[evlatests] Phase Conjugated Holography Data!

[Walter Brisken]

I think this "conjugation" is expected.  The phase should always be 
phase_2 - phase_1 (or the opposite) where phase_2 is the signal phase on 
the higher numbered antenna, and phase_1 is for the lower numbered one. 
The correlator does not know that holography is happening (at least I 
think that is the case). This certainly has always been the case.  uvhol 
is probably the proper place to "un-conjugate" the phases.  With the new 
averaging feature in UVHOL this will be especially important!

-W

On Thu, 11 Oct 2007, Rick Perley wrote:

>    The data taken last night are showing 'global' EVLA to VLA phase
> changes between the holography scans and the calibration (which, due to
> the problems described earlier, was only possible for EVLA antennas at
> the end).  The offsets are visible because the 'zero--point' phase can
> be seen when the center of the beam is on the source.    The
> 'center-beam' phases for the EVLA antennas are 30 to 50 degrees off
> zero, compared to their phases on the single calibration scan.
>
>    These offsets reveal a remarkable fact:  The visibilities are
> conjugated (i.e., the phase is negated) when the reference antenna is
> numbered lower than the moving antenna!  This is true for all EVLA
> antennas, whether the reference antenna is another EVLA antenna, or
> whether it is a VLA antenna.  It is probably true also for VLA antennas
> -- but because holography phases are generally near 0 or 180 (when there
> is enough signal to give stability), and all the EVLA antennas are
> numbered higher than the two VLA antennas I chose to move (6 and 9) it's
> hard to be certain.
>
>
>
>
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