[evlatests] Results from Reference standard switch test

[Keith Morris]

Today we conducted a test of the Master LO system in which we switched 
from the Hydrogen maser (primary) frequency standard to the Rubidium 
(secondary) standard.  We wanted to determine whether (a) timing to the 
correlator would be disrupted, and (b) antennas would lose 
synchronization with the Master LO rack.

Around 9am, we switched from Maser to Rubidium, resynchronized the 1PPS 
timing signal to the GPS receiver, and iterated this switching cycle 
twice.  In each case, all indications were that the array and the 
correlator remained synchronized.  Neither the L350s nor the L305s ever 
required resynchronization; the green lights on the Timing Chips 
(Station Boards and Crossbar Boards) in the correlator remained green; 
correlated phase was constant and continuous through the transitions.

We left the array on the Rubidium standard, with the Maser physically 
disconnected, until approximately 1:40pm, at which time we reconnected 
and switched back to the Maser, and resynchronized to the GPS.  An 
X-band observation ran throughout, and remained happy through all 
switching transitions.

This test gives us confidence that, in the event of a Maser failure, we 
can continue operations with minimal disruption.  Although this test 
demonstrated short-term repeatability, another test will be planned over 
the next few months, to ensure that this behavior is repeatable on 
longer time periods.

-- 
Keith Morris