[evlatests] Stability Tests on Sept 29, 2005

[Jim Jackson]

We looked at antenna 14 today.  IF-A was dead because no D301 DTS module 
was present - it is now installed and working.  We noticed the same 
symptoms as Rick about IF's B and D. Both were not working because the IF 
power was drastically wrong - B was way too high (sampler RMS of about 80) 
and D was way too low (sampler RMS of 1).  Once we setup the T304's and 
installed the D301 all four IF's now look fine at the T5.

Both Antennas should be working for any tests this weekend.

Jim

At 12:29 PM 9/30/2005, Rick Perley wrote:
>    The last attempt at determining baselines for antennas 14 and 16 
> failed, as the phases
>seemed non-sensical.  This encouraged a test, involving cycling around a 
>few sources to
>see if the EVLA antennas phases 'connect' from source to source.
>    The short answer is:     They do not.
>    Details:
>
>    The test ran for 30 minutes, starting at 1PM.  I used C-band, as the 
> weather was
>cloudy with large T-storms passing over at the end of the run.  A 1.6 
>second averaging
>was used, and 50 MHz BW, continuum mode.
>    Antenna 16 was dead at all IFs -- I think it was stowed throughout 
> with Rob doing
>some system work.
>    Antenna 14 worked in only the C IF channel.  Channel A was dead, channel B
>provided correlation values at least 8 times too high (reason unknown), and
>channel D gave values 100 times too high, with phase = -180 and steady.
>Clearly
>not working.
>    It should be noted that no attempt was taken to set the powers at the 
> appropriate
>levels.  The only two gurus who know how to do this (Barry, Ken) were both 
>out.
>    Seemingly useful data were obtained from  channel 14C.
>    A) Amplitude behavior.   Dropouts, last a single integration record 
> (1.3 seconds),
>where the correlated amplitude drops by 10 to 40 %, were noted 
>throughout.  When
>they occur, they are always separated by 10 seconds.  But they do not 
>happen *every*
>10 seconds (in fact, perhaps only 5% of the data are so affected), and 
>when they occur,
>they do not necessarily fall on 10-second 'ticks'.  Each scan was 
>different -- some had
>no dropouts, some had many.   There is no corresponding phase effect for these
>amplitude dropouts.       Other than the dropouts, the amplitude scatter 
>in the solutions is about the same
>as a VLA antenna.
>    B) Phase behavior.          i) Within any one scan (of a single 
> source), the phase behavior is the same as
>an adjacent VLA antenna.          ii)  There is no connectivity in phase 
>from scan to scan.
>However, there is
>good evidence that the same phase returns for a given source.  (The 
>weather became
>very poor at the end, so this conclusion is a bit tentative).   Hence, 
>there could be a
>Bz error in the baseline.  However, if so, it is *very* large, for a 
>change in declination
>by 1.7 degrees changed the mean phase by over one radian -- I figure a 40 
>cm error
>in Bz is needed.
>    More data are needed (in better weather) to confirm this.
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