Intro

Measuring the 1az term (top)

• Use sbh receiver.
• move the tiedowns to the new positions to level the platform
• Run the x102 calibration to measure any pointing error.
• Move the tiedowns back to the standard position for regular observing.

• This data was not taken under "ideal" conditions:
• It often started at 16:30 and relied on a previous rain to keep the temp cool so the tiedown tensions didn't go slack
• Data was taken during the rain.
• The data was edited to remove any patterns that had bad tiedown tensions, or that lacked distomat readings.
• For the data taken 15may thru 25may11 the tiedowns were not placed at the correct position.
• 
  

• td	pre 26may incorrectOffset	post25may Correct offset	cor-incor (inches)
  12	-1.030	-.939	.091
  4	.368	.210	-.16
  8	.661	.729	.07

• 
  
• so the tiedows were off by about .15 inches max.
• In the plots below:
• the first set of plots shows all the data.
• The 2nd set of plots shows the data after 25may11 with the correct tiedown positions.
  
• These source names have A appended to their name.
• I used the 2nd set of plots for the model updates.
• 1st set of plots: All the data
• Page 1:az,za tracks
• Page 2:az and za errors plotted vs za and az
• frames 1,2 za Errors vs za and az
• frames 3,4 az errors vs za and az.
• These were all measured with the telescope in the new position (with the old model).
  
• Page 3: Measured gain,Tsys,Sefd, and beam width .
  
• Some of the sources had no fluxes (J0854+201,J1021+219) but still gave pointing errors.
  
• Some sources did not have accurate fluxes  at 3 GHz (B0838+133).
• Page 4: Arrow plot of pointing errors across dish.
• The direction of the arrow shows the pointing error.
• The amplitude of the arrow is the size of the error (1 tick mark is 10Asecs).
• some of the larger errors at transit are compounded by the fast as slews at  decs close to 18 degrees.
• The platform leveling rotated the platform about az=110 degrees with the north side moving higher.
  
• You can see the pointing errors point perpendicular to this direction.
• Page 5: 1 az fit to the pointing errors:
• the fit was : C0 + C1*sin(az - c2) done separately for za and az errors.
• The red line is the fit.
• Page 6: residuals (errors - fit)
• frames 1,2: za residual errors vs za,az
• frames 3,4: az residual errors vs za,az
• Page 7: residual errors (Err-fit) with az,za errors over plotted.
• The za residuals are 3.6 asecs, the az residuals are 5.5 asecs.
• 2nd set of plots: Data after 25may11 with correct tiedown position.
• page 8: arrow plot of errors
• page 9: errors with 1az fit
• page 10: residuals za,az plotted vs za and az.
• page 11: az,za residuals over plotted vs za and az.
  

Updating the model: (top)

• The fit value needs to be subtracted from the current model terms.
• The fit was c0 + C1*cos(az) + c2sin(az)
• the 1az terms are independent of the receiver (it is the platform tilt)
• the c0 term depends on the receiver position on the turret floor.
  
• Since sbh is not used very much i only used the 1az term to correct the model. The offsets will have to come from measurements that use the other receivers.
• The table below shows the old and new 1az terms. The new values = old values - fitvalues
• 
  

• pointing model changes

  	az cor	za cor
  cos(az) old	0.73	-86.12
  cos(az) new	-3.86	-93.14
  sin(az) old	83.10	2.01
  sin(az) new	90.63	-0.79

  
  

Pointing results after td change and model update.  (top)

• _1,2,3 has been appended to the source name to show when the data was taken (see table above)
  
• Page 1: az,za tracks across the dish
• Page 2: gain,Tsys,sefd, Beamwidth for the data.
• _N in source name specifies when data taken:
• srcnam_1: 17jun11 sbn
• srcnam_2: 21jun11 sbh
• srcnam_3: 01jul11  sbn
• Page 3: pointing error all data
• bottom: az error vs az.
• B2209+080_1 (sbn) and B2128+048_2 (sbh) both have deviations as za increases
• Below sbn and sbh are split into different plots to see if they have different constant offsets.
  
• Page 4: pointing error (only sbn)
• 17jun11, 01jul11
• Page 5: pointing error (only sbh)
• 21jun11

• may11 data with out the 1az fit in the model is compared with 21jun11 data with the 1az fit.
• Both days have the updated tiedown positions.
• Page 1: may11 data without 1az fit in model
  
• Page 2: 21jun11 data with 1az fit in sbh model
• Page 3: overplot data without 1azfit in model (black) with data taken with 1az fit in model (red)
• The table below shows the mean,and rms errors for za and az.
  

• The mean values don't represent the mean of the model since we only have 2 sources.
• The rms values improved with the inclusion of the 1az fit (so the sign must be correct).

Summary: 

• After changing the tiedown positions, the 1az fit to the may sbh data decreased the pointing erorrs for sbh.
• The az errors is showing a za dependence.
• need to be a little careful with fitting sbn and sbh data together since sbh may have a constant az,za offset. Sbn could also have one, but by definition sbn is the one that sets all the models.

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