Some Sample Data

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Next: About this document ... Up: VLBA TEST MEMO 64 Previous: Background.

Some Sample Data

Here I have extracted data from one of the big pointing equation analysis runs. Several pointing runs over a couple of months were combined to form a data set containing a minimum of 71 data points at any frequency/band (over 130 at the vast majority) with over 300 at 1cm and 600 at 7mm at each station. This is a fairly typical data set of the sort I use to check pointing equations. I have not included 3mm, but a quick look at a few stations shows no surprises.

Squint data from PTANAL from the ``End2000'' data set (arc minutes):

            90cm    50cm    21cm    18cm    13cm  13cmsx     6cm     4cm   4cmsx     2cm     1cm     7mm
  
SC  Az:    -0.19   -0.94   -1.46   -1.43    0.51    0.50    0.40   -0.17   -0.64    0.11    0.10    0.01
SC  El:    -0.76   -0.47   -0.56   -0.53    0.83    0.77   -0.12    0.21    0.23   -0.11    0.04   -0.05
  
HN  Az:    -2.27   -1.40   -1.27   -1.44    0.32    0.30    0.48   -0.16   -0.57    0.15    0.06    0.02
HN  El:    -0.33   -0.61   -0.68   -0.56    0.89    0.86   -0.14    0.22    0.21   -0.10    0.02   -0.05
  
NL  Az:    -0.25   -1.49   -1.66   -1.60    0.43    0.42    0.48   -0.17   -0.47    0.11    0.07    0.01
NL  El:    -2.76   -1.28   -0.66   -0.49    1.03    0.96   -0.13    0.22    0.23   -0.09    0.03   -0.04
  
FD  Az:    -1.53   -2.72   -1.55   -1.32    0.33    0.36    0.49   -0.16   -0.45    0.09    0.10    0.02
FD  El:    -0.77    0.48   -0.55   -0.55    0.86    0.81   -0.14    0.21    0.20   -0.10    0.04   -0.05
  
LA  Az:    -1.55   -3.30   -1.56   -1.34    0.62    0.49    0.48   -0.17   -0.48    0.10    0.11    0.02
LA  El:    -1.47   -2.07   -0.72   -0.61    0.89    0.83   -0.14    0.23    0.19   -0.08    0.01   -0.04
  
PT  Az:    -1.28   -1.50   -1.64   -1.30    0.63    0.55    0.47   -0.19   -0.42    0.06    0.10    0.01
PT  El:    -2.15   -1.67   -0.59   -0.41    0.89    0.92   -0.15    0.23    0.18   -0.08    0.04   -0.05
  
KP  Az:    -1.10   -4.39   -1.60   -1.68    0.79    0.79    0.51   -0.17   -0.51    0.11    0.09    0.01
KP  El:    -1.60    1.88   -0.60   -0.47    0.84    0.97   -0.05    0.21    0.21   -0.11    0.04   -0.04
  
OV  Az:    -1.74   -1.38   -1.74   -1.35    0.52    0.49    0.50   -0.18   -0.46    0.12    0.09    0.12
OV  El:    -1.27   -2.05   -1.03   -0.97    0.98    0.92   -0.10    0.23    0.16   -0.11    0.03   -0.14
  
BR  Az:    -0.74    0.50   -1.69   -1.41    0.45    0.45    0.48   -0.16   -0.48    0.13    0.03    0.02
BR  El:    -0.69   -0.19   -0.62   -0.56    0.81    0.77   -0.12    0.21    0.19   -0.14    0.03   -0.05
  
MK  Az:    -1.68    0.42   -1.57   -1.33    0.54    0.50    0.49   -0.17   -0.44    0.11    0.07    0.02
MK  El:    -0.26   -3.41   -0.69   -0.50    0.90    0.85   -0.12    0.21    0.18   -0.11    0.03   -0.05

Below are the same data but converted to amplitude (arc minutes) and angle. The angle is in counterclockwise degrees measured from the elevation axis. These are to be compared with the angles on the feed cone drawings but do not confuse them with the FRM encoder angles set at the antenna or put in the monitor data. The FRM encoder angles have a different zero at each antenna.

             90cm    50cm    21cm    18cm    13cm  13cmsx     6cm     4cm   4cmsx     2cm     1cm     7mm
SC  Amp:     0.78    1.05    1.56    1.53    0.97    0.92    0.42    0.27    0.68    0.16    0.11    0.05
SC  Ang:    -166.   -117.   -111.   -110.     32.     33.    107.    -39.    -70.    135.     68.    169.
  
HN  Amp:     2.29    1.53    1.44    1.55    0.95    0.91    0.50    0.27    0.61    0.18    0.06    0.05
HN  Ang:     -98.   -114.   -118.   -111.     20.     19.    106.    -36.    -70.    124.     72.    158.
  
