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e. Press More to go to the additional Internal
Pulse Status Menu display.
g. Press Internal/External to select the external
source for the modulation signal. The External
Pulse Status Menu is displayed.
h.
Press Front/Rear to select the rear panel
PULSE TRIGGER IN connector.
i.
Press On/Off to turn pulse modulation on.
2. Set up the Spectrum Analyzer as follows:
a. CF: Same as the 682XXB/683XXB CW fre
-
quency noted in step 1.c.
b. Span/Div: 10 kHz
c. RBW: 1 kHz
d. Video Filter: Wide
e. MIN Noise: Activated
f. Reference Level: Adjust to place the signal at
the top graticule of the screen.
3. Connect a short between the 682XXB/683XXB
rear panel PULSE TRIGGER IN BNC connector
center and outer conductors.
4. On the Spectrum Analyzer, decrease the Refer-
ence Level by 20 dB, then measure the signal am
-
plitude and record it on the Test Record. The
measured signal must be ³60 dB from the top
graticule.
NOTE
A 60 dB level change plus a 20 dB decrease
in the reference level equals an 80 dB on/off
ratio (specification).
5. If the signal level drifts slowly after connecting
the short, remove the short momentarily and ap
-
ply it again. (Make the measurement as soon as
possible after applying the short.) This drift is the
result of the Sample/Hold circuit not holding the
level because of the pulse duty factor (ratio of RF
ON to RF OFF). This drift will not be present in
normal pulse operation as the minimum pulse
repetition rate is 0.597 Hz.
6. Remove the short.
3-46 682XXB/683XXB MM
PERFORMANCE PULSE MODULATION TEST:
VERIFICATION RF ON/OFF RATIO