Fig. 6-22. Dispersion calibration adjustments.
d . A d j u s t t h e D I S P E R S I O N C A L R 2 0 8 ( F i g . 6 - 2 2 ) f o r 1
marker/division over the center 8 graticule divisions, then
adjust C358 for display linearity.
e. Repeat the adjustment of R208 and C358 for optimum
dispersion accuracy and display linearity. If the dispersion
linearity is not within tolerance, a slight re-adjustment of
the RF Ampl R290 and the Center Freq Range R251 adjust-
ments may be required. Monitor the voltage at pin P of the
honeycomb square pin connector with the test oscilloscope
to keep the RF voltage amplitude within 0.75 to 1.0 volts and
recheck step 18.
22.
a.
b.
c.
Check Dispersion Accuracy of MHz/DIV
Ranges and Range of IF CENTER FREQ
Control
Test equipment setup is given in step 21.
Center the IF CENTER FREQ controls.
C h e c k t h e d i s p e r s i o n a c c u r a c y f o r e a c h M H z / D I V
setting of the DISPERSION selector as listed in Table 6-4.
The Horizontal POSITION central, or the IF CENTER FREQ
control may be used to align the prime markers to the
graticule divisions.
As the DISPERSION is decreased, the
RESOLUTION control should remain in the coupled posi-
tion.
d. Check the range of the IF CENTER FREQ control plus
the dispersion accuracy and linearity over this range, in
the 5, 2, 1, .5 and .2 MHz positions of the DISPERSION selec-
tor.
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 cen-
ter and noting the frequency shift of the .1 µs or 10 MHz
markers as the control is rotated. Dispersion accuracy and
display linearity must remain within the listed specifications
of Table 6-4 to the + and - 25 MHz positions.
e. Center the coarse IF CENTER FREQ control. Set the
DISPERSION control to 1 MHz position and apply 10 ns and
1 µs markers from the Time-Mark Generator.
f . C h e c k - T h e r a n g e o f t h e I F C E N T E R F R E Q - F I N E c o n -
trol. Must equal or and - 1 MHz from its cen-
tered position.
TABLE 6-4
6-22
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 ...