[evlatests] EVLA Holography -- almost working!

[Rick Perley]

A quick test was done this afternoon to test EVLA Holography.   In this 
test, three VLA antennas and two EVLA antennas were declared as 
references.   The others executed a standard 11 x 11 raster, with twice 
critical spacing (two points per beam). 

Three problems were found -- two of which are fundamental, the other a 
fluke (note:  not Fluke!) 

    A) Fundamental problems.

       1)  The EVLA and VLA are not perfectly synchronized.  Each array 
is executing the proper pattern, but the EVLA is running about 4 seconds 
behind the VLA in its movements! 

    2)  The EVLA's reference antennas are being told to go to the first 
offset holography position -- where they spend 10 seconds -- then they 
are told to do what was intended of them in the first place -- and rush 
off to remained fixed on the source. 

       B) Fluke (NB NOT the Flukes of recent fame) Problem. 

    All EVLA to VLA baselines were low by about a factor of four for the 
first 20 minutes of the 30 minute test.  But the EVLA to EVLA baselines, 
and VLA to VLA baselines were normal, or near normal.  Ken has a 
rational explanation for this, involving the fact that the EVLA antennas 
were not being utilized in the run preceding this test, and were not 
properly returned until well into this test.  The loss of amplitude was 
because the EVLA test was at 12.5 MHz BW, while the antennas were 
apparently left in a 50 MHz BW.   He can explain the curious set of 
circumstances needed to create the effects we see.  He is confident this 
is a 'one-of' type of problem.  (Right, Ken?)