[evlatests] VLBI at the VLA test preliminary report

[Amy Mioduszewski]

This report is preliminary because the experiment has not been correlated yet. 
But I have no reason to believe that looking at the correlated data will change 
the conclusions.

On Monday (August 13, 2007 at 6LST) I did an test of the VLBI capabilities of 
the Modcomp free VLA.  The test was almost identical to the one that Greg did in 
June.  The tests were named TY004A&B and the schedules observed at C band and 
switched between 3C84 and J0310+3814 every 2 minutes.  TY004A (6-6:30LST) was a 
phased VLA test where the 3C84 scans were VA mode (phasing up) and the 
J0310+3814 were in VX mode.  TY004B was single dish.  Mark Claussen and I went 
out the the VLA that morning so that we could cable up an EVLA antenna to use 
for the single dish test.

Results of the phased array test (TY004A):
------------------------------------------
The phased array seemed to work.  The array phased up during the 3C84 scans in 
two or three integration times and held the phase pretty well during the 
J0310+3814 scans.  There was some trouble with antenna 28 but the operator 
recognized the problem (28 had been reported to be finicky) was able to 
reinitialize it and that seemed to fix it.  Also, from what we could tell the 
data was written to disk.  Once the data are correlated I should be more 
definitive about this.

There are two issues that came up:
1) There is no way to set the reference antenna, and it is set to DCS#1 which is 
antenna 24.  Since this antenna is near the end of an arm it is not an ideal 
reference antenna.
        -- Barry said this was a known feature.
2) At the start of the VA scans the phases seemed to be reset to random phases, 
so the phasing up had to start from scratch.

Results of the single dish test (TY004B):
-----------------------------------------
The schedule aborted in the python script.  Since this happened we were not able 
to test if the T8 switch was controlled by the schedule since the default seemed 
to be phased array and we never got far enough into the single dish schedule for 
it to change.
        -- I have reported this to Barry

I will send a second report once I get the correlated data.