Tektronix 491, Maintenance Manual

Page: 108 / 226

Fig. 6-19. Test equipment setup to adjust and check dispersion accuracy.
Type 491
I N T E N S I T Y
F O C U S a n d A S T I G M A T I S M
I N T E N S I F I E R
SCALE ILLUM
POSITION (Horizontal and
Vertical)
T I M E / D I V
VARIABLE
T R I G G E R
SLOPE
LEVEL
S O U R C E
D I S P E R S I O N R A N G 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
D I S P E R S I O N C A L
D I S P E R S I O N B A L
I F A T T E N U A T O R d B
I F C E N T E R F R E Q
V I D E O F I L T E R
V E R T I C A L D I S P L A Y
G A I N
P O W E R
M I X E R P E A K I N G
Display of nominal
brightness
Adjusted for optimum
display definition
O F F
As desired
Adjusted for a
horizontally centered
sweep on the graticule
baseline
20 ms
CAL
+
Triggered sweep
L I N E
M H z / D I V
1 0 M H z / d i v
M i d r a n g e
M i d r a n g e
All switches in off position
Midrange (000)
O F F
L I N
Midrange
O N
S E A R C H
F I N E R F C E N T E R F R E Q Centered
PHASE LOCK Controls
I N T R E F F R E Q
O F F
Test Oscilloscope
Time/Cm
1 ms
V o l t s / C m . 5
I n p u t C o u p l i n g A C
2 1 . A d j u s t M H z / D I V D i s p e r s i o n a n d
o
Linearity
N O T E
Dispersion accuracy is a measure of the frequency
d i s p e r s i o n e r r o r w i t h i n 8 d i v i s i o n s o f a 1 0 d i v i s i o n
d i s p l a y . I t i s m e a s u r e d b y p o s i t i o n i n g t h e 1 s t f r e -
quency marker on the 1st graticule line, then not-
i n g t h e d i s p e r s i o n e r r o r a s t h e d i s t a n c e t h e 9 t h
m a r k e r i s d i s p l a c e d f r o m t h e 9 t h g r a t i c u l e l i n e .
S e e F i g . 6 - 2 0 .
Linearity error is the measured distance any mark-
e r i s d i s p l a c e d f r o m i t s r e s p e c t i v e g r a t i c u l e l i n e
when compared over an 8 major division display.
S e e F i g . 6 - 2 1 .
D i s p e r s i o n a c c u r a c y a n d t h e d i s p l a y l i n e a r i t y a r e
affected by the RF output amplitude, circuit con-
s t a n t s , e t c . D I S P E R S I O N C A L a d j u s t m e n t R 2 0 8 p r i -
m a r i l y a f f e c t s t h e d i s p e r s i o n a c c u r a c y a n d C 3 5 8
t h e l i n e a r i t y . I f t h e s e t w o a d j u s t m e n t s w i l l n o t
6 - 2 0