OPTION DESCRIPTIONS
1. Turn on the unit and wait approximately one hour for the oscillator to warm up and stabilize.
2. Sync one trace of an oscilloscope on the known frequency standard. Using the other trace,
monitor the 10MHz output of the unit.
3. The input of the DAC must be held static prior to nulling the oscillator. This can be
accomplished one of three ways:
• Disconnect the antenna input from the rear of the unit.
• Select the single satellite mode (1SV), and select a satellite that is not in view (or pick
SV33 which doesn’t exist).
• Disable disciplining, refer to Chapter Four, “Disable Disciplining” in the User’s
Guide.
4. Set the DAC value to it’s midpoint 32767. Refer to Chapter Four, “Enter DAC Value” in the
User’s Guide.
5. Adjust the oscillator until the 10MHz output is stable with respect to the frequency standard.
6. Reinstall the screw. Enable disciplining. Refer to Chapter Four, “Enable Disciplining” in
the User’s Guide.
7. After approximately one hour, check the DAC value number again. If it has changed by
more than ±5000 from 32767, repeat steps two through six.
1.3 CALIBRATION - SECOND METHOD
If a known frequency standard is not available, the oscillator may be nulled as follows:
1. Set the unit to operate in the single satellite (1SV) mode. Make sure the unit is tracking a
satellite.
2. Read the DAC value either from the RS-232 I/O port, or from the LCD display.
3. The oscillator is located on the GPS Main Assembly 35002 in location Y1. Remove the
oscillator adjustment access screw to provide access to the oscillator adjustment.
4. SLOWLY (no more than 45
o
each time) adjust the oscillator and watch the DAC value
change. If the DAC value is 65535, turn the oscillator adjustment counterclockwise which
will decrease the frequency and the DAC value. If the DAC value is 00000, turn the
oscillator adjustment clockwise which will increase the frequency and the DAC value.
Symmetricom Inc ET6xxx ExacTime GPS TC & FG (Rev C) C-29
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