[evlatests] Dropouts, continued ...

[Rick Perley]

    New firmware, which it is claimed will fix the antenna 13 dropout 
problem,
was installed on antenna 13 this morning.  Ken and I subsequently ran a fast
continuum observation, to see what  has changed.  Three tests were run:

    A) A short run on 3C84, with 1.33 seconds integration, at X-band. 

    B) A much longer run on 0555+398, with 0.41 sec integration, at X-band.

    C) A short run on 0555+398, at X and C bands, alternating every minute,
with 0.4 sec integration. 

    Short answer:  The dropouts live on -- usually. 

    From test A:  Duration = 2 minutes. 

    No dropouts werre observed on antenna 13. 
    No dropouts were observed on antenna 18, IFs A and C. 
    Dropouts were observed on antenna 18, IFs B and D.  These occurred
are regular 10-second intervals, 'on the 2' (02, 12, 22, 32, etc.)  They 
came in
two amplitudes -- a drop by only a few percent, and of about 25%. 

    From test B:  duration of 50 minutes. 

   Three different behaviors were seen. 

    For the first 7 minutes (from 19:36 to 19:42:40 IAT):

          - antenna 13 showed no dropouts
          - antenna 18 has loads of dropouts, but only on IFs B and D.  
Three different dropout depths are seen.
             The dropouts occured 'on the 5s'. 
          - antenna 24 was not yet on source. 

    There was then a 20 second gap in the data, and when the data 
returned, and entirely different family of behavior was seen over the 
next 37 minutes (19:43 to 20:20 IAT). 

          - antenna 13 dropped regularly on all IFs.  Only a single 
'drop depth' by 24% was seen.  All drops were 'on the 1s'. 
          - antenna 18, on IFs B and D only, continued to drop, but now 
there are two depths -- of 36%, and by 75%.  All drops are now 'on the 
1s'. 
          - antenna 24 came online half way through -- and no drops were 
seen. 

    Then, at 20:20, another abrupt change in behavior (with no gap in 
the data), which changed the 'drop nature' on all three dropping antennas:

          - antenna 13 drops on all IFs, 'on the 4s', by 50%. 
          - antennas 18 drops on IFs B and D only, with two different 
drop amplitudes, `on the 4s'. 
          - antenna 24 drops, also on the 4s, by a factor of 4 (to 25% 
of standard amplitude). 

    Test C:

    This was to check the phase return behavior.  In terms of drops, (at 
X-band)

    - antenna 13 dropped on all four IFs, by a factor of 1.3, on the 1s.
    - antenna 18 dropped on IFs B and D only, on the 1s, with two 
different amplitudes:  a factor of 1.3, and a factor of nearly 6. 
    - antenna 24 showed no drops at all! 

       At C-band, only antenna 13 gave fringest, and it dropped in the 
same manner as at X-band. 

    This test ran for 15 minutes, at which point Ken moved on to other 
tests.