NL  Amp:     2.77    1.96    1.79    1.67    1.12    1.05    0.50    0.28    0.52    0.14    0.08    0.04
NL  Ang:    -175.   -131.   -112.   -107.     23.     24.    105.    -38.    -64.    129.     67.    166.
  
FD  Amp:     1.71    2.76    1.64    1.43    0.92    0.89    0.51    0.26    0.49    0.13    0.11    0.05
FD  Ang:    -117.    -80.   -110.   -113.     21.     24.    106.    -37.    -66.    138.     68.    158.
  
LA  Amp:     2.14    3.90    1.72    1.47    1.08    0.96    0.50    0.29    0.52    0.13    0.11    0.04
LA  Ang:    -133.   -122.   -115.   -114.     35.     31.    106.    -36.    -68.    129.     85.    153.
  
PT  Amp:     2.50    2.24    1.74    1.36    1.09    1.07    0.49    0.30    0.46    0.10    0.11    0.05
PT  Ang:    -149.   -138.   -110.   -108.     35.     31.    108.    -40.    -67.    143.     68.    169.
  
KP  Amp:     1.94    4.78    1.71    1.74    1.15    1.25    0.51    0.27    0.55    0.16    0.10    0.04
KP  Ang:    -145.    -67.   -111.   -106.     43.     39.     96.    -39.    -68.    135.     66.    166.
  
OV  Amp:     2.15    2.47    2.02    1.66    1.11    1.04    0.51    0.29    0.49    0.16    0.09    0.18
OV  Ang:    -126.   -146.   -121.   -126.     28.     28.    101.    -38.    -71.    133.     72.    139.
  
BR  Amp:     1.01    0.53    1.80    1.52    0.93    0.89    0.49    0.26    0.52    0.19    0.04    0.05
BR  Ang:    -133.    111.   -110.   -112.     29.     30.    104.    -37.    -68.    137.     45.    158.
  
MK  Amp:     1.70    3.44    1.71    1.42    1.05    0.99    0.50    0.27    0.48    0.16    0.08    0.05
MK  Ang:     -99.    173.   -114.   -111.     31.     30.    104.    -39.    -68.    135.     67.    158.
Below are the averages using all of the data from all stations. Also shown are the rms deviations from the averages. Columns 6 and 7 show the averages expressed as an amplutude and angle rather than as azimuth and elevation terms. The final column shows the position of the feed on the feed ring for most bands and the subreflector rotation setting used for observations in the case of the 50/90cm prime focus system. 
  BAND   AZavg   AZrms   ELavg   ELrms     AMP   Angle   Feed
  90cm   -1.23    0.67   -1.21    0.81    1.72    226.    251.
  50cm   -1.62    1.53   -0.94    1.50    1.87    240.    251.
  21cm   -1.57    0.13   -0.67    0.14    1.71    247.    251.
  18cm   -1.42    0.13   -0.56    0.15    1.53    248.    251.
  13cm    0.51    0.14    0.89    0.07    1.03     30.     32.
13cmsx    0.48    0.13    0.87    0.07    0.99     29.     32.
   6cm    0.48    0.03   -0.12    0.03    0.49    104.    108.
   4cm   -0.17    0.01    0.22    0.01    0.28    322.    323.
 4cmsx   -0.49    0.07    0.20    0.02    0.53    292.     32.
   2cm    0.11    0.02   -0.10    0.02    0.15    133.    138.
   1cm    0.08    0.02    0.03    0.01    0.09     69.     78.
   7mm    0.03    0.03   -0.06    0.03    0.06    155.    155.

The next table is essentially the same as the last one except that the average was taken a second time rejecting any station that deviated by more than 1.5 sigma. The new final column shows the number of stations used for the average. Given that a few stations have deviant values, these edited averages are the best to use as the standards for comparison. Note the very good agreement between the feed position angle and the squint angle. In fact, the largest offsets other than 4cmsx are at the highest frequencies where the errors due to the fact that I am only working with ascii numbers with two places beyond the decimal can cause much of the error. The results for 4cmsx are not too surprising given that this signal has two additional offset reflections. The theoretical expectation for the ellipsoid/dichroic combination is not known to me.

  BAND   AZavg   AZrms   ELavg   ELrms     AMP   Angle   Feed    NACC
  90cm   -1.37    0.36   -1.17    0.64    1.81    230.      0.      7
  50cm   -1.53    1.14   -0.98    0.93    1.82    237.      0.      8
  21cm   -1.59    0.07   -0.62    0.06    1.71    249.    251.      8
  18cm   -1.40    0.10   -0.53    0.06    1.49    249.    251.      8
  13cm    0.49    0.12    0.88    0.05    1.01     29.     32.      8
13cmsx    0.45    0.08    0.85    0.07    0.97     28.     32.      9
   6cm    0.48    0.01   -0.13    0.02    0.50    105.    108.      8
   4cm   -0.17    0.01    0.22    0.01    0.27    322.    323.      9
 4cmsx   -0.48    0.05    0.20    0.02    0.52    293.     32.      8
   2cm    0.11    0.01   -0.10    0.01    0.15    133.    138.      7
   1cm    0.09    0.02    0.03    0.01    0.09     68.     78.      8
   7mm    0.02    0.01   -0.05    0.00    0.05    162.    155.      9

Finally I show the deviations from the edited averages of the individual station data. The comparison is done as a ratio of amplitudes and as a deviation of the angle. Any station/band that has more than a 20% amplitude offset or more than a 20 degree angle offset is flagged.

