[evlatests] Modcomp Free Line Observing / works sometimes!

[Vivek Dhawan]

Test 1, June 24. Fixed frequency, preset for doppler.

     Setup:   L,K,Q bands, BW=12.5 MHz, mode 4 = RR & LL, IFs 1 & 2.

     Result:  Fringes on all IFs, all baselines, L,K,Q bands, line
              and continuum sources.


Test 2, July 01. Some Doppler tracking, some fixed frequency scans
     (i.e. JOBSERVE made a file it considered legal)

     Setup:  K band, BW=1.56 MHz, mode 2AC = RR & LL, IF 1.

     Result: VLA frequency is wrong. EVLA is correct.

     Details: EVLA-EVLA all baselines fringe nicely. There is a line at
     the expected position in the band in auto and cross spectra. Cali-
     brator also has fringes.

     E-V baselines: no fringes, no line in auto or cross; no fringes on
     continuum calibrator either.

     V-V: Fringes on calibrator. Fringes on the line position are weak
     and resolved (W3OH has a bit of continuum at this position) but no
     line present in auto or cross spectra. Thus the frequency is wrong
     by over 0.8 MHz on VLA when the new system is setting the Flukes.

     Ken checked the frequency on the VLA using the obs2script simulator
     and obs2script output, it appears wrong (it complains) he is looking
     into it a bit more.


Test 3, July 7 IAT 13:40-16:10. All fixed frequency, various BW, L, K, Q
        bands, all 5 sec integration, all mode 4 = RR & LL, IFs 1 & 2.

     Result: 3 types of behaviour, see table below.

        F= Frequency incorrect, symptoms as in Test 2.

        B= Bad and bizarre, with non-closing errors on EVLA
           high fringe rates and extra lines in band. I guess
           something strong is aliasing on some EVLA antennas-
           13, 18, 26 seem the worst. Not sure if it is general
           or just a peculiarity of narrowband / L band.

        M= Lots of data missing, otherwise data look good.
           Maybe output data handling as Walter has warned?

        G= Good, as in Test 1.

     ------------------------------------------------------------
     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
     ------------------------------------------------------------