may14:Alfa calibration scans, rotation angle

    Alfa was reinstalled in the dome on 21may14 after being worked on in the lab. Spider scans (heiles calibration scans) were taken with alfa on 24,26may14 using beams0..6
This data was taken with model18A with the tiedown 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:

• 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 1.1 degrees. It is about 2 asecs less than the value with not rotation offset (what is currently being used).
• The az and za minimums occur and different rotation offsets. This may be from the limited number of measurements we took.
• 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:

• The gain,sefd, cals look ok
• gain looks a bit high for beam0 on a few sources. (cals a little off or source flux?)
• sefd is : beam0:2.5 jy , outer beams about 3Jy
• pointing errors:
• rotating by + 1.1 degrees reduces the non beam 0 rms from 14 to 12 asecs.
  
• 
  

• 	rms Error asecs		mean offset asecs *
  	AzErr	ZaErr	azErr	zaErr
  all Beams	10.7	9.0	-4.75	1.96
  Beam0	4.65	3.24	2.13	-9.79

• Pointing Notes:
• i removed the beam0 mean offsets from the alfa model on 27may14
• the large rms in all beams is partly due to the beam0 mean offsets
•