amplitude with no more than 3 dB dip in the center,
Set the RESOLUTION control fully clockwise. Adjust
the 100 kHz Resolution Cal R543, for a resolution
bandwidth between 100 kHz and 120 kHz at the –6
dB point. Check that the bandpass decreases to less
than 1 kHz with the RESOLUTION control in the fully
counterclockwise position.
❑
24. Adjust the kHz/DIV DISPERSION Calibration.
Page 6-25
Apply 10 ns and 1 µs markers to the RF INPUT. Set
the DISPERSION to 500 kHz/div. Preset the DISPER-
SION BAL to midrange position. Adjust C384 and
C385 for 1 marker per two divisions. Adjust these
capacitors simultaneously in opposite directions to
keep the 200 MHz signal centered on screen. Adjust
kHz/Div Cal R368, for optimum dispersion linearity.
❑
25. Check Dispersion Accuracy of the kHz/DIV Ranges.
Page 6-26
Apply time markers from the Time-Mark Generator
to the RF INPUT as listed in Table 6-4 and check the
kHz/div dispersion accuracy t and – 2.5
MHz change in the IF center frequency. Dispersion
accuracy must not exceed ±3% over the center
8 divisions of the graticule sweep length.
❑
26. Adjust Avalanche Voltage.
Page 6-28
Connect the test oscilloscope to the 1 MHz MARKERS
OUT, turn on the tNT REF FREQ control. Adjust the
Avalanche Volts R1131, from a counterclockwise posi-
tion, clockwise until the avalanche transistor is just
below the point of free running avalanche. Set the
band selector to C. Push the LOCK CHECK button
and tune the RF CENTER FREQUENCY control. Check
for beat signals through band C.
❑
27. Adjust 1 MHz Reference Frequency Range. Page 6-29
Apply the output from the 1 MHz MARKERS OUT
connector, through a 20 dB attenuator, to J100 on the
honeycomb assembly. Adjust L1108 for positive oscil-
lator start as the INT REF FREQ control is turned from
OFF to on position. Adjust L1104 for a frequency shift
of 1.2 kHz in the 1 MHz oscillator, as the INT REF
FREQ control is rotated through its range.
❑
28. Adjust Band C Balance then Band A and B Balance.
Page 6-30
Center the FINE RF CENTER FREQ control. Set the
band selector to C. Push the LOCK CHECK button
and adjust Band C Bal R1140, for a centered trace.
Switch the band selector to B or A. Push the LOCK
CHECK button and adjust band A and B Bal R1150
for a centered trace.
❑
29. Check Dynamic Range of Vertical Display Modes,
Page 6-31
Dynamic range of the 8 division screen is as follows:
L I N
≥ 2 6
d B , L O G
≥ 4 0
d B a n d S Q L A W
≥ 1 3
d B .
❑
30. Check Accuracy of IF ATTENUATOR selectors.
Page 6-31
Apply a signal within the frequency range of one
band, from a Signal Generator with a calibrated vari-
able attenuator output, to an RF INPUT connector
of the Type 491. Check the accuracy of each IF
A T T E N U A T O R d B s e l e c t o r a g a i n s t t h e c a l i b r a t e d
attenuator on the Signal Generator. Accuracy must
equal or exceed ±0.1 dB/dB of attenuation.
❑
31. Check Attenuation Range of IF Gain Control.
Page 6-32
Check the range of the IF GAIN control. Must equa
exceed 50 dB.
❑
32. Check INTENSIFIER Control Range.
Page 6-32
Set the DISPERSION to 100 kHz/div, and the RESOLU-
TION control to maximum. Set the VERTICAL DIS-
PLAY switch to LOG position and adjust the GAIN
control for an 8 division display. Intensified portion of
the display with the INTENSIFIER control fully clock-
wise should measure between 3.5 and 4.5 divisions.
❑
33. Check Signal Amplitude to RECORDER Connector.
Page 6-32
With VERTICAL DISPLAY in LIN position, the signal
output to the RECORDER connector when terminated
into 600
Ω
load should equal or exceed 4 mV/ divi-
sion of displayed signal.
❑
34. Check Video Filter Operation.
Page 6-32
❑
35. Check Incidental Frequency Modulation. Page 6-32
Incidental FM for a 200 MHz IF signal should not
exceed 200 Hz. Incidental FM for a tunable signal
(IF + Local Oscillator) in phase lock condition should
not exceed 300 Hz.
❑
36. Adjust the Narrow Band IF Amplifier Peaking.
Page 6-35
Apply a 200 MHz signal to J100 on the honeycomb
assembly. Adjust T464, T454, C435 and C425, in the
order listed, for optimum signal amplitude and sym-
metry. Adjust L444 for optimum amplitude and stable
70 MHz oscillator operation.
❑
37. Adjust Wide Band Amplifier Response and Check
System Flatness.
Page 6-36
Apply a calibrated 75 MHz signal to J120. Connect a
test oscilloscope to J188. Turn the 20 dB ATTENU-
ATOR switch on.
Adjust L144 for maximum response to 75 MHz signal.
Apply 65 MHz and adjust L147 for minimum response
to 65 MHz. Remove the Signal Generator signal and
test oscilloscope; reconnect honeycomb cables to J120
and J188.
Apply a frequency and amplitude calibrated signal
to an RF INPUT connector and check the response
flatness of the Type 491. Response flatness should
v a r y o v e r ± 1 . 5 d B o v e r 5 0 M H z d i s p e r s i o n f o r
band A, ±1.5 dB over 100 MHz dispersion for bands
B and C.
Adjust C137 and L134 for optimum sensitivity and re-
sponse flatness. Adjust C68 on band B RF Mixer, for
optimum sensitivity and bandpass flatness at the high
frequency end (800 MHz) of band B.
Check system flatness as per Table 6-4, 6-5, and instru-
ctions to check band C. System flatness within ± 1.5
6-6
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 ...