[evlatests] EVLA K-band performance

[Rick Perley]

    Summary:

    All 5 EVLA antennas work at K-band, and work well!  There are some 
exceptions -- see details below. 

    Details:

    This report is from the data taken by Ken and me yesterday, to check 
out the 'alternate UX converter path'.  A separate report on the 
alternate path will follow later today.  This report is specific to 
overall K-band performance. 

    For reasons to be explained in the following report, the two IF 
pairs were set to the same frequency, 22.416 GHz. 
    We used primary referenced pointing to remove any residual pointing 
offsets.  Three solutions (one per hour) were attempted, two were 
obtained.  Ken will need to explain what happened to one of them.  I 
have not reviewed the actual solutions, so cannot comment on the size of 
the offsets. 

    A)  All 5 EVLA antennas fringed well. 

    B) Phase stability was appalling -- but with thunderstorms about, 
and long baselines, we can expect no better than we got. 

    C) Gain, and gain stability were interesting,  Clearly, high 
attenuations almost certainly due to T-storms were causing major changes 
in gain, not corrected by the opacity calculation alone. 

    D) Sensitivity, as judged by AIPS weights show the 5 antennas to be 
very similar to VLA antennas, overall.  But there are exceptions:
          i) 16D has low sensitivity, by a factor of about 40%.  But 
16A, B, and C are normal. 
          ii) 18 is low by about 20%, in all four IFs.
         iii)  24A and 24C are *absolutely terrible* -- a factor of 3 
below the median (a factor of 10 in AIPS weights).  24 B and 24D are 
completely normal.  All four are seeing the sky perfectly equally -- the 
variations in weights (caused by the weather) are all identical, and 
similar to the adjacent antennas. 

    E) Bandpasses, delays, etc. are all normal. 

    F)  There is clearly something wrong with the synchronous power 
measurements on antenna 13.  The antenna amplitudes are far too high 
(and hence the AIPS gain far too low).  After calibration, the computed 
weights are normal, but are very noisy.  I doubt this is due to 
variability in the visibility data, and is much more likely to a very 
noise synchronous power calculation. 

    All in all -- the K-band performance is much better than even I (the 
eternal optimist) had expected!