[evlatests] Other notes from yesterday's short test

[Rick Perley]

    The 250 kHz resolution L-band test done yesterday afternoon revealed 
some other characteristics, mostly good. 

    The observations are of 3C273, for 13 minutes, taken around 1PM 
local time. 

    1) The antenna numbers are mislabelled -- I see them them running 
from 1 through 12.  The reported locations are correct however.  In what 
follows, the antenna numbers reported are the correct physical IDs.

    2) There are essentially no discrepant data points.  No flagging was 
applied, and after calibration, only three discrepant points were seen 
in a UVPLT, out of 50,000 data points plotted in RR, and none at all in 
LL. 

    3) The bandpasses all look very nice, with one curious exception.  
Sub-band 4  (1372 to 1404 MHz) shows a notable roll-off on its low 
frequency edge, in both polarizations and on all antennas.  The other 
subbands show a sharp cutoff at both ends -- dropping about 5 dB in 2 to 
2.5 MHz.  For subband 4, the frequency span for this drop is about 10 
MHz.  The upper edge has a normal cutoff. 

    4) Antenna 9 has a temporal phase wind of 1.5 degrees/second, in LCP 
only.  RCP is steady.  All other antennas are 'rock-solid' in both IFs. 

    5) The coherent amplitude variations reported for 3C273 data from 
Sept 28 are still present -- but are much lower in amplitude.  To recap, 
all antennas, all subbands, and all polarizations show coherent 
variations in fringe amplitude, on timescales of a few seconds.  When 
first discovered on Sept 28, the amplitude variations (expressed in 
terms of power) were by a factor of ~2.  Yesterday, (Oct 6) they are 
down to about 30%.  There is considerable evidence to support a theory 
that scattering in the solar wind is responsible.  I note that on Sept 
28, the sun was about 4.8 degrees from 3C273.  Yesterday it was 8.5 
degrees away. 

    6) Other than the fluctuations noted above, the amplitudes for all 
antennas/subbands/polarizations were very stable over the (short) 
duration of this test.