35. Check Incidental Frequency Modulation
e. Adjust the GAIN control for an 8 division signal
amplitude.
NOTE
f. Check the display frequency modulation (see Fig. 6-37).
Must not exceed 1 minor division ( ≤ 2 0 0 H z ) .
Signal source must supply a very stable 200 MHz
g. Change the DISPERSION to 100 kHz/div and move the
signal to accurately measure incidental FM and
IF feedthrough signal off screen with the IF CENTER FRE-
the Type 491 must be on a vibration-free platform.
QUENCY control. Center the tunable 200 MHz signal on
screen with the RF CENTER FREQUENCY controls.
a. Equipment setup is given in step 34.
h. Turn the INT REF FREQ on and phase lock the display.
b. Set the DISPERSION RANGE switch to kHz/DIV and
See Operating Instructions.
the DISPERSION to 500 kHz/div. Set the TIME/DIV to .1 s.
i. Decrease the DISPERSION to 1 kHz/div, keeping the
phase locked signal on screen with the IF CENTER FREQ
c. Apply a 200 MHz signal from the Time-Mark Generator
controls.
through a 20 dB attenuator to band A RF INPUT connector
and center the IF feedthrough signal on screen.
j. Check the frequency modulation of the display. Must
not exceed 1.5 minor divisions (300 Hz).
d. Change the DISPERSION-COUPLED RESOLUTION to
k. Return the DISPERSION-COUPLED RESOLUTION con-
1 kHz/div, adjusting the IF CENTER FREQ control to keep
the signal centered on screen.
trols to 500 kHz/div.
