Anritsu 680 C Series, Maintenance Manual

Page: 133 / 317

3. FM Wide Mode Sensitivity calibration is accom-
plished by adjusting the FM Gain Control DAC to
obtain 200 MHz and 20 MHz FM deviations at
frequencies of 5 GHz and 15 GHz. Modulating
signal inputs are from the external Function Gen-
erator.
Perform the calibration as follows:
a. At the
$
prompt, type:
calterm 124
and
press <ENTER>.
b. Set up the Function Generator for a 0.4 Hz
square wave with an output level of 2 volts
peak to peak.
c. On the Spectrum Analyzer, set the Span/Div to
50 MHz per division.
d. On the computer keyboard, use the `, 1, 2, and
3 keys to increment and the 7, 8, 9, and 0 keys
to decrement the value of the DAC's setting.
Start calibration by pressing the ` key.
e. While observing the Spectrum Analyzer dis-
play, adjust the value of the DAC's setting to
obtain a 200 MHz peak to peak deviation. This
is the coarse adjustment.
f. On the Spectrum Analyzer, set the Span/Div to
5 MHz per division and adjust the center fre-
quency control to position the low carrier at
the center of the display. Note the frequency
reading.
g. Now, adjust the center frequency control to po-
sition the high carrier at the center of the dis-
play. Note the frequency reading.
h. The difference between these two frequencies
is the actual peak-to-peak frequency deviation.
It should be 200 MHz
±
8 MHz. If not, fine ad-
just the value of the DAC's setting to obtain
this deviation.
i. When finished setting the DAC, press
Q
on the
keyboard to go to the next calibration step (ad-
justing the DAC to obtain 20 MHz deviation).
j. Start calibration by pressing the
1
key.
k. While observing the Spectrum Analyzer dis-
play, adjust the value of the DAC's setting to
obtain a 20 MHz peak to peak deviation. This
is the coarse adjustment.
4-36 690XXB/691XXB MM
FM
CALIBRATION CALIBRATION