[evlatests] Phase jitter

[Steven T. Myers]

Interesting. I'm looking at baseline ea02-ea03 and channel 128 RR
in casaplotms on raw data.  spw 0,4,8 (IF 1,5,9 if exported).

What I see is that the last setting (spw 8~11 XXXX.15 MHz) is the most coherent,
and for the first setting (spw 0~3 XXXX.00 MHz) the beginning of the first scan 
is coherent then suddenly phase jumps and gets noiser between the first and 
second scans (with same lo setting) at 20:05:57.5.  The second setting
(spw 4~7 XXXX.05 MHz) is always noiser (like the end of setting 1).  The amp
scatter also behaves this way (but is harder to see the difference).

Did something change at 20:05:57.5 and when starting the 3rd setting (e.g.
attenuator changes?)

On Thu, 15 Oct 2009, Barry Clark wrote:

> I am probably doing something stupid, but....
>
> dataset SOFTWARE.tlo.evla.55119.83645106482.55119.83662796296
> consists of observations with three slightly different LO
> frequencies:  4488.000, 4488.050, 4488.150, cycling around
> changing frequencies every thirty seconds, on 3C273.  Since
> there is plenty of SNR, I am looking at phase vs time on a
> single channel.  The second-to-second scatter on these plots
> seems to be much lower when the LO is set to 4488.050 than
> on the other two.  I've looked at a reasonable selection of
> channels (near midband) and a few different baselines.
>
> Probably should be checked by somebody who knows what he is
> doing.
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