[evlatests] L-Band

[Rick Perley]

    Some observations of this morning's quick look, at L-band:

    1) 13C was flagged bad, but the data were fine.  Perhaps the 
attenuator was mis-set? 

    2) Antenna 11, on all IFs, had many dropouts, on the B and D IFs 
only.  Unlike the 'short shallow drops' that we still see, these drops 
on 11B and 11D are *total*.  They last for a single 418 ms record.  The 
two records on each side are reduced in amplitude, typically by ~50%.  
There is no phase effect.  There were two L-band scans, and drops were 
seen in both.  However:        
          -- for the first scan, the drops occurred *only* at times 
given by x2, where 'x' is a digit from 0 through 5.  (That is, only when 
the time was 02, 12, 22, 32, 42, 52 seconds in any given minute).  Not 
all 'x2' records were affect. 
          - for the second scan, the dropouts occurred on 'x1' (i.e., 
01, 11, 21, ...) seconds. 

       There is pretty good evidence that 'pulses' in Tsys are uniquely 
associated with these dropouts.   This antenna is at E32. 

       I did not see this curious problem at any other band. 

    3) Antenna 13 on IF 'D' only, shows two distinct gain levels.  Each 
lasts about 70 seconds, and the time spent in each state is exactly the 
same -- it's a nice square wave pattern.  The weaker state is lower by a 
factor of only about 25%, but the gain solutions indicate that the noise 
in the weaker state is much higher.  There is no corresponding effect in 
Tsys -- the variations seen are due to changes in correlator coefficient. 

    4) VLA antennas 4, 6, and 8 all have large, sudden gain jumps -- 
particularly antenna 4.  For all, these jumps are associated with Tsys 
variations.  The antennas are located at W24, W8, and W16, 
respectively.  However, all other antennas on each side, and in between 
these behave perfectly normally in both gain and Tsys.