[evlatests] X-band sensitivity

[Rick Perley]

    We obtained a small amount of data late Monday afternoon (to determine
phase stability).  I've checked it for amplitude stability and 
sensitivity. 

    X-band, 400 msec avg., 50 Mhz continuum.

    1) Amplitude drops:  These are seen throughout (but as usual, not on all
scans), with the same characteristics as earlier noted. 

    2) 14B.  It's gone crazy.  There are two amplitude states, separated 
by a
voltage ratio of about 1.4 (roughly corresponding to ~4 dB in power).  These
are fast -- seen in the 400 msec averages, without any discernable temporal
pattern.  The 'down' state is occupied perhaps 1/3 of the time, and 
never seems
to occupy two consecutive times.   All scans showed this effect. 
There is no corresponding phase effect.

    3) Back-end system temperatures.  Much better than on Saturday morning,
but not completely normal:

                A    B    C    D
    ------------------------------
    14   |   37   35   63   36
    16   | 157   39   34   36

    I don't know what to believe with these

    4) Sensitivity.  As judged by amplitude rms on a weakish calibrator
(< 1 Jy):

          14A,C, and D are 50% too noisy compared to good VLA antennas
          16A,B are ~20% too noisy
          16C,D are with 10% of good VLA antennas. 

          14B is of course far too noisy, but this is due to the rapid gain
oscillation noted above. 

    So, in this run, antenna 16 is close to normal, while 14 is quite 
degraded.