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4. Internal Unlocked Wide FM Mode Sensitivity
calibration is accomplished by adjusting the FM
Variable Gain Control DAC to obtain a 200 MHz
FM deviation at frequencies of 5 GHz and
15 GHz. The modulating signal input is from the
internal Function Generator.
Perform the calibration as follows:
a.
At the
$ prompt, type: calterm 143 and
press <ENTER>.
The screen will display the following menu:
1) Toggle polarity (this lets you go from a
positive deviation to negative deviation.)
2) Change DAC value.
3) Quit.
b. On the Spectrum Analyzer, set the Span/Div to
50 MHz per division.
c.
On the computer keyboard, enter
2 to begin
calibration.
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 100 MHz change in frequency.
f.
On the keyboard, press
Q to return to the
menu, then enter
1 to toggle the polarity.
g. Measure the change in frequency on the Spec
-
trum Analyzer. The change in frequency
should be 200 MHz. If not, enter
2 and adjust
the DAC.
h. Repeat steps 4.f and 4.g as necessary to obtain
a 200 MHz frequency change. When finished
adjusting the DAC, press
Q to return to the
menu.
i. On the Spectrum Analyzer, set the Span/Div to
5 MHz per division and adjust the center fre
-
quency control to position the high (or low)
carrier at the center of the display. Note the
frequency reading.
j.
On the keyboard, enter
1 to toggle the polarity.
682XXB/683XXB MM 4-47
FM
CALIBRATION CALIBRATION