[evlatests] Something wrong with RQ gains ...

[Rick Perley]

     Something is amiss with the RQ gains.

     In the past, application of these gains (in AIPS, using 'TYAPL') 
perfectly restored the observed visibility amplitudes to constant values.

     Now, using exactly the same programs, the visibility amplitudes are 
only partially restored.  Eric and I have confirmed that TYAPL is doing 
the same as it did in the past.  So something seems to be wrong with the 
recorded values.

     Some evidence:  I chose two antennas for which the gain variations 
(due to RQ changes) were fairly large.  Below are the visibility 
amplitudes for ea09 and ea25, along with the RQ values.    These are 
supposed to scale exactly (and have in the past).  Each row is a 
separate, sequential observation of our point-source calibrator.  Units 
are arbitrary.  The values should be proportional to amplitude (voltage).

         ea09R                        ea25R
      Amp     RQ               Amp     RQ
-----------------------------------------------------
    18.2         13             18.9       15.5
    17.9         13             18.5       15.5
    17.9         13             18.9       15.5
    17.9         13             18.5       15.5
    17.9         12.9          19.2       15.5
    13.2         11.9          16.9       14.4
     8.7          10.0           7.4        11.0
    11.5         10.9          11.0       12.0
    14.1         11.5          15.2       13.4
    14.3         11.5          16.1       14.0
    13.7         12.0          16.7       14.5
      8.8         10.4            7.4       11.0
      9.4         10.5            8.3       11.0
------------------------------------------------------

     Were the system working properly, the RQ values should scale with 
the visibility amplitudes.  Hence, their ratio should be constant.  But 
is will be immediately apparent that the RQ values, although showing the 
same trend as the amplitudes, change much less.  Hence, when applying 
them, the correction is far short of what is needed to restore the 
amplitudes to a constant value.

     All IFs (and polarizations) for a given antenna behave 
identically.  Each antenna is different, although some (like the two 
above) are similar.

     This effect is seen identically at both X and C bands (data taken 
the same day).  And for both, the system stability was very good for the 
first 1/3 of the run (as seen above), after which these rather large 
changes were seen.

     Either the RQ values are incorrect, or the amplitudes are.  I see 
no evidence for the latter -- indeed, the quality of the data is very 
good throughout.

     Any idea of what's wrong here?