[evlatests] Polarization Status

[Rick Perley]

    Four hours of dynamic time went wanting on Sunday morning, so I 
submitted a file to check polarization capability at L, C, X, K, and Q 
bands, both in continuum and in line modes. 
    The source selected -- 0038+416 -- is about 1Jy at all bands.  This 
is not enough to see the low-level 'closure', and other 2nd order 
effects that I've commented on before.  The source is about 1 to 3 
percent polarized at all bands. 

    In general, array performance at all bands -- in all polarization -- 
is outstanding.  I made images at all bands in all Stokes, and all are 
noise limited with no sign of any instrumental effects. 

    However, the 12.5 MHz polarization spectral line data (mode 'PA') 
show the enhanced noise that has been reported before.  As the images 
and data are completely noise limited, I could measure very accurately 
the ratio of the noise in the parallel hands to crossed-hands:  It is 
2.60 -- this is the factor by which the parallel hand rms noise is 
increased in mode PA. 

    As earlier tests have shown that this noise increment problem only 
affects 12.5 MHz spectral line modes, and that the problem is eliminated 
when self-test is turned off, I recall there was general agreement that 
we'd have self-test turned off for these modes.  What is the status of 
this?