[evlatests] P-band dipole orientations

[Rick Perley]

In order to check the many changes Eric has implemented in AIPS to 
better handle linearly polarized antennas, I requested, and was given, 
an 8-hour observation of the Moon, at P-band, last December.

The resulting images are very good.  The changes Eric has implemented 
now permit application of ionospheric Faraday rotations -- these do 
indeed correct (actually, slightly overcorrect) the ionospheric RM 
rotation.

The calibration of the data also provide us the dipole position angle 
deviations w.r.t. the reference antenna dipole.  For this work, I used 
ea24.  Following is a table of dipole misorientations (all w.r.t. 
ea24).  Accuracy is about 0.5 degrees.

Antenna     Rotation angle (deg)

------------------------------------------

ea01        +3

ea02    -1

ea03    +6

ea04     +6

ea05    -1

ea06    +1

ea07    -4

ea09    +2

ea10    -3

ea11    -5

ea13    -1

ea14    -6

ea15    +1

ea16    -2.5

ea17    -3

ea18    +1.5

ea19    +3

ea20    +3

ea21    -2.5

ea22    +4.5

ea23    -1

ea25    -6 -- there is strong coupling, not due to rotation, between the 
Vertical and Horizontal channel data.

ea26    +2

ea27    -6

ea28    +1

------------------------------------------------------------

For all antennas other than ea25, the 'leakage' coupling between 
channels ('D' terms) is completely dominated by the dipole rotation.  
Only ea25 shows a significant coupling from other sources -- presumably 
electronic.