[evlatests] X-Band Map Orientations

[Rick Perley]

    Michael took a short observation of our standard field, with a 
target source offset by a known amount, at X-band.  This database has 
full polarization (yeah!), with 2 MHz channel resolution, 64 channels 
per spectrum per baseline. 

    The imaging shows the offset image in the correct place -- we are 
seeing the sky 'right side up'. 

    Some notes on the data and on related issues:

    1) Antennas 6 and 7 gave no fringes in either polarization.  Do they 
have receivers, or where the antennas out of service at the time?
    2) 25 A is still giving integer zeros for visibility. 
    3) All other antennas worked well in both polarizations.
    4) The first scan of the first source had a phase different than all 
subsequent scans (initial scan problem) for nearly all antennas.  I 
flagged this one out. 
    5) The largest delay error is a minuscule 1.2 nsec.   Nice!
    6) There were the usual very small number of perfect zero 
visibilities.  A minor nuisance. 
    7) We have a sign problem somewhere -- applying the delay found by 
FRING, (through CLCOR) doubled the phase slope, instead of removing it.  
Eric remembers (and I agree) that this procedure used to work, and 
correctly handled both upper and lower sideband data. 
    8) Amplitude stability was very good (as always), but the phase 
stability was not as good as I've seen before -- most of the variations 
seen are almost certainly atmospheric, but some may  not be. 
    9) The 'RL' and 'LR' spectra look pretty good, and show there is a 
45 second delay error between the R and L systems.  (I can't tell the 
sign, however). 
    10) The image of 1800+784, with self-cal, but no BLCAL, provided a 
very nice 70,000:1 image.  The noise is uniform, with no sign of any 
artifacts.  1800+784 is now revealed as a double -- a very weak 
secondary feature is found a few arcseconds away. 
    11) 2005+7753 (the target source) images to its correct position.  
The dynamic range is not very good -- but the source is significantly 
resolved.  I made no heroic efforts to improve the image beyond a simple 
selfcal. 
    12) The usual wobbles are seen, on the usual baselines...