[daip] forwarded message from Chris Phillips

[Jim Ulvestad]

He's probably right.  Lorant might know, or even Huib might know,
but I expect Chris has talked about this with Huib already.

jim

Eric Greisen wrote:
> 
> Is he likely to be right?  I suspect so but thought I had better ask.
> 
> E
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> From: Chris Phillips <phillips at jive.nl>
> To: Eric Greisen <egreisen at cv3.cv.nrao.edu>
> cc: Huib Jan van Langevelde <langevelde at jive.nl>
> Subject: CVEL for JIVE data
> Date: Wed, 6 Mar 2002 17:39:21 +0100 (MET)
> 
> Hi Eric,
> 
> One year later, I have finally had the time and the right experiment
> (1000 Jy methanol maser emission from W51) to test whether CVEL works
> properly with JIVE data.
> 
> In a Nutshell, it doesn't. Basically the MarkIV correlators do fringe
> rotation on a baseline basis (like the MarkIII correlators), but the first
> antenna is rotated for MarkIV not the second antenna. For JIVE data, aips
> assumes the first antenna was the reference antenna and gets the frequency
> shift wrong. For EVN baselines with is of the order of 0.5 km/s error.
> (For global baselines it is more like 2 km/s).
> 
> I got it to work with a change in DSHIFT. Basically I made the following
> change:
> 
> C      IF (IREFST.EQ.0) ITEL = IANT1
> C      IF (IREFST.GT.0) ITEL = IANT2
>       ITEL = IANT2
> 
> So, is it possible to either:
> 
>  - Put a test in CVEL for either JIVE or a MarkIV correlator and set ITEL
>    to the correct value (ie IANT2)
>  - The IREFST set above is obviously meant to deal with this problem.
>    However from memory you didn't think it was implemented in the rest of
>    aips so it wouldn't work.
> 
> Let me know if you want any more info from me (or more justification for
> my request, but I guess you don't really want to see a million plots
> which show that CVEL works best with the above fix).
> 
> Cheers
> Chris Phillips
> 
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