                 90cm    50cm    21cm    18cm    13cm  13cmsx     6cm     4cm   4cmsx     2cm     1cm     7mm
SC Amp ratio:    0.43    0.58    0.91    1.02    0.97    0.95    0.83    0.99    1.31    1.05    1.18    1.04
SC Angle diff:   -35.      6.      0.      0.      2.      5.      2.     -1.     -3.      2.      0.      7.
                 ^^^^                                                            ^^^^                        
HN Amp ratio:    1.27    0.84    0.84    1.04    0.94    0.94    1.00    0.99    1.17    1.22    0.69    1.09
HN Angle diff:    32.      9.     -7.     -1.     -9.     -9.      1.      2.     -2.    -10.      3.     -3.
                                                                                         ^^^^    ^^^^        
NL Amp ratio:    1.53    1.08    1.05    1.12    1.11    1.08    0.99    1.01    1.01    0.96    0.83    0.84
NL Angle diff:   -44.     -8.      0.      4.     -6.     -4.      0.      0.      3.     -4.     -2.      4.
                                                                                                             
FD Amp ratio:    0.95    1.52    0.96    0.96    0.91    0.92    1.02    0.96    0.95    0.91    1.18    1.09
FD Angle diff:    14.     43.      2.     -2.     -8.     -4.      1.      0.      1.      5.      0.     -3.
                                                                                                             
LA Amp ratio:    1.18    2.14    1.01    0.99    1.08    1.00    1.00    1.04    1.00    0.87    1.21    0.91
LA Angle diff:    -3.      1.     -3.     -4.      6.      3.      1.      1.     -1.     -5.     16.     -8.
                                                                                                 ^^^^        
PT Amp ratio:    1.38    1.24    1.02    0.91    1.08    1.11    0.98    1.09    0.88    0.68    1.18    1.04
PT Angle diff:   -19.    -15.      2.      3.      6.      3.      3.     -2.      1.     10.      0.      7.
                                                                                         ^^^^                
KP Amp ratio:    1.07    2.63    1.00    1.17    1.14    1.29    1.02    0.99    1.07    1.05    1.08    0.84
KP Angle diff:   -15.     56.      1.      5.     14.     11.     -9.     -1.      0.      2.     -2.      4.
                                                         ^^^^                                                
OV Amp ratio:    1.19    1.36    1.18    1.11    1.10    1.08    1.02    1.07    0.94    1.10    1.04    3.75
OV Angle diff:     4.    -23.     -9.    -15.     -1.      0.     -4.      0.     -3.     -1.      3.    -22.
                                                                                                         ^^^^
BR Amp ratio:    0.56    0.29    1.05    1.02    0.92    0.92    0.99    0.96    1.00    1.29    0.46    1.09
BR Angle diff:    -3.   -126.      1.     -1.      0.      2.     -1.      0.     -1.      4.    -23.     -3.
                         ^^^^                                                            ^^^^    ^^^^        
MK Amp ratio:    0.94    1.89    1.00    0.95    1.04    1.02    1.01    0.99    0.92    1.05    0.83    1.09
MK Angle diff:    32.    -64.     -2.      0.      2.      3.     -1.     -1.      0.      2.     -2.     -3.

The most deviant value in this table is at 7mm at OV where there is a squint of nearly 4 times the normal size. This probably indicates some problem with the optical alignment, but it is not yet clear what. The offsets at BR are probably not too surprising since that site is known to have a fairly serious astigmatism. HN also has surface problems, probably in panel adjustment, although it is not clear that they should affect the squint.

In any case, the largest angle deviation in this table from the average value is 23 degrees. The actual data were taken during the polarization problem at 7mm at MK and the actual squint values were of opposite sign to the ones shown above. I corrected the ones above to help get good averages. With the original signs, the angle offset for MK was close to 180 degrees demonstrating the ability to detect crossed polarization.

I have modified PTANAL to detect deviant squints. It will give a low level check message for amplitudes deviating from those expected by more than 60% and angles deviating by more than 30 degrees. The tolerances are higher at 50/90 cm. If the angle deviates by more than 90 degrees from the expected value, a high level check flag is written to the check file, tick marks are written below the squint in the summary file, and a messages appears on the screen while the program is running. The check message and screen message indicate a probable cross polarization. I hope this will help ensure that we catch polarization problems quickly in the future.

next up previous
Next: About this document ... Up: VLBA TEST MEMO 64 Previous: Background.
Craig Walker
2001-05-14

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