[evlatests] C-band Performance

[Rick Perley]

    A short note on EVLA Cband performance, from the test of Friday night.

    Antenna 16 is not behaving well.  The gains vary by a couple
tens of percent in power, on timescales of tens of seconds. 
    There was no switched power from antenna 16, so the backend Tsys
values were nonsense. 
    By contrast, antenna 14 behaved very well, with extremely good
amplitude sensitivity and stability. 

    Phase stability was generally good, with two notable exceptions:

    a) The phases are definitely not returning to prior values after a 
source
or mode change.  No pattern is obvious.  Only antennas 14 and 16 do
this.  The magnitude of the change is large -- tens of degrees. 

    b) Phase spin occurred only once at this band (in spectral line, with
256 channels over 4 IFs,  3.125 MHz BW, 6.6 second averaging) -- there
were at least 29 other mode combinations I attempted.  This single phase
wind example is useful:  The phase wind was seen only on antenna 14,
and only on IFs A and C.  The rate was -105 degrees/minute. 

    Sensitivity:  Antenna 14, despite its low system temperature (more 
or less
correctly reported by the back-end Tsys) has sensitivity, as measured on
cold sky, no better than a VLA antenna.  This is a disappointing result --
it should be better by at least 30%. 
    Antenna 16's sensitivity is quite poor -- as expected as we know its
system temperature is high.