[evlatests] EVLA status, Wednesday afternoon

[Rick Perley]

    Following maintenance yesterday, the standard continuum stress test 
was run to check performance. 

    Overall, outstanding performance at all bands. 

     Emmanuel will provide a more detailed review later.  In brief:

    a) The *only* global VLAl-EVLA phase jump (and probably the only 
significant phase jump of any kind, other than those due to atmosphere) 
following the P-band observation, which was done at a different bandwidth. 
   
    b) The integration error affecting scans prior to a reference 
pointing scan, did not occur.  It seems that Walter's fix is working. 

    c) The 'square wave' phase seen in antenna 18 in IFs A and C, is now 
gone.  

    Some band dependent issues are noted below:

    P-Band:

    Much better now!  Antenna 13 still doesn't fringe.  Antenna 21 has 
its polarizations reversed.  Antenna 11 has non-functioning dipole, or a 
broken connection between one dipole and the polarizer.  Otherwise, all 
sensitivities (including antenna 21 -- there's an AIPS task that allows 
one to reverse the polarizations, so the data can be analyzed) are 
within acceptable bounds. 

    L-Band:

    16B has a high Tsys, resulting in a factor of 2 loss in 
sensitivity.  As 16A is o.k., this is presumably due to a problem after 
the front-end?
    A peculiar short event was seen in all IFs of antenna 25:  the 
corrrelation coefficients all dropped by a factor of four, for about 1 
minute.  There was no change in Tsys.  Easy explanation is that the 
antenna was off source -- but how could that be? 

    C-Band:

    A significant drop in correlation was seen on the last scan, for a 
number of EVLA antennas:  13C, 16A, 18A, 25A and C, 26 A and C.  Therre 
was no change in Tsys.  The other three scans were normal.  This cannot 
be due to pointing.  No other explanation is offered. 

    X-Band:

    21C was very unstable (variations by a factor of 100 in amplitude) 
early in the run.  This antenna/IF settled down, and was fine later on. 
    14C and D (LCP) has high Tsys -- 2X too high. 
    23C has a sensitivity low by a factor of 2, but Tsys is o.k. 
    26B has a curious problem:  the correlation coefficients are varying 
by 10s of percent, on timescales of tens of seconds.  But the Tsys looks 
stable.  However, it is noted that this IF's Tsys did *not* show the 
change expected when the antennas slewed onto the source.  The other 3 
IFs showed the expected change in power as the antennas changed 
elevation.  This problem does not appear to occur at the other bands, 
but a more careful review is warranted. 

    K-Band:

    Antenna 25 sensitivity low by a factor exceeding 10 -- due to high 
Tsys (about 300 K) 

    Q-Band:

    Antenna 21 sensitivity low by a factor exceeding 5 on all IFs, but 
Tsys o.k.  I suspect bad pointing, as the unstable IF noted above at 
X-band likely prevented a good reference pointing solution.  

    Finally:

    The EVLA data are littered with the 'Short Shallow Drops'.  Although 
this is not a  critical issue by any means (the loss of sensitivity 
should be less than 1%), it would be very nice to diagnose and remove 
this long-standing problem.  Is there any test we can perform to help 
here?