Managing The Oscillator - Spectracom PRISMA VelaSync User Manual

3.4 Managing the Oscillator
need to be set manually again in order for VelaSync to return to its fully synchronized state.
See "The "User/User" Reference" on page 108 and "Manually Setting the Time" on page 92
for more information.
3.4

Managing the Oscillator

The purpose of the built-in oscillator is to provide VelaSync with an accurate and very stable
internal frequency source. This allows VelaSync 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 105.)
VelaSync'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),
VelaSync may become an NTP Stratum 2 or higher reference. If so configured, VelaSync can
use a reference such as an NTP daemon, referred to as a Host Reference . If the Host Reference
becomes active, it will automatically take over the disciplining of the oscillator. This built-in func-
tionality is referred to as Host Disciplining .
Figure 3-2:
Host disciplining
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