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.
2-11
Summary of Contents for 491
Page 4: ...i i Fig 1 1 The Type 491 Spectrum Analyzer ...
Page 24: ...2 16 Fig 2 17 Control set up chart ...
Page 34: ...Fig 3 1 Function block diagram of the Type 491 3 2 ...
Page 42: ...Fig 3 10 Block diagram of the video detector and vertical amplifier 3 1 0 ...
Page 48: ......
Page 53: ...Fig 4 4 Power Supply Circuit board assembly with wiring color code 4 5 ...
Page 54: ...Fig 4 5 Horizontal Display circuit board assembly showing color code to pin connectors 4 6 ...
Page 55: ...Fig 4 6 IF Control board assembly Wiring color code to pin connector 4 7 ...
Page 64: ...Fig 4 20A Tube subassembly removal procedure 4 16 ...
Page 65: ...Fig 4 20B Tube subassembly installation procedure 4 17 ...
Page 68: ...Fig 4 22 Power supply board assembly with component call out 4 2 0 ...
Page 69: ...Fig 4 23 Vertical Amplifier and Blanking board assembly with component call out 4 21 ...
Page 70: ...Fig 4 24 IF control board assembly with component call out 4 22 ...
Page 71: ...Fig 4 24 IF control board assembly with component call out 4 23 ...
Page 72: ...Fig 4 25 Horizontal display board with component call out 4 24 ...
Page 73: ...Fig 4 25 Horizontal display board with component call out 4 25 ...
Page 74: ...Fig 4 26 Phase lock board with component call out 4 26 ...
Page 88: ......
Page 90: ...Fig 6 1 Test equipment recommended for calibration of the Type 491 6 2 ...
Page 138: ......
Page 192: ......
Page 195: ...SECTION II B 3 ...
Page 196: ......
Page 200: ......
Page 201: ...SECTION 9 DIAGRAMS MECHANICAL PARTS LIST ILLUSTRATIONS ACCESSORIES ...
Page 202: ......
Page 203: ...9 1 ...
Page 204: ...9 3 ...
Page 205: ...9 5 ...
Page 206: ...9 7 ...
Page 207: ...9 9 ...
Page 208: ...9 11 ...
Page 209: ...9 13 ...
Page 210: ...9 15 ...
Page 211: ...9 17 ...
Page 212: ...9 19 ...
Page 213: ...9 21 ...
Page 214: ...9 23 ...
Page 215: ...9 25 ...
Page 216: ...9 27 ...
Page 217: ...FIG 1 9 29 ...
Page 218: ...FIG 2 REAR 9 31 ...
Page 219: ...9 33 FIG 3 IF CHASSIS PHASE LOCK ASSEMBLIES ...
Page 220: ...FIG 4 POWER CHASSIS 9 35 ...
Page 221: ...FIG 5 TIME DIV SWITCH OSCILLATOR ASSEMBLIES 9 37 ...
Page 222: ...FIG 6 CRT SHIELD ASSEMBLY 9 39 ...
Page 223: ...FIG 7 CABINET ASSEMBLY HANDLE 9 4 1 ...
Page 224: ...FIG 8 491 STANDARD ACCESSORIES FIG 8 491 STANDARD ACCESSORIES 9 43 ...
Page 225: ......
Page 226: ...PIN 028017 000 ...