TABLE 5-1
10. Check Internal Triggering
a. Requirement-Sweep must trigger on 0.2 division signal
amplitude.
b. With 1 ms and 10 ns markers applied as in step 8,
adjust the Trigger LEVEL control for a triggered display on
the INT position.
c. Decrease the amplitude of the displayed markers by
switching in 20 dB attenuation and adjusting the GAIN con-
trol until sweep triggering can no longer be maintained
with optimum adjustment of the LEVEL control.
d. Check-Amplitude of the markers must be equal to
or less than 0.2 divisions (1 minor division).
11. Check IF Center Frequency
a. Requirement-The center frequency of the IF band-
pass with the IF CENTER FREQ controls centered must be
a d j u s t a b l e t o 2 0 0 M H z w i t h t h e I F C E N T E R F R E Q C A L
adjustment.
b. Apply a calibrated 200 MHz signal from the Time-
Mark Generator (Type 184) to band B RF INPUT connector
through a 20 dB attenuator pad. (Signal input to the Type
491 should be less than -30 dBm to reduce the number
of spurious signals.)
c. Set the Type 491 front panel controls as follows:
P O S I T I O N
Position the trace to the
bottom graticule line
I F C E N T E R F R E Q
Centered (000)
F I N E I F C E N T E R F R E Q
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 - C O U P L E D
10 MHz/div
R E S O L U T I O N
RF INPUT Selector
B
d. Adjust the GAIN control for a signal amplitude of
6 divisions.
e. Adjust the IF CENTER FREQ CAL for minimum signal
shift as the DISPERSION control is rotated between 10 MHz/
div and .2 MHz /div.
f. Position the IF feedthrough signal to the center of the
graticule with the Horizontal POSITION control.
g. Set the DISPERSION control to the .2 MHz/div posi-
tion.
h. Adjust the DISPERSION BAL for minimum signal shift
as the DISPERSION RANGE is switched between MHz and
kHz positions. Set the DISPERSION RANGE to kHz.
i. Adjust the IF CENTER FREQ CAL for minimum signal
shift as the DISPERSION control is switched between 100 kHz/
div and 1 kHz/div positions.
j . C h e c k - T h e r e s h o u l d b e l e s s t h a n ± 2 m a j o r d i v i s i o n
signal shift as the DISPERSION control is rotated down to
the 1 kHz/div position. The IF CENTER FREQ CAL adjust-
ment should not be against the stop.
k. Return the DISPERSION RANGE to MHz position and
the DISPERSION-COUPLED RESOLUTION control to 10 MHz/
div position.
12. Check the Dispersion Accuracy of the MHz/
DIV Ranges and the Range of the IF Center
Frequency Control
a . R e q u i r e m e n t - D i s p e r s i o n a c c u r a c y f o r t h e M H z / D I V
ranges is listed in Table 5-2. IF CENTER FREQ coarse con-
trol range should equal or and - 25 MHz from
its centered (000) position. Dispersion accuracy and display
linearity must remain within the listed specifications of Table
5-2 to the + and – 25 MHz positions of the control.
b. Apply .1µs and 10 ns time markers from the Time-Mark
Generator (Type 184) through a 20 dB attenuator to band
A RF INPUT connector.
c . S e t t h e V E R T I C A L D I S P L A Y s w i t c h t o L O G p o s i t i o n .
Adjust the GAIN control for a display amplitude of approxi-
mately 6 divisions.
Set the SOURCE switch to LINE and
adjust the LEVEL control for a triggered display.
d. Center the IF CENTER FREQ controls.
e. Check the dispersion accuracy and linearity for each
MHz/DIV setting of the DISPERSION selector as listed in
Table 5-2. (See Figs. 5-2 and 5-3.) The Horizontal POSI-
TION control or the IF CENTER FREQ control may be used
to align the prime markers to the graticule divisions. As
t h e D I S P E R S I O N i s d e c r e a s e d , t h e R E S O L U T I O N c o n t r o l
should remain in the coupled position,
f. Check the range, dispersion accuracy and linearity of
the IF CENTER FREQ control in the 2, 1, .5 and .2 MHz
positions of the DISPERSION selector.
Range of the coarse control should equal or
and - 25 MHz from its centered position. It is checked
by rotating the control to both extreme positions from center
and noting the frequency shift of the .1µs or 10 MHz mark-
ers as the control is rotated. Dispersion accuracy and dis-
5-4
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 ...