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5,
(Cgnt'd)
of even minimum level will cause the eye to give a definite
indication:
the shutte
r
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 overlaps by more than I /32
11
,
indication is given
that the frequency of the voltage is correct but that the level is foo high.
a.
To adjust the modulation
frequency
on the i
n
put signal:
(I) If
there
is an external attenuator in the line
,
set it at approxi-
mately 5 DB.
(The setting of the Model 6 70SM is at
·)
,
)
If
there
is
no external attenuator in the line, change the setting
of the ATTENUATION control on the Model 670SM from 5 to
approximately 4.
(2} If the tuning eye does not indicate by moving its shutter toward
closure, SLOWLY
adjust
the
MOD.
FREQ.
control
on
the
M
odel
717 A until
the
tuning
eye
shutter peaks
.
S
tarting
fr
om
the
ex·-
treme
clockwise
position of MOD. FREQ., slowly turn the con-
trol counterclockwise until a
tuning
eye indication is obtained.
(If
the eye shutter does not mo
ve,
return MOD. FREQ. to
its
extreme clockwise position, s
et t
he ATTENUATION
control
on
the Model 670HM at
3, and
readjust the MOD
.
FREQ. control
on the Model 71 7 A until
a
t
u
ning
e
ye indication is
o
btained.
)
CAUTION
:
Care should
be
taken to make c
e
rtain
that
the
correct
modulation frequency is chosen and not some sub-
harmonic of 1,
000
cycles.
For
a
1, 000-
cycle
out-
put
,
the
MOD
.
F
R
EQ.
control
knob s
e
tt
i
ng
will
be
almost completely clockwise.
b.
If the
tuning eye
ove
r
lap
s
by
m
ore
than 1
/32
11
,
reduce
the
leve
l
oJ
the input signal.
(1) If there is an external atte
n
uator
inthe
l ine,
increase
the setting
of the
attenuator,
as requir
e
d,
to
br
i
ng
t
he tuning
eye overlap
to 1
/32
11
or less
.
Leave
the
s etting
of
the
Model
670SM
ATTENUA-
T ION
control
at
O.
(2)
If
there is no external atte
nua
t
or,
r
e
duc
e
the
level
of
t
h
e
output
sign.al
at the Model
670SM
by
adjusting
the setting of the
AT-
TENUATI
ON control.
Calibration (
100%
R eflection
,
Broadband) (S
Band
)
1.
On the Mode
l
670SM oscillator
:
a.
Set the limit stops on the FREQUENCY
-
KM
C
d
ial
for desired rang
e
.
For the S
-
band system being described
,
set one limit stop at 2
.
6
kmc
and the other at 3. 95 kmc.
-
28
-
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