30may16: Alfa calibration scans, rotation angle

Compare to may14 results after re-installation
Compare to may15 results after re-installation

    Alfa was reinstalled in the dome on 13may16  after being worked on in the lab. Spider scans (heiles calibration scans) were taken with alfa on 30may16 using beams0..6
This data was taken with model18A  and with the tiedowns active.

The setup:

• The alfa rotation angle was set to 0 degrees.
• The wapps took data with 100 MHz bw centered at 1440 MHz. The 100 MHz rf filter were used .
  
• The program cycled through the various beams. Beam 0 was sampled more often than the others to get a better measure of the pointing offsets.
  

Calibration run results:

• I removed 2 patterns where the tiedowns had lost tension.
• Page 1: the az/za coverage. Colors specify the beam that was used.
  
• Page 2: gain,Tsys,SEFD, avgBeam width. This used the standard cal values.   Colors show the different beams
• Page 3: coma, 1st side lobe height, beam efficiency (main beam) and (main beam + first side lobe).
• Page 4: Pointing error (all beams)
• Page 5: Pointing error (beam0).
  
• beam0 mean offsets will increase the rms of all beams.
  

Fitting for rotation angle error:

• Compute the change in the pointing error if the alfa rotation error was off by -5 to +5 degrees in .1 degree steps. Do this for each beam separately.
• For each of the .1 degree steps recompute what the pointing error would have been for each measured position.
• Plot the rms error and mean error for these newly computed series. Do this separately for beam 0 (which is not affected by rotation) and the other beams.

• Top: rms pointing error vs rotation angle offset.
• For each offset (-5 to .5 in .1 degree steps) the rms pointing error was recomputed
• + beam 0, * beams 1,2,3,4,5,6
• Black is the total rms (rmsAz, rmsZa added in quadrature)
• Red: Az rms pointing error
• Green: Za rms pointing error.
• The total rms minimizes at a rotation offset of 1.3 degrees. It is about 3 asecs less than the value with no rotation offset (what is currently being used).
• Bottom: mean pointing error vs rotation angle offset
• Black tot Mean error. az and za added in quadrature.
• green: mean za error,
• red : mean az error.
• We probably need to redo with the beam0 offsets removed.
  

Results:

• There aren't as many points as the may15 run so differences may be from the smaller numbers.
  
• The gain,sefd, cals look ok
• Tsys for beam 0 is a little higher then may15 (31 vs 29k)
  
• sefd for beam 0 is also a little higher than may15.. so it is probably a true change in Tsys and not a cal problem.
  
• sefd is : beam0:2.8 jy , outer beams about 3.4Jy (this is a bit higher than may14..)
  
• pointing errors:
• rotating by + 1.3 degrees reduces the non beam 0 rms from 13 to 9 asecs.
• in may15,may14 we got 1.1 deg rotation correction. The difference is probably the small number of measurements made in may16.

• 	rms Error asecs		mean offset asecs *
  	AzErr	ZaErr	azErr	zaErr
  all Beams	8.01	8.82	-1.93	1.25
  Beam0	4.69	2.83	-1.60	-3.72

• Pointing Notes:
• we only did 58 measurements (all beams included).
  
• there was not an even distribution of north, south sources.
• The pointing errors look similar to the last 2 measurements (may15,may14).