
CXR Larus 80-100-400
Issue 1, July 2006
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CXR Larus 80-100-400
Issue 1, July 2006 1-14
1.471 If a reference input is lost, the frequency synthesizer continues with the last
known frequency settings and signals the output cards that it is in holdover.
The output cards switch to use the track and hold output that is still tracking.
After a short period of time, the track and hold card will switch to attempt to
acquire the secondary input reference. If the secondary input is within the
pull-in tolerances, the frequency synthesizer will be able to track it and switch
out of holdover mode.
1.472 If both inputs are lost, the track and hold card will stay in holdover mode.
Typical performance is less than one frame slip in 36 hours for the
Stratum 3E/LNC track and hold cards and two months or more for the Stratum
2/TNC track and hold cards.
1.48
There is also a free running mode where the frequency synthesizer runs at its
nominal center frequency. The track and hold cards will automatically enter the
free run condition after a prescribed time without a suitable input reference.
The oscillators can also be put in free run for testing. If both cards fail, the
system will use either input (if good) to drive the outputs directly. If both track
and hold cards and both inputs fail, all outputs are suppressed.
1.5 Features
1.51
Unless otherwise stated, the features listed below apply to all versions of the
StarClock 200E system:
a. Outputs: redundant T1 or E1 framed all ones; 8 kHz, 1.544 MHz, or 2.048
MHz square wave; or 64/8 kHz composite clock, time of day, or 5/10 MHz
synchronized to a framed DS1, E1, or 10 MHz reference source.
b. Hitless switching: from primary to secondary track and hold card in the
event of an input reference failure, to assure that all outputs are driven by a
track and hold card tracking a valid signal.
NOTE:
Refer to the description of phase alignment in Appendix B.
c. Output frequency: held to less than four DS1 frame slips in the first 24
hours, worst case, for Stratum 3E in the event that both inputs fail (HOLD
state). For Stratum 2, the time to the first frame slip is about seven days.
For LNC, output frequency is held to less than 5.3 E1 frame slips in the first
14.8 hours, worst case. For TNC, time to first frame slip is about 28 hours.
For Stratum 1 and PRC it is more than 70 days.
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