Intro

Setup:

• the wapps were used to take the data.
• beams 0 thru 6 were used.
• Beam6b eventually died so there are not very many measurements.
• beam4a started off with an oscillation. The bias voltages were then changed. This stopped the oscillations, but Tsys increased because of the changes.
  
• The pointing results were computed using beam0.
  

Processing:

• A0 - is usually an offset on the rotary floor in the az,za  direction
• A1 - This is caused by the tilt of the platform
• A3 - The 3 az term is caused by the 3fold symmetry of the triangle.

• page 1: measured pointing errors:
• top: za errors vs za
• 2nd: za errors vs az
• 3rd: az errors vs za
• bottom: az errors vs az
• the different colors, symbols correspond to different sources.
• The pointing errors are:
• za: mean=-5.65 , rms: 4.09 Asecs
• az: mean = 7.56, rms: 6.71 Asecs
• Page 2: arrow plot of   pointing errors on the dish Using beam 0.
  
• Each circle increases the za by 5 degrees.
• Top has the feed in the north (looking at southern sources).
• The length of an arrow is the pointing error at that spot (1 tick mark=10arcsecs)
• The direction of the arrow shows the direction of the error in az,za.
  
• The table at the top summarizes the errors by every 5 deg in za.
• The different colors show different sources.
• Page 3: pointing errors in za and az with the fits over plotted:
• Top: za errors vs azimuth
  
• bottom: az errors vs azimuth
• the black *'s are the measured errors, the red *'s  are the fit.
• The fit residuals:
• zaErrResidual: 3.7 asecs
• azErrResidual:4.6 asecs
• Page 4: pointing errors with the fit removed:
• Page 5: arrow plot of the pointing residuals after the fit is removed.
• The scale is now 1 tick mark = 5 Asecs

Summary:

• Fit results:
•  

  	Constant	1az term		3az term
  		Amp (Asecs)	Phase (deg)	amp (Asecs)	phase (deg)
  zaErr Fit	-5.32	2.1	275.5	1.4	57.8
  azErr Fit	7.89	3.2	208.0	5.3	322.0

  
  
•  The constant offset was -5.32,7.89
• Back in may11 the offset with sbh was: (-3.39,1.22). So this is larger.
  
• The 1 az term is about the same amplitude for az,za. The phase's should differ by 90 Degrees (they differ by  67).
• Back in may11  the 1az fit was 7.6,8.8 Asecs using sbh.
• This means that the platform is tilted differently. If this was caused by the tiedown encoders being reset after a failure, i'd be surprised that it got better!.
  
• The 3az term is much stronger in az than in za.
  
• I wonder if the weight imbalance on the rotary floor is skewing the results.. Maybe for the offset, but probably not for the 1 or 3az terms.
• The 1 and 3az terms affect the gain of the high frequency receivers as well as the pointing.
• To correct the 1az term i need to re level the platform with the tiedowns (using the tiltsensors). Then re measure the pointing error with the new tiedown positions.
  
• For now i'll apply the constant offsets for alfa.
• On oct24 7.89, -5.32 was subtracted from the az,za constant values for the modelALFA
  
• I'll do the 1az and 3az term after releveling the platform.
  

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home ~phil