[evlatests] Antennas 4 and 24, plus antenna efficiency.

[Rick Perley]

    Reviewing the spectral line data, some more information on 4-band 
antennas:

    Antenna 24 has a warped bandpass on all IFs, particularly in IF A.  
The signal is very weak, although I think the polarization is correct. 

    Antenna 4 has a strongly sloped bandpass shape on IFs B and D only.  
IF 'D' is especially notable -- the lower 1/3 of the bandpass has no 
source spectral power at all. 

    I've also gotten a reasonable estimate of the efficiency now.  
Source 3C123 provides about 400 Jy in spectral flux density, enough to 
use the 'correlation coefficient' method to determine Tsys/effic.     
All the antennas whose polarizations are correct give about the same 
value -- about 7000K.  If we believe that Tsys is given by the 
brightness temperature shown on all-sky maps for the direction towards 
3C123 (not an obvious truth -- the forward beam efficiency is very 
likely less than 50%, so most of the power seen is coming from somewhere 
else ...), then Tsys ~ 2100K.  The efficiency then is about 0.30. 

    The Tsys/effic towards Cygnus A is much higher -- about 12000K.  
This is expected, as Cygnus is centered in a very bright region of the 
galactic plane, giving a much higher Tsys.