[evlatests] R/L phase differences.

[Bob Sault]

Following on Barry's suggestion, attached is a plot
of simply differencing the RR and LL phases on a 
particular baseline (and subtracting off an arbitrary
constant so the plot turns out near 0). 

These do show phase changes between the two polarizations
which are significantly greater than expected from thermal
noise (thermal noise should give an RMS of about 0.7 deg
in this plot).

I could not see any periodicities in the data.

These are data with no calibration, so we can presumably
discount off-line software as a cause of the issue.

Regarding the discrepancy I showed at the meeting today, it was a
phase-only effect. The amplitudes calibrated well on
the 1 minute solution interval.

Best regards
Bob
--
---------------------------------------------------
Bob Sault is in Socorro until July 2009

Socorro Phone:   +1-575-8357239
Email:   rsault at unimelb.edu.au
Web:     http://astro.ph.unimelb.edu.au/~rsault 


> -----Original Message-----
> From: evlatests-bounces at donar.cv.nrao.edu [mailto:evlatests-bounces at donar.cv.nrao.edu] On Behalf Of
> Vivek Dhawan
> Sent: Friday, 24 April 2009 6:59 AM
> To: evlatests at nrao.edu
> Subject: [evlatests] R/L phase differences.
> 
> Re short-term changes in cross-polarization, reported by Bob Sault:
> 
> There is something weird happening.
> 
> I still do not think it is in the LO itself, although I'm not as
> sure as I sounded this morning. It could still be something different
> in the path taken by R and L after bifurcation, downconverter onward.
> 
> Some plots are attached, all are 0.4s integration.
> 
> 1. 14 minutes at X band, default 8435 and 8485. The short jagged
> changes are probably mostly from the delay cogs, and are bounded
> to ~10 deg pk-pk. There is no long term trend, but the minute-
> scale periodicity I do not understand.
> 
> 2. Same data, 2 minutes segment - I don't know if the various
> quasi-peroids are expected or not?
> 
> 
> 3. K band on orion, 3MHz conntinuum on a strong line. The phase
> wander looks quasi-random, and very little sign of the delay cogs.
> 
> The other IF pair was tuned to exactly the same frequency, but
> shows (on some antennas) a different variation pattern, and on
> other antennas a curious symmetry - the wander in one pair is flipped
> in sign in the other pair - i.e an up/down symmetry. Again, not sure
> what it means, but does not smell good.
> 
> V.
> 

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