EndRun Meridian II, User Manual

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M e r i d i a n I I U s e r M a n u a l 122
C H A P T E R T E N
123 M e r i d i a n I I U s e r M a n u a l
R E A R - P A N E L I / O
5071A Cesium Control Module
The 5071A Cesium Control Module allows you to discipline the frequency of a 5071A Primary
Frequency Standard to either the UTC(USNO) or GPS timescale via the Meridian II GPS Timebase.
(To view or change the timescale, see Chapter 3 - Control and Status Commands, systimemode and
systimemodeconfig .) In so doing, you can realize the extraordinary short to medium-term stability of
the 5071A while also maintaining strict, long term adherence to the selected timescale. The disciplin-
ing algorithm is optimized to preserve the stability of the 5071A for observation intervals less than
the Allan deviation crossover point. This crossover point is the observation interval at which the
Meridian II GPS receiver accuracy and stability become superior to the 5071A relative to the selected
timescale. Past the crossover point, the 5071A is disciplined with a 3
rd
order phaselock algorithm
to agree with the Meridian II’s idea of UTC(USNO) or GPS time. Before the crossover point, the
5071A is essentially free-running, as its stability is superior to that of the Meridian II.
This module resides in Slots 1 and 2. It is not field-upgradeable. The rear-panel outputs are labeled
with their configured frequency which may be a combination of 1, 5 or 10 MHz sine waves, all
derived from the 5071A 10 MHz signal. These frequencies are not changeable but can be viewed via
the front-panel display by navigating to Main Menu > Option I/O > OptCard1. You can also view
the Low Phase Noise output configuration via the network or serial ports by using console command
pluginopts
(see Chapter 3 - Console Port Control & Status ). For signal definition see Appendix
K - Specifications, Optional 5071A Cesium Control Module .
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The module’s DB9M connector and provided cable allow the RS-232 serial port of the 5071A to be
connected to the Meridian II for bi-directional data communication. The module’s BNC input con-
nector and coaxial cable allow the 10 MHz output signal from Port 1 on the 5071A to be connected to
the Meridian II. The 5071A 10 MHz signal then becomes the reference for all frequency and timing
signals within the Meridian II, in the same way that the other optional oscillators (OCXO, Rubidium,
etc.) operate.
The Meridian II sends commands to the 5071A to steer its frequency, monitor its health and set the
time-of-day clock on its front panel. The 5071A Operation Status and Questionable Data registers
are monitored to determine the overall functional state of the 5071A, and critical 5071A internal
diagnostic parameters are also monitored. All of this information is reported via the various Merid-
ian II user interfaces: CLI, SNMP, HTTP and (except for the Tycho II) the front panel display. All
cesium atomic frequency standards have definite wear-out mechanisms, so monitoring these critical
parameters is recommended, as they can give some advance notice of an impending cesium beam
tube failure.
5071A CESIUM CONTROL
MODULE WITH 10 MHz