Alfa calibration scans, rotation angle

plots:
sbn calibration run on the same sources (.ps) (.pdf)
the alfa calibration results (.ps) (.pdf):
the pointing error vs rotation angle offset (.ps) (.pdf):


Other pages:
sbh runs taken may11
05nov09 calibration and rotation test

    Alfa was reinstalled in the dome on 06sep11 after being worked on in the lab.Spider scans (heiles calibration scans) were taken to check the pointing. Data was taken with sbn on 07sep11 (alfa wasn't ready) and then on alfa starting with 08sep11.

sbn data

• 07sep11: since alfa wasn't ready, calibration scans were done with sbn using the same sources that were used by alfa on 08sep11. This shows the relative offset of alfa pointing to the sbn values. Comparing the two lets you separate out the alfa installation errors with general telescope pointing problems (from the beam repair).

Alfa data:

• Alfa Data was taken on 110908,110911,110915,111005,111006,111017,111019.
• Some problems that were present during the  alfa datataking:
• 110908: Alfa was mounted rotated by 90deg
• I used the alfa motor to rotate alfa back by 90 Deg.
• The analysis was kludged so that it ignored this 90deg rotation.
• On 08sep11 during the day, it was remounted at the correct angle.
  
• beam 6b was intermittently bad so most runs ignored beam 6
• beam 4a was bad for much of the time. When it came back online, it had a Tsys of about 40K.
  

Alfa setup:

• The alfa rotation angle was set to 0 deg (except for 08sep11 when the 90 deg rotation tried to compensate for the mounting problem).
• The 100 MHz filter (1390 to 1490) was used.
  
• The wapps took data with 100 MHz bw centered at 1440 MHz.
  
• heiles calibration scans were done for all good beams. For some days scans were only taken with beam 0 to nail down the mounting offset.
  

Calibration run results:

07sep11 sbn run:

• A lot of the structure seen in the sbn pointing errors was also seen in the sbh runs taken may11 to check for the errors from the beam repair (these changes were never implemented since the tiedowns broke down for awhile).
  

Alfa calibration runs.

• Page 1: the az/za coverage. Colors specify the beam that was used. Black is beam0.
  
• Page 2: gain,Tsys,SEFD, avgBeam width.  Colors show the different beams
• beam 6 has large tsys,sefd and beamwidth. This was fixed (i've been told) on 09sep11 by adjusting the bias's (but later it died..)
  
• Page 3: coma, 1st side lobe height, beam efficiency (main beam) and (main beam + first side lobe).
• Page 4: Pointing error all beams:
  
• Top: za error vs za
• 2nd: za error vs az
• 3rd: az error vs za
• bottom: az error vs az
  
• Notes on some beams:
• The large beam2 offset has been seen in previous x102 runs.
• Page 5: Pointing error beam0:

• 	za Error Asecs	az Error Asecs
  offset	-5.65	7.56
  rms	4.09	6.71

  
  
• There is also a 3az term visible in the errors.
  
• There also looks like there is a linear ramp in za errors vs za. This was also seen back in the sbh runs taken may11.

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.
• Outer beams rms:
  
• For each offset (-5 to .5 in .1 degree steps) the rms pointing error was recomputed
• * beams 1,2,3,5,6
  
• 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 2 asecs less than the value with no rotation offset (what is currently being used).
• Beam 0 rms The  horizontal lines with +:
  
• total rms: 7.9 asecs
• azrms: 6.8 asecs
• zarms: 4 asecs
• Bottom: mean pointing error vs rotation angle offset
• The outer beam mean error decreases out to +4deg rotation.
• The large offset in beam 0 is probably complicating this.
  

Results:

• The gain,sefd, cals look ok, except for beam 6 (which later died) and beam 4 which had an oscillation in 4A. To get rid of the oscillation, the bias currents had to be reduced. This increased Tsys for beam 4a.
  
• pointing errors:
• Beam 0:
• Offset for alfa is larger than sbn. Need to update the model offsets for alfa.
  
• Outer beams:
• similar to the 05nov09 calibration and rotation test
• pixel 2 also has a large za offset back in nov09.
  
• Rotating for minimum error.
  
• Rms is now minimized with a rotation of 1.3 degrees. Back in nov09 it minimized at +2 degrees.