[evlatests] EVLA Phase Slip

[Rick Perley]

    We took some data earlier this afternoon, with the intention of 
tracking down the 180 degree phase jumps.

    Data were taken in L-band, at 7 different frequencies.  Because of 
laziness, the AC and BD pairs (IFs 1 and 2) were set to the same 
frequencies.  Observations of a strong source were made, with a duration 
of 1 minute for each frequency.  Hence, any given frequency was observed 
every 7 minutes. 

    Results:

    A)  The 180 degree phase jump is ubiquitous, seen on all EVLA 
antennas (or, all VLA antennas if an EVLA antenna is reference).   A 
quick look shows the same 180 degrees on all antennas, all frequencies, 
all IFs. 

    B) The phase slip reported earlier is very strong for EVLA antennas 
-- and of different magnitude and sign for the two IFs -- even through 
they are at the same frequency! 

    For example:  at 1725 MHz, the A and C IFs are rotating at about 8.5 
degrees per minute, but the B and D IFs are rotating at -5 degrees per 
minute. 

    I hope this is a useful clue...