[evlatests] Monday stress test results

[Rick Perley]

    I ran a stress test Monday afternoon.  This one was set up in the 
following way, all in continuum at 50 MHz (except P-band, at 3.125 Mhz):

    A) Two consecutive X-band observations, to check for bad first scan

    B) A reference pointing, followed by another X-band observation, to 
check reference pointing application.

    C) K, then Q bands, with reference pointing applied. 

    D) Three consecutive L-band observations, to check for peculiar 
phase jumps upon repeating observations.

    E) One P-band observation

    F) One C-band observation

    G) Alternating between L and C bands, in hopes of inducing the 'lost 
header' problem. 

    General Results:

    0)  Overall, extremely good data.  Phases were excellent at all 
bands, except for VLA antenna 12A and C, where strange 'wanderings' are 
still being noted. 

    1)  The initial pair of X-band observations were identical -- no 
changes in phase or amplitude between them.  No 'dummy' scan was needed 
here. 

    2) Referenced pointing appears to work as expected.  Amplitudes went 
up after application of the corrections, especially for antennas 13 and 
25 (more on these later). 

    3) All is well at K and Q bands. 

    4) The total of 5 L-band scans did show a 'global' phase jump for 
the middle one , but on IFs 'B' and 'D' only -- this represents a change 
in behavior!  However, the two L-band observations at the end (which had 
C-band observations in between) showed to phase jump. 

   Also -- EVLA antenna 25 had a -185 degree phase jump on *all* IFs, 
for this same scan! 

    5) Each time we change band, the next observation has an unflagged 
single record of noise. 

    6) The last 8 seconds of the last scan was rubbish, with an abrupt 
change in phase and amplitude.  This must have something to do with the 
next observation's parameters getting mixed in with the current 
observation?  

    7) The usual 'short shallow drops' were seen at all bands on most 
EVLA antennas.  The usual characteristics are repeated. 
   

    Specific Issues Noted:

    1)  Antennas 13 and 25 are *still* not pointing correctly at high 
frequencies.  The referenced pointing gave a large correction for them 
at X-band, but the subsequent K and Q band observations gave zero 
amplitudes for both antennas. 

    2) At P-Band: 
          a) 26 still gives no fringes whatever in IFs B and D. 
          b) Antenna 11 sensitivity is low by a factor of ~4 (in 
efficiency/Tsys). 
          c)  Antenna 21 sensitivity is low by a factor of ~4.  
Presumably this is due to the filter on that antenna. 
          d)  Antenna 23, IFs A and C, is low in sensitivity by about a 
factor of 1.5
          e)  Antenna 24, IF 'A' only, is low in sensitivity by nearly 
an order of magnitude
          f) Antenna 26, IF 'C', is low in sensitivity by nearly two 
orders of magnitude.    26B and D gives no fringes, but 26A is normal. 

    3) At L-band:
          a) 16B sensitivity low by about a factor of 2. 
          b) No fringes from antenna 12.  No idea why. 
         
    4) At C-Band:
          a)  There were large changes in correlation coefficient in IF 
'D' for evla antennas 16, 17, and 24.  Also in 14C.  No idea why.  All 
others were stable, and normal. 
         
    5)  At X-Band:
          a)  EVLA antenna 14C and D showed large drops in correlation 
coefficient, which were reflected by measured increases in Tsys.  What 
can make the receiver do this?  The changes were very abrupt (1 second 
or less). 
          b) EVLA antenna 25 low in sensitivity by about a factor of 3 
-- all of which is likely due to Tsys being too high by about the same 
factor. 
   
     6)  At K-Band:
          a)  Antenna 11 low in sensitivity by about 20%
          b) Antenna 19 low in sensitivity by about a factor of 2. 

    7)  At Q-Band:
          a) Antnna 18 low in sensitivity by about a factor of 50%
          b) VLA antenna 20 low in sensitivity by about a factor of 2.5. 
          c) VLA antenna 5 showed a monotonic drop in sensitivity in all 
IFs, by about a factor of 2, over the 1-minute observation.