CHAPTER THREE
• If the unit stops tracking satellites at any point after initial power-up, the TRACKING LED
will be turned off. At that time, an internal elapsed time counter will be started and the short
term oscillator stability will be stored in memory. Based upon the type of internal 10MHz
oscillator installed in the unit, the LOCKED LED will remain illuminated until the internal
elapsed time counter has timed out.
For a TCXO oscillator, it will take about 30 minutes.
For a OCXO oscillator, it will take about 60 minutes.
For a Rubidium oscillator, it will take about 4 hours.
3.2 OPERATIONAL CHARACTERISTICS
The standard internal time base is a voltage controlled temperature compensated 10MHz crystal
oscillator. When the disciplining feature is ENABLED, its frequency is controlled/corrected to
the internal GPS 1pps using a DAC (Digital to Analog Converter). Disciplining of the oscillator
occurs only when it is ENABLED and used as the unit’s time base, and when the GPS ExacTime
is actively tracking a satellite. During periods when there are no satellites in view or when the
unit isn’t tracking, the last DAC value is retained, and the unit continues to operate normally.
The outputs are then as accurate as the drift/aging rate of the oscillator. See Chapter Four,
paragraphs titled “Enable Disciplining,” and “Disable Disciplining” in this User’s Guide for
enabling and disabling disciplining.
Disciplining is ENABLED by default when the unit is powered.
3.3 LIQUID CRYSTAL DISPLAY
The front panel LCD Display contains two rows of forty characters per row. It displays at least
ten separate MENU screens that are changed by pushing the front panel MENU keyboard
switch.
3.3.1 MAIN MENU SCREEN
When power is first applied to the TC&FG, the LCD displays an Initial Menu Screen that
contains the unit’s ID followed by four digits that correspond to the serial number of the unit.
After approximately 5 seconds, the display then switches to the Main Menu Screen.
3-4 ET6xxx ExacTime GPS TC & FG (Rev C) Symmetricom Inc
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