[evlatests] 3-bit polarization/stability test

[Rick Perley]

    ... was going to send this to specific individuals ... but it's 
easier to do it this way ...

    We talked yesterday about a longish observation of OQ208 for the 
main purpose of determining variability of the antenna/electronics 
polarization.  There are worries about temperature sensitivities, so an 
observation of a source through dawn was felt to be optimum.  The 
previous test was of 3C286, which has the distinct disadvantage of being 
very highly polarized, making it difficult to isolate small 
antenna-based effects.   Polarization tests are much better done with a 
strong unpolarized object. 

Unfortunately, at this time of year, the highly preferred source -- 3C84 
= 0319+4130 (30 Jy) is an evening source, so OQ208 = J1407+2827 seems 
preferred. 

    But I think 3C84 should still be utilized, and the test be done in 
late afternoon-evening, when temperature differentials are nearly as 
strong as they are in the morning.  3C84 rises just before sundown.  The 
maximum rate of change of temperature in the vertex room is likely to be 
during these evening hours.  I suggest we do this *tonight*, and that we 
use Ku-band.  Amongst other things, we know the polarizer purity at 
Ku-band is better than at X-band, -- making electronics polarization 
changes even easier to detect. 
    One of the distinct advantages of 3C84 is its very high flux density 
-- 15 times that of OQ208.  This is very useful in finding other issues, 
and measuring -- for example -- the bandpass stability. 
    It is now clear at the site, and the winds are lightening up.  A 
nice calm and frosty night is forecast.  It's a good time for this test. 

    Rick