Managing The Oscillator - Spectracom SecureSync 1200 User Reference Manual

3.5 Managing the Oscillator
synchronized state. See "The "User/User" Reference" on page 161 and "Manually Setting the
Time" on page 144 for more information.
3.5

Managing the Oscillator

The purpose of the built-in oscillator is to provide SecureSync with an accurate and very stable
frequency source. This allows SecureSync to go into a holdover mode in the event that external
time or frequency references are lost or become invalid. However, the oscillator can also be
used as a legitimate 1PPS reference during normal operation, in conjunction with an external
time reference (for more information, see "Configuring Input Reference Priorities" on
page 157.)
SecureSync's internal oscillator is normally disciplined to an input reference (such as GNSS,
IRIG input, 1PPS input, etc.) in order to provide the highest degree of oscillator accuracy and
to account for oscillator drift. While disciplining (with a 1PPS input reference input present and
valid), the oscillator's output frequency is monitored and based on the measured frequency, the
oscillator is steered to maintain a very accurate 10 MHz output. If no valid 1PPS input ref
erences are present (or input references are present but not considered valid), the oscillator will
be in Freerun mode instead.
If no external input reference such as GNSS, IRIG, etc. is available (or is temporarily lost),
SecureSync may become an NTP Stratum 2 or higher reference. If so configured, SecureSync
can use a reference such as an NTP daemon, or TimeKeeper, referred to as a Host Reference .
If the Host Reference becomes active, it will automatically take over the disciplining of the oscil
lator. This built-in functionality is referred to as Host Disciplining .
Figure 3-2:
Host disciplining
CHAPTER •
3 SecureSync User Reference Guide Rev. 23
194