Some Notes on VLA / EVLA gain curves and fluxscale

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Some of the EVLA antennas have significant amplitude gain curvature as a function of elevation, owing perhaps to whatever the attenuation and AGCs are doing (or not). Ideally, to derive the flux density of your secondary calibrators using fluxscale, you may want initially to use only the few hours in the middle of an observation, when the calibrator is at higher elevation.

However, at press time fluxscale does not have a timerange input. The following procedure outlines a way to bootstrap the calibrator flux densities based on observations when the source is at higher elevation.

  1. Run gaincal using only the middle few hours to get the solutions at higher elevations.
  2. Run fluxscale to get the calibrator flux using these data only.
  3. Run setjy to enter this calibrator flux manually.
  4. Delete the gain table that was output by gaincal.
  5. Run gaincal again, using the entire observing run.
  6. Finally, use applycal to generate the corrected data.

--Jgallimo 14:39, 30 October 2009 (UTC) (based on an e-mail from Jim Ulvestad)