[evlatests] Fiddly Bits from today's C-band test

[Rick Perley]

    A few odds and ends, mostly already known:

    Antenna 25A has perfect zero amplitudes (integer) -- as before.

    Antennas 3A, 11A and C, 26C, and 27C give only noise.  (Also 13A and 
C, but it has no receiver). 

    A trivial number of zero visibilities were found (other than from 
25A):  0.0022% of all visibilities. 

    No 'drop-downs' were seen that could clearly be identified as such. 

    Phase connection is excellent -- no phase changes from source to 
source greater than 4 degrees was seen.  (There were two sources 
observed, separated by about 12 degrees). 

    Amplitude stability is outstanding -- variations for most antennas 
over the 30 minute observation is very  much less than 1%. 

    One antenna -- 26A -- shows a curious change of gain between the two 
sources.  The amplitude gain differs by 5% between the two.  No other 
antenna/IF shows anything more than 1%.  The 5% offset is very stable 
over the 30 minutes.  If due to an elevation dependency of some sort, it 
is very large, as the two sources were separated by only 5 degrees in 
elevation.  As 26C was flagged out, I cannot say this is an 
antenna-dependent effect. 

    Imaging fidelity was very good.  Following the usual 
self-calibration procedures, we get 80,000:1 on the primary source 
(1800+784 a.k.a. 1800+7828).  Background sources are easily detected -- 
these are beyond the half-power in the beam, and the images show 
negative pixels around them -- something I didn't expect to see.  More 
investigation, with much deeper imaging, may be warranted. 

    The target source, 2005+778, ( a.k.a. 2005+7752) is significantly 
resolved, so the image fidelity is not as high.  The rms noise in 
distant regions is about the same as for the primary source -- about 30 
microJy, which I suspect is near the noise floor. 

    The usual wobbles are still there, with the same characteristics:

    4 x 20 has a 10% amplitude wobble with a 5 degree phase wobble at 
twice the frequency (!).
    2 x 18 shows weaker amplitude wobbles, and possibly phase wobbles at 
twice the frequency. 
    Phase wobbles (only) are present on 2 x 6, 6 x 18, 8 x 24, and 7 x 21. 

    All other baselines look good (but may not be so good if we speed up 
data dumping ...)