Tektronix 491, Руководство по обслуживанию

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Fig. 2-9. Frequency spectrum of a pulsed cw signal.
b . T u n e f o r m i n i m u m s i g n a l s h i f t a s t h e D I S P E R S I O N
R A N G E i s s w i t c h e d f r o m M H z / D I V t o k H z / D I V p o s i t i o n s .
c . W i t h t h e D I S P E R S I O N R A N G E s e l e c t o r a t M H z / D I V
position, adjust the IF CENTER FREQ control for minimum
signal shift as the DISPERSION control is switched through
the 10 to .2 MHz positions.
d. Center the signal with the Horizontal POSITION con-
trol and check the position of the signal on the sweep. The
signal should locate near the center of the sweep with the
sweep extending over the 10 division width of the graticule.
If calibration is required, proceed with the following
adjustments.
N O T E
These adjustments interact, and must be performed
in sequence.
2. IF CENTER FREQ-CAL Adjustment
a. Center the IF CENTER FREQ controls, the DISPERSION
B A L a n d t h e I F C E N T E R F R E Q - C A L a d j u s t m e n t s . S e t t h e
D I S P E R S I O N R A N G E t o M H z / D I V a n d t h e D I S P E R S I O N
selector to 5 MHz/div position.
b. Apply a stable RF signal to the appropriate RF INPUT
connector; then tune to the signal frequency with the RF
CENTER FREQUENCY control. Adjust the GAIN control for
a signal amplitude of approximately 6 divisions.
c. Adjust the RF CENTER FREQUENCY and the FINE RF
CENTER FREQ controls for minimum signal shift as the DIS-
PERSION RANGE is switched between the MHz/DIV and the
kHz/DIV position.
d . W i t h t h e D I S P E R S I O N R A N G E i n t h e M H z / D I V p o s i -
tion, adjust the IF CENTER FREQ-CAL for minimum signal
shift as the DISPERSION is switched through the MHz (10
MHz - .2 MHz) positions.
e . R e t u r n t h e D I S P E R S I O N t o t h e 5 M H z / d i v p o s i t i o n .
Position the signal to the graticule center with the Horizontal
P O S I T I O N c o n t r o l . I f t h e s i g n a l i s m o r e t h a n 1 d i v i s i o n
from the sweep center, it will be necessary to adjust the
internal Sweep Center adjustment R203. See Calibration
section.
3. DISPERSION-BAL Adjustment
a. Preset the front panel
IF CENTER FREQ and
F I N E
D I S P E R S I O N R A N G E
D I S P E R S I O N
b. Tune the RF signal to
controls as follows:
000 (centered)
M H z / D I V
5 MHz/div
the screen center.
c. Adjust the DISPERSION BAL for minimum signal shift
as the DISPERSION RANGE switch is switched between the
MHz/DIV and kHz/DIV positions. (Start the balance adjust-
ment with the DISPERSION selector in the 5 MHz position,
then decrease the dispersion to the .2 MHz-20 kHz position
for the final adjustment.)
N O T E
I f t h e d i s p e r s i o n b a l a n c e c a n n o t b e a c h i e v e d
with the above procedure, the instrument requires
i n t e r n a l a d j u s t m e n t . Refer to the Calibration sec-
tion of the manual.
4. DISPERSION-CAL Adjustment
a. Preset the front panel controls as follows:
I F C E N T E R F R E Q 000 (centered)
D I S P E R S I O N R A N G E
M H z / D I V
D I S P E R S I O N 1 MHz/div
V E R T I C A L D I S P L A Y
S Q L A W
RF Input Selector Band B
I N T R E F F R E Q
Just out of the OFF
detent
b. Connect the 1 MHz MARKERS OUT signal through a
coaxial cable to the band B RF INPUT connector.
c. Tune the RF CENTER FREQUENCY control to align the
tunable markers to the fixed marker signals.
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