Anritsu 680 C Series, Maintenance Manual

Page: 95 / 317

7. Record the FM sensitivity setting, displayed on
the 691XXB, on the Test Record.
8. Compute the FM accuracy with the following for-
mula:
Accuracy in
FM Sensitivity in kHz
( %)
( )
=
æ
è
ç
ö
ø
÷ ´
240
100
9. The calculated result should be between 93.7%
and 106.3%. Record this result on the Test Re-
cord.
Locked FM Mode
1. Set up the 691XXB as follows:
a. Reset the instrument by pressing SYSTEM ,
then Reset . Upon reset, the CW Menu is dis-
played.
b. Press Edit F1 to open the current frequency
parameter for editing.
c. Set F1 to 5.0 GHz.
2. Set up the Function Generator for a 99.8 kHz
sine wave with an output level of
±
1 volt
(2 volts peak to peak).
3. Set up the Spectrum Analyzer as follows:
a. CF: 5 GHz
b. Span/Div: 200 kHz (2 MHz across the display)
4. On the 691XXB, make the following settings:
a. Press MODULATION , then FM . At the result-
ing External FM Status menu, press More to
go to the additional External FM Status menu.
b. At the additional External FM Status menu,
press Locked , then press Previous Menu to
return to the main External FM Status menu.
c. At the main External FM Status menu, press
Edit Sens and set the sensitivity to
0.240 MHz/V.
d. Press On / Off to turn FM on.
3-34 690XXB/691XXB MM
PERFORMANCE FREQUENCY
VERIFICATION MODULATION TESTS