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5.8010 The Model 54591 is a track and hold card with a GPS receiver to provide
Stratum 1/PRC (Primary Reference Clock) performance. There are one or two
54591 cards in the Stratum 1/3E or PRC/LNC system. The 54591-2 supports
the AB input architecture (see Appendix A); the AA input architecture is not
supported. In an oversimplified way, the Model 54591 card is a Model 54522
card with a GPS receiver added.
5.81 Functions
5.8110 The Model 54591 clock card performs the following functions:
a. Accepts one GPS reference signal and provides a smoothed and jitter free
signal to the output cards from an ovenized crystal oscillator tracking a
GPS signal. The card also accepts one of two optional 1.544 MHz signals
for a tracking reference if the GPS receiver should fail. Refer to Figure 5-5
for an algorithm tracking the GPS module.
b. If the GPS receiver fails, monitors the DS1/E1 reference signal for framing,
CRC, and out-of-specification errors. An out-of-specification input signal
forces the card to hold to the last known reference, with a drift of less than
5 x 10
-9
in 24 hours. The signal to the output cards is continuous (no
phase hits) during any switch from track to hold. Frequency and phase
corrections occur over periods of about 3000 seconds. A fast ACQUIRE
state reduces this to 100 seconds for power-up and 300 seconds for return
from the HOLD state.
c. Accepts an alternate external 10 MHz signal from a high stability timing
source such as a GPS receiver, cesium clock, or similar mechanism. This
signal may be used to replace the 10 MHz signal reference from the
on-board precision oscillator or as a tracking input. The external 10 MHz
signal is selected as a reference by on-card switches/jumpers. It is
selected as a tracking reference through user commands to the 54550
Information Management Card.
d. Supplies monitoring and alarm information to the 54550 Information
Management Card and 54560 Alarm Interface Card.
e. Facilitates synchronization status messaging per Bellcore GR-378
(DS1/E1 only)
