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Adjustments
Model
8672A
RELATED ADJUSTMENTS
(Cont'd)
Synthesizer. Tables 5-2 and 5-3
contain the
neces¬
sary
information that
provides
assurance
of
proper
performance.
5-17. Prior to performing the adjustment
proce¬
dures, refer
to
the disassembly procedures in
Sec¬
tion
VIII.
These procedures cover the removal
of
the
top
and
bottom
covers,
the internal
Al
and
A2
assembly
covers,
and
the
A3A9 YTO
Loop
Assembly.
5-18.
ADJUSTMENT LOCATIONS
5-19. The
last
foldouts
in this manual contain
fig¬
ures
that
show the locations
of
assemblies, adjust¬
ments, test points and
chassis parks.
Table 5-1.
Factory
Selected
Components
Reference
Designator
A1A13R1
A2A8C7
A3A1A2C8
A3A1A2L4
A3A1A2R67,
R68 and R69
A3A1A5C38,
R36, R40
&
R41
A3A3R43
A3A7C19
A3A7C48
A3A7R61,
R65 and R75
A3A7R67
A3A9A4R20
Service
Sheet
l-Al
10-A3
2—A3
2—A3
2—A3
5—A3
12—A3
10—A3
10—A3
10—A3
10—A3
9—A3
Range
of
Values
82.5kn
to
1
Mn
100—470
pF
0
to 12.0
pF
0.22 to 0.68
^iH
Refer
to
Table in
VCXO
Adjustment
R36: 82.5
to
56.20
R41: lOOn or
deleted
R40.-51.inor
C38 at
27 pF.
12
kii
to
14.7kn
160
or 220 pF
3.9
to
5.6
pF
R61: 1620 or 1960H
R75:1780
or
21500
R65: 3.16 to
11.0
kn
75 or
1780
348n
to 1.21
kn
Basis of Selection
Matched
to
the
A1A13A1 Preamplifier at
the factory.
Selected for correct output frequency.
Centers frequency
adjustment range
ofA3A!A2C4
about 100
MHz.
Refer
to
the
VCXO
Adjustment
procedure.
Required change in attenuation necessary for
a
-10 dBm
output
level of the 400
MHz
signal. Refer
to
VCXO
Adjustment procedure.
If
the power output from the
IF OUT
jack
(A3A1A5J2
is less
than
-5
dBm at any
frequency between
5
MHz
to 65
MHz
replace
R36
82.50 with
a
56.20
resistor,
R40
51.in
resistor
with
C38
27
pF
capacitor, and remove R41. Proper power output level
is
0
±5 dBm
from
5
to 65
MHz.
If
this range cannot
be
met, service
may
be
required.
Select
so
that pin
2
ofUl
Power
Up/Down
Detector
is 0.1 to
0.2V
lower than the
+5.2V
Power Supply.
Matched
to
the
part number
ofA3A9A3
2.0—6.2
GHz YTO
Assembly
.
160
pF with HP
5086-7131; 220
pF
with HP
5086-7242.
Selected for frequency response on the 100
kHz
and lower
FM
deviation ranges.
Use the
FM
Frequency Response Test Setup (test
oscillator and spectrum analyzer only). Set the
test
oscillator's
controls
so
that
the spectrum
analyzer's display
of the first
FM
sidebands are 30
dB down from carrier at
1
MHz.
At
3.16
MHz
the
sidebands should
be 40
dB down;
at
10
MHz,
50 dB down.
If
the
response
is
peaking, insert
a
smaller value capacitor.
If
the
response
is
rolling
off, insert
a
larger value capacitor.
Normal
values for sensitivity of
10
MHz-pk/Vrms
from front
panel;
R61, 19600; R75, 18200; R65, 51100.
If
sensitivity
is low,
change
R75
to
21500; R65
to
38300.
If
sensitivity
is high,
change
R61 to
16200; R75 to 17800; R65 to
90900.
Measure
the dc
voltage
on the
emitter of Q5.
If
more negative
than
-8.0 Vdc,
reduce the value of R65;
if
more positive
than -0.5 Vdc,
increase the value
of R65.
Matched
to
the part number
ofA3A9A3
2.0—6.2
GHz YTO
Assembly:
1780 with
HP
5086-7131;
750 with HP
5086-7242.
YTO
Loop
gain
crossover
of
20
±2 kHz. Refer
to
the
YTO
Loop
Phase Detector Adjustment.
5-2
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