[evlatests] Antenna 17, phase switching, and L-Band

[Rick Perley]

    We ran another quick stress file, and arranged to have antenna 17's 
phase switching turned off. 

    I analyzed the results from L-band.  I find:

    1) The 1.67 period pulsing is gone.  Antenna 17 behaves normally now 
-- mostly.  The reported Tsys (as found in the AIPS database) is 400K.  
This is nonsense, since the antenna sensitivity is close to normal.  The 
raw amplitudes from this antenna are too high by a factor of about 3.  
Could somebody check the parameters database to see if the values there 
are silly?   

    2) Antenna 25, which yesterday had a sensitivity too low by a factor 
of 10 or more, is now just fine. 

    3) Antenna 13 is still in a very sad shape, with antenna sensitivity 
(essentially, G/T) low by a factor of more than 10.  The Tsys values are 
normal, so the problem lies elsewhere. 

    4) Antenna 21, on IFs A and B (i.e., RCP) has low sensitivity by a 
factor of about 2.5.  The cause is easily found -- Tsys is too high by 
the same factor. 

    5) Antenna 16, on IF B has low sensitivity by a factor of two -- and 
a correspondingly high Tsys.  Curiously, this is only seen on B, and not 
on A.  Normally, Tsys problems affect both IFs from the same polarization. 

    6) Antenna 4 is still doing its major dropout thing.  This is 
clearly related to Tsys fluctuations, which have the same fast (0.4 
seconds) changes on all IFs.  These effects are very large. 

    All else looks quite good. 

    I suggest that until we find the reason the phase switching is 
messing up antenna 17, we leave it turned off for that antenna.