Alfa calibration scans, rotation angle after re installation

    Alfa was reinstalled in the dome on 20apr12 after being worked on in the lab (new amplifiers were installed). Spider scans (heiles calibration scans) were taken with alfa on 27,28apr12 using beams0..6
This data was taken with model17 with the tiedown positions for model17. Pointing model 18 was taken in mar12 but had not yet been installed.

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 was not used (trouble switching it in).
  
• The program cycle 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 4: coma, 1st side lobe height, beam efficiency (main beam) and (main beam + first side lobe).
• Page 5: Pointing error. beam 2 had large za errors. This has been seen in previous years data. It is probably  the offset we are using for this beam.

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).
• beam 0 totRms is 6 asecs, nonBm0 0 rotation=13 asecs, nonBm0 1.1deg rotation=11asecs
• 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.
• minimum mean error occurred at .3 degrees..
• At .3 degree offset, the beam 0 and non beam 0 offsets are the same.

Results:

• The gain,sefd, cals look ok
• Looks like all beams are now working ok.
  
• Back in nov11 after the last time alfa was reinstalled, there were a few beams with Tsys problems.
  
• pointing errors:
• rotating by + 1.1 degrees reduces the non beam 0 rms from 13 to 12 asecs.
  
• 
  

• 	rms Error asecs		mean offset asecs *
  	AzErr	ZaErr	azErr	zaErr
  all Beams	7.7	8.7	-6.2	8.6
  Beam0	5.6	4.9	-7.3	3.l1

• Pointing Notes:
• the beam0 offsets should be close to zero after these offset values are subtracted from the model (03may12).
• The offsets may be biased because we didn't cover all of the dish (and we know there is a 1az tilt).
  
• The pointing model will get updated around 15may12 when the new pointing model is installed. This should fix most of the offset errors..

Still to do:

• look at the new amplifiers response to the radars.