QUESTION:
Is a Rubidium atomic reference suitable for a SDH network to be a PRC?
ANSWER:
A Rubidium atomic standard is considered a "secondary atomic standard" because a free-running Rubidium oscillator by itself does not meet the guaranteed frequency accuracy criteria of a Primary Reference Clock (PRC) as stipulated. The Rubidium standard is extremely stable but its free-running accuracy is likely to be (better than) 1 part in 10E9 whereas a PRC requires an accuracy of 1 part in 10E11. A Cesium atomic clock can provide the PRC level accuracy in "free-running" mode. For a Rubidium unit to have 1-part-in-10E11 accuracy it needs a disciplining source, the most common choice being GPS.
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