[evlatests] System Status from Yesterday's tests ...

[Rick Perley]

    The 'block of four' mode test that MPR made up to test 
multi-configurations within a SB proves to be a useful tool ...

    This test was run again yesterday evening, primarily to see if the 
phase hopping associated with the L302 module swaps had been eliminated. 

    Results:

    1) Phase Hops at scan boundaries are gone -- with a single, special 
exception.  Antenna 2, IFpair A/C, is hopping by 120 degrees, on scan 
boundaries -- but only when we were in the narrowest (31.25 kHz) 
bandwidth.  In reviewing my notes from the previous day's test, I noted 
that antenna 2, for that BW only, had two different 'hop values' whereas 
for the other BWs for that antenna/IFpair, the 'hops' were of a single 
size.  Hence, it seems clear that the phenomenon reported above has a 
different origin, one specific to that narrow bandwidth/observing mode 
(OSRO2). 

    2) Large fractions of blank data (pure zeros) remain.  As before, 
OSRO2 modes are missing all of antennas 14, 15, and 16 if IF 'C'.  All 
the observations (both modes, all BWs) show that some antennas remain at 
zero for up to one minute, following a mode change -- this problem is 
never triggered by a scan change. 

    3) Antenna 17 in RCP is very weak -- amplitudes low by a factor of 
about 4. 

    4) Antenna 12 in LCP is very, very weak -- fringes barely discernible. 

    5) Antenna 26, IF 'C', in OSRO2 mode *only* has no fringes. 

    6) All delays are less than 4 nsec. 

    7) The visibility amplitudes showed excessive short-time scale 
'jitter' -- of order 1%.  (Yes, I'm fussy).  As the winds were blowing 
about 25 mph (average), I'm guessing that this jitter is due to the wind 
-- visible even at 6cm with the sensitivity we now have...