Tektronix 491, Руководство по обслуживанию

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TABLE 5-2
F i g . 5 - 4 . D i s p l a y p a t t e r n w h e n r e s o l u t i o n i s c o r r e c t l y a d j u s t e d .
5 - 6
14. Check Dispersion Accuracy of kHz/div
Selections
Requirement: Dispersion accuracy. within 3% over + and
- 2.5 MHz range of the IF CENTER FREQUENCY.
a. Apply 10 ns and 1 µs markers from the Time-Mark
Generator through a 20 dB attenuator to band A, RF INPUT,
Set the band selector to A, and the DISPERSION to 500 kHz/
div.
N O T E
T h e m a r k e r s i g n a l s m a y a l s o b e a p l i e d t h r o u g h a
20 dB attenuator, a BNC to TNC adapter and the
W a v e q u i d e M i x e r A d a p t e r t o b a n d C R F I N P U T .
( T h i s b y p a s s e s t h e 1 s t m i x e r . )
b. Check-the range of the IF CENTER FREQ control by
rotating the control to the limit each side of center. Count
the number of 1 MHz (1 µs) markers from the IF feedthrough
signal. Must equal or exceed 2.5 MHz, Note the dial read-
ing when the control is 2.5 MHz from center. This reading
will be referred to later in the procedure.
c. Center the IF CENTER FREQ controls and change the
DISPERSION to 50 kHz/div. Apply 10 ns and 10 µs (100 kHz
markers) to the Type 491 RF INPUT.
d. Check-the range of the IF CENTER FREQ-FINE control.
Must equal or exceed 50 kHz either side of center.
e. Center the
IF CENTER FREQ
controls, change the DIS-
PERSION to 50 kHz/div and again apply 10 ns and 1 µs
markers to the RF INPUT.
f. Check-the dispersion accuracy at each DISPERSION
selector position listed in Table 5-3.
Measure dispersion within the center 8 div of the display
for each selector position and over the + and – 2.5 MHz
range of the IF center frequency. Check accuracy with the
IF CENTER FREQ control centered then rotate the control
t
O
the dial reading noted in step b at 2.5 MHz and recheck
dispersion accuracy.