14. Check Dispersion Accuracy of kHz/div
Requirement: Dispersion accuracy. within 3% over + and
a. Apply 10 ns and 1 s 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/
The marker signals may also be aplied through a
20 dB attenuator, a BNC to TNC adapter and the
Wavequide Mixer Adapter to band C RF INPUT.
(This bypasses the 1st mixer.)
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 s) 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 s (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 s
markers to the RF INPUT.
f. Check-the dispersion accuracy at each DISPERSION
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
tO the dial reading noted in step b at 2.5 MHz and recheck
Fig. 5-4. Display
pattern when resolution