[evlatests] OTF Holography Tests

[Rick Perley]

A few weeks back, Ken requested some help in testing out a new 'OTF' 
scanning mode -- to be used for antenna holography.  This initiative was 
spurred by suggested holography measurements for the ngVLA prototype 
antenna.

Last week, a short test was done to see if Ken's initial stab at this 
was in the right direction.  I generated an SB with two orthogonal cuts 
using our traditional 'stop and stare' method. The test had 31 
positions, each 10 seconds, done at X-band on 3C84.  5X oversampling was 
used (i.e., the grid spacing was lambda/5D radians).

To this Ken added two paired orthogonal OTF cuts:  The first pair with a 
scanning speed set to 'match' the stepped test, the second pair to go 
twice as fast.

The usual difficulties expected when trying something new were 
experienced, but with Bill Cotton's help, a data file readable by BDFIn 
was produced.

  Attached are ten UVPLT files -- no calibration was done.  Single 
baseline (fixed x moving:  ea28 x ea01) single polarization.  No averaging.

The first two (#1 and #2) show the standard 'stepped' profiles. First in 
Elevation, second in Azimuth.  (The overshoot on the steps show that 
ea28 has an old ACU).

The last eight show Ken's OTF cuts.   The first four are each 95 seconds 
long, the last four are half that (twice as fast).  By comparing the 
heights of the sidelobes, I can tell that:

#3 and #7 plots are in azimuth, reversed direction from #1.

#4 and #8 are in azimuth, same direction as #1.

#5 and #9 are in elevation, reversed direction from #2

#6 and #10 are in elevation, same direction as #2.

The profiles are just gorgeous!  The motion is clearly smooth and 
continuous.  No sign of problems at beginning or end.  The 
'double-speed' profiles look identical to the 'half-speed' ones. Phases 
look good as well.

That's the good news.

The bad news is that the (l,m) coordinates are rubbish.  All zeros for 
the first seven 'OTFRASTER' scans, and some enormous numbers for that 
last scan.

Ken is now thinking about how to get proper (l,m) coordinate 
information, and in adding various other options.

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