Anritsu 682XXB, 683XXB 4-52 682XXB/683XXB MM

4. Connect the 682XXB/683XXB RF OUTPUT to the
Spectrum Analyzer RF Input.
NOTE
Before beginning this calibration proce-
dure, always let the 682XXB/683XXB
warm up for a minimum of one hour.
FM
Calibration
Procedure
The following steps in the procedure lets you cali-
brate the FM VariableGain Control DAC and the
FM Flatness DAC in both Wideand Narrow FM
modes and store the results in non-volatile memory
(EEPROM) on the A17 CPU PCB.
NOTE
Toensure accurate calibration, each step of
this procedure must be performed in se-
quence.
1. External WideFM Mode Sensitivity calibration is
accomplished by adjusting the FM VariableGain
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 149 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
keyboard to go to the next calibration step.
4-52 682XXB/683XXB MM
PHASE MODULATION
CALIBRATION (FM) CALIBRATION
CENTER FREQUENCY
BESSEL
NULL
Figure 4-16. TypicalSpectrum Analyzer Display
of Bessel Null on M Waveform
NOTE
You may need to adjust the RBW
settingon the Spectrum Analyzer in
order to see the >–40 dBc null.