[evlatests] Initial Results -- 2 GHz-wide data.

[Rick Perley]

    Michael took some 2 GHz-wide data at C-band yesterday afternoon.  
These are at a single frequency (meaning, no changes in LO or band).  It 
seems it was set up as two overlapping 1 GHz-wide tunings, one through 
the AC IFs, the other through the BDs.  There were 8 subbands, each 128 
MHz wide, in each.  AIPS sees these as 16 'IFs'. 

        Here are some (quite encouraging!) results.

    FITLD reported 3.6% of the data were integer zero.  I haven't yet 
found which antennas these were applied to. 

    All antennas in the array (4, 6, 7 and 22 were out), except ea13 
which has no receiver, fringed. 

    All subbands fringed, with one exception:  subband 11, for antenna 1 
only, gave no fringes in either polarization.

    The subbands are misordered.  After some headscratching, the 
perturbation was clear.  Following is a table showing the subband order 
as presented by AIPS, and the order they should have been in: 

    Listed      Actual
    --------------------
       1               4
       2              12
       3                1
       4                2
       5                3
       6                5
       7                6
       8                7
       9                8
      10               9
      11              10
      12              11
      13              13
      14              14
      15              15
      16              16
----------------------------

    Another way to think about this is that the first two listed 
subbands are misplaced -- the first one belongs in slot 4, and the 2nd 
one belongs in slot 12.  All others are correctly ordered. 

    When reordered like this, the frequencies are clearly contiguous in 
the two IF pairs (subbands 1 through 8, then 9 through 16).  I can't 
tell if the frequencies are *correct* -- there are no RFI lines or other 
distinguishing features.  It appears the center frequencies were 5000 
MHz (AC pair), and 5512 MHz (BD pair). 

    Delays are modest -- typically 3 to 5 nsec. 

    Phases, and phase continuity, are simply superb. 

    Three antennas give some very strange amplitude characteristics:

    ea06 shows various strange modulations, which are *different between 
subbands and polarizations*!!!  Gotta be a correlator issue. 

    ea12 shows, on all subbands and polarizations, single-record drops 
of 10% in amplitude.  These are perfectly regular -- once per minute, on 
the minute. 

    ea20 shows, on all subbands and polarizations, a regular ~6% 
modulation in amplitude, with a period of a few minutes.  The modulation 
is not sinusoidal -- there is a steady level, then a gaussian-looking 
dip, then a return to the normal level, and the pattern is repeated. 

    As noted above, antenna 1 gave no fringes in subband 11. 

    All other antennas behaved beautifully.