Fig. 6-30. Adjustments for the kHz/DIV discriminator.
b, Apply 10 ns and 1 µs markers from the Time-Mark
Generator through the 20 dB attenuator to the band A RF IN-
PUT. Set the DISPERSION to 500 kHz/div. Preset the DIS-
PERSION BAL R234, to its midrange position and the kHz/div
Cal R368 (Fig. 6-30) approximately 90° counterclockwise
from its fully clockwise position.
c. Adjust C384 and C385 simultaneously for 1 marker/2
div. Keep the IF feedthrough signal centered on the graticule
as this adjustment is made.
d. Adjust the kHz/div Cal R368, for optimum dispersion
linearity. These adjustments interact, so repeat the adjust-
ments until optimum dispersion linearity and accuracy is
obtained.
N O T E
An alternate source of frequency markers may be
o b t a i n e d b y u s i n g t h e H a r m o n i c M o d u l a t o r ( S e e
equipment list) with a 100 MHz or 200 MHz source
and an accurate audio signal source. Apply the RF
signal to the RF Input and the audio frequency to
the Mod Freq 1 Input of the Harmonic Modulator.
C o n n e c t t h e M o d u H a r m O u t c o n n e c t o r t h r o u g h
a 2 0 d B a t t e n u a t o r t o t h e R F I N P U T c o n n e c t o r o f
t h e T y p e 4 9 1 . T h i s w i l l p r o v i d e a n I F f e e d t h r o u g h
signal modulated by the audio frequency for fre-
quency markers.
25.
a.
b.
Check Dispersion of the kHz/div Selector
Positions
Test equipment setup is described in step 24.
Apply 10 ns and 1
µs m a r k e r s f r o m t h e T i m e - M a r k
Generator through the 20 dB attenuator and proper adapter
to band A RF INPUT or through the proper adapter to the
Waveguide Adapter for band C. Set the band selector to
the appropriate band and the DISPERSION selector to 500
k H z / d i v .
c. Check-The range of the IF CENTER FREQ control by
rotating the control to the limits each side of center. Count
the number of 1 MHz (1
µs) markers from the 200 MHz (20
ns) feedthrough signal. Must equal or exceed 2.5 MHz.
Note the dial reading when the control is 2.5 MHz from
center. This reading will be used later in the procedure.
6-27
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 ...
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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 ...