d. Adjust the GAIN control clockwise until the signal
amplitude is again 8 divisions. This checks that the range
of the control equals or exceeds 50 dB.
20. Check INTENSIFIER Control Range
a . R e q u i r e m e n t - W i t h t h e c o n t r o l i n t h e O F F p o s i t i o n
(fully counterclockwise) the display, plus the baseline, must
be intensified. With the control fully on, the baseline plus
approximately 30% of the signal should be suppressed.
b . C h a n g e t h e D I S P E R S I O N t o 1 0 0 k H z / d i v . U n c o u p l e
the RESOLUTION control and turn the control fully clock-
wise.
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 ,
then adjust the GAIN control and/or the Signal Generator
output for a signal display amplitude of 8 divisions.
d . T u r n t h e I N T E N S I F I E R c o n t r o l t o t h e O F F p o s i t i o n ,
adjust the INTENSITY control for a display of nominal bright-
ness. Set the CONTRAST to midrange. Note that the entire
display is intensified.
e. Turn the INTENSIFIER control full on or clockwise.
Fig. 5-6. Typical display showing incidental frequency modulation.
M e a s u r e t h e h o r i z o n t a l d i s p l a c e m e n t o f t h e s i g n a l a t t h e m o s t
vertical slope of the signal.
f. Check-The remaining intensified portion of the signal
should measure between 3 and 5 divisions.
21. Check Signal Amplitude at the TO
RECORDER Connector
a. Requirement-Signal amplitude at the TO RECORDER
output connector should equal or exceed 4 mV per division
of displayed signal amplitude when terminated into a 600
ohm load.
b. Set the VERTICAL DISPLAY switch to LIN, adjust the
Signal Generator output and the Type 491 GAIN control
for a signal amplitude of 6 divisions.
c. Connect the TO RECORDER connector on the back
panel to the Vertical Input of a test oscilloscope through
a
1×
probe. Terminate the connector into a 600
Ω
load by
connecting a 600
Ω
resistor from the TO RECORDER jack
to chassis ground.
d. Check-Signal amplitude at the TO RECORDER con-
nector should equal or exceed 24 mV
(≥4
mV/div).
22. Check Incidental Frequency Modulation
a . R e q u i r e m e n t - W i t h t h e D I S P E R S I O N R A N G E a t k H z /
DIV the IF incidental FM should not exceed 200 Hz. The
incidental FM of the local oscillator plus the IF with phase
lock must not exceed 300 Hz.
N O T E
S i g n a l s o u r c e m u s t s u p p l y a v e r y s t a b l e s i g n a l
t o a c c u r a t e l y m e a s u r e t h i s p e r f o r m a n c e a n d t h e
Type 491 must be on a stable, vibration-free plat-
form.
I n c i d e n t a l F M m e a s u r e m e n t s f o r b a n d s B
and C must be performed with the MIXER PEAKING
a d j u s t e d t o m a x i m i z e s i g n a l a m p l i t u d e f o r e a c h
d i s p l a y w i n d o w .
b . S e t t h e D I S P E R S I O N R A N G E s w i t c h t o k H z / D I V a n d
the DISPERSION to 500 kHz/div. Set the TIME/DIV to .1 s.
c . A p p l y a 2 0 0 M H z s i g n a l f r o m t h e T i m e - M a r k G e n -
erator through a 20 dB attenuator to band A RF INPUT
connector and center the IF feed-through signal on screen.
d . C h a n g e t h e D I S P E R S I O N - C O U P L E D R E S O L U T I O N t o
1 kHz/div, adjusting the IF CENTER FREQ control to keep
the signal centered on screen.
e. Adjust the GAIN control for an 8 division signal ampli-
tude,
f. Check the amount of signal frequency modulation (see
F i g . 5 - 6 ) . M u s t n o t e x c e e d 1 m i n o r d i v i s i o n .
( ≤ 2 0 0
H z ) .
g . C h a n g e t h e D I S P E R S I O N t o 1 0 0 k H z / d i v a n d m o v e
the IF feedthrough signal off screen with the IF CENTER
FREQUENCY control. Center a tunable 200 MHz signal an
screen with the RF CENTER FREQUENCY controls. Adjust the
MIXER PEAKING control for maximum signal amplitude.
h. Turn the INT REF FREQ on and phase lock the dis-
play. See operating instructions.
i. Decrease the DISPERSION to 1 kHz/div, keeping the
phase locked signal on screen with the IF CENTER FREQ
controls.
j. Check the amount of frequency modulation in the dis-
play. Must not exceed 1.5 minor divisions (300 Hz).
k . R e t u r n t h e D I S P E R S I O N - C O U P L E D R E S O L U T I O N c o n -
trols to 500 kHz/div.
23. Check Display Flatness
a. Requirement-Display flatness with
controls centered,
is 3 dB maximum
the IF CENTER FREQ
amplitude variation
5-9
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 ...