For more information on the TFOM value and Phase Error Limit, see "Configuring the
Oscillator" on page172.
Note: Changes made to the Holdover Timeout always take effect immediately. If
VersaSync is in Holdover and the Holdover timeout is changed to a value that is
less than the current time period that VersaSync has been in Holdover Mode, the
unit will immediately declare loss of synchronization.
What is the recommended setting for the Holdover Timeout period?
The factory default Holdover period is 2 hours (7200 seconds). The value can be increased to
up to 5 years. During this time period, VersaSync will be useable by its NTP clients (or other
consumers) after GNSS reception has been lost.
The length of time is really based on the type of oscillator installed in a unit, and what the typ-
ical accuracy requirements are for the NTP clients. The longer it can run in Holdover mode
before it expires, the longer it can continue being a central time source for all of its clients. But
the longer VersaSync runs in Holdover, the larger the offset to true UTC time will become,
because the undisciplined oscillator will drift over time:
The better the type of oscillator installed, the more stable it is while in Holdover and therefore,
the less its time will drift away from true UTC time. This results in more accurate timing, over
extended durations upon the loss of GPS input. For instance, a Rubidium oscillator will main-
tain significantly better time over a longer Holdover duration than a TCXO oscillator (TCXOs
are considerably less stable than a Rb oscillator).
3.3 Managing References
CHAPTER 3 • VersaSync User Manual Rev. 6.0
169
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