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c. On the Spectrum Analyzer, set the Span/Div to
50 kHz 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 an increment key.
e. 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.
f.
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.
g. Record step completion on the Test Record.
4. External Narrow FM Mode Sensitivity calibra-
tion is accomplished by adjusting the FM Vari-
able 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
external Function Generator.
Perform the calibration as follows:
a.
At the
$ prompt, type: calterm 150 and
press <ENTER>.
b. Set up the Function Generator for a 99.8 kHz
sine wave with an output level of 0.707 volts
RMS (2 volts peak to peak). Use a frequency
counter to verify the output frequency of your
function generator is set to ±1%.
c. On the Spectrum Analyzer, set the Span/Div to
50 kHz 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 an increment key.
e. 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.
f.
When finished setting the DAC, press
Q on the
keybaord to go to the next calibration step.
4-54 682XXB/683XXB MM
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.
NOTE
You may need to adjust the RBW
setting on the Spectrum Analyzer in
order to see the >–40 dBc null.