[evlatests] EVLA short-term behavior, this morning

[Rick Perley]

    We started off today's software time with an 'EVLA System Check', 
using the same setups as usual. 

    Here I report on the 0.41 second 'fast dump' continuum observations, 
taken at each band. 

    1) Referenced pointing was attempted at C, X, K, and Q bands.  Every 
single EVLA antenna failed every single pointing attempt!  This despite 
nearly calm weather.  And yet, the results given below, especially at K 
and Q band, are so good as to make me wonder if the solutions were in 
fact actually were found and applied, but were not communicated to the 
Modcomps to be printed out in the usual manner. 

    2) Antenna 21 was out for outfitting, and antenna 16 is out for 
corrective electrical work.  (Steve Durand reports that antenna 16 will 
return to service a week from tomorrow -- April 11). 

    I report on each band, in order. 

    A) P-Band. 

    Antennas 14, 17, and 23 all work on four IFs.
    Antenna 14C still has the 150 degree phase problem, occuring 
approximately every 10 seconds.  This is seen also at L-band, but at no 
other band!!!
    There are no other unusual phase or amplitude effects to report. 

    B)  L-Band. 

    All antennas (other than 16 and 21) provided good fringes on all IFs.

    Antenna 14C is phase jumping, exactly the same as at P-band.  Phases 
for all other antenna/IFs were normal. 

    Antennas 13 B&D, and 17B&D  have occasional amplitude drops, 
affecting 1 to 2 % of the data.   The drop depth is quite small -- 1% of 
the amplitude.  Both polarizations drop identically, together.  A and C 
showed no drops. 
    In addition, 24B had four single-IF drops. 

    C) C-Band.

    16 and 21 were out, 23 and 26 have no receiver.  All others fringed 
on four IFs. 

    All phases looked normal.

    Many amplitude drops are noted, almost all of which occur in 
opposite polarizations at the same time, and to the same depth.  Note 
that there are about 400 integrations in total, so the fraction of time 
with a drop is very small.  The drop amplitudes are typically 1%.  This 
is not a 'big deal' -- but it would be nice to understand and fix the 
problem!

    17 A and C:  one drop
    17 B and D:  9 drops
    24 A and C:  5 drops
    24 B and D:  6 drops
    24D:  17 additional drops, single polarization. 

    D)  X-Band/

       16 and 21 out, all others fringed strongly on 4 IFs each. 

    Antenna 26 had about 8 phase jumps, typically 20 degrees, which are 
identical on all four IFs.  These look like, but are not, the 'delay 
clunks' we see in D-config data -- the 'clunks' are far too large, and 
they are exactly simultaneous and identical on the four IFs. 

    There were many amplitude drops, whose characteristics are the same 
in general as for C-band.  Details:
       17 B and D: one drop
    18 B and D:   one
    23 A and C: two
    24 A and C: one
    24 B (alone): 15 drops
    24 B and D: one
    26 A and C: three

    E)  K-Band:

    antennas 21 and 16 out.  All other gave lovely strong fringes on all 
four IFs. 

    Antenna 26 gave phase jumps, just like at X-band, but of larger 
amplitude:  ~50 degrees.  All four Ifs identical and simultaneous. 

    Load and Loads of amplitude drops were seen:

    17AandC:  3
    17 B and D: 9
    24 A and C: 2
    24B (alone): ~50
    24D (alond):  2
    26 A and C: ~20
    26 B and D: ~20 (different times than 26 A and C).

    F)  Q-Band:

    Antennas 21 and 16 out.  Antnnas 17, 21 and 26 have no receivers.

    All others gave excellent amplitudes on four IFs. 

    Because of a blunder, the data were dumped at 3 seconds, rather than 
0.418 seconds, integration.  Hence, my ability to see weak amplitude 
drops is severely restricted.  No large drops occurred. 

    No phase effects  -- but note that 26 is not outfitted at Q-band, so 
the effects noted at X and K could not have been detected here.