[evlatests] Switch STability tests, cont.

[Rick Perley]

    A review of the visibility gains from the band change/switch 
stability tests reveals some interesting results.  Some 'global' 
characteristics can be discerned.  There are a large number of 
'one-ofs',  some of which I note below. 

    1) Ku-band is unique in its poor amplitude stability (defined here 
as scan to scan, not within any one scan).  In all cases, all four IFs 
change in similar ways -- this looks like pointing, but this conclusions 
is not supported by review of the higher frequency stability.  This 
could be pointing nonetheless, *if* the collimation values are very 
poor.   For some antennas, the variation in one polarization is similar, 
but larger than, that in the other.  This can also be due to pointing, 
so long as the collimation values are poorly determined. 

    2) K, Ka, and Q bands clearly show the effects of residual pointing 
errors -- despite using 'referenced pointing'.  The variations are 
common to all four IFs, and scale roughly with frequency.  Antennas 
which are especially notable here are:  ea02, ea06, ea11, and ea18.  

    3) Some amplitude variations are seen in all three high frequency 
bands common to the UX converter:  7A, 16D, and 20 C and D. 

    4) L-band shows a number of high variations, looking like switch 
issues.  These are always on both IFs of a single polarization.  The 
antennas are:  12R, 13R, 14R and 14L (variations are different), 18R and 
18L, 24 on all IFs, 25R, and 28L. 

    5) X-band is the most unstable band (discounting the problems noted 
at Ku-band).  At least half the antennas show gain variations well above 
the noise, and much worse than L, S, or C bands. 

    6) S and C bands are remarkably, and gratifyingly stable.  The only 
exceptions are:

   9CD at C-band, 16D at S-band, 18D at C-band, and 24C at S-band. 

    Interested parties in all this should review the (volumnous) 
printouts, in my office.