[evlatests] P-band bandpass issues, and something about ea13 ...

[Rick Perley]

     We are preparing for another 'moon-polarization' observation, to 
occur Sunday night.  For this, a very short observation was taken last 
night, for the purpose of establishing suitable nearby phase 
calibrators.  Key results:

     1) All 27 antennas in the array (15 is in the barn) worked well, 
with similar sensitivities.

     2) However, 3 antennas have very bad bandpasses, with very high 3.2 
MHz ripple.  These are:

     7X, 22X, 26X, 26Y.

     3) I did a polarization calibration.  As usual, there is a wide 
range of leakage values.  Since our (AIPS) software does a 'relative' 
solution, the values obtained reflect the reference antenna's 
cross-polarization.   If (as I believe) the major contributor to the 
cross-polarization is the antenna orientation, then the solution 
amplitudes reflect the mis-orientation of the antennas w.r.t. the 
reference.  Frank tells me that he believes ea20 is the antenna with the 
guaranteed correctly oriented dipoles.  So, I list below the 
cross-polarization amplitudes for all the antennas.  I note that the 'X' 
and 'Y' solutions are in all cases nearly identical -- this is strong 
evidence to support the contention that nearly all the 
cross-polarization is due to dipole misorientation.

     Antenna        Cross-Pol Ampl

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

     1                         2%

     2                       15

     3                       13

     4                       14

     5                         3

     6                       11

     7                         3

     8                         2

     9                         4

     10                     14

     11                       8

     12                       2

     13                     21

     14                     12

     15                      out

     16                      11

     17                       7

     18                      12

     19                      14

     20                      ref

     21                      14

     22                      13

     23                      12

     24                      20

     25                       4

     26                       4

     27                      17

     28                        2

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

     There is a remarkable grouping here -- these values are not evenly 
distributed:

     There are nine antennas between 0 and 4%:  1, 5, 7, 8, 9, 12, 25, 
26 and 28.

     There eleven antennas between 10 and 14%: 3, 4, 6, 10, 14, 16, 18 
19 21, 22, and 23.

     There are four antennas at 15% or greater:  2 (15%), 13 (21%), 24 
(20%) and 27 (17%)

     The two remaining antennas (11 and 17) are 8 and 7%, respectively.

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

     4) The most interesting result comes from looking at the results of 
applying the polarization calibration to the data.  As always noted before:

     a) The values of the cross-hand channels (XY and YX) are up to 20% 
of the parallel hand channels (XX and YY) without applying the 
polarization calibration.  This is consistent with the results cited above.

     b) The values of the cross-hand channels after polarization 
calibration are all below 2% (in the noise) of the parallel-hand 
channels.  Looking good .. but ...

     c) The values of Q and U (which are formed by combining XY and YX), 
for all antennas but one, are also in the noise -- this is the correct 
result.  But for one antenna -- *ea13*, the result of forming Q and U is 
very different -- large values are obtained.  The only way I can think 
of that we have have proper XY and YX amplitudes, but improper Q and U 
values, is if the phase relationship between the dipoles is incorrect.  
The orientation or phasing of the dipoles in ea13 is different than that 
of the other antennas.

     *It would be very useful for somebody to climb up ea13, and check 
if its P-band dipole connections are different than the other antennas*.

     Rick