[evlatests] 3-bit polarization/stability test

[Scheduling Officer]

The EVLA is doing fixed-date observing until about 930pm tonight. - Joan

EVLA/VLBA Scheduling Officers
schedsoc at nrao.edu, NRAO, Socorro, NM, USA
http://science.nrao.edu/facilities/evla/schedules/schedsoc

On Tue, 8 Nov 2011, Rick Perley wrote:

>    ... 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
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