[evlatests] X-Band Oddities

[Rick Perley]

    Some small issues to keep in mind, from the Sunday tests, at
X-band. 

    Antenna 13, on all IFs, showed a varying gain at the beginning of
each calibrator scan.  This is clearly associated with a dramatic change
in (smoothed) system temperature, and only occurs upon a band change.
The duration of the variation is about 1 minute, with the gain
asymptotically approaching the stable, correct level.  This is clearly due
to a sudden change in power level accompanying band change, which
the Tsys smoothing hardware is slow to catch up with.  The Tsys change,
although also visible on the other two antennas, is of much smaller
magnitude, so the 'bad' data are flagged in the normal course of events. 

    Antenna 14, IF 'A' has a bistable gain, of magnitude about 4 percent,
occuring in each of the calibrator scans.  Duration of the 'low' state is
about 30 seconds.  The low and high states are clearly disjoint -- the
effect is closer to a step function than sinusoid.  The other IFs are 
fine. 
    I note that the recorded Tsys values for 14, LCP, is very high -- 65K,
and is quite high in RCP (40K).  Probably this is responsible for the
early noted poor sensitivies ...

    Antenna 16 is great.