[evlatests] Results from WIDAR K-band test

[Robert Dickman]

In re the weather on 12/3, I believe it was snowing from around 11 AM  
onward.

Bob


Sent from my iPhone

On Dec 9, 2009, at 10:42 AM, "Rick Perley" <rperley at nrao.edu> wrote:

>    Michael took some K-band test data on the late afternoon of Dec 3.
> Twelve antennas were operating, observing two sources separated by  
> about
> 6 degrees.  Dual polarization (RR,LL) was utilized, four 128 MHz-wide
> subbands, with 512 channels for each polarization product -- 250 kHz
> resolution.   A total of 30 minutes observing, with 1 second
> averaging.   Scans were 90 seconds long, alternating between the two
> strong (2.3, and 1.6 Jy) sources.
>
>    In general, data quality was very good.  Exceptions are:
>
>    1) Perfectly-zero records are back.  About 0.1% of the visibilities
> are exactly zeros.
>
>    2) About half the antennas had a notable phase jump between the
> first and second scans.  Those seemingly affected are 2, 3, 19, 25,  
> and
> 27.  Perhaps antenna 3 as well.  I flagged the first scan for all
> antennas, to simplify matters...
>
>    3) Antenna 27 was very weak throughout -- amplitudes down by a
> factor of 3 (so it's like we had a constant offset, to the 10 dB power
> point).  I flagged this antenna out.
>
>    4) Antenna 19 was bizarre throughout:  three subbands in LCP (2, 3,
> 4) had ridiculous bandpass shapes -- I flagged all three.  All
> polarizations had phase jumps for the first 6 minutes.  Following  
> this,
> the amplitudes all dropped by about 50%.  Amplitudes and phases were
> stable thereafter. I removed the first 6 minutes, and crossed by  
> fingers ...
>
>    5) Phase stability was very poor, with smoothly changing phases, by
> up to 100 degrees, throughout.  The amplitudes of these phase  
> variations
> clearly increases with baseline length, and there is good evidence  
> that
> the phases connect between sources, and the variations are identical
> between polarizations and subbands -- all are consistent with an
> atmospheric origin.  I hope the weather was truly bad on that  
> evening ...
>
>    I calibrated the data with a flat 6-hour average throughout.  After
> removing the issues noted above, the stability in the bandpasses, and
> between sources is very good.   There is nothing to indicate any
> problems (but -- the sources are not really strong, and the scans are
> short, so sensitivity is not great).  The differential bandpass
> solutions (solutions made for each observations for each source) is  
> dead
> flat -- only noise is seen on all antennas.
>
>    I ran POSSM, to check the connectivity of the subbands, for each
> baseline, for each source, for each scan.  All amplitudes and phases
> connect smoothly -- there are no subband (aka spectral window)
> discontinuities at a level of ~1 percent.  The LCP window of subband 2
> is occasionally displaced by a couple of percent w.r.t. the adjoining
> windows (subbands), but this is seen equally for both sources, and I  
> bet
> it's caused by something fishy with the bandpass solutions.
>
>
>
>
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