from 10 MHz to 12.4 GHz over 50 MHz dispersion on band A
and over 100 MHz dispersion for bands B and C to 12.4
GHz. 6 dB maximum amplitude variation from 12.4 GHz
to 40 GHz, over 100 MHz dispersion.
N O T E
D i s p l a y F l a t n e s s c h e c k f o r b a n d s B a n d C m u s t
be made with the MIXER PEAKING control adjusted
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. Set the front panel controls as follows:
D I S P E R S I O N R A N G E
M H z / D I V
D I S P E R S I O N
5 MHz/div
V E R T I C A L D I S P L A Y
L I N
I F A T T E N U A T O R
20 dB
Band Selector
A
T I M E / D I V
5 ms
c. Apply the output signal from a signal generator with-
in the frequency range of band A through a 20 dB attenu-
ator, (Part No. 011-0086-00) to the band A RF INPUT con-
nector.
d. Set the generator frequency and the RF center fre-
quency to the frequencies that are listed in Table 5-5. Adjust
the signal generator output attenuator and the Type 491
GAIN control for a signal amplitude of 6 divisions.
e. Check band A display flatness by tuning the signal
from the left edge to the right edge of the display screen
with the RF CENTER FREQUENCY control. (Frequency range
+ and - 25 MHz from the RF center frequency.) Signal
amplitude should not change more than ±1.5 dB from its
average amplitude or 3 dB (2.4 div) total.
TABLE 5-5
RF Center
A p p l i e d S i g n a l
Frequency
G e n e r a t o r F r e q .
10 MHz- 60 MHz
35 MHz
50 MHz-100 MHz
75 MHz
100 MHz-150 MHz
125 MHz
150 MHz-200 MHz
175 MHZ
200 MHz-250 MHz
225 MHz
250 MHz-275 MHz
275 MHz
f. Remove the signal to band A, RF INPUT and apply
a signal within the frequency range of band B to RF INPUT
B. Set the band selector to B and set the DISPERSION to
10 MHz/div.
TABLE 5-6
R F C e n t e r
A p p l i e d S i g n a l
Frequency
G e n e r a t o r F r e q .
275 MHz-375 MHz
325 MHz
375 MHz-475 MHz
425 MHz
475 MHz-575 MHz
525 MHz
575 MHz-675 MHz
625 MHz
675 MHz-775 MHz
725 MHz
775 MHz-875 MHz
825 MHz
875 MHz-900 MHz
850 MHz
g. Check display flatness for band B as per Table 5-6.
Maximum amplitude variation over 100 MHz window (± 50
MHz from RF center frequency) must not exceed 3 dB. Ad-
just MIXER PEAKING for maximum signal amplitude before
measuring flatness.
h. Remove the signal from band B INPUT and apply the
output from signal generators, that cover scales 4 through
6 frequency range, to band B Coaxial Mixer.
i. Check response flatness through the frequency range
of the Coaxial Mixer. Maximum amplitude variation over
100 MHx dispersion window must not exceed 3 dB. Adjust
M I X E R P E A K I N G f o r m a x i m u m s i g n a l a m p l i t u d e b e f o r e
measuring flatness.
j. Replace the Coaxial Mixer with the Waveguide Mixer
Adapter.
k. Apply the output from a signal generator, within the
frequency range of scale 8 and 9, through one of the Wave-
guide Mixers and the 2 foot cable (with TNC connectors)
to band C Waveguide Adapter.
l. Check response flatness for the frequency range above
12.4 GHz. Maximum amplitude variation over 100 MHz dis-
persion window must not exceed 6 dB (+2.4 div, -1.3 div).
A d j u s t M I X E R P E A K I N G f o r m a x i m u m s i g n a l a m p l i t u d e
before checking flatness.
m. Remove the Waveguide Adapter and replace the
Coaxial Mixer in the band C receptacle.
24A. Check RF Center Frequency Calibration,
System Sensitivity and Phase Lock Opera-
tion
N O T E
Since signal generators with calibrated attenuators
are required to check sensitivity, dial accuracy can
be checked by the same instruments provided the
s i g n a l s o u r c e h a s a n a c c u r a c y w i t h i n 0 . 1 % a t t h e
d i a l c h e c k p o i n t s . T h e s i g n a l g e n e r a t o r s l i s t e d i n
Table 5-7 may be used if accuracy is checked near
each dial check point, by a frequency counter or
the beat frequency indicator against some accurate
reference frequency.
A secondary or alternate source of accurate fre-
quency markers is the combination of two calibra-
tion fixtures (Harmonic Generator 067-0594-00
a n d a 2 0 0 M H z T r a p 0 6 7 - 0 5 9 5 - 0 0 ) a n d a r e l a -
t i v e l y l o w f r e q u e n c y , a c c u r a t e ( a t l e a s t 0 . 1 % ) ,
s i g n a l s o u r c e s u c h a s a T i m e - M a r k G e n e r a t o r
( T y p e 1 8 4 ) .
T h e h a r m o n i c g e n e r a t a r w i l l p r o d u c e s u f f i c i e n t
harmonic signal power from the Type 184 to pro-
d u c e f r e q u e n c y m a r k e r s i n t o t h e G H z r a n g e . T h e
200 MHz trap attenuates the IF feedthrough spuri-
o u s r e s p o n s e .
This procedure is divided into two steps, with step
24B describing the dial check procedure using the
harmonic generator.
5-10
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 ...