Fig. 6-27. Location of C504 and C508.
d. Adjust L444 (wide band amplifier), T464, T454, C435 and
C425 (Fig. 6-24) in the order listed for optimum signal am-
plitude.
e. Adjust L444 for stable 60 MHz oscillator operation.
The stable point is midway between the oscillator dropout
points when the core of L444 is turned in and out through
the operating range. (Remove the P6041 or P6040 cable if
connected and reconnect the cable to J100.)
f. With 200 MHz signal applied to the RF INPUT as de-
scribed in step b, set the DISPERSION to 50 kHz/div, the
RESOLUTION fully clockwise, IF ATTENUTOR for 20 dB, and
adjust the GAIN control for a signal amplitude of 8 divisions.
Center the display with the IF CENTER FREQ controls. Tune
the RF CENTER FREQUENCY if necessary to minimize inter-
ference from converted signals.
g. Connect a test oscilloscope through a
10×
p r o b e t o
pin B of the honeycomb square pin connector. Adjust the
test oscilloscope sensitivity for a display amplitude of ap-
proximately 6 divisions then adjust the triggering controls for
a stable display. See Fig. 6-25. (Test oscilloscope sweep rate
should be the same as the analyzer sweep rate.)
h. Adjust 100 kHz Resol Cal R543 (Fig. 6-28) so the display
begins to show evidence of over coupling (slight dip in the
center]. Bandpass response on the analyzer display should
decrease to approximately 60 kHz at the -6 dB point when
the RESOLUTION selector is turned counterclockwise one
step from the fully clockwise position.
i. Set, the RESOLUTION selector fully clockwise. Adjust
C504 and C508 (Fig. 6-27) for optimum display symmetry
o n t h e t e s t o s c i l l o s c o p e S e e F i g . 6 - 2 5 . A d j u s t C 5 0 4 f o r
the slope of the response and C508 for symmetry. Turn
the RESOLUTION selector counterclockwise one step from
fully clockwise position. Adjust C601, C604, C607 and C610
for optimum display symmetry and amplitude.
F i g . 6 - 2 8 . l o c a t i o n o f r e s o l u t i o n f i l t e r a d j u s t m e n t s a n d 1 0 0 k H z
Resolution Cal R543.
j. Check display symmetry through each position of the
RESOLUTION selector. When these adjustments are correct,
display will remain fairly symmetrical through the range of
the selector. Remove the
10×
probe and return the RESOLU-
TION selector to the fully clockwise position.
k. Check the Type 491 resolution bandwidth at the -6 dB
point. (This point can be located by switching in the 2
and 4 dB IF ATTENUATOR dB switches and noting the dis-
play amplitude.) Bandwidth must equal or exceed 100 kHz
at the -6 dB point.
1. If the bandpass is less than 100 kHz in step k, adjust
the 100 kHz Resolution Cal R543 (Fig 2-28) to obtain a
bandpass between 100 kHz and 120 kHz at the -6 dB point.
m. Turn the RESOLUTION control one position counter-
clockwise from the fully clockwise position (DISPERSION is
50 kHz.) Readjust the GAIN control for a full 8 division
display and check the bandpass at the -6 dB point. Band-
pass should decrease to approximately 60 kHz.
n. These adjustments interact. When properly set, the
resolution bandwidth should vary from approximately 100
kHz, with the control in the full clockwise position, to 1 kHz
or less with the RESOLUTION control in the fully counter-
clockwise position
kHz/div position,
to approximately
sponse.
As the DISPERSION
the sweep rate must
.2 s/div to maintain
is reduced to the 1
also be decreased
a symmetrical re-
6-25
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 ...