[evlatests] Q-band characteristics

[Rick Perley]

Herein a summary of the Q-band characteristics for the 24-hour run:

All antennas cold, with uniform sensitivities (except ea07 in IF 'C' —see below).

Cross-polarizations are normal.  Bandpasses are normal.  Switched power was working on all antennas except ea01 (same at all bands).  ea07, in IF 'C' had to be flagged due to extremely low amplitudes and poor sensitivity.  Cause unknown to me.

PDif values show the usual drop in gain through the daytime hours due to ambient temperature changes.  The typical power gain range is 25%.  As at all other bands, application of the PDif values corrected all observed gains to an accuracy of better than 5% (this residual is higher at Q-band, since the sensitivity is poorer, and the sources weaker).

Some antennas have very different PDif value characteristics!  These are SPW and polarization dependent.  For example, ea02, RCP, in IF 'A' shows an almost 50% increase in PDif, with large and abrupt fluctuations, while it is normal in LCP on all SPWs, and normal in RCP in IF 'B'.  (This odd behavior was seen at other bands for this antenna as well).

Even more bizarre was ea28, in IFs 'C' and 'D' — the PDif values smoothly rose by 20% over the course of the day, then decreased back to nighttime values — this is exactly reversed from all other (well-behaved) antennas, including ea28 in IFs 'A' and 'C'.  (!)

For all of these oddly behaved antennas, the actual gains changed in accordance with the PDif values, so application of the switched power PDifs corrected the gain effects.

Bottom line in all of this:  Switched power is working, and can do what it was designed to do with accuracies of a couple percent — but only when using the 8-bit samplers, and only after some cleanup of the data (almost always due to RFI in the spectral windows).

Rick

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