[evlatests] Some low-band issues

[Rick Perley]

    A test last night, in preparation for the somewhat-annual 'flux 
densities' run included (for the first time since 2008!), P-band data. 

    A few issues quickly noted:  (note:  ea15 and ea19 were out of the 
array). 

    1) No astronomical signals came from ea03, ea08, ea26 or ea27 -- all 
of which are claimed (on the Coordination Meeting Summary) to have 
low-band receivers. 

    2) Zero-mean PDif values (or values so small they are not 
meaningful) were found in ea01, ea04, ea11, ea13, and ea25.   For all 
these, the PSum values look normal, so it appears the noise diode is not 
switching. 

    3) Clearly incorrect system temperature values (typically, 10K) were 
derived on ea13, ea22, ea23, ea24, and ea28.  The reason is simple:  
These antennas have not had their Tcal values entered into the 
database.  (For these, and for ea01, ea04, ea05 and ea25 the value is 
1.0 -- the default. )

    The sources I looked at are all weak, so no statements on data 
quality can be made.  (The spectral plots are certainly interesting, 
however ... ).