[evlatests] modcomp-free line observing: update / correction

[Vivek Dhawan]

Here is a repeat of the table I sent before.

The mis-set frequency at K band (and U) has been fixed by Ken.

The L band at 0.78 MHz needs clarification: data were missing
but surviving data were fine.

The L band problems at 1.56 MHz I am now blaming on interference.
It initially seemed like an EVLA-only problem, but studying it
some more shows that it is present on the VLA as well at low level.
It is at an apparent sky frequency of 1666.0 MHz and not present
at that sky fequency at the narrower BW, so one guess is that it
is just outside the final bandpass. The differences between VLA
and EVLA are then explained away as different amounts of filter
rejection.

So till proven otherwise, I believe fixed-frequency line observing
works, subject to IDCAF/vispipe problems.

     ------------------------------------------------------------
      Band BW MHz   Nchan/IF  Source   F_center_desired    Comment

      K     3.125      63      W3OH      22240.17 MHz        Freq
      K     6.25       31      W3OH      22240.17            Freq
      K    12.50       15      W3OH      22240.17            Good

      L     1.562     127      W3OH       1665.78 MHz        Bad
      L     0.781     127      W3OH       1665.78            Missing

      Q     6.25       31     Orion       43122.02 MHz       Good
      Q     3.125      63     Orion       43122.02           Good
      ------------------------------------------------------------