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Section V
Model 654A
5-49.During
calibrJtion,
the instrument bottom
cover
is
removed; the top
cover
is removed to make adjustments
and replaced while making frequency
measurements (not
necessary
to replace retaining
screws), all
internal
shields
mllst be in place
and
held firmly
by
retaining
screws.
If
desired Figure 5-17 gives a
scaled
drawing
of
top and
bottom alignment
access
covers
with cut-outs that will
allow adjustments while the covers
are
in place. The
dimensions
are given
in inches.
5-50. FEEDBACK LEVEL ADJUSTMENT.
a.
Connect the equipment shown in Figure
5-15.
b.
Set the
654A controls as follows:
FREQUENCY dial ..........
extreme clockwise
FREQUENCY RANGE ................. XI K
OUTPUT LEVELdBm
......
.
...... +10,0
AMPLITUDE ........
extreme counter-clockwise
IMPEDANCE. .
. .
.
.
.
. . ..
. .....
.
50 UNBA L
------------NOTE-----------
Adjust
A2CI,
S2C2,
and
S2C8,
if
necessary, to
start oscillations.
c.
Adjust
A2R3 (Feedback
Level
Adj.)
for an
indication
on
the dc voltmeter
of -350mV,
+/-IOmV.
d.
For
oscillator
troubleshooting, refer to P,lragraph
5-81
.
5-51. DISTORTION ADJUSTMENT.
a. Connect the
654A
to the distortion
analyzer as
shown
in Figure
5-10.
Set the
654A
controls for
a
frequency of I
X
100.
b.
Adjust A2R4 (Distortion Adj.)
for
minimum
distortion, which should be at least 46dB. If the
tolerance
cannot be
met,
change
the
value of
A2R9*
TEST OSCILLATOR
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VOLTMETER
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TO
A2TP2
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c.
Check distortion
at other
dial
and
range
settings.
-
--
--NOTE - - - - -
You
can
adjust AIR4
at other
frequency
to
get
them into specification providing
that
you still are
in
specification at
I X
100.
d. Disconnect the distortion
analyzer.
5-52. Frequency 0 iar and 1 K Range Adjustment.
a. Preliminary mechanical adjustments
(perfoml only
if necessary).
I)
To prevent
gear
backlash problems
during
alignment, make
sure
that there is no move-
ment between MPI and MP2. See Figure 6-1.
(They
must
be pressed tightly together.) Also
MP3, 4,
and
MP5 spring gear
assembly
must be
under tension.
2)
Check
to make sure that the stop MP6 prevents
the tuning
capacitor
from being completely
closed.
MP6
should
hold the
capacitor at
least
1/16 inch
open.
Adjust if necessary.
3)
With
the
dial
set
to maximum clockwise posi-
tion,
slip
the dial face
such
that the first mark
left
of
I
is
1/16
inch
to the righ
t of
the
fixed
indicator.
To slip dial.
remove
Frequency dial
knob
and
loosen
4
dial rdaining
screws.
After
slipping
dial, retigh ten the
screws.
b.
Connect
equipment
as shown in
Figure
5-15
and
set
the
654A controls as
in
ParagrJph
5-50b.
Record
output
frequency.
c.
Record frequency at dial
settings
1.2.5,8
and
10.
If
some
readings
are
high and
sOllle are
low,
proceed to
step
e. If
all
readings
are
high
or all
.
ELECT RONIC
COUN
T ER
hp
5245L
! I
Figure
5-15.
Frequency Calibration Test Setup
5-14
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