DOC 4380A
4380A O & M Manual
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098-00723-000– Jul 2017 Revision 4.0 SyncSystem 4380A O&M Manual
how long the 4380A has been powered off. After four satellites are being tracked by the GPS receiver, the
PPS output is adjusted so that it is aligned with UTC(USNO). The green “SYNC” light on the front panel
will also illuminate to indicate to the user that the system is currently tracking the GPS signal.
To serve as a Stratum-1 network time protocol (NTP) server requires that the system’s CPU clock be
aligned with UTC(USNO). The process of locking the CPU clock to UTC(USNO) requires setting the
system time to UTC(USNO) and using the PPS received from the GPS receiver to continuously steer the
CPU clock. If the unit has been powered off for a long period of time the CPU time may be multiple
seconds off. In these cases, a coarse adjustment of system time is performed and then the startup sequence
is restarted. This process should only happen once and only in cases where the system has been powered
off.
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