[evlatests] System Temperature

[Rick Perley]

    Antennas 14 and 16 were (sort-of) working at noon today, so I took
advantage of Ken's lunch hour to accumulate some data.  I observed
3C147 (strong point source) at L, C, X, and K bands.  I used mode
'4' (giving four parallel-hand correlations, AA, BB, CC, and DD),
with 32 spectral channels each and 6.25 MHz BW. 

    All data at K-band (both VLA and EVLA) were so weak as to
be unusable.  3C147 is a 1.8 Jy object at these frequencies -- we should
have gotten useable data.  It's as if the antennas were pointed somewhere
else ...

    EVLA antennas 14 and 16 gave useable data at the other frequencies,
on all 4 IFs.  However, the sensitivities were very low for all -- typically
down by a factor of 4 to 10 for all IFs/bands. 

    So I looked at the backend Tsys values:

    Freq.      14R   14L   16R   16L
-----------------------------------------------------
    1465      33      33      57      46
    1365      34      32      81      36

    4885      23      21      X         X
    4835      23      21      X         X

    8435      Y        Y      53      35
    8485      Y        Y      40      100*

    22485     42      42      106      110
    22435     42      42      260      103
-------------------------------------------------

    X = No switched power available
    Y = Tsys turned off for this antenna/Freq.
    * = Tsys is oscillating, with a 40 second period and 15 degree pk-pk 
amplitude. 

    The Tsys values for antenna 14 are all close to what we
expect, on the basis of in-antenna total power measurements made
by Bob Hayward and me. 
    The values for antenna 16 are all significantly worse than
they should be, and variable (compared to what they were last week). 
    A mystery to me is the values of Tsys for the VLA antennas
at K-band -- all values are around 120.  Yet they should be in the
40s or 50s, like antenna 14.  Can the Tcals be off by a factor of 3? 

    Rick