[evlatests] Modcomp-Free data.

[Barry Clark]

The pointing constants are out-of-date for the VLA antennas.  Antenna 7
is especially bad.  But several others have pointing errors approaching
an arcminute.

> From evlatests-bounces at donar.cv.nrao.edu  Mon Apr 16 20:51:08 2007
> Date: Mon, 16 Apr 2007 20:50:47 -0600
> From: Rick Perley <rperley at nrao.edu>
> User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US;
> 	rv:1.8.0.10) Gecko/20070226 Red Hat/1.0.8-0.2.el4 SeaMonkey/1.0.8
> MIME-Version: 1.0
> To: evlatests at aoc.nrao.edu
> Subject: [evlatests] Modcomp-Free data.
> 
>     Perfect, it ain't.  But I think there's hope...
> 
>     I ran a 30 minute test, with the usual modes, with Modcomp-free, 
> then the same file, with Modcomps in charge, 30 minutes later. 
> 
>     *** Special note to Ken and Walter:  The data we were looking at 
> were in fact the Modcomp-on data!!! *** 
> 
>     I reviewed the fast-dump continuum data this evening for L, C, and X 
> bands, for the Modcomp-free data.   There is a wealth of different 
> phenomena.  But some commonality appears:
> 
>     1) The system is slow to get going.  At C-band, the first 15 seconds 
> for all antennas was dead.  At X-band, it was 28 seconds.  At L-band, 
> it's hard to judge, as other curious phenomena (seen also with Modcomps 
> on) dominate. 
> 
>     2) For all three bands, all gains and phases discontinuously jump 
> 10.0 seconds before the end of the scan (as judged by the presence of 
> data).  EVLA antenna amplitudes jump a lot more than VLA antennas.  
> There is no commonality between antennas or even IFs.  Every antenna-IF 
> has its own 'personality'. 
> 
>     3) There is a curious pattern of dead antennas, which only partially 
> (and weakly) reflects which antennas were actually working.  
>     At L-band, 14 and 16 were dead on all IFs.  Antenna 4 had low 
> amplitudes. 
>     At C-band, the pattern was really bizarre.  All IFs for antennas 1, 
> 16, 20, 22, 23, 25, 27 and 28 were dead.  We know 23 has no receiver, 
> but the others?  Antenna 21 has no receiver but gave (weak) fringes on 
> IF A.  In addition to these, 10D, and 26 A, C, and D were dead. 
>     At X-band, 16C, and 14 B and D were dead.  Amplitudes are low on 
> some other antenna-IFs. 
> 
>     4) Some antenna-IFs gave ramp-like gain changes!  (Looks like the 
> delay 'clunk', but in fact these are amplitudes).  I have plots to show 
> the experts. 
> 
>     5) There are large step-changes in phase on some antennas.  These 
> are tens of degrees, and of short (a second of two) in duration.  The 
> phase returns to the original value in each case.  (This is not a common 
> phenomenon, but is certainly easily seen). 
> 
>     6) After removing the first ~20, and last 10 seconds, and flagging 
> the dead and weak antennas, and ignoring the odd amplitude ramp and 
> phase hop, the remainder of the data (by far the majority) look pretty 
> decent. 
> 
>     Despite the litany of ills, this is much better than what I've seen 
> before.  But not prime-time yet ...
>