3-16 REFERENCE
OSCILLATOR
CALIBRATION
The reference oscillator calibration function lets you calibrate the
internal 100 MHz crystal reference oscillator of the 681XXC using an
external 10 MHz, 0 to +10 dBm reference signal.
NOTE
Before beginning calibration, always let
the 681XXC warm up for a minimum of
120 hours.
Toperform calibration of the internal reference os-
cillator,first connect the external 10 MHz reference
signal to the 681XXC rear panel 10 MHz REF IN con-
nector.
Next, press the SYSTEM main menu key.At the
System Menu display,press Cal Menu to go to the
Calibration Menu (below).
Press Refrnce Cal to begin calibration.
Press Previous Menu to return to the System Menu
display.
When Refrnce Cal is pressed, the Calibration
Status Menu (below) is displayed.
Press Proceed to start the calibration.
Press Abort to cancel the calibration and return to
the Calibration Menu display.
3-92 681XXC OM
LOCAL (FRONT REFERENCE
PANEL) OPERATION OSCILLATOR CALIBRATION
NOTE
Thiscalibration is not applicable to
units having Option16, High Sta-
bility Time Base, installed.