Holdover Mode - Spectracom SecureSync 1200 User Reference Manual

3.4 Holdover Mode
Use Current System Time
Apply SecureSync's currently used system time to the GNSS receiver.
Set System Time
Enter a specific date and time, instead of the system time. This may be useful if the system time is
known to be incorrect, or if you need a time in the past or future, e.g. for simulation purposes.
Enter the date and time using the displayed calendar and time sliders.
Manual Position Set
By accurately entering latitude , longitude (both in decimal degrees), and altitude (in meters,
WGS 84) of your antenna, SecureSync can use this data during the satellite track
ing/adjustment process, which typically leads to a quicker "fix". It is recommended to enter the
position as accurately as possible. For more information, see "Manually Setting the GNSS Pos
ition" on page 181.
3.4

Holdover Mode

When input references have been supplying input to SecureSync and input from all the ref
erences has been lost, SecureSync will not immediately declare loss of time synchronization,
but first will go into Holdover mode. While the unit is in Holdover mode, the time outputs are
derived from the internal 10 MHz oscillator incrementing the System Time, but the oscillator is
not disciplined/steered by the external reference e.g., GNSS.
Because of the stability of the internal oscillator, accurate time can still be derived even after all
the primary references are no longer valid or present. The more stable the oscillator is without
an external reference, the longer this holdover period can be and have it still maintain very
accurate outputs. The benefit of Holdover is that time synchronization and the availability of the
time outputs is not immediately lost when input references are no longer available.
While SecureSync is in Holdover, the only difference is the Holdover and associated Minor
alarm are asserted. There are no changes to NTP or any of the other outputs, i.e. while in Hol
dover mode, NTP inside SecureSync continues to be at the same Stratum level it was at before
going into Holdover mode (such as Stratum 1 when synced to GPS). Should the Holdover
period expire, however, or the unit is rebooted, the NTP Stratum will go to 16, preventing any
clients from being able to sync with SecureSync until GPS or another reference has been
restored.
How long will the unit remain in Holdover mode?
190
Note: When manually setting a position, SecureSync must be in one of the sta
tionary modes, Standard or Single Satellite (see "Receiver Mode" above).
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3 SecureSync User Reference Guide Rev. 23