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When the DAC has been completely adjusted,
the program will exit to the
$ prompt.
g. Record step completion on the Test Record.
5. Internal Narrow FM Mode Sensitivity calibration
is accomplished by adjusting the FM Variable
Gain Control DAC to reduce the carrier level as
low as possible at frequencies of 5 GHz and
20 GHz. The modulating signal input is from the
internal Function Generator.
Perform the calibration as follows:
a.
At the
$ prompt, type: calterm 152 and
press <ENTER>.
b. On the Spectrum Analyzer, set the Span/Div to
50 kHz per division.
c. 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 an increment key.
d. While observing the first Bessel null (Figure
4-16) on the Spectrum Analyzer display, adjust
the value of the DAC’s setting to reduce the
carrier level as low as possible.
e.
When finished setting the DAC, press
Q on the
keyboard to go to the next calibration step.
When the DAC has been completely adjusted,
the program will exit to the
$ prompt.
f. Record step completion on the Test Record.
6. Narrow FM Mode Flatness calibration is accom
-
plished by adjusting the FM Flatness DAC to re
-
duce the carrier level as low as possible for a
sensitivity setting of 2.4 Rad/V at 5 Ghz. The
modulating signal input is from the external
Function Generator.
Perform the calibration as follows:
a.
At the $ prompt, type: calterm 156 and
press <ENTER>.
b. Set up the Function Generator for a 400 Hz
sine wave with an output level of 0.707 volts
RMS (2 volts peak to peak). Use a frequency
counter to verify the output of your function
generator is set to ±1%.
682XXB/683XXB MM 4-55
PHASE MODULATION
CALIBRATION (FM) CALIBRATION
NOTE
You may need to adjust the RBW
setting on the Spectrum Analyzer in
order to see the >–50 dBc null.