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’ssetting.
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’ssetting to reduce the
carrier level as low as possible.
f. When finished setting the DAC, press Qon 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’ssetting.
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’ssetting to reduce the
carrier level as low as possible.
f. When finished setting the DAC, press Qon 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
settingon the Spectrum Analyzer in
order to see the >–50 dBc null.
NOTE
You may need to adjust the RBW
settingon the Spectrum Analyzer in
order to see the >–40 dBc null.