[evlatests] More plots to illustrate ... what?

[Rick Perley]

The suggestion made by Barry and others that some elevation- and 
antenna- dependent effect (like droopy cables)  is responsible for the 
weird R-L phase plots was investigated this afternoon.

     As expected, for those antennas showing 'even' symmetry, plots of 
that phase difference against elevation showed very nice alignment for 
all four sources.  For these (few) antennas, the dominant factor is 
elevation-dependent.

     The question of the effects of the reference antenna is important, 
so I spent a good part of the afternoon looking at this as well.

Bottom line is:  The choice of reference antenna is important, but the 
overall message remains unchanged.  Some antennas show an 'even' 
symmetry with HA, some antennas show an 'odd' symmetry.

As it turned out, my choice last week of ea10 as the reference was 
probably the worst one I could have made -- ea10 has nearly the largest 
'odd' symmetry pattern, which made more antennas look 'odd' than there 
probably are.  After trying a number of reference antennas, I chose 
ea09, as this resulted in the largest number of antennas with 'even' 
profiles.

I also simplified the processing.  The plots made Friday made use of 
both 'FRING" (to remove the delays) and 'CALIB' (to form the 
antenna-based solutions).  For the attached plots today, only 'CALIB' 
was used, on a narrow range of central channels.   I'm also using 
1-minute averages in the solutions, as shorter time intervals introduce 
effects due to the 'delay clunking'.  (These are C configuration data, 
so short-duration solutions show much scatter due to this effect).

Attached are the R-L phase plots, as functions of (a) Hour Angle, and 
(b) Elevation, for all antennas (except ea17, which had some serious 
weirdness unrelated to the issues being discussed.)  These data are from 
C-band.  There are four plots per attachment.

For all plots:

3C286 (dec = 30.3) is RED

OQ208 (dec = 28.5) is LIGHT GREEN

3C273 (dec = 2.0) is TEAL (darkish green)

3C287 (dec = 25.2) is BLUE.


*Some observations:*

     The plots against elevation show the dominant effect for most 
antennas -- a simple elevation dependence of the R-L phase.  The 
outstanding examples are ea01 and ea22.   Although these are the 
cleanest (meaning, all four sources follow the same curve), most 
antennas have some (smaller) dependence on elevation as well. Note that 
the phase range can be remarkably large -- 3 to 4 degrees for ea01, 3, 
5, 6, 8, and 22.  Note also that the sign of the phase change is always 
the same -- positive -- meaning the change in 'R' is larger than than in 
'L'.

     But not all antennas show this dependency.  The use of ea09 as 
reference has removed many antennas from the 'odd' symmetry, but not 
all. The plots against HA show that some antennas retain significant 
'odd' symmetry:  ea10, ea16, and ea18 are the best examples.  Note here 
however that there is little sign of elevation dependence in these 
antennas' phase difference.  Also note that in all cases, the magnitude 
of the variation is smaller than the 'even' effects noted above.

     Finally, some antennas are just different.  ea15 is the best 
example -- something else entirely going on here.

*So -- What to Do?*

   There are at least three different things going on here.  If we are 
to pursue these issues, I advise starting with the simplest and largest 
-- the elevation-dependent 'even' phase.  It has the cleanest signature, 
and the largest amplitude.  The antennas with the largest and cleanest 
(meaning, other dependencies are much smaller) effects are ea01, ea03, 
ea05, ea06, and ea22.

     I'm willing to conduct specialized tests, but note that, being in 
the A configuration is not the most optimum for tests involving phase...

Rick

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