CHAPTER THREE
D. 4> SNR (SIGNAL NOISE DENSITY RATIO)
To request the signal SNR of the satellites currently being “tracked” by the receiver,
press the “4” keyboard switch. The information may take up to ten seconds to be
displayed. Each satellite number and its corresponding signal SNR will be displayed.
The signal SNR is measured at antenna input. Typically it is a number between 30 to 55.
(The larger the number, the better.)
Pressing the MENU key of the keyboard will return the display to the “MAIN MENU
SCREEN.”
E. 5> OFFSET (LOCAL TIME OFFSET SELECTION)
Choice “5>” is the local time offset. This allows the user to input a desired time offset
(in ½ hour increments) whereas the LCD, Optional LED display, and/or time output
would be offset from the selected UTC or GPS time by the number of hours input. All
offset entries are positive (0.00 to 23.5) and are calculated as west of the Greenwich
Meridian.
The current offset will be displayed. Pressing the “5” keyboard switch will allow entry
of the new offset.
Example:
California is eight hours later than GMT. The local time offset entry would be 08.0.
Japan is nine hours earlier than GMT. The local time offset entry would be 15.0.
The calculation for negative local time offsets (for example, nine hours earlier) is as
follows:
(Offset) +24 = entry
(-9) +24 = 15
F. 6> SET DAC
Choice “6>” allows the user to enter a DAC (Digital to Analog Converter) value from
00000 to 65535. This value is a digital representation of the analog voltage (0 to +5
volts) that is used to control the internal oscillator. This feature is especially useful when
attempting to null the oscillator (see Chapter Five).
When keyboard switch 6 is pressed, it allows the user to enter a five digit DAC value, the
midrange being 32767.
3-14 ET6xxx ExacTime GPS TC & FG (Rev C) Symmetricom Inc
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