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Adiustment Procedure
-
494A1494Ap
Service Vol. 1
Figure 5-18.
Adiustments
on
the 10
Hzl100 Hz
Bandpass
Filter
assembly.
FILTER
Filter
Locatlon
Preset the
Variable Resolution Gain
and
Band Leveling
(R1030 on
the Post VR
Amplifier
board)
(R2031
on
the
Va
#2 Mother
board).
(R3035 on
the 10
dB Gain
Steps board)
(R2023 and
R2060 on
the
20
dB Gain Steps
board)
The Log Amplifier must be
calibrated
before
adjusting any Variable
Resolution
gain
set-
tings.
Log
Amplifier
calibration can
be
verified
by
applying
a +6
dBm,
10 MHz
sig-
nal to the
input
(J621),
of the Log Amplifier,
and checking
lor
full screen display
with
the
REF LEVEL at
-20
dBM.
a.
Before adjusting
the
Variable Resolution
gain
and band
leveling,
set
the
correction
factors
to
zero
by
pressing
<Blue-SHIFT>
PULSE
STRETCHER,
and
selecting
menu item
5, then
item
2.
b.
Test equipment setup
is shown in Figure 5-14.
Set the
Spectrum
Analyzer
controls
as follows:
FREQ
SPAN/D|V
RESOLUTION BANDWIDTH
REF LEVEL
MIN RF
ATTEN
VERTICAL
DISPLAY
1 MHz
1 00 kHz
-20
dBm
0dB
2 dB/DrV
c.
The
gain
of
the
Post
VR
Amplifier
should be
20 dB
for
best
signal-to-noise
ratio
through the
Variable
Resolution
stages. lf any maintenance
has been
per-
formed
on
this
stage,
perform
the
following
steps.
(1)
Remove
the
cover
for
the VR 2nd
Filter
Select
board.
Disconnect the
jumper
connector
to
the
input
of
the
Post VR Amplifier
(pin
JJ).
(2)
Apply
a
'10
MHz,
-14
dBm
signal, from a 50o
signal
source,
to
pin
JJ
of the
amplifier.
(3)
Adjust
Post
VR
Gain
R1030
on
the
Post
VR
Amplifier
board for
a full
screen
display.
(4) Remove
the
signal
trom
the
input to the
Post
VR
Amplifier
and
replace the
iumper
connector
to
pins
JJ
at
the
input to the
Post
VR
Amplifier.
Replace
the
cover
for
the
VR 2nd
Filter Select
board'
d.
Set
the front
panel
AMPL
CAL
fully counterclock-
wise and
set
the
Band 1
Galn
R2031
0n VR
Mother
baard
#2
(Figure
5-15)
fully
counterclockwise.
1 MHz
10
kHz
1 kHz
100
Hz
10 Hz
Figure
5-17
Figure
5-17
Figure
5-17
Figure
5-17
Figure
5-15
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9.
Table 5-3
5-18