of 1
,
000
cycles
.
However
,
when
the
input
vo
ltage
is
of
correct
frequency
,
an input
signal of even
minimum
level will cause the eye
to
give
a
definite indication:
the shutter
will
move toward
closure.
As
the voltage
of an input
signal of proper frequency
approaches the
maximum level
,
the
eye closes completely
.
If
the eye
ov
erlaps by more than 1/32"
,
indication is given
that the frequency of the voltage is correct
but that the
level is
too high
.
a.
To
adjust the
modulation frequency
on the input
signal:
( 1)
First
,
determine
that is the
modulation frequency on the
signal
that is incorrectand not that the
signal level is
too low
.
Check by increasing the level
of the output from
the signal generator
or
by settin
g
the
EXCESS COUPLER
LOSS
s
witch
at 10 DB
.
If
the eye still
does not
move
toward
c
losure
:
(2)
At the signal
generator
or its
power
source, adjust
the
control
which governs
the frequency
of
the
modulating
voltage.
This
adjustment
must be made
very slowly
while watchin
g
the
tuning
eye on the Mode
1
416A.
SLOWLY
operate
the
frequency
-
determining control
until
the tuning eye shutter peaks.
9 The system should be operated
at the
low
es
t
practical input
power.
When
the input to
the crystal
detector
is
within the
-
50
dbm to
-
10 dbm ran
g
e,
the detec
t
or
is operating largely within its true square
-
law
region
(Fig. 8). A brief discussion of
crystal detector
characteris tics
is given
under Possible Error
if
Input Power to
Detector
Too High,
on page 30.
-
42
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