3. External Unlocked WideFM Mode Sensitivity
calibration is accomplished by adjusting the FM
VariableGain Control DAC to obtain a 200 MHz
FM deviation at frequencies of 5 GHz and
15 GHz. The modulating signal input is from the
external Function Generator.
Perform the calibration as follows:
a. At the $prompt, type: calterm 124 and
press <ENTER>.
b. Set up the Function Generator for a 0.1 Hz
square wave with an output level of ±1 volt
±0.002 volts (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’ssetting.
Start calibration by pressing the ‘key.
e. While observing the Spectum Analyzer display,
adjust the value of the DAC’ssetting 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 ±0.5 MHz. If not, fine ad-
just the value of the DAC’ssetting to obtain
this deviation.
i. When finished setting the DAC, press Qon the
keyboard to go to the next calibration step (ad-
justing the DAC to obtain a 200 MHz deviation
at 15 GHz).
When the DAC has been completely adjusted,
the program will exit to the $prompt.
j. Record step completion on the TestRecord.
4-46 682XXB/683XXB MM
FM
CALIBRATION CALIBRATION