In Unlocked Wide mode, frequency modulation is ac-
complished by applying the modulating signal to
the main tuning coil of the YIG-tuned oscillator. Un-
locked Wide FM mode allows maximum deviations
of
±
100 MHz for DC to 100 Hz rates.
Providing
Frequency
Modulation
To provide frequency modulation, first set up the ex-
ternal signal generator, then connect it to either the
681XXB front or rear panel
FM IN
connector.
Next, press
MODULATION
. At the resulting menu
display, press
FM
. The External FM Status Menu
(below) is displayed.
Now, press the menu soft-key
More
. The additional
External FM Status Menu (below) is displayed.
This menu lets you select the FM operating mode.
Press
Locked
to select the Locked FM operating
mode; press
Unlocked Narrow
to select the Un-
locked Narrow FM operating mode; or press
Unlocked Wide
to select the Unlocked Wide FM
operating mode. The FM status display will reflect
your selection.
Press
Previous Menu
to return to the main Exter-
nal FM Status Menu display (next page).
LOCAL (FRONT
SIGNAL
PANEL) OPERATION
MODULATION
UNLOCKED
When Unlocked Narrow FM or Un-
locked Wide FM is selected ON, this
warning message is displayed on all
menu displays to remind the opera-
tor that the carrier frequency is not
phase-locked.
681XXB OM
3-63
