DOC 4380A
4380A O & M Manual
59
098-00723-000
– Jul 2017 Revision 4.0
SyncSystem 4380A O&M Manual
The fiber optic outputs from the 4372A/4372A-T module, when plugged into a Master 4380A, contain a
proprietary bit stream with 1 PPS marker and time code information. The Slave 4380A decodes this bit
stream, extracts the time code, and steers its internal OCXO to the frequency and phase of the fiber signal.
When shipped from the factory, the downstream 4380As will automatically switch to input B upon loss of
input A. When Fiber A is restored, the unit will automatically switch back to input A after input A is
detected as good for 60 seconds. The user can select manual switching or disable the automatic return to
input A as a reference after input A has failed. A TSC-4340A fiber optic distribution chassis may be
connected to an output of the 4372A module to provide up to 8 outputs which can be connected to
downstream 4380As.
The 4393A Time Interval Counter (TIC) provides the capability to measure up to four external 1PPS
sources against the internal 1PPS. The measurement data is collected by the unit and provided on telnet
ports 2100 and 2101. Port 2100 is the averaged measurement, where the default is 10 seconds. The
averaging time can be changed to 1, 10, 20 60, or 300 seconds using the
ptdavg
command. Port 2101
provides one second measurement data. The 4393A can be used in any of the slots in the 4380A. Multiple
4393A cards can be installed in the unit when more than four 1PPS measurements are required. Data
collected can be used by an external system to create a paper clock based on the measurements.
4.4 GPS Data Collection
GPS measurement data is available to users in a variety of log formats. The 4380A uses a Novatel OEM6
(dual-frequency and WAAS capable) as its GPS receiver and thus any logs generated by the receiver are
available to users. For a complete description of logs and their formats refer to the OEM6 manual at
Logs on the 4380A are handled in two ways. They are either stored in volatile memory for retrieval by
FTP or they are output to the Ethernet port in real-time. Logs stored in volatile memory are referred to as
ionospheric logs and may be compressed to increase the capacity of the storage area. A total of 16 MB is
dedicated to the storage of ionospheric logs and as storage capacity is approached older logs will be deleted
to make room for newer logs. Real-time logs are logs requested by the user for output to the Ethernet port
on the rear panel of the 4380A. They are provided to the user in a timely manner but are not stored on the
system.
All logs must be enabled at startup through the use of configuration files. Ionospheric logs are specified in
the ftp configuration file and real-time logs are specified in the real-time configuration file. Ionospheric
logs are always generated by the 4380A but the Ethernet port (1135) must be configured at startup in order
to receive the desired real-time logs.
4.5 Startup Sequence
A very specific sequence exists for starting each of the internal devices within the 4380A. This sequence
exists to ensure that the unit generates the appropriate timing outputs and that they are all in sync with each
other. Startup time of the 4380A varies from 5 to 45 minutes depending upon how long the unit has been
powered off but the timing outputs are not enabled until 1 PPS and 10 MHz are accurate.
The 10MHz frequency reference measurements are made on either the internal OCXO, Rb oscillator, or an
external Cs source. In either case the 4380A waits for the frequency reference to indicate that it has
warmed up and is providing a stable signal. The internal Rb is generally warm and operational within 10
minutes but external references may take longer. Once the frequency reference is operational, the front
panel indicator “SYNC” will illuminate green. This indicates that the frequency reference is the 4380A is
locked to the frequency reference and the startup operations will continue.
Once the frequency is locked, the GPS receiver is restarted using the 10 MHz signal as its reference. The
receiver will begin generating the 1 PPS outputs but they will not be aligned to UTC(USNO). A search
algorithm is used by the GPS receiver which attempts to acquire and track the signal received from GPS
satellites. This process usually takes 5 to 10 minutes but may take as long as 30 minutes depending upon
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